18-19 November 1999 - Stresa (NO) Italy
PROBLEMSAROUND SLUDGE
WORKSHOP ON
Edited by Heinrich Langenkamp, Luca Marmo
Proceedings
2000 EUR 19657 EN
EUROPEAN COMMISSIONJOINT RESEARCH CENTRE
Work
shop on PROBLEM
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einrich Langenkamp, Luca M
armo
WORKSHOP ON
PROBLEMSAROUND SLUDGEProceedings
Photos by: EISELT E.
18-19 November 1999 - Stresa (NO) Italy
Jointly organised by:
the Directorate-General for the Environment
the Joint Research Centre of the European Commission
Edited by:
Heinrich LangenkampSoil and Waste Unit, Environment Institute
Joint Research Centre
Luca MarmoWaste Management Unit, Directorate-General Environment
European Commission
WORKSHOP ON
PROBLEMS AROUNDSLUDGE
Proceedings
2000 EUR 19657 EN
EUROPEAN COMMISSIONJOINT RESEARCH CENTRE
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Printed in Italy
Preface
This book assembles the contributions to a workshop organised jointly by theDirectorate General for the Environment and the Joint Research Centre Ispra on 18and 19 November 1999 in Stresa (Italy). The aim of the meeting was to provide inputsto the revision of the Community Directive 86/278/EEC on the use of sewage sludgein agriculture. This Directive, now almost fifteen years old, belongs to the few legalmeasures adopted by the European Community in order to protect the soil. Its raisond’être and it’s importance has steadily increased over recent years. Indeed, with theadoption of Community Directive 91/271/EEC on urban waste water, which obligesMember States to provide waste water treatment stations in all agglomerations ofmore than 2.000 population equivalent, it is inevitable that the generation of sewagesludge will increase considerably over the years to come. This fact alone isjustification enough to look critically at the results that Directive 86/278 had onagricultural soils within the Community, on the ways to dispose of sludge and on thepossibilities to improve the present situation.
The twenty contributions and various supporting statements from professional andenvironmental organisations that are assembled in this book endeavour to discuss theproblem of sludge under different auspices. No attempt is made to eliminatecontradictions between the different contributions or to bring them to a singleconclusion. Rather, this book is meant to stimulate the discussion on soil protection inWestern Europe, on agricultural practices, on the generation of sewage sludge and,last but not least, on possibilities and ways to improve the protection of theenvironment. It is hoped that this discussion will continue over the next years, asproblems related to sewage sludge - and this is a certainty - will not disappear.Therefore, the upcoming discussions on how to develop instruments that preventEurope's soils from further degradation will, in part, be influenced by theinterrelationship between sludge and soil.
Heinrich Langenkamp (Ispra) and Luca Marmo (Brussels) took considerable care toassemble these texts and produce this book. They both invested significant time andefforts into the preparation of first the conference and this book, far beyond theprofessional effort one might have expected. Without their personal commitment,their patience and their determination to initiate and stimulate the discussion, thisbook would never have been produced. My thanks go to both of them and I hope thatthe present publication will be rewarding to incite them to continue their efforts for abetter environment on this continent.
Ludwig KrämerHead of Waste Management Unit
DG ENVIRONMENT/E.3
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Table of Contents
Preface .................................................................................................................... 3
Introduction
Urban waste water in Europe – what about the sludge?P. Magoarou ........................................................................................................... 9Sewage sludge and the Community waste strategyL. Marmo................................................................................................................. 17Sludge related issues as seen by the Directorate-General for AgricultureV. Morard ................................................................................................................ 25
Session 1: Sludge treatments and their effects on pathogens
Treatment and disinfection of sludge using quicklimeA.D. Andreadakis ................................................................................................... 31Anaerobic digestion of sludgeI. Angelidakis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Thermal drying – hygienic quality of dried sludgeJ.-P. Chabrier.......................................................................................................... 49
Session 2: Pollutants and nutrients in sludge and their effects on soil, vegetation and fauna
Endocrine disrupters - A general outline of the problemP. Part ..................................................................................................................... 61Limit values for heavy metal concentration in sewage ludge and soil that protect soil microorganismsE. Witter .................................................................................................................. 67Persistent organic pollutants and metals from sewage sludges: their effects on soil,plants and the food chainS. McGrath .............................................................................................................. 75Hygienic aspects of sludge reuseR. Böhm ................................................................................................................... 95Pros and cons of the use of sludge in agriculture as compared to animal manure, mineral fertilisers and other wastesM. Legeas ................................................................................................................ 116The role of sludge in the re-integration of soil fertilityP. Sequi and F. Tittarelli......................................................................................... 120
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The positive effects of organic matter and nutrients on crops grown on sludge amended soilsJ. Gómez-Palacio .................................................................................................... 133
Session 3: Technology and innovative options related to sludge management
Ecological and economical balance for different sludge management optionsJ. Hall ...................................................................................................................... 155Problems about sewage sludge incinerationD. Reimann.............................................................................................................. 173Alternative waste water treatment processes to reduce sewage sludge productionA. Tilche, G. Bortone and M. Dohányos ................................................................. 184Examples of good practice for reducing waste water and sludge contamination – the case of SwedenL. Ulmgren .............................................................................................................. 195Control of industrial discharges and quality assurance system for sludge use in a LIFE project in FranceL. Phan .................................................................................................................... 206
Session 4: Roundtable discussion on sludge use
The poin of view of:The European Union on national associations of water suppliers and waste water services (EUREAU)P. Ockiers ................................................................................................................ 215The European farmersE. Pommaret............................................................................................................ 219The European food industryM. Bruder ................................................................................................................ 221An environmental NGOE. Favoino ............................................................................................................... 222The European local authoritiesO. Huter................................................................................................................... 227
Annexes
Standardisation - An indispensable tool for environmental protection in EuropeC. Bannick ............................................................................................................... 231The Safe Sludge MatrixB. Chambers ............................................................................................................ 239
6
Introduction
Urban waste water in europe what about the sludge?
Pascal MagoarouWater Protection UnitDirectorate-General for the EnvironmentEuropean Commission
What is sludge
Sludge, originating from the treatment process of waste water, is the residue generatedduring the primary (physical and/or chemical), the secondary (biological) and thetertiary (additional to secondary – very often nutrient removal) treatment. Theresidues of the processes of pre-treatment, also called preliminary treatment, are notconsidered as sludge. These residues are mainly coarse solid particles, grits, sands andgrease.
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The obligations under the urban waste water treatment directive
The quantity of sludge has been, for several years, increasing greatly in Europebecause of the implementation of Council Directive 91/271/EEC of 21 May 1991concerning urban waste water treatment1 (Urban Waste Water Treatment Directive).
The objective of the directive is to protect the environment from the adverse effects ofdischarges of urban waste water and of waste water from industrial sectors, mainlyfrom the agro-food industry.
The Directive obliges Member States to:• Provide prior regulation or specific authorisation for all discharges of urban waste
water and industrial waste water from the particular sectors mentioned in theDirective, as well as for all discharges of industrial waste water into urban wastewater systems;
• Provide urban waste water collecting systems (sewerage) and treatment plants forall agglomerations above 2,000 p.e. (population equivalents, a widely usedmeasurement unit for the organic pollution of waste water equal to the averagepollution load of one person per day).
• The general rule for the level of treatment is secondary treatment, i.e. biologicaltreatment. However, the treatment must be more stringent (tertiary treatment) fordischarges to the catchment areas of sensitive areas as identified by Member Statesand may be less stringent (primary treatment) for certain discharges to coastalwaters and estuaries identified as less sensitive areas. This less stringent treatment issubject to certain conditions and has to be authorised. The deadlines for theapplication of the directive are 31/12/1998, 31/12/2000 or 31/12/2005 depending ofthe size of the agglomeration and the sensitivity of the receiving waters (see table inthe following page);
• Ensure that by 31/12/2000 the industrial waste water from the covered sectorsrespects before discharge the established conditions for all discharges from plantsrepresenting 4,000 population equivalents or more;
• Provide before 31/12/1998 general rules or registration or authorisation for thesustainable disposal of sludge arising from waste water treatment and, by the samedate, phase out any dumping or discharge of sewage sludge into surface waters;
• Ensure that the urban waste water discharges and their effects are monitored;• Publish situation reports every two years and establish implementation
programmes.
The table below details the deadlines for the application of the Directive. It clearlyshows that, by the end of the year 2000, all the large cities of Europe should beprovided with waste water collection and treatment plants, producing sludge. Only thesmall agglomerations (less than 10,000 p.e. in sensitive areas and less than 15.000 p.e.in other areas) will have till 31/12/2005 to be in compliance.
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1OJ L 135, 30.5.1991, p.40.
The provisions concerning sludge
The main article of the Urban Waste Water Treatment Directive dealing with sludge isArticle 14. This article stipulates that “sludge arising from waste water treatment shallbe re-used whenever appropriate”. This is a clear priority given to the use of sludge inagriculture, when this use is appropriate, considering in particular the quality of thesludge. The Commission considers that the use of sludge in agriculture should beencouraged since it represents a long-term solution, provided that the quality of thesludge is compatible with public health and environmental protection requirements.
The same article also mentions that “disposal routes shall minimise the adverse effectson the environment” and that “before 31 December 1998 the disposal of sludge fromurban waste water treatment plants shall be subject to general rules or registration orauthorisation”. The Commission is now assessing the measures taken by MemberStates to fulfil these provisions.
Finally, Article 14 also obliges Member States to “ensure that by 31 December 1998the disposal of sludge to surface waters by dumping from ships, by discharge frompipelines or by other means is phased out”. In the past, three Member States at leastwere habitually disposing sludge to the sea. The Commission is also verifying that thisdisposal path is phased out.
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Obligations and deadlines
* Appropriate treatment if discharge to coastal waters
Sensitivity Size of theof the agglomerationreceiving (p.e.)waters
0 ➡ 2,000 ➡ 10,000 ➡ 15,000 ➡ 150,000 Sensitive areas If collection Collection Collection Collection Collection
31/12 2005 31/12 2005 31/12 1998 31/12 1998 31/12 1998Appropriate Secondary* More More Moretreatment treatment advanced advanced advanced
treatment treatment treatmentNormal areas If collection Collection Collection Collection Collection
31/12 2005 31/12 2005 31/12 2005 31/12 2000 31/12 2000Appropriate Secondary* Secondary Secondary Secondarytreatment treatment treatment treatment treatment
Less sensitive areas If collection Collection Collection Collection Collection(coastal waters) 31/12 2005 31/12 2005 31/12 2005 31/12 2000 31/12 2000
Appropriate Appropriate Primary or Primary or Primarytreatment treatment secondary secondary (exceptional)
treatment treatment or secondarytreatment
➡
➡
The control of the industrial waste water connected to the sewer is crucial for thequality of the sludge produced in the treatment plant downstream. Article 11 of theDirective sets out provisions for the discharge of industrial waste water into collectionsystems and urban waste water treatment plants. This discharge must be subject toprior regulations and/or specific authorisations satisfying specific requirements, inorder in particular to “ensure that sludge can be disposed of safely in anenvironmentally acceptable manner”.
The use of sludge in agriculture is regulated by Directive 86/278/EEC on theprotection of the environment, and in particular of the soil, when sewage sludge isused in agriculture2.
The quantity of sludge
In January 1999, the Commission published its first report concerning theimplementation of the Urban Waste Water Treatment Directive3. A part of this reportsummarises the data contained in the implementation programmes received fromMember States.
The graph and table below show the quantities of sludge that are expected to beproduced over the period of implementation of the directive (1992 – 2005) as well asthe planned destination of that sludge.
For all the 13 Member States which have provided information (no information onsludge has been received from Sweden or Italy), the quantity of sludge produced is
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0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1992 1995 1998 2000 2005
Tons of dry solids per year
Surface Water
Reuse
Landfill
Incineration
Other
2OJ L 181, 4.7.86, p.6.3Implementation of Council Directive 91/271/EEC of 21 May 1991 concerning urban waste watertreatment, as amended by Commission Directive 98/15/EC of 27 February 1998 – COM (98) 775final, 15.01.1999
therefore set to increase from 5.5 million tons of dry matter in 1992 to 8.3 million tonsin 2005. At the end of 2000, the quantity should already be 7.9 million tons, i.e. 95%of the final amount. Of particular note is the increase in the proportion due to be usedfor agriculture and soil and that for incineration as well as the slight reduction in theanticipated amount for disposal to landfill. The quantity of sludge to be used wouldrepresent at the end of the implementation period 53% of the total quantity of sludgeproduced.
The quantity of sludge estimated to be produced per day and per population equivalentcan be calculated on the basis of these figures as well as of the number of populationequivalents in the European agglomerations as evaluated by Member States. Theresults, as shown in the table below, vary from 27g dry solids per p.e. and per day to99, with an average of 58. If we exclude the extreme figures, which are almostcertainly the results of wrong calculations, the figures vary between 40 and 80.
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Year Destination B DK D GR E F IRL L NL A P FIN UK TotalSurface water - - - - 38 - 14 - - - - - 282 334Reuse 17 110 1018 1 275 402 4 5 134 63 38 87 472 2626
1992 Landfill 34 25 846 65 180 131 16 4 177 58 75 63 130 1804Incineration - 40 274 - 35 110 - - 12 66 - - 90 627Not specified 8 - 70 - - - 3 - 1 3 13 - 24 122Total 59 175 2209 66 528 643 37 9 324 187 126 150 998 5511Surface water - - - - 54 - 15 - - - - - 267 336Reuse 22 120 1151 1 390 489 7 7 95 63 44 86 648 3123
1995 Landfill 39 25 857 65 257 114 14 3 192 58 88 72 114 1898Incineration - 40 411 - 50 161 - - 56 66 - - 110 894Not specified 17 - 93 - - - 4 - 23 3 15 - 19 174Total 78 185 2513 66 751 764 40 10 365 187 147 158 1158 6422Surface water - - - - 57 - - - - - - - 240 297Reuse 33 125 1270 4 410 572 25 9 100 68 74 85 672 3447
1998 Landfill 37 25 744 82 268 92 17 1 108 58 147 65 118 1762Incineration 11 50 558 - 52 214 - 3 150 66 - - 144 1248Not specified 32 - 89 - - - 1 - 23 4 25 - 19 193Total 113 200 2302 86 787 878 43 13 381 196 246 150 1193 6588Surface water - - - - 57 - - - - - - - - 57Reuse 40 125 1334 6 578 640 65 9 110 68 104 90 1014 4183
2000 Landfill 43 25 608 90 360 71 35 1 68 58 209 60 111 1739Incineration 11 50 732 - 74 269 - 3 200 66 - - 326 1731Not specified 37 - 62 - - - - - 23 4 35 - 19 180Total 131 200 2736 96 1069 980 100 13 401 196 348 150 1470 7890Surface water - - - - 57 - - - - - - - - 57Reuse 47 125 1391 7 589 765 84 9 110 68 108 115 1118 4536
2005 Landfill 40 25 500 92 367 - 29 1 68 58 215 45 114 1554Incineration 14 50 838 - 75 407 - 4 200 65 - - 332 1985Not specified 58 - 58 - - - - - 20 4 36 - 19 198Total 160 200 2786 99 1088 1172 113 14 401 196 359 160 1583 8331
Forecasts of sludge destination (in thousands of tons of dry solids per year)
The type of waste water treatment is the main factor explaining these differences.Some biological treatments produce less sludge than others do. Extensive biologicaltreatment processes, like lagoons or reed beds, well adapted for small and mediumsize agglomerations, produce very small amounts of sludge. On the other hand,physical – chemical removal of phosphorous increases by about 30% the quantity ofsludge produced by an activated sludge plant. A physical – chemical process of wastewater treatment may produce up to 150g dry solids//p.e./day.
The quantity of sludge to be produced, as well as the treatment envisaged(stabilisation, thickening, dewatering, conditioning, drying, disinfection) and itsdestination, are often subject to insufficient attention in the design of waste watertreatment projects. More attention should also be paid to the various products that maybe added to the water and sludge treatment processes, which will be found in thesludge: metallic ions, lime, polymers etc.
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Sludge production per p.e. and per day
Organic loads Sludge production in 2005 g(1000 p.e.) (1000 tds/y) sludge/p.e./day
GR 10,203 99 27A 18,569 195 29E 74,439 1,088 40L 914 14 42F 70,510 1,172 46B 9,164 159 48DK 8,393 200 62NL 17,218 401 64D 106,540 2,787 72UK 58,276 1,583 74IRL 3,918 113 79FIN 5,099 160 86P 9,912 359 99Average 393,155 8,330 58
(total) (total)
Quantity of sludge/type of UWW treatment g dry solids/p.e./day
Filter bed Activated sludge FB with physical/chemical AS with physical/plant (FB) plant (AS) phosphorus removal chemical phosphorus removal57 64 74 84
Source: Water UK
The quality of sludge – action at source
The three categories of pollutants which affect the sludge quality are: pathogens,heavy metals and poorly biodegradable organic compounds, also called persistentorganic pollutants (POPs).
Pathogens, which originate from human and animal metabolism, can be eliminated bysludge treatment, but the removal in the treatment plant of the two other categories ofpollutants does not seem technically or economically feasible. Instead of an “end ofpipe” approach, preventive action should be taken at source, as required by Article174 of the EC Treaty. Discharge of heavy metals and organic compounds in the sewermust be reduced. For that three kinds of discharges have to be considered: dischargesfrom domestic uses and services, discharges from run-off rain water into the combinedsewer system and discharges of connected industrial waste water.
The table above lists some examples of pollutant origins in the different kinds ofdischarges.
The contents of some products used in households, services or industrial processes canbe changed in order to avoid discharges of pollutants into the sewer, and otherdischarges into the sewer can be stopped by collecting and treating separately thepolluted waste. For example, thermometers or dentists’ amalgalm fillings can bemercury free. Residues of paints, solvents, laboratory chemicals etc. must not end intothe sink but be collected, recycled or treated separately.
Two thirds of the European agglomerations are equipped with combined systems. Insuch systems run-off rain waters constitute a large part of the source of pollution ofheavy metals discharged to the sewer. A study carried out on a catchment area of thecity of Marseilles concluded that 63% of the annual load of lead discharged to thesewer came from run-off rain water. Another study carried out in Paris shows that the
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Sources of pollutants in urban waste water
Pollutant sources Domestic use and Run-off rain water Connected industrialservices (combined system) waste water
Pathogens Human metabolism Animals faeces (pets) Limited (meat industry)
Heavy metals Paints (Pb), Amalgam Rain (Pb, Cd, Zn), Variousfillings (Hg), Tyres (Cu, Cd), RoofThermometers (Hg), corrosion (Zn, Cu), OilPipe corrosion (Pb, Cu).. (Pb)...
POPs Paints, Solvents, Wood Oil, Pesticides Varioustreatment, Medicines, (gardens), Tar, RoadDetergents, Cosmetics,... de-icing, Rain,
(pesticides, combustion),...
proportion of zinc and lead coming from run-off rain water represents nearly 90% ofthe pollution sources. This pollution is mainly caused by vehicle traffic, air depositionand roof corrosion.
In 2000, the Commission has launched a study to assess, at the European level, therelative shares of pollutants due to products and materials used in households, servicesand production processes carried out by industry, as well as those of pollutantsintroduced into the combined sewer with the run-off rain water. The aim of the studyis also to identify Community and national measures taken and to be taken at source,which are likely to reduce the contamination by heavy metals and organic compoundsin waste water and sludge.
Conclusion
Safe and long term solutions for the destination of sludge produced by the urban wastewater treatment is a vital element of a sustainable functioning of the waste watertreatment plants implemented all over Europe by application of the UWWT Directive.The recycling of sludge, containing useful organic matter and nutrients, in agricultureis considered by the Commission as the best solution, provided that the quality of theproduct and the way of its use are harmless for human health and environment.
Compliance with the existing legislation is a minimum condition for this safe use. Atthe Community level that means that the provisions contained in the Urban WasteWater Treatment Directive 91/271/EEC and in the Sewage Sludge Directive86/278/EEC OJ L181, 4.7.86, p. 6 are fulfilled. The Sewage Sludge Directive needs tobe updated and the Commission is now working on a revision.
Information and communication are also essential to ensure the development of theuse of sludge in agriculture.
In the same time, efforts must be made for the necessary improvement of the qualityof sludge and the optimisation of its quantity. Actions must be taken at source,upstream the waste water collecting systems, in order to reduce or eliminate thedischarges of pollutants into the sewer. Furthermore the design and the functioning ofthe waste water and sludge treatment plants must be optimised, taking more intoaccount the final destination of the sludge produced.
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Sewage sludge and the Community waste strategy
Luca MarmoWaste Management UnitDirectorate-General for the EnvironmentEuropean Commission
Introduction
Europe’s increasing wealth as well as economic and social development have broughtwaste to the forefront of discussion – and not only amongst experts. The way in whichwaste – sewage sludge included – is collected, processed, recycled and disposed ofaffects the quality of life of every one of us, and the quality of the environment aroundus. These are the reasons why in the 1970s the Community began building up a set oflegal and administrative regulations to ensure that waste is dealt with properly and inan environmental friendly fashion. The way in which the use of sewage sludge iscurrently regulated in the Community stems from this legislative frame.
The Community waste strategy
The Fifth Environmental Action Programme singled out waste management as a keyarea of the Community environment policy. The last ten years have seen a concertedeffort to produce a complete and coherent legislative framework for waste, starting inSeptember 1989 with approval of the Community Strategy on Waste Management1.This strategy set out to ensure a high level of environmental protection withoutdistorting the internal market, with a view to promoting sustainable development. Thiscalled for a consistent approach to waste management in the Community, oneprecondition of which was the introduction of a suitable legal framework providingbasic concepts and definitions. This was achieved with the adoption of two Directivesand a Regulation, which now form the pillars of the Community’s waste managementpolicy. These are Directive 75/442/EEC2 on waste, Directive 91/689/EEC3 onhazardous waste and Regulation (EEC) No 259/934 on the supervision and control ofshipments of waste within, into and out of the European Community.
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1COM(89) 934 final of 18.9.89.2OJ L 194, 25.7.75, p. 31.3OJ L 377, 31.12.91, p. 20.4OJ L 30, 6.2.93, p. 1.
The Community Strategy for Waste Management5, which the Commission adopted inJuly 1996, confirmed the hierarchy of principles already established in 1989 in theearlier Strategy:• prevention of the generation of waste and of its hazardousness,• re-use, recovery of materials (recycling), energy recovery, and• final disposal.
The Communication emphasises that, when it comes to prevention of wasteproduction, the following measures in particular should be pursued: promotion ofclean technologies and products, development at Community level of technicalregulations and standards to restrict the presence of certain hazardous substances inproducts, promotion of schemes to encourage re-use of waste and recycling,appropriate use of economic instruments, eco-balances, eco-audit schemes, productlife-cycle analyses, information campaigns and awareness-raising among consumers,as well as development of the European eco-label scheme.
Regarding recovery, preference should as a rule be given to recovery of materials(recycling) rather than energy recovery. This is based on a number of considerations, primeamong which is that recycling, by its very nature, involves selective collection of wastematerials and so brings end-users and consumers into the waste management chain. Highrates of participation and successful selective sorting are known to depend on widespreadpublic information to bring home the challenges which society as a whole must face up to ifit is to successfully manage the ever growing amount of waste it produces. Another reasonis that, from the energy balance perspective, maintaining the existing material structure ofwaste allows us to minimise the additional material and energy required to create a newproduct. In addition, recovery of materials, as opposed to energy recovery, reduces thequantity of waste sent for incineration, and so reduces the potentially polluting emissions ofincineration plants. Lastly, recycling generally creates more jobs than incineration, so thatprosecution of such a policy ought to help reduce unemployment in the Community.
Where final disposal is concerned, every effort should be made to avoid incineration withoutenergy recovery and to see that the Community’s many illegal landfills are eliminated.
Coherently with this approach to waste management, in 1986 the Council adoptedDirective 86/278/EEC6 that aims at regulating “the use of sewage sludge in agriculturein such a way as to prevent harmful effects on soil, vegetation, animals and man,thereby encouraging the correct use of such sewage sludge” (Article 1).
Directive 86/278/EEC
Directive 86/278/EEC on the protection of the environment, and in particular of thesoil, when sewage sludge is used in agriculture seeks to encourage the use of sewage
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5Communication from the Commission on the review of the Community Strategy for WasteManagement, COM(96) 399 final of 30.7.96.
6OJ L 181, 4.7.86, p. 6.
sludge in agriculture and to regulate its use in such a way as to prevent harmful effectson the environment.
To this end, it prohibits the use of untreated sludge on agricultural land unless it is injectedor incorporated into the soil. Treated sludge is defined as having undergone “biological,chemical or heat treatment, long-term storage or any other appropriate process so assignificantly to reduce its fermentability and the health hazards resulting from its use”(Article 2 (b)).
To provide protection against potential health risks from residual pathogens, sludge mustnot be applied to soil in which fruit and vegetable crops are growing or grown, or lessthan ten months before fruit and vegetable crops are to be harvested. Grazing animalsmust not be allowed access to grassland or forage land less than three weeks after theapplication of sludge. The Directive also requires that sludge should be used in such away that account is taken of the nutrient requirements of plants and that the quality of thesoil as well as the quality of surfacewater and groundwater is not impaired.
The Directive specifies rules for the sampling and analysis of sludge and soil. It setsout requirements for the keeping of detailed records of the quantities of sludgeproduced, the quantities used in agriculture, the composition and properties of thesludge, the type of treatment and the sites where the sludge is used.
Limit values for concentrations of heavy metals in sewage sludge intended foragricultural use and in sludge-treated soils are in Annexes I A, I B and I C of theDirective as shown in the table.
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Annexes I A, I B and I C of Directive 86/278/EEC
Limit values for Limit values for heavy- Limit values for amounts of heavyconcentrations of metal concentrations metals which may be added
heavy metals in soil in sludge for use in annually to agricultural land, based(mg/kg dm) agriculture (mg/kg dm) on a 10 year average (kg/ha/y)
Cadmium 1 – 3 20 – 40 0.15Chromium7 - - -Copper 50 – 140 1 000 – 1 750 12Mercury 1 – 1.5 16 – 25 0.1Nickel 30 – 75 300 – 400 3Lead 50 – 300 750 – 1 200 15Zinc 150 – 300 2 500 – 4 000 30
7Directive 86/278 required the Council to fix limit values for chromium on the basis of a Proposal tobe submitted by the Commission. The Commission made a first Proposal (COM(88) 624 final) onwhich the Council did not reach an agreement. The values were 100–200 in soil, 1000–1750 insludge and 4.5 the annual load. The opinion of the ECOSOC was that the values indicated were toohigh for a systematic long-term application to the soil, so the Commission presented a secondProposal two years later (COM(90) 85 final). The new proposed values were 100–150 in soil,1000–1500 in sludge and 3 the annual load. The Council, once again, did not reach an agreement andthe Commission withdrew its Proposal in 1993.
Potential environmental problems
By its own nature and due to the physical-chemical processes involved in thetreatment of waste water, sewage sludge is potentially contaminated by a whole rangeof polluting substances. It tends to concentrate heavy metals and poorly biodegradabletrace organic compounds as well as potentially pathogenic organisms – viruses,bacteria etc. – present in waste waters.
The top layer of soil is of crucial importance for the well being of soil micro-organisms,plants and animals. Some heavy metals may have the effect of impairing the naturalmechanisms through which soil microbes reproduce and therefore deplete the bio-potential of the soil eco-system. Moreover, if the concentration is high enough heavymetals can penetrate the natural cell barriers in plant roots and end up in the edible partof vegetables. Some heavy metals can then accumulate in animal and human organs andcause poisoning effects, induce cancer or produce mutagenic changes.
The spreading of sewage sludge on agricultural land can result in an increase of theconcentration levels of heavy metals in soil because of the contamination of wastewaters by heavy metals from industrial discharges, products used in households –such as detergents, medicines – or contained in amalgam fillings, pipes, tobacco etc.Directive 86/278 seeks to prevent the accumulation of heavy metals in the soil above athreshold limit which is deemed to be safe for crop yields, animals and man.
There are thousands of chemically synthesised compounds that are in products andmaterials commonly used in our everyday life. Many of them end up in waste waterand are potential contaminants of sewage sludge, although their low concentration oreasiness to be broken down by micro-organisms means that they do not cause a threatto the environment. However, there are some organic compounds that are not easilybroken down during the treatment of waste waters and tend to accumulate in sludge. Ifthe sludge is used in agriculture there may be problems due to the eco-toxicity of thesecompounds or their bio-accumulation in plants, animals or man. Directive 86/278does not fix any limits for concentrations of organic pollutants in sewage sludge usedin agriculture, although some Member States do. Among those regulated there arePCBs (France, Austria, Germany and Sweden), dioxins and furanes (Austria,Germany) and PAHs (France, Denmark and Sweden).
Urban waste waters are composed of a mixture of waste waters from different sources –small shops and businesses, hospitals and medical centres, personal hygiene, washingof dishes and laundry, urine and faeces, run-off from roads and impermeable surfacesetc. The contamination by heavy metals, organic compounds and pathogens varies andis source dependent. For instance, pathogens such as bacteria, viruses and parasites arepotentially present in faeces and urine of humans and animals. Their presence in wastewater depends on the health of the population connected to the sewer, although onaverage waste water will always contain potentially pathogenic organisms that thewaste water treatment concentrates in the sludge. Disease causing agents occur insewage because they are being discharged in the faeces of infected humans or animals.Thus, the species diversity and numbers present will reflect the health of thecommunity and the standards of hygiene which prevail.
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Much has been done to minimise the potential transmission of pathogens by reducinginfectivity of sludges through effective treatment processes and then matchingefficiency of pathogen removal to operational restriction on application practices andland use. In fact, the very few reported cases of animal contamination due to thespreading on land of sewage sludge originate from the non respect of the basicrestrictions for grazing after sludge spreading.
Environmental advantages of using sludge
Sewage sludge is a waste rich in organic matter and that has to be disposed of withoutendangering the environment. Along with potentially hazardous, sewage sludgecontains valuable nutrients and organic matter.
Organic matter
The over exploitation of agricultural soils in the Community is of great concernamong agronomists and soil experts. Intensive agriculture relies on a fast rotation ofdifferent types of crops on the same plot, the only component systematically restoredbeing essential nutrients such as nitrogen and phosphorous via the use of mineralfertilisers. However, what mineral fertilisers cannot supply is the organic matter.Organic matter is a complex mix of proteins, humic and fulvic acids and othercomponents which are essential to the well being of soil, crops and soil biomass. It isproduced by the slow action of microorganisms – bacteria, fungi, earthworms etc –during the course of hundreds of years. Only natural, biological processes based onthe photosynthesis of carbon are able to produce organic matter.
Many soils in the Community, especially those in southern regions, badly needadditional organic matter. A level of between 2.5 and 3% of organic matter in soil isthe bare minimum for the long term use of agricultural soils, however soils with lessthan 1% organic matter are not uncommon. In these conditions agronomists define asoil as in a pre-desertification stage.
The agricultural sector needs a secure, long term supply of nutrients and organicmatter (humus) to compensate for losses through harvest, grazing and leakage intosurface water, groundwater and the atmosphere. Sewage sludge serves both purposes,primarily as a supplier of micro-nutrients and organic matter but also as a supplier ofnutrients such as nitrogen, potassium and phosphorous. Thus, it is well suited to beused as a soil improver and fertiliser on arable land.
The use in agriculture or any other use in soil of sewage sludge contributes on the onehand to the fight against soil depletion, and on the other to build-up of organic carbonin soils. It has been calculated8 that an increase of 0.15% of organic carbon in Italian
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8Communication of Professor Paolo Sequi at the Compost Symposium, Vienna, 29-30 October 1998.
arable soils would lock in soil and soil biomass the same amount of carbon releasedinto the atmosphere in one year in Italy because of the use of fossil fuels. It can beassumed that similar proportions are valid for the whole of the Community. From thisit follows that the use of sewage sludge is an effective and sensible mean of divertingcarbon dioxide from the atmosphere and converting it into organic carbon in soils andtherefore a valid tool for the Community fight against the greenhouse effect.
Sewage sludge as organic fertiliser
Growing of vegetable crops, by its own nature, requires a constant supply of nutrientsto be performed. Nitrogen, phosphorous and potassium have to be constantly suppliedto the plants in order to maintain a steady crop production.
Mineral fertilisers are produced from a variety of sources, however they generallyneed energy to be produced and, sometimes, extraction of raw materials. For instance,the production of a phosphorous-based fertiliser requires shipment of phosphate rocksand an appropriate treatment in order to made the phosphorous readily available forplant growth. The process needs energy to be performed. Moreover, phosphate rocksare usually contaminated by cadmium.
The use of sewage sludge allows the recycling to land of nutrients reducing oreliminating the need for mineral fertilisers. On average and depending on the wastewater treatment process, sewage sludge contains 35 kg of nitrogen and 20 kg ofphosphorous per ton of dry matter. These represent non-negligible amounts ofnutrients that can be cheaply exploited by farmers and make a contribution towards asustainable agriculture.
Sludge management options
Once sludge is produced in a waste water treatment plant it has to be dealt with in asound and cost effective way. Although at Community level use of sludge accountsfor about 50% of the overall sludge production, landfilling as well as incineration insome Member States are the most widely diffuse disposal outlets despite theirenvironmental drawbacks.
Landfilling
Organic matter decomposes in a landfill and is not available for plant growth. Whenless organic matter is landfilled, less landfill gas is produced. Landfill gas, if notcaptured, contributes considerably to the greenhouse effect. In fact landfill gas ismainly composed of methane, which is twenty times more powerful than carbondioxide in terms of climate change effects.
These motivations, among others, are the drive behind the Landfill Directive1999/31/EC OJ L182, 16.7.99, p. 1 that introduces targets for the reduction ofbiodegradable municipal waste to landfill as follows:
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• reduction to 75% of total biodegradable municipal waste (weight) produced in 1995by 2006;
• reduction to 50% by 2009;• reduction to 35% by 2016.
The sludge production in the Community is about 7 million tonnes (dry matter). Thishas to compare with some 200 million tonnes of municipal waste which are generatedeach year in the EU. By keeping sludge away from landfill sites the available landfillcapacity can be used over a longer period of time. This capacity can be used formaterials for which treatment or reuse is not possible. Furthermore, less space is lostfor other purposes, such as infrastructural works – this may especially be ofimportance in densely populated areas. Even if sludge account for a small percentageof non-hazardous wastes that are landfilled it should not be forgotten that sludge isorganic matter. Organic matter decomposes and its drawbacks have widerimplications than just eating up space.
Incineration
Incineration is an expensive disposal option for sludge and leaves the problem of whatto do with the residues, which are about 30% of the input mass. They may be regardedas hazardous waste – a cause of the contamination by heavy metals –especially if thesludge is incinerated along with municipal waste.
Furthermore, when sludge is incinerated the organic matter is decomposed to mainlycarbon dioxide. It is often said that biodegradable waste, or indeed waste in general, isa renewable source of energy and a valid substitute for fossil fuels in order to meet thetargets for carbon dioxide reduction as agreed in Kyoto. This is just part of the picture.
Fossil deposits of coal, oil and gas were generated some millions of years ago and arehuge storage ‘tanks’ for carbon. When fossil fuels are combusted, i.e. oxidised, themineral carbon they contain and the oxygen in the atmosphere combine to give carbondioxide, which is released into the atmosphere. Carbon dioxide, along with othergaseous compounds, is held responsible for the greenhouse effect.
According to the “Kyoto argument”, if the biodegradable waste is incinerated insteadof fossil fuels to produce energy, there is no increase in the quantity of carbon dioxidein the atmosphere because the biodegradable waste is composed of organic matteroriginated from the fixation of carbon dioxide present in the atmosphere through thephotosynthesis process.
However, this balance of carbon in the ecosystem does not take into account animportant factor – time. The time needed for vegetal and animal biomass to fix thecarbon present in the atmosphere to organic carbon can be calculated in hundreds ofyears. Thus, the incineration of sludge will have as a final result an increase of carbondioxide level in the short to medium term and will have a negative impact on theclimate. The correct strategy would then be to lock as much organic carbon as possiblein vegetal and animal biomass in soils so as to decrease the stock of carbon in theatmosphere. Incineration of sludge would just go in the opposite direction. It this
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context it should also be noted that the incineration process destroys the organicmatter, which needs hundreds of years to be formed by the photosynthesis process.
In terms of energy balance it should be borne in mind that mechanically de-wateredsludge has a calorific value of 2000 kJ/kg of dry matter, that is insufficient forsustaining the incineration process – extra fuel is needed. When sludge is thermallydried, its calorific value could be raised up to 11000 kJ/kg, therefore making it moreappealing in terms of energy production. However, the energy needed to dry it shouldalso enter the overall balance.
Conclusion
Sewage sludge originates from the treatment process of waste water. Due to thephysical-chemical processes involved in the treatment, the sludge tends to concentrateheavy metals and poorly biodegradable trace organic compounds as well aspotentially pathogenic organisms – viruses, bacteria etc. – present in the waste water.
Sludge is, however, rich in nutrients such as nitrogen and phosphorous, and containsvaluable organic matter that is useful when soils are depleted or subject to erosion.The organic matter and nutrients are the two main elements that make suitable the useof this kind of waste on agricultural land as fertiliser and organic soil improver.
Directive 86/278/EEC on the protection of the environment, and in particular of thesoil, when sewage sludge is used in agriculture has been quite successful in the pastyears in preventing animal and crop contamination by pathogens. However, some ofthe provisions of the Directive could be improved in order to take account of newscientific evidence and technological progress with a view to ensuring the long-termprotection of Community soils. It is what the Commission is about to do with thecurrent work on the revision of Directive 86/278/EEC.
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Sludge-related issues as seen by the Directorate-Generalfor Agriculture
Valéry MorardDirectorate-General for AgricultureEuropean Commission
Why do we need this discussion
The use of sewage sludge on agricultural land is regulated by the Directive86/278/EEC OJ L181, 4.7,86, p. 6. Actually, this management is facing increasingclaims from some stakeholders organisations (including sometimes farmerorganisations) which are concerned by potential contaminations with heavy metals orpathogens. Despite the existence of strict standards within the Directive, some foodretailers or processers are building binding guidelines for certain products (cannedvegetable, baby food, quality meat…) where the use of sludges is forbidden.
What is at stake now is the brand image of agricultural products and given thiscontext, DG Agriculture welcomes the initiative of such a workshop in order tointensify the exchange of views on this practice: what are the problems, theenvironmental challenges and how should the agricultural sector act in order tocontribute in a positive way to an environmentally-sound solution.
Definition
From the very beginning, one must be clear with the ‘sludge’ definition. I will dealonly with sewage sludge as defined by the Urban Waste Water Treatment Directive91/271/EEC OJ L135, 30.5.1991, p. 40 as follows: “residual sediments from urbanwaste water”. The question of extending the definition to industrial waste watershould be dealt with cautiously.
Anyhow, we should not confuse the issues with all materials which are called ‘sludge’for one reason or another. This concerns particularly the critical issue of certainsludges and animal food processing. This matter is now under the responsibility of theDirectorate General for Health and Consumer Protection.
Pros and cons
DG Agriculture would welcome very much debate where advantages and drawbacks ofeach option for sludge management are clearly identified and assessed. As a priorappraisal, I would like to remind some of the main arguments which are commonly used.
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From one hand, one can argue that the use of such waste in agriculture does not fitperfectly with the precautionnary principle as regards food safety and that it couldharm the brand image of agricultural products.
On the other hand, the spreading of sludges on agricultural soils is not recent (over 30years of practice) and has been constantly improved. While the content in trace-elements has decreased, the fertilizer and soil improver value of these products hasbeen enhanced in the meanwhile.
In the future, only incineration and spreading will be considered for the managementof sludges. What should be focused is the best sustainable option, takingenvironmental impacts and socio-economic cost into account. Being against oneoption or another can be no longer a position if there is not a better or comparablealternative.
Highlighting some important points
Given the above-mentioned context, DG Agriculture would expect that certainconditions are attached to the use of sewage sludges on agricultural soils, beforeconsidering its position on the opportunity on this practice:• it must be assessed against other management alternatives, including especially
incineration (with sustainability criteria);• it must be proven to bring an added value (fertilisation, soil improvement): the fertiliser
value should be assessed and specified, in order the avoid the spreading of waste withoutagronomic value. The use of the sewage sludge should meet an agronomic need;
• certain uses should be left to Member State responsibility with common environ-mental criteria; nevertheless, as regards the use on forest soils, DG Agriculture willfavour a very cautious attitude. In the light of information collected through the soilcondition reports (managed by the Commission and UN-CLRTAP), several argumentsare pleading against the use of sludges on forest; moreover, the regular atmosphericaldeposits cover largely the nutrients needs of forests. It means that use on forest soilsshould normally be exceptional: on short-rotation plantations for instance;
• it should guarantee the absence of contaminations (by heavy metals, organiccompounds and by pathogens) or below binding thresholds; the prevention of heavymetals accumulation in soils should be reinforced;
• the vulnerability of certain crops or certain soils should be evaluated; thereforesome site-specific conditions should not allow the use of sludges;
• in order to favour environmentally-friendly options, codes of good practice shouldbe elaborated which determine the relevant practices to be attached to the use ofsludge in agriculture;
• all the process should be controled, a real traceability should be established;• issues linked to civil liability should be specified.
Other important principles
Sewage sludge is a waste and therefore should be managed as such. The principle ofproximity should be given priority. Even if recycling prevails disposal according to
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the Community Waste Strategy, incineration should remain a real alternative insofaras it guarantees a cheap and safe treatement of sludges.
A recycling strategy should define the general conditions attached to each agriculturalland use category. All recycling outlets should be considered: green areas andreclaimed land also.
If different categories of sludges are being considered, and different categories ofsludge treatment, the product must be suited to the specific conditions of its final use.A differenciated approach might be needed and could enable to broaden the scope ofthe existing Directive.
While different categories of organic waste are currently spread on agricultural land(urban and industrial sewage sludges, food and raw material processing waste,composts etc…), it could be relevant to encompass all of them into a singleframework. What has to be focused at first place is the soil protection and especiallythe protection of agronomic value of soil.
Of course, control, certification, traceability and monitoring are essential parts of themanagement system which should be reinforced. Independent organism (“thirdbody”) should handle the control, while the regular monitoring and traceabilitymanagement could be left under the producer responsibility. The third body shouldalso monitor the soil quality and vulnerability.
Conclusions
Since the directive was adopted in 1986, the practices and the knowledge haveevolved. This workshop is gathering a lot of expertise and DG Agriculture wouldexpect that it brings useful recommendations for improving the management ofsludges, should it be spread on agricultural soils or not.
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