An Insight into the Anaerobic Co-digestion of Municipal Solid Waste and Food Waste: Influence of Co-substrate Mixture Ratio and Substrate to Inoculum Ratio on Biogas Production.

The unbalanced nutrients of municipal solid waste (MSW), particularly high carbon contents, were regarded as a major limiting factor to anaerobic digestion process. In this study, the addition of MSW in food waste (FW) feedstock to have a balanced C/N ratio was studied. Different co-substrate mixtures with C/N ratio of 20 to 40 were subjected to anaerobic batch experiment at lab scale, under mesophilic conditions. The biogas production decreased with the increase in C/N ratio due to insufficient availability of organic nitrogen for anaerobic microbial growth. Specific biogas and methane yields were observed to be 827 and 474.44 mL g-1 VS, respectively, with volatile solids (VS) reduction rate of 88%, at C/N ratio of 20. Furthermore, the effect of the substrate to inoculum (S/I) ratio on digester performance was also studied. The biogas production decreased with the increase in S/I ratio due to the formation of more volatile fatty acids (VFAs) which led to decrease in pH and accumulated unionized ammonia-N. Specific biogas and methane yields were recorded to be 655 and 410.20 mL g-1 VS, with 64% rate of biodegradability at S/I ratio of 0.5. Kinetics and statistics study showed that the higher S/I ratio could lead to VFA accumulation and result in low methane yield.