OrganicWasteSpreadOnLand.pdf

STRATEGIC REVIEW OF ORGANICWASTE SPREAD ON LAND

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Contents

Page No.

1. Executive summary 3

2. Introduction 5

3. Current practice 6

4. Underpinning science 18

5. Current legislation/regulation, guidance and control mechanisms 33

6. Discussion 43

7. Conclusions and recommendations 53

8. References 57

9. Annexes 65

10. Plates


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Annexes

Annex 1 Brief agreed with Scottish Office

Annex 2 Questionnaire

Annex 3 List of persons contacted

Annex 4 Description of sewage sludge types

Annex 5 Sludge use in Agriculture Regulations - monitoring requirements for PTEs

Annex 6 British Retail Consortium Matrix

Annex 7 Exemptions to Waste Licensing

Annex 8 Agricultural wastes statistics & treatment

Annex 9 Particular interests in organic wastes applied to land

Annex 9a Summary of Blairingone Action Group concerns

Annex 10 Nutrients in sewage sludge as spread

Annex 11 PTEs in Scottish soils and sludges

Annex 12 Comparative risks from pathogens associated with land application

Annex 13 Sludge treatment to reduce pathogens

Annex 14 Benefits and disbenefits of the various wastes

Annex 15 Risk assessment matrix

Annex 16 Control options matrix

Annex 17 Risks - exempt wastes

Plate 1 Injection of sewage sludge

Plate 2 Experimental trial using digested sewage sludge

Plate 3 Application of slurry

Plate 4 Application of slurry

Plate 5 Application of farmyard manure

Plate 6 Application of distillery waste

Plate 7 Papermill sludge post application

Plate 8 Composting process


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Executive summary

Introduction

1. The Scottish Office has requested SEPA to undertake a strategic review of organic wastespread on land. The review covers sewage sludge, waste disposal activities exempt fromwaste management licensing (exempt wastes), agricultural wastes, fallen stock andcomposted municipal waste.

Background

2. Current estimates of the tonnage of waste applied to land in Scotland are:

agricultural waste 15,000,000 tonnes 96%exempt industrial waste 367,000 tonnes 3%sewage sludge 200,000 tonnes 1%composted waste ? < 1%

3. If organic wastes are applied correctly to land they can have positive beneficial fertilisingeffects. Other beneficial environmental effects include reduced resource demand, soilconditioning and, indirectly, habitat conservation. There are potential cost savings to farmersdue to reduced inorganic fertiliser requirements when organic wastes are used.

4. Sewage sludge, which comprises 1% of the waste spread on land, is generally applied undercontrolled and regulated conditions. There is considerable public pressure to increase thelevel of treatment of sewage sludge, in particular to phase out the practice of spreadinguntreated sewage sludge on land. The UK Government has recently announced its intentionto phase our the latter practice. A good body of scientific literature exists in respect ofpotentially toxic elements (PTEs) and many pathogens in sewage sludge.

5. Wastes applied to land as an exempt activity include blood and gut content from abattoirs,distillery wastes, paper waste and septic tank sludges. The current system for recordingvolumes of these wastes is not sufficiently accurate to understand the extent of this outlet forsuch wastes or to predict future trends. The current pre-notification period to SEPA is notuseful in managing the activity.

6. Most exempt wastes are not pre-treated or stored at the point of origin, leading to odourproblems and typically are not stored at the point of origin resulting in the possibility thatwastes are not being spread at the time most beneficial to the crop or the land. Neitheragricultural benefit nor ecological improvement, the key justifications for the activity, aredefined in regulations.

7. There is a paucity of data relating to the fate and impacts of nutrients, PTEs and pathogensin exempt wastes. Little is known of the effects of organic chemicals on soil and of theeffects wastes have on soil processes. Pathogen related risks associated with exemptwastes and the agricultural wastes are not quantified or fully understood.

8. Owners/occupiers of the land on which waste is spread are not always fully aware of thenature and content of what is being spread there. Multiple wastes can be applied in additionto inorganic fertiliser without any need for the owner/occupier to take account of synergisticeffects, total nutrient content or total heavy metal loadings.

9. The potential for point source or diffuse pollution of watercourses from waste spread on landis high if incorrectly spread or over-applied or if inorganic fertiliser is not reduced in


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proportion to the organic wastes applied. There is no necessity for waste contractors toemploy operators with a certificate of competency in the activity, which may result in badpractice and increased potential for water pollution.

10. Fallen stock does not yet pose a problem but difficulties may be expected in future years dueto cumulative effects of increased disposal.

11. There is much useful guidance available such as the Prevention of Environmental Pollutionfrom Agricultural Activity (PEPFAA) Code of Practice which includes guidance and refers tostatutory requirements, and the Code of Practice for the Agricultural Use of Sewage Sludgewhich includes all the statutory requirements of the Sludge Regulations. However, the Codesthemselves are not statutory which causes confusion. The Codes are not necessarily knownor followed extensively within the agricultural community.

Conclusions

12. There is a lack of public confidence in the practice of spreading organic waste on land whichthreatens an activity which can have environmental benefits.

13. The current approach to the regulation and management of organic waste spread on land isinadequate and inconsistent, leading to practices which pose a risk to the environment andpose potential public, animal and plant health risks.

Principal recommendations

14. A consistent legislative framework for all organic wastes spread on land should bedeveloped, incorporating the relevant Codes of Practice as necessary.

15. Regulations should cover mixed waste streams and set minimum standards for safeacceptance loadings for different wastes on different soil types. Minimum standards oftreatment for wastes spread on land should be stipulated along with minimum storage at theproducers site.

16. The concept of land management plans should be adopted which would encompass thebeneficial and detrimental aspects of all wastes applied to farmland as well as incorporatinginorganic fertiliser inputs.

17. A competency scheme for contractors should be introduced, similar to the WAMITABqualification for waste management licence operators.

18. Blood and gut contents and septic tank sludges should be prohibited from being spread onland.

19. Injecting waste in land with field drains, spreading outwith daylight hours and spreading indesignated heritage sites should be prohibited.

20. A proposed mechanism for regulating the spreading of organic wastes onto land is set out inthe report, with the objective of ensuring that the responsibility for specific actions rests withthe appropriate person. The scheme would be amenable to an accompanying chargingscheme.


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1. Introduction

1.1 During the course of late 1997 and early 1998 there has been public disquiet in relation to thepractice of spreading organic wastes on land. This has been expressed through mediainterest, complaints to SEPA and internal SEPA Board discussion at both national andregional level. The Scottish Office had also recognised the concerns and subsequently TheScottish Office requested SEPA to undertake a strategic review of organic waste spread onland. A copy of the brief is given in annex 1.

1.2 The work has been directed and carried out by SEPA staff as a consultancy project reportingto a small steering group drawn from The Scottish Office, the Convention of Scottish LocalAuthorities and SEPA. The study has been wide ranging and it was considered necessary toinvolve all relevant stakeholders who have an interest in the practice. A questionnaireapproach was used as the initial data gathering exercise, augmented by personal ortelephone interviews (annex 2).

1.3 SEPA wishes to acknowledge with thanks the individuals and organisations who haveassisted in the provision of information. A list of those concerned is given in annex 3.


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2. Current practice

Introduction

2.1 In this chapter the origin and current practice for disposal of organic wastes are describedbriefly, along with information on the tonnages and outlets. Supplementary detail is given inannexes where information relating to fallen stock is also discussed. It is important to placeeach waste in context against the others and against the total tonnage of organic wastesspread on land. Current estimates of the main waste types applied to land in Scotland are:

Agricultural waste 15,000,000 tonnes 96%Exempt industrial wastes 367,000 wet tonnes 3%Sewage sludge 200,000 wet tonnes 1%Composted waste ? < 1%

Information relating to fallen stock is also discussed

Sewage sludge

Origin and disposal methods

2.2 Sewage sludge is a by-product of the sewage treatment process. The nature of thetreatment process will affect dry solids content, nutrient availability and pathogen content.This in turn influences its suitability for recycling to land. Sludge may be stabilised through adigestion process, the addition of lime, thermal treatment or it may remain unstabilised.Types of sludge and typical dry solids content are summarised in annex 4.

2.3 Responsibility for sewage treatment and hence sludge production, treatment and disposallies with the three water authorities. Only about 20% of sludge applied to agricultural land inScotland is stabilised by digestion before application. This situation is set to change inresponse to various external pressures and it is likely that in the near future a largepercentage of sludges will be pasteurised and stabilised/ thermally dried.

2.4 Sludge is currently applied to agricultural land either by surface spreading of liquid sludgefrom a tanker or by injection to plough depth. A much smaller amount (8% of area) is appliedfrom solid manure spreaders. However, future application methodology will change in stepwith changes in the nature of the sludge product. At present, sewage sludge is applied toland either by the water authorities or, more commonly, by sludge contractors. It is knownthat certain sludge contractors apply sewage sludges mixed with other wastes for example,farm slurries or exempt industrial wastes such as paper crumble as this product is easier tohandle. The extent to which waste streams are mixed at time of application is not known.

2.5 The water authorities are responsible for monitoring sewage sludge and soils to which sludgeis applied for a range of metals and nutrients as defined in the Sludge Use in AgricultureRegulations (annex 5). However, landowners have to assume some responsibility forensuring that such sampling has taken place before sludge application.


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Quantities

2.6 At present some 100,000 tonnes dry solids (tds) of sewage sludge are produced each year,arising as follows:East of Scotland Water (ESWA) - 34,000 tdsNorth of Scotland Water (NoSWA) - 10,000 tdsWest of Scotland Water (WoSWA) - 55,500 tds

Sludge production is set to rise to 177,500 tds by the year 2006 due to additional treatmentrequirements imposed by the Urban Waste Water Treatment Directive (91/291/EEC) whichtakes effect progressively from 31 December 1998.

Outlets

2.7 Each water authority has developed a different approach to dealing with the sludgeproduced, largely inherited from the former Regional Council water and seweragedepartments, and affected by land availability. At present 89,000 tds pa are disposed of atsea and only 24,000 tds (19% of total produced) is recycled to land, equating toapproximately 200,000 wet tonnes, assuming a typical dry solids content for Scottish sludgesapplied to land of 11.2% ds. The current estimate of sludge which will be recycled to land bythe year 2005/6 is 120,000 tds with the majority likely to be applied to agricultural land andonly a small amount recycled to other land-based outlets such as land reclamation andforestry. (Gendebien et al, 1998).

2.8 The total area of agricultural land currently used for sludge recycling is just over 4,000ha, ata total of 597 sites. The majority of sludge is recycled to arable farmland (378 sites, 2,815ha)and a smaller amount to pasture (219 sites, 1389 ha) (Gendebien et al, 1998). The practiceof recycling to land varies geographically with NoSWA currently recycling 66% to land,ESWA recycling 38% to land and WoSWA applying 6% to land. The suitability of land forreceiving sludge varies across Scotland, depending upon the soil type, topography, the metalcontent and pH of the soil. Estimates (Towers, 1995) have indicated that the potentiallyavailable areas are as follows: NoSWA 7597 km2, ESWA 4176 km2, and WoSWA 4550 km2.

Impending changes

2.9 Recently considerable public pressure has been exerted on the UK water industry to ceaseapplying raw sludge to land. There are a number of drivers, mainly relating to pathogen risksassociated with application of untreated sludges to land.

2.10 The nineteenth report of the Royal Commission on Environmental Pollution on SustainableUse of Soil (RCEP, 1996) found there to be no reported instances in the UK in which a linkhas been established between controlled application of sewage sludge and occurrence ofdisease in the general population through food or water contamination. However, it wasobserved that untreated sludge will contain a variety of pathogens and recycling toagricultural land therefore presents a theoretical pathway by which infections could return tothe general population. The committee recommended that the use of untreated sludge toagricultural land be phased out on precautionary grounds. The committee also advised that areview of scientific evidence relating to the Code of Practice for the Agricultural Use ofSewage Sludge be undertaken. This was subsequently commissioned by the Department ofEnvironment, Transport and the Regions, and reported in July 1998 (Carrington et al, 1998).

2.11 The House of Commons Environment, Transport and Regional Affairs Committees report onSewage Treatment and Disposal (HoC, 1998) also highlighted the requirement for increasedunderstanding of the scientific basis for the Code of Practice and recommended that by the


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year 2002 all sludge that is to be recycled to land should be subjected to stabilisation andpasteurisation, subject to confirmation that these processes also remove the pathogens ofnew interest and would effectively remove any microbiological hazard from sewage sludgerecycling to agricultural land. Recommendations were also made for a new Code of Practicefor consumers written in non-technical language and circulated to farmers and users.

2.12 The Select Committee on the Environment, Transport and the Regions - Sewage Treatmentand Disposal - Government Response (July, 1998) considered that the case has not beenmade for requiring stabilisation and pasteurisation on public health grounds but recognisedthe potential risk of transfer of pathogens to food by spreading of sewage sludge toagricultural land and proposed that a structured programme of research and risk assessmentbe carried out into the use of all organic wastes on land. It was agreed that spreadinguntreated sludge on land will be phased out by 2002 and further precautionary changes toexisting controls were recognised.

2.13 Both the public and food retailers as represented by the British Retail Consortium (BRC)have raised concerns regarding the risk of disease through application of sludge toagricultural land and the effects on the whole food chain. Food retailers have voiced theneed for scientific evidence relating to the safety and security of the practice. This is toinclude processes and systems that deliver assurances from the point of treatment to fieldapplication with an audit system which monitors the whole process. An agreement has beenreached by the Water industry and retailers which lays out a framework for use of sludge inagriculture. Details of this are given in annex 6.

2.14 The view of the farming community as voiced by the National Farmers Union of Scotland isthat where Scottish farmers cannot compete with foreign imports in terms of price they haveto compete on quality. Consequently, farmers would note be prepared to take risks by usinguntreated sewage sludge if public perception is such that this is not acceptable (NFU, perscomm, 1998). There is a consensus that farmers do not wish to use raw sewage sludge, thuseasing adoption of this agreement by the farming community.

2.15 In addition, land owners are concerned about potential liabilities arising from sewage sludgebeing applied to their land. In England and Wales the Country Landowners Association(CLA) has suggested that owners should enter into agreements with water undertakers toensure that the best methods of treatment are used and to ensure that owners have anindemnity in respect of any problems which may arise as a result of their land being used forsludge disposal. A Model Agreement has been drawn up. This approach is not followed bythe Scottish Landowners Federation (SLF) (pers comm, Maurice Hankey, 1998). Instead, theSLF is encouraging its members to follow the guidance given in the Prevention of PollutionFrom Agricultural Activities Code of Practice (the PEPFAA Code) and to consider carefullythe long term impact on their land.

2.16 The consequence of such drivers is that the Scottish water authorities are revisiting theirsludge strategies to ensure that the demand for higher level treatment is satisfied. Detailsare given below, from information provided by ESWA, NoSWA and WoSWA.

East of Scotland Water Authority

2.17 ESWAs future policy is to ensure beneficial re-use of sludge, recognising that there is a needto secure more than one outlet. A number of outlets have been considered includingagriculture, forestry, horticulture, energy recovery, and incineration in a cementmanufacturing process. ESWA has responded rapidly to the BRC, who in their view aredriving the issue. Consequently it is intended that sludge be treated by the year 2000 (withtreatment including digestion, lime stabilisation or thermal treatment). The application of


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liquid digested sludge will be phased out by 2005. The long-term strategy is to pasteurise allsludge and it is intended that all new sludge treatment centres will be capable ofpasteurisation to provide effective barriers to pathogen transmission. Thermal drying ofsludge is being considered as market research has shown farmers have a preference forthermally dried sludge pellets. As an interim solution ESWA will use a licensed landfill.

North of Scotland Water Authority

2.18 NoSWA has a good landbank for spreading and the availability of this outlet is beingencouraged. NoSWA has promoted the use of farm waste management plans with a strongemphasis on Quality Assurance. NoSWAs future strategy takes a flexible balancedapproach, continuing with beneficial recycling to land whilst securing incineration as apossible future option. Local solutions will be adopted in certain areas, taking into accountgeographical and operational limitations and transport costs. Approximately 90% of sludgeproduced will be from treatment works progressed under three PFI schemes. NoSWA alsointend to form major centres and undertake lime stabilisation, dewatering and application ofcake sludge to land. Lime stabilisation as a long term solution is still subject to evaluation.

West of Scotland Water Authority

2.19 It is intended that 90% of the sludge generated within WoSWA will be used for energyrecovery using sludge cake as a secondary fuel source with an annual throughput of 65,000tds. The plant is to be completed by mid 2000 and in the interim period untreated sludge willbe dewatered at major wastewater treatment works and landfilled. Options are still beingconsidered for Ayrshire, Argyll and Dumfries and Galloway where it is likely that the strategywill be for enhanced treatment and recycling to land.

Industrial wastes which are exempt from licensing - exempt wastes


2.20 Since the introduction of the Waste Management Licensing Regulations 1994 a variety ofnon-agriculturally derived wastes, often referred to as industrial wastes, have been applied toland, under legal exemptions from licensing. These wastes, which are commonly referred toas exempt wastes are listed in annex 7. The most common wastes in Scotland includedistillery waste, paper waste and blood and gut contents from abattoirs. The terminologyexempt waste will be used throughout this report to describe these wastes which arerecovered through recycling to land and are exempt from licensing. It is the process ofapplication, not the waste itself, which is exempt.

2.21 These wastes are not usually treated although technologies which can be used include limestabilisation, dewatering, digestion, composting and heat treatment. Treatment of many ofthese wastes would produce a much more stable product making such wastes more suitedfor storing for longer periods of time without leaching or causing odour nuisance and wouldalso improve the consistency of the product, reducing transport costs and improvingagronomic value. The extent to which such wastes arising in Scotland are treated is notknown but is considered to be small.

2.22 Most landspreading of exempt wastes in Scotland is carried out by two contractors. In orderto satisfy the criteria that these wastes are exempt from licensing it is essential that theirapplication provides agricultural benefit or ecological improvement, terms which are notdefined. The wastes are analysed to determine nutrient content, pH and any chemical orphysical properties which would allow the waste to act as a soil conditioner. Typically,analysis is undertaken at the start of a particular waste stream being used, and are not


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necessarily re-analysed at intervals over the following weeks or months during which thewaste is applied. Some wastes are inconsistent in nature, resulting in wide variation incomposition from batch to batch over time. Generally microbiological analysis is notundertaken.

2.23 The most common practice is for waste to be collected from the site of production bycontractors. Solid wastes are usually transported in dumper trucks or skips whilst liquidwastes are transported in tankers. Very few waste producers have the ability to store wasteson their premises, resulting in the need for storage at the site of application. Storage-relatedproblems at the site can arise such as escape of waste, leaching of potentially pollutingeffluents and odour nuisance, as well as transport related issues.

2.24 Liquid wastes are stored mainly in field storage tanks; sludges are stored in lagoons orheaped in fields if the solids content is high enough; cakes and crumbles are stored inheaps. There are no specific minimum standards for the storage of these wastes in terms ofbunding and drainage, in contrast to the regulations applying to agricultural slurries.

2.25 The method of application to land is dependent upon the waste involved, the soil type andthe nature of the crop being cultivated. Liquid wastes are either injected using an umbilicalinjection system or surface spread using dribble bars. Solid wastes (taken to be > 12% drysolids) can be spread by muckspreaders or specialist solids spreaders. The method chosen isdetermined by the potential of the waste to cause nuisance, and the risk of swardcontamination by pathogens, chemical residues or litter.

2.26 Wastes are currently applied to land 52 weeks a year, due to lack of storage facilities.Consequently wastes are applied to land during inappropriate weather conditions, forexample during periods of heavy rainfall when soils are at field moisture capacity and thewaste is likely to be washed away on application. Wastes are also applied at times of theyear when low temperatures result in limited plant growth and hence limited nutrient uptake.As a result, nutrients are likely to be leached from the soil particularly if available in a solubleform.

2.27 Exempt wastes are occasionally spread at night, a practice which is unacceptable to personsliving in the vicinity who are suspicious of the legitimacy of the activity (BAG, pers comm,1998). Concern has also been expressed that contractors are purchasing land to use asdedicated disposal sites, although there is no evidence to support this view.

Quantities

2.28 The actual amounts of exempt wastes spread to land in Scotland are not known accurately.This is due to the recording system currently used whereby the sludge contractor is requiredonly to give pre-notification of maximum amounts intended to be spread in a six-monthperiod. The information is provided as maximum area to which the waste is to be appliedand maximum application rate. Figures were collated from SEPA records (SEPA, 1998) andtable 1 shows the total amounts for which notifications were received from the contractors in1997. All figures are given as wet tonnes, the dry solids content of most of the wastes notbeing known.


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Table 1 - Exempt waste spread on land in ScotlandWaste Amount recycled to land 1997

(max. figure) wet tonnesWaste wood, bark or other plant matter to agricultural land 1,000Molasses 6,000Dredging from inland waters 5,000Septic tank sludges 9,000Press sludge 16,000Waste soil or compost to agricultural land 11,000Waste lime 12,000Waste soil or compost to non agricultural land 21,000Blood and gut contents from abattoirs 26,000Paper waste (of which paper crumble is 46,000) 49,000Sludges from biological treatment plant 52,000Waste food, drink etc. (of which distillery waste is 63,000) 76,000Mixture of wastes 84,000Estimated total 368,000

Outlets

2.29 The potential maximum amount applied to land shows a wide geographical variation. Almost290,000 was applied in SEPA East Region, 60,000 tonnes in SEPA West Region and 14,000tonnes in SEPA North Region. Records are not available for the total areas of land to whichthese exempt wastes are currently applied and it should be recognised that the maximumfigures do not necessarily represent the actual figures.

Agricultural waste


2.30 There are a number of different types of agricultural waste which are collected, stored orprocessed and then applied to farmland in Scotland as part of a controlled disposaloperation. For the purposes of this study, agricultural wastes are taken to be manures,livestock slurries and silage effluent. The management of these wastes is a basic andintegral part of any farm business which has livestock. It has been part of farming practicefor as long as settled livestock husbandry has been practised and, as such, is viewed as anatural process. It is only with the advent of intensive agriculture that controls have beenintroduced over some of the practices, especially storage, otherwise it is unrecorded and notcontrolled.

2.31 Livestock wastes are generally classified by the type of stock and the physical form of thewaste. Most livestock wastes collected in Scotland originate from the dairy, beef, pig andpoultry sectors. Livestock wastes may either be solid, semi-solid or liquid. Solid wastes aregenerally termed manures, and form a stable mass. Semi-solid and liquid wastes arereferred to as slurries. Detailed information is given in annex 8. The options available forthe storage, transport and land application of livestock waste, as well as the environmentaland health risks associated with these stages in the handling process are directly dependenton its physical characteristics.


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Quantities

2.32 It has been estimated (SAC, 1998) that 15,000,000 tonnes of agricultural waste, mainly inliquid form, are recycled to land each year. These figures are based on numbers oflivestock and estimated volumes produced per head and whilst not exact figures, areconsidered to be of the correct order of magnitude. Thus, the quantity of agricultural wastewhich is stored, processed and applied to land is considerably greater than other types ofwaste. However, additional amounts of agricultural wastes are deposited directly viadefecation from grazing animals and it is estimated that a further 10,000,000 tonnes areexcreted directly on to land in Scotland by grazing animals. Similar percentages have alsobeen quoted by (Mawdsley et al, 1993).

Composted waste


2.33 Composting is used to describe the natural degradation of organic material by the action ofbacteria, fungi, insects and animals in an adequate air supply to reduce it to a stable materialwhich can be used to improve the fertility of soil (IWM, 1994). Whilst composting representsa natural process, its efficiency can be improved by careful management of processconditions and material inputs. Composting can be accomplished by a range of methodsincluding simple windrow systems, in-vessel systems and static pile aeration systems.Interest is also growing in the development of home composting systems. Any material whichis biological in nature has the potential to be composted, but some materials are moresuitable than others.

Quantities

2.34 Very little waste is reduced by composting in Scotland. To date it has not been cost effectiveto select composting over landfill, and there is a lack of demand for the product as farmershave easy access to affordable chemical fertilisers and free sewage sludge (CA, 1997). Thesituation in the UK is in contrast to that in Germany and other European countries, as well asto that in the US and Canada, where composting is utilised to a greater extent, generallydriven by legislation restricting the quantity of organic material that can be accepted bylandfills.

2.35 Notwithstanding this, the extent of composting in the UK has been steadily increasing, goingfrom four composting plants in 1990 to 44 in 1996 (CA, 1997). This has largely been inresponse to changes in legislation and in anticipation of further incentives to diversify wastemanagement and recycling practices (HDRA, 1998). In Scotland in 1994, the composting of14,000 tonnes of household waste was reported by 22 local authorities. Of the compostproduced from this waste, 250 tonnes were sold to the public, 300 tonnes were used forpublic parks and the rest was sold to farmers and public/local professional gardeners (Bionet,1998). However very few applications for exemptions for use of composted waste have beenmade under the Waste Management Licensing Regulations 1994 (final quarter of 1997: 8tonnes), first quarter 1998: 2 tonnes) (SEPA, 1998).

2.36 There is currently no composting of MSW in Scotland. However, a number of localauthorities have experience of composting green wastes segregated from the MSW wastestream. Source-separated botanical waste derived from 11,800 households along withbotanical waste from commercial premises, civic amenity sites and parks and gardens hasbeen carried out by Dundee City Council since 1991 (Olsen and Collier, 1994). BordersCouncil has experience of composting and Dunfermline District Council conducted early trialscollecting household botanical waste and composting but with little success. A number of


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local authorities have pilot tested a wide range of home composting systems but to date nomajor implementation of this approach is evident.

2.37 In terms of private sector activity, only one company in Scotland has been involved withcomposting organic wastes on a large scale (pers comm, Peddie, 1998). It is anticipated thatthe level of composting activity in Scotland will markedly increase in the future (pers comm,Olsen, 1998). Central to this expansion will be a number of composting initiatives.

Local authorities in Tayside (Angus, Perth and Kinross and Dundee City Councils) arelooking to provide a centralised closed composting system. It is anticipated that theintention to fix charges for the acceptance of waste for composting will provide theincentive for contracts to be established with food processing and other businesses in thearea. Dundee City Council will also be promoting composting by businesses, chargingonly for uplift, and also within self contained communities such as military bases andprisons

Renfrewshire Council is looking into composting green wastes in partnership withneighbouring local authorities and the private sector (pers comm, Eving, 1998) and arealso looking to promote home composting.

2.38 Other composting activities in Scotland include co-operation between the University ofAbertay, Dundee and Dundee City Council. Furthermore, the University of Aberdeen hasstarted work on the composting of green waste in conjunction with the City of AberdeenCouncil, whilst the Macaulay Land Use Research Institute (MLURI) has specific interests inthe novel composting of distillery and other exempt industrial wastes as well as the novelapplication of composted products, for example their use as biofilters (pers comm, Campbell,1998).

Fallen stock


2.39 The problems in disposing of fallen stock are a consequence of the impact of BSE in the late1980s which reduced the value of by-products from the animal industry (Tweddle, 1998).Prior to the BSE controls farmers would receive a modest sum for fallen stock from theknackery which would salvage hides or skins and meat not for human consumption. Theremaining waste material would be sold to or collected by renderers who could extract furtherby-products. The closure of these outlets has resulted in an increase in the number of fallenstock requiring alternative disposal routes. Renderers charge for treating material and therelatively few renderers in Scotland have a market advantage. Knackeries now have to payfor rendering wastes and the industry has increased its charges for uplifting fallen stock.Consequently the customer base has declined and only four businesses continue to operate.The result of this situation is that on-farm burial of fallen stock is increasing.

2.40 As a percentage of estimated fallen stock, the knackeries in 1997 dealt with approximately50 to 66% of all cattle but only about 5% of all sheep. The inference is that one-third to onehalf of cattle and the majority of sheep are either disposed of by burying or naturaldecomposing of sheep on high ground. Pigs and horses are also dealt with by the knackeryand rendering system whilst poultry may be disposed of by incineration in-house by the largercompanies.


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Table 2 - Numbers of animals collected by knackeries in Scotland 1997. (Source: Tweddle,1998)

Cows Stirks Calves SheepTotal 10183 8914 24741 21842As % of estimated deaths 56 80 55 6

2.41 If present trends continue the practice of on-farm burial will increase to such an extent thatthe already depleted knackery industry will be jeopardised. Those farmers for whom on-farmburial is not feasible or is restricted will face severe problems in disposing of fallen stock,which may lead to improper or bad practice becoming more commonplace. Many parts ofScotland are not suitable for on-farm burial because of high water table levels or thin soils.The UK is unique within the EU in allowing widespread on-farm burial, albeit as the leastfavoured option after knackeries, hunt kennels, landfill and incineration. Guidelines for safedisposal methods are stated in the PEPFAA Code of Good Practice, which is not statutory;neither does it take into account the differing geological conditions across Scotland.

Key players

2.42 There are many groups who have a legitimate interest in the subject of organic wastesspread on land. The groups are wide ranging in origin and remit and as many as possiblehave been contacted to provide information and background as part of this study. Annex 9and 9a lists a those who are considered to be key players in Scotland and details their roleand particular interest. The principal players include :

Waste producers; Waste carriers; Waste contractors who apply the waste to land; The landowners / occupiers on whose land the waste is applied; The public living in the vicinity of the applications; The Regulators (SEPA, SOAEFD, Local Authorities); Farm advisers such as Scottish Agricultural College; Food retailers and those in the chain from farm to fork; and Environmental NGOs

2.43 The studys researches have produced a considerable amount of data and opinions. In orderto reduce the volume of text, all the important issues arising from a section have beensummarised in as brief a form as possible and presented as summary and issues. Thedetailed arguments behind each statement are not necessarily given in the text, but the basicbackground information is available either in the relevant section or the annexes.

Public perception

2.44 The role of public perception as a key driver in the acceptability of spreading organic wasteon land should not be underestimated. Many of the changes in practice which havehappened over the last year such as the intention to cease putting untreated sewage sludgeon land have resulted from public pressure. Similarly, at a local level, the public concerns atBlairingone have precipitated much media interest in the topic. The questions of whoconstitutes the public and whether the public lead or are led by major interest groups suchas the British Retail Consortium with its links to the supermarkets is not important in thiscontext instead, it is enough to recognise that the public in all its guises must haveconfidence in the process if it is going to continue.


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2.45 It only becomes necessary to identify the source of the concern in more detail when action isto be taken because the concerns of one particular audience may differ from that of another.For example, those living next to land where the activity takes place have different concernsto those of the retail sector, although all share a common interest. The way each audience isaddressed will be different.

2.46 In general the public concerns about wastes going to land relate either to general issues suchas the fear of disease transmission, the effect of chemicals in the environment and theconcept of pollution of land and water or to the immediate and direct impact of odournuisance or vehicle movements in the vicinity of communities. Effective communication isrequired to convey the degree of risk or otherwise and to promote the concept of beneficialrecycling of materials.

2.47 The ability of local interest/action groups to collate evidence of nuisance/risks associatedwith waste application should not be underestimated, nor should the political pressure whichsuch groups can exert. In particular, access via the Internet to international web sitesdevoted to waste-related issues enables such groups to be well informed, thereby requiring aresponse which fully recognises the knowledge-base already held by such groups. It isimportant to avoid greenwashing whereby coverage of issues of real concern is treatedsuperficially and the benefits of recycling are addressed disproportionally to the risk andconcerns.

2.48 Transparency of information is crucial. Communication in a format easily accessible toconsumers could have the greatest impact on acceptability of waste recycling to land. Theview of the Scottish Consumers Council is that consumers tend to believe supermarketsrather than governments because governments are thought to act in the interest of certainindividuals such as farmers (Heaney, pers comm, 1998). Information needs to becommunicated in such a way as to advise, using a non-technical format where appropriatebut quoting reliable sources and informing how to get access to information.

2.49 The media are clearly major shapers of public perception in this field and it is important thatthe regulators of waste application work with them to provide factual and relevantinformation. Strong lines of communication from all sectors involved in the practice arerequired with consumers, and these could be strengthened by various means.

2.50 As a means of addressing public stakeholder interest, consideration should be given tomanaging the issue on both a local and a wider basis. This could take the form of :

Informing the public of large scale operations prior to them going ahead; Providing a clear definition of the type of wastes and the nature of the treatment it

has received; and providing a central register of waste recycling which is accessible to the public.


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Summary and issues

1. Current estimates of the percentages of the various wastes applied to land inScotland are:

agricultural waste 96%exempt industrial waste 3%sewage sludge 1%composted waste < 1%

2. The amount of sewage sludge is likely to increase, but the increase is still very smallcompared to the amount of agricultural waste applied.

3. There is currently considerable pressure to increase the levels of treatment ofsewage sludges to reduce the risk of pathogen transmission. This is not reflectedwith exempt wastes although there is concern over odour, which can be controlledthrough treatment.

4. There is currently no accurate record of the amounts of exempt wastes applied toland, nor any indication of future trends.

5. The six month pre-notification system for exempt wastes does not provide sufficientlevel of information and there is no requirement to incorporate the information intoany farm plans.

6. The current notification periods cause problems. Often the notification comes tooclose to the application for a SEPA officer to attend. There is no real opportunity todetermine when the activities will take place as the wastes could be applied at anypoint during the six months and dates may be changed due to inclement weather.

7. Storage of exempt wastes is not practised at the point of origin, leading to problemsof handling and odour.

8. Lack of storage means the requirement to carry out spreading to coincide withcrop/land demands is disregarded, leading to environmental problems in times ofunsuitable weather or low crop uptake.

9. Multiple wastes can be applied to the same land without the landowner/occupierneeding to take account of any synergistic effects etc. or to have a farm waste ornutrient management plan.

10. Information pertaining to the nature of exempt wastes and agricultural wastes islimited compared with that for sewage sludges.

11. Farmers are often unaware of the nature of what is being applied to their land.

12. Agricultural wastes applied to land are in general not treated.

13. There is a lack of vocational training and certification for staff advising on applicationof wastes and for contractors undertaking the application.

14. Composted waste is currently a very minor arising but levels may increase in thefuture. Little research has been carried out into its behaviour on land.


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15. Fallen stock does not currently pose a problem but difficulties might be expected infuture years due to cumulative effects of increased disposal.


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3. Underpinning science

3.1 The scientific knowledge base which underpins disposal practices for the organic wastesincluded in this review is extensive in some aspects but lacking in others. The knowledgebase sometimes lags behind the issues and often reflects the pressure of different drivers atdifferent times. Research is often reactive, carried out in response to the issues as theyarise. This is not unusual or unexpected but there are differences in the extent of theknowledge needed now to satisfy an informed public which is increasingly sensitive to scarestories and which is increasingly sceptical of official information.

3.2 This change in public reaction to perceived risk, real or otherwise, is one which mustincreasingly be taken into account in the formulation of policy and the design of researchwork. The way in which results are promulgated will also require careful thought, given thetendency of the media to overplay possible risks and the public to distrust science. Thedisposal of organic wastes on land is an area which has the potential to be incorporated intoa wide range of scare stories, given the closeness of the activities to the food chain. Goodquality, reliable scientific information is a pre-requisite in underpinning the recycling of wasteto land and in ensuring that practices are discontinued where an unacceptable risk exists.

3.3 There are many benefits to be obtained from recycling wastes onto land, the most significantof which relate to nutrient addition and soil conditioning. One of the interesting findings ofthe study is how little the potential benefits are understood even by the farming communityand how the nutrient addition from what is in effect a free source is generally discounted.

Benefits of waste recycling

Fertilising benefits - nutrient addition

3.4 Fertilising can be defined as the application of materials containing nutrients which areessential to plant growth. Many wastes can contain significant quantities of the followingnutrients:

- Nitrogen N- Phosphorus P- Potassium K- Magnesium Mg- Calcium Ca- Sulphur S- Sodium Na

Nitrogen is often present as ammonium-nitrogen (NH4-N) and nitrate (NO3) which are morereadily available for plant uptake, or in a bound organic form requiring mineralisation bymicrobial activity in the soil to convert it to plant-available mineral nitrogen. Wastes whichcontain significant quantities of these materials can, if rates and timings of application arematched to the nutrient requirements of the growing crop, act as valuable fertilisers. Traceelements may also be present in wastes, including iron (Fe), manganese (Mn), copper (Cu),zinc (Zn), molybdenum (Mb), boron (B), and chloride (Cl). The concentration of theseelements is important because with many of them only low concentrations are acceptable.

3.5 Sewage sludges contain significant amounts of nitrogen and phosphorus, the total amountsand availability being dependent upon the treatment to which the sludge has been subjected.In general a surface application of liquid digested sludge applied at 50m3/ha can supply 100


19

kg of N, and 50kg of P. Figures relating to total and available nutrients in sludge as spreadare given in annex 10.

3.6 Exempt wastes also contain varying amounts of nutrients. Nitrogen is the most commonbeneficial element but some wastes such as gypsum will contain very little whilst others, forexample abattoir waste, contain high levels. Other nutrients such as P, K, Mg and S are likelyto be present. For most of the exempted wastes there is little or no evidence from fieldexperience or trials with which to optimise rates of application to the land to meet croprequirements for nutrients. This represents a considerable gap in the scientific knowledgerelating to these wastes.

3.7 Agricultural wastes such as manures and slurries contain nitrogen mostly bound to organicmatter. The fertiliser value of manures and slurries varies from farm to farm, and isdependent upon such factors as the type of livestock, the feed ration and the waste handlingsystem. Typical loadings of nutrients for various agricultural wastes are shown in the tablebelow. In order to place the data in context, it should be recognised that most crops take upless phosphorus than is applied, usually less than 75kg P/ha .

Table 3 - Typical loadings of nutrients for different agricultural wastes (Aitken, 1998)

Application (assumingapplied at 50m3/ha)

Plant-available N(kg)

Phosphate (kg) Potash (kg)

Cattle slurry 37 25 112Pig slurry 200 100 135Poultry broiler litter 1250 850 700Sewage sludge 100 50

3.8 At present in Scotland, the potential fertiliser value of all of the slurry and manure collectedduring the winter has been estimated at 21 million (SOAEFD, 1997). However, the amountof nutrients applied to farmland from livestock manures is low in comparison with thecontribution from inorganic fertilisers, shown below.

Table 4 - Amount of Nutrients Applied to Farmland in Scotland (Aitken, 1998)

Nutrient N addition(t/yr)

P2O5 addition(t/yr)

Inorganic fertiliser 212,200 (86%) 81,100 (89%)Livestock manures 33,750 (14%) 10,635 (11%)Sewage sludge (1991) 290 (0.1%) 242 (0.2%)Other exempt industrialwastes (estimate)

1000 - 2000 ? 200 - 500 ?

3.9 Composts, unlike peat-based alternatives, contain good quantities of nitrogen, phosphorus,potassium and other trace elements, but a large proportion of the nutrients in compost arenot immediately available and hence compost can be effective as a slow-release fertiliser.

Soil conditioning effects

3.10 Certain wastes can act as soil conditioners and may add useful amounts of organic matter tothe soil. This improves soil condition by increasing its water holding capacity, reducingevaporation, improving drainage and aeration. The structure, density, workability andaggregation of soils all benefit from the addition of organic matter. When soil organic matterfalls below 3% the soil becomes unstable as a growing medium and needs reclamation. For


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these soils in particular, the application of organic material is important. Wastes with a veryhigh calcium content such as gypsum can improve the structure of soils which have a highclay content or which are saline. Wastes such as lime sludge can have a high neutralisingvalue which makes the waste a useful liming material in acid soils.

3.11 Compost contains a lot of organic matter and the use of composted waste can giveconsiderable improvement in soil quality as well as reducing the demand for peat basedfertilisers. (The extraction of peat has the potential to damage sensitive ecosystems). Someresearch has shown that there may be an increased resistance to disease in plants afterexposure to compost (HDRA, 1998; Roy et al., 1997).

General environmental benefits

3.12 There are many beneficial properties common to all the wastes covered in this review. Thekey ones are summarised below:

The use of such wastes as fertilisers should lead to decreased dependence on chemicalfertilisers, and their associated costs. Estimates are that the current economic value oforganic wastes, if considered as a replacement for inorganic fertilisers in Scotland, couldamount to 25M per annum (pers comm, Aitken, 1998);

The application of organic wastes can reduce the requirement for inorganic fertilisersand their use is thus a potentially more sustainable approach than reliance on continuoussupplies of nitrogen fertilisers manufactured using energy intensive processes, andphosphate fertilisers and peat soil conditioners derived from finite sources. Thiscontributes to habitat conservation and protection;

The overall environmental impacts are generally less than for incineration with itsassociated problems of emissions in terms of greenhouse effect and ash to be disposedof, loss of nutrients and energy imbalance and requirement for large centralised facilities;

Assuming there is sufficient land within the vicinity of the site where the waste arises thenthe waste can be recycled to land without the need for (and environmental cost of)transporting a distance to a licensed disposal facility. This reduces the use of fossil fuelsand reduces the costs to the waste producer in dealing with these wastes;

The advantages over landfill are not just economic, although the current disposal chargeof 7 per tonne plus tipping charge is a strong inducement to recycle. The proposed EULandfill Directive requires each member state to reduce the quantity of biodegradablematerial sent to landfill for disposal, thus increasing the pressure to recycle. The EU wastehierarchy places recycling above disposal although there is a need to take the fullenvironmental impact of waste disposal options into consideration. In many situationsrecycling of waste to land is the Best Practicable Environmental Option (BPEO). ABPEO methodology for sewage sludge has been developed (Powlesland and Frost,1990).

Potential environmental impacts of waste recycling to land

3.13 Waste recycling has several potential environmental impacts on land, air and water. Thebest documented impact is on the water environment where the practice can have immediateeffects due to spillage or seepage from stored wastes and during application or soon afterapplication in the event of rainfall. There are also longer term insidious effects due to diffusepollution. The impact on soil is one of the areas where scientific knowledge lags behind theconcerns. Most research has been concentrated in the past on the effects of nutrients and


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metals in soil whereas current concerns are based on the presence of organic contaminantsand their long term impact. Air pollution is primarily a local nuisance issue or else of moregeneral concern relating to release of greenhouse gases.

3.14 In SEPAs recently published Environmental Strategy fifteen main environmental issues wereidentified. The disposal of organic waste to land has potential to contribute to seven ofthese, if carried out in an incorrect manner (SEPA,1998). These are:

Climate change; Biodiversity pressure and decline; Accumulation of toxic chemicals in Scotlands waters; Endocrine disrupting chemicals - gender benders; Accumulation of toxic chemicals in soil; Eutrophication of surface waters; and Reduced oxygen status in controlled waters.

3.15 SEPAs State of the Environment report, published in 1996 (SEPA, 1996) also highlightedthe management of soils, the pollution of watercourses by diffuse pollution sources such asagricultural run-off, enrichment and eutrophication of surface and marine waters as being keyissues for it to address. The potential environmental impacts and the relevant scientific dataare presented below according to the receiving medium.

Potential impacts on water quality - nutrient enrichment

3.16 Application of organic wastes to land can result in both diffuse and point source pollution ofsurface waters and groundwaters. The risk of water pollution is influenced by the manner inwhich wastes are applied and the timing of application, with greater potential for pollution ifwastes are applied in close proximity to watercourses, injected close to field drainagesystems or into porous soils above field drainage systems. Injection or surface spreadingonto sloping ground can result in run-off and drainage to surface waters.

3.17 Where farm nutrient plans do not exist, over-application of nitrogen and phosphorus can takeplace, especially if the amount of inorganic fertiliser applied is not reduced. Nutrientenrichment and oxygen depletion are the principal impacts of this over-application.

3.18 There is good documentation of the loss of nutrients over time, especially nitrogen andphosphorus, through surface run-off, transfer via field drains and leaching, causingeutrophication in receiving waters. High levels of nitrate in drinking water can be harmful tohumans and animals. Wastes need to be applied under properly controlled conditions inorder to minimise losses. Much nitrogen leaching can be controlled by the timing ofapplication and the application methodology.

3.19 Poorly managed phosphate inputs can result in phosphorus enrichment of soils and losses towatercourses where it can lead to the formation of algal blooms. These can result indepleted oxygen levels in water and eutrophication. Phosphorus concentration is the rate-limiting factor for eutrophication of lentic and inland waters. In severe cases, the algal scumproduced can be toxic to humans and livestock. Although phosphorus tends not to leachreadily from soils, there is concern that phosphorus-saturated soils may leach phosphorus.There are no restrictions on phosphorus inputs to soils despite evidence of leaching andeutrophication. Phosphorus is often applied above the limits at which crops can utilise it,typically taken as 75kg/ha.

3.20 The form in which phosphorus is present is important. The solubility of phosphorus applied insewage sludge to achieve 60mg/l extractable phosphorus is far lower than that derived from


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animal manures. Information is lacking for exempt wastes. Despite the risks associated withnutrient enrichment if organic wastes are incorrectly applied, the quantities should be placedin context against the very substantially larger inputs from inorganic fertilisers.

Sewage sludge

3.21 The majority of water pollution incidents arise from runoff from fields where sludge has beenapplied in inappropriate weather or where sludge is injected into field drains. Hydraulicoverloading with liquid sludges can lead to anaerobic conditions. Storage of sludge hascaused environmental problems, especially through leaching to groundwaters from driedsludges. However, nitrogen release from sludges is very low relative to inorganic fertilisersand the contribution of nitrogen loading to UK soils from sewage sludge is only 1% of the Npotentially spread on farmland from animal wastes (Smith, 1996).

Agricultural waste

3.22 Since 1982, there has been a general upward trend in the number of pollution incidentsassociated with the run-off from animal wastes on farmland in Scotland (Scottish FarmWaste Liaison Group/Scottish Agricultural Pollution Group annual statistics). Over the sameperiod, there has been a reduction in the number of pollution incidents associated with slurrystores and silos. The focus on the prevention of pollution from livestock wastes in Scotlandhas shifted from the steading (point source) to the field (diffuse source).

3.23 The risk of nitrate leaching is high if livestock wastes with a high percentage of nitrogen insoluble form are applied when the uptake by crops is low or non-existent (SOAEFD, 1998).Timing of application is crucial as leaching losses range from 0% if applied in spring to 90%if applied in autumn. Nitrate leaching following applications of farmyard manure whichcontains most of its nitrogen in organic rather than immediately available form is less likelyand thus the timing of the application is not as important.

3.24 Livestock manures and slurries can also be a source of phosphates. Research in NorthernIreland indicates that excessive applications of slurry are a significant source of phosphate inloughs (Foy, 1996). Agriculture is believed to be the second largest contributor tophosphates in freshwaters, after sewage discharges. There is not such a direct associationbetween phosphate losses and fertiliser additions as there is with nitrates.

Exempt waste

3.25 It is SEPAs experience that the application rate of the waste is seldom if ever matched to thenutrient needs of the growing crop where exempt wastes are disposed on land. As a result itis suspected that nutrient leaching occurs widely. There is no published information relatingto this topic in respect of exempt wastes.

Compost

3.26 Studies (Insam and Merschak, 1997) have shown that use of compost causes only minorincreases in nitrate and ammonium in soil water and leachate. The high organic mattercontent of compost results in lower concentrations of soluble/available nutrients and heavymetals. Nitrogen is less readily available from composts than from other organic wastes(HDRA, 1998), and presents less of a potential impact. Furthermore, compost can reducewater pollution arising from run-off of applied mineral fertilisers (DoE, 1996).


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Potential Impacts on water - oxygen depletion

3.27 Certain wastes have a high Biochemical Oxygen Demand (BOD). If such wastes enterwatercourses after application, their breakdown by micro-organisms depletes or totallyremoves the available oxygen and can result in ammonium levels which are toxic to manyaquatic animals. Wastes with high BODs added to wet soils can give rise to anaerobicconditions within the soil resulting in temporary soil oxygen depletion and poor plant growth.For comparative purposes, a good quality, class A2 river will have a BOD of less than 4 mg/l.

Table 5 - Examples of typical BOD of various wastes

Pollutant BOD5 (mg/l)Raw milk 140,000Silage effluent 30,000 - 80,000Pig slurry 20,000 - 30,000Liquid sewage sludge 10,000 - 20,000Cattle slurry 10,000 - 20,000Liquid effluent from slurry stores 1,000 - 2,000Food and drink wastes Up to 260,000

3.28 Many agricultural wastes such as slurries and silage effluent have very high BOD levels(SOAEFD, 1998). Manures and slurries also contain suspended solids, which can increaseturbidity in water and smother benthic fauna and flora. All exempt industrial wastes have thepotential to cause water pollution if they drain into a watercourse. Many are highly pollutingwith BOD levels as high as 260,000mg/l for some food and drinks wastes (Davis and Rudd,1998), and pH values as low as 3.4 for pot ale from a distillery.

Potential impacts on soil - potentially toxic elements

3.29 Historically there has been much concern about the heavy metal content of sewage sludgeapplied to land, especially where the soils are of low pH. The generic term potentially toxicelements (PTEs) is used to describe the wide range of metals which originate in sewage.Effective trade effluent control has ensured that many of the most toxic metals do not nowoccur in sewage effluent but metals such as zinc and copper occur in domestic sewage andneed to be managed through controls on sludge spreading. Little is known about the effect ofother elements such as platinum and palladium which originate in car catalysts and entersludge through the road drainage system. If uncontrolled, PTEs can build up in the soilleading to deleterious effects on soil microbial activity, as well as phytotoxic and zootoxiceffects. The quantity of metal applied depends on the source of the sludge. Other PTEsinclude sodium and salinity which can affect soil structure and crop growth (Davis and Rudd,1998). Distillery wastes which contain copper at levels of up to 1000mg/kg dry matter, canhave a beneficial effect on copper-deficient soils.

3.30 In the past, soil was seen as a receptor for wastes and emphasis was placed on ensuring thatcontaminants were locked into the soil system thereby avoiding pollution of watercourses oruptake into the food chain. In recent years more attention has been given to developing agreater understanding of the sensitivity of those soils to which wastes have been applied andthe effects on soil ecosystem functioning and soil sustainability. Soil microbial biomass iscritical to soil organic matter breakdown and recycling of plant nutrients. McGrath (1994)carried out a review of the effect of sludge-derived metals on soil microbial processes andconcluded that the aim of a soil protection strategy should ultimately focus on soil fertility.


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Table 6 - Impacts of PTEs on plant and animal health

Effect Causal elementPhytotoxicity Zn, Cu, Ni. Possibly CrHuman food chain via crop uptake CdHuman food chain via offal from meat fromanimals ingesting soil with elevated levels ofPTEs

Cd, Pb

Animal health Cu, As, Se, Mo and FSoil Fertility Zn

(from Carrington et al, 1998)

Sewage sludge

3.31 Good trade effluent control and waste minimisation initiatives have reduced metals at sourcein industrial waste streams but less pressure has been placed on the producers of exemptwastes or manufacturers of animal feeds/inorganic fertilisers to minimise levels of metals.The EU Directive 86/278/EEC sets metal levels to protect soil fertility, plant yield, human andanimal health and allows a lower recommended and a higher mandatory level for eachmetal. The UK has adopted the maximum permissible concentration at or near the upperpermitted mandatory levels whereas other states have adopted a more precautionaryapproach. These controls do not exist for other wastes applied to land.

3.32 The recent review of the scientific evidence underlying the limits set for PTEs (Carrington etal, 1998) suggests that the limits for Cu, Ni, Cd, are acceptable for the protection ofplants/animals/humans although the review suggests that further research is requiredregarding intake of cadmium in the diet of sheep. However, it is recommended that a revisedlimit of 200mg lead/kg would provide additional protection to avoid accumulation in liver andkidneys. Further data are given in annex 11.

3.33 A recent study (Towers and Paterson, 1997) has shown that the majority of soils in Scotlandwhich may receive sewage sludge in future have a strong or very strong metal bindingcapacity. However, it is essential to maintain the soil pH at current levels for this to besustained. The small proportion of sites which have low metal binding capacity should beprecluded from sludge recycling. The risk to groundwater has been found to be high or veryhigh in only 5% of sites, partly due to the hydrogeology of Scotland where there are fewmajor aquifers. Movement by surface runoff may be more of a problem. Little informationhas been reported on the impact of sludge application on metal losses to surface andgroundwaters in Scotland.

Agricultural wastes

3.34 Manures and slurries can contain high levels of PTEs, particularly zinc and copper. Thequantities of manures and slurries added to farmland are such that these additions can beappreciable. For example, the manure from fattening pigs may contain 300-2,000 mg Cu perkg in the dry solids and 200 - 1500 mg Zn per kg (mean 600) (MAFF, 1985). These levelsmay even be exceeded if the diets of fattening pigs are supplemented with Zn (Smith, 1996).The application of these wastes to uncultivated grazing land has the potential for greateraccumulation of metals and pathogens in the upper layers. For comparative purposes, themaximum levels of zinc and copper which can be applied in sewage sludges is 15 kg/ha and7.5 hg/ha (annual rate of PTE addition over a 10 year period).


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Exempt wastes

3.35 Certain exempt wastes can contain high levels of metals, for example copper in distillerywastes. Little information exists on the overall PTE levels in exempt wastes because of thelack of analytical data. The origin of PTEs which are loaded on to soils are given below indata for England and Wales. This shows the percentage loading by source for selectedheavy metals. The importance of atmospheric deposition should be noted, putting the datainto context.

Table 7 - The percentage of PTEs deposited on soil, given by origin (figures for England andWales)

PTEZn Cr Cu Pb Cd

SourceSewage sludge 10 19 17 18 7Animal manures 45 45 10 14Atmospheric deposition 35 24 70 50Industrial by productsand wastes

40

Inorganic fertilisers 16 20

(from Carrington et al, 1998)

Potential impacts on soil - organic contaminants

General

3.36 Sewage sludges and certain exempt wastes may contain volatile organic compounds (VOCs)such as benzene, chlorinated benzenes, chloroform, cyclohexane, tetracholoroethylene,toluenes and xylenes. Endocrine disrupting chemicals, phthalates, phenols and polyaromatichydrocarbons can also occur in wastes, as can surfactants from detergents and persistenttrace organics. Although at low levels in the wastes, these will significantly elevate levels insoil. The problems associated with the presence of organic compounds include:

leaching losses; persistence in the soil; and toxicity to grazing animals and soil biomass.

3.37 It is thought that the main risk with respect to organic contaminants is from surfaceapplication of wastes to grassland and transfer to tissue fat and milk of grazing livestock. Itis considered that the detergent residues and plasticising agents represent the mostsignificant sources of organic contaminants in sludge (Carrington et al, 1998), although thesecontaminants degrade quickly in aerobic soil environment, having a half-life of several days.However, in general, the effects of these compounds on soil properties and organisms arenot well known. Although the potential risk posed by these organic compounds is thought tobe low, the uncertainty of their fate and rate of breakdown and the lack of current UKstandards in soils demonstrates a clear need for further research.

Exempt wastes

3.38 The data for exempt wastes are very sparse. It is known that waste with a high BOD cangive rise to anaerobic conditions within soils. Other wastes such as papermill sludge, can


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result in limited benefit but due to the high carbon:nitrate ratios can result in nitrogen beinglocked-up in the soil. Consequently, papermill wastes require prior treatment or needorganic matter to be added at the time of spreading in order to benefit the soil. Fungicidesand bactericides are used in many industries, including paper, and are likely to be present inpaper wastes. Research on organic contaminants in exempt wastes is reviewed by (Davisand Rudd, 1998).

Agricultural waste

3.39 Some veterinary products from agricultural practices and their metabolites can haveunwelcome environmental effects when excreted by farm animals (RCEP, 1996). Forexample, the widely-used anti-parasitic drug, ivermectin, is persistent and residues in thefaeces of treated livestock reduce the number and variety of dung beetles and insects,affecting in turn insect-eating birds and mammals.

Potential impacts on air quality

General

3.40 Spreading organic waste on land results in the release of various gases to the atmosphere,including ammonia, methane and nitrous oxide. The extent of release depends not only onthe type of waste, but on the timing and method of application. Volatilisation andatmospheric losses can be reduced by injection of wastes or avoiding sprays and aerosols,for example by using bandspreaders. The use of rainguns should be avoided.

3.41 Ammonia emissions can result in detrimental effects on the environment, including:

acidification of the soil through deposition of ammonia and ultimate transformation tonitrate;

addition of nitrogen by deposition to upland areas, which may result in vegetation changesor increased nitrate leaching losses to watercourses; and

promotion of increased sulphur dioxide deposition by atmospheric chemical reactions withammonia.

Methane is the second most significant anthropogenic greenhouse gas. Although itsatmospheric concentration is much less than carbon dioxide, its impact as a greenhouse gasis significantly greater. Nitrous oxide has a global warming potential 320 times higher thancarbon dioxide on a 100-year timescale.

Sewage sludge

3.42 Atmospheric emissions from sludge depend on the type of sludge. For example limestabilised sludges have a significantly reduced ammonia content. Ammonia emissions fromsludge-treated soils are small compared with total ammonia losses from livestock wastes.Injection or immediate incorporation prevents volatilization although the losses of nitrousoxide can increase when sludge is injected.

Agricultural waste

3.43 Ammonia losses during the spreading of manures and slurries can be considerable,particularly when waste is applied in the spring or summer, when all the ammonium nitrogencould be lost (Aitken, 1996). Some 90% of the UKs emissions of ammonia are believed tocome from agriculture (IGER et al, 1996). Emissions in Scotland are mainly derived from the


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volatilisation of ammonium compounds from farm manures. It is estimated that, of the totalof 70,000 tonnes of ammonia emitted in Scotland each year from agriculture, excretionduring grazing is the largest source (c. 24,500 t/yr), followed by emissions during spreading(c. 21,000 t/yr) and storage of wastes (c. 14,000 t/yr) (Aitken, 1996). Poultry producesubstantially more ammonia than pigs and cattle (SOAEFD, 1997). Such atmosphericemission results in the loss of a valuable nutrient.

3.44 In the UK, agriculture activity contributes 32% of the total anthropogenic methane emissions,which is the second most significant contribution after landfills, with production from cattlebeing the largest agricultural source. Methane is produced during storage and treatment ofagricultural wastes especially in liquid systems which encourage anaerobic conditions andproduce substantial amounts of methane. Solid waste (manure) management produces littleor no methane emissions.

Exempt wastes

3.45 Excess nitrogen applied to the soil and not taken up by the crop can be lost by denitrificationto the atmosphere as nitrogen and nitrous oxide gas in heavy textured soils during wetconditions. Ammonia may be volatilised if present in the waste (Davis and Rudd, 1998).Little information is available on atmospheric emissions from these wastes.

Potential impacts on animal and human health

3.46 Sewage sludges, some exempt wastes and agricultural wastes may all contain pathogensposing potential risks to receptors such as humans, crops and grazing animals. Thesignificance of these risks is dependent on the potential for pathogens to occur in the wastestream, the decay rates subsequent to application, the presence or absence of barriers totransmission (for example treatment or land use restrictions) and the sensitivity of thereceptors.

3.47 The pathogens of concern include bacteria, viruses, and protozoa. Some of the particularoganisms are:

Escherischia coli including E.coli 0157; Salmonella spp.; Cryptosporidium; Campylobacter;

Giardia; and Cytopathic enteroviruses and rotaviruses.

A summary of the potential risks from pathogens associated with the different wastes is givenin annex 12. Further details relating to these pathogens and occurrence in organic wastes isgiven in (Davis et al, 1998). Many pathogens are host specific whereas others such as E.coli0157 and campylobacter are freely transmissible between man and animals. Such zoonoticpathogens present problems in the control of animal and public health. (Davis and Rudd,1998).

Sewage sludge

3.48 The effects of the various pathogens known to be found in sewage sludge are welldocumented for example Carrington et al, 1998, and Smith 1996 which includes a detailedreview of occurrence of pathogens in sludge, fate of pathogens in sewage and sewage


28

treatment, survival in soils and on vegetation, movement in soil and risks to water sources,constraints on planting, and effects on natural ecosystems. It is important to note thatdespite the potential risks, there are no reported incidences of links between disease and theapplication of sewage sludge to land (RCEP, 1996). This view is supported by ProfessorPennington in the Scottish context (pers comm, Pennington, 1998).

3.49 The approach adopted by the Code of Practice for the Agricultural Use of Sewage Sludgerelies on a break in the cycles of transmission from pathogens in sludge throughcontamination of soil and water to food, animals, crops and humans. This is achieved bysludge treatment to significantly reduce pathogens and restriction of land use afterapplication. Details of this are summarised in annex 13. Definitions of processes effective inreducing pathogens are based upon a 90% reduction in numbers of salmonella and 99%reduction in coliforms. In addition a further barrier is provided by specifying constraints onland use to allow pathogens to decay further ie by specifying waiting periods between theapplication of treated sludge and resumption of grazing or cropping. Co-ordination of sludgeapplications with planting and prohibition in applying it to growing fruit and vegetable cropsprovides further effective barriers.

3.50 A review has recently been undertaken of the scientific principles underlying the approachused by the Code (Carrington et al, 1998) and the adequacy of current controls for otherorganisms not considered in the development of the Code. In general the earlier approach isconsidered to be appropriate . However, the review identified several issues which need tobe resolved, namely:

The need for the terms pasteurisation and stabilisation in the context of sludgetreatment to be defined in terms of efficiency of microbial removal;

The need to describe treatment parameters; The need for definitive information on the survival of some of the more recently

identified pathogens, including Listeria monocytogenes, E.coli 0157:H7, Giardia,Cryptosporidium and viruses, particularly during liquid storage of sludge at lowtemperatures, and following application. It has been noted that more sensitivemethods are required for detecting and measuring levels of bacteria and virusesfollowing sludge application. Research cited has shown that L. monocytegenes cansurvive for eight weeks. Research is currently being carried out into the survivabilityof pathogenic organisms contained in sewage sludge applied to land. This willinform the effectiveness of the legislation and PEPFAA Code. It is currentlybelieved that E.coli may be able to survive 180 days and may in fact be able tomultiply given the right conditions in the soil (pers comm, The Scottish Office).These proposed studies would inform the controls on the land use management afterapplication of the sludge; and

The need for a review of the effectiveness of sludge treatment processes .

3.51 The Code has controls in place to prevent the transfer of pathogens to potatoes andvegetables which are eaten raw. However, no such controls are in place for othervegetables brought into the home. There is also concern that inappropriate use of sewagesludge could lead to the infection of livestock, on previously clean farms, with bacterial orparasitic organisms (pers comm, The Scottish Office). This could lead to zoonotic diseasecycles being established with implications for human health.

3.52 The discussion so far has concentrated on the disposal of sewage sludge from treatmentworks. Sludge from septic tanks is also collected and disposed of on land. This sludge hasbeen subject to a far lesser degree of treatment and can be aesthetically offensive. It is, ineffect, untreated and there is a widely held view that spreading it on land should beprohibited.


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Exempt wastes

3.53 Due to the varied nature of these wastes the potential health impacts also vary considerably.Whilst many of the impacts will be similar to those from sewage sludges which are relativelywell researched and understood, other potential impacts have received little or no study andare therefore not well understood. Pathogen content is variable depending on which carriersexist in the community which has contributed to their existence. However, occurrence maybe sporadic and routine examination of each waste is considered unrealistic, due primarily toinsufficiently sensitive detection techniques (Davis and Rudd, 1998). A risk assessmentapproach is more appropriate, based on a knowledge of the pathogens, the level oftreatment, the waste outlet and land use.

3.54 The approach put forward in Carrington et al 1998 is that wastes should be categorised. Highrisk categories would include faecal-containing material such as abattoir waste. Such wastesshould be subsurface injected and incorporated into the soils. Medium risk wastes which maycontain pathogens include wastes from food industries, compost, waste soil and tannerywastes. Low risk wastes include those from beverage industries, paper and textile waste andwood as well as green plant waste. Paucity of data again precludes informed commentaryon the actual risk.

Agricultural wastes

3.55 In Scotland, 96% of the organic waste spread on land is agricultural in origin, mainly manuresand slurries. On the whole, these wastes are applied without treatment to removepathogens, and routes for faecal contamination of food animals are always going to bepresent because of natural defecation. In addition, the restrictions on the application to landof agricultural wastes are less stringent than other wastes, particularly sewage sludge.Manures and slurries present a greater risk because of the large volumes, compared withother wastes, for possible contamination of meat, poultry, dairy products and vegetables.

3.56 The infection route for pathogens that are excreted in faeces is generally by mouth. Infectiontends to spread in crowded situations and as a result of poor hygiene. Therefore, in anagricultural unit when infection with a specific pathogen occurs, most members of the herdwill become infected (Carrington et al, 1998). In many cases, manures and slurries arespread on the same farm they originated from. While this practice does not reduce the risk tohumans or wild animals, the resident animal population is likely to have developed somedegree of immunity and consequently is less likely to become re-infected. Many of thoseinterviewed during this study were concerned to ensure that farms are kept as closed cyclesfor potential pathogens through not importing wastes from other sources.

3.57 It is believed that E.coli 0157 is present in 2% of the national herd (Jenkinson, 1996; Ball,1997) although it is not easy to identify animal infection as there is no visible illness.Available evidence suggests that the most significant source of the spread of infection is viaanimal faeces from infected livestock (Pennington, 1997) and E.coli can remain viable forover 70 days on grassland (Jenkinson, 1996). Although there is evidence of water, crop andvegetable contamination from E.coli 0157, the impact of spreading manure and slurry onland has not been fully evaluated and the available evidence is conflicting. It is notsufficiently strong to suggest that spreading of such wastes should be prohibited (Pennington,1997). However, there is a need to evaluate slurry treatment methods and due care shouldbe exercised in the use of untreated manure and slurry in the vicinity of crops, fruits orvegetables and near sources of private and potentially untreated water supplies.


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3.58 Cryptosporidium is present in agricultural wastes and is difficult to destroy although it can bereduced by composting or by storage of manures. Salmonella spp. can survive severalmonths in stored slurry, and can survive up to 100 days in slurry applied to grass (Carringtonet al, 1998).

Compost

3.59 Organic wastes which contain materials of animal origin may contain a number of humanpathogens, such as E.coli 0157. When applied to land, a transmission pathway exists for thetransfer of pathogens to crops, which when eaten raw, can pose a risk. Work is currentlybeing carried out at the US Department of Agriculture to consider pathogen destruction incomposting manures, with attention being given to the variety of composting techniques usedby farmers (Gilbert, 1998a). Most wastes of plant origin contain only plant pathogens. Anotable exception is the fungus Aspergillus fumigatus. This is particularly associated withcomposting plant materials because it is capable of both degrading cellulose and surviving attemperatures of up to 60oC. If inhaled as a bioaerosol, it can cause allergies, inflammationand infections in humans (CA, 1998).

Potential impacts on plant health

3.60 Data on plant health issues are sparse in relation to all the wastes. Certain codes of practiceor legislation relate to managing known pathogenic issues related to plant health but ingeneral there is little published information. There is no indication at present that sewagesludge is a vector in the transmission of pathogens other than potato cyst nematodes. This iscontrolled by the provisions of the Code of Practice for Agricultural Use of Sewage Sludge(DoE, 1989). Potato cyst nematodes can survive the sewage treatment process and hencethe only effective barrier to transmission is an absolute prohibition on the application ofsewage sludge to land which is certified free from the nematode. Sewage sludge is notimplicated in the spread of brown rot in potatoes although there is circumstantial evidencethat effluent from sewage overflows has led to outbreaks.

3.61 The risks associated with the application of agricultural and horticultural wastes are not welldocumented. (pers comm, The Scottish Office, 1998). This is particularly so with waste ofvegetable origin but few data are available. Vegetable wastes are not within the remit of thisstudy. Blood and gut contents are not thought to cause a problem in plant health terms butagain there is a paucity of data as far as exempt wastes are concerned.

3.62 Farm slurry spreading is not perceived to be a risk to plant health because it usually takesplace on the farm of origin. It is possible that potato cyst nematode may pass through theanimal gut if it is present in feed and therefore be contained in slurry. Composting may notkill all plant diseases, especially those of vegetable origin but few data are available.

Odour nuisance

3.63 Odour as such is not a health issue. However in terms of public perception it is often linkedwith alleged health complaints and must not be dismissed. Odour can travel long distancesand cause considerable discontent and distress to a receiving population. Odour emissionshave an instantaneous effect, it is usually easy to trace their source and there is a goodcorrelation between odour concentration and distance from the source. Odour is classified asa nuisance by local authorities and odour complaints are usually dealt with by EnvironmentalHealth departments.

3.64 Application of undigested liquid sewage sludge is often associated with odour complaints.However, digestion significantly reduces odours and thermal drying does so to an even


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greater extent. However, there are many variables and sludge odours may be singular forparticular sludges and can depend on age of sludge before being dried.

3.65 Good practice in terms of application can reduce odour, for example using appropriateequipment such as low trajectory irrigation if surface spread. The addition of oxidising agentscan also have a part to play whilst soil injection significantly reduces odour problems.Storage of dried sl

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