Enhancing Operational Efficiency in Wastewater Treatment: STOAT Modelling and Optimization of the Kurunegala WWTP

This study evaluates the energy optimization potential of the Kurunegala Wastewater Treatment Plant (WWTP) using STOAT, a freely available wastewater process simulation tool. The plant’s treatment process, based on an anoxic-oxic (AO) configuration, was modelled and calibrated using measured influent and effluent quality parameters. The validated model accurately predicted key performance indicators such as BOD, TSS, ammonia, and nitrate, confirming STOAT’s reliability. Sensitivity analysis identified influent flow rate and return activated sludge (RAS) ratio as the most critical parameters influencing effluent quality. Simulation-based optimization was conducted to assess the impact of dissolved oxygen (DO) and RAS variations on treatment efficiency and energy consumption. Results demonstrated that reducing DO from 2.0 to 1.0 mg/L and RAS from 0.667 to 0.4 achieved a 46.4% reduction in energy consumption without compromising effluent quality. The study also identified operational thresholds for BOD and NH₄⁺-N in influent to maintain compliance with Sri Lankan discharge standards. These findings highlight the practical value of STOAT in supporting data-driven decision-making for energy-efficient and sustainable wastewater treatment, especially in resource-constrained contexts.