Conversion of the solid fraction of food waste separated by a screw press using an integrated hydrothermal carbonization and anaerobic digestion process

The treatment of food waste by anaerobic digestion (AD) still faces several challenges. Fractionating the waste, with a screw press separator, into a liquid phase rich in soluble compounds and a solid fraction could contribute to reduce these challenges, provided that the solid fraction is valorized. To do so, hydrothermal carbonization was shown to be a promising option. Indeed, HTC produced a hydrochar having an energy content 8–38 % higher than the initial feedstock and a process water that could be further converted to methane through anaerobic digestion, with a yield of 160–230 mL CH₄ per g of COD. The methane production was shown to be influenced by the recalcitrance of certain HTC products, with hardly no inhibition detected. The integrated 3-step process produces as much energy as conventional anaerobic digestion, while reducing challenges associated to low loading rate and digestate handling.