Publication DetailsTitle : Well-to-Wheels Analysis of Compressed Natural Gas and Ethanol from Municipal Solid Waste
Publication Date : October 28, 2016
Authors : U. Lee, J. Han, M. Wang
Abstract : The amount of municipal solid waste (MSW) generated in the United States was estimated at 254 million wet tons in 2013, and around half of that generated waste was landfilled. There is a huge potential in recovering energy from that waste, since around 60% of landfilled material is biomass-derived waste that has high energy content. In addition, diverting waste for fuel production avoids huge fugitive emissions from landfills, especially uncontrolled CH4 emissions, which are the third largest anthropogenic CH4 source in the United States.
Lifecycle analysis (LCA) is typically used to evaluate the environmental impact of alternative fuel production pathways. LCA of transportation fuels is called well-to-wheels (WTW) and covers all stages of the fuel production pathways, from feedstock recovery (well) to vehicle operation (wheels). In this study, the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET®) model developed by Argonne National Laboratory is used to evaluate WTW greenhouse gas (GHG) emissions and fossil fuel consumption of waste-derived fuels. Two waste-to-energy (WTE) pathways have been evaluated – one for compressed natural gas (CNG) production using food waste via anaerobic digestion, and the other for ethanol production from yard trimmings via fermentation processes. Because the fuel production pathways displace current waste management practices (i.e., landfilling waste), we use a marginal approach that considers only the differences in emissions between the counterfactual case and the alternative fuel production case.
The results show that the renewable CNG from food waste can reduce GHG emissions by 28–157% compared with CNG from fossil sources, while the ethanol from yard trimmings waste can reduce GHG emissions by 52–146% compared with gasoline. Most of the reduction results from avoiding the emissions associated with the counterfactual scenario, mainly uncontrolled CH4 emissions from landfills. Because waste-derived fuels are non-fossil fuels, WTW fossil fuel consumption is also reduced dramatically: by 106% for the CNG produced from food waste compared with that of natural gas, and 74% for ethanol produced from yard trimmings compared with that of gasoline. However, the results depend on the conditions of both the counterfactual scenarios and the alternative fuel production scenarios. In order to refine the results, further investigation is needed for the parameters of landfill gas (LFG) emissions, which are subject to many uncertainties.