Rapid urbanization and population growth have significantly increased the generation of municipal wastewater, necessitating efficient treatment before discharge into natural water bodies. The activated sludge process (ASP) remains one of the most widely applied biological treatment technologies for municipal wastewater due to its flexibility and high removal efficiency of biodegradable organic matter. This study investigates the performance of a laboratory-scale activated sludge reactor operated in batch mode for the treatment of real municipal wastewater collected from Kolkata, India. The reactor was operated with an initial mixed liquor suspended solids (MLSS) concentration of 2000–2500 mg/L and influent biochemical oxygen demand (BOD₅) ranging from 220–230 mg/L. Treatment performance was evaluated over multiple batch cycles by monitoring BOD removal efficiency and biomass behavior. Results indicate a progressive improvement in treatment efficiency, achieving approximately 70% BOD removal under optimized operating conditions. The findings demonstrate the technical feasibility of ASP for municipal wastewater treatment at laboratory scale and provide insight into its applicability for small- to medium-scale wastewater treatment systems.