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48 Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 However disposal to land may reduce in coming years as legislative and practical constraints limit this route. 67 The available land bank may reduce due to a reluctance to have food products grown on land treated with this waste, although the growth of energy crops would provide a (small) mitigating land availability. 67 The impact of the Nitrates Directive (Nitrate Vulnerable Zones Regulations) may be a reduction in the volume of sludge that can be applied in certain areas. Landfill A small amount of sludge is disposed of to landfill, which is largely used only as a fall back option as it can be used at very short notice. 56 This route is not sustainable in the longer term and the costs associated with it are increasing as landfill tax levels go up and void space is reduced. In addition, due to the high water content of bio-solids only a limited number of sites are willing to accept it due to the potential impact on the landfill sites’ leachate management programme. Incineration Incineration is the second largest disposal route, generally used by the larger treatment works. 56 The heat generated is often used on site to meet the heating needs of the process, i.e. to dry the bio-solids, and generate electricity. Several stages of cleaning of the flue gases are incorporated within the process to ensure they meet EU emission limits set by the Waste Incineration, the Integrated Pollution Prevention and Control (IPPC) and the Landfill Directives. 68 The calorific value of bio-solids is dependent on the type of material, its water content (the degree of dewatering) and the concentration of organic matter present, solids content, calorific values and biomass contents vary according to the type of treatment. Incineration is a relatively expensive option, so it is only of interest in areas where alternative disposal methods are not available or the cost of transportation is prohibitive. Incineration of bio-solids involves burning the sludge at 600-900°C to destroy the organic content, leaving a residue of mineral ash for final disposal (usually to landfill or controlled waste re-use such as land reclamation). The net calorific value of dried bio-solids, i.e. its energy content after deducting the heat required to evaporate the remaining water is around 23MJ/kg of volatile solids. 69 Co-incineration The bio-solids, either as dewatered cake, but generally as dried pellets, can be burnt in adapted (WID compliant) plants, often co-fired with coal. It is possible to burn bio-solids with municipal waste, however, the burner design system must be capable of handling both fuels. 67 Thames Water 25 year Sludge Strategy, 2008, http://www.thameswater.co.uk/cps/rde/xbcr/SID-54091C65-CAD380F4/corp/sludge-strategy.pdf 68 Waste Incineration Directive http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2000:332:0091:0111:EN:PDF, Integrated Pollution Prevention and Control, original legislation, http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31996L0061:EN:HTML, Landfill Directive http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:1999:182:0001:0019:EN:PDF 69 Sewage Sludge Disposal: operational and environmental issues, Bruce A.M. and Evans, T.D., Foundation of Water Research, 2002.
Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 20% 1% 11% 4.4.5 Future Arisings 4% 64% Farmland Landfill Incineration Land reclamation/restoration Other Figure 9 Disposal of bio-solids in 2004 70 The volumes of bio-solids created are increasing, through increased population, and through increased levels of treatment of municipal sewage, and at times dedicated industrial effluent treatment plants run by the water companies. The increase is also in part due to the increased levels of sewage treatment required through tightened Regulations. 71 In 2004-5 1.72 Mt of dry bio-solids were produced. Work carried out internally in AEA has estimated that this will increase to 2.5 Mt by 2030 due to changes in industry practice brought about by legislation relating to requirements for improved treatment practices. One water company, Thames Water, have estimated the future arising of bio-solids until 2021, and extrapolated further to 2035. 72 The prediction is for a steady increase in their production of bio-solids year on year. The volume of bio-solids available for conversion into fuels and energy is likely to increase in future years, due to increasing populations in some areas, and decreasing opportunities to utilise traditional disposal methods in all areas of the UK. 70 Sewage sludge arisings and management 1986/97 – 2005, Defra. 71 th Determining sludge production from wastewater treatment, Clode, K., Khraisheh, M., Ballinger, D., 2008, 13 European Biosolids and Organic Resources Conference and Workshop. 72 Thames Water 25 year Sludge Strategy, 2008, http://www.thameswater.co.uk/cps/rde/xbcr/SID-54091C65-CAD380F4/corp/sludge-strategy.pdf, based on Local Authority growth projections, taking in consideration such variables as new development and housing density until 2021, and then linearly extrapolated to provide best future estimates to 2035, with no specific allowance been made for additional sludge arising from currently unknown changes in legislation treatment standards, customer behaviour or other factors, such as impact of Local Authority waste strategies. 49
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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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