Effect of hydrochar from biogas slurry co-hydrothermal carbonization with biomass on anaerobic digestion performance of food waste

Abstract

Anaerobic digestion is a promising method for converting food waste into renewable methane-rich biogas. However, challenges, such as significant biogas slurry generation, poor stability, and low methane production, limit its widespread adoption. This study produced 15 types of hydrochars by co-hydrothermal carbonization of biogas slurry with sugarcane leaves, cellulosic ethanol residue, or food waste digestate at 180–260 °C to enhance anaerobic digestion performance and methane yield. The methane yield was influenced by both the raw materials and hydrothermal carbonization temperature. The hydrochar derived from sugarcane leaves at 180 °C exhibited the highest methane yield of 461.59 mL/g VS, which is a 13.69 % increase over the food waste group. Additionally, different doses of SL-180 were tested for their effects on the anaerobic digestion performance in food waste. The cumulative methane yield increased from 379.68 mL/g VS to 543.26 mL/g VS with SL-180 dosages ranging from 5 g/L to 40 g/L, enhancing cumulative methane yield by 3.90–48.66 % compared to the food waste group. The primary factor influencing methane yield was hydrochar degradation, whereas secondary factors included maintaining system stability and enriching methane-producing microorganisms, particularly Methanosaeta and Methanomassiliicoccus. Energy assessment and economic analysis indicate that combining hydrothermal carbonization with anaerobic digestion can achieve high energy output and economic benefits. This study offers insights and recommendations for managing biogas slurry, resource recovery, and improving the stability and methane yield in the anaerobic digestion of food waste.