Integrated Life Cycle Assessment and Techno-economic Analysis for Hydrothermal Liquefaction of Carbonaceous Municipal Solid Waste with Variable Composition

We developed a gate-to-grave life cycle assessment (LCA) and techno-economic analysis (TEA) framework to elucidate the sustainability implications of hydrothermal liquefaction (HTL) as a valorization technology for municipal solid waste (MSW). This thermochemical treatment method can convert biomass components into bio-oil and biochar and synthetic plastics components into oil and/or monomers. Component additivity models for oil production from the HTL of MSW were integrated with LCA and TEA modeling to perform dynamic cost and life cycle environmental impact assessments. Characterization factors from the US EPA TRACI database were used for impact assessment. Displacement credits were applied for coproduced biochar, terephthalic acid, and bisphenol A. Uncertainties were characterized through Monte Carlo simulation, and global sensitivity analyses identified the key drivers for economic and environmental impacts. Model results showed that simulated municipal waste in the New York City metropolitan area can be processed via HTL (at 425 °C) with a global warming impact of −600 ± 350 kg CO2-eq per ton feedstock processed using displacement allocation and produce a gasoline–diesel blend with a minimum fuel selling price of 1.48 ± 0.51 $/gallon. The results indicate that HTL has a potential greenhouse gas saving of 330 kg of CO2 per ton MSW processed when compared to current MSW waste management practice, i.e., mechanical recycling (25%), composting (10%), combustion (13%), and landfilling (52%). On the other hand, with an energy recovery of 22.6% and energy rate of return (EROI) of 1.21, this pathway falls short of the general recommendation for advanced fuel technologies like HTL, which require an EROI of 2–3, indicating a need for further process optimization. Using higher feedstock–water ratios and lower process temperatures to reach higher process yields could increase the net EROI