Rapid conversion from food waste to electricity by combining anaerobic fermentation and liquid catalytic fuel cell

Abstract

Energy recovery from food waste through anaerobic digestion is an important pathway for municipal waste treatment and renewable energy development. Slow methanogenesis and inhibition risk derived from accumulated volatile fatty acids are two technical challenges in anaerobic digestion of food waste. In this study, a novel system combining anaerobic fermentation and a liquid catalytic fuel cell (denoted AFFC for brevity) is proposed as an efficient alternative in which the fermentation products are used as the cell’s fuel. Results show that the fermentation liquid had an organic content of 15.3 g/L with the majority constituted by volatile fatty acids. The maximum power density of the cell reached 1.2 mW/cm2. After 12 h of continuous operation, the conversion rates of acetic, propionic, butyric, and valeric acids reached 90%, 72%, 71%, and 94%, respectively. Furthermore, total organic carbon content decreased by 93.1% from 6.3 to 0.4 g/L in 60 h, while the removal rate of total nitrogen exceeded 82%. Gas-composition analyses verified that organic carbon and ammonia were converted into CO2 and N2, respectively. Compared with direct treatment of food waste in a cell, the pre-positive anaerobic fermentation degraded macromolecular substances into volatile fatty acids, aided the decomposition of lipids, accelerated the cell reaction, and improved the discharge performance. Compared with conventional anaerobic digestion, AFFC exhibited a higher electrical efficiency of 34% with a shorter treatment time of 6.5 d, implying that AFFC could be a promising method for food waste utilization.