Optimisation of Anaerobic Co-Digestion Parameters for Enhanced Biogas Production from Poultry Manure in Oyo State

This study optimises the anaerobic co-digestion of poultry manure with crop residues for enhanced biogas production in Oyo State, South West Nigeria. Oyo State hosts a significant concentration of commercial poultry operations generating large volumes of manure that present both environmental management challenges and underexploited biogas feedstock potential. Co-digestion with carbon-rich crop residues including maize stover and cassava peel improves the carbon to nitrogen ratio of the feedstock, enhancing microbial community balance and methane yield. This study uses a Box-Behnken experimental design to optimise three co-digestion parameters: poultry manure to crop residue ratio, total solids concentration, and hydraulic retention time. Batch digestion experiments are conducted in 20-litre laboratory digesters at 35 degrees Celsius mesophilic conditions. Response variables include cumulative biogas yield and methane content percentage. Response surface methodology identifies optimal parameter settings and interaction effects. Findings reveal that the optimal co-digestion ratio is 60:40 poultry manure to crop residue, with total solids of 7 percent and hydraulic retention time of 30 days. Under these conditions, cumulative methane yield reaches 0.38 cubic metres per kilogram of volatile solids, representing a 44 percent improvement over mono-digestion of poultry manure alone. The interaction between co-digestion ratio and hydraulic retention time is the most significant two-factor interaction. The study concludes that optimised co-digestion significantly improves biogas system performance and recommends a combined poultry waste management and energy recovery programme for Oyo State commercial poultry operations.

Keywords: anaerobic co-digestion, biogas optimisation, poultry manure, Oyo State, methane yield.