Application of Response Surface Methodology Combined Box–Behnken Design with Desirability Function for Optimizing Wastewater Pretreatment Process

Response surface methodology combined with a three-level Box–Behnken design was a novel alternative to optimize wastewater pretreatment. The independent variables were included as aluminum sulfate concentration (A: 0.1–0.5 M), ferric chloride concentration (B: 0.1–0.5 M) and temperature (C: −0.5 to 0.5 °C) for the optimization process against the responses. The pretreatment procedure involved granules, sand, charcoal and cotton. The comparative approach was to replace sand with sawdust, keeping the other reagents unchanged. The pH and conductivity were in the range of 3.02–7.11, 212.9–1422 µS/cm, 2.55–6.8 and 294–1524 µS/cm with sawdust and sand, respectively. The desirability function helps to optimize all the independent variables based on their maximum responses. The pretreatment process showed better results in quantifying TDS, TSS, alkalinity, sodium and chloride with values of 12.5–128.35, 0.15–0.4, 20–85, 40–185, 8–89.5 mg/L and 10.4–101.2, 0.1–0.25, 12–58, 30–141, 6–77.1 mg/L, respectively, with sand and sawdust, which enhanced sawdust was more significant compared to sand. However, all results were acceptable after the pretreatment process. ANOVA was integrated to determine the model’s adequacy. The method was a low-cost, effective, straightforward procedure to purify and reuse the wastewater for our benefit.