Coupling hydrothermal liquefaction and anaerobic digestion for energy valorization from model biomass feedstocks

- Anaerobic digestion was tested as a complementary step to hydrothermal conversion.
- Hydrothermal liquefaction (200-350 °C) of model feed mixtures was evaluated.
- Changes in hydrothermal conditions substantively altered aqueous phase composition.
- Higher temperature resulted in higher oil yields and lower aqueous phase yields.
- Biodegradability of hydrothermal aqueous phase was lower for higher temperatures.

Hydrothermal liquefaction converts food waste into oil and a carbon-rich hydrothermal aqueous phase. The hydrothermal aqueous phase may be converted to biomethane via anaerobic digestion. Here, the feasibility of coupling hydrothermal liquefaction and anaerobic digestion for the conversion of food waste into energy products was examined. A mixture of polysaccharides, proteins, and lipids, representing food waste, underwent hydrothermal processing at temperatures ranging from 200 to 350 °C. The anaerobic biodegradability of the hydrothermal aqueous phase was examined through conducting biochemical methane potential assays. The results demonstrate that the anaerobic biodegradability of the hydrothermal aqueous phase was lower when the temperature of hydrothermal processing increased. The chemical composition of the hydrothermal aqueous phase affected the anaerobic biodegradability. However, no inhibition of biodegradation was observed for most samples. Combining hydrothermal and anaerobic digestion may, therefore, yield a higher energetic return by converting the feedstock into oil and biomethane.

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