Site‐Specific Evaluation of Sequencing Batch Reactor Systems for Municipal Wastewater Treatment Using Environmental Indices in Erbil City, Iraq

Abstract

Rapid urbanization in semi‐arid regions places increasing pressure on municipal wastewater treatment systems, necessitating reliable and operationally flexible technologies. This study evaluated the performance of two full‐scale municipal sequencing batch reactor (SBR) systems operating in Erbil, Iraq, using an integrated multi‐index assessment framework. Wastewater samples were collected monthly over a 12‐month period, and influent and effluent data were analyzed as monthly means to capture seasonal variability. Physicochemical parameters and nutrients were measured using standard analytical methods. The SBR systems achieved substantial reductions in organic and particulate pollutants. Turbidity and total suspended solids removal exceeded 80%, while chemical oxygen demand and biochemical oxygen demand reductions ranged between 77%–91%. Phosphate removal exceeded 80% at both stations, and nitrate concentrations were reduced by up to 76%. Dissolved oxygen concentrations increased significantly after treatment, confirming effective aeration and biological activity. Composite pollution indices demonstrated marked improvement following treatment. The Comprehensive Pollution Index decreased from 38.08 to 4.08 (S1) and from 24.73 to 3.10 (S2), while the Nemerow Pollution Index declined from 178.84 to 13.12 and from 74.93 to 8.16, respectively. Water Suitability Index values were substantially reduced, indicating enhanced effluent quality. Overall, the findings confirm that SBR technology provides stable and efficient municipal wastewater treatment under semi‐arid urban conditions. The integrated index‐based framework applied in this study offers a practical multidimensional tool for evaluating treatment performance in data‐limited developing regions.