Life cycle assessment of conventional and advanced two-stage 1 energy-from-waste technologies for methane production 2

12 This study integrates the Life Cycle Assessment (LCA) of thermal and biological technologies for 13 municipal solid waste management within the context of renewable resource use for methane 14 production. Five different scenarios are analysed for the UK, the main focus being on advanced 15 gasification-plasma technology for Bio-Substitute natural gas (Bio-SNG) production, anaerobic 16 digestion and incineration. Firstly, a waste management perspective has been taken and a functional 17 unit of 1 kg of waste to be disposed was used; secondly, according to an energy production 18 perspective a functional unit of 1 MJ of renewable methane produced was considered. The first 19 perspective demonstrates that when the current energy mix is used in the analysis (i.e. strongly based 20 on fossil resources), processes with higher electric efficiency determine lower global warming 21 potential (GWP). However, as the electricity mix in the UK becomes less carbon intensive and the 22 natural gas mix increases the carbon intensity, processes with higher Bio-SNG yield are shown to 23 achieve a lower global warming impact within the next 20 years. When the perspective of energy 24 production is taken, more efficient technologies for renewable methane production give a lower GWP 25 for both current and future energy mix. All other LCA indicators are also analysed and the hot spot of 26 the anaerobic digestion process is performed. 27 2