Anaerobic Co-Digestion of Pig Manure and Rice Straw: Optimization of Process Parameters for Enhancing Biogas Production and System Stability

The objective of this study was to optimize the process parameters of the anaerobic co-digestion of pig manure and rice straw to maximize methane production and system stability. In this study, batch experiments were conducted with different mixing ratios of pig manure and rice straw (1:0, 1:1, 1:5, 1:10, and 0:1), total solid concentrations (6%, 8%, 10%, 12%, and 14%), and inoculum accounts (5%, 10%, 15%, 20%, and 25%). The results show that a 1:5 mixing ratio of pig manure to rice straw, a 12% total solid content, and a 15% inoculum account yielded biogas up to 553.79 mL/g VS, which was a result of co-digestion increasing the cooperative index (CPI > 1). Likewise, the evolution of the pH and VFAs indicated that the co-digestion system was well-buffered and not easily inhibited by acidification or ammonia nitrogen. Moreover, the results of the Gompertz model’s fitting showed that the cumulative methane production, delay period, effective methane production time, and methane production rate under optimal conditions were significantly superior compared to the other groups employed.