Sustainable valorization of food wastes into solid fuel by hydrothermal carbonization.

The aim of this study was to comparatively evaluate the effect of hydrothermal carbonization (HTC) conditions on the yield and the fuel properties of hydrochar obtained from food waste (FW) and its digestate (FD). The mass yield of hydrochars from FW and FD were found between 47.0 and 69.8%, 43.0 and 58.2%, respectively, under tested conditions. Based on both mass and energy yields, optimum temperature and duration were selected as 200 °C and 60 min for FW and 200 °C and 30 min for FD. FW and FD hydrochars produced optimum conditions had similar properties to lignite. The selected hydrochars were also subjected to steam gasification and combustion experiments. The combustion reactivity of hydrochars was found to be higher than that of lignite. Steam gasification produced 57-59 mol H2/kg hydrochar. The overall results emphasize the potential of H2 production by integrated systems of dark fermentation, HTC and steam gasification, besides production of solid fuel.