Assessment of the effects of dry anaerobic codigestion of cow dung with waste water sludge on biogas yield and biodegradability

Dry anaerobic digestion has been treated as feasible process for potential renewable energy recovery with nutrient-rich fertilizer and sustainable solid waste management. Dry methane fermentation of undiluted cow manure (CM), waste water sludge (WWS) and their mixtures into different ratios were conducted at 35°C in the laboratory-scale single-stage batch reactors for 63 days. The specific biogas production obtained for the CM/WWS ratios of 1:0, 4:1, 3:2, 2:3, 1:4 and 0:1 were 56.94, 58.51, 61.64, 63.12, 59.30 and 55.39 L/kg, with methane yield were 32.01, 33.14, 35.31, 36.91, 34.76 and 32.63 L/kg respectively. The experimental results showed that the co-digestion with CM/WWS ratio of 2:3 obtained highest total biogas production of 63.12 L/kg, methane yield of 0.328 m³/kgVS and total solid (TS), volatile solids (VS), chemical oxygen demand (COD), total organic carbon (TOC) reductions of 34.24, 54.80, 55.22 and 70.71% compared to the other co-digestion ratios and single digestions. It was also revealed that co-digestion resulted in 3.11-13.99% higher methane gas yields, due to synergistic effect. The synergistic effect is mainly attributed to more balanced nutrients and increased buffering capacity.