Impact of Temperature on Aerobic Biological Treatment of Pharmaceutical Wastewater in the Ahmedabad Industrial Cluster, Gujarat, India

Pharmaceutical wastewater is among the most challenging industrial effluents due to its high organic load, residual active pharmaceutical ingredients (APIs), and recalcitrant compounds. Aerobic biological treatment using the activated sludge process (ASP) is widely employed for its remediation. However, treatment performance is critically governed by temperature, which directly influences microbial metabolism, enzyme kinetics, oxygen solubility, and sludge characteristics. This study investigates the impact of seasonal temperature variation on aerobic treatment efficiency at a pharmaceutical Effluent Treatment Plant (ETP) in Ahmedabad, Gujarat, India — a primary pharmaceutical manufacturing hub experiencing ambient temperatures ranging from 10°C (winter) to 49°C (summer). Fifty paired influent–effluent samples were collected between May 2024 and December 2024 and analysed for Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), ammoniacal nitrogen (NH₄⁺-N), Mixed Liquor Suspended Solids (MLSS), and Mixed Liquor Volatile Suspended Solids (MLVSS). Results demonstrated that maximum treatment efficiency was achieved at moderate mesophilic temperatures of 25–35°C, with COD removal reaching up to 96.5% and BOD removal exceeding 95%. Ammoniacal nitrogen removal efficiency reached 82% within the optimal range but declined significantly at high (>40°C) and low (<15°C) temperatures. ANOVA confirmed statistically significant differences in removal efficiencies across temperature regimes (p < 0.05). Biomass parameters (MLSS and MLVSS) were highest during the mesophilic phase, confirming enhanced microbial activity. These findings underscore the need for temperature-adaptive management strategies in pharmaceutical ETPs operating under semi-arid climatic conditions, and provide evidence-based guidance for regulatory compliance and operational optimization.