Environmental and economic assessment of transportation fuels from municipal solid waste

Abstract

Municipal solid waste (MSW), comprising food waste, residential rubbish and commercial waste, has been identified as a potential feedstock for the production of alternative fuels. Conversion of MSW to fuel could displace petroleum-derived fuels to mitigate greenhouse gas (GHG) emissions from transportation, and also avoid the GHG emissions associated with existing waste management strategies such as landfilling. This thesis quantifies the lifecycle GHG emissions and economic feasibility of middle distillate (MD) fuel, including diesel and jet fuel, derived from MSW in the United States via three thermochemical conversion pathways: conventional gasification and Fischer-Tropsch (FT MD), plasma gasification and Fischer-Tropsch (Plasma FT MD) and, conventional gasification, catalytic alcohol synthesis and alcohol-to-jet upgrading (ATJ MD). Expanded system boundaries are used to capture the change in existing MSW use and disposal, and parameter uncertainty is accounted for with Monte Carlo simulations. The median lifecycle GHG emissions are calculated to be 32.9, 62.3 and 52.7 gCO2e/MJ with standard deviations of 7.2, 9.5 and 13.2 gCO2e/MJ for FT, Plasma FT and ATJ MD fuels, respectively, compared to a baseline of 90 gCO2e/MJ for conventional MD fuels. These results are found to be sensitive to MSW composition, the waste management strategy displaced, plant scale and associated fuel yield, feedstock transportation distance and the co-product allocation method. Median minimum selling prices are estimated at 0.99, 1.78 and 1.20 $ per litre and standard deviations of 0.14, 0.29 and 0.27 $ per litre with the probability of achieving a positive net present value of fuel production at market prices of 14%, 0.1% and 7% for FT, Plasma FT and ATJ MD fuels, respectively. The sensitivity of these results to the discount rate, income tax rate, implementation of carbon price, feedstock cost, scale and process efficiency indicate that policy measures, MSW tipping fees and technological advancements can improve the economic viability of MSW fuels. Considering a societal perspective (e.g. social opportunity cost of capital, social costs of GHG emissions) increases the probability of positive net present value of fuel production to 93%, 67% and 92.5% for the FT, Plasma FT, and ATJ MD fuels, respectively.