Optimization of Coagulation Process Parameters for Reactive Red 120 Dye Using Ferric Chloride via Response Surface Methodology

In this study, the removal of Reactive Red 120, a dye commonly present in textile wastewater, was investigated using Ferric Chloride (FeCl₃) as a coagulant. Process optimization was carried out through Response Surface Methodology based on a four-factor experimental design, considering initial pH (2–12), coagulant dose (100–500 mg/L), mixing speed (50–250 rpm), and initial dye concentration (25–250 mg/L). A second-order polynomial model was developed and evaluated by ANOVA to assess the individual and interactive effects of these parameters on color removal efficiency. The maximum removal efficiency of 96.28% was obtained at pH 3, coagulant dose 400 mg/L, mixing speed 100 rpm, and dye concentration 200 mg/L. The Response Surface Methodology model showed good agreement with the experimental data and predicted a theoretical maximum efficiency of 98.33% under optimized conditions. Overall, the results confirm that FeCl₃-based coagulation, when optimized by Response Surface Methodology, is a robust and scalable pretreatment option for textile wastewater, capable of achieving near-complete decolorization and providing practical operating ranges for implementation.