Among the options for biomass to energy schemes, anaerobic digestion to produce biomethane is probably the most established route, with applications ranging from wastewater management to agricultural biomass. However, this process also yields a nutrient and carbon-rich side stream, commonly known as digestate. Due to pathogen and zoonotic agent load, this waste biomass requires further treatment. Established schemes involve energy intensive drying and hygienization prior to its use for plant cultivation, neglecting the energy content of the biomass. Furthermore, application to arable land is limited depending on the local legal framework, leading to costly storage and transportation. This constitutes a waste management problem, which requires novel solutions.<br/>Hydrothermal liquefaction (HTL) can be used as an alternative technology for increased value creation. At conditions close to the critical point of water (647 K, 22 MPa) the biomass breaks down and recombines to form an energy-dense biocrude oil, which has received attention as a potential precursor for aviation and transportation fuels, an aqueous phase rich in organic compounds, and a hydrochar. In this study, HTL of digested sewage sludge, digested manure, and digested urban waste is performed in a mini-batch (20 mL) setup. Response surface methodology is applied to investigate the influence of the biochemical composition of the input material, temperature, and reaction time on biocrude yield and composition, energy recovery, as well as the mobility of nutrients (N, P, K) among the product phases. The results will provide a further understanding of the influence of said parameters on the process and highlight pathways towards the exploitation of waste biomass by means of energetic and material use.

Energetic and material valorization of digestate via hydrothermal liquefaction: Influence of input material and process parameters

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ACS Fall 2022

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