Characterisation of Biogas-Producing Microbial Communities in Anaerobic Digesters Processing Agricultural Waste in Benue State

Anaerobic digestion of agricultural waste for biogas production offers a renewable energy solution relevant to the energy access challenges of North Central Nigeria, while the microbial community structure governing digestion efficiency in these systems remains under-studied in local contexts. This study characterises biogas-producing microbial communities in anaerobic digesters processing cattle dung and crop residues at four community biogas plants in Makurdi and Gboko, Benue State. Biogas production rates and methane content were monitored over eight weeks. Digester slurry samples were collected at weeks 2, 4, 6, and 8 for microbial analysis using 16S rRNA gene amplicon sequencing targeting the V4 region. Phylogenetic diversity was analysed using QIIME2 and community functional prediction was performed using PICRUSt2. Active digesters producing above 0.4 m3 methane per kg volatile solids were dominated by Methanosaeta, Methanobacterium, and Syntrophobacter genera. Dysbiosis characterised by Firmicutes overgrowth and reduced methanogen abundance was associated with process instability and low methane yield. Temperature fluctuation above 10 degrees Celsius over 24 hours correlated with community disruption. PICRUSt2 analysis confirmed enrichment of methanogenesis and acetogenesis pathways in high-yield digesters. The study establishes a community microbiology basis for optimising biogas digester performance under Benue State climate conditions. Keywords: biogas, anaerobic digestion, microbial community, 16S rRNA, Benue State