Biogas Production from Co-Digestion of Cow Dung with Agricultural Residues under Mesophilic Conditions

Access to reliable and affordable energy remains a challenge in sub-Saharan Africa, where over 85 million Nigerians lack grid electricity. Dependence on fossil fuels worsens environmental degradation, while agricultural residues are often indiscriminately discarded, contributing to pollution. Biogas technology offers a sustainable alternative, yet mono-digestion of cow dung is constrained by poor carbon-to-nitrogen (C/N) ratios, low methane yields, and process instability. Co-digestion with crop residues provides an opportunity to balance nutrient profiles and improve biogas performance. However, limited empirical evidence exists on the comparative effectiveness of different substrates under mesophilic conditions in Nigeria. This study investigated the co-digestion of cow dung with yam peel, maize husk, and cassava peel using laboratory-scale digesters. Feedstocks were analysed for C/N ratios, nutrient content, and heavy metals, while daily and weekly gas yields were monitored over seven weeks. Results revealed that cow dung + yam peel produced the highest cumulative yield of 486.7 mL, while cow dung + maize husk extended retention to 38 days with 316.6 mL yield. Cow dung only and cow dung + cassava peel produced similar lower yields at approximately 206 mL. ANOVA confirmed significant weekly variation at p < 0.05, but no significant differences in cumulative yields among treatments at p = 0.562. The study concludes that yam peel and maize husk are promising co-substrates for enhancing biogas yield and stability, while cassava peel requires further pre-treatment. Co-digestion presents a low-cost, sustainable pathway to improve rural energy access and reduce agricultural waste in Nigeria.