Characterization of acidogenic and methanogenic performance in high-solid mesophilic anaerobic co-digestion of rice straw and food waste

In this study, the effects of co-digestion of food waste (FW) with high proportions of rice straw (RS) (40%, 60%, 80%, and 100%) under mesophilic conditions were investigated. The results showed the optimal co-digestion effect at an RS ratio of 40% (CH4 yield of 381.7 ml/g-TS, removal efficiency of cellulose exceeding 75%); while, once the RS ratio surpassed 60%, the removal efficiencies significantly decreased. Specifically, at an RS ratio of 80%, the imbalance between acidogenesis and methanogenesis caused volatile fatty acids (VFAs) accumulation (1500 mg-COD/L), which led to declines in both efficiency and stability. Furthermore, the study confirmed the long-term and stable potential of RS during the mono-anaerobic digestion (AD) process; the abundance of functional enzymes associated with the hydrolysis and acidogenesis of cellulosic substances increased, which may be related to the underlying influence of FW. This study provides important experimental evidence for targeted optimization of the mesophilic RS-AD process.