(427c) Techno-Economic and Life-Cycle GHG Emission Assessment for Aqueous-Phase Product Treatment and Valorization Options of Wet Waste Hydrothermal Liquefaction Process

Waste-to-fuel via hydrothermal liquefaction, a promising technology with high fuel yield and carbon efficiency, can simultaneously decarbonize the transportation sector and reduce the landfill demand. However, a significant amount of carbon, and nitrogen in the feedstock (23.2%, and 50.4%, respectively) goes to the aqueous phase product, and results in an aqueous-phase stream with high chemical oxygen demand. Treatment is required before disposal, of which the cost, utility consumption, and emission can be high when using conventional activated sludge process in the state-of-art design for hydrothermal liquefaction. In this work, four alternative treatment and valorization options were investigated for the hydrothermal liquefaction aqueous-phase product, including two catalytic hydrothermal gasification technologies using different catalysts, steam-phase catalytic reduction of wastewater and ambient-pressure aqueous-phase catalytic upgrading. Techno-economic and life-cycle assessments were conducted based on continuous-flow experimental data and rigorous process models developed in Aspen Plus V11. The results suggest that a treatment option producing valuable by-products will simultaneously improve the economic performance and reduce the life-cycle greenhouse gas emission of the entire process. Among all treatment options investigated, the ambient-pressure aqueous-phase catalytic upgrading technology achieved the lowest minimum fuel selling price (13% lower than the state-of-art) and lowest life-cycle greenhouse gas emission (39% lower than the state-of-art). It is because this technology requires less severe operation conditions (less energy consumption and capital investment) and less expensive catalyst to enable deep chemical oxygen demand reduction and production of fuel gas and fertilizer as by-products.