Enzyme-assisted hydrothermal treatment of food waste for co-production of hydrochar and bio-oil

Food waste was subjected to enzymatic hydrolysis prior to hydrothermal treatment to produce hydrochars and bio-oil. Pre-treatment of food waste with an enzyme ratio of 1:2:1 (carbohydrase:protease:lipase) proved to be effective in converting food waste to the two products with improved yields. The carbon contents and calorific values ranged from 43.7% to 65.4% and 17.4 to 26.9 MJ/kg for the hydrochars obtained with the enzyme-assisted pre-treatment, respectively while they varied from 38.2% to 53.5% and 15.0 to 21.7 MJ/kg, respectively for the hydrochars obtained with no pre-treatment. Moreover, the formation of carbonaceous microspheres with low concentrations of inorganic elements and diverse surface functional groups was observed in the case of enzyme-assisted food waste hydrochars. The enzymatic pre-treatment also facilitated the formation of the bio-oil with a narrow distribution of organic compounds and with the highest yield obtained at 350 °C.