Technoeconomic evaluation of integrating hydrothermal liquefaction in wastewater treatment plants

This study provides a techno-economic analysis (TEA) of biocrude production via hydrothermal liquefaction (HTL), focusing on decentralized HTL plants integrated within wastewater treatment plants (WWTPs) of typical sizes (0.1 to 1.0 million population equivalents, PE). The analysis uses a typical WWTP in Denmark, serving 150 k PE, as a base case. Steady-state process simulation in Aspen Plus®, employing a detailed kinetic HTL model, provides mass and energy balances for the TEA. Results indicate that operational expenses, including utilities, maintenance, and salaries, dominate overall costs. Processing 323 kg/h of dry solids produces 94 kg/h at a minimum biocrude selling price (MBSP) of 1.4 €/kg (1.5 $/kg), with a range of 0.9 to 1.8 €/kg depending on plant size. A typical sludge handling credit enables competitive production costs for WWTPs larger than 300 k PE. Sensitivity analysis identifies biocrude yield, labor costs, and sludge dry matter content as critical factors influencing MBSP.