Management and valorization of digestate from food waste via hydrothermal

•1 High ash and protein content limited the energy conversion of food waste digestate.•2 HTT reduced both the volume and dry mass of food waste digestate.•3 Multivalent metals were concentrated in the solid residue.•4 Organic matter and carbon was mostly solubilized from solid to liquid during HTT.•5 Digestate liquid could be valorized as an energy resource after moderate HTT. Hydrothermal treatments (HTT) at moderate temperatures (120–200 °C) were investigated in this study for the management and valorization of food waste digestate (DFW). The dehydration was the main reaction in HTT at a temperature lower than 180 °C. After HTT, the hydrophobicity and dewaterability of DFW were improved significantly, which resulted in a 69% and 37% reduction in the digestate cake volume and solid residue mass, respectively. During HTT, the organic matter and carbon were mostly solubilized from solid to liquid, while the multivalent metals were concentrated in the solid residue. The more stable characteristics of the digestate cake after HTT eliminated its environmental risk. The accumulation of organic carbon and a reasonable ammonia nitrogen concentration in the HTT liquid increased the biochemical methane potential from 147 to 245 mL CH4/g TCOD, which demonstrated the feasibility of recovering energy from the HTT liquid. [Display omitted]