Impact of Substrate to Inoculum Ratio on Methane Production in High Solids Anaerobic Digestion (HS-AD) of Food Waste, Yard Waste, and Biosolid

High solids anaerobic digestion (HS-AD) is an alternative for managing the organic fraction of municipal solids waste (MSW), which produces mainly methane (CH4) and fertilizer as byproducts. HS-AD offers a potentially more economically and environmentally sustainable option compared with landfilling or incineration waste-to-energy facilities. However, HS-AD is a complex process requiring specific microbial communities working together symbiotically. Previous studies have found that the substrate to inoculum (S/I) ratio affects CH 4 production and yield in HS-AD reactors by affecting substrate mass and energy transfer as well as microbial activity. In this thesis, biochemical methane potential (BMP) assays were used to investigate the effect of S/I ratio on CH4 production and chemical properties during the digestion of food waste, yard waste, and biosolids. The results indicate that the S/I ratio of 1.0 based on total solids (TS) content was the optimum ratio for the mixtures, compared to 2.0 and 3.0 based on TS as well as an inoculum only blank. Specifically, the S/I ratio of 1.0 based on TS had the greatest cumulative CH4 production of 2,320-mL and maximum cumulative CH 4 yield of 126 mL-CH4/ (g VSadded) over 47 days while reducing total TS and VS in the reactors. Weekly chemical analyses showed that the optimum values were produced in BMPs with S/I of 1.0 because this set was the least influenced by pH, volatile fatty acid (VFA), total ammonia nitrogen (TAN) induced microbial inhibition. Overall, these findings may assist in the design and operation of HS-AD systems with greater CH 4 volume and CH4 production for the digestion of the organic fraction of MWS.