Hydrothermal liquefaction as a treatment technology for anaerobic digestate: A review

Christian Klüpfel, Bomin Yuan, Patrick Biller and Benjamin Herklotz

Renewable and Sustainable Energy Reviews, 2025, vol. 210, issue C

Abstract: Digestate, the side-product of anaerobic digestion (AD), poses both an environmental and economic problem. Hydrothermal liquefaction (HTL) is discussed as a potential process to treat this waste biomass and yield valuable products, e. g. biocrude. This review outlines the state of the art of digestate treatment and assesses the state of knowledge concerning the HTL of digestate. Options for process integration and synergies in the framework of the proposed biorefinery concept consisting of HTL and AD are discussed. Optimum biocrude yield in the reviewed literature is usually achieved in the range of 300–350 °C and 15–30 min. Feedstock composition varies depending on origin of the digestate. Product characterisation elucidates phenols, fatty acids, and N-heterocycles in the biocrude and significant nutrient load in the hydrochar. Further research should address feedstock dependency, aqueous phase treatment and hydrochar utilisation to develop the process towards large scale application.

Keywords: Hydrothermal liquefaction; Digestate; Biofuel; Waste valorisation; Anaerobic digestion (search for similar items in EconPapers)
Date: 2025
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DOI: 10.1016/j.rser.2024.115156

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