Effect of process variables on hydrothermal carbonization of food waste

Abstract

The hydrothermal carbonization (HTC) of food waste (FW) was examined in this study under a variety of conditions, including temperatures of 200 °C, 225 °C, and 250 °C, reaction times of 1.5, 3, 6, and 12 h, and FW-to-water ratios of 12.5, 25, and 50 g/150 mL. HTC was selected as the treatment method due to its suitability for high-moisture feedstocks like FW, as it operates under relatively mild conditions without requiring energy-intensive drying. In this study, a simulated FW mixture was used, composed of commonly discarded household items including canned green beans, canned baked beans, baked potato, baked chicken, and cheese. The study explored how variations in process parameters influenced both the yield and structural properties of hydrochars, revealing their critical role in determining final product characteristics. The hydrochars exhibited higher carbon and lower oxygen weight percentages compared to the FW. Fuel ratio (FR) values ranged from 0.20 to 0.83, with most hydrochars demonstrating moderately stable solid biofuel characteristics. Based on the heating values, it was observed that the hydrochars' values ranged between ∼28 and ∼33 MJ/kg, aligning with the heating value of bituminous coal. The prominent compounds detected in the aqueous phases included nitrogen-containing cyclic compounds, phenols, ketones, and amides. Overall, the findings demonstrate the potential of HTC as a sustainable waste-to-energy strategy, effectively converting FW into hydrochars with favorable fuel properties and supporting energy recovery from organic waste streams.