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Anaerobic Digestion of farm and food processing residues GoodPractice Guidelines Page1

ContentsContentsContentsContentsIntroduction 2What is Anaerobic Digestion? 2Using these guidelines 4Why establish an AD project? 5Scale 7Benefits and problems of AD 8Deciding to develop an AD project 12

Consultation 13Timing 14Who to consult? 14Whose responsibility? 15Preparing for consultation 15Consultation methods 15

Feedstock and products 16Which feedstocks? 17Quantity and quality of feedstock 17Storage of feedstock 20Transport of feedstock 20Products of AD 22

Project development 25Feasibility 26Economics 27Site and location 28Design and planning issues 29Planning permission 32

Construction and operations 36

Construction 37Electricity connection 38Training 38Monitoring 38Minimising operational risks 39Optimising performance 40Start up and shut down 41

Appendices 42Appendix 1: Glossary 42

Appendix 2: Contacts 44

Appendix 3: Publications and regulations 45

Appendix 4: Development of the guidelines 46

Appendix 5: Summary of management options for farm residues 47

Appendix 6: Electricity connection 49

Appendix 7: Effects of AD on parasites andpathogens 51

Appendix 8: Walford College: case study 52

Summary of AD for public information 53


Introduction

AD is a process which manages farm and foodprocessing residues (Photo: ETSU)

What isWhat isWhat isWhat isAnaerobicAnaerobicAnaerobicAnaerobicDigestion?Digestion?Digestion?Digestion?Anaerobic digesters produce conditions that encouragethe natural breakdown of organic matter by bacteria inthe absence of air. Anaerobic digestion (AD) providesan effective method for turning residues from livestockfarming and food processing industries into:

• Biogas (rich in methane) which can be used togenerate heat and/or electricity

• Fibre which can be used as a nutrient-rich soilconditioner, and

• Liquor which can be used as liquid fertiliser.

he process is already used for treating agricultural,household and industrial residues and sewagesludge. It has been used in the UK agriculturalsector in the form of small on-farm digesters

producing biogas to heat farmhouses, dairies and otherfarm buildings. Experience has shown that an AD projectis most likely to be financially viable if it is treated as partof an integrated farm waste management system inwhich the feedstocks and the products from AD all play apart. Larger scale centralised anaerobic digesters (CADs)are also now being developed, using feedstock importedfrom a number of sources.

This document avoids the term ‘waste’ in the context of theresidues from livestock farming and food processingindustries because ‘waste’ implies that the material is aproblem rather than a resource. These guidelines thereforeuse the term ‘residues’ wherever possible to reinforce theimportance of seeing these materials as a renewableresource.

These residues offer positive opportunities to contribute toAD as a new and sustainable industry. Feedstock is the termused to describe the material introduced into the digester; inthese guidelines it refers specifically to residues fromlivestock farming (such as dairy, beef and pig slurry, or

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poultry litter) and the food processing industries(including vegetable preparation and dairy foodprocessing).

At present, any waste from premises used foragriculture is not controlled waste, including foodprocessing waste. However, food processing wastefrom other premises is controlled waste and issubject to waste management licensing controls.

How does AD work?The digestion process takes place in a warmed,sealed airless container (the digester) which createsthe ideal conditions for the bacteria to ferment theorganic material in oxygen-free conditions. Thedigestion tank needs to be warmed and mixedthoroughly to create the ideal

Figure 1.Overview of the AD process

conditions for the bacteria to convert organic matter intobiogas (a mixture of carbon dioxide, methane and smallamounts of other gases).

There are two types of AD process.

• Mesophilic digestion. The digester is heated to 30 -35oC and the feedstock remains in the digester typicallyfor 15 - 30 days. Mesophilic digestion tends to be morerobust and tolerant than the thermophilic process, butgas production is less, larger digestion tanks are requiredand sanitisation, if required, is a separate process stage.

• Thermophilic digestion. The digester is heated to55oC and the residence time is typically 12 - 14 days.Thermophilic digestion systems offer higher methaneproduction, faster throughput, better pathogen and virus‘kill’, but require more expensive technology, greaterenergy input and a higher degree of operation andmonitoring.


During this process 30 - 60% of the digestible solidsare converted into biogas. This gas must be burned,and can be used to generate heat or electricity orboth. It can be burned in a conventional gas boilerand used as heat for nearby buildings includingfarmhouses, and to heat the digester. It can be usedto power associated machinery or vehicles.Alternatively, it can be burned in a gas engine togenerate electricity. If generating electricity, it isusual to use a more efficient combined heat andpower (CHP) system, where heat can be removed inthe first instance to maintain the digestertemperature, and any surplus energy can be used forother purposes. A larger scale CHP plant can supplylarger housing or industrial developments, or supplyelectricity to the grid.

As fresh feedstock is added to the system, digestateis pumped from the digester to a storage tank.Biogas continues to be produced in the storage tank;collection and combustion may be an economic andsafety requirement. The residual digestate can bestored and then applied to the land at an appropriatetime without further treatment, or it can beseparated to produce fibre and liquor. The fibre canbe used as a soil conditioner or composted prior touse or sale. The liquor contains a range of nutrientsand can be used as a liquid fertiliser which can besold or used on-site as part of a crop nutrientmanagement plan.

AD products can, therefore, help farmers reducetheir requirement for non-renewable forms ofenergy such as fossil fuels, and the digestate, ifcorrectly used, can reduce demand for syntheticfertilisers and other soil conditioners which may bemanufactured using less sustainable methods.

Using theseUsing theseUsing theseUsing theseguidelinesguidelinesguidelinesguidelinesThese guidelines cover good practice for existing andpotential AD plants using residues from livestockfarming and food processing: they do not cover allpossible feedstocks for AD. They specifically do notcover wastes such as sewage sludge, municipal solidwaste or specified bovine material or other abattoirresidue, all of which are covered by other guidelinesand regulations.

Whether an on-farm digester, or a larger scale centralisedanaerobic digester (CAD), is being considered, theprinciples remain the same. These good practiceguidelines aim to help new projects to proceed in anappropriate and sensitive manner so that the industry as awhole can continue to expand with a responsiblereputation. The guidelines will also be useful for localauthority officers and councillors, who may beconsidering applications for planning permission for adigester, or establishing waste management or renewableenergy projects themselves or in partnership with others,and for local communities and neighbours. They havebeen developed by a whole range of organisations andindividuals with extensive experience of AD developmentas developers, farmers, users, environmental bodies andplanners.

The guidelines cover reducing the risks of environmentalpollution, ways of maximising economic viability, andconsultation with local communities. They show howAD can reduce the risk of farm pollution throughintegrated waste management, reduce greenhouse gases,generate energy from a renewable, relatively non-polluting source, and provide soil conditioner andfertiliser, reducing input costs. The guidelines stress that,although AD is a proven and relatively simplytechnology, the importance of health and safety shouldnot be underestimated and management must alwaysconsider safety as well as effective production andenvironmental impact.

All new developments have some negative environmentalimpacts. It is the responsibility of the developer of anyAD scheme, whether a farmer, a co-operative or acommercial CAD developer, to consider itsenvironmental and health and safety impacts and itsacceptability to local communities, as well as itseconomic viability - minimising any negative impactsthrough appropriate developments for localcircumstances and good practice in establishment and


management. All these issues are consideredthroughout these guidelines.

Renewable EnergyRenewable energy is the process of producing energywithout using finite resources. By replacing fossil fuels(such as coal and oil), it can avoid the pollution that causesclimate change and acid rain. Any development producingenergy from renewable sources is generally considered tobe environmentally beneficial.

All renewable energy developments must be seen in thecontext of UK and EU policy on sustainable development:that is, development which meets the needs of thepresent without compromising the ability of futuregenerations to meet their own needs. Energy productionis a vital element of such a future. Problems of pollution,current rates of consumption of finite fossil fuels, anddependence on imported fuels associated withconventional methods of energy production are generallyseen as unsustainable.

Energy from AD offers great potential for using arenewable resource for electricity, heat, and combinedheat and power generation. It is also carbon neutral (iedoes not generate extra carbon dioxide), and cantherefore reduce overall quantities of carbon dioxide inthe atmosphere, reducing dangers of climate change, whenit is used to replace energy from fossil fuels. Adoption ofthe AD process can lead to improvements in themanagement of farm and food processing residues, andthere may be significant further environmental andecological

Why establishWhy establishWhy establishWhy establishan an an an ADADADAD project? project? project? project?AD projects may be initiated from several perspectives:

• Commercial interests such as electricity companies,fertiliser and compost manufacturers

• Residue (waste) producers (farmers, land ownersand food processors)

• Local community initiatives such as partnershipsbetween local authorities and farmers.

The full environmental and practical impacts of AD aregiven in detail on pages 8 – 10. Different interests willhave different priorities in wanting to establish an ADproject. Some of the main reasons for developing an ADproject are summarised below.

Reduction of pollution through integratedwaste management• AD offers an opportunity to reduce odour.

• AD can reduce nitrate pollution of water coursesbecause run-off is reduced through more effectivecontrol of nutrient application to land.

• If applied correctly, AD may reduce the risks of thespread of disease and weed seeds.

• Well-managed AD can control methane emissionsmore effectively than some other waste managementmethods.

• AD therefore helps farmers and others to respond tonew regulations and public pressure to increase theeffectiveness of farm residue management.

Increased income and savingsAD can generate income from sale of biogas (as

electricity), liquor and fibre products.

AD can offer financial savings through the use ofthe products on-site avoiding the costs of syntheticfertilisers, other soil conditioners and energy from othersources.

Figure 2.Factors affecting the development of an AD project

FeedstockSee Feedstock andproducts p16-22

ProductsWasteSee Introduction p2-4See Feedstock andproducts p22-24

See Introduction p2-4See Appendix 5 onmanagement options

Technology Size Finance Environment See Introduction p3-4

See design of the plantp31, Construction andoperations p39-40

See Introduction p7-8See Projectdevelopment p26-31

Economic BenefitsSee Introduction p9-10

FeasibilitySee Projectdevelopment p26-28

EnvironmentalbenefitsSee Introduction p8-9

EnvironmentalregulationsSee Projectdevelopment p28-35

Health and SafetySee Feedstock andproducts p19-24,Construction andoperations p37-40,Appendix 7

Markets See Introduction p7-11See Feedstock andproducts p20-24, Projectdevelopment p26

Energy Liquor Fibre

See Feedstock andproducts p17-18 andp22-23, Projectdevelopment p26-28,Construction andoperations p38,Appendix 6

See Feedstock andproducts p24, Projectdevelopment p26-27

See Feedstock andproducts p23-24,Project developmentp26-27

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Changing legal and political context• Public perceptions are changing, and consumers

are increasingly demanding farming practicesthat are environmentally sensitive.

• There are increasing legislative and regulatorypressures on farmers in relation to local wastemanagement and wider environmental concernsabout farming practices.

Growing demand and market forrenewable energy• Heightened concern about global warming and

climate change have influenced UK Governmentand EU action plans. Prior to the election theLabour Party’s manifesto made a commitment toreduce UK carbon dioxide emissions by 20% of1990 levels by 2010.

• Government and EU policy is to increase theproportion of energy from renewable sources.The UK is considering what would be necessaryand practicable to achieve 10% of the UK’selectricity needs from renewable sources by2010.

• The energy industry is being opened up to fullcompetition, offering new and expandingmarkets for energy from alternative sources suchas AD.

Community issues• AD projects can directly boost the local rural

economy through creating jobs in ADdevelopments, and indirectly through increasingdisposable incomes in rural areas.

• AD can provide a waste management optionwith positive environmental and economicbenefits.

• AD can offer an opportunity to realise potentialin local communities through stimulatingassociated new developments.

ScaleScaleScaleScaleAD can be done on a variety of scales:

• On-site, using residues produced only on that farmor food processing unit

• As a co-operative enterprise between several farmers

• By developing a centralised anaerobic digester (CAD)project supplied with feedstock from several sourcesincluding industrial sources.

Large on farm digester (Photo: WRI Services)

Small on farm digester (Photo: ETSU)


Potential resourceLivestock slurry and food processing residuescurrently exist in large quantities and should be seenas resources which, among other things, provide anopportunity to develop the AD industry. Forexample:

• Every year in the UK about 150 million wet tonnesof livestock slurry (pig and cattle) and about 3.4million wet tonnes of used poultry litter andexcreta (1.8 million dry tonnes) are produced.

• It is estimated that, every year, in excess of onemillion tonnes of food production residues (suchas vegetable or dairy processing residues) could besuitable for AD.

Some of these residues are already used in otherways, such as being spread on the land, or disposedto landfill. Although AD will never be able to dealwith all these residues, there is clearly potential forAD to reduce the negative impacts of otherapproaches to managing residues from theseindustries.

These resources offer enormous potential forelectricity generation. If all the farm residues thatcan be collected are used for AD, the potential forelectricity generation is a total of 9.4 TWe hours peryear (see Table 1). The total UK energy use in 1995was 315 TWh, of which 4 TWh were in theagricultural sector, and 101 TWh were in thedomestic sector. To put this into perspective, thereis the potential to produce twice the amount ofenergy per year from AD as was used in 1995 in theagricultural sector.

Table 1.

Livestock populations and farm residues in theUK and their potential for methane generationand electricity output.

Benefits andproblems of ADEnvironmental benefitsEnergy balanceA properly designed and operated AD plant can achieve abetter energy balance (taking emissions from transportoperations into account) than many other forms ofenergy production. The energy balance relates to theamount of energy consumed in order to produce energy.

Reducing greenhouse gases• Methane is a major greenhouse gas if it escapes to the

atmosphere. Current disposal practices for slurry andfood residues cause methane to be released throughnatural processes. AD exploits this process so that thegas can be used as a fuel. A well-managed AD schemewill aim to maximise methane generation, but notrelease any gas to the atmosphere, thereby reducingoverall emissions.

• AD provides an energy source with no net increase inatmospheric carbon. Using fossil fuels for energyproduction creates carbon dioxide which causesclimate change, resulting in a warming of the planet.By replacing energy from fossil fuels,

Resource PopulationPotential methane yield(m3/day)

Potential annualelectricity output(Twhe/year)

Cattle 12,200,000 5,700,000 6.2

Pigs 7,900,000 800,000 0.9

Poultry 124,000,000 1,000,000 1.1

TOTAL - 8,600,000 9.4


AD can help reduce overall quantities of carbondioxide in the atmosphere and reduce dangers ofclimate change and its potential impacts including sealevel rise, storms, drought and flooding.

Displacing use of finite fossil fuelsThe feedstock for AD is a renewable resource, anddoes not deplete finite fossil fuels. Energy generatedthrough this process can help reduce the demand forfossil fuels (if used to replace energy from fossilfuels). The use of the fibre and liquor as acontribution to fertiliser regimes can in turn reducefossil fuel consumption in the production ofsynthetic fertilisers.

Recycling nutrientsAD products (liquid fertiliser and fibre), if correctlyapplied, can reduce the need for synthetic fertiliserswithin an overall fertiliser programme.

Reducing land and water pollutionPoor disposal of animal slurries can cause land andground water pollution. AD creates an integratedmanagement system which reduces the likelihood ofthis happening, and reduces the likelihood of finesbeing imposed for such pollution.

Reducing demand for peatThe fibre produced by the AD process can be used asa soil conditioner, in some instances as an alternativeto peat (although they are not strictly comparable aspeat is nutrient-free). Peat extraction is a majorenvironmental problem, destroying the fragileecosystems of the peatlands.

Supporting Organic FarmingAD has the potential to support Organic Farming ifused as part of a closed loop (see Box on AD andOrganic Farming).

Reducing odourAD can reduce the odour from farm slurries and foodresidues by up to 80%.

Efficient electricity distributionLocal power generation reduces transmission lossesand can strengthen the grid.

AD and Organic FarmingAnaerobic digestion is the bacterial fermentation of organicmaterial in oxygen free conditions. In this context, organicmeans any plant or animal material that contains carbonand so can be broken down in this way.

This should not be confused with Organic Farming.Although AD could be used within the context of anOrganic Farming system, it is not necessarily the case.

Organic Farming is a production system which is recognisedthroughout the world as one in which the use of fertilisers,in the form of soluble mineral salts, and pesticides isavoided. As far as possible, Organic Farming systems relyon crop rotations, crop residues, animal manures, legumes,green manures, off-farm organic wastes, and aspects ofbiological pest control to maintain soil productivity and tilth,to supply plant nutrients and to control insects, weeds andother pests. In addition, animal husbandry must meet theanimal’s physiological, behavioural and health needs.

Although the fibre and liquor produced as a result of ADare not regarded as artificial fertilisers, they would containresidues (such as artificial pesticides) if the plant and animalwastes being digested had come from a conventionalfarming system.

AD can be used to provide Organic Farmers with soilconditioners and liquid fertilisers if developed within aclosed loop Organic Farming system. However, the greatmajority of the feedstock for AD will come fromconventionally farmed sources and in this case, use of thefibre and liquor can be used as part of an integrated farmmanagement system to reduce the amount of inorganicfertilisers used on the land, but is unlikely to replace themaltogether.

Economic and practicalbenefitsMany of the environmental benefits outlinedabove will translate into economic benefits, andvice versa. AD will have further economic andpractical benefits as outlined below.

Improving farm waste management• Establishing an AD project does not eliminate

wastes, but it can make them easier to manage.Although there are costs, with careful planning andmanagement, AD can be a cost effective, efficientand environmentally sound method of integratedwaste management on farms or food processingplants. However, in any particular circumstancesall options will need to be considered to find themost appropriate method. The options for farmwaste management include composting, aerationsystems, mechanical separation, weeping walls,storage and spreading residues directly on to land.


The merits and problems associated with thedifferent options are described in Appendix 5.

• The AD process stabilises slurries (so they do notputrefy or create odour), which allows them to bestored more easily and for longer.

• Slurry handling costs are reduced because thedigestate liquor is easier to pump than slurry:conventionally, slurry has to be tankered on to theland which can incur contracting costs.

• Costs can be saved by not having to use alternativeforms of residue disposal: spreading raw animalmanures requires heavy plant and machinery andwill often be contracted out, whereas liquor can bespread with existing lightweight farm equipment.

• Farmers supplying feedstock to CAD projects mayfind the treatment burden of residues removedcompletely, which is especially useful to farmerswith little land.

Reducing spread of weeds and diseaseAD destroys virtually all weed seeds, so digestedslurry can be spread with minimal risk of weedspread, reducing the need for costly herbicide andother weed control measures.

Contribution to nutrient regimesThe quality of unprocessed slurries which are spreadon the land can be difficult to manage. After AD thenutrient content of the liquor and the fibre is moreconstant, allowing it to be more precisely usedwithin a fertiliser management system, reducingwastage. AD can therefore reduce fertiliser costswhile making a major contribution to nutrientregimes, provided that applications of inorganicfertiliser are adjusted to take account of the nutrientcontent of the organic fertiliser.

Financial incentivesThere are two aspects to the financial incentives fordeveloping an AD project: firstly in saving costs (seeabove), and, secondly, by converting residues intopotentially saleable products: biogas, soilconditioner, liquid fertiliser. It can also contribute tothe economic viability of farms, by keeping costs andbenefits within the farm if the products are used onsite. In addition, some funding may be available tosupport infrastructure investments (such as gridconnections) for larger CAD developments underEuropean Structural Funds, although this is onlylikely to be relevant where significant social benefitsto the region can be demonstrated.

Biogas and energy• AD can provide an on-site energy source for the

farmer or food processor, displacing theirexisting bought-in electricity.

• Due to Government policy promoting energyfrom renewable sources, and the opening up ofthe electricity market in the UK, the market forelectricity from renewable sources such as AD islikely to grow significantly, and opportunities forAD operators to sell their energy will thereforebe increased.

Local economic development• AD can contribute to rural regeneration by

creating or maintaining jobs; for example, inlocal support businesses, transport and operatingstaff for CAD plants.

• A 1MW plant can create 2 to 5 jobs on the plant,depending on the process used.

• AD can stimulate new industries, creatingstructural changes in the local economy andgenerating further new jobs: for example, fishfarms or local greenhouses may be able to uselocal heat produced by AD projects.

Meeting new regulatory pressuresThere are increasing regulatory and public pressureson farmers and others to ensure that residues aredealt with in new ways which are moreenvironmentally sound, and carry less risk to humanand animal health than traditional methods. UK andEU legislation and regulations are likely to beincreasingly stringent on these issues. Properlymanaged AD schemes will help farmers meet thesepressures.

Reducing pathogensIt is possible that, in future, another significantbenefit of AD could be the reduction of pathogens inresidues; further research is needed in this area. Itshould be noted that heat treatment to 700C isneeded to kill all pathogens.

Potential problemsof ADAnaerobic digestion projects, as with anydevelopment, will create some risks and have somepotential negative environmental impacts. Theseneed to be removed wherever possible, or at leastminimised. The specific potential problems with ADprojects are outlined below.

With good design and proper management ofdigesters, and the appropriate technology in the right


place in the right circumstances, all the potentiallynegative environmental and economic implicationsof AD can be minimised or removed completely.More detail on reducing all these risks and impacts isgiven later in these guidelines.

CostsAD has significant capital and operating costs (see theProject Development section for details). Giventhese, it is unlikely that AD will be financially viableas a source of renewable energy alone and thereforemust always be seen as an integrated system.However, it is likely to be cost effective for thosewho can use (or have or can develop a market for)the other products of AD: better waste management,liquid fertiliser and fibre.

Potential emissionsAD produces certain emissions and effluents, to air,ground and water, which need treatment to avoiddamage to human health and the environment.Proper management should ensure that all these risksare controlled, and the best available technologyshould be used in all cases. See the Construction andOperations section for more details on the risks ofemissions and mitigation.

Traffic movementsAll waste management systems create trafficmovements (lorries already collect food residues)but, although overall quantities of vehiclemovements may not be a major issue, the traffic maybe more concentrated in a small area, especiallywhere a CAD project is established. All ADdevelopments should aim to minimise trafficmovements to reduce potential pollution andnuisance, and alternative methods of transport shouldbe investigated. The energy balance of the ADproject overall will be crucial to its success, not leastin terms of cost, obtaining planning permission andmeeting other regulations. See the Feedstock andproducts section for details on minimising transportimpacts.

NoiseAD projects can generate noise. Consideration needsto be given to potential noise from deliveries,pumps, compressors, the power plant and the overallscheme should be designed to minimise noise. Seethe Project development section for details on design,and the Construction and operations section fordetails on minimising noise from plant operations.

Health and safetyThere may be some risk to human health from thepathogenic content of the feedstock and digestate.

There may also be some risk of fire and explosion,although no greater than with systems using naturalgas. See the Construction and operations section fordetails on minimising these risks.

Animal healthThere may be some risk of animal diseasetransmission between farms in CAD schemes throughcross contamination from vehicle movements andcentralised collection of feedstock. Strict qualitycontrol measures are likely to be needed. See theFeedstock and products section for details onminimising the risks from parasite and pathogentransfer, and Appendix 7.

Visual impactLarger CADs may have some visual impact, althoughthe digester can be partially sunk into the ground toreduce visual impact and make it easier to load.Screening with trees can also reduce the visual impactof AD plants. See the Project development section fordetails of site design.

Animal welfareA potential public concern is likely to be animal welfareissues. AD does not influence the ways in which animalsare housed or kept; it simply uses the by-products oflivestock farming by any methods, from intensively rearedto free range animals. AD is never going to be thedetermining factor for any husbandry method; it will alwaysonly be part of an integrated waste management strategy.It would never be economically feasible for farmers tochange farming practices to maximise the production offeedstock for AD and worsen conditions for animals as aresult.


Deciding todevelop anAD projectAny decision to establish an AD project will bebased on an assessment by the farmer or developerof the marginal increased costs (if any) set againstthe additional benefits and opportunities created.AD will generally be a more expensive capitaloption for farmers (or food producers) seekingsolutions to their residue and/or pollution problemsthan alternative waste management solutions.Financial and other costs are covered in detail inthe Project development section but, in summary,include:

• Capital costs in establishing a digester

• On-going maintenance and replacement costs

• Obtaining planning permission and adhering toother regulatory frameworks

• Training for operators.

The decision to establish an AD project dealing withfarm residues is likely to be based on answering thequestions:

• Do the extra benefits from the process and theopportunities for possible increased incomestreams warrant spending the extra (marginal)investment

• Do I have the time, inclination and necessary skillsto consider it as a viable option?

More specifically, the decision process for a farmer orfood processor on whether a ‘stand-alone’ AD plantwill be viable for their business, or whether theyshould consider other options (includingparticipating in a CAD project), is likely to includethe following questions:

• What capacity plant would I require to process myfeedstock?

• What are the marginal costs for me to consider anAD plant?

• What return would I want to consider this extrainvestment?

• Can I adequately utilise the liquor produced? Howmuch land do I have access to?

• Can I utilise the energy produced within my farmbusiness? What is the value of this to me?

• What price can I get for the energy if I sell it?

• Is there a shortfall between the value of the energyproduced and the return I require?

• Can I make up this shortfall from reduced operatingcosts, increased yields, sales of compost, incomefrom handling other farm or food processingresidues?

If a farmer or food processor cannot show a surplusfrom this process, a stand-alone plant would not beappropriate and they could then consider the benefitsof co-operating on a CAD plant, or other options forwaste management. All these issues are considered inthe Project Development section of these guidelines.A case study of Walford College AD project,including detailed costings, is given in Appendix 8.


ConsultationAs with any new development, establishing an AD plant will require consultation with statutory and non-statutorybodies, local communities and near neighbours to discuss concerns, share information and adapt proposals to takeinto account particular worries. The extent to which formal consultation is required will depend on the scale ofthe proposed development: a small on-farm digester is likely to be affected by fewer regulations and generatefewer anxieties than a CAD plant.

Visitors to a farm AD plant (Photo: ETSU)


Statutory and non-statutory consulteesThe bodies which are consulted will depend on the scale, location andnature of the proposal. However, it would be good practice to considerwhich of the following bodies are likely to have an interest in, or be affectedby, the digester and its operations and consult them at an early stage. This isby no means an exhaustive list, and may be extended to include specificlocal organisations, or additional organisations relevant to particular localcircumstances.Within local governmentWithin local governmentWithin local governmentWithin local governmentDifferent departments within the local authority may require consultation.Some of these may require consultation across the boundaries of theresponsibilities of county and district authorities, or may be within a unitaryauthority:• Planning (Policy, Economic Development)

Under the Town and Country Planning (Assessment of EnvironmentalEffects) Regulations 1988, the local planning authority is required to consultthe following bodies when an environmental statement is produced:a) any body which the local planning authority would be required byarticle 15 of the General Development Order (amended by SI 1986/435),or any direction under that article, to consultb) the following bodies if not included in paragraph (a):i) any principal council for the area where the land is situated, if not thelocal planning authority (including consultation of the county council by thedistrict council)ii) the Countryside Commission (or Countryside Council for Wales,or Scottish Natural Heritage)iii) English Nature (formerly the Nature Conservancy Council)iv) the Environment Agency (formerly HMIP, NRA and wasteregulation authorities).Environmental Health• Engineer/Technical Services/Building Regulations• Highways• Waste Disposal• Minerals• Archaeology• Environment/Countryside Management/Wildlife Conservation• County Fire OfficerOther consulteesIt will be appropriate, depending on the size and nature of the scheme, toconsult with a range of other consultees. The following sample list is notexhaustive:• Government Office (generally, when a major scheme is proposed;

Department of Transport/Highways Agency if a trunk road is affected)• Town and Parish councils• Regional/local water company• English Heritage• Local amenity groups (eg preservation group, wildlife/naturalist trust, town

society)• Local environmental groups (eg Friends of the Earth local groups)• Local community and residents groups• Ramblers Association, for proposals which affect a public right of way• British Gas, British Telecom or other telecom company or Railtrack if near

one of their installations, land or equipment• Civil Aviation Authority or Ministry of Defence, for major proposals in

close proximity to a civil airport or military installation• The Royal Society for the Protection of Birds (RSPB) regional office• The county wildlife trust

Almost all digesters are likely to needplanning permission, which will involveformal public consultation as well asdiscussions with the planning authority.Planning permission is covered in detailin the Project development section.Consultations with the EnvironmentAgency, as the agency responsible forwaste management and control ofpollution, are also likely to be needed.Advice on health and safety issues isavailable from the Health and SafetyExecutive (HSE).

Issues that may arise, for all plants, includeconcerns about visual impact, odour,transport implications, environmentalimpact and health; many of these issuesare dealt with in these guidelines. Page 53gives a summary of the key facts about ADand has been designed to be copied anddistributed to interested parties.

The remainder of this section providesgeneral guidelines on consultation whichshould be useful in projects of all sizes,although the extent to which they will allneed to be used will vary.

TimingEarly consultation is particularly importantin AD projects as they are relatively new inthe UK. Most people will know little aboutthe visual appearance of a plant or thepotential impact it may have on localpeople and the environment. Earlyinformation to local people on all aspectsof AD, as well as quick responses toparticular concerns, will help people feelconfident about this new industry in theirarea. Local people will welcome theopportunity to comment at an early stage.

Early consultation with statutoryconservation agencies over locations fordigesters may also be helpful. Thesestatutory agencies are used to dealing withinformal consultations in confidence.

Consultation should continue throughoutthe development stages of a scheme, andwill need to cover all aspects including thedesign and management, construction andoperation of the digester, andtransportation of the feedstock. To someextent, consultation can be structuredalongside the process of obtaining formalplanning permission for the digester, butmay need to be extended.


Who to consult?People who live and work in the immediate vicinity ofthe proposed scheme, the parish or community council,specific local interest groups and statutory agencies areall likely to have an interest in the development of an ADscheme. The project leaders for the development willneed to identify all the likely areas of concern andinvolve interested groups at the most appropriate stages.Different stakeholders will have concerns about differentaspects of the project. A sample list of statutory andnon-statutory consultees is given opposite.

Whose responsibility?For large CAD schemes, the developer will usually haveoverall responsibility for managing the consultationprocess. However, the farmer setting up a small on-farm digester, or farmers supplying feedstock to a CADwill also want to manage their activities in a mannerwhich is sensitive to the environment, health and safetyand other local concerns, and may become involved inconsultation processes. Even where the digester is a co-operative community project, run by local people, therewill still be a need for wide consultation andinvolvement.

Preparing for consultationConsultation needs to be planned and integrated into theoverall development process. The following steps mayhelp to maximise the effectiveness of consultation andenable the developer or farmer to address any concernsthat arise:

• Developers should analyse the community, orcommunities, that might have an interest (stakeholderanalysis). Information will also be needed on localissues that may be relevant. This will enable developersto prepare their consultation and communicationsstrategy.

• AD is a relatively new industry and it may beappropriate to produce information for local peopleabout the nature of the industry and the specific localdevelopment, what it will look like and the impact andbenefits it will have (see page 53).

• Consultation needs to start as early as possible in theplanning and design stage. It needs to be planned, butalso be flexible enough to meet the needs of changingcircumstances.

• Honesty, openness and commitment toconsultation are essential. Although developers wouldnot be expected to resolve all concerns expressed, theyshould always respond to concerns. If somethingcannot be altered, a clear explanation of the reasonsshould be provided.

Consultation methodsA number of consultation methods may be used,depending on local circumstances such as theparticular needs of the community and otherinterested organisations and the scale of theproject. These might include:

• eaflets outlining proposals and invitingcomments

• Exhibitions

• Open days, and visits to similar sites already inexistence

• Public meetings

• Questionnaires

• Special meetings for key local organisations(such as parish councils)

• Workshops for mixed groups of stakeholders toconsider particular issues.

Any printed materials produced should alwaysinclude a contact name, address and telephonenumber so that local people can ask questions andcomment on proposed developments.Consultation is a two-way process and channelsmust be kept open.

Liaison should continue after plant construction iscompleted. For example:

• Visitors to the farm, digester or CAD: localgroups and others may be interested in visits.

• Links may be made to the environmentalprogrammes of local schools.

• A liaison forum could be established betweenthe developer, the local authority and localcommunities, building on contacts made duringthe development stages. This could be linked toformal and informal monitoring, which may berequired in any case under the conditions of theplanning permission.


Feedstock comes from cattle slurry, chicken litter, pig waste and food processing residues (Photo: ETSU)

Feedstock andproductsThis section covers the main issues relating to feedstock for, and products from, anaerobic digestion, includingchoice of feedstock, maintaining quantity and quality control, storage and transport. The nature and potential usesof products are also covered.


WhichWhichWhichWhichfeedstocks?feedstocks?feedstocks?feedstocks?The focus of these guidelines is anaerobic digestionusing farm residues and food processing residues. Theseinclude residues from:

• Cattle and pigs (manure and slurry)

• Poultry manure (with or without litter)

• Vegetable processing residues (eg from potatoes, sugarbeet)

• Silage effluent

• Dairy processing residues (eg cheese and yoghurtprocessing).

CAD schemes may use additional feedstocks tosupplement the above residues. The content of anyimported feedstock will require careful assessment as itwill affect the nature of emissions and outputs.Feedstocks for CAD schemes may also include:

• Brewery residues

• Fish oil and fish processing residues

• Bleaching clay (from the paper-making and textileindustries)

• Milk processing residues (eg whey and bioplantsludges)

• Crushed oil waste (eg rape and sunflower seed).

An environmental assessment should identify the impactof the use of different feedstocks. Materials in additionto those listed above may be used as feedstock for ADbut are not covered by these guidelines because they arecovered by different licensing arrangements andregulations; these include sewage sludge and municipalsolid waste.

It is essential that toxic substances are minimised infeedstock, and certain materials should never be fed todigesters because they will arrest or kill the process.These include:

• Toxic materials that inhibit digestion (eg highammonia levels, pesticide residues, sheep dip, heavymetals, oil)

• Bioagents (aflatoxins, antibiotics)

• Disinfectants (eg creosol, phenol, arsenic).

Long straw and non-biodegradable materials should beavoided as they can cause blockages in the system.

Quantity andQuantity andQuantity andQuantity andquality ofquality ofquality ofquality offeedstockfeedstockfeedstockfeedstockThe main aim of managing the quantity andquality of feedstock for the digester is tomaximise the quality and quantity of the outputs,and therefore the economic and environmentalbenefits from the feedstock. Different prioritiesfor outputs will affect the quality criteria for thefeedstock.

For example:

• To maximise gas yields, the key factors will beorganic matter content and the percentage ofdry matter (5-12.5% maximum of feedstockshould be dry/solid waste). Different feedstocksproduce different amounts of gas: 1 tonne ofcattle manure will not produce the same as 1tonne of chicken manure. The gas productionperformance of different feedstocks will vary, asshown in Table 2.

• If the main objective of the project is wastemanagement, the main criterion will be to avoidanything which may arrest or kill the process.

The amount of different feedstocks which areneeded at different times depends on whichproducts are a priority. There are two keyprinciples related to the quantity of feedstockrequired for digesters:

• Whichever product is chosen as the priority(biogas, liquor or fibre), the others will beaffected. A balance will always need to besought because it is only through producing allthree products that the digester is likely to beviable: one product alone will not generatesufficient income.

• Summer top-ups may be needed for when stockare outside, and mixtures might have to change.Alternatively, an on-farm digester can beallowed to become dormant.

If there is a problem with the digester, caused byquality failures or a break in the continuity


TABLE 2

Biogas production and energy outputpotential from 1 tonne of various fresh feedstocks

FeedstockNo of animals toproduce 1tonne/day

Dry matter contentBiogas yield(m3/tonnefeedstock)

Energy value(MJ/m3 biogas)

Cattle slurry 20 – 40 12 25 23 – 25

Pig slurry 250 – 300 9 26 21 – 25

Laying hen litter 8,000 – 9,000 30 90 – 150 23 – 27

Broiler manure 10,000 – 15,000 60 50 – 100 21 – 23

Food processingwaste

- 15 46 21 – 25

Notes.

1 Figures should be taken as indicative values

2 Cattle slurry covers both dairy and beef cattle

3 Poultry manures are highly susceptible to ageing andshould be used as fresh as possible

4 1m3 of biogas (at an assumed 20MJ/m3) would typicallygive the following:

• electricity only: 1.7 kWh of electricity (assumedconversion efficiency 30%)

• heat only: 2.5 kWh of heat (assumed conversionefficiency 70%)

• combined heat and power: 1.7 kWh of electricity and 2kWh heat

of the feedstock supply, it can be rested. Forexample, a dairy farmer may be able to keep thedigester going at full capacity during winter monthswhile cows are in sheds, and ticking over in summerwith slurry collected from the yard when the cowsare outside. Alternatively, if the digester is not fed itwill simply slow down. To ensure the regularity ofsupply of products, it is cost-effective to have thedigester working all year, but if the demand forproducts is also seasonal, the digester can be allowedto become dormant.

Different feedstocks will require different loadingsystems, depending on the consistency of thefeedstock (ie how solid or liquid it is). Examples ofpre-treatments include:

• Screening for foreign matter (eg bricks, sand, gritand long straw).

• Adding water, or taking water out. In general, it isnot advisable to add water as the more water thereis in the feedstock, the more energy is needed forthe process; however, some water may need to beadded to ensure the feedstock is the rightconsistency.

• Conditioning the waste (eg chopping straw),although the equipment for this can be expensive.

• Stirring the feedstocks.

The quality of the feedstock in terms of its gas yieldwill partly depend on its freshness: the fresher it isthe higher the gas yield will be and the less dangerthere is of it becoming acidic. An acidic feedstockmay inhibit or even kill the bacteria in the digester.Ideally, the pH range in the digester should be 6.8 -8.

Even though AD is by and large a robust processwhich can adjust to slow changes, drastic changes offeedstock should be avoided and the operator must


be diligent in monitoring the input and mix itaccording to the products required. Every digester isunique in terms of the feedstock used, and it willchange over time; during the life of a plant it is likelythat the feedstock will change several times.

An on-farm scheme will have less problem managingthe quality of the feedstock because the operator willcontrol the farm’s own wastes. Some screening can bedone by farmers using natural techniques of settlementand drainage. A co-operative would need to appoint amember with the appropriate knowledge andexperience to take responsibility for monitoring qualitycontrol.

A CAD scheme will require a formal quality control andassurance system, as there will be a risk of cross-contamination which could affect operations.Therefore, CAD plants are likely to provide farmers andother suppliers with detailed contracts andspecifications of the appropriate content for feedstock,and any feedstock which fails to meet the specificationis likely to be rejected. Certainly, if one of thesupplying farms has a notifiable disease in its livestock,it could both contaminate the plant and be passed on toother supplying farms: obviously, suppliers in thesecircumstances must never take feedstock to the CAD.

It is good practice to test feedstock before processing, aswell as the resulting products. Larger CAD plants arelikely to need on-site laboratory facilities to testfeedstock before processing for elements which maycontaminate or arrest the digestion process. It may alsobe necessary to check for moisture loads and for healthand safety reasons. After processing, such facilities arelikely to be needed to check the quality and safety ofproducts. Holding facilities may be needed to storefeedstock, check it and then pass it on for processing ordistribution.

Planning permission may be given to a schemespecifying a certain feedstock and in thesecircumstances the feedstock will not be able to bechanged without the further prior approval of theplanning authority. A CAD plant will need to belicensed under the Waste Management LicensingRegulations 1994 if it imports industrial waste (ie foodprocessing residues). The subsequent disposal of liquorby spreading on agricultural land becomes an activitythat requires pre-notification to the local EnvironmentAgency office. Neither of these controls applies to ADplants treating or spreading digestate sourced from theirown animals and returned to their own land.

Parasites and pathogens infeedstockFeedstock for AD inevitably contains plant or animalpathogens (such as Salmonella) and parasites (suchas Cryptosporidium) to different degrees in differentmaterials, which can be a danger to human andanimal health. Precautions are therefore needed inAD projects, especially in CAD projects whichinvolve transporting residues from various sourcesto a central point, which could lead to cross-contamination unless appropriate preventativemeasures are taken.

Mesophilic anaerobic digestion will reducepathogenic organisms and bacteria, but will noteliminate them from the waste. Thermophilicdigestion will further reduce the levels, but againcannot guarantee total removal. Pasteurisation(holding the waste at 700C for 30 minutes, or forlonger at a lower temperature eg 550C for fourhours) is the only method which will ensure thecomplete elimination of pathogens. It should benoted that pasteurisation may affect the energybalance: the hotter and quicker the pasteurisation,the more energy is used.

As neither mesophilic or thermophilic digestion islikely to totally eliminate the pathogens in thefeedstock, considerable care is needed. In somecases, depending on the initial quantity of pathogensin the feedstock, levels of pathogens after AD willstill be high enough to cause ill health for thoseworking with the feedstock before and aftertreatment, and for those who may come into contactwith the treated feedstock. For those occupationallyexposed, the employer’s COSHH assessment shouldindicate the level of risk and the measures that willbe put into place to control it. This is a complexarea in which research is continuing. Further detailsare given in Appendix 7 about the effects ofdifferent AD processes on parasites and pathogens.Advice is available from the Health and SafetyExecutive (HSE).


Storage ofStorage ofStorage ofStorage offeedstockfeedstockfeedstockfeedstockCAD plants will require access to up to severalhundred tonnes of feedstock at any time, soextensive storage facilities are likely to be needed toensure continuity of supply over weekends (whentraffic movements may be controlled) and holidays.Ten days is likely to be the maximum storage periodfor a CAD plant as, in general, feedstock should beused as soon as possible. Feedstock providers maybe required to take the liquor back, which will alsohave storage implications.The storage of farm slurry is covered by the Control ofPollution (Silage, Slurry and Agricultural Fuel Oil)Regulations 1991, which specify minimum standardsrelating to the design, construction and operation ofany farm slurry storage system. The regulationsrequire the store to be big enough to hold at least fourmonths slurry production unless a safe year-rounddisposal system is ‘approved’ by the EnvironmentAgency. The production of a Farm WasteManagement Plan which includes details on feedstockstorage, digester operation and liquor spreading(including locations, rates and times of year) wouldnormally be considered an acceptable alternative tothe four month rule. Further information is availablefrom the local Environment Agency office.Feedstock may be stored near the digester orelsewhere, although the need to minimise transportmovements will affect the decision on siting storage.Feedstock needs appropriate storage facilities whichmust be planned in accordance with environmental,health and safety issues and regulations. It may benecessary to balance the planning requirements (suchas for feedstock to be stored in a totally enclosed spacewith tank covers to reduce the escape of odour), withhealth and safety regulations (that substances arecontrolled so that there is no exposure to substanceshazardous to health).Methane continues to be produced from the digestatein storage. Up to 15% of usable gas, from the totalthat can be obtained from the feedstock, can berecovered from slurry storage tanks. It is possible toextract the gas given off the stored feedstock, and thenflare it or draw it into the combustion chambers of anengine.

Transport ofTransport ofTransport ofTransport offeedstockfeedstockfeedstockfeedstockTransport movements at on-farm digesters are notlikely to have greater impact than normal farmactivities. However, CAD plants will draw trafficto their central location as feedstock is deliveredand products are distributed. The impact of thesetransport movements needs to be minimisedthrough logistics and use of alternative methods oftransport (such as rail), as well as careful design ofthe location of storage tanks so that distancestravelled are minimised between the production ofthe feedstock, the storage tanks and the digester.The potential for pumping (suitable for pig slurry)should be investigated for cost and environmentalreasons, including reducing emissions and reducingthe need for transport.Where vehicles are moving onto and around a site,it will be important to have a system to controlrisks, with turning areas, one-way systems,pedestrian walkways, barriers and so on.

Other issues in transporting feedstock are likely toinclude those outlined below.

Planning restrictionsThe conditions of any planning permission mayrestrict deliveries to a CAD plant. These restrictionsmay result in some farmers having to store thefeedstock on their farms. There may also be otherplanning conditions or obligations (agreements):

• Data and monitoring on the frequency of lorrymovements may be required.

• An assessment of the suitability of certain roads forthis traffic is likely to be needed. CAD developersshould be encouraged to site plants in areas alreadyserved by appropriate infrastructure such asindustrial estates, which may also have the benefitof being away from residential areas, in order toavoid the need to upgrade roads, with all the costand environmental impacts that would create.Where roads are not considered suitable, thedeveloper of the CAD plant may be expected tocontribute to the costs of upgrading them.


Figure 3.

Transport movements

NoteSupermarket vehicle deliveries taken from Goodwin et al.Transport Studies Unit University of Oxford

• Specification of routes may be required, for exampleavoiding villages.

• There may be a requirement that open-topped vehiclesare sheeted. Chicken wastes are normally moved insheeted open-topped lorries. Pig and cattle slurry isusually moved in enclosed tankers.

• There are likely to be restrictions on timing ofdeliveries to reduce noise nuisance to neighbours. Forexample, deliveries may only be allowed Monday toFriday (7am to 7pm) and Saturday morning (7am to1pm).

EmissionsDelivery vehicles using conventional fossil fuels willproduce carbon dioxide and other emissions, anddeplete non-renewable resources. Fuel efficient vehiclesshould be used. The energy required to transportfeedstock and products needs to be balanced against theenergy yielded from the AD process. This element ofthe energy balance requires further investigation. Thenegative nature of the consumption of fossil fuels can bepartly avoided by using vehicles which run on thebiogas produced by AD (once it has been cleaned),

although this technology is still in the early stagesof development.

Catchment areaGenerally speaking, it is financially viable totransport chicken and broiler waste transportedup to 40km, thick cattle slurry 15 - 20km, andpig slurry only

5 - 10km because it is more liquid. A number ofplants pump pig slurry to avoid the need fortransport and reduce the risk of spreading disease:a maximum of 6km has been achieved.

CostThe unpleasantness of the load may increase thecost of transport and handling. Specialistcontractors, who may need to use dedicatedvehicles, will be able to provide an appropriatetransport service and will be aware of the natureof the loads.

Business considerationsThe whole project can become uneconomicunless transport movements (and thereforetransport costs) are minimised. Transport costscan make the difference between the success ofone scheme and the failure of another.


Handling feedstockFarmers are likely to be aware of the dangers of diseasefrom farm residues, although lorry drivers and otherworkers may need special training to avoid health risksto themselves as well as the risk of spreading infection toother sites. The main health and safety risks are:

• Pathogenic micro-organisms

• Parasites

• Fumes and inhalation of slurry gases.

These dangers can be reduced by taking precautionsincluding:

• Using known and reliable sources of feedstock.

• Analysing feedstock and careful quality control.

• Monitoring and screening for disease in the animalscreating the feedstock.

• Personal hygiene ie washing people, clothes andvehicles; it is also recommended that work clothing isleft at the CAD site.

All material going in or out of a CAD scheme will needstrict controls to avoid pathogen transfer including:

• Being able to isolate the site.

• Vehicle wheel washing is likely to be compulsory atCAD plants and desirable for farms, to avoid cross-infection. Disposal of contaminated wash water needsto be considered.

• Liquid leaving the site needs to be carefully contained;fibre must be exported in covered lorries.

Figure 4.

Anaerobic digestion mass balance

ProductsProductsProductsProductsof ADof ADof ADof ADThe AD process creates biogas, fibre and liquor.In order for a scheme is to be financially viableoverall, markets and/or uses for all AD productsneed to be developed and balanced.Consistency of supply, and of quality, as well asincreasing public knowledge of theenvironmental advantages of AD products, willinfluence the growth and development ofmarkets.

The balance of the different products from AD isshown in Figure 4.

BiogasThe biogas produced in the digester is primarilycomposed of methane (approximately 60%) andcarbon dioxide (approximately 40%), with tracesof hydrogen sulphide and ammonia. The qualityof the feedstock used in the digester willdetermine how much gas is produced and itsconstituents.

Cleaning the gas

The biogas produced through the AD processusually needs to be cleaned to varying degrees assoon as possible after generation for two mainreasons:

• The gas is corrosive and may damage engines.

• For health and safety reasons (see Constructionand operations section for the health and safetyimplications of biogas); a risk assessment may

be needed.


Alternatively, zoning can be used to exclude peoplefrom areas which may have health and safety risks. Ingeneral, it would be unwise to burn ‘as produced’ gasanywhere other than in an engine to produce electricityor in a boiler to produce heat.

There are many different ways of cleaning the gas. Thebest advice is to choose the appropriate equipment,consult the manufacturer as to the best methods forspecific plant requirements, and ensure that anyoneusing it is fully trained to operate it efficiently.

Using the biogasUp to one third of the biogas energy will be needed tosustain the heat in the digester; the remaining two-thirds will be surplus and can be put to various uses:

• The gas can be burned to generate heat, either on siteor piped elsewhere. Small AD units are likely toproduce heat only. The gas can be used for cooking(using safe equipment), to heat the farmhouse, dairyor other nearby buildings, without any need to convertit to electricity. However, contaminants in the gasmay restrict its use for any purpose other thanelectricity generation unless it is cleaned.

• The gas can be used as fuel for an engine connected toa generator to produce electricity which can then beused on site, marketed to the grid and to othernetworks. Details on the planning permissionsneeded, and on electricity connection, are given in theProject Development section of these guidelines.

• If a combined heat and power (CHP) plant is used, allgas will be consumed to provide both electricity andheat. This is a more efficient use of the availableenergy; the whole digester heat requirement isnormally provided from the heat recovered from theengine and exhaust gas.

• The biogas is of a lower calorific value than natural gasand it would generally not be cost effective to storelarge volumes on site. However, the value ofelectricity produced may be enhanced if small volumesof gas are stored overnight (4 - 8 hours) and used forgeneration at peak demand times during the day.

• It is also possible to use the gas (if carbon dioxide isremoved through the use of water towers, and the gasis compressed), to run motor vehicle engines, whichwould need to be converted to use the gas. Theprocesses to clean and compress the gas for thispurpose, and the conversion of the vehicles, areexpensive, but may become more viable in future.

Electricity from renewable resources will continue to bea growth market. Currently, the Non-Fossil FuelObligation (NFFO) requires regional electricity

companies to purchase a certain amount of energyfrom renewable sources, and NFFO contracts ofup to 15 years, offering premium rates, may beawarded to suppliers. There are currently (1997)seven NFFO contracts for energy from AD which,if all are built, will provide a total of 7MWcapacity. There are also increasing opportunitiesoutside NFFO to sell energy from renewableresources to a growing niche market as energymarkets are liberalised.

DigestateThe digestate which remains after the gas hasbeen removed is pumped to a storage tank, afterwhich it can be spread directly on to the land.However, this digestate can only be consideredpartially treated at this stage, and should be storedready for applying to the farm land at theappropriate rate (see MAFF Code of GoodAgricultural Practice for the Protection of Water,as well as specific guidelines in Nitrate SensitiveAreas and Nitrate Vulnerable Zones). It may benecessary to consult the Environment Agency.Alternatively, the digestate can be separated intofibre and liquor.

FibreThe fibre produced from AD is bulky and containsa low level of plant nutrients. It can be used as asoil conditioner, and the most efficient use for thefibre is to return it directly to the land locally.This is much easier to do after processing thanconventional land-spreading as spreading the fibrerequires much less power and can be done using asmall tractor rather than specialised equipment. Itis also much less offensive to neighbours, havingno odour after digestion.

AD fibre can be used to condition the soil, and asa low grade fertiliser. In some cases the fibrefrom AD can be used as an alternative to peat,although it does not have exactly the samepurpose as peat (which is nutrient-free). Apossible strategy for increasing the value of thefibre is to further compost it aerobically afterprocessing to produce a pottingcompost/growing medium. This process can bespeeded up through careful management andcontrol such as adding heat or insulating thecomposting bins. However, market developmentis required to make the commercial sale of fibreviable on any large scale. For any sale of fibre,access to local markets is crucial as it would not beeconomically viable or environmentally sound totransport it long distances.


Storage facilities will be needed for the processed fibre.The market is seasonal, so storage could be needed forup to six months output. Stored fibre will continue tocompost aerobically, so it will need to be carefullymanaged and controlled, using methods such asstabilising through further composting. Fibre needs tobe stored under cover to prevent rainwater getting in.Flies may also be a problem around stored fibre, sositing the storage facilities will need to take that intoaccount.

LiquorThe liquid from the AD process has a low level butdiverse range of nutrients. It can be used as a liquidfertiliser in a planned fertiliser regime. As it has a highwater content, the liquor also has irrigation benefits, soit can be used for ‘fertigation’ on agricultural land.However, as it contains particles, it should not be usedfor fertigation in greenhouses because it can blockfeeder pipes if not separated effectively.

The liquor is generally used on the farms on which itwas produced. A potentially wider market has yet to befully developed, although some AD schemes havesuccessfully bottled and sold the liquor as a liquidfertiliser.

Spreading and application methods for the liquordepend on the type of crop being grown. As with anyfertiliser containing nitrogen, the liquor should only beused on actively growing crops, in certain locations andon certain types of soil. Liquor from the AD processshould be used or disposed of in a way which preventsexcess run-off to underground or surface waters.Production of a Farm Waste Management Plan willassess and devise pollution prevention measures, inaccordance with MAFF Codes of Good AgriculturalPractice for the Protection of Water and Soil.

The liquor should be applied as part of anintegrated fertiliser programme to ensure that theoptimum nutrient requirements for the crop aresupplied. It is good practice for the farmer oroperator to regularly analyse the soil, and the ADliquor, to assess the appropriate application rate,and to quantify the amount of chemical fertiliserto be applied to crops and grassland. Overapplication causes vegetation scorching.

Liquor can be stored on the farm, or at the CADplant. Once cooled, it can be stored in lagoons orlarge tanks. If possible, these should be locatedadjacent to the areas where the liquid will beapplied. These containers will need to beconstructed to meet HSE and planningregulations. Some liquid storage facilities mayneed bunding around storage silos; bunding willcertainly be required on CAD sites. While it isstill warm, the liquor will continue to producesmall amounts of methane.

Once stored, the sediment in the liquor will settle,so it will need to be stirred or agitated to ensureuniformity throughout before application ortransporting. If bulk transport is needed fromCAD plants, it is possible to use the same tankerswhich have delivered feedstock to export theliquor, although they would need to bethoroughly cleaned in between to avoid cross-contamination (this would have energyimplications, and care would need to be takenover the disposal of any wash water). As theliquor is pumpable, where appropriate it shouldbe pumped away from the process plant to longterm storage sites.

Liquor (gms/100 litres) Fibre (% of dry matter)

Nitrogen 800 3

Phosphate 500 4

Potash 500 2

TABLE 3.NUTRIENT ANALYSIS OF THE FIBRE AND LIQUOR FROM THE AD OF FARM SLURRY/MANURE

NOTES:

1 FIGURES ARE NOT FOR ELEMENTAL MASS BUT MASS OF COMPOUNDS OF NITROGEN, PHOSPHATE AND POTASH.

2 THE FIBRE AND LIQUOR ALSO CONTAIN TRACE ELEMENTS INCLUDING MAGNESIUM, MANGANESE, SULPHUR, CALCIUM, ZINC,COPPER, BORON AND SODIUM.

THERE IS CONSIDERABLE SCOPE FOR INCREASING NITROGEN LEVELS IN FINAL LIQUOR OR CHANGING THE BALANCE OF FINAL EFFLUENT

NITROGEN, PHOSPHATE AND POTASH RATIONS BY MANIPULATING FEEDSTOCK SOURCES IN LARGER DIGESTERS


Digester under construction (Photo: WRI Services)

ProjectdevelopmentThis section covers all the main issues for developing an AD project from assessing feasibility to designing thefacility. Site and location, environmental assessment and obtaining planning permission are also covered. Theprinciples of this section will apply to all schemes, although the extent to which all the guidelines need to be appliedwill depend on the scale of the project. For smaller scale projects, many of the impacts will be less and the issuesmore easily dealt with.


FeasibilityFeasibilityFeasibilityFeasibilityThe development of an AD project, either on-farm oras a CAD scheme, is not a simple process, and thestarting point depends on the motivation of thedeveloper. For example, it may be a farmer or a foodprocessing company needing a solution to the problemof waste disposal, or to take up an opportunity tosupply a CAD scheme, or a local authority energyteam wanting to develop a community CAD scheme asa local source of renewable energy. The first stage istherefore likely to be a mixture of decisions aboutscale, products and markets, feedstock availability andtechnology (see Figure 2).

A technical feasibility study will be needed, although thecomplexity and cost of this will depend on the scale ofthe scheme. Even a small on-farm AD project, with allfeedstock being supplied by the farm itself and all theproducts used on the farm, will need some calculationsas to the continuous availability of feedstock, thequantities of the products and the opportunity to usethem. A large scale scheme is likely to need a detailedformal plan covering all key issues which can be used toraise finance.

There are six factors which will typically determine theeconomic feasibility of any scheme:

• Type and quantity of feedstock available, andsecurity of supply.

• A sustainable outlet for the liquor: the potential forthe land application of the liquor is likely to be themain constraint on the size of the plant, in order tomeet local standards (especially in a NitrateVulnerable Zone or similarly controlled area).

• There are outlets, or uses, for the fibre; all productsmust be used if the scheme is to be viable.

• There are outlets, or uses, for the biogas as heatand/or electricity.

• The size and location of the plant, if using thebiogas for electricity production, will need to beconsidered as this will affect planning and gridconnection restrictions and costs.

• Transport costs and logistics.

All schemes should seek expert advice, on costs andpotential income, from local energy teams, agriculturalbusiness advisers, suppliers of equipment, electricitysupply companies who might buy the electricity

generated, British Biogen and others with experience ofestablishing and running AD projects.

A case study of Walford College’s AD project is inAppendix 8, including detailed costings.


EconomicsEconomicsEconomicsEconomicsCostsThe main financial costs of establishing an AD projectare likely to include capital costs, project developmentcosts and training costs.

Capital costsThe equipment has to be manufactured to a highstandard to prevent corrosion, and the resulting highcapital costs may only be justified if the equipment has along active life. In this respect, a digester may beregarded more as a mortgageable infrastructural projectlike a house than a piece of equipment like a tractor.Construction of the plant and associated site works,including any landscaping required under planningpermission, will also incur costs.

The capital costs for an AD plant will vary between£3,000 to £7,000 per kWe of electricity generatingcapacity. For example:

• A small digester of 10kWe capacity, using residuesfrom 100 head of cattle or 1000 pigs (requiring adigester with a capacity of 150 m3 ), is likely to cost£60,000 to £70,000.

• A CAD plant of 1MWe capacity (requiring a digesterwith a capacity of 10,000 m3 ) is likely to cost £3million to £4 million.

Project development costsThese can be very significant and may include:

• Technical, legal and planning consultants’ fees, andthe farmer or developer’s own time, in negotiationswith legal and statutory bodies (for example inobtaining planning permission and consulting theEnvironment Agency)

• Financing and legal costs, including the costs ofarranging finance

• Electrical connection costs

• Costs of licences (for example, if imported foodprocessing residues are used, a Waste ManagementLicence will be required, which will involve aninitial charge and an annual fee)

Running costsThe running costs vary enormously depending

on variations in design and operating circumstances.They are likely to be in the order of

£7,000 - £10,000 per year for an on-farm project, or upto £100,000 per year for a CAD project. Running costswill include:

• Staff costs: management of an on-farm digester withpower generating equipment is likely to require twostaff days per week

• Insurance

• Transport costs

• Annual fees for licenses and pollution controlmeasures

• Other maintenance and operating costs.

Training costsThe people who run AD projects, of whatever size, needto be fully trained in the safety, financial andenvironmental implications of the project. These skillswill need to be updated as technology and knowledgedevelop.

Income

The largest revenue streams from AD are likely to befrom electricity (including avoided cost and sales) andfibre sales. Markets for all the products will need to bedeveloped and balanced for the project to beeconomically viable. The way the project developsdepends on the priority product for the developer (thatis, energy, fibre or liquor), which will have implicationsfor the technology which should be chosen.

In summary, income streams are likely to include:

• Electricity sales (or displaced purchases); energyfrom renewable sources is likely to continue tocommand premium rates

• Heat sales (or displaced purchases)

• Fibre sales (or displaced fertiliser costs)

• Liquor sales (or displaced fertiliser costs)

• Gate fees: charges made for processing wastes (thismainly applies to CAD projects using foodprocessing wastes; gate fees are increasing ascharges for alternative waste management methods,such as landfill taxes, also increase)

• Savings on slurry handling and other wastemanagement costs.

It is important for all those involved in the industry tobe in touch with the relevant networks so they are awareof the latest market developments. British Biogen is agood first point of contact.

Financing the projectAn AD scheme, whether single farm or CAD, willrequire a large amount of capital investment and, inmost cases, developers will require finance from anexternal source.

There are two types of loan: those secured against thedeveloper’s existing assets (on-balance sheet financing),


and those secured against future cash flows (limitedrecourse project financing). Most farmers andcommercial developers will be familiar with these andbe able to make an informed decision about which is thebest route to follow, although the decision may be madefor them by the lending bank. It is unlikely that a lenderwill finance 100% of a project’s costs. Between 20% -40% may have to be funded by the developer.

The maximum amount of money that a local clearingbank might be expected to lend is about £200,000. Thislevel of loan would be sufficient for a single farm AD orvery small CAD. Investment banks usually have aminimum level of investment of about £2 million, and aminimum loan arrangement fee which can be as high as£100,000. There is therefore a financing gap intowhich many projects may fall, and these developers mayfind great difficulty in raising finance.

Traditional investors do not recognise the environmentalbenefits and sustainability of AD and view it in the sameway as any other high-risk commercial project,demanding high security and high returns on investedcapital, leaving less for other investors and shareholders.Ethical or ‘green’ banks and funds are beginning toappear. They take a more sympathetic view ofrenewable energy in general and seem willing to investon less onerous terms. These should be sought by ADproject developers, particularly those whose projects fallinto the financing gap described earlier. CertainRegional Electricity Companies (RECs) may be interestedin supporting (through investment) alternativerenewable energy sources in some areas.

Grant aid may be available for large AD projects fromEuropean Union funding programmes, administered byMAFF, for rural development. More information can befound in Financing Renewable Energy Projects-A guidefor developers, published by ETSU for the DTI. MAFF’sFarm Waste Grant Scheme provides help to farmers inNitrate Vulnerable Zones who are installing orimproving farm waste facilities. Grants are not availablefor anaerobic digesters but funds may be available forstorage which could be used for part of an AD scheme.More information can be found in the MAFF leafletFarm Waste Grant Scheme: Nitrate Vulnerable Zones.

Site and locationSite and locationSite and locationSite and locationPlanning permission is likely to be required for mostAD projects, so the proposed development will needto be acceptable in terms of site, layout, theappearance of the buildings, any impact on localamenity or landscape and any environmental risks suchas water contamination. On-farm digesters are likelyto be sited near other farm buildings so there may belittle new impact. However, decisions on the locationof all new plants, especially CAD developments, willneed to take the following into account whenconsidering sites for the digester:

Feedstock and transport• A local supply of feedstock needs to be available so

that transport costs and environmental impacts arekept to a level which would provide a positiveenergy balance.

• Accessibility to road links for the import offeedstock and export of products is essential.

Markets for products• Secure uses, outlets and markets are needed for

liquor and fibre products (both can be storedrelatively easily but at a cost).

• Access to potential uses or markets for excess heat,or reaching a niche electricity market, will beimportant.

• Distribution networks. The right location can savethousands of pounds on grid connection costs, andthe value of the electricity is enhanced byminimising transmission losses; the closer it can beconnected to its end users when sold off site thebetter.

Planning and environmental restrictions• Impacts on neighbours. CAD plants may be best

sited in areas designated for industrial developmentin the development plan of the local planningauthority. All plants need to consider noise, smelland traffic impacts on local residents.

• Sufficient land available. It would be good practicefor a farm to produce a Farm Waste ManagementPlan to demonstrate to the Environment Agency thatthere is sufficient land available for the storage andspreading of digestate on the farm.

• Landscape designations. Additional care needs to betaken with landscaping and building design indesignated areas such as Areas of OutstandingNatural Beauty (AONBs) and National Parks, and it


is possible that planning permission will not beforthcoming in these areas.

• Ecological impacts. Consult the statutoryconservation agencies (English Nature, CountrysideCommission, Countryside Council for Wales andScottish Natural Heritage) informally beforeconsidering a site in or near to a designated areasuch as a Site of Special Scientific Interest (SSSI),Special Protection Area (SPA), Special Area forConservation (SAC), RAMSAR sites (sites ofinternational importance listed under theConvention of Wetlands in the UK; sites aredesignated as SSSIs) and county wildlife sites, asthere are likely to be objections to developments inthese areas. Any international, national or localnature conservation designation is a clear indicatorof the sensitivity of the intrinsic ecological value ofthe site and these areas should be avoided.

• Water courses. Consult the Environment Agency atan early stage to ensure compliance with anyregulations to prevent pollution.

Visual impact of digester and otherbuildingsA digester, storage buildings (for feedstock andproducts) and reception tanks will all be required; thesize and number of the buildings will depend on thescale of the project. The buildings may need to be up to6 or 7 metres high to allow for lorry tipping in somecases - about the same height as normal farm buildings.This should be taken into consideration when choosingthe site.

TechnologyThe size of the digester tank will influence the choice ofsite and location. The size of the digester depends onthe length of time required for the conversion cycle;this depends on the priorities of the developer in termsof products (eg biogas) and other objectives (eg odourreduction).

Water pollutionConstruction sites should be selected so as to minimisewater pollution. This can be done by avoiding sitesliable to flood, sites with a high water table, sites whereunderdraining has been installed, sites where differentialsettlement is likely to occur, and steeply sloping sites.Alternatively, expensive ground preparation may beneeded to prevent subsidence on some types of land.

DesignDesignDesignDesignand planningand planningand planningand planningissuesissuesissuesissuesAn AD project will require detailed design and planningto ensure the development is not only economicallyviable, as discussed above, but also that allenvironmental impacts will be minimised. It is goodpractice for the developer of an AD plant to makecontact with the planning authority at an early stage toseek advice on the making of a planning application andto enlist their help in structuring the projectdevelopment and designing the site. It is good practiceto consult with local people on design and planningissues (see Consultation section for details).Planning permission is likely to be needed in almost alldevelopments of AD projects, even for small on-farminstallations, because the planning definition ofagriculture does not include AD which is anindustrial/waste treatment process. In a minority ofsmall on-farm projects, where the feedstock originatesand the products are used entirely on their own land,planning permission may not be required because theproposed development may be held to be ancillary toagriculture carried out on the farm and be ‘permitteddevelopment’ (under Part 6 of Schedule 2 of the Townand Country Planning (General Permitted Development)Order 1995) providing all the relevant conditions setout in the Order can be complied with. In cases wheresmall on-farm projects are accepted as ‘permitteddevelopment’, an application to the local planningauthority is needed for a determination as to whethertheir prior approval will be required in respect of thesiting, design and external appearance of thedevelopment.

Design of the siteThe main issues which need to be taken into account indesigning the site and obtaining planning permission areoutlined below.

TrafficAny planning application will require information onthe suitability of access roads for increased volumes oftraffic, and any improvements that may be requiredboth during construction and operation of the plant.


Digester landscaped into a site (Photo: WRI Services)

Measurement of the existing traffic levels will beimportant as this will form the context in whichadditional traffic movements will be judged. See theFeedstock and products section for details on trafficimpacts.

Emissions to airPlanning authorities will also consider any potentialemissions to the atmosphere from the construction andoperation of the plant, and the vehicles transportingfeedstock and the products. There are regulations forcontrolling emissions and statutory nuisances under theEnvironmental Protection Act 1990.

Emissions to ground and waterThe Environment Agency require that all tanks anddigesters are surrounded by containment bunding ofeither concrete or clay. The relevant standards will alsobe required for any lagoons built for storing liquor.

NoiseThe conditions of the planning permission are likely tospecify noise limits which must not be exceeded atspecific identified points. Expert advice is required ineach case to identify and negotiate acoustic measures (ifthese are required) and noise conditions. Although notalways essential, the developer and/or the localauthority may wish to carry out a background noisesurvey to establish the ambient level of noise in theenvironment prior to the development.Sources of potential noise need to be identified, such asengines and pumps, and plans can then be made tomitigate these through appropriate design of the site andbuildings by using acoustic enclosures, creating hedgeor tree barriers around the plant, and appropriatetechnology.Noise is regulated by the planning and environmentalhealth departments of local authorities, and by theHealth and Safety Executive in relation to noise at workregulations.

Visual impactThe visual impact of the digester and associatedbuildings can be minimised in on-farm schemes if newbuildings are grouped with existing farm buildings.Bunding, planting around the site and partial burial ofthe digester and storage or reception tanks will help toreduce the visual impact of the new development.However, these measures will increase the costs of theplant and may only be viable in sensitive locations.There is also potential for dividing the plant up; forexample, the digester could be located separately fromliquor and fibre storage to reduce visual impact,although the transport implications of this would needto be considered.New electricity connections will have a visual impactboth on-site and off-site (ie lines or cables to make theconnection to the grid). The visual effect of overheadlines can usually be mitigated to an acceptable level bycareful route selection. Developers will plan for thelikely route of a grid connection at the same time as theyare planning the power generating plant. Where a gridconnection already exists, there will still be an impacton-site (ie simple fixing to existing grid system).Underground connection reduces the visual impact andmay in certain cases be economic in comparison withoverhead lines. In this case, the visual intrusion is onlyshort term whilst the work is carried out.

Control of odour levelsA properly managed AD plant will reduce odour overall.However, odour from the feedstock will be released as itis stored, and especially whenever it is moved or mixed,and this odour needs to be carefully managed. In aproperly designed and operated facility, the compoundswhich cause odour should be effectively containedand/or destroyed. Odour from AD is regulated by thelocal authority under the Environmental Protection Act1990. Potential problems need to be addressed throughthe design of the site, and expert advice is required ineach individual case to consider what is likely to bedischarged, what are the potential risks and how theycan be avoided or at least minimised. To meet planningrequirements, it is likely that all manures and feedstocksfor CAD plants will have to be contained in buildings ortanks with negative ventilation systems fitted with bio-filters to control and contain odours.

Design of the plantDecisions about the equipment and technical design ofthe plant also need to be considered. The mainrequirements for good design for AD plants include:• Minimising mechanical and electrical equipment• Effective insulation properties, and corrosion

resistant materials• Simple design and automatic operation


• Equipment fail safe devices throughout• Environmental controls.Although the main process stage is the anaerobicdigestion tank, there are a range of preliminary andpost-digester units necessary for an integrated plant. Fora farm-scale digester, feedstock conditioning may belimited to minimising the water content of the materialand preventing large lumps reaching the digestion tank,whereas a CAD plant will require special feedstockhandling and storage units. Overall, there will be arange of structures, depending on scale including:• Appropriate waste reception and loading facilities• Digester; the size depends on projected volume and

nature of waste to be dealt with, and on thetemperature and retention time in the digester

• Mixing devices• Gas holder• Gas handling equipment including pipework,

valves, flare stack/heat dump• Electricity generating equipment, powered by

ignition engines converted to run on methane, gasturbines and electricity generators

• Boilers to provide heat for the digester• Pipework to remove the water which condenses out

from the saturated gas which is produced by AD• Appropriate storage for liquor and fibre• Control and monitoring equipment• Odour control equipment.CAD operations are also likely to require equipment forvolume recording and analysis facilities for qualityassurance and contractual requirements, as well asmonitoring equipment for safety and operationalpurposes.The crucial factor is to identify the appropriate plantdesign to meet the user’s requirements for the wholeproject. The plant, to be successful, should have both aquality guarantee from the feedstock suppliers and aperformance guarantee from the plant installers anddesigner. The performance guarantee should includefactors such as:• Heating performance, eg keep digester contents at

350C with an ambient temperature of -100Cprovided adequate feedstock is being added

• Digester contents mixing, which can be defined asthe total contents being mixed within 30 minutes

• Temperature differential does not exceed 20C acrossthe digester vessel

• The digester loading system will handle thefeedstock

• The unloading system will handle the digestate atthe designed rate, including separation (whenappropriate)

• The generator should, when supplied with thecorrect amount of biogas, produce the specified

electrical and heat loads, for a minimum of thestated number of hours per year

• The developer should choose the best availabletechnology to minimise environmental impact; theperformance guarantee should cover operation torequired environmental standards.

Consultations Planning application prepared Consultations

Registration and administrationChecks to ensure that all forms, plans and fees are correct; if theapplication is valid then an ackowledgement letter is sent

●

Application entered on statutory planning register and plotted onOrdnance Survey maps

●

Technical background information prepared for Case Officer●

Publicity and consultationApplication details appear on a weekly list of applicationsappearing in the local press and a notice posted on or near thesite OR either a site notice or a neighbour notification letter(s);minimum publicity period is 21 days

●

Statutory and technical consultations undertaken; minimumconsultation period is 14 days

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Publicity and consultation carried out in parallel●

Case officerInspects site and its surroundings●

Assesses proposal against planning policies, DETR PlanningPolicy Guidance, previous planning history on the site and normaldevelopment control criteria

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Takes into account any letters of representation received and theresults of consultations; may negotiate changes to proposal

●

Prepares either report and recommendation to the planningcommitteee OR draft decision for Chief Planning Officer

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Committee agenda Delegated decisionPublic release of Chief Planning Officer reportand recommendation

Taken by Chief Planning Officer, for usually minordevelopment or where the application isunopposed.

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Committee decisionSome aspects may be delegated

Committee site visit: usually where proposal iscontroversial, or raises unusual issues.

Section 106Planning Obligation

(if necessary) prepared andnegotiated

Permission Refusal

Notice, usually with conditions, issued Notice, with reasons, issued

AppealThe applicant can APPEAL to the Secretary of State if:(i) Permisiion is refused(ii) Applicant is unhappy with conditions imposed on a permission ORwhere no decision has been made on the expiry of the statutorydetermination period

Figure 5.Planning Process

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PlanningPlanningPlanningPlanningpermissionpermissionpermissionpermissionThe process of applying for and obtaining planningpermission is a crucial element of the overalldevelopment of an AD project regardless of scale.This process is outlined in Figure 5 and the detailedsummary below.

This summary of the planning process is not a step-by-step guide, since the actual procedure will varyaccording to the size and type of plant and to therequirements of different planning authorities. Also, allassessments will be done in parallel, rather than one at atime. Moreover, this procedure does not cover all theactions required of the developer: others are necessarybefore and after planning permission is applied for andgranted.

Some digesters may require an EnvironmentalAssessment (EA) (see Box 1 overleaf), as well asregulation and monitoring by the Environment Agency.Whether a statutory Environmental Assessment andenvironmental statement are required will depend onthe location, scale and nature of the scheme (see Box 2for when an EA is required; see Box 3 for what anenvironmental statement should cover). Some localplanning authorities may request an EA at theirdiscretion. Even if a formal EA is not required, it wouldbe good practice to produce simple environmentalinformation for the public on any potentially adverseenvironmental effects of the proposed development andhow they will be mitigated. As well as showing that therisks of any impacts have been considered, informationproduced and distributed at an early stage can reduceproblems created by misunderstandings later in theproject development process, and therefore save timeand money in the long term.

The way the planning procedure will work in normalcircumstances is shown in Figure 5 and detailed below.

1 The developer will make contact with theplanning authority at an early stage. The planningauthority with jurisdiction for the development will beeither the district or county council, or unitaryauthority, depending on the local government structurein the area and the nature of the project. In areas coveredby both county and district councils, the county councilis the authority which deals with matters relating towaste management or treatment. Early discussions withthe local authority’s building control and EnvironmentalHealth Officers are also important.

The initial contact should be with the Chief PlanningOfficer or with one of his senior officers, who willdecide who should deal with the matter (it may bedelegated). There may also be contact with theeconomic development officer about larger schemes. Atthis stage, the project may not reach the public domain,although early provision of information to localcommunities is always recommended.

2 Between initial contact and a formal applicationfor planning permission, most of the preparatory workfor the development will be carried out. This willinclude regular contact with the planning authorities,especially relating to initial work on any EA required (oralternative provision of environmental information).The scope of the EA can be developed informally indiscussion, or more formally in correspondence. Thelatter approach would mean that the project will becomemore widely known because the planning authority willconsult statutory consultees. The need for a statutory EAwill depend in part on how far, in negotiations, thedeveloper agrees with the planning authority to addressenvironmental issues which will be covered in detail aspart of the application procedure.

While planning applications and EAs require a highdegree of technical input, it is important to recognisethat these are public documents, and developers shouldensure that results are presented in as accessible a formas possible, with the minimum of technical or scientificjargon. In addition, the developer will be required toproduce a non-technical summary planning statementfor public information, and a formal summary will berequired if there is an EA. There will also be detailedconsultation with the local community and withstatutory and non-statutory consultees, at a sufficientlyearly stage for plans to be adapted in response to localconcerns. Only when all this is completed, and all issuesof concern have been addressed, should a formalapplication for permission be made.

3 If a CAD plant is planned, a more intensivedialogue between the developer and the planningauthority, prior to the submission of the planningapplication, is recommended. It is good practice tosubmit the environmental statement (or informalenvironmental information) at the same time as theplanning application. It is good practice to state ‘nosignificant impacts anticipated’ where this is the case,although if this statement is used, and subsequentlyfound to be inaccurate, there is likely to be seriousquestioning of the entire project.

4 The formal process begins with the submissionof the planning application, which will lead to someform of statutory consultation. The planning authority isobliged to publicise the planning application as soon as


it is formally received, at which point anyone can makecomments on the proposals. The planning authority willtake into account any representations received whenmaking a decision on the application. The decisioncould be made by either a planning committee or thechief planning officer using delegated powers.

If the development does require a formal EA, the localauthority has 16 weeks to deal with the application. Ifno formal EA is required, the local authority has up to 8weeks. The developer has the right to appeal against thefailure of the local authority to decide the application atthe end of 8 or 16 weeks. Such an appeal must be madeno later than 6 months from the statutory determinationdate.

5 Where an adopted or approved developmentplan contains relevant policies, Section 54 (a) of theTown and Country Planning Act 1990 requires that aplanning application or an appeal shall be determined inaccordance with the plan unless material considerationsindicate otherwise. Regard should also be had to DOEPlanning Policy Guidance Notes (PPGs), and particularlyPPG22 on Renewable Energy.

6 The Secretary of State has the ability to call inplanning applications, at which point they are taken outof the hands of the local authority. This may happen ifthere is considered to be a breach of the developmentplan policy or if the Government Regional Office (inEngland only) considers that the proposed developmentraises issues of more than local concern. If the developeris working effectively with the local authority and localcommunity, any such issues and potential problems willhave been identified at an early stage.

7 If planning permission is granted, developerswill be aware of the need to comply with any agreedvoluntary planning obligations and planning conditionswhich could be imposed, which will normally havebeen negotiated prior to granting any permission.Discussions will have been held with planningauthorities to agree methods of complying with thoseconditions, which may involve some form ofmonitoring. Some elements could be dealt with througha liaison forum set up from the links the developer hasalready established with the local community. Theremay also need to be agreement to off-site highwayimprovements, which would involve discussions withthe highway authority and local landowners.

8 If planning permission is refused, or conditionsmade with which there is disagreement, developers havea right to appeal within six months.

Overall, if a site is suitable, and a well-consideredplanning application is made which seeks to take intoaccount the concerns or likely concerns of local

communities and statutory consultees, it is much morelikely to receive a positive response.


Box 1What are Environmental Assessmentsand statements?Environmental Assessment (EA):‘A technique and a process by which information about theenvironmental effects of a project is collected, both by thedeveloper and from other sources, and taken into account bythe planning authority in forming their judgement on whetherthe development should go ahead ... the whole processwhereby information about the environmental effects of aproject is collected, assessed and taken into account inreaching a decision on whether the project should go aheador not. The term ‘environmental impact assessment’ (EIA) isalso in common use and for practical purposes is synonymouswith EA’ .Environmental Statement:‘A document setting out the developer’s own assessment ofhis project’s likely environmental effects, which he preparesand submits in conjunction with his application for consent’.

Taken from Environmental Assessment-A guide to the procedures,HMSO/Welsh Office 1989.

BOX 2When is an EA required?Statutory EA is only mandatory for a thermal power stationwith a heat output of 300 MW or more referred to as aSchedule 1 development under the Town and CountryPlanning (Assessment of Environmental Effects) Regulations1988, and no AD projects are likely to reach anything like thissize.However, smaller plants will require an EA if they are likely tohave significant effects on the environment because of theirnature, size or location (referred to as Schedule 2developments under the 1988 regulations).‘Significant effects’ have no general definition, butGovernment guidance lists three main criteria of significance:• Whether the project is of more than local importance,

principally in terms of physical scale• Whether the project is intended for a particularly

sensitive location, for example, a National Park or Site ofSpecial Scientific Interest (SSSI), and for that reason mayhave significant effects on the area’s environment eventhough the project is not on a major scale

• Whether the project is thought likely to give rise toparticularly complex or adverse effects, for example, interms of the discharge of pollutants.

Taken from Environmental Assessment-A guide to the procedures,HMSO/Welsh Office 1989.Exactly what supplementary environmental information maybe required in any application for planning permission wouldneed to be negotiated in each individual case with theplanning authority concerned. The regulations governing thisprocedure are the Town and Country Planning (Assessmentof Environmental Effects) Regulations 1988 (as amended)implementing EU Directive 85/337. These regulations includedetails of the matters to be addressed by an EA, and provideuseful guidelines for any supplementary environmentalinformation produced by developers (see Box 3)

BOX 3What should an environmental statement cover?It is not possible to offer a definitive list of topics for an environmentalstatement, and developers will need to look at both wider and more localissues which cannot be identified in general guidelines. Also, circumstancesand technologies change over time. Developers are advised to discuss it withthe local authority and the Environment Agency to clarify specific local issues.However, the 1988 Regulations (Schedule 3, paras 2, 3 and 4) state that anenvironmental statement should provide certain specified informationincluding:(a) a description of the development proposed, comprising informationabout the site and the design and size or scale of the development(b) the data necessary to identify and assess the main effects which thatdevelopment is likely to have on the environment(c) a description of the likely significant effects, direct and indirect, onthe environment of the development, explained by reference to its possibleimpact on:• human beings• flora• fauna• soil• water• air• climate• the landscape• the interaction between any of the above• material assets• the cultural heritage(d) where significant adverse effects are identified with respect to anyof the foregoing, a description of the measures envisaged in order to avoid,reduce or remedy these effects(e) a summary in non-technical language of the information specifiedabove.

An environmental statement may include, by way of explanation oramplification of any specified information, further information on any of thefollowing matters:(a) the physical characteristics of the proposed development, and theland-use requirements during the construction and operational phases(b) the main characteristics of the production processes proposed,including the nature and quality of the materials to be used(c) the estimated type and quantity of expected residues and emissions(including pollutants of water, air or soil, noise, vibration, light, heat andradiation) resulting from the proposed development when in operation(d) (in outline) the main alternatives (if any) studied by the applicant,appellant or authority and an indication of the main reasons for choosing thedevelopment proposed, taking into account the environmental effects(e) the likely significant direct and indirect effects on the environmentof the development proposed which may result from:(i) the use of natural resources(ii) the emission of pollutants, the creation of nuisances, and theelimination of waste

This includes secondary, cumulative, short, medium and long term,permanent, temporary, positive and negative effects(f) the forecasting methods used to assess any effects on theenvironment about which information is given under subparagraph (e), and(g) any difficulties, such as technical deficiencies or lack of know-how,encountered in compiling specified informationWhere further information is included in an environmental statement in thisway, a non-technical summary of that information shall also be provided.Taken from Town and Country Planning (Assessment of EnvironmentalEffects) Regulations 1988.


Constructionand operationsConstructing and operating an AD project, and managing a digester, is an art as much as a science: operators mustlearn about and understand their digester and feedstock. This section covers all the main issues relevant toconstructing and operating an AD project, including planning and managing construction, electricity connection,training, monitoring, minimising operational risks and optimising performance.

Digester control panel (Photo: ETSU)


ConstructionConstructionConstructionConstructionThe level of the impacts of construction work willdepend on the scale of the plant being constructed.An on-farm heat generating plant is likely to haveminimal impacts during construction. In largerenergy generating schemes, in which electricity isexported via the distribution network, a purpose-built power generating plant will be constructed,which is likely to entail new building, creating greaterimpacts which need to be mitigated. As with anynew development, there are specific issues arisingfrom the construction of the power generating plantwhich are more related (for neighbours) to livingnear to a building site than to a power plant. Theseinclude construction noise and dust, impact on theaccess road, transport noise, light pollution, oilspillages, soil erosion, establishing a constructioncompound which may be larger than the final site,and negotiations for wayleaves.A developer can apply to the local authority for a priorconsent over times of working, noise levels, andsimilar issues (under the provisions of Section 61 ofthe Control of Pollution Act 1974). This may helpprovide reassurance to local residents: difficulties atthis stage can damage the reputation of a plant beforeit even starts operation. It would also be good practiceto consult with the local authority’s EnvironmentalHealth Officers, as they would deal with anycomplaints and could defuse any local antagonismmore quickly if they can give answers directly.The Construction (Design and Maintenance)Regulations 1994 place new duties upon clients,clients’ agents (where appointed), designers andcontractors to take health and safety into account, andco-ordinate and manage it effectively throughout allstages of a construction project from conception,design and planning through to the execution of workson site and subsequent maintenance and repair. Ahealth and safety plan (to bring together all relevantinformation from those responsible, starting in pre-construction) and a health and safety file (an enlargedmaintenance manual to inform future decisions) willbe required.The degree of the detail required of all duty holdersto comply with the Regulations should be adapted tothe scale and complexity of the project. Projectsinvolving minimal high risk work will call for simplehealth and safety plans and few, if any, specialist skills.Large projects or those involving high risk work will

call for correspondingly more detailed assessmentand specialist skills.


METHOD STATEMENTThe method statement should spell out specific measures whichdevelopers plan to take to minimise disruption and mitigate anyundesirable impacts during construction. It will have beennegotiated as part of the planning permission and should be builtinto the contract with the contractors for the building. The methodstatement will need to provide detailed guidance for theconstruction contractors, but it would be good practice to producean additional summary in plain English for local communities and thelocal planning authority.It is likely to include:NoiseReducing noise nuisance as much as possible by working only duringthe normal working day. It would be good practice to consult thelocal authority’s Environmental Health Officer who can advise onacceptable construction site noise levels. Developers will wish toconsult and have regard to British Standard (BS) 5228 on NoiseControl on Construction and Demolition.TimingTiming construction carefully, to avoid damage if the area orsurroundings are environmentally sensitive (eg at certain times ofyear): there should also be consultation with the local planning andhighway authorities regarding proposed traffic movements.

DustWater can be used to suppress dust. Care is needed, however, toavoid excessive application of water so that suspended silt is notwashed into a drain or watercourse.LightingConsultation is recommended with the local authority’sEnvironmental Health Officer for advice on guidelines on lightpollution (details on light pollution are given on page 40).Size of construction compoundThe site will need to be sufficiently large to allow space formitigation of any construction impacts, as well as simply meeting thephysical needs of construction. Attention should be given toreturning the surrounding area to its original status afterconstruction.SpillagesMeasures to reduce or contain spillages, such as bunding, wouldprobably be a condition of planning permission.Duration of constructionAn estimated construction timetable should be included in themethod statement; construction of an AD plant would normally takefrom 3-12 months.Transport and trafficThe construction process might require consideration of:• Off-site highway changes such as setting back hedges, hedge-

trimming• Bridges: need to consider loading and height• Road developments eg road widening.Such works should be the subject of early discussions with theplanning authority and highway authority as they will need to beidentified in the planning application. Road widening and otherhighway alteration works are likely to be covered by legalagreements under the Town and Country Planning Act 1990 andthe Highways Act 1980.


Method statementMost larger AD projects will be subject to theConstruction (Design and Maintenance) (CDM)regulations, except projects which take less than 30days for construction, or less than 500 person workdays.

A method statement may also be required as part of theplanning permission. This should be drafted by thedeveloper, and discussed with the planning officers,the building control officers and the environmentalhealth department of the relevant local authority andwith community representatives and local people. Thiswill help to demonstrate that the developer hasthought about the possible problems and theirmitigation, as well as about residual impacts and howto address them. The issues the method statementshould address are outlined in the Box above.

ElectricityElectricityElectricityElectricityconnectionconnectionconnectionconnectionIf an AD plant is constructed on a new site it willgenerally require an electricity connection to the localelectricity distribution network to provide energy tooperate ancillary equipment and other site loadsduring maintenance and shut-down periods, unlessstand-by generation equipment is also installed.

An electricity connection and appropriateimport/export metering will be required if the gasproduced by an AD plant is to be used to generateelectricity which cannot be consumed within thecurtilage of the plant and associated businesses. Theoperator will then have to decide on a number oftrading options depending upon the size and locationof the generator and to whom the electricity is sold orconsumed, and address various technical, regulatory,commercial and contractual issues.

The risks and benefits with each option will need to beappraised and understood by the prospective developerto maximise the value of the energy generated and toensure that the appropriate agreements, contracts andlicenses are entered into by the developer.

The Regional Electricity Company (REC) has statutoryobligations under the Electricity Act 1989 in respect ofthe safety and quality of electricity supply to itscustomers and will determine the method and thepoint at which connection can be made to thedistribution network, depending upon the export

capacity of the AD plant and the relative parametersof the immediate distribution network.

The cost of connection could vary considerablydepending on where the AD plant is located withinthe REC’s distribution network. The cost ofconnection will in part reflect the distancesinvolved. However, because the REC for operationaland economic reasons needs to use standardcomponent sizes for its own assets, the connectioncost will not tend to rise smoothly with increasingplant capacities, but will tend to increase in steps asthe thresholds for requiring particular assets andvoltage levels are crossed. If the developer hassome flexibility as to where the plant can be locatedwithin a particular area, they should discuss withthe REC the respective connection costs fordifferent sizes of generator and, if practicable, sizeand locate the installation accordingly.

In some cases, some benefits may also accrue to thelocal REC and/or the licensed second tier supplierwho contracts to sell the electricity and it may bepossible to negotiate agreements to optimise thecosts to the developer and maximise the value ofthe energy generated. A summary of the options,benefits and the associated agreements, contractsand licence requirements is given in Appendix 6.

TrainingTrainingTrainingTrainingGood practice requires that all operators of ADplants are trained to the highest possible standardsin the engineering aspects of the running of theequipment, be trained in and fully understand thehealth and safety aspects, and be trained torecognise problems and how to respond to them.Farmers and developers may obtain training on theuse of equipment from manufacturers andequipment suppliers. A number of consultants canalso offer training on health and safety andoperating procedures.

MonitoringMonitoringMonitoringMonitoringAn AD project should be regularly monitored in

order to:

• Optimise economic and environmentalperformance

• Assess quality control of feedstock and productsregularly


• Check records of what is produced and what hasgone through the system

• Monitor and control emissions, and ensureemissions on site are within set limits (this may bea planning condition)

• Check comments made by members of the publicand neighbours of the plant

• Ensure planned actions are carried out effectively.

MinimisingMinimisingMinimisingMinimisingoperational risksoperational risksoperational risksoperational risksGood practice requires careful planning andmanagement to ensure that the benefits of theproducts of AD, including sustainable energyproduction, are matched by sensitively and effectivelymanaged systems for operations. As with anyagricultural or small industrial development, theoperation of the scheme will have some risk ofnegative environmental impacts. All of these willneed to be addressed in order to obtain planningpermission and may be governed by planningconditions. Some of these impacts, and thereforeany mitigating activities, may be negligible in smallerschemes. However, even the largest AD plant can becompared more easily with other agriculturaldevelopments than with any conventional industrialfacilities. Nevertheless, and especially in largerschemes, attention needs to be given to thefollowing, all of which are covered in more detailbelow:

• Emissions to air

• Emissions to ground and water courses

• Light

• Transport and traffic (see Feedstock and Productssection)

• Feedstock and product storage (see Feedstock andProducts section).

The regulations which will be in force depend on thescale of the development, as will the identity of theregulatory authority: it is likely to be the localauthority and the Environment Agency.

Emissions to air

Environmental impactsThere is the potential for emissions of methane (agreenhouse gas) to the atmosphere from leaks fromthe plant. It is also important to ensure efficientcombustion as carbon monoxide (human healthrisk), nitrogen oxide (precursor to acid rain) andvolatile organic compounds (VOCs - toxic airpollutants) are released at unacceptable levels if thebiogas is combusted inadequately. Propermanagement should ensure that all these risks arecontrolled, and the best available technology shouldbe used in all cases.

The Environment Agency will apply IntegratedPollution Control regulations to larger plants whichwill control emissions to all media (not just air);this will apply to larger on-farm schemes as well asCAD plants.

Health and safety risksBiogas is primarily composed of methane andcarbon dioxide, with traces of ammonia andhydrogen sulphide. Ammonia and hydrogensulphide may arise during fuel gas production,from stored feedstock and in the mixing pits orconveying plant. Exposure to any of these gasesmay result in ill-health or death, and levels in thebiogas may vary widely and cyclically. Carbondioxide, ammonia and hydrogen sulphide are alltoxic gases, and are subject to the COSHHregulations as substances hazardous to health.

Employers of people working in biogas plants mustassess the risk from exposure to the gases (andother hazardous substances such as pathogens inthe feedstock), and take steps to control that risk.For new plants, the risk of operators or othersbeing exposed to toxic gases should be consideredat the design stage under the Construction (Designand Management) Regulations 1994.

Identifying the hazards in the plant design, whetherin the construction stage, under normal running orduring maintenance and repair, will enable manyrisks to be designed out and thus subsequentoperation of the plant will be easier.

The COSHH assessment will identify hazards fromoperating the plant, and the extent of risk to becontrolled. The assessment will lead the operatorof the plant to institute the necessary procedures tocontrol exposure down to or below the legal limits,known as Occupational Exposure Standards (OES),which must not normally be exceeded. The mainhazards of these gases are outlined below.

• Methane is an asphyxiant (its presence at highconcentrations in air reduces the oxygen


content to such an extent that life cannot besupported) but is not subject to COSHH.

• Carbon dioxide is colourless, odourless andheavier than air. As well as being mildly toxic, itis an asphyxiant and has an Occupational ExposureStandard (OES) of 5000ppm.

• Hydrogen sulphide is a colourless gas which smellsof rotten eggs at low concentrations. At higherand more dangerous concentrations it has nosmell. It is heavier than air. Due to its toxicity, ithas an OES of 10ppm.

• Ammonia is a pungent and lachrymatory gaswhich is lighter than air. The OES is 25ppm, toprotect the eyes and mucous membranes fromirritation.

Good practice entails using reasonably practicablemeans to control risks. Controls may includeremoving the toxic elements of the gas, establishingtotally enclosed systems, systems which minimise orcontain the hazardous substance, local exhaustventilation, general ventilation or, as a last resort,personal protective equipment. The controls institutedshould not rely on venting (which may create riskselsewhere due to the heavier than air nature ofhydrogen sulphide and carbon dioxide) or onunforced general ventilation. Health and safety issueswill be regulated by the Health and Safety Executive.

Emissions to ground and water courses• Water. Water courses could possibly be affected

by discharges resulting from poor storage offeedstock, inappropriate storage of liquor, spillageor spreading of liquor. Site containment will berequired. If there are accidental spillages orleakages into water courses, the EnvironmentAgency should be notified immediately. TheEnvironment Agency is responsible for controllingemissions to rivers and land. Water companiesregulate any discharge into public sewers.

• Soil. Pollution prevention measures will be dealtwith at the planning stage in consultation with thelocal authority environmental health departmentand the Environment Agency. Any accidentalcontamination should be reported to theEnvironment Agency immediately.

LightCAD plants are likely to operate 24 hours a day sothere may be a problem with light spillage. There areno statutory criteria for light pollution althoughmeasures can be taken to reduce unnecessary obtrusivelight: light pollution can cause serious physiologicaland ecological problems, and wastes energy and

money. The Institution of Lighting Engineers’Guidance Notes for the Reduction of LightPollution suggests a number of measures,including:

• Lights should be directed at and not above theirtarget; if aimed at observers, the main beamangle should be no more than 70°.

• In certain environmental zones, such asNational Parks, Areas of Outstanding NaturalBeauty (AONBs) or other ‘dark landscapes’,only light from public roads should be deemedacceptable for all night lighting. Similarguidelines apply to other special areas.

• Curfews should be introduced, for examplebetween 11pm and dawn, when lights notrequired for security are shut off.

• Further advice can be obtained from the localauthority Environmental Health Officer, or theInstitution of Lighting Engineers.


OptimisingOptimisingOptimisingOptimisingperformanceperformanceperformanceperformanceIt is possible to automate AD plants, but they willalways need daily management and monitoring forquality, performance and health and safety.Anaerobic digestion is a robust process, but toensure optimum performance the following aspectsof management and monitoring should be considered:

• Choice of appropriate technology for the specificcircumstances

• Security of supply and disposal routes

• Achieving the desired dry solid content offeedstock: the more dry solids, the more gas perkg of feedstock that will be produced

• Ensuring efficient mixing

• Maintaining the correct temperature in the digesterand ensuring sufficient heat transfer and capacity

• Regular process monitoring

• Efficient management, including operator trainingand the establishment of environmentalmanagement systems

• Regular maintenance of moving parts and heattransfer surfaces

• Maintenance of pH in the digester.

MaintenanceGeneral points to be considered include:

• Maintenance contracts for digesters and generators

• The potential for letting an operations contract (torun the digester and generator)

• Pressure systems, as defined by the PressureSystems and Transportable Gas ContainersRegulations 1984, require a formal written schemeof examination drawn up by a competent person;this would specify the intervals betweenexaminations

• Operation and/or maintenance contracts need totake the timespan of specific contracts into account(eg NFFO contracts may run for 15 years).

Start up andStart up andStart up andStart up andshut downshut downshut downshut downStarting up and shutting down the digester can beone of the most risky procedures in running anAD plant. Training must be provided for alloperators to ensure they understand and complywith procedures and advice sought fromspecialists.

If the heat is turned off, a typical digester will loseat least 0.50C to 10C a day if loading of feedstockceases. Once the temperature has dropped to 280C,the gas production will reduce significantly. Tostart the digester up again, the contents should bemixed continuously, so there is no mat on the top,and then slowly warmed up again. This processcan be used if the operator is in any doubt aboutcontaminated feedstock: if feeding is stopped thedigester will recover.

As a matter of good practice, any developer of ascheme of any size will also need to take intoaccount what will be done when the digesterreaches the end of its useful life. It is likely that anyplanning consent will require decommissioning tobe addressed, and advice should be taken from theEnvironment Agency and the Health and SafetyExecutive on any plans for decommissioning thedigester and plant.


Appendix Appendix Appendix Appendix 1111Glossary

The following terms are used in these guidelines, and thedefinitions given below refer to their meaning in thecontext of this document: other sources may use theterms differently.

AD: Anaerobic digestion; the process by which bacteriathat act only in airless (anaerobic) conditions decomposeorganic matter with the concurrent production of biogas

Bacteria: Microscopic single celled organisms whichbreak down the organic matter of the feedstock

Bio-filters: Remove unwanted substances usingbiological processes

Biofuel: Liquid fuels produced from biomass sources;biomass is any mass of biological material

Biogas: Gas evolved from the anaerobic digestionprocess which is typically 60% methane, 40% carbondioxide, with other trace compounds

Bleaching clay: Porous clay filter media used forclarifying edible oils

BOD: Biological Oxygen Demand

Bunding: A barrier constructed around the site toprevent discharge entering water courses in the event ofan accident

CAD: Centralised Anaerobic Digester; digester whichimports feedstocks from a variety of sources

CHP: Combined Heat and Power: In normal mode ofa generator, the major sources of heat, engine coolingwater and exhaust system, are normally discharged toatmosphere; CHP recovers this heat via heat exchangers,increasing the efficiency of utilising fuel

COSHH: Control of Substances Hazardous to Health,Regulations 1994

Decommissioning: Closing and removing the facilityafter its useful life

Digestate: The digested output from the AD process

Digester: The closed container in which anaerobicdigestion takes place

Dioxins: A group of harmful chlorinated organiccompounds

DOE: Department of the Environment; Governmentdepartment; now called Department ofEnvironment, Transport and the Regions

Dry solids: The residue remaining when water isevaporated away from the residue and dried underheat

EA: Environmental Assessment; see box in ProjectDevelopment section for details

Energy balance: Comparison of energy going into aprocess (inputs), to energy coming out of theprocess (outputs)

ETSU: Energy Technology Support Unit; managerof the Department of Trade and Industry’s New andRenewable Energy Programme

EU: European Union

Feedstock: The material fed to the digester

Fertigation: Irrigation with water containingnutrients

Fibre: The coarse solids which have beenmechanically separated from the liquid portion ofthe digestate

Fossil fuel: Any energy source derived from finitefossil sources eg coal and oil

Fossil Fuel Levy: Levy on electricity generated fromfossil fuel sources used to fund NFFO

Heavy metals: Potentially toxic metals such asnickel, cadmium, etc present through natural orother causes

HMIP: Her Majesty’s Inspectorate of Pollution;duties now undertaken by the Environment Agency

HSE: Health and Safety Executive

Leachate: Water which flows through the soil orground and ends up in the water course and cancause pollution

Liquor: The liquid fertiliser which has beenmechanically separated from the coarse fibre portionof the digestate

Mesophilic digestion: Digestion involving micro-organisms with a growth optimum around 20-45oC

MAFF: Ministry of Agriculture, Fisheries and Food;Government department

NFFO: Non-Fossil Fuel Obligation, obligationrequiring Regional Electricity Companies topurchase a certain amount of electricity from non-fossil fuel sources

NFPA: Responsible for purchase of electricity underNFFO


Nitrate Vulnerable Zone: Catchment areas where waterquality standards for nitrates at risk of being exceeded

NRA: National Rivers Authority; duties now undertakenby the Environment Agency

OES: Occupational Exposure Standard

Organic Farming: see box in Introduction section fordetails

Pathogens: Organisms that can cause disease

pH value: A numerical scale for expressing the acidity oralkalinity of a liquid, ranging from 0 for strong acids to14 for strong alkalis, with 7 representing the neutralitypoint. The ideal pH range in an anaerobic digestershould be 6.8 - 8.

Planning conditions: Conditions relating to theconstruction and operation of a development imposed aspart of the granting of planning permission

Pool (Electricity): Mechanism for centrally controlledtrade of electricity

REC: Regional Electricity Company; holds franchise tooperate and maintain the local electricity distributionnetwork

Reception tank: Storage tank for feedstock prior todigestion

Second tier supplier: Licensed supplier (other than thelocal REC) contracting to supply electricity to customersconnected via the electricity distribution networks

Separator: Machine used to separate digestate into fibreand liquor

Siltation: Settlement of solid particles in the digestercausing blockage and reducing digester volume

Soil conditioner: A material which improves thefriability of a soil (eg peat, garden compost or fibre fromAD); soil conditioners may or may not contain nutrients

Sustainable development: Development which meetsthe needs of the present without compromising theability of future generations to meet their own needs

Thermophilic digestion: Digestion involving micro-organisms that grow above 40oC, typically kept at about55oC

Tilth: The condition of soil (ie fine, water retentive etc)which has been prepared for planting

Transmission losses: The decline in energy when it ismoved from the point of generation to the point of use

Triad: Three half hours of system peak during whichpower take off by a REC is used as the basis for the use oftransmission system charge

Volatile solids: Those solids in the feedstockswhich are volatile (ie will convert into gases whenheated) and which are therefore digestible

Wayleaves: Rights of way for the provision ofservices

Weeping Wall: Slurry contained by a wall withhorizontal or vertical gaps, through which liquidpasses leaving a relatively dry manure; the liquidrequires collection and treatment

UNITS OF POWER

Kilowatt (kW) = 1000 watts

Megawatt (MW) = 1000 kW

Gigawatt (GW) = 1 million kW

Terawatt (TW) = 1 thousand million kW

When ‘e’ added (eg kWe) = electrical power,

so kWe = kilowatt of electrical power

When ‘t’ added (eg kWt) = thermal power (heat),

so kWt = kilowatt of thermal power


Appendix Appendix Appendix Appendix 2Contacts

AD TechnologyWindover Farm, Longstock, Stockbridge, Hampshire SO20 6DJTel: 01264 810569

The Association of Electricity ProducersFirst Floor, 41 Whitehall, London SW1A 2BXTel: 0171-930 9390

Barton Willmore Planning PartnershipIntercell House, 1 Coldhams Lane, Cambridge CB1 3EPTel: 01223 322 444

Bow MauriceBarton Farmhouse, Dartington Hall, Totnes, Devon TQ9 6EDTel: 01803 867 891

British Biogen7th Floor, 63-66 Hatton garden, London EC1N 8LETel: 0171-831 7222

Council for the Protection of Rural England(CPRE)Warwick House, 25 Buckingham Palace Road, London SW1W 0PPTel: 0171-976 6433

Countryside CommissionJohn Dower House, Crescent Place, CheltenhamGlos GL50 3RATel: 01242 521 381

EnertechEngineering Consultants1a Barnsley Road, Ackworth, Nr PontefractWest Yorkshire WF7 7BSTel: 01977 612 391

Environment AgencyHafren House, Welshpool Road, Shrewsbury,Shropshire SY3 8BBTel: 01743 272 828

Environmental Energy LtdPO Box 3, Knighton, Powys LD8 2WDTel: 01544 267 880

ETSUHarwell, Didcot, Oxfordshire OX11 0RATel: 01235 433 302

Farm Energy CentreNational Agricultural Centre, Stoneleigh Park,Kenilworth, Warwickshire CV8 2LSTel: 01203 696 512

Farming and Rural Conservation AgencyBrooklands Avenue, Cambridge CB2 2BLTel: 01223 462 762

Farming and Wildlife Advisory Group, National AgriculturalCentre, Stoneleigh, Kenilworth, Warwickshire CV8 2RXTel: 01203 696 699

Friends of the Earth26-28 Underwood Street, London N1 7JQTel: 0171-490 1555

Greenfinch LtdBurford House, Tenbury Wells,Worcs WR15 8HQTel: 01584 810 777

Health and Safety Executive (Agricultural Sector), The PearsonBuildings, 55 Upper Parliament Street, Nottingham NG1 6AUTel: 0115-971 2800

Hydro Agri (UK) LtdImmingham Dock, Immingham, NE Lincolnshire DN40 2NSTel: 01469 554 784

Linking Environment and Farming (LEAF)National Agricultural Centre, Stoneleigh Park, Kenilworth,Warwickshire CV8 2LZTel: 01203 413 911

Livestock SystemsThe Long Barn, Clevedon Road, Tickenham,Nr Bristol BS21 6RYTel: 01275 857 799

MAFFNobel House, 17 Smith Square, London SW1P 3HXTel: 0171-238 6000

Maltin Pollution Control Systems (1967) LtdGould’s House, Horsington, Somerset BA8 0EWTel: 01963 370100

National Farmers Union (NFU)Agriculture House,164 Shaftesbury Avenue, London WC2H 8HLTel: 0171-331 7200

National Farmers Union ScotlandAgriculture House, Rural Centre, West Mains, Ingleston,Newbridge, Midlothian EH28 8LTTel: 0131-472 4000

National Trust36 Queen Anne’s Gate, London SW1H 9ASTel: 0171-222 9251

Northern Chicken GrowersThe Elms, Ottringham, East Yorkshire HU12 0DXTel: 01964 622 278

Nigel ParkerMAFF/EU Objective 5b Facilitator, Chessels,Daws House, Launceston, Cornwall PL15 7JFTel: 01566 777 422

Practically Green Environment ServicesSolar House, Magherafelt, Northern Ireland BT45 6HWTel: 01648 32615

Shropshire Energy TeamShropshire County Council Environment Department,The Shirehall, Abbey Foregate, Shrewsbury SY2 6NDTel: 01743 252 565

Soil AssociationOrganic Food and Farming Centre86-88 Colston Street, Bristol BS1 5BBTel: 0117-929 0661

Walford College,Walford, Baschurch, Shrewsbury SY4 2HLTel: 01939 262 100

WRI ServicesDonnington, Wroxeter, Shrewsbury SY5 6PUTel: 01952 740 414


Appendix Appendix Appendix Appendix 3Publications and regulations

Anaerobic Digester Performance at Hanford Farms, Dorchester. ADAS, 1994. RefB/M3/00388/17/REP. Available from ETSU Enquiries Bureau on01235 433601 ext 2450.

Anaerobic Digestion Fact Sheets from ETSU:AD1. Anaerobic digestion as a treatment process for farm slurries. Overview.AD2. Farm Wastes. Summary of Disposal Options.AD3. Anaerobic digestion as a treatment process for farm slurries. Scale andOpportunities.Available from ETSU Enquiries Bureau on 01235 433601 ext 2450.

Anaerobic Digestion of Pig Slurry: Piddlehinton. Hanford plc. Ref CS25.Available from ETSU Enquiries Bureau on 01235 433601 ext 2450.

Anaerobic Digestion in the UK. A Review of Current Practice. ADAS, Silsoe, 1993.Ref B/FW/00239/REP. Available from ETSU Enquiries Bureau on01235 433601 ext 2450.

Centralised Anaerobic Digestion. Review of Environmental Effects. MAFF, 1996.CSA 2730. Available from ETSU Enquiries Bureau on 01235 433601ext 2450.

Code of Good Agricultural Practice for the Protection of Air. MAFF. 1992. Freefrom MAFF Publications, London SE99 7TP or telephone 01645556000.

Code of Good Agricultural Practice for the Protection of Soil. MAFF. 1993. Freefrom MAFF Publications, London SE99 7TP or telephone 01645556000.

Code of Good Agricultural Practice for the Protection of Water. MAFF. 1991.Free from MAFF Publications, London SE99 7TP or telephone 01645556000.

Energy from Agricultural Animal Wastes. ETSU Technology Status Report,1993, TSR009. Available from ETSU Enquiries Bureau on 01235433601 ext 2450.

Environmental Assessment. A Guide to the Procedures. Department of theEnvironment/Welsh Office. HMSO/Welsh Office, 1989.

Environmental Assessment - the treatment of landscape and countryside recreation issues.Countryside Commission CCP 326 (1991). Available from PostalSales, PO Box 124, Walgrave, Northampton NN6 9TL. Tel: 01604781848.

Environmental Statements. Getting them right. CPRE, May 1990. (Freeinformation sheet aimed at developers and consultants to improve thequality of environmental statements; also a checklist for planners andthe public.)

Equity and Debt Financing for Centralised Anaerobic Digestion of Farm Wastes: Afeasibility analysis. Sceptre Management Ltd. Ref B/00/00173/REP.Available from ETSU Enquiries Bureau on 01235 433601 ext 2450.

Farm Waste Grant Scheme: Nitrate Vulnerable Zones. PB 2529. Free from MAFFPublications, London SE99 7TP or telephone 01645 556000.

A Farmers Guide to the Planning System. DOE/Welsh Office/MAFF. DOE, 1996.

Fertiliser Recommendations for Agricultural and Horticultural Crops, produced for MAFFby ADAS. Available from HMSO, ref RB209, £8.50.

Financing Renewable Energy Projects. A guide for developers, published by ETSU.

Guidance Notes for the Reduction of Light Pollution. Institution of Lighting Engineers,1994.

‘Hygiene and Sanitation Requirements in Danish Biogas Plants’, by H.J. Bendixen, inProceedings of 9th European Bioenergy Conference, Copenhagen, 1996.

Landscape Assessment Guidance. Countryside Commission CCP423 (1993).Available from Postal Sales, PO Box 124, Walgrave, Northampton NN6 9TL.Tel: 01604 781848.

Monitoring of the Anaerobic Digestion and CHP Installation at Newlands Mill, NewmarketHesketh, Cumbria, with various types of animal excreta as feedstocks. Enertech Ltd, 1983.Ref B/M4/00487/04/REP. Available from ETSU Enquiries Bureau on01235 433601 ext 2450.

Nature Conservation Guidelines for Renewable Energy Projects. English Nature, 1994.Ref A5.6.

Potential for Biogas on Farms. 1990 update. VFA Services. Ref B1295. Availablefrom ETSU Enquiries Bureau on 01235 433601 ext 2450.

Renewable Energy in the UK. Financing options for the future. CPRE, August 1995.(Document arguing for change in the policy and financing system forrenewable energy.)

Review of Planning and Environmental Issues relating to Centralised Anaerobic DigestionFacilities. Barton Willmore Partnership, 1995. Ref B/M4/00487/09/REP.Available from ETSU Enquiries Bureau on 01235 433601 ext 2450.

Technical Monitoring of a Mesophilic Anaerobic Digester fed with Poultry Manure, BitterlyCourt Farm, Shropshire. Enertech Ltd, 1983. Ref B/M3/00388/27/REP.Available from ETSU Enquiries Bureau on 01235 433601 ext 2450.

‘UK Strategy for Centralised Anaerobic Digestion’, by Steve Dagnall of ETSU, inBioresource Technology 52 (1995) 275-280.

Regulations affecting AD projectsControl of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations1991. SI 1991 No 324. HMSO. ISBN 011 03880 0

Environmental Protection Act 1990

European Commission Nitrate Directive [need publication details]

Health and Safety (Emissions to the Atmosphere) Regulations 1983 (SI1983/943)

Town and Country Planning (Assessment of Environmental Effects)Regulations 1988 (Amended 1990, 1992).

PPG22 Renewable Energy. Department of the Environment Planning PolicyGuidance Note.Water Act 1989. HMSO. ISBN 0 10 544 3905


Appendix Appendix Appendix Appendix 4Development of the guidelines

The processThese guidelines were produced using consensus buildingtechniques. Environmental Resolve, an undertaking of TheEnvironment Council, designed and managed the process, whichbrought together the industry, environmentalists, planners andgovernment agencies in order to address potential stakeholderconcerns and support the development of the industry in a sensitivemanner. The process was guided by a steering group led byEnvironmental Resolve and made up of British Biogen, Friends ofthe Earth, National Farmers Union and ETSU.This approach involved a series of workshops and small sub-groupmeetings, during the first half of 1997. Participants used theirexperience to develop and agree detailed guidelines on whatconstitutes good practice in developing an economic, efficient,environmentally sound and publicly acceptable AD industry. Draftmaterial was written up by the editor, circulated and amended byagreement at a final workshop, and then collated by the editor. A fulllist of all those involved is given below.The following attended one or both of the main workshops:Ewan Bent, Shropshire Energy TeamPeter Billins, British Biogen (Steering Group member)Chris Bow, Bow MauriceFergal Callaghan, Chemical Engineering Department, University ofBirmingham (provided special help on dealing with pathogens andparasites, including(Appendix 7)Henry Chesshire, WRI Services (provided special help with Appendix5)Michael Chesshire, Greenfinch LtdKen Dann, Walford CollegeLes Gornall, Practically Green Environment ServicesJohn Harrison, Shropshire County CouncilBob Harvey, Environment AgencyIan Higham, ETSU (Steering Group member)Joanne Hirst, National Farmers Union (Steering Group member)Graham Hurd, Shropshire Energy Team (provided special help withsection on electricity connection, including Appendix 6, inconsultation with Midlands Electricity plc personnel)George Macpherson, Home Grown Energy LtdChris Maltin, Maltin Pollution Control Systems (1967) LtdRobin Maynard, Friends of the EarthJames Murcott, Woodhouse FarmMatthew O’Brien, Farming and Wildlife Advisory GroupDan O’Connell, ETSUTamzin Phillips, National TrustChris Preece, Torridge District Council (provided special help withsection on planning processes)Chris Reynell, AD TechnologyMichael Sebastian, Health and Safety ExecutiveRalph Simms, ETSUAnna Stanford, Friends of the Earth (Steering Group member)Gerald Tetchner, EnertechGregg Tillotson, Barton Willmore Planning PartnershipPeter Tipping, W.S. AtkinsPenny Troop, Hydro Agri (UK) Ltd (provided special help withAppendix 5)

John Wase, Chemical Engineering Department, University ofBirminghamRoger C. White, Glenfield FarmDiana Wilkins, Ministry of Agriculture, Fisheries and FoodRobert Wilson, Chatwall FarmJames Wyllie, National Farmers Union, Scotland.

The following individuals also participated in drafting groupmeetings:Peter Billins, British BiogenFergal Callaghan, Chemical Engineering Department, Universityof BirminghamHenry Chesshire, WRI ServicesBob Harvey, Environment AgencyIan Higham, ETSUJoanne Hirst, National Farmers UnionGraham Hurd, Shropshire Energy TeamChris Preece, Torridge District CouncilRalph Simms, ETSUGerald Tetchner, EnertechPeter Tipping, W.S. AtkinsPenny Troop, Hydro Agri (UK) Ltd.

The following commented on written drafts only:Michael Browne, University of Westminster, Transport StudiesGroupNigel Parker, MAFF/EU Objective 5b Facilitator.

EditorDiane Warburton drafted text on behalf of the participants andacted as overall editor.

DesignChris Lord Information Design

Environmental Resolve teamPippa Hyam (project manager)Schia Mitchell (project co-ordinator)Environmental Resolve,The Environment Council,21 Elizabeth Street,London SW1W 9RP


Appendix Appendix Appendix Appendix 5Summary of management options for farm residues

Storage, treatment, then disposalOption

Anaerobic Digestion

Merits

• Good odour control.• Energy production.• Valuable digestate: fibre (soil

conditioner), and liquor(liquid fertiliser).

• Continuous flow process.• Improves storability.• Ease of handling.• Reduces spreading costs.• Reduces methane emissions.

Problems

• High capital costs for fullsystem.

• Operational costs.• Needs to be integrated into

whole business.• Requires daily management.

Conclusions

• Comprehensive.Management driven.

• May entail a separatebusiness.

• Suitable for producers with aspecific waste managementproblem, and are preparedto give extra commitment toovercome problems

Aeration Systems • Mixes at same time as itaerates to maintainconsistency.

• Various types andtechniques of aeration.

• Reduced BOD and odour.

• Management important.• Medium capital costs.• Some operational costs.• Not applicable to high dry

matter slurries > 4%.

• An option for thin slurryodour control.

Composting of manures andfor Fibrous Solids

• Alleviates nuisance odours ifproperly managed.

• Markets already in existence.• Many organic wastes can be

composted.

• If badly managed can causeodour problems andemmissions.

• High marketing cost.• Medium/high capital costs

associated with requirementfor covered yards andconcreted areas.

• Management and operationalcosts.

• May entail a separatebusiness.

• Suitablefor producers thatare prepared to give extracommitment to wastemanagement problems.

• Requires marketing.

Mechanical seperation • Reduces the size of thestorage tanks required.

• Reduces capping over thetop of the store.

• Slurry easier to pump.• Produces a saleable fibre.Enhanced utilisation of the liquidon the crops.


Storage, then disposalOption

Weeping Wall

Merits

• Convenient: all manure orslurry conveyed to onestore.

• Passive seperation of solidfrom liquid fraction.

• Liquid fraction used as liquidfertiliser.

Problems

• Medium/high capital cost• Requires storage for the

seperated liquid.• Two types of spreading

equipment required.• Potential odour problems..

Conclusions

• Practical option for dairy andpig farms.

Manure/solid residuestorage

• Allows for better timing ofapplications to land, as theresidues are stored and thenspread when required.

• Convenient at cleaning outtimes.

• Low capital costs.

• Rainfall causes effluent run-off and nutrient loss.

• Potential risk of pollution.

• Commonly practised.• Siting of manure/solid

residues subject to MAFFCode of Good AgriculturalPractice for Protection of Water.

Liquid residue storage • Allows for better timing ofapplications to land, as theresidues are stored and thenspread when required.

• Convenient at cleaning outtimes.

• Problems can occur with thecapping of stores.

• Requires a powerful mixingsystem.

• Energy costs associated withmixing.

• Medium capital cost.• Potential odour problems.

• Appropriate option in manycases.

• Application to land subject toMAFF Code of GoodAgricultural Practice forProtection of Water.

Direct disposalSpread residues directly toland

• Routine process.• Saves storage and treatment

costs.• Avoids peak in work load

associated with cleaning outstores, yards etc.

• Access to land may berestricted at certain times ofthe year.

• Potential risk of pollution dueto run off, particularly in highrainfall areas.

• Poor utilisation of nutrients.• Potential damage to soil

structure by applicationmachinery.

• Still an option in limited cases,subject to MAFF Code of GoodAgricultural Practice forProtection of Water.

Direct disposalExport manure from Farmvia Contractors

• Limited farm handlingfacilities required.

• Low management input.

• High charges on a continualbasis.

• Loss of nutrients from thefarm.

• Appropriate where the farmhas no land for spreading.

Dry manure as fuel(poultry)

• Income from sales.• Continual off-take from

farm.• Reduces the requirement

for storage.

• Applies only to dry poultrymanures eg broiler litter.

• Low price paid to the farmer.Nutrients lost from the farm ienot recycled back to the land.

• Appropriate where the farmhas no land for spreading.

Derived from Department ofTrade and Industry, Agriculture and Forestry Fact Sheet 2.November 1993.


Appendix Appendix Appendix Appendix 6666Electricity connection

The majority of schemes will require an electricity connectionto the local electricity distribution network to provide energyto operate ancillary equipment and other site loads duringmaintenance and shut-down periods, unless stand-bygeneration equipment is also installed.

If the gas produced by the AD plant is to be used to generateelectricity then the operator will have a number of tradingoptions depending on the size and location of the generatorand who consumes or buys the electricity. These include:

• Consumption by the operator for own on-site business

• Sale as an on-site generator, that is, sale to a singlecustomer or a qualifying group of customers relatedthrough common ownership on the same site

• Sale to the local Regional Electricity Company (REC)

• Sale via the Non-Fossil Fuel Obligation

• Sale through the electricity supply pool

• Sale to a second tier supplier through the Non-PooledGeneration Scheme

• Sale direct to own customer(s)

• New outlets which may emerge following deregulationof the energy market.

Each of these options will raise technical, planning,regulatory, commercial and contractual issues; some of theoptions involve mandatory licensing arrangements with costimplications and some will involve commercial risks. Therisks and benefits need to be appraised and understood by theprospective developer to improve the negotiating position andto maximise the value of the energy generated. This appendixprovides an introduction to the issues; more detailedinformation is available in Electricity Production Connected tothe Local Network - A Guide, published by the Association ofElectricity Producers.

The final option(s) chosen will determine the nature of theagreements and contracts and licences entered into by thedeveloper and the equipment that will form part of theinstallation. These may include:

• A connection agreement with the local REC determiningthe connection cost, import and export capacity, and anyoperational restrictions which may be applicable.

• An agreement with the local REC or other second tiersupplier (post 1998) to supply electricity for standby andtop-up purposes, either for on-site use or by contractedcustomers.

• A meter connection agreement with a licensedmeter operator to measure and record the half-hourly import and export of electricity by thegenerator and/or contracted customers.

• Purchase contract(s) with the local REC, second tiersuppliers, NFPA (for NFFO contracts) or contractedcustomers for electricity supplied and/or for spillexport when surplus to agreed declared generationcapacity.

• Interlocks on stand-by generators and contractualagreements to restrict the use of fossil fuels if theelectricity is sold via a NFFO purchase contract.

• Arrangements with the local REC or other secondtier supplier for the benefits accruing fromreduction in triad peak capacity charges and otherembedded generation benefits.

• A generator’s licence if exporting more than 50MWto anyone other than a single on-site customer (orexporting more than 10MW from a plant with anoverall capacity greater than 100MW).

• A DUoS agreement with the local REC to pay thetariff charges for use of their distribution systemwhere the generator is also operating as a secondtier supplier and selling the electricity generated tocontracted customers (DUoS refers to charges to bepaid to the local REC for use of their distributionsystem to export electricity to other users orsuppliers).

• A second tier suppliers licence if exporting morethan 500kW to anyone other than the pool or alicensed supplier.

• If gas leaves the plant, an OFGAS license will berequired because the operator is then classified as agas producer.

• Electricity Pool membership to cover fees applicableto generator registration, data collection andsettlement reconciliation for electricity generatedand consumed by contracted parties.

Even if a generator is not required to have a licence, theymay still apply for Pool membership on a voluntarybasis, although this would not normally be beneficial toa generator with output capacity lower than 30MW.

An electricity connection to the local electricitydistribution network will be required for any electricityexported, even if this is only during periods of spillwhen the output of the generator is greater than demandon-site or by its own contracted customers.

It is therefore advisable to establish a dialogue with thelocal REC at the earliest opportunity to appraise thevarious options, and to determine the relative terms andconditions for connection.


The REC will determine the method and the point at whichconnection can be made to the distribution network,dependent on the export capacity of the AD plant, the relativeparameters of the immediate distribution network and thepre-existing requirements of other electricity users in thevicinity. The scope for connection to the local network inrural areas with few industrial and commercial electricityusers may be limited and it may be necessary for connectionto be made at a higher voltage level on the primarydistribution networks.

The REC has statutory obligations under the Electricity Act1989 in respect of the safety and quality of electricity supplyto its customers and they need to ensure that generatorsconnected to the distribution network do not impose risksthat will affect their ability to fulfil this duty. However,connection of generators to the distribution network can insome cases be beneficial to the REC. In some cases it may

• Reduce the level of transmission and distributionlosses (nationally it is calculated that 7% of electricitygenerated is lost annually due to heating in cables andtransformer iron losses)

• Reduce the cost of purchase of electricity from the pool(particularly at times of peak demand when prices can behigh)

• Reduce triad peak capacity charges

• Defray the need to reinforce the local network

• Avoid Fossil Fuel Levy surcharges if generated fromrenewable energy resources outside NFFO

• Be a valued source of reactive power to assist in voltagecontrol.

The cost of connection could vary considerably depending onwhere the AD plant is located within the REC’s distributionnetwork. The cost of connection will in part reflect thedistances involved; but the connection cost will tend toincrease in steps (rather than smoothly) as the thresholds forrequiring particular assets and voltage levels are crossed.

If the developer has some flexibility as to where it can locatewithin a particular area, they should discuss with the REC therespective connection costs for different sizes of generator andthe potential benefits that may accrue to the REC in order tooptimise the costs to the developer and maximise the value ofthe energy generated.

The REC is required by its licence obligation to offer terms forconnection to the distribution network within three monthsof receipt of all the technical information in relation to thesize, location and operation of the generating plant, but thiswill generally be qualified subject to planning permissionapprovals and wayleave consents. To provide the terms forconnection, the REC will need to appraise the impact onseveral voltage levels of their distribution networks andensure that safety and statutory obligations to all connectedcustomers (including the generator to be connected) are notcompromised. However, they will generally provide aninitial estimate based upon the perceived least constrainedsupply route (usually by underground cable connection alongthe path of public highways) to give a ceiling price for the

guidance of the developer, with an undertaking toprovide a detailed quotation on examination ofalternative routes involving securing landownerwayleave consent and planning permissions if overheadline construction and/or transformer substationconstruction would be required. The REC may charge afee to appraise the connection implications but thiswould generally be set against the final connectioncharge if the project proceeds.

The connection point would usually be at the curtilageof the generation plant and if the connection chargesquoted are accepted by the developer, then the RECwould take on the responsibility to complete thestatutory procedures required for excavation on publichighways and to secure any wayleave consents andplanning permissions required. All the plant andequipment, cables etc would remain in the ownership ofthe REC and they would accept all future liability formaintenance and replacement if subsequently damaged.The benefit to the REC would be that the additionalnetwork installed could be utilised for future connectionof other customers and/or generators.

All the installation work required would generally becarried out by staff or contractors employed by the REC,although the developer can opt to use an approvedcontractor to carry out some of this work which is‘contestable’ if they feel they can secure a morecompetitive quotation (the elements that are‘contestable’ generally relate to the supply andinstallation of the new equipment, providing it meetsthe technical specifications set by the REC); the finalconnections, energisation and moving of existingconnected assets, however, for safety reasons are ‘non-contestable’ and have to be carried out by the REC.

In some cases, where the developer is able to secure hisown wayleave consents, he can opt to nominate thepoint of connection to the distribution at the pointwhere it is coupled into the existing network. Thedeveloper may derive some benefit from cost reductionsin equipment specification (particularly if capacity of theconnection determined with standardised planspecifications by the REC cannot be fully utilised byincreasing generator capacity) but the developer willthen be fully responsible for the ongoing maintenanceand replacement costs and will need to include theworks involved in the application for planningpermission for the AD plant.

Good practice would suggest that the local planningauthority should be consulted on the route of the line, asthey have an opportunity to make representations orrequests for amendments, or indicate that they have noobjection. Developers may also feel it would beappropriate to consult local residents over the potentialroute of the line at this stage. County councils anddistrict councils (or unitary authorities) are consulteeson the application for consent, and objection by eithercouncil means that there is likely to be a public enquiry.


AppendixAppendixAppendixAppendix 7777Effects of AD on parasites andpathogens

The following paragraphs outline the effects of the anearobic digestion (AD)process on different pathogens.

Parasites

Anaerobic digestion at 350C (known as mesophilic digestion, used by thevast majority of farm digesters), has been shown to reduce the numbers ofviable larvae and eggs of some parasitic worms to undetectable levels afterone week, although there is generally poor control of Ascaris, Tacnia andCryptosporidium. However, the oocysts (a type of egg) of these worms,which can infect any animal ingesting them, remain viable after 50 days at350C. Digestion at 550C significantly reduces the numbers of oocysts, butmany viable units still persist, even after digestion for extended periods oftime. Mesophilic anaerobic digestion will not significantly reduce theinfectivity of slurry contaminated with parasites.

Pathogenic bacteria

Experiments with pig slurry have shown that mesophilic digestion for fourdays will destroy 90% of a population of Salmonella bacteria, although lowlevels of the bacteria persisted even after 70 days digestion. This persistencemay be due to poor mixing within the digester, allowing pockets of bacteriato survive in a crust on the surface. Properly managed, thermophilicdigestion can reduce bacterial levels by an even greater factor, but again lowlevels may persist due to poor mixing. Mesophilic anaerobic digestion willsignificantly reduce the levels of pathogenic bacteria, but will not eliminatethem completely from the waste and so the COSHH assessment willdetermine the measures required to control the potential damage to humanhealth.

Viruses

Research findings have shown that mesophilic anaerobic digestion reducesvirus numbers in sewage samples, but viable virus units may still be found tobe present, even after extended periods of digestion.


Appendix Appendix Appendix Appendix 8888Walford College:case study

Location

Walford College Farm, Baschurch, Shrewsbury, Shropshire is ownedand operated by Walford College, a county-based further educationestablishment for agricultural and land-based industries.

Concept

The 260-hectare mixed farm attached to Walford College includes a130 dairy cow herd, 160 sows and progeny, plus beef cattle and dairyyoung stock. These produce some 3000 tonnes of organic manure perannum. Environmentally acceptable disposal of this waste presented aproblem. In 1990, the college decided to introduce an integratedfarm slurry management system based on anaerobic digestion (AD) toassess its advantages over the previous method of spreading rawmanure directly to land. AD involves the breakdown of organic wasteby bacteria in the absence of oxygen; products include a methane-richgas which can be used as a fuel.

As part of a three year demonstration project, an AD systemincorporating an Enviropower combined heat and power (CHP)facility was installed in 1994, rated at 35 kWe (kilowatts of electricity)and 58kWt (kilowatts of heat) output. Actual output has averaged18.22kWe for 19.5 hours per day. Approximately 30kWt is harnessedto maintain the digester at the requisite temperature of 35-370C. Thesystem also produces 15m3 per day of treated liquid slurry or ‘liquor’and 3 tonnes per day of separated fibre. The liquor, which isodourless and easier to handle than raw manure, has an averageanalysis of 2.32kg nitrogen, 1.32kg phosphate and 5.3kg potash per1000 litres and is spread on grazing land. The fibre is made intocompost for the college’s own use and for sale to garden centres andother customers.

Technology

Slurry is fed from the pig and dairy units via flow channels to areception pit. A chopper pump then pumps the slurry into a 335m3above-ground digester. Digestion takes 16-20 days. Digestionproduces 450m3 per day of biogas which fuels the CHP unit drivingan electricity generator; heat is recovered from the engine’s coolantsand exhaust system. A stand-by boiler is used to heat the digester inthe event of failure of the CHP unit. After digestion, the treated slurryis passed over a sieve separator; the fibre is removed to a compostingshed and liquor is fed to a 950,000 litre storage tank. It is planned touse the farm’s existing irrigation main to irrigate the liquor onto thegrass fields.

Legal and planning requirements

The planning application was submitted in December 1993. Specificproposals for the erection of buildings or other works relating to ADare normally determined by the county council in shire areas. AtWalford College chicken litter is imported as a supplementaryfeedstock for the digester when the farm’s dairy herd is in the fields.The application was dealt with by Shropshire County Council.Planning permission was granted in February 1994.

Construction

Construction work began in February 1994. A singlecontractor was engaged to supply, install and commission thedigester, CHP unit and composting shed. The contractor wentinto receivership before completion and Walford Collegeengaged other companies to provide the CHP unit andcomposting shed. The system was commissioned in October1994. Seed material was imported from a working digester tostart the AD process.

Operating experience

The system requires no more than one hour per day from thecowman, who is very enthusiastic about the installation. Actualrepair costs are likely to stabilise as the system settles down andteething problems are overcome. The lack of slurry smellsaround the unit is noticeable. The area around the digester iscleaner than might be expected from a slurry disposal system.

Costs and financing

The project is jointly funded by Walford College and theEuropean Community’s LIFE programme.

Capital costCapital costCapital costCapital cost ££££

Digester 89,349

CHP unit 34,700

Composting unit 9,600(including site infrastructureand connections) _______

£ 133,649£ 133,649£ 133,649£ 133,649

BenefitsBenefitsBenefitsBenefits actual (£) inactual (£) inactual (£) inactual (£) in first 6 months first 6 months first 6 months first 6 months potential (£)potential (£)potential (£)potential (£)

Value of electricity generatedannum 18.22kW x 19.5hrsx 365 days x £.08 10,374 (30kW)17,082

Avoided contractors’ spreading costs 2,500 2,500

Value of fertiliser saving to grassland(summer 6 months), nitrogen only34.8kg/day x 180 days x £.32kg 2,004 2,004

Compost sales 400 (1460m3 x £10/ m3)14,600

Waste hot water20kW x 20hrs x 365 daysx £0.18/kWh 2,628Annual income generated £15,278 £38,814Running costs: repairs and callouts (2,100) (2,100)Net annual income £13,178 £36,714Labour: 1hr/day @ £8/hr £(2,920) £(2,920)

The need to allow for addition of labour charge will depend onindividual farm case, whether worked in overtime or absorbedin working day etc.

For further information contact Ken Dann, Walford College,Baschurch, Shrewsbury, Shropshire SY4 2HL,

tel: 01939 260461, fax: 01939 261112.

Summary Page54

Anaerobic digestion for public information

What is Anaerobic Digestion?Anaerobic digesters produce conditions that encourage the naturalbreakdown of organic matter by bacteria in the absence of air.Anaerobic digestion (AD) provides an efficient and effective methodfor converting residues from livestock farming and food processinginto useful products.

Feedstocks include animal slurry (from cattle, pigs and chickens) andresidues from food processing industries. Other organic materials canalso be digested.

The initial reasons for developing an AD plant will vary but are likelyto include one or more of the following:

• A wish to manage food processing residues and farm slurriesmore effectively, including control of odour

• A wish to utilise biogas to offset farm or factory energy costs

• A wish to sell electricity off-site (through the grid or other localuser)

• A wish to utilise or sell fibre and liquor as soil conditioner andliquid fertiliser.

Whatever the initial reasons, for a scheme to be successful it mustutilise all the products of AD.

What does the process involve?The feedstocks are placed into a digester (a warmed sealed airlesscontainer). The materials ferment and are converted into a gas and asolid called the digestate, which in turn can be separated out into fibreand liquor.

The AD plant could be a small on-farm facility run by a farmer usingonly the slurry produced on the farm and using all the resultingproducts on the farm. Alternatively, it could be a larger scaledevelopment known as a Centralised Anaerobic Digester (CAD), takingfeedstock from local farmers and food processors and marketing theproducts on a larger scale. The process is the same whatever the scalebut the safe running of the digester and marketing of products is morecomplex for a CAD scheme.

What are the benefits of AD?AD has a number of potential and actual benefits.

Reducing emission of greenhouse gases

Methane is the main constituent of the biogas and is a majorgreenhouse gas. By burning the gas as a source of heat and/orelectricity, the amount of methane lost to the atmosphere is likely tobe reduced. Equally, by using this renewable source of energy it

could displace the need to use energy from fossil fuels such ascoal and oil.

Reducing odour

• AD can reduce the odour from farm slurries and foodresidues by up to 80%.

• Reducing land and water pollution

• Land and water pollution can be reduced through efficientwaste management.

• Badly managed disposal of animal slurries can lead to landand ground water pollution. AD can reduce the risk ofpollution by stabilising and allowing more control ofresidues.

Nutrient recycling

• The nutrients available in the liquor and fibre can be usedas part of an overall fertiliser programme and reduces theneed for inorganic fertilisers.

Effective waste management

• AD can be regarded as part of an integrated wastemanagement plan. The process stabilises slurries, makingthem easier to handle and reducing odour. New legislationis placing increased pressures on the safe handling of waste.Properly managed AD schemes will help farmers meetthese pressures.

What are the problems of AD?Costs

• AD has significant operating and capital costs. It is likely tobe most viable for those people who can utilise all theproducts effectively.

Control of dangerous emissions

• Some of the trace gases found in the biogas are toxic anddangerous to human health (hydrogen sulphide andammonia). This means the gas must be cleaned and onlydealt with by trained operators.

Traffic

• If a CAD plant is being developed it will involvetransporting feedstock to and from the site. Considerationneeds to be given to the impact on local communities andthe overall distance it will be viable to transport residues.

Summary Page55

Animal health

• There may be some risk of animal disease transmission betweenfarms in CAD schemes, through cross contamination from vehiclemovements between farms and the centralised site. Strict qualitycontrol measures are needed.

Careful planning, design and operating will reduce the problems andmaximise the benefits of AD. Good Practice Guidelines have beenproduced in partnership by a wide range of organisations which havean interest in AD including the AD industry, farmers, planners,electricity companies and environmental groups. They explain indetail all the issues that must be considered in any AD scheme.

For more information contact British Biogen,

7th Floor, 63-66 Hatton Garden, London EC1N 8LE, or on:

telephone +44 (0) 171-831 7222, fax +44 (0) 171-831 [email protected].

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