PNNL

Abstract

US municipal wastewater contains approximately 160 TBtu/y of influent chemical energy, but very little of this energy is recovered or utilized nationwide. Hydrothermal liquefaction (HTL), a thermochemical process that can convert biomass into liquid fuels, provides an opportunity to enhance energy recovery at US wastewater treatment plants (WWTPs) by transforming underutilized municipal wastewater solids into a renewable, cost-effective feedstock for transportation biofuels. In this study, we estimate total national economically sustainable sludge feedstocks using a site-specific discounted cash flow analysis to assess the net present value of 30-year HTL and anaerobic digestion (AD) energy investments. This analysis is the first to model HTL technology deployment across the real-world fleet of US WWTPs. Analyses indicate WWTPs could economically supply more than 10 million dry tons per year of dry solids feedstock to produce nearly 1 Bgal/y of biocrude, thereby increasing energy, environmental, and financial sustainability while reducing disposal costs and operational and environmental risk.