Assessment of the effects of dry anaerobic co- digestion 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 m/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.