Enhancing the energy potential of food waste digestate via catalytic co-hydrothermal treatment: The pyrolysis and combustion performance of hydrochar

Catalytic hydrothermal treatment is considered one of the most promising technologies for recovering energy from carbonaceous wastes. In so doing, it facilitates the realization of waste-to-energy and resource utilization efforts. In this study, hydrochar was prepared from food waste digestate and wood waste via catalytic co-hydrothermal treatment using potassium carbonate (K₂CO₃) and sodium carbonate (Na₂CO₃) as alkali catalysts. Based on the physicochemical properties of hydrochar, including proximate analysis, element distribution, high heating value (HHV), surface functional groups, and morphology, the gaseous products of pyrolysis and the combustion performance of hydrochar were further investigated using TG-FTIR-MS and TG-DSC, respectively. In addition, the hydrochar combustion kinetics and thermodynamics were probed. Specifically, the hydrochar obtained from Na₂CO₃ catalysis (HC-Na) demonstrated a higher heating value (26.85 MJ·kg⁻¹) with higher calcium retention, while the hydrochar obtained from K₂CO₃ catalysis (HC-K) had a greater number of functional groups and larger carbon content. Moreover, the pyrolysis gaseous products of hydrochar were rich in hydrocarbons. HC-K exhibited better comprehensive combustion performance with the activation energy (Ea) values of 79.32 kJ·mol⁻¹ and 67.91 kJ·mol⁻¹ using the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods, respectively. These results provide a prospect for enhancing the comprehensive utilization of carbonaceous solid waste through catalytic co-hydrothermal treatment.