This study investigated the anaerobic digestion (AD) of Municipal Solid Waste (MSW) collected from Uttar Pradesh, India, with the aim of optimizing biogas production and process stability. Initial characterization revealed a high volatile solids (78.5%) content and a favorable C/N ratio (24.5:1), confirming MSW’s suitability as a substrate. The inoculum, obtained from a working digester, exhibited optimal pH (7.25) and alkalinity (4,200 mg/L), ensuring a stable microbial environment.

Biogas production was assessed under mesophilic (35 °C) and thermophilic (55 °C) conditions. Thermophilic digestion yielded 480 L/kg VS added, a 37% increase over mesophilic conditions, while methane content improved from 55% to 68%. Variation of the C/N ratio demonstrated its critical role: the optimal 25:1 ratio achieved the highest biogas yield (0.45 m³/kg), whereas imbalances led to instability due to ammonia toxicity (low ratios) or nutrient limitation (high ratios). Process stability was further linked to pH and alkalinity management, with optimal performance maintained within pH 6.8–7.2 and VFA/alkalinity ratios below 0.4.

Cumulative biogas production confirmed that optimized conditions (balanced C/N, stable pH, adequate alkalinity, and controlled mesophilic temperature) achieved the highest methane yield (0.35 m³ CH₄/kg VS added). These findings underscore the interdependence of operational parameters in achieving efficient AD.