Changes in methanogenic performance and microbial community during gradual transition from co-digestion with food waste to mono-digestion of rice straw

This study investigated the performance and phase-specific characteristics of mesophilic co-digestion of food waste (FW) with rice straw (RS) at different RS proportions (40 %, 60 %, and 80 %), as well as mono-digestion of RS. The system achieved optimal performance at 40 % RS content, with a methane yield of 383.8 mL/g-VS and cellulose removal efficiency exceeding 75 %. When RS content increased beyond 60 %, process performance declined notably. At 80 % RS ratio, an imbalance between acidogenesis and methanogenesis led to volatile fatty acids (VFAs) accumulation (1500 mg-COD/L), compromising both efficiency and stability. Notably, during the transition to mono-digestion, the system maintained stable operation, characterized by increased abundance of functional enzymes associated with cellulosic substance hydrolysis and acidogenesis. This enhanced enzymatic activity may be attributed to the microbial adaptation induced by previous co-digestion with FW. These findings provide valuable insights for optimizing mesophilic RS digestion through strategic co-digestion approaches.