Co-digestion of Pretreated Chicken – Goat and Untreated Cow Manure at Different Substrate to Inoculums Ratios and Total Solids for Biogas Production

Biogas production can be greatly affected by inoculum addition and total solids. The effect of the substrate to inoculum ratios and total solids of chicken, goat and cow manure on biogas production was studied using a 0.15m3 laboratory-scale batch digester at a constant temperature of 35°C. Feedstocks were mechanically minced to 3 mm effective particle sizes prior to co-digesting with untreated cow manure from a free-range dairy rearing system. Different amounts of cow substrate inoculum were used at ratios of 2:1, 3:1, 4:1, 5:1 and 6:1, while total solid levels between (7.5% and 10.5%) at intervals of 0.5% were used to study their effects on biogas production. Increasing inoculums and total solids resulted in increased biogas production with peaks at a substrate to inoculum ratio of 4:1 (20% inoculum addition) and 9% total solids. Biogas production rates of 0.61 and 0.63m3/m3d were realized respectively. Keywords: Biogas Production, Chicken-Goat-Cow Manure, Substrate to Inoculum Ratios, Total Solids