Effect of inoculum to substrate ratio (I/S) on municipal solid waste anaerobic degradation kinetics and potential

► Impact of inoculum to substrate ratio (I/S) on the anaerobic degradation of reconstituted MSW. ► Tested I/S ratios: 0 (no inoculum), 0.015, 0.03, 0.06, 0.12, 0.25, 1, 2 and 4 (gVMinoc/gVMwaste). ► Maximum methane at I/S = 2, decrease in latency until I/S = 4 and maximal dissolved OC at I/S = 0.12. ► Shift in methanogenic populations (hydrogenotrophic to acetoclastic) with different I/S ratios. The goal of this study is to evaluate the impact of the inoculum to substrate ratio (I/S) on the anaerobic degradation potential of municipal solid waste (MSW). Reconstituted MSW samples were thus incubated under batch anaerobic conditions and inoculated with an increasing amount of inoculum originating from a mesophilic sludge digester. I/S tested values were 0 (no inoculum added), 0.015, 0.03, 0.06, 0.12, 0.25, 1, 2 and 4 (gVMinoculum/gVMwaste). The results indicate that the apparent maximal rate of dissolved organic carbon accumulation is reached at I/S=0.12. Under this level, the hydrolysis process is limited by the concentration of biomass and can thus be described as first order kinetics phenomena with respect to biomass for I/S ratios below 0.12. The maximum methane production rate and the minimal latency are reached at a ratio of 2. In addition to that, both methane signature and ARISA show a shift in the methanogenic populations from hydrogenotrophic to acetoclastic.