Hydrothermal-based Wastewater Solids Management for Targeted Resource Recovery and Decarbonization in the Contiguous...

Wastewater solids management is a key contributor to the operational cost and greenhouse gas (GHG) emissions of water resource recovery facilities (WRRFs). This study proposes a 'waste-to-energy' strategy using a hydrothermal liquefaction (HTL)-based system to displace conventional energy- and emission-intensive practices. The proposed system directs HTL-produced biocrude to oil refineries and recovers regionally tailored nitrogen and phosphorus fertilizers. In an independent facility analysis, 576 WRRFs in the contiguous U.S. (CONUS) could deploy financially viable HTL-based wastewater solids management, simultaneously achieving cost savings of 4.81M [4.04M to 5.51M] $·day^-1 and a GHG reduction of 1,300 [351 to 2,140] tonne CO₂ eq·day^-1 while offsetting ∼ 1 to 2% of synthetic fertilizers. Key sustainability drivers include the biochemical composition of solids and internal rate of return (IRR), though IRR becomes less impactful at larger WRRFs. In a hub analysis, shared processing of wastewater solids at HTL-based treatment centers expands financially driven decarbonization opportunities to WRRF networks with solids mass flow rates higher than 5 to 7 tonne·day^-1 and average transportation distances less than 80 to 155 km. Overall, this study highlights the potential of HTL-based systems for financially viable wastewater solids management while reducing GHG emissions and achieving targeted resource recovery in the CONUS.