The fate of active pharmaceutical ingredients in a hydrothermal liquefaction process

Abstract Sewage sludge contains active pharmaceutical ingredients (APIs) that persist after anaerobic digestion, posing challenges for its direct use as an organic amendment. This study presents a proof-of-concept investigation of the degradation of APIs through hydrothermal liquefaction (HTL), supporting the sustainability of using digested sewage sludge (DSS) as a feedstock for bio-oil production. In this work, the degradation of the four APIs carbamazepine, sertraline, telmisartan, and citalopram during HTL was investigated. Two experimental series were conducted at 330 °C for 4 h: one with APIs and formic acid only, and one with APIs, formic acid, and DSS. Formic acid was added to the reaction system as a hydrogen donor. Quantitative analyses of the organic product phases using GC–MS revealed complete degradation of all four APIs. The proposed degradation schemes provide detailed insights into the degradation pathways of the APIs during HTL, and the results suggest a greatly reduced likelihood of remaining pharmacological activity in the resulting products. These findings represent a significant step towards understanding and mitigating the risks associated with APIs in DSS and encourage further research to optimise the HTL process.