Abstract The increasing demand for sustainable energy and improved waste management strategies has intensified interest in biogas production from organic wastes. This study evaluated the biogas production potential of cassava mill effluents (CME) co-digested with gutter sludge under anaerobic conditions. Samples were collected from Nise community in Awka South Local Government Area, Anambra State, Nigeria, and subjected to microbiological, physicochemical, and nutritional analyses before and after a 32-day anaerobic digestion period. Microbial enumeration revealed the presence of Staphylococcus aureus, Bacillus cereus, Aspergillus spp., and Candida spp., indicating active biodegradation potential. Significant reductions in cyanide concentration (75.0 to 40.0 mg/L) and selected heavy metals, namely, chromium and cadmium, were observed. Nutritional parameters such as crude protein, fatty acids, nitrogen, phosphorus, and potassium decreased, reflecting microbial utilization, while carbohydrate content increased due to hydrolysis of complex polymers. Biogas production was confirmed by flammability tests from Day 16. The findings demonstrate that co-digestion of CME and gutter sludge is a feasible and environmentally beneficial approach for renewable energy generation and waste remediation, with significant implications for sustainable waste management and energy security in developing regions.