MSW Incineration_Technologies and Environmental Impacts

SOLID WASTE INCINERATIONTechnologies, Impacts and Perspectives

FERNADO J. M. ANTUNES PEREIRAProfessor of Environmental Engineering Science

Curso de Verano “La problemática del ambiente urbano”Universidad de Castilla e León

SEGOVIA, 10-13 Septiembre, 2002.

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“After pollutants from an incineration facility disperse into the air, somepeople close to the facility may be exposed directly through inhalation or

indirectly through consumption of food or water contaminated by depositionof the pollutants from air to soil, vegetation, and water. For metals and other

pollutants that are very persistent in the environment, the potential effectsmay extend well beyond the area close to the incinerator. Persistent

pollutants can be carried long distances from their emission sources, gothrough various chemical and physical transformations, and pass numerous

times through soil, water, or food.”

National Research Council (2000)

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PROLOGUE

Three important issues have brought waste incineration to the forefront of waste management discussion: the recently implemented Landfill Directive, the need to comply with the philosophy of the 6th Environmental Action Programme (6EAP), and the failure of the governments to implement clean technologies, reduce waste production and comply with increasing recycling targets.

The EU Landfill Directive 1999/31/EC stipulates a requirement to decrease biodegradable waste going to landfill to 35% of 1995 levels within 15 years (in 3 steps). This legislation may even out some of the variations in incineration capacity between Member States. The greatest impact is likely in the UK, Spain and Italy where incinerator capacity is currently low. Landfilling is presently the most used method of waste management across the EU (it covers about 60% of all MSW, as we shall see later on), and therefore the obligation to divert such a large amount of waste from land disposal requires finding new ways of waste disposal, incineration being one of the waste recovery options available (but not the only one, all discussed later).

The 6th Environmental Action Programme (6EAP) outlines the European Commission’s main environmental priorities for the next five years (2001-2006). One of the 6EAP’s key objectives is to ‘decouple resource use from economic growth through significantly improved resource efficiency’. But at the same time, it assumes that a significant reduction in the quantity of waste going to final disposal can be reached through waste. Unfortunately most EU countries are not complying with established recycling targets.

The EU Incineration Directive 2000/76/EC was passed into EU law late in 2000. This directive will accelerate the move towards tighter standards in terms of protecting health and the environment. It applies to all existing and new installations. It sets operating conditions for all incinerators to be met across all Member States including strict dioxin emission limits and reporting obligations by January 2003, making incineration a safer technology.

All these facts have highlighted the importance of incineration as a means off waste disposal. In any event, the use of incineration in the future should increase, as it is one of the main waste recovery options available. As a result of strict regulation of incinerators under both community and member state legislation, a very marked improvement in emissions has been achieved. However, this is a controversial issue and there is opposition to the use of incineration as a form of waste disposal generally and, at a local level, the siting of incinerators in particular.

Despite the on-going controversy, waste incineration is still currently being accepted as long as it is part of a more general integrated waste treatment, where there is room for waste minimization (reduce, reutilize, recycle) and biological treatment, whenever social, economical and environmental conditions are appropriate. If we are to achieve a sustainable waste management system, then incineration with energy recovery will need to play a full and integrated part in local and regional solutions developed over the next few years. Waste to energy incineration must be considered in the context of an integrated approach to waste management that encourages waste reduction, re-use

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and recycling. Where incineration with energy recovery is the best practicable environmental option, the potential for incorporating combined heat and power should always be considered in order to increase the efficiency of the process.

This lecture covers the most important issues relating to municipal solid waste incineration.

Incineration is widely used to reduce the volume of municipal solid waste, to reduce the potential infectious properties and volume of medical waste, and to reduce the potential toxicity and volume of hazardous chemical and biological waste

Whether incineration is an appropriate means of managing waste has been the subject of much debate. A major aspect of the debate is the potential risk to human health that might result from the emission of pollutants generated by the incineration process; some of those pollutants have been found to cause various adverse health effects. Although such effects have generally been observed at much higher ambient concentrations than those usually produced by emissions from an incineration facility, questions persist about the possible effects of smaller amounts of pollutants from incineration facilities, especially when combined with the mix of pollutants emitted from other sources. The possible social, economic, and psychological effects associated with living or working near an incineration facility also have been topics of concern.

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ACRONYMS

AD Anaerobic DigestionAHP Analytical Hierarchic ProcessAPCD Air Polution Control DevicesAPCR Air Polution Control ResiduesASSURRE Association for the Sustainable Use and Recovey of Resources in EuropeATSDR Agency for Toxic Substances and Disease Registry (USA)CCGT Combined Cycle Gas TurbineCFC Chloro Fluoro CarbonsCHP Combined Heat And PowerCV Calorific ValueD/F Dioxins, FuransDeNOx Denitrification (NOx removal from flue gases)EU European UnionFBC Fluidised Bed CombustorGCV Gross Calorific ValueGHG Greenhouse GasGIS Geographical Information SystemGJ Giga JouleGWP Global Warming Potential (of Greenhouse Gases, relative to CO2, over a specified

time horizon)HCFC Hydro Chloro Fluoro CarbonIPCC Intergovernmental Panel on Climate ChangeIRWM Integrated Resource and Waste ManagementIWM Integrated Waste ManagementLDPE Low Density PolyethyleneLFG Landfill GasLULU Locally Unwanted Land UsesMBT Mechanical and Biological TreatmentMBT Mechanical Biological TreatmentMJ Mega JouleMRF Materials Reprocessing FacilityMSW Municipal Solid WasteMSWI Municipal Solid Waste IncinerationNCV Net Calorific Valueng nanogramNGO Non Governmental OrganizationNIMBY Not In My BackyardNIMTE Not In My Term NOx Nitrogen oxides (NO+NO2)NRC Nacional Research CouncilOCGT Open Cycle Gas TurbinePAH Policyclic Aromatic HydrocarbonsPCB, PCT Polychlorobifenil, PolychlorotrifenilPCDD Polichlorinated dioxinesPCDF Polichlorinated furanesPE PolyethylenePET Polyethylene Terephthalatepg picogramPIC Products of Incomplete CombustionPM Particulate MatterPOP Persistent Organic PolutantsPP PolypropylenePVC Polyvinyl ChlorideRDF Refuse Derived FuelRTS Refuse Transfer Station

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TCDD TetrachlorodibenzodioxinTCDF TetrachlorodibenzofuranTDI Tolerable Daily IntakeTEF Toxic Equivalence FactorTEQ Toxic EquivalentTJ Tera JouleUSEPA U.S. Environmental Protection AgencyVOC Volatile Organic CarbonsWEEE Waste Electrical and Electronic EquipmentWHO World Health OrganizationWTE Waste To Energy

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1-INTRODUCTION

Because municipal solid waste (MSW) is self-combusting, its incineration is an old practice in Europe. The first dedicated waste incinerators were built more than a century ago (1876) in Great Britain to eliminate waste while avoiding the deleterious effects of rotting organic material.

Incineration subsequently developed during the latter part of the 19th century as a means of reducing the bulk and hazardousness of waste produced in the rapidly growing metropolitan areas. It soon became used as an opportune means of energy recovery. By 1912, there were some 76 incinerators operating in England, recovering energy as heat or electricity. New economic prosperity following the Second World War led to an increase in the amounts of waste produced per head of population, and incineration enjoyed a considerable growth in capacity. However, the communities in which they were located often regarded waste incinerators poorly. Even as late as the 1970s, emission control on incinerators was usually limited to simple cyclones for reducing dust emissions. Poor plant design and operating standards resulted in lack of control over combustion conditions, giving rise to emissions of smoke, odors and high levels of residual organic matter in the ash. Incinerators were identified as major urban sources of heavy metals, dust, acid gases and NOx, and products of incomplete combustion, such as dioxins and other toxic organic micro-pollutants. Concern over the public health impacts of these emissions led to the introduction of the 1989 incineration directives, the first community wide legislation to set minimum environmental standards for waste incineration. The 1989 directives resulted in the closure of existing plant that could not be upgraded to higher standards, and set minimum limits for all new incinerators. A further tightening of environmental standards for waste incineration will come about through the new incineration directive, which is due to be implemented in 2002.

As a result of strict regulation of incinerators under both community and member state legislation, a very marked improvement in emissions has been achieved. Nevertheless, incineration remains a highly contentious waste management option, not least because of remaining concerns over emissions, especially of dioxins.

1.1-EU waste policy

1.1.1-The Waste Hierarchy

Waste management varies quite a lot across the member countries of the EU, as shown in Figure 1.1.

Waste policy in the EU widely accepts the waste hierarchy of waste management to be (in order of priority) as seen in Figure 1.2.

Waste prevention Re-use Recycling Thermal decomposition with energy recovery (i.e. incineration with energy

recovery).

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Figure 1.1-Range of MSW treatment processes in the EU.

Figure 1.2-The EU waste hierarchy in waste management.

It also recommends the following principles:

Proximity principle Self-sufficiency principle

In spite of this general consensus, and a growing coherence of this hierarchy in policy lines of individual EU member states as a consequence of EU-Directives, the majority of waste in Europe is either landfilled or incinerated. Importantly, these are the

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methods which also entail the highest and most serious environmental and health risks.

The waste hierarchy. Within the hierarchy, the Governments do not expect incineration with energy recovery to be considered before the opportunities for recycling and composting have been explored

The proximity principle requires waste to be disposed of as close to the place of production as possible. This avoids passing the environmental costs of waste management to communities which are not responsible for its generation, and reduces the environmental costs of transporting waste

The self-sufficiency principle. The Governments believe that waste should not be exported from one country to another for disposal. Waste Planning Authorities and the waste management industry should aim, wherever practicable, for regional self-sufficiency in managing waste.

With regards to the EU Waste hierarchy, not everything has gone well, however. A move towards a waste policy aimed at reducing health effects should put more emphasis on prevention and re-use. Presently, EU waste policy is not founded upon health data. Fortunately the available data on health effects from waste management do not conflict, and in important aspects even coincide with the hierarchy proposed by the EU. For example, waste prevention is deemed to be the most important (no waste equals no health effects), followed by re-use and recycling. Despite this, the lack of consideration of the environment and human health is clearly visible in EU policy.

For instance, regulations put in place for incineration by the EU together, with national limits on this issue, are based on what is technically achievable rather than on health and environmental data.

Although emission limits set in the new EU directive have resulted in the closure and upgrading of some older incinerators in European countries, the policy itself is already outdated with regard to the OPSPAR agreement to phase out the releases of all hazardous substances within one generation. The EU directive is based on the conception that small releases of hazardous substances are acceptable. This is the conventional (though misguided) approach, which proposes that chemicals can be managed at "safe" levels in the environment. However, it is already known, or is a scientific opinion, that there are no "safe" levels of many environmental chemical pollutants such as dioxins, other persistent, bio accumulative and toxic chemicals and endocrine disruptors. In addition, the abandonment of the principle is increasing in political circles.

1.1.2-The Way Forward: Adoption of the Precautionary Principle and Zero release Strategy

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Adoption of the Precautionary Principle. The precautionary principle acknowledges that, if further environmental degradation is to be minimised and reversed, precaution and prevention must be the overriding principles of policy. It requires that the burden of proof should not be laid upon the protectors of the environment to demonstrate conclusive harm, but rather on the prospective polluter to demonstrate no likelihood of harm. The precautionary principle is now gaining acceptance internally as a foundation for strategies to protect the environment and human health.

Current regulation for incinerators is not based on the precautionary principle. Instead it attempts to set limits for the discharge of chemicals into the environment which are designated as "safe". In the current regulatory system the burden of proof lies with those who need to ‘prove’ that health impacts exist before being able to attempt to remove the cause of the problem and not with the polluters themselves. Based on knowledge regarding the toxic effects of many environmental chemical pollutants, which has accumulated over recent decades, a more legitimate viewpoint is that "chemicals should be considered as dangerous until proven otherwise".

We have now reached a situation, and indeed did some time ago, where health studies on incineration have reported associations between adverse health effects and residing near to incinerators or being employed at an incinerator. These studies are warning signs that should not result in government inactivity, but rather to decisions being taken which implement the precautionary principle.

There is already sufficient human health and environmental contamination evidence to justify a phase out of the incineration process based on the precautionary principle.To wait for further proof from a new generation of incinerators from an already harmful and dirty technology would probably be a blatant disregard for the environment and human health.

Adoption of Zero Discharge . The aim of "zero discharge" is to halt environmental releases of all hazardous substances. Although it is sometimes discussed as being simplistic or even impossible, it is a goal whereby regulation can be seen as resting places on the way to achieving it.

Zero discharge necessitates the adoption of clean production techniques both in industry and agriculture. It is essential that the change to clean production and material use should be fully supported by fiscal incentives and enforceable legislation.

The principle of clean production has already been endorsed by the Governing Council of the UNEP and has received growing recognition at a wide range of international fora. For instance, the adoption of the one generation goal for the phase out of all hazardous substances by the OSPAR Convention in 1998 necessitates instigating clean production technology under a zero discharge strategy.

In terms of waste management strategies, incineration is a dirty technology that can never fulfil the criteria of zero discharge. The way forward for waste management in line with a zero emissions strategy and hence towards sustainability, lies in waste prevention, re-use and recycling. In other words the adoption of the already well-known principle of "REDUCE, RE-USE AND RECYCLE".

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Implementation of REDUCE, RE-USE and RECYCLE. We live in a world in which our resources are generally not given the precious status by industry and agriculture which they deserve. In part, this has led to the creation, particularly in industrialised countries, of a "disposable society" in which enormous quantities of waste, including "avoidable waste" are generated. This situation needs to be urgently changed so that the amount of waste produced both domestically and by industry is drastically reduced.

Ways to help waste reduction include the use of economic instruments and environmental taxes. The use of these measures is supported by the EC and a number of environmental taxes are already in place in several European countries. However, far more action is presently required to stimulate the change needed for much more waste reduction to become a reality.

Current levels of recycling in European countries vary considerably. For instance, The Netherlands recycles 46% of municipal waste whereas the UK only manages 8%. Intensive re-use and recycling schemes could deal with 80% of municipal waste. It is recognised that fiscal measures can play a considerable role in encouraging re-use and recycling schemes whilst discouraging least desirable practices such as incineration and landfill.

Measures to be taken in the drive towards increased waste reduction, re-use and recycling, and therefore towards lessening the adverse health effects from waste management should include:

• The phase out of all forms of industrial incineration by 2020, including MSW incineration. This is in line with the OSPAR Convention for the phase out of emissions, losses and discharges of all hazardous substances by 2020.

• Financial and legal mechanisms to increase re-use of packaging (e.g. bottles, containers) and products (e.g. computer housings, electronic components).

• Financial mechanisms (such as the landfill tax) used directly to set up the necessary infrastructure for effective recycling.

• Stimulating markets for recycled materials by legal requirements for packaging and products, where appropriate, to contain minimum amounts of recycled materials.

• Materials that cannot be safely recycled or composted at the end of their useful life (for example PVC plastic) must be phased out and replaced with more sustainable materials.

In the short term, materials and products that add to the generation of hazardous substances in incinerators must be prevented from entering the waste stream at the cost of the producer. Such products would include electronic equipment, metals and products containing metals, such as batteries and florescent lighting, and PVC plastics(Vinyl flooring, PVC electrical cabling, PVC packaging, PVC-u window frames etc) and other products containing hazardous substances.

And more generally:

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• Further the development of clean production technologies which are more efficient in terms of material and energy usage, produce cleaner products with less wastes and which ultimately can operate in a "closed loop" configurations to serve the needs of society in a more equitable and sustainable manner;

• Implement fully the Precautionary Principle, such that, in the future, we may be better able to avoid problems before they occur. The continuation and further development of scientific research has a fundamental role to play in identification of potential problems and solutions, but we must be ready to take effective precautionary action to prevent environmental contamination and degradation even in the face of considerable and often irreducible uncertainties.

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1.2-IRWM (Integrated Resource and Waste Management) and incineration Waste in itself is an old issue. Now it has become important to examine the whole system, including the economic - and even social - burden on the environment. The key challenges are how to de-couple the increase in quality of life from growth in waste generation and how to use fewer materials but use them more efficiently. This will require us to focus more on resource efficiency as well as on how we manage waste. Underpinning this approach are two fundamental concepts: (i) that waste is a resource and not necessarily a burden; and (ii) that flexibility as regards system design and operation is essential for effective resource management. 1.2.1-Sustainability and resource and waste management

Historically, public health and safety have been the major concerns associated with waste management. These concerns still apply, but now society demands more than this - as well as being safe, waste management must also be sustainable. Sustainability can be thought of as a triangle, with one of the three elements; environmental effectiveness, economic affordability and social acceptability, placed at each of the angles. Sustainability is about balancing these three elements, and a stable balance requires all three elements to be considered equally.

Environmental benefits cannot be engineered into the development of a waste management system unless that system is both economically viable and socially acceptable.

1.2.2-Evolution from waste to resource management systems

A wide range of waste management systems is currently operated in Europe. Anevolutionary trend can be observed that began with waste management primarily addressing the issue of public health. Then, through an organized system of waste management optimization, this initial approach was superseded by a simplified environmental hierarchy approach which, in turn, was overtaken by an integrated approach to waste management where economic and environmental concerns were added to the system (the hierarchy being retained only as a default classification of options for waste managers), See Figure 1.3. This evolution of waste management systems should be encouraged, as this process will lead to more sustainable urban environments.

1.2.3-Flexibility is essential

An overall approach to waste management combines a range of collection and treatment methods to handle all materials in the waste stream in an effective, affordable and acceptable way. An integrated waste system includes a suitable waste collection and sorting system, followed by one or more of the following options:

Recovery of secondary materials (recycling) Biological treatment of organic materials (composting and/or biogasification); Thermal treatment (energy recovery) and (controlled) landfill.

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Together these form an integrated resource and waste management (IRWM). To manage all wastes in an environmentally and economically sustainable way requires a range of these options. The balance across these options will vary as it naturally reflects varying local conditions see Figure 1.4.

Figure 1.3-The evolution of municipal solid waste management

Figure 1.4-System boundaries for IRWM.

Effective IRWM schemes need the flexibility to design, operate and adapt systems in ways which best meet prevailing social (including legislative), economic and environmental needs. These are likely to change significantly over time and vary by geography. The need for consistency in quality and quantity of recycled materials, compost or energy supply, the need to support a range of disposal options and the benefit of economies of scale, all suggest that IRWM systems should be organized on

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a large-scale, regional basis. Any scheme incorporating recycling, composting or energy from waste technologies must also be market orientated.

1.2.4-The future

Eventually an IRWM system can itself become part of a resource management strategy, where all resources such as water, power, CO2 balance and waste are managed within a single optimized system in a cohesive and coherent way. In the area of natural resource and waste policy for example, decision-makers are beginning to accept the idea that a successful resource conservation policy must aim for an increase in resource efficiency and a reduction in environmental burden. This thinking will demand a paradigm shift towards an integrated resources management approach. The challenge for all stakeholders will be to move waste and resource management thinking into this broader context.

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1.3-Thermal treatment (general)

The purpose of thermal treatment of waste (which in the narrow sense usually means combustion in incinerators) is to reduce the bulk of waste needing ultimate disposal in landfills to an inert inorganic ash residue. Organic carbon compounds are oxidised to CO2 and water vapour, which are discharged to the atmosphere in the stack gas. Incineration of fossil carbon in plastics (for example) therefore makes a net positive contribution to global warming, but incineration of short-cycle carbon compounds (in paper, food, vegetation etc) is neutral in global warming terms. Residual organic matter remaining in the ash residue should be reduced to a very low level if the combustion process is carried out efficiently. The ash will therefore have virtually no capacity to form organic leachates or gas after disposal in landfills.

Heat, power or both can be recovered from thermal treatment. Most new incinerators are designed for energy recovery, and the new incineration directive (2000/76/CE) will require energy to be recovered as far as possible.

Thermal treatments of waste include combustion-based techniques and advanced thermal conversion (ATC) techniques. The most common form of incineration in use at present is large scale mass burn incineration, with annual throughputs usually in excess of 100,000 t/year.

Smaller plants burning specialised wastes or refuse-derived fuels (RDF), sometimes co-fired with peat, wood or coal are also available, often based on fluidised bed combustors. In the future we may see an expansion of ATC options such as pyrolysis/gasification. FBC and pyrolysis reduce overall emissions of harmful combustion products such as nitrogen oxides (NOx). Waste can also be co-incinerated in power plants, blast furnaces or cement kilns.

Since there are several types of waste and several types of combustion furnaces, there always the opportunity to find the best combination, i.e., which technologie(s) is best suited for a given waste(s).

Tables 1.2 and 1.3 summarize the most important situations.

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Table 1.1-Waste treatment options

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Table 1.2-Furnace designs for MSW, HW, and MW incineration

In this lecture we will be dealing with the following options:

1-Mass burn incineration

2-Pyrolysis/Gasification

3-Vitrification

4-Gas recovery Anaerobic digestion Landfill gas

5-Co-Incineration

6-RDF combustion in: Fluidised bed combustors (FBC) Co-combustion in coal-fired power

plants and cement kilns

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NOTE: with the exception of landfill gas recovery, all other technologies divert waste streams from landfill. Nevertheless some landfill is still required for the residues remaining after the recovery of energy if acceptable market outlets for these do not exist.

1.3.1-Mass burn incineration

Incineration of municipal and other wastes is a dedicated facility equipped with energy recovery equipment for production of heat and/or electricity.

The exhaust gases from waste incineration facilities may contain many potentially harmful substances, including particulate matter; oxides of nitrogen; oxides of sulphur; carbon monoxide; dioxins and furans; metals, such as lead and mercury; acid gases; volatile chlorinated organic compounds; and polycyclic aromatic compounds. Some pollutant emissions are formed, in part, by incomplete combustion that may in turn lead to the formation of pollutants such as dioxins and furans. The formation of products of incomplete combustion is governed by the duration of the combustion process, the extent of gas mixing in the combustion chamber, and the temperature of combustion. Good combustion efficiency depends upon maintaining the appropriate temperature, residence time, and turbulence in the incineration process. Optimal conditions in a combustion chamber must be maintained so that the gases rising from the chamber mix thoroughly and continuously with injected air; maintaining the optimal temperature range involves burning of fuel in an auxiliary burner during start-up, shutdown, and process upsets. The combustion chamber is designed to provide adequate turbulence and residence time of the combustion gases. 1.3.2-Pyrolysis and gasification

The related processes of pyrolysis and gasification break down waste materials into liquid and gaseous fuels. Both are being developed to treat or utilise a wide range of wastes and biomass fuels. These relatively new technologies are still at an early stage of commercial development.

Pyrolysis and gasification are methods of recovering value from waste by thermal treatment. In this objective, they are similar to incineration, but they achieve their results in different ways. Whilst incineration fully converts the input waste into energy and ash, these processes deliberately limit the conversion, so that combustion does not take place directly. Instead, they convert the waste into valuable intermediate materials that can be further processed for material recycling or energy recovery.

Pyrolysis is the thermal degradation of waste in the absence of air to produce char, pyrolysis oil and syngas.

Gasification is the breakdown of hydrocarbons into a syngas by carefully controlling the amount of oxygen present.

These technologies provide more flexibility, in waste-to-energy terms, as the resultant fuel can be tailored to the specific application, can be stored or transported, and there are more options for converting the fuel into energy.

1.3.3-Vitrification

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Vitrification of solid wastes involves much higher temperatures than in conventional incineration and pyrolysis and gasification (>1500ºC). These temperatures can be achieved through plasma technologies. These technologies do not differ substantially from those used in fly-ash treatment inertization.

1.3.4-Gas recovery

Energy - in the form of methane gas - can be extracted from landfilled waste or anaerobic digestion. While practised in some EU countries, these methods are not nearly as widely available as incineration with energy recovery. Vitrification, pyrolysis and gasification are even less frequently used.

Landfill gas collection. Landfill gas is produced by the decomposition of organic wastes in a landfill site. Such gases normally contain around 55% methane and 40% carbon dioxide. They are collected through networks of pipes and wells. Since methane is a greenhouse gas, its recovery and use has the additional benefit of reducing the potential for global warming. Most landfill gas is presently collected and just flared off, but an increasing number of facilities are being installed on sites where gas generation rates are high enough and the gas is used as a fuel to power the generation of electricity.

Anaerobic digestion. Organic waste can be treated in an anaerobic digestion (AD) process and the methane drawn off collected and used. The main difference between AD and landfill gas collection is a higher efficiency with AD. This is due to the use of an enclosed digester (operated under controlled conditions for temperature, pH, mixing and nutrient loading) rather than the uncontrolled processes taking place in a landfill and the difficulty of collecting landfill gas over the large surface area of a landfill. Its use for MSW treatment, often in combination with sewage sludge provides a methane rich fuel which, like landfill gas, can be used (after the removal of contaminants) to directly fire burners to generate electricity or which can be cleaned and added to gas supplies. AD produces a solid residue that can be aerobically composted and then used as a fertiliser.

1.3.5-Co-incineration and RDF combustion Co-incineration is the burning of waste in other furnaces than those dedicated to conventional incineration. It can take place in cement or lime kilns, blastfurnaces, metal smelters, etc (see Section 1.4.2 and 2.2.4). The same happens with RDF. The latter is a solid fuel prepared from MSW components (essentially paper and plastic) by sorting, shredding and extruding into pellets. These pellets can be burn in convencional furnaces, such as coal power plants.

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1.4-Incineration in the EU

1.4.1- Statistics

It is difficult to compare data on waste management across European countries. There is a great deal of variation on how data are collected and comparisons are difficult asMember States use different waste classifications. In addition, there is no obligation toproduce any data. The EU is currently in the process of producing regulations on waste management statistics to establish a harmonised system that will allow comparisons to be made across the EU (13).

According to a recent study by the Company Juniper Consultants, and reported by the Association for the Sustainable Use and Recovery of Resources in Europe (ASSURRE, 2002) and by Rylander and Hankohl (2002), the situation of WTE in the EU can be summarised as follows.

Waste quantities incinerated: of the nearly 134 Mt/y of MSW produced, about 18% are incinerated and 71% landfilled. The incineration capacity of the various countries is shown in Figure 1.5 in global terms, and in terms of per capita, respectively. These graphs show the “installed capacity”, and therefore slightly overestimate the actual amounts incinerated, since not all plants work full capacity. Denmark, Holland, Sweden and Switzerland are the countries with higher WTE production per capita.

Figure 1.5-Waste to energy capacity in the EU.

Waste management options: the methods of waste treatment vary widely across the Western Europe, as shown in Figure 1.6; Denmark, Switzerland and France are the countries where incineration is the dominant mode of waste treatment (more than 50% of the waste treated); on the other end we can find Spain, Italy and Finland.

Countries that dispose of a significant proportion of their waste by recycling also tend to have higher incineration rates. This is probably a combination of two factors: the reduced availability of suitable landfill sites and the implementation of the wastehierarchy, which defines reduction, reuse and recycling of waste as the preferred option and landfill as the least desirable form of waste disposal. Incineration with energy recovery is seen as preferable to landfill within this framework

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Figure 1.6-treatment and disposal of MSW, by method, in Europe.

Number of incinerator plants: there are about 304 incinerator sites in EU (18) and 295 in EU (15), with capacities of more than 30 000 t/y distributed across Europe, as shown in Figure 1.7. The trend in EU (18) has been to decrease their number until 1997, followed by an increase afterwards (Figure 1.7).

Figure 1.7-Number of incinerator plants in Europe.

Energy recovery: in almost every country with waste incineration plants, there is some kind of energy recovery. In general, there are two important uses for the energy recovered. Scandinavian countries use a high percentage of the recovered energy to produce hot water for district heating; the other countries, meanwhile, mainly produce steam for electricity production, mostly without using the remaining energy, which simply goes to waste. However, outside Scandinavia, there are moves towards more effective use of produced heat, as well as a significant tendency in the Scandinavian countries for more and more combined heat and electricity production (called co-generation).

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Of the 269 MSWI plants in EU approximately 88,5% have energy recovery; it is estimated that about 44 400 GWh/y of energy are produced, representing nearly 2% of the inland energy consumption. Of this energy, about 30% is in the form of electricity and 70% as heat (Figure 1.8). The co-generation ratio (i.e., the relative proportions of electricity and heat produced from waste incineration) varies much across the EU countries (same Figure 1.8). Germany, Holland, Portugal and Spain are the countries where electricity production predominates over heat production; on the other hand heat distribution is particularly important in countries where heat can be used for district heating systems (Denmark, France, Germany and Sweden).

Figure 1.8-Energy production from waste incineration in Europe.

The total EU energy capacity, and the capacity per capita are shown in Figure 1.9.

Figure 1.9-Total energy capacity, and capacity per capita in the EU.

Emissions control: almost every country has its own legislation concerning emissions from MSW incineration. However, all member countries of the European Union have to comply with the same EU Directives as a minimum. To achieve national and EU standards, advanced flue gas cleaning systems have to be installed; strict directives on emissions can be complied with by using state-of-the-art cleaning techniques, although this will still require considerable effort. In principle, newly designed flue gas cleaning systems often use the following sequence of equipment:

Electrostatic precipitators Multi-stage wet scrubbers with wastewater evaporation Fabric filters or wet electro-venturies with lime injection/active cokes

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SCR-DeNOx or SNCR-DeNOx.

Today, almost all incineration plants have some kind of flue gas cleaning system, and several have more than one (for instance, wet scrubbing combined with an electrostatic precipitator). Figure 1.10 illustrates the most common flue gas cleaning systems and their use as a percentage of the furnaces in 13 of the EU countries.

Figure 1.10-Flue gas cleaning systems in percentage

Waste incineration residues disposal: as emissions to the air are now very well controlled and cleaning technology is very advanced, research and development is increasingly focusing on the safe handling and better use of residues.

In general, the only part of the residues that can currently be reused is the bottom ash (slag). Before reuse, this can be crushed and/or sieved, with iron scrap being removed and in many cases recycled. Dependent on the quality of the bottom ash, it can be recycled and used in construction work, for instance. Several processes are under development, which will improve the bottom ash quality, to ensure it can be disposed of when the regulations are toughened. The bottom ash that is not reused is landfilled; however, because of the large amounts of bottom ash produced in waste incineration, there is pressure to reuse as much of it as possible. In some countries, the 'gravel' fraction of the bottom ash is used in the construction of roads, car parks and so on. Figure 1.11 shows the percentage of the bottom ash recycled and deposited in 1999. It should be noted that not all incineration plants are included in the data.

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Figure 1.11-Relative proportions of depositing/recycling of bottom ash.

There is a very limited reuse of residues from the different flue gas cleaning systems but most of it is landfilled in a secure way - stacked in big bags, stabilized with binders or in some other way safely landfilled.

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1.4.2-Incinerator costs and sizes

The costs and sizes of incineration plants. The average incinerator size in the EU is about 177 000 t/y (this means 20 t/h, or 500 t/d), varying from country to country (Figure 1.12): 83 000 t/y (in Norway) to 488 000 t/y (in The Nederlands). The same figure shows that the average size of MSWI plants has increased since the 1980’s.

Figure 1.12-Incinerator capacities by site.

Treatment costs vary from 20 to 160 €/t, as shown in Figure 1.13; the lowest prices in Spain and Denmark and the highest in Germany. The same figure shows that the EU average is about 75 €/t, and that the prices have been increasing all the time.

Figure 1.13-Incinerator treatment costs.

The cost of incineration is an ill-defined concept. Large variations between countries and facilities exist depending on the size of the facility, its age, the environmental standards applied, the technology used, income from sales of energy or recyclable materials, etc. However, European harmonization is at work and differences should keep decreasing over the next 10 to 20 years.

The trend towards ever stricter emission controls has led to significant increases in the cost of incineration. Certain industrial actors judge some cost increases excessive in relation to the environmental benefits obtained. However, the cost of incineration

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seem to be getting close to its maximum, and in some cases there even seems to be scope for decrease. In recent state-of-the-art facilities of some northern European countries, the lion’s share of investment goes to flue gas cleaning: typically 1/3 for furnace and boiler and 2/3 for flue gas cleaning (e.g. a minimum of 40% in the Netherlands). Reportedly, this is not the case in countries such as the UK, France or Spain, where the current cost of state-of-the-art flue gas cleaning seems to reach only about 20% of the cost of the furnace. This could be due to differences in the technology used, the newer systems becoming ever cheaper for the same efficiency.

So far, income from sales of energy or recovered materials has remained limited, even if countries like the UK or Italy subsidise electricity from waste. This means that large amounts of money are still needed to finance the building and operation of waste incinerators. For industrial wastes, industries generally cover the entire cost of treatment and disposal of their wastes. Interestingly, increases in the cost of incineration do not always result in an increase in the price of waste incineration services. For example, underused dedicated waste incinerators in Germany reportedly practice very aggressive pricing policies, sometimes with the help of regional authorities. One must also note that end-of-pipe environmental solutions always lead to a decrease in the efficiency of potential energy recovery.

According to some sources, the use of non-integrated pyrolysis followed by the combustion of the char (and eventually the gas) as fuel in cement kilns could sometimes be cheaper than incineration in dedicated incinerators. Economic relevance of waste reduction. In view of the large costs associated to waste management in general and to waste incineration in particular, the reduction of the amounts of waste generated delivers immediate economic benefits, without speaking about the associated environmental benefits. Of course, the higher the price people have to pay to get rid of their wastes, the more incentive they have not to generate them. All the actors agree on this point.

However, two main factors contribute to limit progress towards reducing waste generation. The first is thermodynamics: zero waste processes cannot exist (entropy is always increasing). Therefore, human activity will always generate waste.The second is regulatory. While it is relatively easy to set targets for recycling rates or for emission limits applicable to designated facilities, it is not so easy to design and legislate controllable waste reduction objectives. This is because there is a multitude of factors controlling potential waste reduction, and they are dispersed at all levels of economic and social life. Nice extra wrappings added in the shops or at home for Christmas gifts are clearly unnecessary packaging. Can they easily be legislated away? A third factor may also come into play. A number of economic actors involved in waste management do not have any interest in seeing the amounts of waste (following the broad European legal definition) generated decrease because the amount of waste, scrap, residues and other waste-derived materials they handle could decrease and their profits suffer. One case in point is the existing waste incinerators. Their economic health lies for a large part in the amount of material they process because they get paid per tonne processed. Reducing waste would reduce the amount of material they process. One only has to see how some waste incinerators which have become oversized in Germany because of mandatory separation of waste at source for recycling are struggling for survival. This is reportedly compounded by the future

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entry into force of regulations excluding most organic wastes from landfills. In some cases, this seems to have led landfill operators to lower their prices and catch as much waste as possible (away from incinerators) to maximize profit before the restrictions. However, in many places such as France or Spain, incineration capacity is perceived by the actors to be still largely insufficient.

This explains why so far, most progress in this area has come from process and product optimisation and the implementation of cleaner technologies in Industry. The implementation of “Best Available Techniques” (BAT) following the introduction of the European IPPC directive (99/61/EC) is expected to contribute to a reduction of industrial waste generation on the long-term, but probably to a smaller extent than regulatory restrictions on landfilling and the general increase in the cost of waste management.

Commercial competition. In the cases where there is commercial competition for a given waste between waste incinerators and industrial players practicing co-incineration, the latter often benefit from an economic advantage.

While the dedicated waste incinerator only has costs and needs to be paid for its service, the industries involved in co-incineration are replacing an existing fuel cost by waste, for which they are often paid. The higher the price of fossil fuels, the larger this advantage. Indeed, they need to build and operate proper waste handling facilities that have a cost, but they can generally undercut the price asked by the incinerators for eliminating the waste. Co-incineration plants have already made their investments and they have flexibility in operation, which allows them to continue to operate even if waste should not be available. They also usually benefit from a high energy recovery efficiency.

Some industrial facilities also operate less expensive pollution control devices than waste incinerators. As a result, they tend to set their prices relatively to the prices practiced by the dedicated waste incinerators in order to maximize profit. Nevertheless, because of technical limitations (in particular chlorine content) and limited capacity, they cannot take all the available waste. It is difficult to know which fraction of the waste would be technically unsuitable for co incineration, but, considering the robustness of the cement manufacturing process and the possibilities of pre-treatment, it is likely to be small. In any case, the pursuit of profit in waste management should under no circumstances lead to compromises on the environmental profile of waste treatment.

An emerging factor can contribute to offset this situation. In a competitive market, in order to provide maximum convenience for their clients, and to capture as much of the waste as possible, the actors involved in waste combustion can become involved in waste management at large and offer one-stop solutions to their clients. This way, they have an economic incentive to develop recycling and recovery activities that generate income from the sale of the products obtained (e.g. energy, basic raw materials, recycled solvents). However, electricity recovered from waste in the EU appears to be often paid less than that produced by the traditional power plants. In the UK and Italy, on the other hand, electricity from waste incinerators is paid well above market rates.

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Under such circumstances, a dedicated waste management company may prepare waste streams meeting certain specifications and sell them for co-incineration. In parallel, a company involved in co-incineration may send pre-treated fractions, undesirable for its own process, to a waste management company. Such examples already exist in Europe and use market mechanisms to optimise globally the management of waste.

However, national institutional structures can be a major barrier to this sort of developments, in particular if responsibilities for waste management remain fragmented in the hands of municipalities. The waste incinerators operated by public authorities seldom participate in this type of “multiservice” market developments because of administrative rigidities and of their dependence on a different economic logic than private or semi-private operators. In general, across Europe, markets are private for hazardous wastes and public for municipal solid wastes. Hazardous waste treatment facilities are usually also privately owned and do not hold concessions. As a result, the hazardous waste market is significantly more liberal than the municipal solid waste market and hazardous waste treatment is not supported by public funding.

At this point, it must be said that dedicated waste incinerators offer a higher long-term guarantee for the treatment of waste than other industrial sectors for which the use of waste is “opportunistic”, and usually follows economic considerations. A flexible market within a clearly regulated frame can help direct each waste towards the optimal management option.

Fairness. In the context presented above, it is difficult to resolve the issue of fairness of competition between the various actors involved in waste management. Fairness can be evaluated in different perspectives according to the objectives pursued.In an environmental protection perspective, all emissions should be reduced to their no-impact level, irrespective of their source or of the economic impact on the sources.

One approach can be to set comparable emission levels for single emissions for all sectors. To be meaningful, these limits must be established in terms of fluxes of contaminants. While attractive in principle, this approach has the draw back to imply widely different costs for the reduction of emissions according to their origin. The economic efficiency of the total reduction is not taken into account.

Another approach, introduced in European policy by the IPPC directive, is to look for a global reduction of all emissions at each industrial site. In this approach, there is an incentive to use the “Best Available Technique”, providing the best result overall without necessarily achieving the same individual emission limit values for all. Because the IPPC approach focuses of the rate of improvement, a few critics say theIPPC approach gives an unfair advantage to those who pollute most because it is generally easier to achieve a given percentage of reduction in emissions on a dirty facility than on one which already meets stringent environmental standards (law of diminishing returns). This approach provides some degree of optimisation along techno-economic lines but a safety net of emission limit values for contaminants of particular concern (e.g. mercury) can be combined with this approach.

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A third approach is to use tradable emission permits, which undoubtedly allow to minimize the cost of emission reductions but raise issues about the fairness of their attribution at the start (again, an “unfair”(?) advantage at the start to those who pollute most).

Today, the directive on large combustion plants (not waste) allows the release of higher fluxes of the same contaminants (NOx, SOx, etc) than the directives related to the incineration of waste and the coherence of European policy can be questioned on that point.

In a static and local economic perspective, local employers must be preserved. Therefore, the ones will defend their incinerators, the others their cement kilns or their power plants, depending on which is where. This perspective can play at local, regional, national and European level, with different outcomes according to the level considered. These days, for example, the Asian crisis has led to a large cement production overcapacity in Asia. Current low transport costs could allow Asian cement to reach Europe at a cost well below European production cost. Increased economic pressure on European cement kilns because of tighter environmental regulations can therefore encourage multinational cement companies to close European sites.

Thirdly, the social perspective also has different dimensions. In the “quality of life” dimension, on the one hand, the famous “NIMBY syndrome” (NIMBY is the acronym for “not in my back-yard”) translates the fact that nobody wants to bear the unavoidable nuisances inherent to waste management or other heavy industrial activities. In the “socio-economic” dimension, on the other hand, people want to benefit from the economic activities of our society (jobs at an incinerator, a power plant or a cement kiln, taxes paid by these activities to the municipalities, etc). Again, at this point, interests will diverge according to the current position of the actors, their flexibility in terms of employment, their geographical mobility and other factors.

Again here, different levels at which the issue is considered may lead to different conclusions.In any case, the debate about the fairness of the competition between cement kilns and dedicated incinerators is currently very hot. Existing European waste legislation sets emission standards for all waste incinerators while it sets standards for co-incineration only in the case of hazardous wastes.

The new legislation for the incineration of waste calls for identical emission standards for waste-related emissions for both waste incinerators and cement kilns using waste. A resolution of the dispute will likely be achieved when one of the perspectives presented above will be chosen by all the main actors concerned and applied according to the main European policy objectives.

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1.4.3-Future trends

Most development within waste-to-energy takes place within existing technologies:

Improved incineration conditions in the furnaces, with more effective incineration of the organic content in waste and in flue gases

Improved energy recovery, with measures to minimize corrosion problems Improvements in flue gas cleaning equipment.

To some extent, new technology is being introduced in the field of flue gas cleaning, but even here, most development takes place within existing systems.

Incineration on grates is still the prevalent technology, with several designs of fluidised bed system as the alternative. Most waste-to-energy processes take place in large units and in large plants, though interesting installations with grates in small units and small plants have been introduced and operated in recent years. This small-scale technology can be of considerable interest to smaller cities, municipalities and different industries, if it is shown to work satisfactorily in the long term.

For some time, efforts have also been made to develop and introduce gasification and pyrolysis as methods for the thermal treatment of waste. So far, there has been very little success, and a number of failed attempts. For the time being, all those interested in waste treatment and waste-to-energy are following results, and experience from the full-scale Thermoselect plant in Karlsruhe closely. However, there is at present no clear indication that the full-scale technology works in an entirely satisfactory way. At the small scale, gasification technology has been introduced at some plants in Scandinavia, though once again, the long-term results and experiences will be closely watched, before any certain conclusions can be drawn.

As we have seen earlier, landfilling is still by far the most widely used waste disposal option in the EU. However, many experts believe that the various types of incineration of waste will widely benefit from the restrictions on landfilling introduced by the new directive and from the requirements on “recovery” of packaging waste. In fact the Landfill Directive came into force in 1999, its main aim being to prevent or reduce as far as possible the negative effects of landfilling waste on the environment and human health. The Directive sets targets for Member States to reduce the amount of their biodegradable municipal waste sent to landfill.

Biodegradable waste was focused upon because it is the biodegradable element of waste that breaks down to produce methane, which is a powerful greenhouse gas. In addition, new space available for landfill is limited and this means that ways need to be found both of reducing the amount of all types of waste produced and of disposing of the waste that is produced.

To ensure compliance with the Landfill Directive the Government has set national targets for recycling of MSW and reduction of biodegradable MSW being sent to landfill. The overall aim is to raise national recycling rates to at least 17% by 2003/04 and at least 25% by 2005/2006 and reduce landfill discharges to 35% of the 1995 value until 2015 (2020 in some states).

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Additionally, the amount of municipal solid waste incinerated in the EU is expected to increase from 31 million tonnes in 1990 to more than 56 million tonnes in 2004 and the amount of sewage sludge incinerated is also expected to increase steeply in the next few years. This probably explains why, in spite of the current general reluctance of the European public for waste incineration, a majority of municipal solid waste incinerator operators in Europe appear to expect an increase in their activity over the next five years (Figure 1.14).

Dedicated incineration and co-incineration are often seen as direct competitors. However, in some cases, they seem to be evolving towards a common goal. They started from very different points corresponding to their original functions. The waste incineration companies were created to eliminate waste, or at least stabilize them and reduce their volumes. The cement kilns and power producers were created to make cement and power.

Figure 1.14-Operators expectations of the utilization of their incineration capacity for MSW: 2005 vs 1998.

A combination of increased environmental consciousness, environmental regulations and competition for the same waste led to a range of positive developments. On the one hand, it pushed the dedicated waste incinerators to increase recovery and recycling whenever possible in order to decrease costs and increase profitability: today, all the new waste incinerators recover energy. This is most obvious for the private of semi-private operators. On the other hand, it pushed the cement kilns and the power plants to generally improve their environmental profile. As a result, since the 1970’s the energy requirement per tonne of cement produced has decreased by 30% and wastes are increasingly viewed as a resource that can be fed into productive economic activities.In Belgium for example, some waste incinerators and some cement kilns are simultaneously competitors and customers on a fairly open waste market. Today, both provide a better optimised combination of products and services (better “industrial ecology”). This can be a beneficial trend provided health and environmental safeguards are preserved. This is a sound basis to allow the flows of what may one day no longer be called “wastes” to reach their optimum treatment option.

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“Industrial ecology” is a concept being increasingly referred to. According to this concept, economic activities, and in particular industries must be associated so as to create a sort of symbiosis minimizing overall nuisances (e.g. the wastes from one industry can be used as raw material by a neighbouring industry). This offers interesting perspectives for the long-term.

In terms of R&D, the main drivers for waste incinerators over the last ten years appear to have been the improvement of ash management methods (stabilising, recycling), the improvement of the thermal conversion systems (resulting in more stable ashes) and to a lower extent the improvement of flue gas treatment. Factors such as inconsistent market demand, lack of agreed test methods and quality criteria and confused legal provisions are hindering the development of ash recycling.

With respect to technology choices, a recent industry survey by Juniper consultancy indicates that fluidised beds, pyrolysis and gasification are likely to increase their market penetration in the next few years. R&D is continuing on co-incineration and co-gasification technologies with improved efficiencies.

In particular, the following are the more often-anticipated evolution trends.

Larger, more economic plants with better environmental performance, improved energy efficiency and lower unit operating costs.

Tighter standards and greater public scrutiny in terms of protection of health and the environment. With the right investment in technology, all existing and new installations can meet EU standards as stipulated in the new EU Incineration Directive (2000/76/EC).

Less regulatory pressure entailing a wider use of so-called 'economic instruments' such as carbon tax, tradable permits etc.

Recycling residues from incineration. Many European countries now require further recycling of residues from waste incineration. The bottom ash is, frequently used as a roadbed material. Fly ash and other scrubber residues will increasingly have to be stabilised either by cold stabilisation with cement or by thermal processes such as vitrification.

As deregulation in the energy sector gather pace, the private sector will play a greater role in ownership and plant operation.

The EU Landfill Directive 1999/31/EC stipulates a requirement to decrease biodegradable waste going to landfill to 35% of 1995 level within 15 years (in 3 steps). This legislation may even out some of the variations in incineration capacity between Member States. The greatest impact is likely in the UK, Spain and Italy where incinerator capacity is currently low. In any event, the use of incineration in the future should increase, as it is one of the main resource recovery options available.

Treatment costs rose by 3.5% per year between 1997 and 1999 - a slower rate of increase than in previous years

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In short, the predictions are:

Use of landfill for disposal of untreated waste being phased out. So, need for

much more waste treatment capacity

Improvements in combustion technology to increase efficiency and reduce need for pollution abatement equipment

Resource recovery integrated with waste treatment (ferrous and non-ferrous metals, energy recovery, use of ash for construction applications)

Increasing interest in novel processes using gasification and pyrolysis as alternatives to incineration

Greater role for the private sector in ownership and operation of plants

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1.4.4-Summary

We could summarize the WTE situation in the EU in the following way.

a) Relevance of waste incineration:

Certain sorted waste has a high calorific value. Power generated from mixed plastics waste, for example, represents a calorific value similar to coal while achieving a reduction of 29% in CO2 equivalent emissions in comparison to coal power stations.

Energy from waste directly saves fossil fuels and makes an important contribution to the reduction of EU dependency on foreign imports. It is estimated that just 10% of EU municipal waste would cover 5% of EU energy needs, saving up to 14 million tonnes of oil per year.

Energy from waste reduces overall greenhouse gas emissions in two ways. Firstly, it avoids methane and other emissions from waste disposed in landfill; secondly, it generates lower CO2 emissions than traditional fuels. An analysis1 of CO2 equivalent emissions per kWh of electricity produced by energy from waste showed that the global warming potential of energy from

waste is less than coal, fuel and even natural gas (as shown in the Report: “

Life cycle comparison of energy production of a waste to energy facility to other major fuel sources”, by Ecobalance, Washington, May 1997).

Energy from municipal solid waste already contributes 3% of EU electricity production from renewable energy sources. Furthermore, the overall emissions from municipal waste incinerators – which now must apply the strictest environmental standards – compare well to gas power stations, which are usually considered one of the cleanest technologies.

b) Facts and figures:

There are 304 facilities in 18 European countries. 96% of these recover energy from waste.

The average unit capacity is 177,000 tones per year. Units vary in size from an average of 83,000 tones per year per site in Norway to 488,000 tones per year per site in the Netherlands. Size of unit has an impact on treatment/operating costs.

On an annual basis, Europe has 50.2 million tones of capacity to treat household and related waste.

49.6 TWh (TWh = Tera Watt hours) of energy is recovered per year. 70% of this energy is used for district heating, 30% for electricity generation. Types of energy produced vary between countries, depending on optimum technology and local demand.

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The annual amount of energy generated from incineration is equivalent to the total electricity demand of Switzerland.

Per capita, energy recovered from incineration is highest in Denmark, Sweden and Switzerland. It is lowest in Spain, UK, Italy and Finland.

Treatment costs vary widely between countries, ranging from € 25 - 30 per tone in Spain and Denmark to € 160 per tone in Germany. (OBS: Treatment costs are defined as (operating cost + residue disposal costs + overheads + depreciation + finance costs) minus (value of energy + materials sales) but excluding profit, subsidies and taxes)

Capacity is heavily utilized, an indicator that incinerating MSW with energy recovery is an essential waste treatment option.

Waste Treatment methods vary by country; nevertheless, landfill is still the main disposal route.

c) Trends and policy directions

There is a trend towards larger, more economic plants with better environmental performance, improved energy efficiency and lower unit operating costs.

The trend is towards tighter standards and greater public scrutiny in terms of protection of health and the environment. With the right investment in technology, all existing and new installations can meet EU standards as stipulated in the new EU Incineration Directive (2000/76/EC).

Treatment costs rose by 3.5% per year between 1997 and 1999 - a slower rate of increase than in previous years.

As deregulation in the energy sector gather pace, the private sector will play a greater role in ownership and plant operation.

The EU Landfill Directive 1999/31/EC stipulates a requirement to decrease biodegradable waste going to landfill to 35% of 1995 level within 15 years (in 3 steps). This legislation may even out some of the variations in incineration capacity between Member States. The greatest impact is likely in the UK, Spain and Italy where incinerator capacity is currently low. In any event, the use of incineration in the future should increase, as it is one of the main resource recovery options available.

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1.5-Alternatives to incineration in thermal waste treatment

Waste management policy in the EU enshrines the principles of sustainable development in the familiar waste management hierarchy, which underpins policy in this area. The hierarchy of waste management options places the greatest preference on waste prevention. Where wastes cannot be prevented, the order of preference decreases in order re-use, recycling, recovery of energy and finally (as the least preferred option) the disposal in landfills of stabilised wastes from which no further value can be recovered. With some 60% of MSW within the EU still being disposed of to landfill without any form of pre-treatment and extensive reliance on incineration for treatment of most of the remainder, it is clear that there is considerable scope for improvement.

As part of the suite of measures to improve the sustainability of waste management, the Landfill Directive (1999/31/EC) introduces requirements on member states to reduce the amount of biodegradable wastes disposed untreated to landfills. To achieve this objective, the Directive has introduced targets for reducing biodegradable waste disposed of to landfills to 75% of 1995 levels by 2006, reducing to 50 and 35% by 2009 and 2016. The directive also requires improvements in environmental standards of landfills, in particular by requiring greater use of landfill gas collection and energy recovery from the methane in it, in order to reduce the main greenhouse gas impact of this waste management option. To help meet the targets in the landfill directive, the European Commission is currently considering introducing further measures to encourage the adoption of alternatives to landfill for managing biodegradable wastes. The general principles developed for the treatment of biodegradable wastes (‘biowastes’) are, in order of preference, as follows:

Prevent or reduce biowaste production and its contamination by pollutants; Re-use biowastes (e.g. cardboard); Recycle separately-collected biowaste into original material (e.g. paper and

cardboard) whenever environmentally justified; Composting or anaerobic digestion of separately-collected biowaste that is not

recycled into original materials, with the compost so produced being used in agriculture or for other environmentally beneficial purpose;

Mechanical and biological treatment (MBT) of non-source separated biowaste as a pre-treatment for landfill disposal, and, finally;

Use of biowaste for energy recovery.

These options are shown schematically in Figure 1.15.

Landfilling. Landfilling involves the managed disposal of waste on land with little or no pre-treatment. Landfilling of biodegradable wastes results in the formation of landfill gas. The methane emitted in landfill gas is thought to represent the main greenhouse gas impact of MSW management. Currently about 60% of MSW in the EU is disposed of directly to landfills. As the least favoured option in the waste management hierarchy, landfill should be reserved for stabilised wastes from which no further value may be recovered. Landfill gas may be collected and either disposed of by flaring or used as a fuel. All components of MSW are currently acceptable for landfilling, including residual fractions left over after the separation of materials for

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recycling and the residues from pre-treatment processes such as incineration and MBT.

Mechanical–Biological Treatment (MBT). MBT is a pre-treatment option for landfilling. Raw MSW (or residual waste enriched in putrescible wastes after the removal of materials for recycling) is processed by a combination of mechanical and biological steps (shredding, sieving, composting and sometimes anaerobic digestion) to reduce the bulk and biological activity of the processed waste, which is then landfilled or used for landfill site cover or restoration. Recyclable or combustible materials may be removed from the waste for recycling or incineration. Pre-treatment of MSW by MBT prior to landfilling significantly reduces methane emissions from the landfilled waste, compared with untreated MSW. MBT is currently mostly confined to Austria and Germany.

Figure 1.15- Waste management options

Composting. Composting and the related process of anaerobic digestion (see below) are used for food and garden wastes. Composting makes use of microorganisms to oxidise biodegradable wastes to carbon dioxide and water vapour, using oxygen in the air as the oxidising agent. A humus-like residue is left that is then used as a soil conditioner in agriculture or land reclamation or possibly as a growing medium in gardening orhorticulture. Use of compost may have beneficial effects on greenhouse gas fluxes by replacing other products like fertiliser and peat and may also lead to increased storage of carbon in the soil (carbon sequestration). Industrial scale composting can be undertaken in open heaps that are turned and mixed mechanically (windrows), or alternatively in closed vessels with internal mixing and aeration. Composting can, of course, be undertaken with minimal equipment at home in most houses with suitable garden space. Efficient source segregation of food and garden wastes destined for centralised composting is an absolute prerequisite if the resultant compost is to be of sufficient quality for marketing.

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Anaerobic digestion (AD). Like composting, AD is a biological process, but it takes place in sealed vessels in the complete absence of air (i.e. under anaerobic conditions). The process converts biodegradable waste to a biogas containing methane and carbon dioxide. The biogas is then used as a fuel, potentially displacing fossil fuels. AD is essentially a controlled and accelerated decomposition process using the same types of microorganisms that produce methane in landfills. The volume-reduced solid residue (digestate) is used like compost, but usually after a period of maturation by composting. Clean source segregated feedstock is essential if the compost is to be suitable for marketing

Recycling. Recycling diverts components of the waste stream for reusing the materials contained within them. Provided the greenhouse gas impacts of separating and processing the recycled material into new products are less than those of manufacturing the products from primary material, then net saving results. Some materials can be recovered mechanically from bulk-collected MSW, such as metals recovered in incinerator ash and metals and glass recovered from MBT. The subsequent clean up of these materials for recycling is relatively straightforward and so there may be a market for them. To obtain higher quality of material requires segregation from other wastes at source. This is usually essential for paper and plastics recycling, and for all wastes, a higher price and better market access is usually achieved for source-segregated materials.

NOTE: Landfill and anaerobic digestion (AD) are, in fact, biological treatments; however as the main products issuing from them are combustible gases, they will be described in more detail in Section 2.4.2 later on, in the sense that these processes can also be envisaged as specific and sui generis pre-treatments of a waste in order to produce a gaseous fuel to feed an incineration unit.

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2-INCINERATION TECHNOLOGIES



Incineration subsequently developed during the latter part of the 19th century as a means of reducing the bulk and hazardousness of waste produced in the rapidly growing metropolitan areas. It soon became used as an opportune means of energy recovery. By 1912, there were some 76 incinerators operating in England, recovering energy as heat or electricity. New economic prosperity following the Second World War led to an increase in the amounts of waste produced per head of population, and incineration enjoyed a considerable growth in capacity. However, the communities in which they were located often regarded waste incinerators poorly. Even as late as the 1970s, emission control on incinerators was usually limited to simple cyclones for reducing dust emissions. Poor plant design and operating standards resulted in lack of control over combustion conditions, giving rise to emissions of smoke, odours and high levels of residual organic matter in the ash. Incinerators were identified as major urban sources of heavy metals, dust, acid gases and NOx, and products of incomplete combustion, such as dioxins and other toxic organic micro-pollutants. Concern over the public health impacts of these emissions led to the introduction of the 1989 incineration directives, the first community wide legislation to set minimum environmental standards for waste incineration. The 1989 directives resulted in the closure of existing plant that could not be upgraded to higher standards, and set minimum limits for all new incinerators. A further tightening of environmental standards for waste incineration will come about through the newly issued incineration Directive, which is due to be implemented in 2002. As a result of strict regulation of incinerators under both community and member state legislation, a very marked improvement in emissions has been achieved. Nevertheless, incineration remains a highly contentious waste management option, not least because of remaining concerns over emissions, especially of dioxins.

An incinerator plant does not necessarily need to be an ugly place: Figure 2.1 illustrates the Edmonton incinerator (in UK), processing about 2000 t/d of MSW.

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Figure 2.1- Edmonton (UK) incinerator.During combustion, the waste is burnt in the presence of a good supply of air, so that organic carbon is essentially completely oxidised to CO2, which, along with water vapour and trace products of combustion, is discharged to the atmosphere. Energy is recovered in the form of steam, which is used to drive turbines for electricity generation. Some incinerators may also provide steam or hot water for process or community heating schemes as well as electricity in combined heat and power (CHP) applications. There are two main approaches to waste combustion – mass-burn incineration and process and burn incineration, in which a refuse derived fuel (RDF) is first prepared. Mass-burn incineration is currently the most widely deployed thermal treatment option, with about 90% of incinerated waste being processed through such facilities. As the name implies, waste is combusted with little or no sorting or other pre-treatment.

The typical main blocks constituting a MSWI plant are:

Waste handling and storage area Combustion furnace (including energy recovery) Air pollution control devices (APCDs)

as shown in Figure 2.2. Some plants do have also, included in the APCD the Inertization System for the air pollution control residues (APCRs), mainly constituted by fly-ash, alkaline additives and activated carbon; as shall be seen later on, these APCDs can be of the dry, semi-dry and wet types (or combinations thereof).

Figure 2.2-Main bloc components and gas, liquid, and solid streams of a MSWI plant.

The basic operation of an incinerator plant is described as follows. Waste arriving at a mass-burn incinerator is tipped into a loading pit and from there transferred by crane and grab system into the combustion chamber loading chute. The waste is then conveyed through the combustion chamber, usually on a moving grate system (of which there are many designs) or through the slow rotation of the combustion

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chamber itself (rotary kilns). Whatever system is used, its purpose is to ensure thorough mixing and even combustion of the waste, so that complete burnout has occurred by the time the ash residue is discharged into a water-filled quenching tank at the end of the combustion chamber. Air is introduced from below and above the grate at flow rates adjusted to suit the rate of combustion. The hot combustion gases pass through heat exchange sections of the combustion chamber, where steam is generated for energy recovery. The cooling combustion gases then pass through various stages of emission control. These include dry or wet scrubbers for removing acid gases (SO2, HCl), injection of reducing agents such as ammonia or urea for controlling NOx emissions, activated carbon injection for dioxin control, and finally particulate removal by filtration or electrostatic precipitators, before the cleaned gases are discharged to the atmosphere. 2.1-Description of a typical incineration plant

In Figure 2.3 a typical modern incineration plant is shown schematically.

Figure 2.3-Description of a typical incineration plant

Storage and Handling Area

The solid waste storage and handling area consists of either a large tipping floor or tipping pit onto which waste is discharged directly from collection vehicles.

The tipping floor and tipping pit are usually enclosed in a building to control wind and odour problems, as well as to keep precipitation from increasing the moisture content of the waste. This area should be large enough to handle at least three to five days’ waste generation volume. This additional space allows for waste storage during weekends, plant outages, and periods of heavy precipitation, when incinerator loadings may need to be reduced to allow for proper burning of wet waste.

A large waste-tipping floor or pit also facilitates the operator in mixing the waste (i.e., dry stored waste may be mixed with incoming wet waste after a rainfall). This results in a more uniform heat feed rate into the furnace.

For facilities with a tipping floor, waste is normally pushed into the furnace using a small tractor. At a facility with a tipping pit, a crane lifts the waste from the pit and

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drops it into a hopper. When loading the furnace, plant operators normally remove large, bulky non-combustible items from the furnace feedstock.

Combustion furnace (firing technique)

The waste is transferred with a crane (2) from the bunker (1) to the hoppers above the furnaces, and is fed continuously into the grate (3) as it is burnt. Combustion air is admitted via induced-draught fans (4).

When the waste is completely burnt, the ash falls down into a slag tank containing water (5) and is then conveyed to the slag bunker for subsequent transport to a landfill for final deposition.

Heat recovery system

The hot flue gases in the hearth rise upwards. The boiler walls consist of water-filled tubes. The flue gases heat the water to steam, which is collected in the steam drum (6).

Flue gas cleaning (APCD)

The flue gases that are formed are cleaned in several stages. Recirculation of the flue gases (7) halves the amount of the nitrogen oxide (NOx) emissions. The injection of urea or ammonia into the hearth (8) achieves a further halving of the NOx emissions (SNCR process).

The electrostatic precipitator (9) separates particulate matter from the flue gases.

The flue gas passes through a scrubber (10) where the content of hydrochloride, heavy metal, ammonia etc is removed. In the condenser (11) the moisture is condensed to water and the flue gas is cooled by district heating water.

In a rotating air-preheater (12) the flue gas is cooled even more. Condensed water from scrubber, condenser and pre-heater is cleaned and neutralized (13) before it's pumped to the receiver.

Lime (14) is injected into the flue gas stream to remove sulphur dioxide. Finally, the flue gases pass through a fabric filter (15) to remove lime and particulate matter and to reduce the mercury content. Large forced-draught fans (16) then eject the cleaned flue gases through the stack (17).

Electricity production

Figure 2.4 shows more details of the heat recovery system with electricity production.

a)Heat production alone:

All steam produced in the waste incineration boilers (1) passes to the direct condenser (2), where it is condensed and the heat transferred to the district heating water. Its temperature is raised from 50°C to 90-115°C, depending on the season.

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b)Heat and electricity production:

Steam from the waste incineration boilers (1) passes to the heat recovery steam generator (HRSG) (3), where it is superheated to 430°C. The steam then passes to the steam turbine (5), where 30 per cent of its heat content is converted to kinetic energy for driving the generator (6).

After this, the steam is condensed in the heat condensers (7) and the heat transferred to the district heating water. Its temperature is raised from 50°C to 90-115°C.

The hot gases (535°C) from the gas turbine exhaust (4) pass to the HRSG (3). Here, the temperature of the gas is gradually lowered to 135°C at the top of the stack. An SCR reactor is located in the middle of the HRSG.

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Figure 2.4-Electricity production in the heat recovery system.

The feed water pumps (9) supply the waste incineration boilers with water from the feed water tank (8).

The steam drum (10) is a vessel used to separate boiling water and steam.

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The condensate pumps (11) pump the condensate back to the feed water tank (8) thereby closing the water circuit.

The Figure 2.25 shows the main components of the turbine generator. The steam turbine (1) is of low-pressure type, consisting in principle of horizontally split casings and a rotor.

Figure 2.25-Components of the turbine generator.

Steam with a pressure of 16 bar and a temperature of 430°C from the gas turbine's HRSG expands on its passage through the steam turbine. Guide-vane carriers are mounted in the outer casing. The rotor is coupled to one end of the generator. An inlet/governing valve block controls the amount of steam and thereby the turbine load. The rotor is carried in two bearings. After passing through the turbine, the steam is condensed in a condenser connected to the district-heating network. The steam turbine has an electrical output of 25 MW.

The generator (2) converts mechanical energy to electrical energy. It consists of a stationary part, the stator, and a rotating part, the rotor. Both have an iron core forming a magnetic circuit.

The rotor is coupled to both the gas turbine and the steam turbine, which are geared to rotate at the same speed.

Coupling both the gas turbine and the steam turbine to a common generator simplifies the installation and gives a low first cost.

The gas turbine (3), of type GT10, consists of a gas generator and a power turbine. The gas generator is a ten-stage axial compressor. The first two compressor stages have an adjustable geometry. A two-stage turbine through a transition shaft drives the compressor. The combustor section is of annular design and is suitable for a wide range of liquid and gaseous fuels. Low-sulphur oil is used as fuel at Gaarstad (Sweden).

The two-stage power turbine is of overhung design with two bearings located in the cool area. The power turbine rotor has a nominal speed of 7,700 rpm, which is geared down to the speed of the generator.

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The complete gas turbine unit is mounted on a base frame containing the lubricating oil tank. The auxiliary systems are located in a separate room close to the gas turbine. The gas turbine has an electrical output of 25 MW.

NOx reduction with SCR

Figure 2.26 shows details of the SCR-DeNOx process.

Figure 2.26-Flue gas denitrification using the SCR DeNOx process.

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Several different methods are used to limit the environmental impact of a gas turbine. Controlled combustion minimises particulate matter emissions to less than 10 mg/MJ. The use of low-sulphur oil limits 502 emissions, while an SCR reactor and ammonia reduce NOx emissions.

In the Selective Catalytic Reduction (SCR) process ammonia (NH3) is injected into the flue gas. Ammonia converts the nitrogen oxide gases (NO and NO2, collectively termed NOx) to nitrogen (N2) and water. This takes place spontaneously at a temperature of 950°C. However, since the flue gases have a maximum temperature of 535°C, the reaction has to be activated by the SCR reactor. This is located in the HRSG, where the temperature is 350°C.

Ammonia and nitrogen oxides react with one another on " active seats" of the catalyst modules, which consist of a large number of corrugated metal plates forming channels through which the flue gases flow. The surface is coated with a carrier, titanium dioxide (Ti02), which gives a large reaction surface. The carrier also includes the active component, vanadium pentoxide (V2O5), where the reaction itself takes place.

A NOx removal efficiency of over 90 per cent can normally be achieved. The activity of the catalyst element modules decreases with time due to contamination and poisoning and the modules must therefore be replaced at regular intervals. Residue Control

The products of combustion include the combustor bottom ash and fly ash.

The bottom ash includes the heavy non-combustible materials (i.e., ferrous and nonferrous metals, glass, ceramics, etc.), and ash residues from the combustible material. Bottom ash is normally cooled by quenching in water and then moved by a conveyor system to a temporary storage and truck load-out area.

The lighter products of combustion and products collected in the emission control equipment are collected and transported in totally enclosed conveyors to a water-conditioning area to moisten the fly ash residue products and then discharged onto the bottom ash conveyor for truck load-out. Depending on the facility’s size and other economic factors, the ferrous metals in the bottom ash can be removed for recycling by magnetic separation. Some new systems can recover nonferrous metals as well.

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2.2-Incinerator furnace configurations (combustion chambers)

As we have seen, there are a number of combustible waste categories requiring disposal of which municipal solid waste (MSW) and non-hazardous industrial waste (NHIW) form the great bulk of the tonnage; other categories only represent a small part of the total. For historical reasons MSW has been the category that has been burned most in the past despite NHIW often having better fuel characteristics. However, both MSW and NHIW have poorer combustion characteristics than fossil fuels. All wastes therefore need to be burned in specifically designed combustors.

The nature and amounts of emissions and residues from the incineration of waste depend largely from the following conditions:

Nature of the waste treated and sometimes the presence of a pre-treatment (e.g. for recycling)

Technologies used and Operating conditions in the facility.

One overall parameter is that the combustion temperature should be in the range 850°C to 1100°C. The lower limit is that necessary to ensure complete destruction of harmful organic chemicals and the upper limit is that above which the production of thermal NOx becomes unacceptably high.

Various types of incinerators are currently manufactured. The choice of technology depends on the combustibility and characterization of the wastes as liquid, sludge or solid. Gases will not be considered here. The most suitable technology can then be identified based on the specifications of the waste (see Section 1.3, Table1.2).

Waste can also be burned in combination with other fuels in existing industrial processes: this is co incineration. In that case, it is either burned in power plants, blast furnaces, and lime kilns or in cement kilns, which are large rotary kilns operated at high temperatures. In all cases, the characteristics of the pre-treated waste feed must be compatible with the industrial processes considered in order to maintain operational and product quality criteria (see Sections 1.4.2, 2.2.4 and 2.2.5). The emission standards of these processes are different than for dedicated incinerators. This is a key issue in the debate. The incineration of waste is far from being always performed under the same conditions. The technology is constantly evolving in order to meet ever stricter environmental standards. Currently, the main technological advances introduced include on the one hand those that increase combustion and energy production efficiency, and, on the other hand, those that improve the efficiency of end-of-pipe emissions control. In all types of furnaces, energy recovery occurs through a boiler located after the combustion chamber or integrated to its exhaust. The boiler uses circulating water to recover the heat from the combustion gases in the form of steam or hot water. A number of different designs are used to that effect (e.g. water wall, bundles of water filled steel tubes, etc.).

There are basically four different conventional furnace configurations:

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Grate Rotary drum Fluidised bed Vitrification hearth (plasma, gas or electrically heated)

Sometimes the co-incineration process is also considered, another type of furnace, since it uses thermal reactors, such as: cement kilns, foundries, pulverized fuel (PF) furnaces, etc, for concomitant combustion of a supplemental fuel (solid waste); in this sense there are as many co-incineration furnaces as there are such those types of processes. The same applies to Refuse Derived Fuel (RDF) combustion. All these configurations will be described next.

There are, however, other technologies akin to combustion (incineration) that use also moderate to very high temperatures, but do not involve a straightforward combustion of the waste, such as the one happening in conventional incineration. Instead, they involve some form of extensive waste pre-treatment, or pre-conditioning, much more than in incineration. This pre-treatment can be either thermal or physicochemical: in the first case we have the so called “starved-air combustion” (pyrolysis and gasification), and in the second case the Anaerobic Digestion (AD) and Landfill Gas (LFG) processes. These will be dealt with later in Section 2.4.

2.2.1-Grate furnaces

Grate furnace incinerators are by far the most common technology for the incineration of MSW. They perform the so-called mass burn, which requires minimal pre processing (such as sizing, shredding, etc.) and occurs in facilities of varying size (from 50 to more than 2000 tonnes of waste per day) usually fed continuously. The waste streams they receive are not always very consistent.

As indicated by their name, grate furnace incinerators consist of a furnace in which the waste burns over a grate (see Figure 2.6). They usually operate in a gas temperature range of 750°C to 1000°C. Air for combustion is supplied by fans or blowers under and over the grates. The main variations in this technology are associated with the design of the grates (either fixed or moving). The moving grates are designed to increase mixing and air flow in the mass of burning waste in order to achieve a more complete combustion. These variations result in significant differences in terms of gaseous emissions from the incinerators and in both quantity and quality of the ashes produced. The large excess (in the order of 100%) of air needed for the satisfactory combustion of wastes in these furnaces has two main disadvantages: energy loss in the stack through the gases and need for a large boiler volume to handle the extra volume of gases.

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Figure 2.6-Grate combustion chambers.

2.2.2-Rotary kiln furnaces

Rotary kiln waste incinerators are not so popular for the mass incineration of waste in Europe but are commonly used for the incineration of hazardous wastes. A rotary kiln rotates the waste in a cylindrical furnace in order to optimise mixing and provide a

Figure 2.7-Rotary kiln combustion chamber.

uniform burn (see Figure 2.7). It usually operates in a gas temperature range of 800°C to 1000°C, possibly with a post-combustion chamber reaching temperatures of 850°C to 1200°C, and resists well to high temperatures. Gases, liquids, pastes, solids and even some items that are somewhat bulky can be handled in large quantities by rotary kilns. Even though they are mostly used in a continuous mode, they can also be operated in batch mode. Small ones can even be mobile and allow on-site treatments.

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2.2.3-Fluidised bed furnaces

This technology consists in a bed of sand kept in a fluid motion by hot air flowing upwards through it. This air is also used as primary combustion air. Fluidised beds for waste incineration typically operate in a maximum temperature range of 750°C to 1000°C, more typically from 750°C to 850°C and they have a high combustion efficiency.

Two main types of fluidised beds are used in Europe for the combustion of waste. In ‘bubbling’ beds, air velocity is maintained close to the maximum above which bed material is carried away. In ‘circulating’ beds, air velocity is high enough to entrain part of the bed material, which is then captured and returned to the bed. This second design allows more fuel to be burned in the bed because more heat can be carried out of the bed by the recirculated material. In terms of efficiency of energy recovery, fluidised bed combustors have an advantage over grate furnaces because they can operate with only 30-40% excess air. Both types are shown in Figure 2.8.

Figure 2.8-Fluidised bed furnaces.

Fluidised beds can handle liquids, solids, pastes and gases as long as they can be injected through nozzles and neither melt nor slag. This bars the incineration of bulky items but has the advantage of maintaining a more uniform temperature in the furnace. This is why they are mostly used for refuse-derived fuel (RDF) after significant pre-treatment. RDF is a material proceeding from waste specially prepared so that it can be used as a fuel. It has been processed and brought to known

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specifications for combustion (e.g. calorific value, ash content, particle size) even though it does not fulfill the stringent criteria of fuels and remains legally a waste. RDF is mostly pre-treated municipal solid waste. In rare cases, fluidised beds are also used for the incineration of municipal solid waste but their presence is expected to grow in the next few years. 2.2.4-Co-incineration

Wastes can also be burned in other installations than dedicated waste incinerators. These industrial facilities face few technical barriers to take advantage of the calorific value and/or of the mineral content of the waste provided it is pre-treated to suit the process. The main limitations derive from the composition of the waste and its possible contamination with elements that can impact the quality of the industrial products. In practice, the main industrial candidates to incinerate waste, besides the waste incinerators, are the steam and electricity producers, the blast furnaces, the lime kilns and the cement kilns.

The primary objective of the waste incinerators was traditionally to stabilize and reduce the volume of wastes. However, energy recovery has now also become an essential objective. The primary objective of the candidates to co-incineration is the production of industrial products such as energy, iron, lime or cement. The cement producers prefer to talk about “co-processing” because they use the mineral fraction of the wastes as raw material for the clinker. In short, one can say that while the dedicated incinerator must adapt to the waste, the co-incinerators adapt the waste they take to their processes.

The industrial actors involved in co-incineration have specific requirements for the waste they use. The energy producers want to obtain or maintain as high as possible a thermal conversion efficiency while the cement and steel producers also need to preserve the quality of their products. This imposes both process requirements and specific characteristics on the waste to be used such as calorific value, ash content, chlorine content or metals content. For example, the presence of chlorine in the waste feed is a major concern for co-incineration because it leads to the accelerated corrosion of the facilities, and in the case of cements it ends up as an undesirable impurity of the clinker. In the case of heavy metals, while cadmium or nickel from wastes may be interesting for the production of certain steel alloys, copper is mostly a nuisance for the quality of the product. An energy producer is not at all interested in the metal content of the waste for its electricity production while a cement producer wants calcium, silicium, iron and aluminium. However, all are concerned about the emission of heavy metals to the environment. Each can therefore best take advantage of different types of wastes. Section 1.3 (Table 1.1) proposes a schematic comparison of the various technical options for the incineration of waste.

2.2.5-RDF (Refuse derived Fuel) burning

As explained earlier, RDF burning is not exactly a different type of furnace, but more a different kind of furnace operation; in fact any of the furnaces described hitherto can burn RDF, but due to the special physical form of this fuel and its very high calorific value, some combustion chamber modifications have to be made on conventional furnace chambers. Although it can have various forms and compositions, RDf is

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usually composed of the paper and plastic fraction of MSW; this mixture is, in most cases, shredded, compressed and extruded into pellets.

RDF burning is in fact a form what is known as “process and burn technologies”, since it needs an extensive pre-treatment of the waste before it can be used as a fuel. Process and burn technologies differ from mass-burn incineration in the amount of pre-treatment applied to the waste, giving rise to a fraction enriched in combustible materials that can be used as a refuse-derived fuel (RDF). Processing the waste allows materials for recycling to be removed from the combustible residue, along with wet organic materials such as food and garden wastes for separate treatment. The combustible fraction (consisting of paper, card, plastic film etc) may then either be burnt directly as a coarse flock (c-RDF) or compressed into dense pellets (d-RDF) for sale as a supplement fuel in industrial boilers. An advantage of the RDF over mass-burn incineration is that because the waste is sorted and shredded before combustion, the combustion equipment can be smaller, less robust and therefore less expensive.

Fluidised bed boilers are finding widespread application for RDF combustion, which offers some advantages in terms of ease of emission control. They are also less sensitive to variations in CV of the incoming fuel.

RDF may be used as a fuel source in energy-requiring processes. RDF has, for example, been used with coal, wood and peat for power generation. High heat value wastes are also used in cement manufacture, where they can substitute directly for conventional fuels such as coal. The ash residue in this case becomes incorporated into the cement clinker. It is also possible to separate the plastics fraction of the waste (i.e. the highest calorific value component) for separate incineration, thus avoiding the inefficiencies associated with combustion of lower CV wastes. RDF and co-incineration are not major disposal routes outside a few niche applications. RDF technology developed considerably in the UK in the early 1980s, but the market has since been static and limited to a few of the surviving initial schemes. Some RDF combustors also operate in Italy, Finland and Germany. Similarly, there have been a few demonstrations of burning RDF with coal in conventional pulverised fuel power stations, but the added complexities of dealing with an additional fuel in the power stations have tended to militate against its more widespread uptake. RDF has been successfully used as a fuel in cement kilns, especially when enriched in high CV plastic waste, but generally the main waste-based fuels used for this purpose have been tyres, solvents and plastics collected from commercial sources.

2.2.6-Vitrification

Waste vitrification is the process that transforms waste materials into chemically durable, environmentally safe products. The process has already been adapted to municipal incinerator ash, municipal solid waste, medical wastes, contaminated soils and several hazardous wastes and even radioactive sludges and combustible wastes containing heavy metals and organics. The technology’s versatility and environmental and economic advantages provides a platform to manage almost all of the waste streams, often within the same integrated vitrification system.

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When dirt, soils and rock or inorganic oxides, are heated to sufficiently high temperatures, the materials melt. Molten lava is a natural example of this process and state of matter. In the high temperature (1300 to 1550°C), molten state, the liquid has no consistent crystalline structure or is vitreous.

When the molten material is drained from the smelter and cools rapidly enough, this non-crystalline, vitreous state is frozen into the solid. Longer cooling times will result in glass-ceramic composites. Complex organics such as wood, paper, oil, plastic and other combustibles cannot exist at high temperatures at normal atmospheric pressures except as much simpler organic gases like carbon monoxide, methane, ethylene and propane. Waste vitrification causes waste materials to pyrolyze.

Vitrification of solid wastes involves much higher temperatures than in conventional incineration and pyrolysis and gasification (>1500ºC). These temperatures can be achieved through plasma technologies (see an example of a full plant in Figure 2.14 and Figure 2.15); these figures also show the kind of products that can be recovered from the process. These technologies do not differ substantially from those used in fly-ash treatment inertization (see Section 3.2). Figure 2.9 shows a vitrification hearth for waste destruction.

Figure 2.9-Vitrification hearth chamber.

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2.3-Incinerator plants configurations

The majority of the furnaces are of the fixed grate type. Apart from the furnace configuration, what varies more from plant to plant are: (i) the APCD (Air Pollution Control Device), and (ii) the type of energy recovery and production.

Since there are various furnace designs and different APCDs, there can exist quite a number of combinations of the two to piece together a full MSWI plant. In the following figures (Figures 2.10 to 2.15) several complete plants configurations are shown.

The special cases illustrated cover the following situations:

Figure 2.10: a plant producing RDF pellets, for energy production

Figure 2.11: three possible applications of the excess combustion heat, in the co-generation mode of operation (CHP for district heating): in house heating, greenhouses, and swimming pools. Other alternatives (not shown): hot water, and low-pressure steam for nearby industries.

Figure 2.12: a state-of-the-art incinerator plant with cumulative dry scrubbing system, wet scrubbing system, and NOx reduction.

Figure 2.13: district heating in Gaarstad (Sweden); besides co-generation (or CHP, i.e., production of both heat and electricity) the plant uses a CCGT-Combined Cycle Gas Turbine.

Figures 2.14 and 2.15: two waste vitrification plants, showing the variety of final products that can be recycled.

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Figure 2.10-RDF plant

Figure 2.11-Heat recovery in co-generation (or CHP) during waste incineration.

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Fiugure 2.12-State of the art incinerator plant.

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Figure 2.13-Gaarstad (Sweden) CHP and combined cycle gas turbine (CCGT),

Figure 2.14-Plasma waste vitrification plant.

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Figure 2.15-Waste vitrification plant, and process products.

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2.4-Other thermal waste conversion processes

There are waste treatment technologies akin to incineration; they use different technologies, but have in common with incineration the fact that they all use more or less high temperatures for waste destruction (thermal treatments). The most important are: pyrolysis, gasification, anaerobic digestion (AD), and landfill gas (LFG) combustion. Whether or not AD and LFG are considered thermal waste treatments is purely subjective and a matter of convenience; they are essentially biological treatments, but as the main products issuing from them are combustible gases (methane), they will described now in more detail, only in the sense that these processes can also be envisaged as specific and sui generis pre-treatments of a waste in order to produce a gaseous fuel to feed an incineration unit.

2.4.1-Pyrolysis and gasification

Along with the combustion technologies outlined above, there is increasing interest in the advanced thermal conversion technologies of pyrolysis and gasification as applied to MSW. Pyrolysis is sometimes designated also as thermolysis.

These technologies are imported from early 1980’s coal and biomass pyrolysis and gasification technologies, only adapted to the new fuel (waste). The Industrial Revolution was fueled by gas starting in 1800 (primarily from coal) initially used for city and home lighting, then for cooking and power generation. The internal combustion engine was invented for producer gas about 1880. By 1900 most world cities had a "gasworks" and gasholders on the horizon, supplying gas to residents.

All of this changed starting in 1930, when natural gas from oil wells began to be used and now few of us remember the producer gas (manufactured , city, water gas etc.) era.

During World War II over a million gasifiers were built for the civilian sector while the military used up all the gasoline. Now that world oil supplies are being depleted and global warming is perceived as a threat to our environment, there is renewed interest in gas from biomass.

These technologies differ from combustion in that the waste is first heated in either the complete absence of air (pyrolysis), or with a very restricted quantity of air (gasification). Organic matter in the waste breaks down thermally to give a mixture of solid, liquid and gaseous products that are then used as secondary fuels or chemical feedstocks for industry. The secondary fuels are used to provide the heat input for the process and to run engines for power generation. The only combustion air required is for the engines, so that a very much lower volume of exhaust gas is produced for cleaning than in conventional incineration, allowing much lower emissions to be achieved.

Pyrolysis and gasification are, therefore, methods of recovering value from waste by thermal treatment. In this objective, they are similar to incineration, but they achieve their results in different ways. Whilst incineration fully converts the input waste into energy and ash, these processes deliberately limit the conversion, so that combustion

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does not take place directly. Instead, they convert the waste into valuable intermediate materials that can be further processed for material recycling or energy recovery.

Pyrolysis is the thermal degradation of waste in the absence of air to produce char, pyrolysis oil and syngas.

Gasification is the breakdown of hydrocarbons into a syngas by carefully controlling the amount of oxygen present.

These technologies provide more flexibility, in waste-to-energy terms, as the resultant fuel can be tailored to the specific application, can be stored or transported, and there are more options for converting the fuel into energy.

A wide range of alternative designs are being developed, but so far there are only about five plants in commercial operation in the EU (all of which are in Germany), with a further eight at the proposal stage. Commercial scales of operation are around 100,000 tonnes/ year of bulk MSW. Similar considerations regarding the demand for available waste of defined composition throughout the life of the plant apply as outlined for mass burn incineration.

Pyrolysis

Unlike the classic waste combustion technologies, pyrolysis is a thermal physico-chemical pre-treatment in the absence of oxygen. It does not achieve a complete oxidation of the waste. In the non integrated (single) pyrolysis processes, the closed reactor produces combustible gases containing condensable hydrocarbons and a solid (char). These products can be burned elsewhere. In the integrated processes, both gas and solid are directly burned or gasified (syngas). This leads some people to consider pyrolysis as a recycling technology not to be considered in a discussion about the incineration of waste. Others consider that non-integrated pyrolysis is a pre-treatment of waste. It is a more complex process than incineration.

Typical products from a pyrolysis process are shown in Figure 2.16 next.

Figure 2.16-Main products of pyrolysis processes.

During pyrolysis, the organic matter is decomposed by external heat (450-750°C). In modern installations, about 10% of the energy generated by pyrolysis is thus used to provide the process heat. Classic incinerators can also be operated locally, close to the

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grates, in a deficit of oxygen and perform pyrolysis to some extent. In Figure 2.17, the decomposition processes of two organic substances (such as cellulose and wood) is demonstrated. In Figure 2.18 a more detailed mechanism is shown.

Figure 2.17-Thermal decomposition processes during organic molecules pyrolysis.

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Figure 2.18-Mechanisms of biomass pyrolysis.

When biomass decomposes at elevated temperatures, three primary products are formed: gas, bio-oil and char. At high temperatures the bio-oil vapours are decomposed in secundary products like gas and polymetric tar. Yields of the primary pyrolysis products are temperature dependent. It can be observed that a maximum oil yield of 79 wt.% is obtained at 500 ºC. For the temperature range studied, the char yield decreases and the gas yield increases with temperature (see Figure 2.19).

Figure 2.19-Product yields in biomass pyrolysis.

When biomass is heated the molecular bonds of the biomass break; the smallest molecules gaseous, the larger molecules are called primary tars. These primary tars, which are always fragments of the original material, can react to secondary tars by further reactions at the same temperature and to

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tertiary tars at high temperature. This tar formation pathway can be visualised as follows:

Mixed Ogygenates

>Phenolic Ethers

>Alkyl Phenolics

>Heterocyclic Ethers

> PAH >Larger PAH

400 oC 500 oC 600 oC 700 oC 800oC 900 oC

The mechanism which gives rise to one of the pyrolysis components (tar) is shown in Figure 2.20. Many definitions of biomass tar have been given by as many institutions working on biomass gasification like:

the mixture of chemical compounds which condense on metal surfaces at room temperature

the sum of components with boiling point higher than 150°C all organic contaminants with a molecular weight larger than benzene

However, one general (uniform) definition does not exists. Apart from the general definition of tars, definitions have been given for heavy tars, gravimetric tars and light tars.

Figure 2.20-Tar formation during biomass pyrolysis.

The technology for pyrolysis and gasification is still considered by many people as lacking industrial maturity but a number of small capacity plants (~30 000 t/year) are in operation or in start up phase in Germany. In spite of a number of plant failures in the past, novel combinations of better proven process steps (e.g. pyrolysis + gasification) are giving this technology a new lease of life.

Examples of pyrolysis complete plants are shown in Figures 2.21 and 2.22.

One of the main advantages of pyrolysis is its capacity to produce combustible gases and a sort of char that can be used in industrial operations. Typically, 1 tonne of promised municipal solid waste produces approximately 200 kg of water during pre-drying, 390 kg of hot gases (calorific value: 13 MJ/kg) and 410 kg of solid residue containing 240 kg char (17 MJ/kg) and 160 kg minerals and metals. These values may

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vary according to the MSW treated and to process conditions: for example, a higher temperature will lead to a higher production of gas and will leave fewer solids.

Figure 2.21-Pyrolysis reactor (BTG-Biomass Teccnology Group). Biomass particles are fed near the bottom of the pyrolysis reactor together with an excess flow of hot heat carrier material such as sand, where it is being pyrolysed. The produced vapours pass through several cyclones (not shown) before entering the condenser, in which the vapours are quenched by re-circulated oil. The pyrolysis reactor is integrated in a circulating sand system composed of a riser, a fluidized bed char combustor, the pyrolysis reactor, and a down-comer. In this concept, char is burned with air to provide the heat required for the pyrolysis process. In this case the plant is self sustaining. Oil is the main product; non-condensable pyrolysis gases are currently flared-off, but application in a gas engine is foreseen. Excess heat can be used for drying the feedstock. BTG has demonstrated the rotating cone pyrolysis technology on the scale of 250 kg per hour based on wood residues

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Figure 2.22-Pyrolysis plant.

The solid carbon residue is like a char or a low volatile high ash bituminous coal, poor in sulphur but contaminated with some heavy metals.

Regardless of the process, after screening to separate ferrous, non-ferrous metals and minerals, the char can be sent to a combustion or to a gasification unit in an integrated process or washed with water in order to be stored. In the non-integrated process, the char is an alternative fuel for cement works, lime industry, steel works or classic power plant. The design size of integrated facilities is large (more than 100 000 tonnes per year). Non-integrated facilities are smaller (typically less than 50 000 tonnes per year) and are adapted to conditions of dispersed waste generation.

Unlike the classic grate incinerators, which require operating close to their nominal capacity (60-100%) to avoid problems, pyrolysis installations can reportedly operate in a wider range of capacity (40% to 150%). If this technology gains acceptance, this could provide the flexibility to adapt to variations such as seasonal tourist populations or changes in waste management systems. In spite of the recent progress in the development of this technology, many voices call for further demonstration of the merits of pyrolysis at industrial scale. A number of uncertainties about cost and final residues also need to be addressed. Nevertheless purchasing intentions for these technologies in Europe appear to be increasing.

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Gasification

Gasification is a thermal degradation of organic matter in the presence of a few percent of oxygen. This process has long been used for biomass in some European countries but is newly being developed for municipal solid waste. The main interest of gasification is to allow, besides the classic combustion and steam generation, the use of gas turbines with electricity generation efficiencies much higher than those achieved by steam turbines. R&D in this area is continuing.

Generally, biomass gasification is a thermal conversion technology where a solid fuel is converted into a combustible gas. A limited supply of oxygen, air, steam or a combination serves as the oxidizing agent. The product gas mainly consists of carbon monoxide, carbon dioxide, hydrogen, methane, water, nitrogen, but also contaminants like e.g. small char particles, ash and tars. After cleaning the gas makes is suitable for boiler, engine use, and turbine use to produce heat and power (CHP).

The substance of a solid fuel is usually composed of the elements carbon, hydrogen and oxygen. In the gasifiers considered, the biomass is heated by combustion. Four different processes can be distinguished in gasification: drying, pyrolysis, oxidation and reduction (see Figure 2.23).

Figure 2.23-Gasification mechanisms.

The water gas shift reaction determines to a large extent the final gas composition. The equilibrium constant (Kw) can be written as:

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Kw = [CO2] x [H2] / [CO] x [H2O]

In practice, the equilibrium composition of the gas will only be reached in cases where the reaction rate and the time for reaction are sufficient. Below 700 ° the water-gas shift becomes so slow -without a catalyst- that the equilibrium is said to be 'frozen'. The gas composition then remains unchanged. Methane equilibrium will only be reached at very high temperatures ( > 1200 °C) (see Figure 2.24)

Figure 2.24-Equlibrium reactions in gasification (system C-H-O).

Gasifiers are already investigated for more than a century, and many different types have been developed. The figure below summarizes the main types and their typical operating window (Figure 2.25).

Figure 2.25-Gasifiers types.

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Dependent on the application, type of gasifier and contaminants in the fuel, a certain level of gas conditioning (cleaning/cooling) is required. The most frequent impurities are hydrocarbons (tar), dust (particulates), ammonia, sulphur, chloride, alkalies, etc. which need to be removed or converted. Dust is usually removed by cyclones and fabric filters. Ammonia, sulphur and chloride can be removed by scrubbers or by using additives. The most critical component to be handled however is tar (see tar removal). Cooling is required for (i) combustion in gas engines, (ii) when filters are applied with a maximum allowable temperature or (iii) when compressors are incorporated like with atmospheric IGCC.

Fixed-bed. The different fixed-bed reactor types are often characterised by the direction of the gasflow through the reactor (upward, downward or horizontal) or by the direction of respectively the solid flow and the gas stream (co-current, counter-current or cross-current).

For specific feedstocks a co-current gasifier is used with the advantage that the tar content in the producer gas is low. Additional gas cleaning -prior to fuelling a prime mover- is avoided. Obviously this will reduce the investment and operational costs.

Fluidized bed. In a fluidized bed gasifier air and biomass are mixed up in a hot bed of solid material (e.g. sand). Due to the intense mixing the different zones -drying, pyrolysis, oxidation, reduction- can not be distinguished; the temperature is uniform throughout the bed. Contrary to fixed bed gasifiers the air-biomass ratio can be changed, and as a result the bed temperature can be controlled. The producer gas will always contain certain amounts of tar, which need to be removed.

Figure 2.26 shows an example of a complete gasification plant.

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Figure 2.26-Gasification plant.

The technology is close to commercialization and therefore BTG has informed the international community in detail about the status for many years, i.e. about the current installations and the current manufacturers. Details can be found on www.gasifiers.org . Over 90 installations and over 60 manufacturers are listed now indicating the large interest in biomass gasification.

2.4.2-Anaerobic digestion (AD) and landfill gas (LFG)

Energy - in the form of methane gas - can be extracted from landfilled waste or anaerobic digestion. While practised in some EU countries, these methods are not nearly as widely available as incineration with energy recovery.

Anaerobic digestion

Organic waste can be treated in an anaerobic digestion (AD) process and the methane drawn off collected and used. The main difference between AD and landfill gas collection is a higher efficiency with AD. This is due to the use of an enclosed

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digester (operated under controlled conditions for temperature, pH, mixing and nutrient loading) rather than the uncontrolled processes taking place in a landfill and the difficulty of collecting landfill gas over the large surface area of a landfill. Its use for MSW treatment, often in combination with sewage sludge provides a methane rich fuel which, like landfill gas, can be used (after the removal of contaminants) to directly fire burners to generate electricity or which can be cleaned and added to gas supplies. AD produces a solid residue that can be aerobically composted and then used as a fertiliser.

NOTE: with the exception of landfill gas recovery, all other technologies divert waste streams from landfill. Nevertheless some landfill is still required for the residues remaining after the recovery of energy if acceptable market outlets for these do not exist.

Chemistry. Anaerobic digestion is the biological degradation of organic material without oxygen present. This results in the production of biogas, a valuable (energy containing) product.

Biogas is a mixture of several gases and vapours, mainly methane and carbon dioxide. Methane also is the main component in natural gas and contains the bulk energy value of the biogas. Biogas occurs naturally, hence its name, amongst others in swamps and lakes when conditions are right. Anaerobic digestion can be used to produce valuable energy from waste streams of natural materials or to lower the pollution potential of a waste stream.

The definition above contains four parts: biological, degradation, organic material and without oxygen:

Biological: This implies that the process is carried out by bacteria, which have to be kept in a healthy condition and in good living conditions. The bacteria have to be grown and nurtured in the process to get a good production of biogas.

Degradation: This means that the substrate/organic material is broken down into its building blocks and subsequently for a large part into biogas.

Organic material : The (dry) material in greenhouse residues consists of organic, or natural, material and anorganic materials like sand. Part of the organic material is broken down into biogas.

Without oxygen: This means that air is not allowed to interact with the greenhouse residues. In degrading greenhouse residues there are a few competing biological processes: with and without the presence of oxygen. To promote the production of biogas as a valuable product of the degradation, oxygen must be kept away from the reactor contents.

Biological steps. The biological anaerobic degradation of greenhouse residues can be divided into four steps:

hydrolysis : high weight organic molecules (like proteins, carbohydrates, fat, cellulosis) are broken down into smaller molecules like sugars, aminoacids, fatty acids and water.

acidogenesis: further breakdown of these smaller molecules into organic acids, carbondioxide, hydrogen sulfide and ammonia occurs.

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acetogenesis: the products from the acidogenesis are used for the production of acetates, carbondioxide and hydrogen.

methanogenesis : methane (finally), carbondioxide and water are produced from the acetates, carbondioxide and hydrogen (products of acidogenesis and acetagenesis).

There are several groups of bacteria that perform each step; in total dozens of different species are needed to degrade a heterogeneous stream completely.

Process parameters. The anaerobic digestion process can be carried out quite different conditions. All of these conditions have specific influences on the biogas production. Additionally, from a technological viewpoint, the biological process can also be carried out in more than one reactor, which has some, mainly economical, implications.

"Dry" digestion vs "wet" digestion. In digestion processes water is an important parameter. Water is needed for life in general and for digestion bacteria too. It is the transport medium for nutrients, for half-products and it is a very good reaction medium for digestion.

Digestion is practised in two different ranges of water content: dry digestion, with a typical dry solids content of 25-30% and wet digestion, with a dry solids content of less than 15%. These ranges have technological and economic reasons: higher solid contents lead to smaller (and thus cheaper?) reactors, lower solids contents (more water) lead to much better mixing possibilities but to a higher energy input (more water to be heated) and a bigger reactor.

Natural wastes from plants (like greenhouse residues) have an estimated dry solids content of 25%. This dry solids content opens the possibility to perform the digestion without addition of water.

Thermophilic vs mesophilic digestion. Digestion bacteria have a temperature range in which they are most productive in terms of production rates, growth rates and substrate degradation performance. The several groups of bacteria involved in anaerobic digestion all have (slightly) different temperature optimums. This results in two main temperature ranges in which digestion usually can be performed optimally and most economically. These ranges are: 25-38°C called the mesophilic range, and 50-70°C called the thermophilic range.

These ranges have different characteristics, advantages and disadvantages of which the most important ones are: compared to the mesophilic process, the thermophilic process usually results in a higher degradation of the substrate at a faster rate at the expense of a less stable process. It is less attractive from an energetic point of view since more heat is needed for the process.

Batch processes vs continuous processes. In process technology the two main types of process (models) are used, the batch process and the continuous process. In the batch process the substrate is put in the reactor at the beginning of the degradation period after which the reactor is closed for the entire period without adding additional

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substrate. In the continuous process, the reactor is filled continuously with fresh material and also emptied continuously.

As explained before, digestion consists of several consecutive steps. In a batch reactor all these reaction steps occur more or less after each other. The production of biogas (end product) is non-continuous: at the beginning only fresh material is available and the biogas production will be low. Halfway through the degradation period the production rate will be highest and at the end, when only the less easily digestible material is left, production rate will drop again.

In a continuous process, fresh substrate is added continuously, and therefore all reactions will occur at a fairly constant rate resulting in a fairly constant biogas production rate. Several mix forms of these two models are developed in process technology including the so-called plug-flow reactor and the sequencing batch-reactor all of which try to combine the advantages of the two extremes.

Residence time. The longer a substrate is kept under proper reaction conditions the more complete its degradation will become. But the reaction rate will decrease with increasing residence time. The disadvantage of a longer retention time is the increasing reactor size needed for a given amount of substrate to be treated. A shorter retention time will lead to a higher production rate per reactor volume unit, but a lower overall degradation. These two effects have to be balanced in the design of the full-scale reactor.

Acidity or pH-value. The groups of bacteria needed for digestion not only have an optimum temperature but also an optimum acidity at which they are most productive. Unfortunately, for the different groups of bacteria the optimum pH-value (measure for acidity) is not the same. The complexity of the entire system is increased by the fact that the intermediate products of the digestion have a tendency to lower the pH, making the later steps in the process more difficult. This makes balancing the pH in the reactor an important design and operation issue.

Organic loading. Bacteria have a maximum production rate depending on the type of reactor, substrate, temperature etc. Organic loading is one of parameters used to describe this production rate. It is the amount of organic material put into the reaction medium per time unit.

Landfill gas collection

Landfill gas is produced by the decomposition of organic wastes in a landfill site. Such gases normally contain around 55% methane and 40% carbon dioxide. They are collected through networks of pipes and wells. Since methane is a greenhouse gas, its recovery and use has the additional benefit of reducing the potential for global warming. Most landfill gas is presently collected and just flared off, but an increasing number of facilities are being installed on sites where gas generation rates are high enough and the gas is used as a fuel to power the generation of electricity.

There is a tendency to operate landfills as true anaerobic digesters in order to increase gas (LFG) production and decrease possible environmental impacts duration time.

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A bioreactor landfill operates to rapidly transform and degrade organic waste. The increase in waste degradation and stabilization is accomplished through the addition of liquid and air to enhance microbial processes. This bioreactor concept differs from the traditional “dry tomb” municipal landfill approach.

A bioreactor landfill is not just a single design and will correspond to the operational process invoked. There are three different general types of bioreactor landfill configurations:

Aerobic - In an aerobic bioreactor landfill, leachate is removed from the bottom layer, piped to liquids storage tanks, and re-circulated into the landfill in a controlled manner. Air is injected into the waste mass, using vertical or horizontal wells, to promote aerobic activity and accelerate waste stabilization.

Anaerobic - In an anaerobic bioreactor landfill, moisture is added to the waste mass in the form of re-circulated leachate and other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. Landfill gas, primarily methane, can be captured to minimize greenhouse gas emissions and for energy projects.

Hybrid (Aerobic-Anaerobic) - The hybrid bioreactor landfill accelerates waste degradation by employing a sequential aerobic-anaerobic treatment to rapidly degrade organics in the upper sections of the landfill and collect gas from lower sections. Operation as a hybrid results in the earlier onset of methanogenesis compared to aerobic landfills

Figure 2.27x illustrates these concepts.

Figure 2.27-Aerobic and facultative landfills.

The bioreactor accelerates the decomposition and stabilization of waste. At a minimum, leachate is injected into the bioreactor to stimulate the natural biodegradation process. Bioreactors often need other liquids such as stormwater, wastewater, and wastewater treatment plant sludges to supplement leachate to enhance the microbiological process by purposeful control of the moisture content and differs from a landfill that simple recirculates leachate for liquids management.

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Landfills that simply recirculate leachate may not necessarily operate as optimized bioreactors.

Moisture content is the single most important factor that promotes the accelerated decomposition. The bioreactor technology relies on maintaining optimal moisture content near field capacity (approximately 35 to 65%) and adds liquids when it is necessary to maintain that percentage. The moisture content, combined with the biological action of naturally occurring microbes decomposes the waste. The microbes can be either aerobic or anaerobic. A side effect of the bioreactor is that it produces landfill gas (LFG) such as methane in an anaerobic unit at an earlier stage in the landfill’s life and at an overall much higher rate of generation than traditional landfills.

Decomposition and biological stabilization of the waste in a bioreactor landfill can occur in a much shorter time frame than occurs in a traditional “dry tomb” landfill providing a potential decrease in long-term environmental risks and landfill operating and post-closure costs. Potential advantages of bioreactors include:

Decomposition and biological stabilization in years vs. decades in “dry tombs” Lower waste toxicity and mobility due to both aerobic and anaerobic

conditions Reduced leachate disposal costs A 15 to 30 percent gain in landfill space due to an increase in density of waste

mass Significant increased LFG generation that, when captured, can be used for

energy use onsite or sold Reduced post-closure care

Research has shown that municipal solid waste can be rapidly degraded and made less hazardous (due to degradation of organics and the sequestration of inorganics) by enhancing and controlling the moisture within the landfill under aerobic and/or anaerobic conditions. Leachate quality in a bioreactor rapidly improves which leads to reduced leachate disposal costs. Landfill volume may also decrease with the recovered airspace offering landfill operators the extend the operating life of the landfill.

LFG emitted by a bioreactor landfill consists primarily of methane and carbon dioxide plus lesser amounts of volatile organic chemicals and/or hazardous air pollutants. Research indicates that the operation of a bioreactor may generate LFG earlier in the process and at a higher rate than the traditional landfill. The bioreactor LFG is also generated over a shorter period of time because the LFG emissions decline as the accelerated decomposition process depletes the source waste faster than in a traditional landfill. The net result appears to be that the bioreactor produces more LFG overall than the traditional landfill does. This underlies the concept of a sustainable landfill (see Figure 2.28).

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Figure 2.28-“Sustainable landfill”.

2.4.3-Comparison of the most used thermal waste treatment processes

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The various thermal waste treatment technologies are briefly compared in Table 2.1.

Table 2.1-Relative merits of dedicated waste incineration, co-incineration, pyrolysis, electrical power plants, and cement production.

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3-EMISSIONS CONTROL

Combustion thermally decomposes matter through oxidation, thereby reducing and minimizing the volume of wastes, and destroying their pathogenicity along with the part of their toxicity linked to organic compounds. It can be applied to industrial, municipal, and hazardous wastes, provided that they contain organic material since it is primarily organic substances that can undergo and sustain thermal oxidation.

After combustion, wastes are converted into CO2, water, ash and small amounts of a wide range of volatile and solid residues (e.g. CO, soot, etc). Depending on the composition of the initial waste (and sometimes of the fuels used to support combustion), compounds containing halogens, sulphur, nitrogen and metals may be produced. These compounds, are deleterious to the atmosphere, and highly regulated (emissions limits). Thus, to meet regulations, incinerators need to be equipped with end-of-pipe devices such as scrubbers, precipitators, filtration units or membranes. The nature and amount of these emissions depend to a large extent on the nature of the waste, but also on the conditions of combustion (physical properties of the waste, level of oxygen present, turbulence, temperature, duration, and so on). Good combustion combines the advantages of minimising boiler fouling and corrosion as well as the emission of most undesirable organic substances.

In the case of heavy metals their possible sources in the incinerator emissions can be traced to some of the waste components, as shown in Table 3.1.

Table 3.1-Possible sources of metal compounds in the incinerator residues.

3.1-Emissions characterization

Looking at a typical incinerator bloc diagram (see Figure 2.2, in Section 2), we can see that three main types of material flows leave the incinerator plant: (i) Flue gases, (ii) Solid wastes, and (iii)Wastewaters:

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Flue gases, leaving through the stack (chimney) Solid wastes (from the removing of ashes and pollution control additives in the

APCDs) Wastewaters (particularly important in the so-called wet absorption systems,

resulting from the treatment of the gas scrubbing liquids)

Besides water, the composition of these flows is indicated in Table 3.2.

Table 3.2-Main streams and their compositions, in incinerator emissionsFLUE GASES SOLID WASTES WASTEWATERS

Main flow Main constituents Main flow Main constituents

Particulate matter

-Mineral matter (fly ash)-Heavy metals ads. -Hydrocarbons ads.

Bottom ashes

-Mineral matter vitr. -Heavy metals vitr.-Hydrocarbons ads.

(Essentially the same constituents of flue gases and solid wastes)

APCR (Air Pollution Control Residues)

-Fly ash-Adsorbents (lime, limestone)-Activated coal

Permanent gases

1- Acid gases and Permanent gases:HClHFSO2 NOx(CO)(CO2)(H2O)

2-Heavy metals compounds: Hg, Cd, Pb, As, Cu, Zn, Cr, Ni, Fe, Al, Tl, etc

Vapours(PICs)

1-Heavy metals compounds:

Hg, Cd, Pb, As, Cu, Zn, Cr, Ni, Fe, Al, Tl, etc (ads.)

2-Organics:DioxinsFuransVOCsPAHsPCBs, etc

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( ads.)

NOTES: ads: adsorbed abs: absorbed vap: as vapour vitr:vitrified

3.1.1-Flue gases

In the flue gases we will normally find three kinds of components:

Particulate matter (fly-ash) Permanent gases (CO2; CO; Acidic compounds: HCl, HF, SO2, NOx) Vapours (Inorganic: heavy metal compounds; Organic: PICs such as

dioxins/furans, PAHs, PCBs, etc)

Particulate matter (fly-ash)

Fly ash contains essentially mineral (incombustible) matter originated from the input waste fuel, some unburned organic matter (in the form of char, or carbon), and, adsorbed, a variety of inorganic and organic products from incomplete combustion (PICs), respectively heavy metals and PICs (dioxins/furans, PAHs, PCBs, etc). It constitutes the most toxic stream out of the incinerator stack; we will find it again in the solid wastes generated in the APCDs. [See more information on these particles, below in Section 3.1.2-Solid wastes].

Permanent gases

Like in the case of any other combustion facility, permanent gases may contribute to global warming (CO2, CH4), acidification (HCl, HF, SO2, NOx) and to a small extent to ozone depletion (chlorinated hydrocarbons) and to tropospheric smog (aliphatic and aromatic hydrocarbons). They also have effects on human health (e.g. irritation of the lungs by breathing sulphur oxides and NOx, and toxicity to most internal organs) and corrode the boilers. Toxic air pollutants, or air toxics, are those pollutants that cause or may cause cancer or other serious health effects, such as reproductive effects or birth defects. Air toxics may also cause adverse environmental and ecological effects.

Breathing air pollution such as ozone (a primary ingredient in urban smog), particulate matter, carbon monoxide, nitrogen oxides, sulphur dioxide, and lead can have numerous effects on human health, including respiratory problems, hospitalisation for heart or lung disease, and even premature death. Some can also have effects on aquatic life, vegetation, and animals.

CO2 is the main responsible for the GHG (Greenhouse Gas) effect. Global warming refers to an average increase in the Earth's temperature, which in turn causes changes in climate. Rising global temperatures are expected to raise sea level, and change precipitation and other local climate conditions. Changing regional climate could alter forests, crop yields, and water supplies. It could also threaten human health, and harm birds, fish, and many types of ecosystems.

Obviously, incinerating waste generates CO2. However, the source of this CO2 is both renewable (from paper, wood, vegetable residues and other biological material) and non renewable (mostly from plastics). The debate is therefore open on determining to what extent the incineration of waste contributes to the greenhouse

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effect. In the general production of CO2 by our economies, the amount is likely to be negligible. This debate has opened a discussion to determine to what extent energy produced from waste can be called renewable energy and can be used to achieve CO2 reduction objectives.

Several perspectives can be taken here:

First, the landfill versus incineration perspective. If the waste that is burned were sent to landfills, it would produce methane, a much more potent greenhouse gas than CO2. Most landfills do not collect methane and those that do only achieve low rates of recovery (typically <30%).

Second, the relative energy recovery perspective. Here, one can compare the amount of CO2 emitted by producing 1 kWh of electricity using waste to that emitted by producing the same kWh in “classic” power plants. In this perspective, the incineration of waste is usually at a disadvantage because of the generally low efficiency of its electricity production. This disadvantage decreases, or can even in some cases disappear completely if combined heat and power production, like in the city of Copenhagen but also possible for power plants, is considered. So far, district heating from incinerators is not very widespread across the EU, in part because low public acceptance tends to “exile” waste incinerators to sites far from urban centres where the heat could be used, but this can be addressed. When wastes are burned in co-incineration, they also replace fossil fuels, with the corresponding benefits.

Third, the intrinsic perspective. If one considers that CO2 from biomass does not lead to a net generation of CO2, the only net contribution from the incineration of waste is from its non-renewable fraction (synthetic chemicals and plastics), but this replaces the use of other fossil fuels. The large fraction of biological material in wastes and the fact that waste generation cannot be stopped (i.e. waste can be seen as a “renewable” resource) leads some people to call energy from waste “renewable energy”.

Another point that can be raised is the saving in transport and processing energy that can be made if wastes are used for energy recovery locally versus fossil fuels that must be brought in from far away and manufactured. In any case, continuous efforts must be made to increase the efficiency of energy recovery in all the processes using wastes. CO2 is not a major issue in waste incineration.

NOx (as NO2). Nitrogen dioxide is a reddish-brown, highly reactive gas that is formed in the ambient air through the oxidation of nitric oxide (NO). Nitrogen oxides (NOx), the term used to describe the sum of NO, NO2, and other oxides of nitrogen, play a major role in the formation of ozone, particulate matter, haze, and acid rain. The major sources of man-made NOx emissions are high-temperature combustion processes, such as those that occur in automobiles and power plants. Home heaters and gas stoves can also produce substantial amounts of NO2 in indoor settings.

Combustion conditions influence the type of emissions produced. For example, high temperature combustion (>1400°C) increases the emission of thermal NOx from atmospheric nitrogen. The presence of chlorine or sulphur in the waste will cause the

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emission of HCl and SOx, but in cement plants equipped with a cyclone pre-heater kiln, they will be to a large extent neutralized by the basic raw materials. NOx, SOx and HCl contribute to the acidification of rain.

CO. Carbon monoxide is a colourless and odourless gas, formed when carbon in fuel is not burned completely. It is a component of motor vehicle exhaust, which contributes about 60 percent of all CO emissions nationwide. Nonroad vehicles account for the remaining CO emissions from transportation sources.

High concentrations of CO generally occur in areas with heavy traffic congestion. In cities, as much as 95 percent of all CO emissions may come from automobile exhaust. Other sources of CO emissions include industrial processes, non-transportation fuel combustion, and natural sources such as wildfires. Peak CO concentrations typically occur during the colder months of the year when CO automotive emissions are greater and nightime inversion conditions (where air pollutants are trapped near the ground beneath a layer of warm air) are more frequent.

SO2. Sulphur dioxide belongs to the family of SOx gases. These gases are formed when fuel containing sulphur (mainly coal and oil) is burned and during metal smelting and other industrial processes. Most SO2 monitoring stations are located in urban areas. The highest monitored concentrations of SO2 are recorded in the vicinity of large industrial facilities. Fuel combustion, largely from coal-fired power plants, accounts for most of the total SO2 emissions.

Breathing air pollution such as ozone (a primary ingredient in urban smog), particulate matter, carbon monoxide, nitrogen oxides, sulphur dioxide, and lead can have numerous effects on human health, including respiratory problems, hospitalisation for heart or lung disease, and even premature death. Some can also have effects on aquatic life, vegetation, and animals

Ozone (O3). There are two kinds of ozone locations: (i) ground level, or tropospheric ozone, which is the unwanted form, and (i) stratospheric ozone, which is the “good” one.

Ground-level ozone (the primary constituent of smog) continues to be a pollution problem throughout many areas of the Globe. Stratospheric ozone occurs naturally about 22 miles above the Earth's surface (in the stratosphere), and provides a protective layer high above the Earth. This layer protects us from the sun's harmful ultraviolet radiation. This protective shield is being damaged by chemicals such as CFCs, halons, and methyl chloroform, and can lead to harmful health effects such as skin cancer and cataracts

Ozone is not emitted directly into the air but is formed by the reaction of VOCs and NOx in the presence of heat and sunlight. Ground-level ozone forms readily in the atmosphere, usually during hot summer weather. VOCs are emitted from a variety of sources, including motor vehicles, chemical plants, refineries, factories, consumer and commercial products, and other industrial sources. NOx is emitted from motor vehicles, power plants, and other sources of combustion. Changing weather patterns contribute to yearly differences in ozone concentrations from region to region. Ozone

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and the pollutants that form ozone also can be transported into an area from pollution sources found hundreds of miles upwind.

The stratosphere, located about 6 to 30 miles above the Earth, contains a layer of ozone gas that protects living organisms from harmful ultraviolet radiation (UV-b) from the sun. Over the past three decades, however, it has become clear that this protective shield has been damaged. Each year, an “ozone hole” forms over the Antarctic, and ozone levels there can fall to 60 percent below normal. Even over the United States, ozone levels are about 3 percent below normal in the summer and 5 percent below normal in the winter.

As the ozone layer thins, more UV-b radiation reaches the Earth. The 1998 Scientific Assessment of Stratospheric Ozone firmly established the link between decreased ozone and increased UV-b radiation. In the 1970s, scientists had linked several substances associated with human activities to ozone depletion, including the use of chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl bromide, and methyl chloroform. These chemicals are emitted from commercial air conditioners, refrigerators, insulating foam, and some industrial processes. Strong winds carry them through the lower part of the atmosphere, called the troposphere, and into the stratosphere. There, strong solar radiation releases chlorine and bromine atoms that attack protective ozone molecules. Scientists estimate that one chlorine atom can destroy 100,000 ozone molecules.

Acid rain is not exactly a pollutant in the strict sense of the word; however as it is a mixture formed by the combination of several pollutants, and possessing synergistic effects, is an important source of pollution and environmental impact.

"Acid rain" is a broad term describing acid rain, snow, fog, and particles. Sulphur dioxide and nitrogen oxides released by power plants, vehicles, and other sources cause it. Acid rain harms plants, animals, and fish, and erodes building surfaces and national monuments. In addition, acidic particles can hurt people's lungs and reduce how far we can see through the air.

Acidic deposition or “acid rain” occurs when emissions of sulphur dioxide and nitrogen oxides in the atmosphere react with water, oxygen, and oxidants to form acidic compounds. These compounds fall to the Earth in either dry form (gas and particles) or wet form (rain, snow, and fog). Some are carried by the wind, sometimes hundreds of miles, across state and national borders.

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Coal-fired electric utilities and other sources that burn waste and fossil fuels emit SO2 and NOx.

Vapours

Dioxins and furans (D/F). These compounds are released during the incineration of waste; it thought that three mechanisms could account for their formation:

They may come from D/F already present in the waste that escaped destruction due to insufficient incineration temperatures (<800°C). This is now rare.

They may be formed at temperatures of 500 to 700°C in the gas phase if organic molecules and chlorine donors (such as NaCl, PVC, HCl) are present.

They can be formed by a variety of solid phase mechanisms at less than 500°C on particles flowing through the incinerator (e.g. soot). Certain metals can catalyse the formation of D/F at these low temperatures (e.g. in particular Cu at 400°C). For example, fly ash in its cooling phase can provide an ideal ground for the formation of D/F.

Therefore, the important parameters controlling the formation of D/F are the combustion conditions, the rate of cooling after combustion and content of sulphur or metals (in particular copper) in the feed waste. Studies have shown that good combustion conditions and a fast cooling before the particulate filter kept the amount of D/F released down. Soot is favourable to their formation and a lot of D/F is associated to particles. There does not appear to be a relationship between the amount of chlorine present in the feed and the amount of D/F emitted. Sulphur dioxide appears to contribute to suppress the formation of D/F as shown by co-combustion tests with high sulphur coal.

There are organic (hydrocarbon) molecules that can be formed as PICs (products of incomplete combustion), as can be anticipated from reading the earlier Section 2.4-Other thermal waste conversion processes, regarding pyrolysis and gasification. (see Figures 2.17 and 2.18); the ones with most toxicological relevance are the VOCs, PAHs, and PCBs. The main danger from these organic molecules released as vapours, or adsorbed in the fly ash, in the flue gas, lies in potential effects on human health (e.g. volatile organic compounds). These effects can be direct or indirect by bioaccumulation and biomagnification through the food chain, and are difficult to quantify (e.g. dioxins). However, organic compounds can be destroyed either by heat, photo degradation or biodegradation. Therefore, a complete oxidation is essential.

Heavy metals are released both in vapour state (but not in the metallic form, except a small proportion of the mercury) in the form of volatile compounds such as chlorides, oxides, etc., and also adsorbed on the fly ash (particulate matter); they are of concern for their human toxicity and ecotoxicity. However, to be able to exert this toxicity, they must be bioavailable. For example, lead dissolved in water can exert its neurotoxicity while cadmium or chromium in steel alloys used for furniture are not a

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public health hazard because they are fixed and not bioavailable. However, unlike organic molecules, heavy metals cannot be destroyed. All efforts must therefore be made to avoid the presence of heavy metals in wastes, but for the unavoidable fraction, the heavy metals present in wastes must be returned to the environment in a non-bioavailable form, i.e. non breathable and non leachable. One way to avoid these issues is to use pre-treatment and classification in order to stop as much of the heavy metals as possible from entering the furnaces in the first place. During incineration of waste, part of the heavy metals go to the flue gas and part to the solids (ashes, slag, etc). The distribution between the various phases depends on the metal itself, the amount of metal entering the process and the conditions in the process. It is therefore difficult to give precise a priori indications in this respect, but certain heavy metals are more volatile than others (e.g. mercury, cadmium, etc). The capture of these metals is usually performed in flue gas treatment leading to the highly hazardous character of flue gas treatment residues. Immobilisation of the collected dust, ashes and slags after combustion is possible but expensive.

Heavy metals can be grouped into various classes, each with its specific issues. Metals such as cadmium (Cd), chromium (Cr), mercury (Hg) or lead (Pb) can be highly toxic. However, while Cd and Cr recovery can be interesting in metallurgy, uses for Hg and Pb are decreasing fast. For Hg, uses in thermometers and batteries are disappearing and will hopefully result in lower concentrations in waste in the long-term. For Pb, uses in pipes and gasoline are ending while use in accumulators is likely to decrease dramatically in the next few years thanks to emerging battery technologies.

Copper (Cu) and nickel (Ni) tend to be less toxic than Cd, Hg or Pb, but they are potent catalysts and contribute to a complex organic chemistry in the flue gases of combustion plants. In particular, they can contribute to the post-formation of dioxins in the flue gases. In terms of recovery, Cu is undesirable in steel making but, along with Ni, it is potentially worth being recovered for use in the non-ferrous metals industry.

Iron (Fe) and aluminium (Al) are less toxic and can also act as catalysts. However, they are essential elements for cement making and get captured in the clinker, contributing as raw material. In general, studies have shown that leaching of metals from cement mortar is very limited and does not appear to be a cause of concern during service life, but some controversy goes on.

In the past, automotive sources were the major contributor of lead emissions to the atmosphere. As a result of regulatory efforts to reduce the content of lead in gasoline, however, the contribution of air emissions of lead from the transportation sector, and particularly the automotive sector, has greatly declined over the past two decades. Today, industrial processes, primarily metals processing, are the major source of lead emissions to the atmosphere. The highest air concentrations of lead are usually found in the vicinity of smelters and battery manufacturers

3.1.2-Solid wastes

Fly- ash

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Very fine mineral dust (fly ash), and in particular the famous PM10 (particles of less than 10 microns) is mostly a problem for the lungs if breathed and should therefore be captured and fixed. Apart from the gases, all the other flue gas contaminants are bound to each other and form particles because of their electrostatic and adsorption properties. Bottom ash is a coarser type of mineral dust removed from the bottom of the furnaces.

While in the case of dedicated waste incineration all the mineral elements in the emissions come from the waste and the combustion air, in the case of co-incineration, they also come from the other fuels used and in the case of cement production mainly from the raw materials used. The exact nature of emissions is also a function of process conditions (e.g. amount of air, process temperature, time). For example, in a cement kiln, gas temperatures are typically 800°C to 1200°C higher than in a waste incinerator. This creates conditions that are much more favourable to the formation of thermal NOx from the combustion air. This chemical reaction cannot be avoided. Therefore, NOx production in a cement kiln is largely independent from the presence of waste. Along similar lines, flue gas concentrations of non-volatile heavy metals and often SO2 from a cement kiln are usually more related to natural levels in the raw materials and fuels used than to the waste, as long as the waste is fed at the flame end of the kiln. If process conditions have allowed an efficient combustion, solid residues contain little organic matter but concentrate most of the heavy metals that entered the process. The main environmental issue to solve here is to avoid a remobilisation (in particular leaching) of the heavy metals. Therefore, use of this material as ballast or road building material, or landfilling must not allow their leaching. This is usually not perceived by the technical experts as difficult. Vitrification, sintering or fixation in concrete blocks can perform fixation of the heavy metals. This latter technique is commonly used in landfills to fix fly ashes. In cement kilns, the non-volatile fraction of the metals entering the process gets trapped and fixed in the clinker (e.g. lead) and the volatile metals such as mercury and thallium must be caught in the flue gas. Cement naturally contains variable levels of heavy metals from the raw materials and existing studies indicate minimal leaching of heavy metals from cement blocks. Therefore, limited input of heavy metals from waste is unlikely to raise serious issues. However, this should not be an open door for wastes containing high levels of heavy metals and the controversy on this point between incinerators and cement producers is still very alive. A better recognition of standard leaching methods followed by solid environmental safety assessments is needed in this area.

Bottom ash

Bottom ash production by the various incineration technologies varies. While cement kilns do not produce any ash (most of the minerals are incorporated into the clinker, but dust is collected in the flue gas and may have to be landfilled), the other alternatives produce from from 10% to 30% depending on he nature of the waste and the efficiency of thermal destruction.

Considering the variations in waste and in technologies, the gaseous emissions are difficult to compare in general. However, a few rules of thumb can be given:

The higher the process temperature, the higher the production of NOx.

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The higher the sulphur content of the input (waste, raw materials), the higher the production of sulphur oxides (this may be different in cement kilns). The same holds true for volatile heavy metals such as mercury.

Also, the better the combustion (according to the 3T rule: time, temperature and turbulence) the less soot and organic carbon in the flue gas.

For dioxins, the higher the combustion temperature and the faster the cooling of the flue gases to less than 200°C, and the less dioxins will be formed.

3.2-Emissions formation and control

In view of the environmental and health concerns raised by all the emissions from combustion installations, European and national environmental regulations have set emission limit standards. The immediate response of the operators of combustion installations was to apply end-of-pipe flue gas treatment systems to reduce specific emissions: dust, SO2, etc. The array of technologies implemented is large: post-combustion chambers, dry and wet scrubbers, electrostatic precipitators, cyclones, activated carbon filters, bag filters, etc. These processes use energy to transfer the airborne pollution to a solid phase. The wet scrubbers transfer the contaminants to a water phase that needs further treatment. All flue gas treatments impact negatively on the energy balance of the systems that burn waste.

Control of the incineration emissions can be made in three ways, in the global sequence involved in the combustion process: (i) upstream, (ii) in the furnace, and (iii) downstream.

Upstream control: involves the need to pre-sorted waste, therefore preventing the contaminants from entering the combustion chamber; this is achieved by removing certain waste components such as: batteries, plastics containing chlorine, etc., which would release heavy metals and POPs in the gases and ashes.

Increasing attention is being paid to pre-sorting and pre-treatment of waste before incineration for both economic and environmental reasons. The nature and quality of waste being placed in incinerators directly impacts both the efficiency of energy produced and the level of emissions from the process, because:

Waste is a wet material. In some areas of Europe it can contain more than 50% moisture. The amount of water in waste decreases its energy content and in the form of steam increases the amount of exhaust air to be treated. The water content also keeps the waste biologically reactive and makes it very difficult to store for a longer time or transport over longer distances as can be easily done with any traditional fuel.

Incineration works better the more homogeneous the waste. A rotten orange could lie beside a sofa before being put in the furnace together. It is just not realistic to expect homogeneous burning with low emission rates from a ‘fuel’ such as this.

Waste contains inert materials. Inert materials such as such as stones, glass and ceramics cannot produce energy. Analyses have shown that these elements can be up to 20% of the waste and should be recycled before combustion.

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Waste contains valuable metals. On the other hand, waste can contain metals whose value may be reduced if they are incinerated. Hence, removing them before the combustion process makes both economic and environmental sense.

Expensive flue gas treatments are necessary for burning untreated waste. Large size, costly flue gas treatments as ‘end of pipe’ technology are a necessity when burning untreated waste. Sorting out toxic materials such as batteries and electronic scrap before combustion results in ‘leaner’ and more competitive flue gas treatment with the same or even better results.

Within the combustion chamber: control in here is practiced in order to increase the combustion efficiency through appropriate combustion controls and on-line monitoring (continuous), thereby avoiding the formation of particulate matter (fly ash, in particular), PICs (in particular CO, dioxins/furans, PAHs, etc).

Operation of the incinerator also affects the emission of heavy metals, chlorine, sulphur, and nitrogen that may be present in the waste fed into the incinerator. Such chemicals are not destroyed during combustion, but are distributed among the bottom ash, fly ash, and released gases in proportions that depend on the characteristics of the metal and the combustion conditions. Mercury and its compounds, for example, are volatile, so most of the mercury in the waste feed is vaporized in the combustion chamber. In the cases of lead and cadmium, the distributions between the bottom ash and fly ash depend on operating conditions. At higher combustion-chamber temperatures, more of the metals can appear in the fly ash or gaseous emissions. Therefore, combustion conditions need to maximize the destruction of products of incomplete combustion and to minimize the vaporization and entrainment of heavy metals, especially when adequate control of emissions is lacking. High temperatures and the presence of nitrogen-containing wastes promote formation of oxides of nitrogen. In this aspect, on-line monitoring of furnace operating conditions is of crucial importance; Figure 3.1 shows the usual locations for installing the monitoring sensors.

Figure 3.1-On line measurement and control points in an incineration plant.

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Downstream the combustion chamber: consists in using “end-of-pipe” technology (or abatement technologies, or APCD-Air pollution Control Devices), when everything else failed! There is an array of techniques, tailored to each pollutant characteristics; this is the worse situation, since the use of APCDs not only increases the size and complexity of the plant design and control, but also aggravates the investment and operating costs. We shall describe the most important APCDs next, and will end with an assessment of how each of them can control each kind of pollutant.

Due to their more relevance, we will briefly describe next the downstream control processes.

In the last 10 years, significant advancements have been achieved in controlling emissions from WTE facilities, including improved combustion controls and advanced acid gas and particulate emission controls. In the past, incinerator emission control was achieved with electrostatic precipitators to collect particulates. At the time, no other controls were anticipated. Today, however, WTE facilities incorporate not only particulate controls, but also acid gas, organics, and nitrous oxide (NOx) controls. These new controls have resulted from a better understanding of the potential environmental impacts of waste combustor emissions; municipal solid waste composition; and the effects of uncontrolled emissions of acid gas constituents (i.e., sulphides and chlorides), organics and heavy metals.

The four main classes of technologies used in pollution control at MSWI plants are summarized in Table 3.3.

Table 3.3-Main technologies used in incinerator pollution control.

Equipment type Examples Pollutants addressed

AParticulate collectors

-Cyclones Particles[and indirectly, all the adsorbed/deposited pollutants: organics and metals]

-ESP (electrostatic precipitators)-Bag filters

BScrubbing systems

-Alkaline absorbents: Dry Semi-dry Wet

Acid gases with: HCl HF SO2

-Activated carbon Dioxins and furans Hg VOCs PAHs

CChemical reduction (catalytic and non-

catalytic)

-SNCR (Selective Non Catalytic Reduction) NOx

Dioxins and furans

-SCR (Selective Catalytic Reduction)

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E

Inertization processes

-Solidification Fly ash APCRs

[rarely for whole MSW; often for HZW and contaminated soils, etc.]

-Vitrification

In the following table (Table 3.4) crossed information on APCDs and the types of pollutants removed is presented.

Table 3.4-APCDs and main pollutants removed

A-Particulate Collectors

Using fabric filters or bughouses has become the most common method of controlling particulates. Bag-houses control particulate emissions by channelling flue gases through a series of tubular fabric filter bags. The bags are set together in an array through which particulates are directed then trapped. Due to the fineness of the fabric mesh and the resulting build up of fine particulates on the bag, the recovered particulates act as an additional medium to further filter out particulates. The collected particulates with the precipitated end products from the scrubber are removed from the bag by various mechanical methods, including reversing the gas flow of cleaned flue gas through the bags by shaking or pulsing the bags. An inherent advantage of the bag house systems is that the filtering process also acts as a secondary acid gas scrubber. The collected particles include the unreacted calcium from the scrubber, which also builds up on the bags and will react with any untreated acid gases.

Other particulate collectors include ESP (Electrostatic Precipitators), which use very high voltage fields to produce ionised gas molecules which adhere to particles deflecting their flow trajectory towards vertical grounded planes where their loose their electric charge and drop to the bottom, this way being removed from the gas stream. Figure 3.2 shows a filter bag and an ESP.

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Figure 3.2-APCDs: filter bag and ESP, respectively.

B-Scrubbing systems

Scrubbing acidic gases from the combustor can control acid gas emissions exhaust gas. The products of scrubbing can be recovered either as a dry powder residue or as a liquid. The most common acid gas scrubber technology used is probably the spray-dry scrubber (Figure 3.3). The flue gas from the combustor is ducted into a reactor vessel, where the incoming flue gas is sprayed with a lime slurry. The lime particles react with the acid gases to form a calcium precipitate. The slurry water cools the incoming combustor exhaust and the water is vaporized; the lime is chemically combined with the chlorides and sulphates and condensed. Lower temperatures are used to promote the chemical reaction with the lime, to promote condensation of most heavy materials in the gas stream, and to control the flue gas temperature in the particulate control device. The same configuration exists for the dry scrubber, except that the additives are injected in the powder form.

In the wet system the flue gases are scrubbed with one or more alkaline solutions; in this case a heavily contaminated wastewater stream is produced, which has to be treated before discharging (see Figure 3.4).

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Figure 3.3-Semi-dry process for flue gas treatment.

Figure 3.4-Wet process for flue gas treatment, with wastewater treatment. A developing control technology is the use of activated carbon as an additive to the scrubber process. The carbon is injected into the flue gas before it enters the bag

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house to provide additional control of volatile organics and for controlling mercury. Another option is the addition of a carbon filter after the bag house.

C-Chemical reduction (for NOx, and dioxins/furans controls): catalytic and non-catalytic

NOx (gaseous oxides of nitrogen: NO+NO2) can be controlled in the combustion process or by adding additional controls. Selective Noncatalytic Reduction (SNCR) is now the most common method for controlling NOx from waste combustors. With SNCR, ammonia is injected into the combustor’s boiler bank above the fire zone. The ammonia reacts with the nitrogen in the combustion gases to form nitrogen dioxide and water. Another method of controlling NOx is with staged combustion, in which the combustion temperatures are controlled to minimize thermal NOx generation. Either or both of these options may be appropriate depending on the combustion technology to be used.

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The Figure 3.5 shows the SCR system.

Figure 3.5-SCR DeNOx system.

It has been found that these NOx catalysts are also very effective in dioxine/furan destruction also. Dioxins and furans are also effectively destroyed (in contaminated solids) by the Hagenmeyer process (Figure 3.6). The solids (fly-ash, for instance) is heated above 300ºC in the absence of air.

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Figure 3.6-Thermal destruction of dioxins and furans in solids (Hagemmeyer process).

D-Electron-Beam (EB) In this process the gases are literarily bombarded by a stream of high-energy electrons, thereby destroying the organic molecules, as shown in Figure 3.7.

Figure 3.7-Electron-beam process for flue gas treatment.

This process is mostly used in Japan, and still have little penetration in Europe.

E-Solid waste inertization and disposal

A WTE facility and its emission control system produce a variety of residues. By far, the largest quantity is bottom ash, the unburned and non-burnable materials discharged from the combustor at the end of the burning cycle. The process also produces a lighter emission known as fly ash. Fly ash consists of products in particulate form which are produced either as a result of the chemical decomposition of burnable materials or are unburned (or partially burned) materials drawn upward by thermal air currents in the incinerator and trapped in pollution control equipment. Fly ash includes what is technically referred to as air pollution control residues (APCRs).

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Fly ash normally comprises only a small proportion of the total volume of residue from a WTE facility; the quantity ranges from 10 to 20 percent of the total ash.

The type of combustion unit largely influences distribution of bottom and fly ash. Excess air systems produce the most fly ash; controlled air units produce the smallest amounts. Constituents in both ash and scrubber product vary, depending on the materials burned. In systems burning a homogeneous fuel such as coal, oil, or tires, levels of pollutants in residuals may be relatively constant. Systems burning a more heterogeneous mixture, such as municipal, industrial, or medical waste, may experience wide swings in the chemical composition of residuals. The major constituents of concern in municipal waste combustion ash are heavy metals, particularly lead, cadmium, and mercury. These metals may impact human health and the environment if improperly handled, stored, transported, disposed of, or reused (for example, using stabilized ash in construction materials such as concrete blocks).

According to the EU legislation (European Waste Catalogue) bottom ash is not considered as an hazardous waste, whereas fly ash (and all of the APCRs) are hazardous and need pre-treatment previous to final deposition.

When dirt, soils and rock or inorganic oxides, are heated to sufficiently high temperatures, the materials melt. Molten lava is a natural example of this process and state of matter. In the high temperature (1300 to 1550°C), molten state, the liquid has no consistent crystalline structure or is vitreous.

When the molten material is drained from the smelter and cools rapidly enough, this non-crystalline, vitreous state is frozen into the solid. Longer cooling times will result in glass-ceramic composites. Complex organics such as wood, paper, oil, plastic and other combustibles cannot exist at high temperatures at normal atmospheric pressures except as much simpler organic gases like carbon monoxide, methane, ethylene and propane. Waste vitrification causes waste materials to pyrolyze.

Figure 3.8 shows a vitrification process using electricity and gas heat for melting.

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Figure 3.8-Ash melting systems: electrical, and fuel burning, respectively.

Ash vitrification is used practically only in Japan, although some plants have already begin to appear in Europe. It is essentially used for hazardous waste (such as contaminated soils), and much less frequently to the whole MSW.

Solidification involves incorporating the wastes in a matrix of cement or an organic polymer, so that pollutants are therehein retained, decreasing the risk of environmental leaching. In this process the waste is transformed in solid blocs that can then be landfilled (see Figure 3.9).

Figure 3.9-Cement blocs of solidified fly-ash, or APCRs.

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4-ENVIRONMENTAL IMPACTS

Incinerators have various environmental impacts. The emissions released into the atmosphere from the incineration, though in the case of most pollutants greatly reduced, can have implications for atmospheric pollution. The impact of transporting waste to and from incinerators also has environmental implications. In addition the siting of incinerators can have implications for the amenity of a local area.

The following are the possible negative environmental impacts:

Emissions of toxic substances to air Emissions from transport (including noise) Production of hazardous waste (fly ash) Contaminated waste water Combustion produces carbon dioxide, a green house gas. Odours and possible vermin at waste storage prior to incineration Aesthetic Land degradation

Emissions from transport of waste, together with odours and other associated problems, are issues that affect all waste management facilities to a lesser or greater degree.

4.1- Toxic gaseous emissions

Emissions from incinerators have implications not only from a health point of view, but also from an environmental one. Emissions of acid gases from industrial processes, incineration and transport result in acid rain and the environmental impacts associated with this. Increased acidification of the atmosphere over the past century resulted in acid damage to buildings, the water environment and forests. Carbon dioxide emissions as a result of combustion of waste also have implications in relation to climate change. Land-retained pollutants originating as stack or fugitive emissions are of increasing concern. Bioaccumulation and subsequent ingestion from food is indirect exposure route resulting from land-retained emissions.

4.2-Transport

One of the frequently stated objections to the siting of large incinerators is the increased heavy traffic that will result as waste is imported from surrounding areas. Transport of waste over large distances not only has implications for air quality, but also for climate change through increased energy use and subsequent carbon dioxide emissions.

Truck traffic is the greatest source of noise pollution resulting from WTE plant operations. Well-maintained and responsibly operated trucks will help minimize this problem. Local ordinances may restrict truck traffic to certain hours of the day and to specified truck corridors. Under these conditions, noise pollution should not be a significant factor.

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Noise resulting from plant operations and air handling fans associated with the combustion and emissions control equipment is also a potential problem. Noise levels are likely to be highest in front of waste tipping floor doors, ash floor doors, and in the vicinity of the air emissions stacks.

4.3- Ash

The operation of an incinerator results in the production of waste ash that requires correct disposal.

A modern municipal waste combustion plant with energy recovery, processing400,000 tonnes per year of municipal solid waste, will reduce a tonne of waste toabout 291 kg of bottom ash residues and 45 kg of fly ash. The volume of the original waste is reduced by 90% and the weight by 70%.

Bottom ash is a gross material from the bottom of an incinerator and usually contaminated with dioxins and heavy metals but not severely so, and therefore can be recycled in various ways.

Fly ash is fine and ultra fine material collected in the stack by various filter systems of an incinerator and is always highly contaminated. Currently fly ash, which is considered hazardous waste, can be co-disposed of to landfill by mixing with nonhazardous waste, often bottom ash. From 2002, under the Landfill Directive, hazardous waste will no longer be co-disposed of; instead it will have to go to special hazardous landfill sites.

4.4-Aesthetic impacts

Negative aesthetic impacts can be prevented or minimized by proper site landscaping and building design. Such impacts are much less problematic the facility is sited in an industrial area and not adjacent to residential or commercial districts. Local zoning ordinances may ensure that aesthetic pollution does not occur. Environmental impact assessments should discuss potential aesthetic effects from a WTE project.

Keeping the process building at negative pressure can prevent undesirable odours from escaping outside of the building. Using air internal to the process building for combustion air in the plant processes will destroy most odours. Visible steam or vapour plumes can be emitted by some facilities.

Smoke resulting from improper conditions in the combustion chamber can also be problematic. Air emissions stacks and cooling towers may also be unappealing anomalies in the skyline of some areas. If external lights on buildings prove objectionable to neighbours, perimeter lights on stands directed toward the plant may be preferable.

4.5-Land use compatibility

Ideally, a WTE plant will be located where it is considered a compatible or nondisruptive land use. Choosing an incompatible site can serve as a catalyst for any

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existing public opposition to siting a facility. Construction in an industrially zoned area may be considered an example of siting in a compatible land use area.

The availability of undeveloped land around the facility will mitigate any unexpected and undesirable impacts by the facility. Having additional land available is also desirable for future expansion and the installation of additional energy recovery or emission controls as conditions change over the life of the facility.

An environmental impact statement should thoroughly document the impacts of WTE operations on environmentally sensitive areas. Contaminant levels of metals and other substances should be established downwind and near the facility to use as a baseline for measuring future impacts on environmentally sensitive areas.

The facility siting issues are dealt with later on in Sections 6 and 8.

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5-HUMAN HEALTH EFFECTS OF INCINERATOR EMISSIONS

Why do incinerators emit dangerous chemicals?

Matter cannot be created or destroyed, only transformed into other forms. It follows that incinerators do not destroy waste but transform it into ash and gases. The high temperatures in an incinerator causes chemical reactions that produce and release many extremely dangerous chemicals. These chemicals are dispersed into the environment through the chimney, the residue collected in the pollution filters and the grate (bottom) ash. Disposal of these ashes can also lead to contamination of the food chain.

Some toxic chemicals are present already in the waste for example fluorescent tube light bulbs often contain mercury, PVC plastic may contain cadmium or organic tin. Electrical equipment and batteries can contain brominated flame retarding compounds as well as lead, cadmium and chromium. Some of these heavy metals are partially vaporised in the intense heat of the furnace and the chemical reactions can also cause volatile compounds containing the original metals to be formed. Some of these toxic gases are captured in the pollution control system but a proportion pass out through the chimney.

The main pathway for pollutants to get into the environment from a waste incineration facility is, as for many other sources, through emission to the atmosphere. A large number of substances have been detected-most of them at very low concentrations-in the gaseous and particulate emissions from waste incineration. Among the emitted pollutants are metals and other non-combustible matter; acid gases; and products of incomplete combustion that include a large number of organic compounds as well as oxides of nitrogen, sulphur, and carbon. These pollutants are partitioned among the gas and particulate phases of the stack emissions from an incineration facility. As the pollutants disperse into the air, facility workers and people close to a facility might be exposed directly through inhalation or indirectly through consumption of food or water contaminated by deposition of the pollutants to soil and vegetation. Other people can be exposed through a different mix of environmental pathways after the pollutants travel some distance in the atmosphere; go through various chemical and physical transformations; or pass through soil, water, or food (see Figures 5.1 and 5.2). As part of estimating the amount of incineration-released contaminants that people are exposed to and the patterns of such exposure, investigators seek to track the concentration and movement of, and changes that occur in, the contaminants as they move through the environment from the incineration facility to a point of contact with people. Such information is also helpful in determining the contribution of incineration to the mix of environmental contaminants from all sources.

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Figure 5.1-Global pollutant dispersion pathways in the Environment.

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Fig 5.2-Dioxins and furans dispersion pathways in the Environment.

Substances released from combustion sources are ultimately dispersed among, and can at times accumulate in, various environmental compartments (e.g., soils, vegetation, indoor dusts, animals, and humans). Some contaminants that are released

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from incineration facilities are likely to contribute primarily to environmental compartments on a local scale (within 10 km). However, others that are more persistent in the environment, can be distributed over much greater distances--even up to a regional scale over hundreds of kilometres. Most of the substances released from incineration facilities to air do not remain in air but are deposited to soil, vegetation, or surface water and can come into contact with humans through a series of complex environmental pathways that include transport through several environmental media (see Figure 5.3).

Figure 5.3-Possible pathways from emissions of substances to human exposure.

To understand the possible health effects attributable to waste-incineration emissions, information is needed on contributions made by incineration to human exposures to potentially harmful pollutants and the responses that might result from such exposures. As discussed bellow, various tools have been used in attempts to evaluate effects of incineration. Of these tools, all of which contribute to our understanding, risk assessment methods have provided the most-detailed information for regulatory decision makers. Although past regulatory risk assessments have suggested that the risks posed by emissions from a well-run incinerator to the local community are generally very small, the same may not be true for some older or poorly run facilities. Some of the available assessments, however, may now be considered inadequate for a complete characterization of risk, for example, due to their failure to account for changes in emissions during process upsets, or because of gaps in and limitations of the data or techniques of risk assessment available at the time. There are limitations in the data and techniques of risk assessment, for example, in considering the effect of potential synergisms between chemicals within the complex mixtures to which humans are exposed, or the possible effects of small increments of exposure on unusually susceptible people. In addition, there are important questions not typically addressed by the usual risk assessment for single facilities such as the collective effect of pollutants emitted from multiple units; regional-scale effects of persistent pollutants; and the effects on workers in the facilities themselves.

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5.1-Tools for assessing the risk effects

We shall examine next the main tools used to evaluate the potential for health effects from incineration facilities. The two primary tools are environmental epidemiology and risk assessment. In addition, environmental monitoring studies provide immediately useful estimates of ambient concentrations, while biomarker studies hold some promise for future application.

5.1.1-Epidemiological studies

Epidemiological studies are conducted to test hypotheses about the occurrence (usually prevalence or incidence) of a health outcome, to measure the strengths or size of relationships between such outcomes and quantifiable factors (e.g., the magnitude of exposures) or qualifiable factors (e.g., exposure status), or to generate testable hypotheses about such relationships.

The principal strengths of epidemiological studies are:

The people studied include those likely to have been exposed to the material of interest. For incinerator emissions, there is no extrapolation necessary from single chemicals to the complex mixtures to which humans are actually exposed.

Humans themselves are studied in actual exposure conditions-there is no extrapolation from different animal species or different conditions.

Individual and group variability in both exposure and sensitivity are necessarily taken into account.

The principal challenges to be addressed by epidemiological studies in establishing causality include:

Identifying suitably exposed populations of sufficient size Identifying effect modifiers and/or potentially confounding

factors Identifying biases (including reporting biases) in data

collection Measuring exposures Measuring effects that are small, might occur only

infrequently, or take many years to appear

There have been few epidemiological studies in populations characterized as exposed to contaminants emitted by incineration facilities. Thus, there is a lack of evidence of any obvious health effects related specifically to incinerator exposure. That is, there have been few anecdotal reports that indicated any particular concern for incinerators (as opposed to air pollution in general, for example) or that generated testable hypotheses. Moreover, it would be difficult to establish causality given the small populations available for study, the possible influence of factors such as variations in the susceptibility of individuals and emissions from other pollution sources, and the fact that effects might occur only infrequently or take many years to appear.

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5.1.2-Risk assessment studies

Risk assessment is the use of procedures to estimate the probability that harm will arise from some action such as the operation of a facility. The procedures used to perform risk assessments vary widely, from a snap judgment to the use of complex analytic models. However, risk assessments of incineration or incineration facilities have become more structured and formalized, following a four-step paradigm (see Figure 5.4). These steps are followed sequentially and consist of: hazard identification, dose-response assessment, evaluation of exposure, and risk characterization. This last step of the risk-assessment paradigm, risk characterization, involves integrating the results of exposure assessment, dose-response assessment, and hazard assessment in such a way as to "develop a qualitative or quantitative estimate of the likelihood that any of the hazards associated with the agent of concern will be realized in exposed people". Risk-assessment results are generally expressed as lifetime cancer risks (calculated by taking the sum-over the pollutants of interest-of the products of lifetime average exposure to each pollutant and its potency slope) or as summary hazard indices (the sum over various chemicals of the ratio of estimated dose of each chemical to its reference dose).

Figure 5.4-Four step paradigm of risk assessment.

Risk assessment of waste incineration facilities can involve the following aspects:

Measurement or estimation of emission rates from specific facilities Modelling designed for tracking the flow of substances of concern through the

environment A large body of information on toxicity of many emitted substances, in

particular of dose-response information. Characterization of the expected effect of new incinerators, or of what might

happen in the future with any incinerator.

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Such risk assessments are congruent with most regulatory schemes-the principal inputs to risk assessments are also characteristics of incinerators that are usually regulated, for example, emission rates. The lack of complete data leads to uncertainties involved and the problem of communicating such uncertainties. Those uncertainties arise from the following:

The lack of complete emission data, especially for non-standard operating conditions.

The problem of dose-response assessment at low doses, and in particular of low-dose, cross-species, inter-route, and temporal dose-pattern extrapolation.

The lack of toxicity data on most products of incomplete combustion. The lack of physical and chemical information on relevant characteristics of

substances of concern. The use of unverified models of transport of substances in the environment,

due to incomplete knowledge as to how such transport occurs. The variability of all aspects of the assessment, due to variations in physical

conditions (e.g., topography, temperatures, rainfall, soil types, and meteorological conditions), characteristics of people (e.g., eating habits, residence times, age, and susceptibility), and so on, leading to wide ranges of exposures and risks for different people.

The possibility of errors and omissions in the assessment (e.g., omission of an important pathway of exposure).

Because of the variability and uncertainty, most risk assessments have not been designed to quantify actual health risks; rather they have been designed solely for regulatory purposes to yield upper-bound estimates of health risks that may be compared to regulatory criteria.

The main information on potential health effects that might arise in populations potentially exposed to substances emitted by incineration facilities comes from risk assessments of individual chemicals emitted by incinerators, combined with monitoring of emissions from incinerators. Such assessments typically indicate that, of the many agents present in incinerator emissions and known to be toxic at high exposures, only a few are likely to contribute the majority of any health risks and such health risks are typically estimated to be very small.

The toxic agents were selected for discussion on the basis of the current state of knowledge of the nature of emissions from incinerators and the results of various risk assessments. They are particulate matter (PM), carbon monoxide (CO), acidic gases (i.e., NOx, SO2, HCl) and acidic particles, certain metals (cadmium, lead, mercury, chromium, arsenic, and beryllium), dioxins and furans, polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs).

Particulate matter, CO, lead, and acidic gases and acidic particles have been under regulatory scrutiny for the longest period. Typically, there are well-defined statutory limits on their emission rates or allowable ambient concentrations or increments in ambient concentrations under environmental regulations.

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Although there are occupational-exposure limits for most of the other metals and organic compounds listed above, there are no well-defined ambient or emission standards under federal or some state regulations; however, in risk assessments, those materials are typically found to contribute to the majority of the estimated risk, either in contribution to lifetime cancer risks or in contribution to potential noncancer effects. Historically, risk assessments have identified the dioxins and furans as the principal contributors to estimated risks posed by most incinerators with arsenic often next. However, estimates of relative contributions of pollutants to total risk depend on incinerator emission characteristics, populations potentially exposed, potential routes of exposure, and, to some extent, the amount of information that has been collected. 5.1.3-Other studies

Environmental monitoring and biological markers of exposure or effect are two tools often used in conjunction with epidemiological or risk assessment investigations. These tools aid in identifying or confirming pollutants that may give rise to adverse health effects. Life-cycle assessment (LCA) has been used to evaluate the resource consumption and environmental burdens associated with a product, process, package, or activity throughout its lifetime over large geographic regions. LCA can be used in conjunction with risk assessments to assess effects over a broad scale-from the time of introduction of a chemical into the environment to its destruction.

Environmental Monitoring Studies. In principle, it is desirable to measure concentrations of certain pollutants directly from the incinerator in the surrounding environment. Such monitoring is most commonly of the ambient air, but soil, water, sediments, vegetation, and foods have at times been monitored for some of the emitted pollutants.

Environmental monitoring is principally useful because it directly measures the concentrations of certain materials from a particular incinerator, in some cases in the media of immediate interest (e.g., dioxins in vegetation and cows' milk). No health effects are measured. For use in evaluating health effects, however, environmental monitoring suffers from several disadvantages, because:

There is usually a problem in distinguishing the contribution of the incinerator to environmental concentrations

Monitoring measurements are limited both in space and in time while concentrations are often highly variable in both time and space

For these reasons, environmental monitoring is usually most useful in confirming, calibrating, or disproving the modelling efforts used in risk-assessment methodology.

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Biologic Markers (Biomarkers) of Exposure or Effect. There is now considerable interest in the use of biologic markers of exposures or effects in epidemiological studies of the health risks posed by some occupational and environmental exposures. Some of these studies are relevant to likely exposures to substances emitted from incinerators-for example, measurements of specific congeners of PCDDs and PCDFs in blood and adipose tissues of exposed workers, analyses of chlorophenol and pyrene metabolites in blood and urine of incinerator workers, analysis of selected DNA adducts in blood samples of incinerator workers and measurement of various indexes of metal exposure in workers.

Such studies are likely to be generally useful for evaluating exposures to specific materials that might be present in incinerator emissions or evaluating the presence of effects that might be associated with incinerator emissions. However, no biomarker of exposure or effect associated uniquely with incinerator emissions has been identified. Nor is any such biomarker likely to be identified, inasmuch as incineration emissions as a class do not (so far as is now known) have components that are peculiar to them nor that cause unique effects.

Thus, although the use of biomarkers might add substantially to the accuracy of measurement of exposures and effects in epidemiology, it is not likely to reduce substantially other major sources of uncertainty that are entailed in the application of epidemiology to incinerator emissions.

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5.2-The human health effects

There is insufficient data on health impacts from incinerator emissions of dioxin, furans, lead, and mercury, just to name the most relevant known. The same goes for the range of health effects and their intensity at likely emission levels. There are very few data on the actual human health impacts of incinerator emissions on the health of communities near incinerators. Epidemiological investigations have rarely been conducted, nor have studies of disease and illness patterns been undertaken. For example, ATSDR staff conducted a recent literature search of the 10 most frequently used computerised databases. As part of the search over 1,000,000 entries were identified. Approximately 72,000 of those entries dealt with incineration. Only one single entry discussed the conduct of a population-based study conducted in a community living in the vicinity of an incinerator. In the absence of human health data reliance is placed on using toxicity data for individual substances released into the environment. The effect of any toxic substance depends on factors such as duration of exposure, concentration of the substance in the environment, biological uptake and a person’s susceptibility factors (e.g., age). All these factors have to be considered in any estimate of impact of incinerator emissions. Adequate information does not exist to support speculation on what, if any, human health effects might be associated with incinerator emissions. However, our experience with public health associations related to hazardous waste sites would suggest the need to conduct two kinds of human health investigations. One kind of investigation would look at cancer, birth defects and respiratory disease rates in areas thought to be impacted by releases from incinerators. A second kind of study would be site specific. Community health surveys would help clarify whether any unusual exposure or morbidity is occurring that might be associated with a given incinerator.

There is insufficient data that has been gathered on additive, multiple, and synergistic impacts when there is exposure to more than one chemical, as would be the case with incinerator emissions. One could expect those impacts to be greater than from a single chemical exposure alone. There are few data available in the scientific literature on specific interactions of contaminates that may be released from waste incinerators (dioxin, furans, lead, mercury). In the absence of specific studies using combined contaminants, and limited understanding of the mechanisms of action for some substances, it is prudent to assume that the effects of exposure to these contaminates is additive.

There is also insufficient data that has been gathered on the sensitivity of various populations, by age, gender or ethnic background, to these chemicals, specially infants and elderly people:

Infants. Infants and children are arguably the most sensitive segment of the human population to toxic exposures. Infants and children are at special risk because: (i) they play outdoors, (where they spend more time than adults), (ii) they ingest or mouth foreign objects, (iii) they are smaller (greater chemical doses per pound) than adults (children are nearer the ground than adults and most chemicals are heavier than air), (iv) they also breathe more air (25 to 30 times a minute compared to an adults 15), (v) they are nutritionally challenged (because of protein-calorie requirements to support rapid growth), and finally (vi) they are under going developmental changes that make

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them especially vulnerable to chemical exposure. Moreover, they have the longest life expectancies during which long-term adverse health effects may manifest. Certain disorders may not become evident until a child reaches a particular developmental stage, which may occur long after the damage was done. Some of the largest environmental health programs (e.g. lead, asbestos) are directed at children.

Elderly persons and persons with chronic illnesses. Elderly persons and the chronically ill tend to be more susceptible to respiratory irritants. Long-standing public health policies such as immunisation guidelines for influenza support this notion. The elderly are also nutritionally challenged, often due to reduced protein-calorie intake and combined with the metabolic changes that occur during this stage of life. Underlying illnesses such as is the case in the chronically ill may increase their susceptibility to particular toxicants. For example, persons with chronic diseases of the kidney system may experience more harmful effects from exposure to renal toxicants such as lead and cadmium compared to a healthy individual.

There are data gaps that prevent us from determining the exact health impacts from incineration. The data that impede an accurate assessment of the public health impact of incineration can be divided into two categories: (i) those associated with the technology and the facility itself, and (ii) those related to environmental health. Following are examples of some key data gaps in both categories. Also listed are actions that should be considered in order to ensure the protection of the public’s health. These data gaps and recommended actions are based on ATSDR’s experience in providing consultations concerning hazardous waste incinerators.

(i)Key data gaps associated with the incineration technology/facility include:

The often inadequate identification and quantification of waste feed as well as fugitive emissions associated with specific incinerator facilities.

The deposition rates to soil and water for all potential incinerator stack emissions are not well known.

The identification and quantification of emissions during incinerator process upsets are frequently not measured.

When stack emissions are analysed for metals the specific metal compounds or species present are not usually identified.

Concentrations of contaminates in environmental samples around incinerator facilities, e.g. soil, water and ambient air are typically not measured.

There are limitations in the current stack testing, air monitoring and air modelling methods. Some of these methodologies need further validation.

Often there is a lack of data on the concentration of contaminates present in foods that are grown near a facility, such as vegetables from gardens, cattle, fish or shellfish etc.

(ii)Key data gaps in the second category of data gaps concerns the area of environmental health, and can be summarized as follows:

Limited demographic and health data on the surrounding community. Lack of environmental data such as types and concentrations of contaminates

present and the environmental media contaminated.

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Limited number of exposure, health monitoring and surveillance activities in communities living near operating incinerator facilities.

Data gaps in our knowledge about the adverse health effects from specific substances.

Toxicological data on the mixture of substances from incinerators. Efforts by federal and state environmental and health agencies are underway to address a few number of these data gaps. In addition to these efforts, attempts should be made to coordinate and collaborate in order to maximise the results in each individual area of data needed.

In the absence of human health data reliance is placed on using toxicity data for individual substances released into the environment. There are somewhere in the region of 80,000 chemicals in use daily throughout industry. Knowledge of the toxic properties of most of these chemicals is poor or non-existent. There is some reliable toxicological data on the effects of perhaps 5,000 chemicals on animals in laboratory conditions, while sound information on environmental impact is probably restricted to only a few hundred. A substantial amount of toxicity data is withheld from the public and independent research scientists’ by industry supposedly due to “commercial confidentiality.

Suppose we wanted to study 2 chemical combinations among the most commonly used 500 industrial chemicals. To do this we would have to do 124,749 different experiments. To study 3 chemical combinations among only 100 of these chemicals would require an amazing 20.7million experiments. An impossible task!!!…

Industry still continues producing and disposing of chemicals with no idea of their environmental or health impact. Many of the chemicals being emitted by incinerators are known to work in different, frightening ways to cause ill-health. The regulatory system has not yet caught up with the concept of endocrine disrupting chemicals and consequently does not take them into consideration. It remains to be seen when the government will acknowledge the danger and how it will regulate them.

Next, we will describe briefly some of the more relevant human health aspects related with toxic pollutants released during waste incineration.

People exposed to toxic air pollutants at sufficient concentrations may experience various health effects, including cancer, damage to the immune system, as well as neurological, reproductive (e.g., reduced fertility), developmental, respiratory, and other health problems. In addition to exposure from breathing air toxics, risks also are associated with the deposition of toxic pollutants onto soils or surface waters, where they are taken up by plants and ingested by animals and eventually magnified up through the food chain. Like humans, animals may experience health problems due to air toxics exposure

5.2.1-Particulate matter (dust, fly-ash)

Particles that are small enough to get into the lungs (those less than or equal to 10 µm in diameter) can cause numerous health problems and have been linked with illnesses and deaths from heart and lung diseases. Various health problems have been

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associated with long-term (e.g., multiyear) exposures as well as daily and even, potentially, peak (e.g., 1-hour) exposures to particles. Particles can aggravate respiratory conditions such as asthma and bronchitis and have been associated with cardiac arrhythmias (heartbeat irregularities) and heart attacks. Particles of concern can include both fine and coarse-fraction particles, although fine particles have been more clearly linked to the most serious health effects. People with heart or lung disease, the elderly, and children are at highest risk from exposure to particles. In addition to health problems, PM is the major cause of reduced visibility in many parts of the world. Airborne particles also can impact vegetation and ecosystems and can cause damage to paints and building materials.

A significant proportion of particulate matter from an incinerator will be very fine particulate matter (PM10 or less). These microscopic particles can reach the deepest part of the lungs where evidence suggests they can cause respiratory and heart related illnesses. The European Commission is concerned that these sorts of particulate emissions may be having health impacts on local populations. It has been estimated that for every 10mg/m3 increase in PM10 there is a 0.5 to 1.5% in daily mortality due to respiratory and heart disease. The SELCHP incinerator in South London, often cited by the industry as one of its best examples of a modern incinerator, emits between 4 and 22 mg/m3 of particulate matter in its stack gas, a significant proportion of which is PM10 or less. (This will of course be diluted as it leaves the chimney and is dispersed).

5.2.2-Permanent and acid gases

Hydrogen Chloride: Is an eye irritant and at high concentrations causes pulmonary oedema and laryngeal spasms.

Hydrogen Fluoride: Human exposure to greater than 3ppm have shown redness of the skin, burning/irritation of the nose and throat and digestive disorders. CO enters the bloodstream through the lungs and reduces oxygen delivery to the body’s organs and tissues. The health threat from levels of CO sometimes found in the ambient air is most serious for those who suffer from cardiovascular disease, such as angina pectoris. At much higher levels of exposure not commonly found in ambient air, CO can be poisonous, and even healthy individuals may be affected. Visual impairment, reduced work capacity, reduced manual dexterity, poor learning ability, and difficulty in performing complex tasks are all associated with exposure to elevated CO levels.

SO2. High concentrations of SO2 can result in temporary breathing impairment for asthmatic children and adults who are active outdoors. Short-term exposures of asthmatic individuals to elevated SO2 levels during moderate activity may result in breathing difficulties that can be accompanied by symptoms such as wheezing, chest tightness, or shortness of breath. Other effects that have been associated with longer-term exposures to high concentrations of SO2, in conjunction with high levels of PM, include aggravation of existing cardiovascular disease, respiratory illness, and alterations in the lungs’ defences. The subgroups of the population that may be

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affected under these conditions include individuals with heart or lung disease, as well as the elderly and children.

Ozone (O3). We shall distinguish tropospheric from stratospheric ozone, since they have completely different effects in those two places.

a) StratosphericSome UV-b radiation reaches the Earth’s surface even with normal ozone levels. However, because the ozone layer normally absorbs most UV-b radiation from the sun, ozone depletion is expected to lead to increases in harmful effects associated with UV-b radiation. In humans, UV-b radiation is linked to skin cancer, including melanoma, the form of skin cancer with the highest fatality rate. It also causes cataracts and suppression of the immune system.

The effects of UV-b radiation on plant and aquatic ecosystems are not well understood. However, the growth of certain food plants can be slowed by excessive UV-b radiation. In addition, some scientists suggest that marine phytoplankton, which are the base of the ocean food chain, are already under stress from UV-b radiation. This stress could have adverse consequences for human food supplies from the oceans. Because they absorb carbon dioxide (CO2) from the atmosphere, significant harm to phytoplankton populations could increase global warming (read about global climate change).

b) TroposphericShort-term (1- to 3-hour) and prolonged (6- to 8-hour) exposures to ambient ozone have been linked to a number of health effects of concern. For example, health effects attributed to ozone exposure include significant decreases in lung function and increased respiratory symptoms such as chest pain and cough. Exposures to ozone can make people more susceptible to respiratory infection, result in lung inflammation, and aggravate pre-existing respiratory diseases such as asthma. Also, increased hospital admissions and emergency room visits for respiratory problems have been associated with ambient ozone exposures. These effects generally occur while individuals are actively exercising, working, or playing outdoors. Children, active outdoors during the summer when ozone levels are at their highest, are most at risk of experiencing such effects. Other at-risk groups include adults who are active outdoors (e.g., some outdoor workers) and individuals with pre-existing respiratory disease such as asthma and chronic obstructive pulmonary disease. In addition, longer-term exposures to moderate levels of ozone present the possibility of irreversible changes in the lung structure, which could lead to premature aging of the lungs and worsening of chronic respiratory illnesses.

Ozone also affects vegetation and ecosystems, leading to reductions in agricultural crop and commercial forest yield, reduced growth and survivability of tree seedlings, and increased plant susceptibility to disease, pests, and other environmental stresses (e.g., harsh weather). In long-lived species, these effects may become evident only after several years or even decades, thus having the potential for long-term effects on forest ecosystems. Ground level ozone damage to the foliage of trees and other plants can also decrease the aesthetic value of ornamental species as well as the natural beauty of our national parks and recreation areas.

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NOx (as NO2). Short-term exposures (e.g., less than 3 hours) to low levels of NO2 may lead to changes in airway responsiveness and lung function in individuals with pre-existing respiratory illnesses and increases in respiratory illnesses in children. Long-term exposures to NO2 may lead to increased susceptibility to respiratory infection and may cause irreversible alterations in lung structure. NOx reacts in the air to form ground-level ozone and fine particle pollution, which are both associated with adverse health effects.

NOx contributes to a wide range of environmental effects directly and/or when combined with other precursors in acid rain and ozone (see environmental discussion under Ozone and Acid Rain). Nitrogen inputs to terrestrial and wetland systems can alter existing competitive relationships among plant species, leading to changes in community composition and diversity. Similarly, direct nitrogen inputs to aquatic ecosystems such as those found in estuarine and coastal waters (e.g., Chesapeake Bay) can lead to eutrophication (a condition that promotes excessive algae growth, which can lead to a severe depletion of dissolved oxygen and increased levels of toxins harmful to fish and other aquatic life). Nitrogen, alone or in acid rain, also can acidify soils and surface waters. Acidification of soils causes the loss of essential plant nutrients and increased levels of soluble aluminium that are toxic to plants. Acidification of surface waters creates conditions of low pH and levels of aluminium that are toxic to fish and other aquatic organisms. Finally, NOx is a contributor to visibility impairment.

Acid rain. Acid rain is not specifically an individual pollutant, but in fact a mixture of gaseous pollutants (and some times particles, also) that possess synergistic toxic effects on animals and plants. In the environment, acid deposition causes soils and water bodies to acidify (making the water unsuitable for some fish and other wildlife) and damages some trees, particularly at high elevations. It also speeds the decay of buildings, statues, and sculptures that are part of our national heritage. The nitrogen portion of acid deposition contributes to eutrophication in coastal ecosystems, the symptoms of which include algal blooms (some of which may be toxic), fish kills, and loss of plant and animal diversity. Finally, acidification of lakes and streams can increase the amount of methyl mercury available in aquatic systems. Most exposure to mercury comes from eating contaminated fish. Reductions in SO2 and NOx have begun to reduce some of these negative environmental effects and are leading to significant improvements in public health.

5.2.3-Heavy metal compounds

Metals, being elements, can be neither degraded nor metabolised, they are examples of ultimate persistence. The metals that have severely affected ecological or human health in the last 25 years include lead, chromium, arsenic, mercury, cadmium, selenium and tin. Of these tin, selenium and cadmium are new problems in the sense that their presence in the environment had not previously been considered a hazard. Lead is associated with learning impairment and behavioural problems in children. High levels of cadmium are associated with lung cancer and a range of other effects, mercury exposure has been found to affect behaviour and lead to renal damage even at low levels. Hexavalent chromium is associated with cancer.

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Antimony: Acute inhalation exposure to antimony causes irritation of the nose and mouth, abnormalities in the circulatory system and disruption of the respiratory tract. Chronic exposure may result in cardiac lesions and lung changes.

Arsenic: Arsenic is an established human carcinogen. Lung cancer is regarded as the critical effect following inhalation exposure.

Cadmium: Cadmium is a silvery white brittle metal. It has no role in living systems but is used increasingly in numerous industries. Causes cancer in rats and 5 ppm in drinking water shortened rats lives by 15%. Inhalation of 40mg with retention of 5mg is fatal to humans. In Japan, cadmium from a smelter contaminated irrigation water leading to a disease named itai-itai (or ouch-ouch) because of the extreme pain. Short-term exposure to high levels of inhaled cadmium causes respiratory effects such as pneumonitis. Oral exposure to high levels results in severe gastrointestinal upsets. It has been linked epidemiologically to prostate cancer in humans. The long-term effects of continual exposure to inhaled cadmium include emphysema, anaemia and cancer.

Chromium: Chromium V1 is a known carcinogen causing lung cancer via inhalation and possibly digestive tract cancer via ingestion.

Cobalt: Its toxic effects include lung irritation, immunological deficiency, heart disease, cancer and death.

Copper: Intake of excessively large doses of copper causes ill effects such as mucosal irritation/corrosion, capillary damage, liver and kidney toxicity and disruption of the central nervous system.

Lead: The toxicity of lead and mercury was thought to have been known for many years but some scientists now believe their effects have been underestimated. Exposure to lead occurs mainly through inhalation of air and ingestion of lead in food, water, soil, or dust. It accumulates in the blood, bones, and soft tissues and can adversely affect the kidneys, liver, nervous system, and other organs. Excessive exposure to lead may cause neurological impairments such as seizures, mental retardation, and behavioural disorders. Even at low doses, lead exposure is associated with damage to the nervous systems of foetuses and young children, resulting in learning deficits and lowered IQ. Recent studies also show that lead may be a factor in high blood pressure and subsequent heart disease. Lead can also be deposited on the leaves of plants, presenting a hazard to grazing animals and humans through ingestion

Lead is inherently toxic and has no useful function in the mammalian organism. Acute poisoning causes intestinal cramps, renal failure, sterility, irreversible brain damage (cerebral palsy and mental retardation and anaemia). In milder cases, tiredness, irritability, abdominal pain, anaemia and in children behavioural changes. Long-term exposure appears to be decreased neurological development in children and increased blood pressure and hypertension in adults. Children below six are at the greatest risk resulting in greater incidence of mouthing behaviour, greater gastrointestinal absorption of lead, incomplete development of the blood-brain barrier and greater sensitivity to neurological and haematological effects since the placenta is an ineffective barrier to the entry of lead into the foetus. Pregnant mothers are also a

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high-risk group. Some scientists now believe that there is no safe threshold for the developmental toxicology for lead.

Mercury: Mercury as an element is indestructible. Mercury vapour causes tremors and erythrism, a disease that involves a variety of psychological difficulties including short-term memory loss and social withdrawal. Methyl mercury also acts on the nervous system, and in particular the sensory and coordination centres. In Iraq 459 people died and 6,530 illnesses were reported following consumption of methyl mercury treated grain during a famine. Many of the uses of mercury have been eliminated but the waste accumulated from past production cannot be easily cleaned up. Foetal exposure to methyl mercury has shown to cause cerebral palsy.

Nickel: Inhalation of all forms of nickel causes irritation, lesions and various immunological responses. It is allergenic, some forms are carcinogenic and it has been shown to cause birth defects in certain species of animals.

Thallium: Is one of the most toxic elements and is capable of causing lethal effects due to its degenerative action on nerve fibres.

5.2.4-Organic vapours

The most toxic ones, and the more studied and reported are the dioxins and furans. Next we will describe with some detail their main properties and toxic effects.

What are dioxins? Dioxins, as they are commonly (and improperly) called, are polychlorinated dibenzo-para-dioxin (PCDDs). Chlorinated dibenzodioxins (CDDs), chlorinated dibenzofurans (CDFs) and Polychlorinated biphenyls (PCBs) are related compounds believed to be equally as harmful as dioxin. Therefore, all the above are collectively named “dioxin”. The PCDDs and PCDFs are obtained by substituting 1 to 8 chlorine atoms for an equal number of hydrogen atoms in the CDD and CDF molecules, respectively. Considering the number of all the possible combinations of the 8 chlorine atoms, one obtains a total of 210 different compounds (named congeners).

Much of the environmental behaviour of PCBs can be related to their physical characteristics. The non-polar nature of PCBs means that they are strongly hydrophobic and thus strongly lipophilic. They exhibit a high predilection for smooth surfaces, and combined with their lipophilic and hydrophobic properties, this explains their presence absorbed on to soil and sediment particles. The high surface concentration of lipids and organic compounds tend to concentrate and stabilize PCBs on the surface of water bodies. All PCDDs and PCDFs are organic solids with high melting points and low vapour pressures. They are characterised by extremely low water solubility, and have a tendency for being strongly adsorbed on surfaces of particulate matter. The water solubility of dioxin and furans decreases and the solubility in organic solvents and fats increases with increasing chlorine content. PCDDs and PCDFs are chlorinated, aromatic compounds, each with a triple ring structure consisting of two benzene rings inter-connected to each other by two or one oxygen atoms respectively. The general structure is (Figure 5.5):

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Figure 5.5-Formulas and structures of PCDD/Fs.

Toxicity is associated with the existence, number and location of the chlorine atoms in the positions 2, 3, 7 and 8:

and the corresponding compounds are named 2,3,7,8-tetrachlorodibenzo-p-dioxin (or 2,3,7,8-TCDD) and 2,3,7,8-tetrachlorodibenzo-p-furan (or 2,3,7,8-TCDF). The are, on the whole, 75 congeners of PCDDs and 135 congeners of PCDFs; there are less dioxin congeners due to the molecule’s symmetry, which makes some of chlorine atoms combinations redundant.

Considering all the allowable combinations of the possible 8 chlorine atoms, one obtains a total of 210 different compounds, but not all have the same toxicity. The 2,3,7,8-tetrachlorodibenzo-p-dioxin (or 2,3,7,8-TCDD) is the most toxic one (in fact it is the most toxic chemical known to man); therefore it is the reference to which all the other congeners are compared with.

The group of dioxin-like compounds includes all substances similar in chemical structure and biological effects to 2,3,7,8-TCDD; among these are certain polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), as well as a number of coplanar polychlorinated biphenyls (PCBs). The

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toxicity of a mixture of dioxin-like compounds can be expressed in toxic equivalency (TEQ) units, a single term that represents the sum of the concentrations of each dioxin-like substance, adjusted by its toxicity relative to that of 2,3,7,8-TCCD, the most toxic dioxin. Some 419 types of dioxin-related compounds have been identified but only about 30 of these are considered to have significant toxicity, with TCDD being the most toxic.

In the 1950s, dioxin was first discovered as the cause of severe health problems among workers who had been exposed to the by-products of explosions in chemical plants that manufactured certain chlorine-based pesticides. In these accidents, dioxin was formed and released into the workplace environment, causing systemic health problems among workers.

In the 1960s and 1970s, dioxin was identified as a contaminant in the pesticides themselves -- the components of Agent Orange -- and health problems began to emerge among soldiers and civilians exposed to Agent Orange in the Vietnam War. Subsequently, toxicological and epidemiological studies showed that dioxin was an extraordinarily potent carcinogen and caused damage to a variety of organs and systems in laboratory animals.

In the 1980s, the scope of the problem suddenly exploded. Dioxin, it was discovered, is formed not just in the manufacture of a few pesticides, but also in a wide range of industrial processes involving chlorine or chlorinated materials. Trash incinerators and pulp and paper mills that used chlorine as a bleaching agent were found to release particularly large quantities of dioxin. The scope of environmental contamination by dioxin also turned out to be much greater than previously thought: dioxin was discovered in air, water, and wildlife on a truly global basis -- from the Great Lakes to the deep oceans to the North Pole. Significant dioxin concentrations were found in the bodies of the general human population and "market-basket" studies of the human food supply. By the end of the 1980s, it was clear that every person in the world is now exposed to dioxin.

Only in the 1990s, however, has the health risk posed by universal dioxin exposures become clear. In 1994, the U.S. Environmental Protection Agency (EPA) released its long-awaited "Dioxin Reassessment", a project originally begun when the chemical and paper industries pressured the agency to revise downward its estimate of dioxin's toxicity and thus weaken regulations on dioxin sources. Contrary to the industry's intent, however, USEPA's reassessment concluded that dioxin might pose a long-term, large-scale hazard to the health of the general population. New toxicological and epidemiological studies have indicated that in addition to its potential to cause cancer in humans and in animals, extraordinarily small quantities of dioxin can disrupt the body's hormone system, leading to severe effects on reproduction, offspring development, and the function of the nervous and immune systems.

Dioxins are environmental "repeat offenders". They have the dubious distinction of belonging to "dirty dozen club" - a special group of dangerous chemicals known as persistent organic pollutants (POPs). Once dioxins have entered the environment or body, they are there to stay due to their uncanny ability to dissolve in fats and to their rock-solid chemical stability. Their half-life in the body is, on average, seven years. In the environment, dioxins tend to bio-accumulate in the food chain. The higher in the

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food chain one goes, the higher is the concentration of dioxins. Besides their toxicity, this persistency and the bioaccumulation are two environmentally relevant issues.

Therefore, two aspects of the environmental behaviour of dioxin-like compounds make them particularly troublesome. First, they are extraordinarily persistent, resisting physical, chemical, and biological degradation for decades and longer. As a result, even dilute discharges accumulate in the environment over time, reaching particularly high levels in aquatic sediments and in the food chain. Because they are so long-lived and can be transported long distances through the atmosphere, dioxins are now distributed on a truly global basis. Inuit natives of Arctic Canada, for instance, have some of the highest body burdens of dioxins, furans, and polychlorinated biphenyls (PBCs) recorded, due to a diet dependent on fish and marine mammals from a local food chain contaminated by dioxin from distant industrial sources.

Second, dioxins are highly oil-soluble but insoluble in water; they thus bio accumulate in fatty tissues and are magnified in concentration as they move up the food chain. In species high on the food chain, dioxin body burdens are typically millions of times greater than the levels found in the ambient air, soil, and sediments. Dioxins are also extraordinarily persistent in human tissues: estimated half-lives in humans are typically 5 to 10 years (see Figure 5.6).

At the apex of the food chain, the human population is particularly contaminated. A spectrum of dioxin-like compounds has been identified in the fat, blood, and mother's milk of the general population. Virtually all human exposures to these compounds occur through the food supply, particularly through consumption of fish, meat, eggs, and dairy products. Significant quantities are passed from mother to child, during the most sensitive stages of development, across the placenta and via mother's milk. The daily PCDD/PCDF dose of an average nursing infant in the U.S. is 10 to 20 times greater than the average adult exposure. A nursing infant thus receives about 10% of the entire lifetime exposure to these compounds during the first year of life.

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Figure 5.6-Biomagnification of dioxins.

Work on the molecular and cellular effects of dioxins to date suggests that the way in which they act is broadly the same. This is important, because it allows assumptions to be made of the effects for many dioxins that have not been tested toxicologically.It is generally believed that the toxic effects of dioxins are initiated by the binding of the dioxin to the intracellular aryl hydrocarbon receptor (AhR). This binding leads to a subsequent regulation of gene expression. This mechanism of action of TCDD parallels in many ways that of the steroid hormones.

Dioxin-like compounds elicit a broad spectrum of responses in experimental animals. Among these effects are:

· Liver damage (hepatoxicity)· Suppression of the immune system (immunotoxicity)· Formation and development of cancers (carcinogenesis)· Abnormalities in foetal development (teratogenicity)· Developmental and reproductive toxicity· Skin defects (dermal toxicity)· Diverse effects on hormones and growth factors· Induction of metabolising enzyme activities (which increases the risk of metabolising precursor chemicals to produce others that are more biologically active)

Cancer was for long considered as the critical effect, i.e. the most sensitive effect, ofdioxin exposure. However, in recent years, the foetus and newborn offspring of several species have been shown to be particularly sensitive to TCDD, resulting ineffects on reproduction, immune function and behaviour.

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In humans effects associated with exposure to dioxins are mainly observed in accidental and occupational exposure situations. A number of cancer locations, as well as total cancer, have been associated with exposure to dioxins (mostly TCDD).

In addition, an increased prevalence of diabetes and increased mortality due to diabetes and cardiovascular diseases have been reported. In children exposed to dioxins and/or PCBs in the womb, effects on neurodevelopment and neurobehaviour and effects on thyroid hormone status have been observed at exposures at or near background levels.

At higher exposures, children exposed transplacentally to PCBs and PCDFs show skindefects, developmental delays, low birth-weight, behaviour disorders, decrease in penile length at puberty, reduced height among girls at puberty and hearing loss. It is not totally clear to what extent dioxin-like compounds are responsible for these effects, when considering the complex chemical mixtures to which human individuals are exposed.

TCDD is the only dioxin congener for which the toxicity is relatively well characterised. However, based on the concept of a common mechanism of toxicity, alldioxins are assumed to be able to cause the same toxic effects as TCDD. The congeners are not equally potent, but the potential difficulty this presents, in assessing the likely effect of a particular mixture of congeners on health, has been overcome byexpressing the toxic potency of each congener as a Toxic Equivalency Factor (TEF).

The Toxic Equivalent (TEQ) is the sum of the concentration times the TEF for allindividual congeners of a sample. Recognising the necessity for a consistent approachtowards setting internationally agreed TEFs, the WHO-European Centre forEnvironment and Health (WHO-ECEH) and the International Programme on Chemical Safety (IPCS), organised a consultation in order to assess the relativepotencies of PCDDs, PCDFs and dioxin-like PCBs. In 1997 the WHO expert meetingderived consensus TEFs for both human and wildlife risk assessment. In spite ofuncertainties, it was concluded that the TEF concept is still the most plausible andfeasible approach for risk assessment of halogenated aromatic hydrocarbons withdioxin-like properties.

All risk assessments reviewed here, except the USEPA risk assessment, use the uncertainty, or safety, factor approach. Depending on the choices of critical effect anduncertainty factors, the recommended TDIs were in the range of 1-10 pg TCDD perKg body weight. These risk assessments supported the use of the TEF-scheme in riskassessment and risk management of PCDDs, PCDFs and PCBs. The WHO riskassessment from 1998 was based on the most up-to-date information and knowledgeregarding critical effects, dose-response relationships and quantitative risk extrapolation. A tolerable daily intake of 1-4 pg TEQ per kg body weight wasrecommended. These questions are very important, since it is now known that the predominant exposure pathway is by ingestion (see Figure 5.7).

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Figure 5.7-Dioxin pathways to human beings.

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6-SOCIOECONOMIC IMPACTS The siting and operation of waste-incineration facilities (such as incinerators and industrial boilers and furnaces) has social, economic, and psychological effects, or impacts, some negative, some positive.

The social, psychological, and economic impacts of incineration facilities on their locales are even less well documented and understood than the health effects of waste incineration. When environmental-impact assessments are required for proposed federal or state actions, they typically must include socio- economic-impact assessments, but the latter are often sketchy at best. They also might be given short shrift in the decision-making process. Furthermore, these socio-economic assessments attempt to be prospective-that is, they assess the likely effects of proposed actions. Little research has been done to evaluate systematically the socio-economic impacts of controversial waste-treatment or waste-disposal facilities that have been in place for several years or more. One reason for the lack of cumulative, retrospective impact-impact research is the lack of sufficient data. Although incineration facilities must routinely monitor and record emissions of specified pollutants, health-monitoring studies before or after a facility begins operation are only rarely performed, and periodic studies of the socio-economic impacts of a facility over time are virtually nonexistent, partly because of methodological problems and the absence of regulations that necessitate continued monitoring of socio-economic impacts.

Whether predictive or retrospective, the fact is that socio-economic impact assessments share the challenge (also faced by health-effects assessments) of confounding factors. Isolating the impacts of a single facility from other contributing conditions is often difficult, especially as those conditions change over time. Furthermore, the demographic composition of the area around the facility can be expected to change as time passes, making it difficult to assess the relationship between the facility and the changing group. Individuals also vary among themselves and over time in their sensitivity to socio-economic impacts, such as a decline in property values.

The scant information that is available on predicted or observed socio-economic impacts of various types of controversial waste-treatment or waste disposal facilities cannot be readily generalized to waste-incineration facilities, nor can the impacts of one waste incinerator be generalized without qualification to other waste incinerators. The host areas and the facilities themselves are, in many instances, too dissimilar to permit drawing inferences from one facility to another without many caveats. As discussed further below, simply identifying the geographic boundaries of an affected area can present problems. Opposition to incineration of municipal solid waste, medical waste, and hazardous waste has been routinely reported. Proposed facilities are often targets of citizen concern; existing facilities appear to receive less attention but are not altogether ignored. Groups opposed to incineration tend to focus on the adverse health and environmental effects of the facility but may also express concerns about socio-economic impacts. Such groups do not necessarily represent the sentiments of all others living in their vicinity; in fact, it can be expected that a number of community members will be indifferent and that, among those who do care, some will advocate or

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be willing to consider the start-up of the facility while others will be adamantly opposed. As is true of identifying the affected area, identifying who should be included as part of the "community" can be difficult.

6.1-Geographical assessment of the impacts The boundaries of the area potentially affected by a waste-incineration facility are not necessarily the same as the boundaries of the local jurisdiction. The affected area might be a relatively small section of the local jurisdiction; or, as illustrated in Figure 6.1, if an incinerator is at the edge of the jurisdiction, the affected area might extend into one or more other jurisdictions.

Complicating matters is the fact that different impacts (including health effects and socio-economic effects) have different reaches across space and time. Some impacts, such as those on traffic volume, might occur mainly along narrow corridors; others, such as those on air quality or on property values, might be more diffuse. Some might be relatively transitory, such as those due to a demand for workers during facility construction or to an episode of unusually high emissions due to a process upset or an accident at a facility; others might be cumulative or of long duration, such as those due to chronically high emissions or continued employment opportunities at a facility.

Furthermore, health and socio-economic effects vary in their intensity because of variations at the source, along environmental pathways, and among receptors. Consequently, preliminary mapping of the potentially affected area might necessitate a complex set of overlays for different types of impact (see Figure 6-2), each with its own gradations, boundaries, and time dimensions. Identification of areas for study and

Figure 6.1-Example of possible transjurisdictional impacts of an incineration unit.

F1GURE 6.2-Hypothetical example of overlay mapping of different types of impacts of an incineration facility.

assessment will necessarily be somewhat arbitrary; what is crucial is that areas that are expected to receive substantial impacts should be included.

Identifying an affected area according to where, when, and to what extent impacts occur has at least two important implications for interactions with those who live and work in the vicinity of an incineration facility. First, it highlights considerations for local government decisions concerning waste incineration and other controversial

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facilities. Second, it describes what constitutes the “community" in less-formal, non government interactions concerning the facility

6.1.1-The Affected Area and Local Decision-Making

Typically, those making decisions or entering into negotiations about an incineration facility's location, size, and so on are the elected or appointed officials of the jurisdiction that the planned facility would be in, such as the mayor and city councillor the county executive and county commissioners. When they consider the facility, they are likely to have in mind the interests of the jurisdiction as a whole, not just those of the affected area.

Waste facilities, like other land uses that have potentially undesirable side effects, present the possibility of uneven benefits and costs. A facility might produce substantial benefits, both for the larger region (by providing management capacity for some of its wastes) and for the host jurisdiction as a whole, but might have net adverse impacts on the immediately affected area. For example, as discussed further below, current approaches to the siting of large, controversial facilities sometimes include substantial payments to the host jurisdiction, which are then used as revenue to alleviate taxes or improve local schools, roads, and so forth. Depending on how the extra revenue is allocated, it might or might not benefit the affected area primarily.

When facilities like hazardous-waste and medical-waste incinerators are proposed, a general rallying of opposition-including opposition by local officials- sometimes occurs, if only because of the fear of the stigma that the facilities may bring. When facilities like municipal solid-waste incinerators are proposed, in contrast, elected officials and most voters in the jurisdiction may favour them, especially to the extent that they can help to meet local waste-management needs. If members of the affected area are only a few among many in local decisions concerning a facility, they run the risk of having their interests and concerns overruled. Decision-making about the facility might then have the appearance, but not the actuality, of fairness and impartiality. To correct for that possibility, augmentation of traditional forms of decision-making solely by elected officials or popular referenda is being explored, as discussed furtl1er below.

6.1.2-The Affected Area and Community Interactions

Although the term community is widely used, what counts as a community is often not clear. Communities are usually thought of as place-based, but the term is also used to refer to groups that, although widely dispersed, share interests (for example, a research community). Even when the term is used in its geographic sense, it is ambiguous: place helps to define a community, but other attributes-particularly those concerning social exchange-are often deemed essential. On the basis of such attributes, people living or working in a particular area form their own conceptions of the boundaries and composition of the community. Thus, an affected area does not necessarily constitute a discrete community; instead, it might contain parts or the entirety of several communities (see Figure 6.3), or it might lack the social cohesiveness to have any communities.

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Figure 6.3-Hypothetical example of relationship of affected area to local communities.

If a single community does not mirror the affected area, informal interactions by facility proponents and regulators with members of the affected area may be more difficult to conduct. As has been noted elsewhere, "Success for risk communication does not require that every citizen be informed about the risks presented in every regulatory decision, but people need to be confident that some person or group that shares their interests and values is well informed and is representing those positions competently in the political system". However, it is important that every citizen have an opportunity to be informed, whether they become so or not. The opportunity should not entail unnecessary burden. Communication between facility developers, regulators, and members of the affected area is often essential; lacking a single, cohesive community, the conduits for communication with members of the affected area may not be readily apparent. In addition, people who live or work outside or at the far reaches of the affected area may have strong views about a proposed facility but not be part of the community (or communities) in the immediate vicinity of the facility; whether and how to integrate them into informal interactions concerning the facility can be among the most-difficult issues that arise in local interactions.

6.2-Assessment of socio-economic impacts of incineration facilities

A list of possible socio-economic effects of an incineration facility is provided in Table 6.1. These effects may be favourable or adverse, and they may be economic (such as job creation and decrease in property values), psychological (such as stress and stigma), or social (such as community fractionalisation and unity). The effects can occur in individuals, groups in the affected area, or the entire population in the jurisdiction as a whole. In addition, different kinds of impacts can interact; for example, impacts that are primarily economic might have psychological and social elements as well.

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TABLE 6.1-Potential impacts of incineration facilities to be considered in socio-economic impact assessments

Increase or decrease in population Change in migrational trends Change in population characteristics Disruption of ~settlement patterns Change in economic patterns Increase or decrease in overall employment or

unemployment and change in occupational distribution Increase or decrease in income Change in compliance of land use with land-use plans Increase or decrease in land values Change in taxation resulting from change in land use and

income Change in types of housing and in occupancy Change in demand on health and social services Change in demand on educational resources Change in demand on transportation systems Relocation of highways and railroads Change in attitudes and lifestyles Disruption of cohesion Change in tourism and recreational potential

Different types of incineration facilities will have different effects on the surrounding geographic areas. Some incineration operations are within large facilities that have other functions, such as manufacturing; others are new, standalone facilities. Facilities in residential areas may have greater socio-economic effects on the surrounding area than facilities in big industrialized areas.

6.2.1-Economic impacts

A waste-incineration facility may provide jobs, both directly and by attracting industry to the region because of the services offered by the facility. In addition, such a facility may contribute to the cogeneration of electricity, district heating. A waste facility may have an adverse effect on local economic prosperity however, if businesses leave the affected area or decide not to locate the Public perceptions may make the risk seem larger, lead to the stigmatisation of affected communities.

Stigmas can have both direct and indirect economic impacts. Local employment opportunities may be adversely affected, and a stagnation or decline local retail businesses may necessitate travelling outside the neighbourhood shop for food, clothing and so on.

A waste-incineration facility may affect local public finances favourably insofar as it adds to local tax revenues or decreases the cost of local-waste disposal. However, such a facility may affect public finances adversely insofar as it increases the need for public services, such as improvements in roads and emergency preparedness, increases the cost of local-waste disposal, or requires large investments of time by

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local and state officials in permitting and other regulatory activities. In some cases, the net effect on local public finances will depend at least partly on special mitigation and compensation measures.

An incineration facility might also affect property values in its vicinity. Whether it increases or decreases them will depend primarily on what the neighbourhood was like before the facility was introduced.

6.2.2-Psychological impacts

People in the surrounding area may be psychologically affected by the prospect or reality of an incineration facility in their midst. The risk associated with industrial activity is increasingly recognized as including a wide array of adverse and sometimes long-lived psychological impacts, which may be, but are not always, correlated with negative attitudes toward the risk source. Concerns about adverse health effects on oneself or one's children, parents, spouse, and so on, as well as fear of adverse economic effects, can contribute to stress or depression, which in turn can produce physical symptoms, such as headaches and sleeplessness. Stress or depression may also be experienced if family, work, and social relationships are altered or terminated (through divorce or job loss) because of protracted outlays of time and energy to understand and combat a proposed or existing waste incinerator. In addition, feelings of powerlessness, distrust, and alienation may be fostered if people feel that their neighbourhood has been "captured," is not within their control, or lacks protection from the government.

Favourable psychological impacts may also be experienced under some circumstances. In particular, if their basic needs, like better sanitation works, transport services, etc, have been substantially improved as a result of compensation measures after the project implementation. 6.2.3-Social impacts

In addition to having favourable or adverse effects on the economic, physical, and mental well being of individual people in the affected area, a proposed or existing incineration facility can affect the area's social fabric. Some changes may be precipitated by economic factors, but others may be structural; that is, they may concern the formal and informal relationships of groups and individuals in the area.

Like other potentially controversial land uses, an incineration facility can provoke fractionalisation in the affected area among those who are opposed to it, those who favour it, and those who do not want the area harmed by heated, widely publicized conflict. Local controversies over major facilities (and sometimes over relatively small-scale ones) can last for years and leave scars and permanently alter formal and informal relationships in the area.

If individual health and well-being, property values, and the quality of life in a neighbourhood are substantially affected by a proposed project (or even if it is expected that they will be affected), the neighbourhood’s character may begin to change. Change may be seen in an increasing ratio of industrial to nonindustrial activities in the area, in the types of homes and businesses, and in the demographic

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composition of residents. People who can afford to move out may do so, sometimes altering the ethnic mix and age composition of the area. The changes do not happen overnight, but they are likely to be more rapid and destabilizing than the gradual demographic changes that occur in all communities because of births, deaths, and migration.

After a facility has been in operation for a long time, many of the impacts described above, if they occurred at all, will be in the past. The surrounding area may (or may not) have undergone wrenching changes because of the facility when it was in its formative stage, but over the years the area will have altered and adapted to its presence. The facility may continue to have adverse health effects, but it will not be likely to precipitate major new socio-economic impacts; instead, to the extent that it continues to affect the character of the surrounding area and its residents, it may contribute to feelings of either acceptance or quiet powerlessness and alienation.

6.3-Assessment of people’s perceptions and values

Even economic, psychological, and social impacts considered to be small by scientific and technical experts may be considered unbearable by people living in the affected area. Psychologists have identified a number of characteristics or risk attributes that help to explain the divergence between experts and the lay public-the so-called perception gap. It is well documented that members of the public tend to fear most the hazards that they do not impose on themselves voluntarily and that result in severe effects that are delayed (such as cancer). Other attributes, such as blame and distrust, have been singled out as especially important in shaping people's perceptions.

The differences between expert and lay perceptions reflect differences in values, however, not merely differences in information and understanding. Simply introducing public-education programs and information campaigns therefore cannot bridge them. Indeed, efforts to inform and educate the public about controversial technical issues may actually exacerbate public concern and opposition. Furthermore, the inherent uncertainties and variability of technical issues make risk communication difficult, and disagreement among experts may itself exacerbate public concern.

Members of the public often become enraged by technical assessments and public review processes that implicitly or explicitly rule values to be outside the boundaries of discussion. Three key issues are whether those responsible for developing operating, and regulating incineration facilities can be trusted; whether the facilities are needed; and whether fair processes are used to site them.

6.3.1-Social Distrust

Nowadays public has less and less trust in the institutions and people responsible for the siting and management of potentially hazardous facilities, such as incinerators.

Apart from whether facility operators and regulators are regarded as honest, competent, and well intended, scientific uncertainties can contribute to a lack of trust, especially in the case of facilities such as waste incinerators, for which questions remain about environmental transport and fate and about dose-response relationships of various emissions.

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6.3.2-Need

One of the first questions likely to be asked by people in the prospective host area of a waste-incineration facility (or other waste facility) is, "Is this really needed? If proponents cannot convincingly demonstrate a pressing need for a new or expanded incineration facility, people who are skeptical of the need for the facility, or are otherwise opposed to it, will be disinclined to negotiate on other issues about it.

As grassroots environmental movements began to flourish, pressure was brought to bear to reduce or, if possible, eliminate waste volumes and waste toxicity. With more-stringent regulations and greater corporate attention to release of environmental pollutants, that pressure has led to more-advanced production and waste-management technologies and to reduced demand for hazardous waste facilities, relative to population size and goods produced. However, there will always be some need for facilities to manage waste by-products of goods and services, thus society will still have to address how many facilities are needed, of what size, with what technologies, and-the hardest of all-in whose backyards.

6.3.3-Fairness

The second question typically asked by people in the prospective host area is, "Why here?" Siting a facility, such as an incinerator, presents an inherent and inescapable need to address equity: Whatever site is chosen, potential health risks and other adverse impacts are necessarily borne by a relatively small group, but the benefit (waste treatment or disposal) can accrue to a larger population. Although building new facilities may create new jobs and provide substantial tax revenues and other benefits (such as property-value guarantees), there is a well-documented tendency (known as loss aversion) for people to focus on adverse impacts more than on possible benefits.

Aside from actual or perceived outcomes (benefits and costs), the process for choosing a particular site is often perceived to be unfair. In many cases, residents living near a proposed facility will feel that they have been unfairly singled out and that they have had little or no substantive input into the decision. Possible attendant risks will be considered an imposition, and the degree of involuntariness will exacerbate perceived risk.

6.3.4-Environmental justice Results of several studies indicate that hazardous-waste treatment, storage, and disposal facilities are more likely to be located within or adjacent to low-income and minority-group communities, which results in an environmental justice (equity) issue. Some researchers have disputed those findings, however.

It has been found that there are identifiable communities of concern that experience higher levels of exposure to environmental contaminants. In addition, such communities are less able to deal with these exposures as a result of limited knowledge and disenfranchisement from the political process. Moreover, factors directly related to their socio- economic status, such as poor nutrition and stress, can

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make people in those communities more susceptible to the adverse health effects of environmental hazards and less able to manage them by obtaining adequate health care, turning the issue into a vicious cycle.

Often low-income communities and communities of colour speculate that some sources of environmental degradation were placed in their communities because land was cheap and the citizens lacked economic and political power- including access to technical and legal expertise--to keep it out. Other sources of environmental degradation may have been in place for a long time, with disadvantaged communities growing up around them because of low incomes, low property values, and discriminatory exclusion from other areas.

Results of some studies indicate that additional factors worsen the environmental burden on low-income and minority-group people. Environmental pollution in the areas where they live and work may be worsened by lax and irregular enforcement of regulations and by inadequate public services, such as water- treatment and sewage systems. And the effects on local residents may be graver for a number of reasons. For example, members of sensitive populations (children, the elderly, pregnant women and their foetuses, people with impaired immune systems, and people with chronic diseases) who are poor often cannot afford to move elsewhere. In addition, because of necessity or tradition, their diets rely heavily on locally caught fish and homegrown food and to recreation on local lands and in local water. Also, those living in the affected areas often are exposed to occupational health hazards.

A growing awareness that health problems, as well as socio-economic problems, are, at least partly, environmental in their origins has led a number of disadvantaged communities to mobilize against further assaults on the air, water, and land in their locales. They face an uphill battle, however. Many of the problems are slow to surface, so cause-effect arguments are difficult to make. And many problems result from factors that are cumulative and interactive, whereas regulatory standards have tended to focus on single sources of pollution, on single chemicals in a single transport medium, and on health and environmental effects exclusively, with little or no attention to related socio-economic effects. However, even if it were determined that facilities like waste incinerators contribute only marginally to increased environmental degradation, they may be regarded by their host areas as presenting unacceptable additional increases in risk. 6.4-Risk communication

6.4.1-Background

Risk communication has been broadly defined as any "purposeful exchange of information about health or environmental risks between interested parties" and by the National Research Council Committee on Risk Perception and Communication as "an interactive process of exchange of information and opinion among individuals, groups, and institutions". A wide variety of activities can be considered risk communication, including individual exchanges (such as phone conversations) among members of the public, agency officials, and industry representatives; informational campaigns by government agencies and industry; and elaborate processes of stakeholder involvement and decision-making.

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Good risk communication may ease community concerns, but there are no guarantees. Poor risk communication will almost certainly exacerbate public concerns.

To know whether a risk-communication process is good or bad, one needs to know what the goals of the process are and what constitutes success. Different participants in the process may have strikingly dissimilar goals and criteria for success. Generically, risk communication can have several goals:

To inform and educate To encourage behavioural changes and protective actions To notify in case of emergencies To encourage joint problem-solving and conflict resolution

Communicating about the health and environmental risks of incineration facilities is likely to involve elements of the 1st and 3rd goals, but most commonly will focus on the 4th. Given the extent of public distl1lst of industry and government roles in siting processes in general, the public often views risk communication with severe skepticism. Members of the public sometimes view risk-communication efforts as a thinly veiled attempt to foist unwanted facilities on unwilling communities rather than as sincere efforts in joint problem-solving and conflict resolution. Even well meaning efforts to inform and educate the public may be viewed as, at best, attempts to bring public perceptions into line with expert assessments of risk and, at worst, attempts to obfuscate the issues and belittle public concerns. Some government and industry representatives see risk communication merely as a means to a particular end (in this context, a siting decision). 6.4.2-Possible Approaches

Given the nature of the problem (differing perceptions and values, procedural and outcome inequities, and public distrust), what is the best way to proceed in communicating about the risks associated with incineration facilities? There are three possible strategies: ignore public perceptions and concerns (including equity), try to change them, or work with them. Ignoring public perceptions and merely "informing" the public about events-the decide-announce-defend (DAD) approach-is now considered undemocratic, undesirable, and ineffective. Trying to change public perceptions, attitudes, and concerns through education to bring them more into line with expert views of the issues is doomed to disappoint; the public has a rich, multidimensional view of risk that is extremely resistant to change, and risk controversies often result from deeper debates about the relationship between technology and society. Working with public perceptions and concerns-accepting them as legitimate and involving the public in consultative and participatory processes-makes the most sense; see NRC (1996), USEPA (1996), USEPA (1998a), USEPA (1998b), Chess and Purcell (1997), USEPA (2000a), USEPA (2000b), USEPA (1999), Franklin Pierce Law Centre (2001).

Compensation needs to be closely targeted to possible economic losses (such as loss in property values), and the form and content of any compensation package must be carefully negotiated with the affected parties. As noted above, siting an incineration facility necessarily creates inequities, and compensation may be the only way to try to

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redress them. There are two types of equity .One is procedural {who is involved and how) and the other is outcome (the distribution of harms and benefits). A compensation package needs to address both forms. Thus, negotiating the compensation package in an open, inclusive, participatory process that attempts to minimize any harms (for instance, with property-value guarantees) and maximize benefits (for instance, via preferential employment and purchasing) is more likely to be successful.

It should be noted that compensation is not a cure-all. In the absence of a good participatory decision-making process, no amount of compensation can ensure public acceptance. 6.5-Conclusions

6.5.1-Assessing socio-economic impact.

During and after the siting and building of a waste incineration facility, it may have various effects on members of the surrounding area in addition to physical health effects. The effects may be favourable or adverse, and they may be economic (such as job creation or decrease in property values), psychological (such as stress or stigma), or social (such as community fractionalisation or unity). They can affect individuals, groups, or the entire population in the surrounding area.

There is little reliable information on the socio-economic impacts of waste incineration facilities on their host areas. The previous text aimed at identifying issues that appear to merit attention, but these issues will not necessarily arise in the case of every incineration facility. Much more empirical research is needed, including longitudinal research on effects during the siting of the facility, as well as during its operation.

When research is conducted on the socio-economic, health, and environmental impacts of a facility, the boundaries of the potentially affected area should not be predetermined; instead, they should be defined as a function of where, when, and to what extent various impacts may occur. That approach permits a more accurate and more comprehensive analysis of the nature of the impacts. It also permits a better understanding of problems that may arise in connection with local interactions and decision-making concerning the facility.

6.5.2-Understanding citizen concerns

Even though a large body of research is not yet in hand on the possible health, environmental, and socio-economic impacts of different types of waste incineration facilities in different settings, it is clear that citizen concerns about these facilities do exist. The concerns need to be heard and understood, if only because escalated conflicts over waste incinerators may result and increase the time and expense of developing facilities that are potentially beneficial to society. Opposition to facilities also can indicate that important concerns are being given short shrift. Differences between expert and lay perceptions are not due merely to differences in information and understanding; they are also due to differences in values-particularly values concerning trust, need, and equity.

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One of the first questions often asked by members of the prospective host area is likely to be, "Is this facility really needed?" If facility proponents cannot convincingly demonstrate a pressing need for a new or expanded waste facility, people who are skeptical of or opposed to the facility will be disinclined to negotiate on other issues regarding the facility.

Siting a facility like a waste incinerator presents an inherent and inescapable need to address equity. Whatever site is chosen, the associated health risks, if any, and other effects are necessarily borne by relatively small groups, whereas the benefits of waste treatment or disposal (for example, jobs and substantial tax revenues) can accrue to a larger population. More and smaller local facilities may alleviate, but cannot eliminate, this dilemma and may create other problems, such as an increase in total emissions. Equity issues are exacerbated when a facility is placed in a low-income or otherwise disadvantaged community, where it raises broader concerns about disproportionate health, environmental, and socio-economic burdens already being borne.

6.5.3-Public Involvement

A good risk-communication program is not a panacea, but poor risk communication will nearly always make matters worse. Good risk communication is a continuing process at existing facilities or future facilities after siting.

People's perceptions are extraordinarily resistant to change, in part because they reflect underlying values. Efforts that ignore or try to change these perceptions radically are likely to fail. Given fundamental value differences, concern over procedural and outcome inequities, and distrust, there is growing consensus among academics and practitioners that effective risk communication should accept as legitimate the perceptions and concerns of various members of the public and involve them in consultative, participatory processes. Not only do members of the public have a democratic right and responsibility to be involved in the assessment and management of hazards in their communities, but also such involvement may result in improved assessments and management strategies.

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7-LEGISLATION

Until recently, waste incineration was regulated by three EU Directives: one covering the incineration of hazardous (formerly Directive 94/67/EC) and two covering non-hazardous waste (Directives 89/369/EEC and 89/429/EEC). They have been replaced, or merged into a new one. The new Directive 2000/76/EC on the incineration of waste was published on 28 December 2000 in the Official Journal of the European Communities (L332, p.91) (it can be assessed in the EU internet site: http://europa.eu.int/comm/environment/wasteinc/Documents%20available). The European Parliament voted on 16 November 2000 and Council gave its agreement on 21 November. The formal adoption was on 4 December 2000.

The aim of this Directive is to prevent or - where that is not practicable - to reduce as far as possible negative effects on the environment caused by the incineration and co-incineration of waste. In particular, it should reduce pollution caused by emissions into the air, soil, surface water and groundwater, and thus lessen the risks that these pose to human health. This is to be achieved through stringent operational conditions and technical requirements and by setting up emission limit values for waste incineration and co-incineration plants within the Community.

7.1-Key pollutants to be reduced

Although the volume of waste incineration is forecast to increase across the EU in the near future, the Directive will lead to significant reductions in emissions of several key pollutants. Moreover, controls on releases to water will - for the first time - reduce the pollution impact of incineration on marine and fresh water ecosystems. Considerable reductions will be achieved for acid gases such as nitrogen oxides (NOx), sulphur dioxide (SO2) and hydrogen chloride (HCl) as well as for heavy metals. Emissions of cadmium throughout the EU are expected to fall from 16 tonnes per year in 1995 to around 1 tonne in 2005. Over the same period, mercury emissions should fall from an annual 36 tonnes to around 7 tonnes.In addition, the Directive targets the incineration of non-hazardous waste, which has been identified as the largest source of emissions of dioxins and furans into the atmosphere. The Directive will reduce such emissions from Community incineration from an annual 2,400 grams in 1995 to only 10 grams after full implementation in 2005.

7.2-Main points of the 2000/76/EC incineration Directive Some of the main points in the new Directive are:

Exclusion of some special wastes from the regulation Clear distinction between incineration and co-incineration, in particular in

cement kilns Improved access to information for the public Stricter NOx emission limit

Essentially, the Directive has a much broader scope (see figure 1), and aims at covering all waste. Furthermore, it will introduce far stricter provisions than those found in the former municipal waste incineration Directives (89/369/EEC and

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http://europa.eu.int/comm/environment/wasteinc/Documents%20available

http://europa.eu.int/comm/environment/wasteinc/index.htm#Documents%20available

89/429/EEC) and in the hazardous waste incineration Directive (94/67/EC). However, it excludes some forms of waste such as:

Biomass (such as non-treated agriculture and forest residues), which falls under the scope of the large combustion plants Directive;

Experimental plants with a limited capacity used for research and development of improved incineration processes.

Vegetable waste, radioactive waste and animal carcasses

By establishing Community emission standards and conditions for discharges of wastewater, the Directive fills a gap in the former Directives on the incineration of waste. It makes a clear distinction between (see Figure 7.1):

Incineration plants (which may or may not recover heat generated by combustion);

Co-incineration plants (such as cement kilns, steel or power plants whose main purpose is energy generation or the production of material products).

It sets emission limit values for air (in particular for dust, SO2, NOx, and for heavy metals), introduces dioxins as a new parameter for discharges into water and stipulates that residues from the combustion process must be minimised in their amount and harmfulness and recycled where appropriate, and, if not possible, disposed of only under certain conditions.

The Directive envisages procedures for the application and granting of operating permits and sets a series of operating conditions (such as recovery, as far as practical, of heat generated during the incineration process).

Figure 7.1-Types of wastes envisaged in

the waste incineration Directive

Figure 7.2-Timetable for the

implementation of the waste incineration

Directive.

Finally it provides for public consultation, access to information and participation in the permitting procedure. Namely all incineration plants with a nominal capacity of more than two tonnes per hour will publish an annual report including information on the plant’s emissions.

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The new Directive entered into force on 29 December 2000 (see figure 2). Transposition into national legislation is necessary by 28 December 2002. From this date on new incinerators will have to comply with the provisions of the Directive; the deadline for existing plants will be 28 December 2005. Then all old Directives (89/369/EEC, 89/429/EEC und 94/67/EC) are repealed.

In order to reduce the toxicity of combustion products, the 2000/6/EC Directive imposes an 850ºC lower limit (1100ºC, if waste content in chloride is > 1%), and a minimum 2 seconds gas residence time, both for the flue gases after secondary air injection after the secondary air injection.

Tables 7.1 and 7.2 summarize the emission limits of the regulated pollutants: HCl, HF, SO2, NOx, PCDDs/Fs (dioxins and furans), and heavy metals (Cd, Tl, Hg, As, Pc, Cr, Co, Cu, Mn, Ni; V). Wastewater discharge limits and gas monitoring specifications are also defined.

Table 7.1-Emissions limits to the atmosphere in waste incineration (Directive 2000/76/EC)

Poluente Média24 h

Média30 min (100%)

Média30 min (97%)

Média6-8 h

Frequência de amostragem

Partículas totais (mg.m-3) 10 30 10 ContínuoTOC (mg.m-3) 10 20 10 ContínuoHCl (mg.m-3) 10 60 10 ContínuoHF (mg.m-3) 1 4 2 Contínuo

SO2 (mg.m-3) 50 200 50 ContínuoNOx (mg.m-3) 200 400 200 ContínuoCd + Tl (mg.m-3) 0.05 0.1 2 vezes por ano

Hg (mg.m-3) 0.05 0.1 2 vezes por ano

Sb + As + Pb + Cr + Co + Cu + Mn + Ni + V (mg.m-3)

0.5 1 2 vezes por ano

Dioxinas e furanos (ng.m-3) 0.1 2 vezes por ano

CO (mg.m-3) 50 100 150 ContínuoTemp. (°C) 850 Contínuo

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Table 7.2-Emissions limits in the wastewater resulting from the flue gas treatment in waste incineration (Directive 2000/76/EC)

Poluente Valor limite expresso em concentração mássica para amostras não-filtradas

Sólidos suspensos totais (mg.l-1) 30 (95%) 45 (100%)Hg (mg.l-1) 0,03Cd (mg.l-1) 0,05Tl (mg.l-1) 0,05As (mg.l-1) 0,15Pb (mg.l-1) 0,2Cr (mg.l-1) 0,5Cu (mg.l-1) 0,5Ni (mg.l-1) 0,5Zn (mg.l-1) 1,5Dioxinas e Furanos 0,3

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8-URBAN PLANNING AND INCINERATOR SITING ISSUES

An important consideration relevant to public health, and frequently raised by the public, is the location of the incinerator with respect to the community. More specifically, what are the possible health impacts associated with living or working in the path of incinerator emissions? To address those concerns, when reviewing the location of an incinerator, regulatory agencies use generally accepted air dispersion models in conjunction with local meteorological data to determine the permit conditions necessary to protect human health and the environment. Such modelling results can be particularly helpful in identifying prevailing wind transport patterns and their effect on downwind pollutant concentrations. Ideally, the site should not be where modelled high ground-level concentrations of stack emissions coincide with population centres. Dispersion models can also help evaluate the need for, and the location of, off-site air monitors used to detect fugitive emissions associated with incinerator operations and related hazardous materials-handling activities. If there is concern about the impact of incineration on a specific major food resource, such as a fish hatchery, and ATSDR has data regarding the uptake of the contaminants of concern by the particular food chain species, dispersion modelling can serve to estimate the concentration of emissions that would be available at ground level for food chain uptake. Finally, it should be noted that there is little flexibility in selecting a site for a Superfund incinerator, except with regard to where it is placed within the boundaries of the actual site. However, modelling as mentioned here is still useful in reviewing whether or not to use incineration for cleanup of a particular site.

8.1-The need for establishing siting criteria

At all tiers of government and at all levels within government organisations, from strategic to operational, decision makers face “messy” problems when evaluating and assessing development proposals. Environmental planning decisions are typical examples of complex problems involving numerous interacting factors and often conflicting technical, societal, environmental and political objectives. To derive at a successful decision, decision makers have to consider not just all the essential information and hard data but also the goals and the criteria that influence and affect the decision. According to Saaty (1994a), it may appear that certain kinds of data which appear most urgent scientifically would not impact on the goals and objectives of the decision problem as much as other less precisely quantifiable information. This author further elaborates that the best decisions often do not depend on great precision of measurement because the measurements must eventually be interpreted in terms of our not very precisely understood goals. Thus, how we structure and apply our judgement to make a decision are as essential, if not more so, than having a great deal of data about the problem but no effective way to make tradeoffs among the different kinds of information (Saaty, 1994a). Decision-making places much emphasis on value and its priority (Saaty, 1996).

8.2-Siting criteria: the AHP (Analytic Hierarchic Process)

There are many siting criteria, both qualitative and quantitative. Most countries have very detailed qualitative criteria: see for instance USEPA (1997), USEPA (2000), USEPA (1993), Franklin Pierce Law Centre (2001), USEPA (1999); but however

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useful they can be for decision makers, they have an inherently subjective nature which limits their application; more recently quantitatively methods have been developed, which makes the final decision more objective and undisputable; they use Operations Research techniques (linear and dynamic programming, Monte Carlo simulation, etc). In what follows we will show the application of hierarchical multicriteria models in assessing development projects, namely the AHP (Analytic Hierarchic Process), as developed by Saaty (1994a), and applied to a fictitious example of siting an incinerator plant in the city of Geneva, Switzerland (MUTATE, 2001).

The theoretical basis of the AHO methodology were initially developed in 1980 by T.L. Saaty (Saaty, 1980), being subsequently perfectioned by Saaty himself (Saaty, 1987, 1990a, 1990b, 1994a, 1994b, 1995, 1996, 1999); eventually a mathematical program was developed for its application by Expert Choice Inc, Pitts, PA, USA (Expert Choice, 2000). Some limitations to the application of this tool have been later on been reported (Triantaphyllou and Mann, 1994)

There are other mathematical tools for applying AHP, such as:

Model ELECTRE (Roy, 1991) Model HIPRE, developed by the Systems Analysis Laboratory of the Helsinki

University of Technology ( http://www.hipre.hut.fi ) On-line Java applets in the WWW, such as JAVA AHP

(http://chris.tag.csiro.au/JavaAHP/javaahp-introduction.htm)

The AHP (Analytic Hierarchic Process) developed by Saaty is a theory for measuring impact priorities in a hierarchical structure or more generally, in a feedback network, when the diverse concerns of a decision problem: the goal, criteria, sub criteria, activities and risky outcomes, cannot be put in levels as in a hierarchy where only the elements in a lower level depend on those in higher level but not the other way around (Saaty, 1994a). According to Saaty (1994a) a sound decision process must use known procedures that capture the best rank from judgements, through weighting and synthesizing them in a hierarchy in a way that is compatible with how we synthesise in a network with all sorts of dependencies.

The science of decision making is concerned with the relation between alternative actions or choices that need to be made and our system of values since our values help us in identifying different properties and measure intensities within each property (Saaty, 1996). This is why hierarchic and network structures are of essence in this undertaking. The success of using the AHP in modelling the decision problem is also based on the decision maker’s prior knowledge or commitments to meet expectations by being able to modify the ranking which results from the mathematics without considering the commitments (Saaty, 1994a). This method of decision modelling not only facilitates the timeousness of the approval process of development projects by taking into account all perspectives and human values of the relevant stakeholders in the decision process in a relatively short time period (by virtue of group decision support), but also allows for greater transparency in the decision process thereby aiding in the prevention of using Environmental Impact Assessments (EIAs) as a rubber stamp in the approval process of development projects.

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http://chris.tag.csiro.au/JavaAHP/javaahp-introduction.htm

http://www.hipre.hut.fi/

The hierarchical modeling of the decision problem is useful when dealing with complex phenomena if both reductionism and holism are considered simultaneously. The AHP enables decision makers to structure a complex decision in the form of a hierarchy. Although the reductionism of the AHP model simplifies the process of comparing the criteria in the models, it derives its durability from taking into account and aggregating the strengths of the judgments holistically through a process of synthesis. The type of AHP modeling can vary depending on the preferences of the decision maker. The models proposed are not absolute; hence, the inclusion and exclusion of criteria and factors influencing the criteria can vary according to the needs of a particular project. These models make allowances for the conflict and polarized viewpoints/opinions which are characteristic of the decision processes governing the assessment of development projects.

The model has sustainable development as the driving goal since all development projects are judged from the point of view how it contributes to sustainable development. Three aspects of the problem are incorporated into the sustainable development model: the economical, the environmental, and socio political environs that comprise sustainable development. To achieve sustainable development, all of these factors have to be carefully considered and a balance between these items needs to be attained. The decision problem thus involves both tangible (physical) and intangible (psychological) attributes. The AHP is a method that can be used to establish measures in both the physical and social domains (Saaty, 1996) and allows the decision maker(s) to compare tangible with intangible attributes since this type of comparisons typifies decision making in reality. The model in Figure 8.1 aids the decision maker(s) in prioritizing the social, environmental, economic and political factors when assessing the siting of obnoxious waste treatment plants (like incinerators), and in general, of any LULU (Locally Unwanted Land Uses).

Figure 8.1-First and second level decision criteria (in red, green, and blue), together with five admissible (proposed) siting locations: Cheneviers, Bois de Bay, Z.I. Meyza, Velodrome, and Les Rupiers.

According to Saaty (1996), in using the AHP to model a problem, one needs a hierarchic or a network structure to represent that problem, as well as pair wise comparisons to establish the relations within the structure. According to the procedure

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Figure 8.2-Aerial view of the studied area

for the AHP, the elements in each level of the hierarchy are compared with the parent or root of the cluster in a pair wise fashion. The software package, Expert Choice, can be used to derive the priorities of the various criteria in the hierarchical model. This software package also allows one to conduct a sensitivity analysis to test the effect of the uncertainty in the criteria on the choice of the best alternative. The scale of comparisons among pairs of elements in a level, as devised by Saaty, consists of verbal judgments and the corresponding absolute numerical judgments. The steps in building an AHP model as described by Saaty (1996) are:

Structure a problem as a hierarchy or as a network with dependence loops. The overall goal is at the top of this structure with the lower levels consisting of the criteria which guide the decision and the factors that affect them. Elicit judgments that reflect ideas, feelings, and emotions. Represent those judgments with meaningful values/numbers. This can be achieved by conducting pair wise and absolute comparisons. Synthesize results in the form of local and global priorities. Analyze sensitivity to changes in judgment.

8.3-The Geneva incinerator (fictitious) example

The following describes a fictitious case of finding the best location for siting an incinerator plant. A municipal waste incinerator must be built in an urban community

in Switzerland composed of several communes. The waste incineration plant is a costly investment that can be used in a context of integrated resource management, the heat from incineration being used for power generation and, possibly district heating. The fundamental economic parameters of the plant are given below.

Investment cost: CHF 10'000'000 for a nominal capacity of 40 000 tones of waste per Year

Waste transportation cost: CHF per tone per km Interest rate: 3% Life time: 40 years

There are many dimensions to this problem. Let us list a few "objectives" and "constraints" that the decision makers have identified:

Dimension the plant (s) to satisfy the demand Locate the plant (s) in such a way that the operating cost be as low

as possible Contain the nuisance due to the transport of waste in populated

areas

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Limit the exposure of the population to air pollution (a waste incinerator emits high quantities of NOx)

This problem is spatially structured in many ways: one has to locate one or several plants, the demand results from a population that is distributed over a region, the noise nuisance is associated with the proximity of roads with populated areas and air pollution is the result of a dispersion process. This is typically a situation where a GIS (Geographical Information System) can contribute a lot in providing a satisfactory solution.

The urban community considered here has established a co-ordinated geographical data collection effort (SITG for "système d'information du territoire à Genève") in which participate different departments and utilities involved in urban development. The data available consist in:

The population census (1990) The road network (streets and roads, with capacities and distances

between nodes) The power and heat networks (existing and potential) The current average concentration of NO2 over a typical year

represented on a kilometric grid.

One of the striking advantages of using SIG results from the fact that the application of the AHP method uses “layered information”, i.e. superimposing several maps to obtain correlations among parameters: for instance, if we want to calculate the number of persons affected by the waste transport, it will be necessary to “superimpose” the digitalized grids of the population and of the waste truck routes, as we shall see later.

The following digitalized information was gathered and processed to arrive at the most acceptable location as follows:

Map of the region served by the plant (Figure 8.3)

Population density (Figure 8.4)

Yearly volume of waste produced in all of the communes (Figure 8.5)

Identify admissible zones for the plant location (industrial, more than 2ha lots, publicly owned) (Figure 8.6); they are Cheneviers, Bois de Bay, Z.I. Meyza, Velodrome, and Les Rupiers

Identify the main roads from each commune center to each of the admissible sites, and calculate the optimum (shortest distance) using the Simplex Method (Figure 8.7, for the commune of Céligny as an example)

Calculate the ”nuisance corridor” for each optimized route (a 100 m buffer zone for each side of the road, representing the noise buffer zone; see Figure 8.8) and a 1Km “nuisance circle” (representing the visual and noise impact around each admissible site); the cumulative representation is shown in Figure

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8.9); for each case the number of affected people is calculated, by superimposing with the population map, Figure 8.3

Use a Gaussian atmospheric pollution dispersion model to calculate the stack plume intersection with the ground, giving the NOx concentration profiles at the ground (Figure 8.10), and calculate the number of people affected

Use the AHP method to determine which of the 5 admissible sites is less affected by the incinerator plant; this is shown in Figure 8.11), where Z.I. Meysa has the highest score and is therefore the definite choice for siting the incinerator plant.

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Figure 8.3- Map of the region served by the plant Figure 8.4- Population density

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Figure 8.5- Yearly volume of waste produced in all of the communes

Figure 8.6- Identification of admissible zones for the plant location (industrial, more than 2ha lots, publicly owned); they are Cheneviers,

Bois de Bay, Z.I. Meyza, Velodrome, and Les Rupiers

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Figure 8.7- Identification of the main roads from each commune center to each of the admissible sites, and calculation of the

optimum (shortest distance) using the Simplex Method (for the commune of Céligny as an example)

Figure 8.8- Calculation of the ”nuisance corridor” for each optimized route (a 100 m buffer zone for each side of the road, representing the noise buffer zone) and a 1Km “nuisance circle” (representing the visual and noise impact around

each admissible site); the cumulative representation is shown in Figure 8.9); for each case the number of affected people is calculated, by superimposing with the

population map, Figure 8.3

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Figure 8.9-Nuisance “buffer zones for transport, visual and noise impact

Figure 8.10- Use of a Gaussian atmospheric pollution dispersion model to calculate the stack plume intersection with the ground, giving the NOx concentration profiles at the

ground, and calculation of the number of people affecte

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Figure 8.11- Use of the AHP method to determine which of the 5 admissible sites is less affected by the incinerator plant; Z.I. Meysa has the highest score and is therefore the definite choice for siting the

incinerator plant.

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9-A VIEW FROM THE ENVIRONMENTAL NGOs

Almost all environmental NGO’s (Non Governmental Organizations) strongly oppose the building and operation of MWI plants, basically using the same arguments; these run from socioeconomical to environmental and human health reasons, the tonic being generally the last one, as summarized below.

9.1-Incinerators as waste generators

It is a common misconception that things simply disappear when they are burned. In reality, matter cannot be destroyed – it merely changes its form. This can be exemplified by looking at the fate of some substances in wastes which are burned in municipal solid waste (MSW) incinerators.

These incinerators are typically fed mixed waste streams that contain hazardous substances, such as heavy metals and chlorinated organic chemicals. Following incineration, heavy metals present in the original solid waste are emitted from the incinerator stack in stack gases and in association with tiny particles, and are also present throughout the remaining ashes and other residues.

Incineration of chlorinated substances in waste, such as polyvinyl chloride (PVC) plastic, leads to the formation of new chlorinated chemicals, such as highly toxic dioxins, which are released in stack gases, ashes and other residues.

In short, incinerators do not solve the problems of toxic materials present in wastes. In fact they simply convert these toxic materials to other forms, some of which may be more toxic than the original materials. These newly created chemicals can then reenter the environment as contaminants in stack gases, residual ashes and other residues.

All types of incinerators release pollutants to the atmosphere in stack gases, ashes and other residues. A multitudinous array of chemicals is released, including innumerable chemicals that currently remain unidentified.

The chemicals present in stack gases are often also present in ashes and other residues. Such chemicals include dioxins, polychlorinated biphenyls (PCBs), polychlorinated napthalenes, chlorinated benzenes, polyaromatic hydrocarbons (PAHs), numerous volatile organic compounds (VOCs), and heavy metals including lead, cadmium and mercury. Many of these chemicals are known to be persistent (very resistant to degradation in the environment), bioaccumulative (build up in the tissues of living organisms) and toxic. These three properties make them arguably the most problematic chemicals to which natural systems can be exposed. Some of the emitted chemicals are carcinogenic (cancer-causing) and some are endocrine disruptors. Others such as sulphur dioxide (SO2) and nitrogen dioxide (NO2) as well as fine particulate matter, have been associated with adverse impacts on respiratory health.

It is a popular misconception that the weight and volume of the original raw waste are reduced during incineration. It is often quoted that the volume of waste is reduced by about 90% during incineration. Even if only the residual ashes are considered,

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however, the actual figure is closer to 45%. The weight of waste is supposedly reduced to about one-third during incineration. However, this once again refers only to ashes and ignores other incinerator emissions in the form of gases, which result in an increased output in weight. In sum, if the mass of all the outputs from an incinerator, including the gaseous outputs, are added together, then the output will exceed the waste input.

9.2-Environmental and human exposure to incinerator releases

The research carried out on environmental contamination and human exposure to pollutants released by incinerators is limited and has focused mainly on dioxins and heavy metals. Research has demonstrated that both older and more modern incinerators can contribute to the contamination of local soil and vegetation with dioxins and heavy metals. Similarly, in several European countries, cow’s milk from farms located in the vicinity of incinerators has been found to contain elevated levels of dioxins, in some cases above regulatory limits.

Populations residing near to incinerators are potentially exposed to chemicals through inhalation of contaminated air or by consumption of contaminated agricultural produce (e.g. vegetables, eggs, and milk) from the local area and by dermal contact with contaminated soil. Significantly increased levels of dioxins have been found in the tissues of residents near to incinerators in the UK, Spain and Japan most likely as a result of such exposure. Two studies in the Netherlands and Germany however, did not find increased levels of dioxins in body tissues of residents living near incinerators. At an incinerator in Finland, mercury was increased in hair of residents living in the vicinity, most likely due to incinerator releases. Children living near a modern incinerator in Spain were found to have elevated levels of urinary thioethers, a biomarker of toxic exposure. Elevated levels or more frequent occurrence of certain PCBs occurred in the blood of children living near a hazardous waste incinerator in Germany.

Several studies have reported elevated levels of dioxins (total TEQ), and/or certain dioxin congeners, in the body tissues of individuals employed at both modern and older incinerators. This is thought to be a consequence of exposure to contaminated ashes in the workplace. Similarly, some studies have reported increased levels of chlorinated phenols, lead, mercury and arsenic in the body tissues of incinerator workers.

9.3-Health impacts

Experimental data confirm that incinerators release toxic substances and that humans are exposed as a consequence. Studies on workers at incinerator plants, and populations residing near to incinerators, have identified a wide range of associated health impacts. These studies give rise to great concerns about possible health impacts from incinerators even though the number of studies (particularly those that have been conducted to appropriately rigorous scientific standards) is highly limited. These should be seen, however, as strongly indicative that incinerators are potentially very damaging to human health.

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EXECUTIVE SUMMARY



Incineration subsequently developed during the latter part of the 19th century as a means of reducing the bulk and hazardousness of waste produced in the rapidly growing metropolitan areas. It soon became used as an opportune means of energy recovery. By 1912, there were some 76 incinerators operating in England, recovering energy as heat or electricity. New economic prosperity following the Second World War led to an increase in the amounts of waste produced per head of population, and incineration enjoyed a considerable growth in capacity. However, the communities in which they were located often regarded waste incinerators poorly. Even as late as the 1970s, emission control on incinerators was usually limited to simple cyclones for reducing dust emissions. Poor plant design and operating standards resulted in lack of control over combustion conditions, giving rise to emissions of smoke, odours and high levels of residual organic matter in the ash. Incinerators were identified as major urban sources of heavy metals, dust, acid gases and NOx, and products of incomplete combustion, such as dioxins and other toxic organic micro-pollutants. Concern over the public health impacts of these emissions led to the introduction of the 1989 incineration directives, the first community wide legislation to set minimum environmental standards for waste incineration. The 1989 directives resulted in the closure of existing plant that could not be upgraded to higher standards, and set minimum limits for all new incinerators. A further tightening of environmental standards for waste incineration will come about through the new incineration directive, which is due to be implemented in 2002.

As a result of strict regulation of incinerators under both community and member state legislation, a very marked improvement in emissions has been achieved. Nevertheless, incineration remains a highly contentious waste management option, not least because of remaining concerns over emissions, especially of dioxins.

Whether incineration is an appropriate means of managing waste has been the subject of much debate. A major aspect of the debate is the potential risk to human health that might result from the emission of pollutants generated by the incineration process; some of those pollutants have been found to cause various adverse health effects. Although such effects have generally been observed at much higher ambient concentrations than those usually produced by emissions from an incineration facility, questions persist about the possible effects of smaller amounts of pollutants from incineration facilities, especially when combined with the mix of pollutants emitted from other sources. The possible social, economic, and psychological effects

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associated with living or working near an incineration facility also have been topics of concern.

1-TECHNOLOGIES AND EMISSIONS Mass-burn incineration

During combustion, the waste is burnt in the presence of a good supply of air, so that organic carbon is essentially completely oxidised to CO2, which, along with water vapour and trace products of combustion, is discharged to the atmosphere. Energy is recovered in the form of steam, which is used to drive turbines for electricity generation. Some incinerators may also provide steam or hot water for process or community heating schemes as well as electricity in combined heat and power (CHP) applications. There are two main approaches to waste combustion – mass-burn incineration and process and burn incineration, in which a refuse-derived fuel (RDF) is first prepared. Mass-burn incineration is currently the most widely deployed thermal treatment option, with about 90% of incinerated waste being processed through such facilities. As the name implies, waste is combusted with little or no sorting or other pre-treatment.

The basic operation of an incinerator plant is described briefly next (see Figure 1).

Figure 1-Idealized flow-sheet of an waste incinerator with energy recovery.

Waste arriving at a mass-burn incinerator is tipped into a loading pit and from there transferred by crane and grab system into the combustion chamber loading chute. The waste is then conveyed through the combustion chamber, usually on a moving grate system (of which there are many designs) or through the slow rotation of the

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combustion chamber itself (rotary kilns). Whatever system is used, its purpose is to ensure thorough mixing and even combustion of the waste, so that complete burnout has occurred by the time the ash residue is discharged into a water-filled quenching tank at the end of the combustion chamber. Air is introduced from below and above the grate at flow rates adjusted to suit the rate of combustion. The hot combustion gases pass through heat exchange sections of the combustion chamber, where steam is generated for energy recovery. The cooling combustion gases then pass through various stages of emission control. These include dry or wet scrubbers for removing acid gases (SO2, HCl), injection of reducing agents such as ammonia or urea for controlling NOx emissions, activated carbon injection for dioxin control, and finally particulate removal by filtration or electrostatic precipitators, before the cleaned gases are discharged to the atmosphere.

Mass burn incinerators are specifically designed to cope with all components in the MSW stream, which generally has a relatively low average gross calorific value (GCV), in the range 9-11 GJ/tonne, about one third that of coal or plastics. However, individual types of waste vary markedly in their calorific values, from zero for wet putrescible wastes to over 30 GJ/tonne for some plastics. Loading an even mixture of wastes into the combustion chamber is therefore very important to ensure that the overall heat input stays in 9-11 GJ/tonne range for which the plant is designed to operate. Wastes are therefore mixed in the loading pit to even out obvious differences in composition before loading the combustion chamber. Excess amounts of high CV waste like plastics can lead to high temperature corrosion of heat exchange surfaces due to the high concentrations of chloride found in MSW. The need to avoid high temperature corrosion by limiting combustion chamber temperatures is one of the main reasons why the thermal efficiency of waste incinerators is low, compared with coal-burning steam cycle power stations.

On the other hand, if the GCV of incoming waste falls much below about 7 GJ/tonne, then the waste may not burn properly (or even at all) under the conditions inside the combustion chamber, and efficiency of energy recovery would markedly decrease. A pilot fuel would therefore be required to sustain efficient combustion and to ensure that statutory temperature conditions are achieved to prevent the formation of harmful products of incomplete combustion. Such conditions may occur when high quantities of wet garden waste come through the waste stream, especially in spring and autumn. Energy is recovered from mass-burn incinerators as heat (in the form of steam and hot water). The heat may then be used directly for (e.g.) district heating, or some of it is converted into electricity, by mean of a steam turbine/alternator. Combined heat and power and heat-only incinerators are widely deployed in some northern European countries, such as Denmark and Germany, where significant markets for the heat exist and where a tradition of investing in the considerable cost of a heat distribution system has grown up. Elsewhere, power only schemes are more widespread, because of the lower costs of marketing electricity, even though, as outlined below, the overall efficiency of power only is much less than that of CHP or heat only.

A recent study of energy recovery from waste incineration in a number of western European countries indicated that energy recovery was roughly divided between heat and electricity on the basis of equal amounts of waste going to CHP and power-only plant.

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Several material streams emerge from mass-burn incineration. The greatest of these is the ash residue discharged from the combustion chamber, which may represent between 20 – 30% of the mass of waste consumed. The ash may be processed by stabilising and grading to form a useful secondary construction material that can be used for low-grade applications such as road or car park base layers. Re-use of incinerator ash varies from country to country. Half of existing incinerators in the UK and all plants in the Netherlands have an ash processing facility.

Ash that cannot be re-used is landfilled. Metals can also be recovered from the bottom ash and sold to reprocessors. In plants with an ash-processing facility, nearly all of the ferrous metal can be recovered; otherwise up to 90% can be recovered. Non-ferrous metal can also be recovered in plants with ash processing.

Emissions standards for incinerators have recently been tightened through new emission limits imposed under the new incineration directive and extensive treatment of the flue gases is necessary to meet the new limits. Residue is produced from the air pollution control system, representing about 2-4% by weight of the incoming waste. This material consists of salts and surplus alkali from acid gas neutralisation, although some plants using wet scrubber systems currently discharge the scrubber residues to water as a salts solution. In addition, fly ash containing dioxin and heavy metals is produced. This material requires disposal at hazardous waste landfills, usually after some form of stabilisation or immobilisation in an inert medium such as cement has taken place. In Germany, salt caverns are used for storage of such hazardous materials.

Mass burn incinerators represent a considerable capital investment, in the order of 75 to 150 million Euros for a medium sized facility of about 400,000 tonnes throughput per year. Capacities range from about 100,000 to over 1 million tonnes of waste per year. Considerable economies of scale apply, especially just above the lower end of this range, and few new mass burn facilities much below this figure exist. Modular designs are common, with larger facilities consisting of several incineration lines working in parallel. The working life of an incinerator is typically around 20-30 years, although extensive maintenance and re-fitting of worn-out parts occurs during the working life.

To be cost-effective, mass burn incinerators require a guaranteed supply of waste within known limits of composition, available throughout the life of the plant. Because of the large scale of operation, such facilities may effectively ‘lock-in’ supplies of waste that could otherwise go for recycling. In addition, the requirement for bulk waste to be provided within a relatively narrow range of calorific value means that removal of particular waste streams for recycling could cause the remaining waste to fall outside the acceptable range. For example, removal of paper and / or plastics for recycling would increase the relative proportion of putrescible waste in the residue and lower its calorific value. On the other hand, removal of putrescible wastes as well, for composting, would help to keep the calorific value of the residue in the acceptable range, but reduce the overall quantity of waste available for processing. Reduction in either the calorific value or quantity of waste consumed would reduce the amount of energy recovered, the sale of which provides one of the main income streams (along with the disposal fee) of the incinerator. Reductions in

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the sales value of energy would then feed through into higher disposal charges for the waste.

Factors affecting combustion efficiency and pollutant emissions

The principal gaseous products of waste incineration, like other combustion processes, are carbon dioxide and water vapor. And, like many combustion processes, incineration also produces by-products such as soot particles and other contaminants released in exhaust gases, and leaves a residue (bottom ash) of incombustible and partially combusted waste that must be emptied from incinerator chambers and properly disposed. The composition of the gas and ash by-products is determined, at least in part, by the composition of the wastes fed into an incineration facility. This feed stream composition can be altered by other waste-management activities, such as reducing the amount of waste generated, reusing materials, and recycling waste materials for use as feedstocks for various manufacturing processes.

The exhaust gases from waste incineration facilities may contain many potentially harmful substances, including particulate matter; oxides of nitrogen; oxides of sulphur; carbon monoxide; dioxins and furans; metals, such as lead and mercury; acid gases; volatile chlorinated organic compounds; and polycyclic aromatic compounds. Some pollutant emissions are formed, in part, by incomplete combustion that may in turn lead to the formation of pollutants such as dioxins and furans. The formation of products of incomplete combustion is governed by the duration of the combustion process, the extent of gas mixing in the combustion chamber, and the temperature of combustion. Good combustion efficiency depends upon maintaining the appropriate temperature, residence time, and turbulence in the incineration process. Optimal conditions in a combustion chamber must be maintained so that the gases rising from the chamber mix thoroughly and continuously with injected air; maintaining the optimal temperature range involves burning of fuel in an auxiliary burner during start-up, shutdown, and process upsets. The combustion chamber is designed to provide adequate turbulence and residence time of the combustion gases.

Operation of the incinerator also affects the emission of heavy metals, chlorine, sulphur, and nitrogen that may be present in the waste fed into the incinerator. Such chemicals are not destroyed during combustion, but are distributed among the bottom ash, fly ash, and released gases in proportions that depend on the characteristics of the metal and the combustion conditions. Mercury and its compounds, for example, are volatile, so most of the mercury in the waste feed is vaporized in the combustion chamber. In the cases of lead and cadmium, the distributions between the bottom ash and fly ash depend on operating conditions. At higher combustion-chamber temperatures, more of the metals can appear in the fly ash or gaseous emissions. Therefore, combustion conditions need to maximize the destruction of products of incomplete combustion and to minimize the vaporization and entrainment of heavy metals, especially when adequate control of emissions is lacking. High temperatures and the presence of nitrogen-containing wastes promote formation of oxides of nitrogen.

In addition, air-pollution control devices can greatly influence emissions from waste-incineration facilities. For example, airborne particles can be controlled with electrostatic precipitators, fabric filters, or wet scrubbers. Hydrochloric acid, sulphur

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dioxide, dioxins, and heavy metals can be controlled with wet scrubbers, spray-dryer absorbers, or dry-sorbent injection and fabric filters. Oxides of nitrogen can be controlled, in part, by combustion-process modification and ammonia or urea injection through selective catalytic or noncatalytic reduction. Concentrations of dioxins and mercury can be reduced substantially by passing the cooled flue gas through a carbon sorbent bed or by injecting activated carbon into the flue gas.

With current technology, waste incinerators can be designed and operated to produce nearly complete combustion of the combustible portion of waste and to emit low amounts of the pollutants of concern under normal operating conditions. In addition, using well-trained employees can help ensure that an incinerator is operated to its maximal combustion efficiency and that the emission control devices are operated optimally for pollutant capture or neutralization. However, for all types of incinerators, there is a need to be alert to off-normal (upset) conditions that might result in short-term emissions greater than those usually represented by typical operating conditions or by annual national averages. Such upset conditions usually occur during incinerator startup or shutdown or when the composition of the waste being burned changes sharply. Malfunctioning equipment, operator error, poor management of the incineration process, or inadequate maintenance can also cause upset conditions.

Typically, emissions data have been collected from incineration facilities during only a small fraction of the total number of incinerator operating hours and generally do not include data during start-up, shutdown, and upset conditions. Furthermore, such data are typically based on a few stack samples for each pollutant. The adequacy of such emissions data to characterize fully the contribution of incineration to ambient pollutant concentrations for health effects assessments is uncertain. More emissions information is needed, especially for dioxins, furans, heavy metals, and particulate matter.

2-ENVIRONMENTAL AND HUMAN HEALTH IMPACTS After pollutants from an incineration facility disperse into the air, some people close to the facility may be exposed directly through inhalation or indirectly through consumption of food or water contaminated by deposition of the pollutants from air to soil, vegetation, and water. For metals and other pollutants that are very persistent in the environment, the potential effects may extend well beyond the area close to the incinerator. Persistent pollutants can be carried long distances from their emission sources, go through various chemical and physical transformations, and pass numerous times through soil, water, or food.

Dioxins, furans, and mercury are examples of persistent pollutants for which incinerators have contributed a substantial portion of the total national emissions. Whereas one incinerator might contribute only a small fraction of the total environmental concentrations of these chemicals, the sum of the emissions of all the incineration facilities in a region can be considerable.

Results of environmental monitoring studies around incineration facilities have indicated that the specific facilities studied were not likely to be major contributors to local ambient concentrations of the substances of concern, although there are

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exceptions. However, methodological limitations of those studies do not permit general conclusions to be drawn about the overall contributions of waste incineration to environmental concentrations of those contaminants.

Although emissions from incineration facilities can be smaller than emissions from other types of sources, it is important to assess incinerator emissions in the context of the total ambient concentration of pollutants in an area. In areas where the ambient concentrations are already close to or above environmental guidelines or standards, even relatively small increments can be important.

Computational models for the environmental transport and fate of contaminants through air, soil, water, and food can provide useful information for assessing major exposure pathways for humans, but, in general, they are not accurate enough to provide estimates of overall environmental contributions from an individual facility within a factor of 10. The models suggest that fish consumption is the major pathway of human exposure to mercury, and that meats, dairy products, and fish are potentially the major exposure pathways for dioxins and furans. For assessment of persistent pollutants, there is usually a poor correlation between total ambient concentrations and local emissions from an incinerator. Few epidemiological studies have attempted to assess whether adverse health effects have actually occurred near individual incinerators, and most of them have been unable to detect any effects. The studies of which the committee is aware that did report finding health effects had shortcomings and failed to provide convincing evidence. That result is not surprising given the small populations typically available for study and the fact that such effects, if any, might occur only infrequently or take many years to appear. Also, factors such as emissions from other pollution sources and variations in human activity patterns often decrease the likelihood of determining a relationship between small contributions of pollutants from incinerators and observed health effects. Lack of evidence of such relationships might mean that adverse health effects did not occur, but it could also mean that such relationships might not be detectable using available methods and data sources.

Pollutants emitted by incinerators that appear to have the potential to cause the largest health effects are particulate matter, lead, mercury, and dioxins and furans. However, there is wide variation in the contributions that incinerators can make to environmental concentrations of those contaminants. Although emissions from newer, well-run facilities are expected to contribute little to environmental concentrations and to health risks, the same might not be true for some older or poorly run facilities.

Studies of workers at municipal solid-waste incinerators show that workers are at much higher risk for adverse health effects than individual residents in the surrounding area. In the past, incinerator workers have been exposed to high concentrations of dioxins and toxic metals, particularly lead, cadmium, and mercury.

3-LEGISLATION

In the EU, the operation of solid waste incineration plants is regulated by the new Directive 2000/76/EC. The aim of this Directive is to prevent or - where that is not practicable - to reduce as far as possible negative effects on the environment caused

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by the incineration and co-incineration of waste. In particular, it should reduce pollution caused by emissions into the air, soil, surface water and groundwater, and thus lessen the risks that these pose to human health. This is to be achieved through stringent operational conditions and technical requirements and by setting up emission limit values for waste incineration and co-incineration plants within the Community.

Although the volume of waste incineration is forecast to increase across the EU in the near future, the Directive will lead to significant reductions in emissions of several key pollutants. Moreover, controls on releases to water will - for the first time - reduce the pollution impact of incineration on marine and fresh water ecosystems.

Considerable reductions will be achieved for acid gases such as nitrogen oxides (NOx), sulphur dioxide (SO2) and hydrogen chloride (HCl) as well as for heavy metals. Emissions of cadmium throughout the EU are expected to fall from 16 tonnes per year in 1995 to around 1 tonne in 2005. Over the same period, mercury emissions should fall from an annual 36 tonnes to around 7 tonnes.

In addition, the Directive targets the incineration of non-hazardous waste, which has been identified as the largest source of emissions of dioxins and furans into the atmosphere. The Directive will reduce such emissions from Community incineration from an annual 2,400 grams in 1995 to only 10 grams after full implementation in 2005.

4-PLANNING AND SITING ISSUES OF INCINERATION PLANTS In addition to possible physical-health effects, a waste-incineration facility may have other effects on individuals, groups, or the entire population in the surrounding area. The effects might be economic (such as job creation or decrease in property values), psychological (such as stress or stigma), or social (such as community fractionalisation or unity). However, there is little rigorous information on those impacts of waste-incineration facilities.

Citizen concerns need to be heard and understood. Conflicts can increase the time and expense of conducting waste incinerators and other facilities that might be potentially beneficial to society. Opposition to the facilities also can indicate that important concerns are not being addressed adequately.

Much public opposition to waste incineration might be due to a lack of understanding of the relative health risks posed by incineration in comparison with other waste-management methods. But health is not the only issue, and the differences between expert and public perceptions are not due merely to differences in information and understanding; they can also be due to differences in social values. People's perceptions are often extraordinarily resistant to change, in part because they reflect underlying values. Efforts that ignore or try to change these perceptions radically are likely to fail. Risk communication should accept as legitimate the perceptions and concerns of various members of the public and involve them in consultative, participatory processes. Not only do members of the public have a right and responsibility to be involved in the assessment and management of hazards in their communities, but also such involvement might result in improved assessments and management strategies.

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Developing effective participatory programs is very difficult, but some general principles are beginning to emerge. The process of public involvement should be open, inclusive, and substantive, and members of the public in an affected area should be involved early and often. Major concerns are likely to include issues of safety, compensations, and local oversight and control. Satisfying the public’s need for information on incinerator safety requires continual assessment and demonstration of regulatory compliance with existing standards.BIBLIOGRAFIA

ASSURE (2001). “Energy from Waste Fact Sheets - December 2001” www.assurre.org

Franklin Pierce Law Center (2001). “Fairness and Siting” . http://www.fplc.edu/risk/siteIndx.htm

MUTATE - A GIS Based Decision Support for Environmental Management. Université de Genève, 2001. (http://ecolu-info.unige.ch/~haurie/mutate/Mutate_final/NRC (1996). “Understanding Risk: Informing Decisions in a Democratic Society”.

Roy, B. (1991). The outranking approach and the foundation of ELECTRE methods , Theory and Decision, Vol. 31, pp. 49-73.

Rylander, H. and Haukohl, J. (2002).”Waste-to-energy - Status and future”. Waste Management World, May-June 2002, http://www.jxj.com/wmw/index.htmlSaaty, T.L. (1980). The Analytic Hierarchy Process: Planning, Priority Setting, Resource Allocation. NY, McGraw-Hill.

Saaty, R.W. (1987). The Analytic Hierarchy Process – What it is and how it is used. Mathematical Modelling, Vol. 9, No. 3-5, pp.161-176.

Saaty, T. L. (1990a). How to Make a Decision: The Analytic Hierarchy Process. European Journal of Operations Research 48 (1990), pp 9-26.

Saaty, T.L. (1990b). Multicriteria Decision Making: The Analytic Hierarchy Process. AHP Series Vol. 1, RWS Publications, Pittsburgh, PA.

Saaty, T.L. (1999). Decision Making for Leaders. Belmont, CA: Lifetime Learning Publications.

Saaty, T.L. and Forman, E.H. (1995). The Hierarchon: A Dictionary of Hierarchies. AHP Series, RWS Publications, Vo. V, 496 pp.

Saaty, T.L.(ed)1994a. Prioritisation of Environmental Impacts using hierarchical structures. University of Pittsburgh, Pennsylvania, USA.

Saaty, T.L.(ed)1994b. Decision making in complex situations: The Analytical Hierarchy Process as a multivalued logic. University of Pittsburgh, Pennsylvania, USA.

Saaty, T.L.(ed)1996. Decision making with dependence and feedback - the Analytic Network Process. RWS Publications, Pittsburgh, USA.

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(http://www.expertchoice.com/), Expert Choice Inc., Pittsburgh, PA.

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USEPA (1999). “Sites for our solid waste: a guidebook for effective public involvement”. Office of Solid Waste Office of Policy, Planning, and EvaluationU.S. Environmental Protection Agency.

USEPA (2001). “Stakeholder Involvement & Public Participation at the U.S. EPA Lessons Learned, Barriers, & Innovative Approaches”. United States Environmental Protection Agency, Office of Policy, Economics, Innovation (1801), Report EPA-100-R-00-040 www.epa.gov/stakeholders

USEPA (2000b). “Public Involvement in Environmental Permits”. United States Environmental Protection Agency, Office of Solid Waste and Emergency Response (5103), Report EPA-500-R-00-007www.epa.gov/permits

USEPA (2000a). “The model plan for public participation”. United States Enforcement and Environmental Protection Compliance Assurance Agency (2201A), Office of Environmental Justice, Report EPA-300-K-00-001(Originally Published as Report EPA-300-K-96-003)http://www.epa.gov/oeca/ej/main/nejacpub.html

USEPA (1993). “Criteria for Solid Waste Disposal Facilities. A Guide for Owners Operators”. United States Environmental Protection Agency, Solid Waste and Emergency Response, Report EPA/530-SW-91-089. Chess, C. and Purcell, K. (1997). “Public Participation and the Environment: What Works”. Center for Environmental Communication, Rutgers University,31 Pine Street, New Brunswick, NJ 08901-2883.

USEPA (1998b). “Improving Dialogue with Communities: A Risk Communication Manual for Government”. New Jersey Department of Environmental Protection, US.

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USEPA (2000). “Social Aspects of Siting RCRA Hazardous Waste Facilities”. United States Environmental Protection Agency, Solid Waste and Emergency Response (5305W), Report EPA530-K-00-005. http://www.epa.govUSEPA (1996).“RCRA Expanded Public Participation Rule”, United States Environmental Protection Agency, Report EPA530-F-95-030

USEPA (1997). “S e n s i t i v e E n v i ronments and the Siting of Hazardous Wa s t e Management F a c i l i t i e s”. U.S. Environmental Protection A g e n c y, Solid Waste and Emergency Response (5305W).h t t p : / / w w w. e p a . g ov / e p a o s we r / h a z w a s t e

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INDICE PROLOGUE 3

ACRONYMS 51-INTRODUCTION 7

1.1-EU waste policy 71.2-IRWM (Integrated Resource and Waste Management) and incineration 13

1.3-Thermal treatment (general) 161.4-Incineration in the EU 21

1.5-Alternatives to incineration in thermal waste treatment 372-INCINERATION TECHNOLOGIES 40

2.1-Description of a typical incineration plant 422.2-Incinerator furnace configurations (combustion chambers) 49

2.2.5-RDF (Refuse derived Fuel) burning 532.3-Incinerator plants configurations 56

2.4-Other thermal waste conversion processes 62 3-EMISSIONS CONTROL 80

3.1-Emissions characterization 803.2-Emissions formation and control 904-ENVIRONMENTAL IMPACTS 101

5-HUMAN HEALTH EFFECTS OF INCINERATOR EMISSIONS 1045.1-Tools for assessing the risk effects 108

5.2-The human health effects 1136-SOCIOECONOMIC IMPACTS 127

6.1-Geographical assessment of the impacts 128

6.2-Assessment of socio-economic impacts of incineration facilities 1306.3-Assessment of people’s perceptions and values 133

6.4-Risk communication 1356.5-Conclusions 137

7-LEGISLATION 1398-URBAN PLANNING AND INCINERATOR SITING ISSUES 143

8.1-The need for establishing siting criteria 1438.2-Siting criteria: the AHP (Analytic Hierarchic Process) 143

8.3-The Geneva incinerator (fictitious) example 1469-A VIEW FROM THE ENVIRONMENTAL NGOs 154

9.1-Incinerators as waste generators 1549.2-Environmental and human exposure to incinerator releases 155

9.3-Health impacts 155EXECUTIVE SUMMARY 156

BIBLIOGRAFIAINDICE 167

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