Methane Production, Microbial Community, and Volatile Fatty Acids Profiling During Anaerobic Digestion Under Different Organic Loading

The organic loading rate (OLR) is a crucial parameter in the anaerobic digestion of lignocellulosic biomass. Optimizing the OLR ensures a balanced substrate release for gradual hydrolysis, thereby preventing the accumulation of inhibitors that can disrupt methanogenesis. Its significance lies in its direct impact on the stability, efficiency, and overall performance of the digestion process. This study investigated the long-term anaerobic co-digestion of lignocellulosic biomass (Sida hermaphrodita) and cattle manure under varying organic loading rates (S1: 2 kgVS/m3·d, S2: 3 kgVS/m3·d, and S3: 4 kgVS/m3·d). Methane production, microbial community dynamics, and volatile fatty acid (VFA) profiles were analyzed. During S1 and S2, methane production was stable, achieving 446.3 ± 153.7 NL/kgVS and 773.4 ± 107.8 NL/kgVS, respectively. However, at S3, methane production declined, accompanied by a pH drop from 7.68 to 6.11, an increase in the FOS/TAC ratio from 0.272 to 0.35, and the accumulation of acetic and propionic acids at the end of the digestion cycle. Microbial analysis revealed that the abundance of Firmicutes increased with higher OLRs, reaching 93.6% in S3, while the Bacteroidota abundance decreased, reaching 3.0% in S3. During S1, methane production occurred through both acetoclastic and hydrogenotrophic pathways.