Impacts of biochar addition on anaerobic digestion of food waste with hydrogen.

Anaerobic digestion is a promising waste-to-energy method for treating organic solid waste. However, the unavoidable generation of CO2 decreased its calorific value and potential application. This study presented a novel method to enhance the methane yield and decrease CO2 production of digestion by coupling biochar and hydrogen. The comparison of digesters for food waste treatment with exogenous hydrogen but with (HCBR) and without (HBR) biochar were conducted under a long-term operation. The results showed that biochar addition significantly improved methane yield, hydrogen utilization efficiency, and microbial adaptability and activity under elevated hydrogen partial pressure and changed sparging rate. The highest methane yield achieved by HCBR was 722 ± 60 mL/g-VS, which was 95 % higher than that of conventional anaerobic digestion (BR), with a CO2 removal efficiency of 39.5 ± 6.5 % and a hydrogen utilization efficiency of 88.0 ± 2.0 %. The HCBR also demonstrated enhanced system tolerance to operational changes and the recovery ability from inhibition. Spearman correlation analysis among key gas-, liquid- and solid-phase indicators indicated that biochar may alleviate inhibitory effects without significantly altering the liquid chemistry but improve hydrogen utilization and CO2 to methane conversion. A techno-environmental-economic assessment further confirmed the potential of HCBR in a hybrid biogas upgrading systems with reduced greenhouse gas emissions and improved economic benefits. Its total profit reached 50.5 USD/m3-fed, representing a 47 % and 20 % increase over the systems with BR and HBR, respectively.