Optimization of Biogas Production from Co-Digestion of Pig Dung, Plantain Stem, and Potato Peel Using Response Surface Methodology

Biogas production through anaerobic digestion of agricultural residues offers a sustainable pathway for renewable energy generation and waste management, particularly in developing regions. However, mono-digestion of individual substrates often results in process instability and low gas yields due to nutrient imbalance. This study investigates and optimizes biogas production from the co-digestion of pig dung, plantain stem, and potato peel using Response Surface Methodology (RSM). A Box–Behnken experimental design comprising 54 runs was employed to evaluate the effects and interactions of substrate proportions, carbon-to-nitrogen (C/N) ratio, pH, and hydraulic retention time (HRT) on biogas yield in a laboratory-scale batch digester. Statistical analysis indicated that a two-factor interaction (2FI) model adequately described the process, with a high coefficient of determination (R² = 0.996) and a non-significant lack of fit (p > 0.05). Among the studied factors, HRT and substrate interactions exerted the most significant influence on biogas production. Optimal operating conditions were achieved at a near-neutral pH, C/N ratio between 20 and 30, and extended retention time, resulting in a maximum biogas yield of 2.975 L under the experimental conditions. The results demonstrate that RSM is an effective tool for optimizing anaerobic co-digestion systems and highlight the synergistic potential of combining animal manure with lignocellulosic and carbohydrate-rich residues for enhanced biogas production.