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138 Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 Open Composting Systems Most compost is generated through open air techniques, which places the organic waste in piles exposed to the air. The waste is commonly formed into elongated triangular piles that are called windrows, which allow optimum exposure to the atmosphere whilst minimising the land area taken up. Once the waste is prepared for composting the principal control mechanism for the process is the air requirement of the micro-organisms and the dissipation of the heat generated. Introduction of air into the waste can be achieved either though active pumping of air into the waste or through the mechanical lifting and mixing of the waste to introduce air into the pile. These two approaches are called static aerated pile and turned windrow. Windrow composting is well established in the UK with a large number of facilities treating source separated garden waste. Such systems for green wastes are typically quoted at between £20 and £25/t of waste treated although there is strong regional effects due to the potential for markets of the compost. In-Vessel Composting Systems Reactor or enclosed composting is a relatively new composting development that provides a faster active biodegradation process, reducing the area required. The use of a ‘closed’ vessel allows much greater control over the process and this helps both with the speed of the process but also the consistency (hence quality) of the compost product. The reactors come in a variety of forms and have varying degrees of automation. However, the basis of reactor composting is that materials are enclosed in a drum, silo, or similar structure and air is injected into the composting material to maintain the optimum conditions for composting. Following the foot and mouth outbreak in 2001, any waste which contains or could contain meat or meat products has to be treated at a certain temperature for a minimum period of time, thus any source separated waste which includes the collection of kitchen waste from households, would need to be composted in an in-vessel system. In-vessel composting facilities are not as well established, with less than 20 operational in the UK. These systems are more expensive than windrow systems with potential gate fees in the range £35-£50/t of waste treated. However, in Europe the number of facilities is large with in-vessel composting becoming the norm for organic wastes other than green garden wastes. Outputs Compost is stabilised organic material consisting of the refractory and slowly degradable cellulosic components. The main use of this compost is as a soil improver. The quality of the compost is largely determined by the feedstock provided to the process. Relatively uncontaminated feedstocks will give rise to uncontaminated products and these are generally composted from source-separated materials. The residues from the composting process are those materials that do not readily degrade, such as wood and these can either be returned to the front of the process to be shredded or they can be disposed of. The ratio of soil improver product to reject fractions will vary markedly with the feedstock and process but typically the product material might only be 50 to 60% of the incoming waste with 15-30% loss of mass through the biodegradation for source separated materials whilst residual (mixed waste) compost may only generate 10-20% compost product with up to 60% being reject to landfill. 9.2.1 Composting of MSW The use of composting schemes is growing, especially as the organic fraction of MSW to landfill must be reduced. While composting does not produce either energy or fuels from waste, it does produce a viable product as an output, and it gives an indication of the proportion of organic material, largely from MSW, currently being treated.
Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 In 2006-07 3.6M tonnes of source segregated waste was composted, a 5% increase on the previous year. 267 The vast majority of this waste is from MSW, and of this 48% was from civic amenity sites while 46% was from kerbside collections. There are many composting sites in the UK, of varying sizes, types and longevity. Identifying a complete list of sites is difficult as many waste operators are experimenting with this process, and so sites are developing rapidly at the moment, as decisions are taken on whether to pursue this disposal method. Some of the better known examples of large scale composting sites in the UK are: Table 71 Large scale composting examples in the UK Name and Location Volume Operational Glasgow Fruit Market, Glasgow 268 2,000 tonnes p.a. 2005 Council run and output is sold. Twycross Zoo, Warwickshire 269 Lynnbottom, Isle of Wight 270 St. Ives, Cambridgeshire 271 Wharton, Herefordshire 272 * Enclosed composting of waste fruit, vegetables, paper, card and pallet wood 800 tonnes p.a. Enclosed composting of animal wastes and garden waste. Up to 60 tonnes per day Originally composting of garden waste in windorws. More recently taking food waste in-vessel. 100,000 tonnes p.a. Conversion of kitchen and green waste in 4 composting tunnels, 2 of which are part of Defra Demonstrator Programme. 10,000 tonnes p.a. In vessel anaerobic digestion technique to compost garden and kitchen waste. Also one of the Defra Demonstrator Programmes. 2008 1992 2002 Parham, Suffolk 273 * Site takes garden and food waste, shredded paper and cardboard, from Suffolk Coastal District Council 2006 * The operating company went into administration in February 2009, at which point the site in Parham was taken over by Country Style group and continues to operate. 267 Compost Information Sheet, Waste Online, http://www.wasteonline.org.uk/resources/InformationSheets/Compost.htm 268 Chronicle of Glasgow’s Fish, Fruit and Flower Markets, http://www.glasgow.gov.uk/en/Business/Markets/chronicleofglasgowsfishfruitvegetableandflowermarket.htm 269 Twycross Zoo Recycles Poo! http://www.twycrosszoo.com/news/currentnews.htm 270 Lynnbottom Composting Facility, http://www.wrightenvironmental.com/pdf/IsleofWight_print.pdf 271 Envar, Services, Composting, http://www.envar.co.uk/services/composting.html?menu_pos=services 272 Bioganix Research Limited, Defra Factsheet, http://www.defra.gov.uk/environment/waste/wip/newtech/dem-programme/pdf/Bioganix.pdf 273 Greenprint Forum and Green Issues Task Group visit the Parham Compost Facility, http://www.suffolkcoastal.gov.uk/yourdistrict/greenissues/greenprint/forum/parhamvisit/default.htm 139
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South East 327 - - 55% of MSW by 20
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Appendix 3 MBT Methods Specific in
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Figure 27 Orchid Environmental proc
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