Optimisation of Biogas Production from Co-Digestion of Organic Waste Streams of Kolhapur Municipal Corporation Using Response Surface Methodology

Kolhapur Municipal Corporation (KMC) generates approximately 488 tonnes of municipal solid waste daily, of which nearly 57% is biodegradable organic matter presently disposed of without energy recovery. This study characterises five major organic waste streams of KMC — food waste, vegetable market waste, fruit market waste, cattle dung, and slaughterhouse waste — and optimises their co-digestion ratio using Response Surface Methodology (RSM) with a D-optimal mixture design. Individual substrate characterisation revealed complementary carbon-tonitrogen (C/N) profiles, motivating a co-digestion strategy. A 38-run mixture design was executed in bench-scale CSTR digesters, yielding a statistically significant model (F = 48.52, R² = 0.981). The optimised blend — 40% food waste, 25% vegetable waste, 20% fruit waste, 10% cattle dung and 5% slaughterhouse waste — achieved a C/N ratio of 24.8:1 and a specific biogas yield of 724 mL/g VS, validated experimentally within 1% of the model prediction. A conceptual 200 MT/day plant based on this formulation shows techno-economic viability (IRR 18.4%, payback period 6.8 years). The findings demonstrate that systematic co-digestion optimisation, grounded in a rigorous waste characterisation and experimental design methodology, can substantially improve biogas recovery from municipal organic waste in Tier-2 Indian cities.