Evaluation of Pollutant and Heavy Metal Removal Efficiency at the Municipal Sewage Treatment Plant

ABSTRACT

This study evaluates the performance of the sewage treatment plant in Islamabad, which treats wastewater from 25 sectors. Wastewater samples were collected from the influent, primary outlet, and final effluent to evaluate treatment efficiency on the basis of physicochemical parameters, organic load indicators, and heavy metal concentrations. Temperature across the treatment process ranged from 20°C to 27°C, whereas pH values remained within 6.8–8.2, indicating stable biological and chemical conditions. Electrical conductivity (EC) decreased from 700 to 830 µS/cm in the influent to lower values in the effluent, reflecting partial reduction of dissolved ions. Influent turbidity reached 95 Nephelometric Turbidity Units (NTU), which was reduced by up to 90% after treatment. Total suspended solids (TSS) decreased from 270–360 to 25–30 mg/L, corresponding to 85%–91% removal. Total dissolved solids (TDS) exhibited removal up to 95%, demonstrating effective sedimentation and filtration processes. Organic pollution indicators showed a notable reduction, with chemical oxygen demand (COD) decreasing from 250–330 to 55–110 mg/L, and biochemical oxygen demand (BOD) decreasing from 80 to 100 mg/L to significantly lower levels in the final effluent, yielding 60%–80% removal efficiency that meets National Environmental Quality Standards (NEQS). Arsenic and aluminum showed 92%–99% reduction, lead and chromium exhibited 95%–100% removal, whereas cadmium and copper showed variable but effective removal efficiencies ranging from 55% to 95%, depending on industrial inflow and operational conditions. Overall, the plant achieved 55%–95% removal efficiency, though copper remained one of the more persistent metals due to industrial contributions.