A Comparative Study of Biogas produced from selected Animal Wastes at less-populated settlements in Awka North and South Local Government Area in Anambra State, South-East Nigeria.

Abstract Background Biogas is a renewable source of energy generated from anaerobic digestion of biomass. A comparative analyses of biogas produced from anaerobic digestion of animal wastes (cow dung, goat droppings and chicken droppings) in Awka North and South Local Government Area, Nigeria were studied. Methods Laboratory scale digesters (1000 cm3 conical flasks) were used for the anaerobic digestion with retention period of 30 days and the experiment was carried out at room temperature. The biogas produced was trapped in inverted measuring glass cylinder to get the volume of gas produced and in poly vinyl chloride ball to hold the biogas for analysis of its constituent compositions. The animal wastes were mixed with water in the ratio of 1:2. Data were analyzed using ANOVA. Results Twenty bacteria genera belonging to six phyla including Firmicutes, Proteobacteria, Bacillota, Actinomycetota, Spirochaetota and Bacteroidota were identified to be involved in the anaerobic digestion process using 16S rRNA targeted genomic sequencing. The findings revealed the cumulative biogas yield by chicken droppings (CnD), cow dung (CwD), goat droppings (GtD), cow dung – chicken droppings, cow dung – goat droppings, chicken droppings – goat droppings and cow dung – chicken droppings – goat droppings were 5472 cm3, 1546 cm3 and 2072 cm3, 4607 cm3, 1253 cm3, 4788 cm3 and 4111 cm3 respectively. Biogas slurries for anaerobic digestion of animal wastes (cow dung, chicken droppings and goat droppings) were prepared in 3 designs (first digester without dark covering, second digester with dark covering and the third digester has dark covering with their pH raised to pH 8) with all the animal wastes producing highest percentage (CnD 70.43%, GtD 75.57%, CwD 76.96%) of methane (CH4) at the digesters with dark covering at pH 8. Statistical analysis on ANOVA reveals the biogas compositions of the animal wastes shows that they were not significant at p < 0.05. Conclusion The findings reveal the animal wastes with highest biogas yield were chicken dropping > co-digestion of chicken droppings and goats dropping > co-digestion of cow dropping and chicken droppings. These animal wastes produced highest percentage of methane gas at alkaline pH with dark covering. The chicken dropping with the highest biogas yield could be a good source for energy resource alternative, and or curb control for groundwater contamination, or used to reduce organic waste in landfills.