Hydrochar prepared from digestate improves anaerobic co-digestion of food waste and sewage sludge: Performance, mechanisms, and implication.

This work reported a new waste functionalization and utilization method, which use digestate to prepare hydrochar to improve methane production from food waste (FW) and sewage sludge (SS). Experimental results presented that 10 g/L hydrochar obtained the cumulative methane production of 133.11 ± 1.18 mL/g volatile solids added, 26.99 % higher than that without hydrochar addition. By monitoring the conversion of model metabolic intermediates, 10 g/L hydrochar was determined to favor hydrolysis, acidogenesis and methonogenesis bio-processes involved in methane production, thus improving the degradation of solubilized organics and consumption of short-chain fatty acids (SCFAs) during the co-digestion. Microbial investigation revealed that 10 g/L hydrochar enriched the microbes relevant to methane production (e.g., Methanosaeta and Syntrophomonas), but reduced the abundances of hydrolysis- and acidogenesis-related microbes (e.g., Acinetobacter). This hydrochar-based preparation and utilization strategy might offer a novel paradigm for waste-control-waste, bringing economic and environmental benefits.