Christian Toochukwu Ogbonna^1,, Ondiba Hesborn Andole¹, Zhenya Zhang²

Methane production from cowpea hull via anaerobic digestion is an environmentally friendly technique for renewable energy generation and organic waste management in Nigeria, where over half of its global production came from. However, the laboratory study on the anaerobic digestion of cowpea hull has not been sufficiently established. This study investigated the feasibility of methane production from Cowpea hull mono digestion compared to the performance of the conventional anaerobic digestion feedstock. Mono digestion of waste-activated sludge or rice straw under the same anaerobic digestion condition was set up for this purpose. Furthermore, we investigated the effectiveness of cowpea hull co-digestion with waste-activated sludge or rice straw on biogas optimization. Lastly, the optimum mixing ratio of cowpea hull to waste-activated was also quantified. Seven batch setup was subjected to 16 days of fermentation under mesophilic anaerobic conditions. Cowpea hull under mono digestion produced the highest total cumulative biogas of 203.19 mL/g-VS_added, followed by Rice straw (177.24 mL/g-VS_added). Waste-activated sludge had the least biogas 148.71 mL/g-VS_added). Compared to mono digestion, we realized a 27.05 % or 18.95 % optimization of biogas production from cowpea hull co-digested with rice straw or waste-activated sludge. An optimum mixing ratio of cowpea hull to waste-activated sludge was established at 3:1 (75:25) in this study. Our study is the second to investigate the bio-gasification of cowpea hull and the first to test its co-digestion and solid content characterization necessary for future investigation on cowpea hull anaerobic digestion.

anaerobic digestion, methane, cowpea hull, co-digestion, mixing ratio