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Effect of inoculum to substrate ratio (I/S) on municipal solid waste anaerobic degradation kinetics and potential
Anthony Boulanger1, Elisabeth Pinet, Marielle Bouix
1CEMAGREF, Hydrosystems and Bioprocesses Unit, Parc de Tourvoie, 92163 Antony, France. anthony.boulanger@veolia.com
Abstract:
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 (gVM(inoculum)/gVM(waste)). 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.
Insights
Optimizing the inoculum to substrate ratio (I/S) is key for efficient municipal solid waste (MSW) anaerobic degradation. The study found specific ratios maximize dissolved organic carbon and methane production, influencing microbial community shifts.
Area of Science:
- Environmental Microbiology
- Waste Management
- Biotechnology
Background:
- Anaerobic degradation is a crucial process for managing municipal solid waste (MSW).
- The inoculum to substrate ratio (I/S) is a critical factor influencing the efficiency of anaerobic digestion.
- Understanding microbial dynamics is essential for optimizing biogas production from MSW.
Purpose of the Study:
- To investigate the impact of varying inoculum to substrate ratios (I/S) on the anaerobic degradation of municipal solid waste (MSW).
- To determine the optimal I/S for maximizing dissolved organic carbon accumulation and methane production rates.
- To analyze shifts in methanogenic populations in response to different I/S levels.
Main Methods:
- Batch anaerobic digestion experiments using reconstituted MSW.
- Inoculation with mesophilic sludge digester inoculum at various I/S ratios (0 to 4 gVM(inoculum)/gVM(waste)).
- Monitoring dissolved organic carbon accumulation, methane production rates, and analyzing microbial communities using ARISA and methane signature.
Main Results:
- The maximal rate of dissolved organic carbon accumulation was observed at an I/S of 0.12, indicating biomass limitation below this ratio.
- The highest methane production rate and shortest latency were achieved at an I/S of 2.
- Shifts in methanogenic populations from hydrogenotrophic to acetoclastic were detected at higher I/S ratios.
Conclusions:
- The I/S ratio significantly influences the kinetics of anaerobic degradation and methane production from MSW.
- An I/S of 0.12 optimizes hydrolysis, while an I/S of 2 maximizes methane yield and rate.
- Adjusting the I/S ratio can modulate the microbial community structure, favoring specific methanogenic pathways.
