Response Surface Optimization of Electrocoagulation for Color Removal and COD Reduction in Textile Wastewater

Textile wastewater contains recalcitrant dyes and organic matter, requiring efficient, scalable treatment technologies. This study optimized an aluminum-based electrocoagulation (EC) process to maximize color removal (Y1) and chemical oxygen demand (COD) reduction (Y2) using synthetic textile wastewater (SWW), and evaluated the practical transferability of the optimized conditions using real textile wastewater (RTW). A rotatable central composite design (CCD) coupled with response surface methodology (RSM) was used to assess the effects of treatment time, NaCl concentration, and applied voltage on both responses. From a modeling perspective, the results reveal the coexistence of symmetric and asymmetric response behaviors; quadratic effects define locally symmetric regions around the optimum, while interaction terms introduce asymmetry due to coupled electrochemical phenomena. Under the optimized conditions (16.5 min, 2.9 g·L−1 NaCl, 18 V), removal efficiencies reached 99% for color and 97% for COD reduction, with a specific energy consumption of 6.6 kWh·m−3 and sludge moisture content of 92–94%. To assess applicability beyond bench scale, the optimized voltage, current, and electrolyte concentration were applied to a 50 L batch of RTW collected from the final rinsing stage of a denim dyeing process. Treatment time was extended to 84 min to compensate for the lower current density at the larger scale; under these conditions, 95% color removal and 80% COD reduction were achieved.