Evaluation and Optimization of COD Removal Performance for a Domestic Wastewater Treatment Plant by Response Surface Methodology: The Case of Van Muradiye

ABSTRACT In this study, the performance of the Van Muradiye Domestic Wastewater Treatment Plant was evaluated with Response Surface Methodology (RSM). The effects of pH, conductivity, dissolved oxygen (DO), and suspended solids (SS) on the chemical oxygen demand (COD) removal efficiency were evaluated using samples collected from the plant's inlet and outlet. Biomass concentrations (Mixed Liquor Suspended Solids (MLSS): 3200–3500 mg/L; Mixed Liquid Volatile Suspended Solids (MLVSS): 2600–2900 mg/L) and Sludge Volume Index (SVI) values (100–150 mL/g) were within acceptable operating ranges. ANOVA results showed that pH and conductivity were statistically significant factors ( p < 0.05), whereas DO had a moderate effect and SS had a limited effect within the studied range. The second‐order model developed exhibited strong predictive capability ( R 2 = 0.9176; adjusted R 2 = 0.8406; CV = 1.08%). Optimization modeling predicted that maximum COD removal efficiency would be 92.27% at pH 7.3, conductivity 765.6 μS/cm, DO 1.06 mg/L, and SS 84.2 mg/L. The RSM‐based optimization results demonstrated strong predictive capabilities and predicted potentially optimal conditions for improving COD removal (%). These findings were evaluated in the context of the operating conditions observed during January–June 2025. To more comprehensively demonstrate the model's accuracy across different seasonal conditions and its applicability to similar full‐scale wastewater treatment plants, it is recommended that monitoring studies be conducted year‐round and that the identified optimal conditions be validated using data.