Influence of the Sludge Ratio on the High-solids Thermophilic Methane Fermentation of the Organic Fraction of Municipal Solid Waste and Bio-sludge

The influence of the sludge ratio on the high-solids thermophilic methane fermentation of the organic fraction of municipal solid waste (MSW) and bio-sludge was investigated by using a semicontinuous flow completely mixed reactor. The methane fermentation experiments were conducted at a constant influent total solid (TS) concentration of 12-13% and a constant retention time of 15 days by altering the sludge ratio from 0% to 50% under thermophilic condition (55°C) . As the sludge ratio in the influent TS increased from 0% to 50%, the degradation efficiency of volatile solid decreased from 78% to 49%, while the biogas production yield decreased from 0.8 to 0.5 L/g-VS. For maintaining high rate stable methane fermentation, addition of minerals to the feed was necessary for the MSW-rich cases when the sludge ratio in the influent TS was lower than 10%, while successful operation was possible without mineral addition when the sludge ratio was higher than 25%. The energy production in an integrated biogas system of thermophilic methane fermentation and power generation using biogas was calculated based on the experimental results obtained from this study.