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166 Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 11 Potential GHG Reductions Wastes arisings in the UK represent a potential resource and feedstock available to be converted into products for further use. Assessing the most environmentally friendly disposal option for a particular waste can be challenging as there are often a range of disposal options available and limited data on which to base assumptions of potential environmental costs and benefits. The key advantage of utilising waste materials for the generation of energy or transport fuels is that they displace the use of fossil fuels and divert material that would otherwise likely be disposed of to landfill. The quantification of the environmental costs and benefits is required to ensure the most appropriate solutions are developed. Recent work performed by AEA and North Energy for the EU Commission, DG Environment (awaiting publication) has identified that ‘waste-based bio-energy pathways offer the highest GHG emissions savings’. 301 This is due to the absence of production emissions for the material, and the displaced fossil fuels. Below, two scenarios of converting a waste material to energy or a transport fuel, and the GHG savings such conversions would achieve, have been explored: • Converting source separated food waste, through anaerobic digestion, to a digestate and a biogas, and subsequently converting this biogas to CHP, electricity or alternatively a transport fuel. • Converting waste wood, through combustion, to electricity. These scenarios were selected to complement our identification of these feedstocks in Section 5 as likely to make a substantial contribution to renewable energy from wastes in the future. They also illustrate the insights that can be gained through this type of analysis as they cover an extensive life cycle extending in to feedstock supply and alternative uses. Both scenarios are been explored through the use of BEAT. Box 4: Biomass Environmental Assessment Tool (BEAT) BEAT was originally developed for the UK Department for Environment, Food and Rural Affairs (Defra) and the UK Environment Agency (EA). Hence, the nature of the technologies, performance characteristics and related assumptions are based on UK circumstances. It is designed to provide a means of assessing biomass schemes by: 1. Providing a comparison of GHG emissions from the proposed plant and fossil fuel based plant; 2. Providing information on key potential environmental impacts; 3. Identifying potential options for mitigating environmental impacts; 4. Providing an estimate of production costs and of support mechanisms. While the tool can consider all stages of the fuel chain, modification of the analysis is readily achievable through altering the system boundaries and the reference pathway. BEAT was launched on 13th November 2008, when the tool/dataset were also made publicly available. Beat is available from the Biomass Energy Centre www.biomassenergycentre.org.uk. 301 Implementation of the EU Biomass Action Plan and the Biofuel Strategy: Comparing GHG emission reduction performance of different bio-energy applications on a life cycle basis, AEA and North Energy,
Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 Some of the key features of the BEAT systems and the criteria that have been used here are: • System boundary: In this work the systems begin at the point the waste is available for use as a resource, taking no consideration of the environmental impacts of creating the waste. Once use of the waste as a feedstock commences all subsequent stages are incorporated, e.g. emissions from processing the waste, manufacture of machinery and ash disposal, to cite a few stages. • GHG Emissions: Emissions of the three main GHGs, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are included. While carbon dioxide and, to a lesser extent, methane emissions are widely publicised, sources of nitrogen giving rise to the emission of nitrous oxide (N2O) from the soil is a less well known effect. A complex series of reactions and processes transform some of the nitrogen present into N2O, potentially a critical issue as the global warming potential of N2O is nearly 300 times that of CO2. Individual GHG emissions are converted into equivalent CO2 using quoted values of Global Warming Potentials (GWPs). • CHP: In all cases emissions savings have been derived assuming the displacement of compressed natural gas, or the displacement of grid electricity. • Reference system: Reference systems are used here to address the alternative fate of a waste product. The disposal of a waste product will be avoided if it is used as a biomass feedstock for energy production. The GHG emissions that would have arisen from disposal are taken into account by deducting from the total GHG emissions of the pathway. • Fossil Fuel Displacement: Assumptions about the fossil fuel displaced (e.g. coal, oil, or gas) and the efficiency of the conversion technology for heat and electricity production can make a significant difference to the savings calculated. Using BEAT to follow the two waste disposal scenarios outlined below allow establishment of the potential GHG reductions that could be achieved were the alternative disposal route to be pursued and the final products fully utilised. The results have been presented in terms of the kilograms of GHG saved per tonne of waste, as waste utilisation is the primary aim, with energy generation the secondary aim. 11.1 Scenario 1: Food Waste Domestic food waste can be collected separately as part of the MSW disposal route. This waste represents a resource that can be widely available throughout the UK, although collection and transport are likely to be more efficient in urban areas. It is estimated that there is potentially 5 million tonnes of MSW food waste each year, as well as nearly 7 million tonnes of C&I food waste (for England, Wales and Scotland), although it is unlikely all would be available for collection. The majority of this waste stream currently goes to landfill, often with energy recovery through landfill gas. This situation is rapidly changing with the requirement of the Landfill Directive that levels of biodegradable municipal solid waste (MSW) sent to landfill must be reduced to 75% by 2010, by 50% 2013 and by 35% by 2020 of 1995 levels. The alternative disposal options available are to compost or anaerobically digest the waste. Food waste treated at a compost site will produce a soil conditioner material. The composting process will be required to be carried out in a sealed container as the material may contain meat or meat products. Food waste treated at an AD site will produce an organic digestate output, which can be used as a soil conditioner. It has been assumed that a compost soil conditioner and a digestate soil conditioner, although having different physical forms, have the same value as a soil conditioner. In addition biogas 167
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