Microbial Valorisation of Cassava Processing Residues for Bioenergy Recovery in Kogi State, Nigeria

Cassava processing generates peel, bagasse and mill effluent containing organic matter that may be recovered through biological conversion. This study evaluated the physicochemical and microbiological characteristics of these residues and their performance during laboratory-scale anaerobic digestion in Kogi State, Nigeria. Individual residues and a mixed substrate were digested under mesophilic conditions for 30 days, and biogas production, methane yield, microbial populations and changes in organic-load indicators were assessed. Volatile solids accounted for 82.45–89.34% of total solids across the substrates, while organic carbon ranged from 38.64% to 49.27%. The residues contained hydrolytic, fermentative and methanogenic microorganisms, including Bacillus, Clostridium, Bacteroides, Saccharomyces, Methanobacterium and Methanosarcina species. The mixed residue yielded the greatest cumulative biogas volume (6,480 ± 196 mL), with a biogas yield of 0.58 ± 0.03 L/g volatile solids and a methane yield of 0.35 ± 0.02 L/g volatile solids. Its measured methane concentration was 60.34 ± 1.08%. In the inoculation comparison, the combination of an indigenous microbial consortium and cow-dung inoculum produced 0.62 ± 0.03 L/g volatile solids of biogas containing 61.2 ± 1.0% methane. Anaerobic digestion reduced chemical oxygen demand, five-day biochemical oxygen demand and free cyanide by 76.04%, 79.79% and 76.63%, respectively. These findings indicate that microbial digestion of mixed cassava-processing residues can support methane recovery alongside organic-load reduction under the experimental conditions.