PNNL

Abstract

Producing renewable fuels from waste via hydrothermal liquefaction has gained increasing interest in the past decades to decarbonize the transportation sector and reduce waste sent to landfills. While this technology has a high fuel yield and carbon efficiency, a significant amount of the carbon and nitrogen in the feedstock reports to the aqueous phase product. As this aqueous-phase stream typically has high chemical oxygen demand and ammonia concentration, treatment before disposal may be necessary or at the very least prudent to minimize impacts to the municipal water treatment plant. In this work, techno-economic and life-cycle assessments were conducted for the state-of-technology baseline (direct recycle to a wastewater resource recovery facility) and four other treatment and valorization options for the hydrothermal liquefaction aqueous-phase product based on experimental data. The results suggest that a treatment option producing valuable by-products will not only reduce the aqueous-phase treatment cost and the minimum selling price of biocrude and biofuels, but also reduce the life-cycle greenhouse gases emission of biofuels derived from wet waste hydrothermal liquefaction process. Among all treatment options investigated in this study, the ambient-pressure aqueous-phase catalytic upgrading technology achieves the lowest minimum fuel selling price (13% lower than that of the state-of-art baseline) and lowest life-cycle greenhouse gas emission (39% lower than that of the state-of-art baseline), because it requires less severe operating conditions and a lower priced catalyst to enable deep removal of chemical oxygen demand and production of fuel gas and fertilizer as by-products for cost and greenhouse gas emission credits.