Optimizing Biogas Production and Digestive Stability through Waste Co-Digestion

This study aimed to enhance the nutrient balance of municipal solid waste (MSW), characterized by a high carbon-to-nitrogen (C/N) ratio, which is a critical factor in the anaerobic digestion process. The investigation involved the addition of MSW, which is rich in carbon content, to food waste (FW) with high nitrogen content. The goal was to determine an optimal co-substrate mixing ratio of MSW and FW for anaerobic co-digestion at mesophilic temperatures, aiming to improve process stability and performance to achieve higher biogas yield. The co-digestion experiments encompassed five mixing ratios of MSW and FW with C/N ratios of 20, 25, 30, 35, and 40 under mesophilic conditions in a laboratory. The results indicated that the highest specific biogas yield, reaching 827 L/kg VS, was attained when the co-substrate feedstock had a balanced C/N ratio of 20, surpassing the 520 L/kg vs. obtained from MSW digestion alone. As the proportion of MSW increased in the co-substrate mixing feedstock, the biogas production rate decreased. Additionally, the study explored the optimal substrate-to-inoculum (S/I) ratio, focusing on the co-substrate feedstock with a C/N ratio of 20. Four S/I ratios (0.5, 1.0, 1.5, and 2.0) were examined, revealing that the highest specific biogas yield, at 642 L/kg VS, occurred at an S/I ratio of 0.5. An accumulation in volatile fatty acids (VFAs) was observed at higher S/I ratios, attributed to the lower abundance of inoculum microorganisms in the anaerobic digestion process. Overall, the findings suggested that the optimum C/N ratio for co-digestion of MSW and FW falls within the range of 20–25/1, while the preferred S/I ratio is 0.5.