Methods for enhancing the properties of products from food waste via hydrothermal carbonation (HTC): Gradient-enzymatic-pretreatment-nitrogen-migration-strategy

Gradient enzymatic pretreatment is an effective method for improving the quality of hydrothermal carbonation products from food waste. Food waste mainly contains polysaccharides, proteins, fats, and indigestible fibers. In this study, food waste model compounds formulated according to the survey were subjected to enzyme-assisted hydrothermal carbonation. Results showed that the high heating value of the hydrochar reached 31.62 MJ/kg at 240 °C for 25 min when the meat content of the raw material was high. Increases in reaction temperature and residence time remarkably changed the species of compounds in the aqueous phase. The increase in the amount of the key nitrogen-containing components doping in the aqueous phase after enzyme-assisted hydrothermal carbonation was the major factor that enhanced its luminescence intensity. The concentration of total nitrogen in the aqueous phase reached 1403.31 mg/L at 220 °C for 25 min. The gradient enzymatic pretreatment method combined with hydrothermal carbonation process facilitates the nitrogen migration of food waste in the aqueous phase, thus ensuring sustainable production and enhancing the product properties of food waste for high-valued applications.