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

Abstract

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 gVS, 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 gVS, 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.

Effect of the Substrate to Inoculum Ratios on the Kinetics of Biogas Production during the Mesophilic Anaerobic Digestion of Food Waste

“…Similarly, another study [33,36] has signalled the biomethane potential and specific methane yields of 725.00 and 683.00 mL/gVS added, respectively, for kitchen waste as a feedstock. The 2019 study [37] shows that specific biogas and methane yields were recorded to be 655.00 and 410.20 mL/gVS at an S:I ratio of 0.5.…”

“…The biogas production decreased along with the rise in S:I ratios signalling the increased formation of volatile fatty acids (VFAs). This lead to a decrease in pH in the first weeks of incubation and also longer incubation times [37].…”

Mesophilic batch co‐digestion of municipal solid waste and food waste: improved digester performance and stability at optimum organic loading rates

“…12,13 Conversely, several elements affect the performance of AD processes, such as feedstock composition, digester design, and operational conditions. 14 The C/N and OLRs are important parameters because they indicate the digester stability and process performance. However, the main hindrances of the AD process are the slow biodegradation rate because of the unbalanced C/N ratio of feedstocks and the chemical structures of lignocellulosic feedstocks.…”

“…Co-digestion may favor the methanogenic/ acidogenic processes by balancing the nutrient and carbon contents, reducing inhibitory compounds, regulating the moisture content, or growing the system's buffering capability. Many researchers have reported different AD studies, for example, co-digestion of FW with MSW, 14 sewage sludge waste and organic MSW, 8 fruit waste and vegetable waste with cattle manure slurry, 22 fish waste and sisal pulp, 23 cardboard waste, paper waste, and tissue waste into FW. 12 The benefits of balancing the C/N ratio through co-digestion with complimentary feedstock include high biogas yield and reduction of potentially toxic ammonia concentration.…”

Assessment of Biological Degradability of the Waste Produced by Food Industry

“…In comparison with aerobic decomposition, anaerobic degradation is a process, in which clean energy is produced. Anaerobic digestion process can convert the degradable organic waste into bio-methane, which can be utilized to produce economically cheaper heat and power [4]. The main product -biogas is produced.…”