Statistical experimental design and analysis of mixed natural-synthetic coagulants for the reduction of total suspended solids and turbidity in sewage wastewater treatment

The investigation of mixed natural-synthetic coagulants for sewage wastewater treatment offers great insight into the process. The purpose of this study is to compare the efficacy of watermelon and rockmelon seeds as natural coagulants versus hydrated lime as a synthetic coagulant for sewage wastewater treatment. Batch coagulation experiments were carried out by using the jar test method, with pH (5.0–7.0) and coagulant dosage (50–100 mg/L) being adjusted. The agitation speed and time of fast mixing were 150 rpm and 1 min, respectively, followed by slow mixing at 50 rpm for 30 min, and then settled for 1 h at 30 ± 2 °C. Central composite design or Box-Wilson response surface design (BWRSD) is used to maximize the percentage removal of turbidity and suspended solids at optimum pH and coagulant dosage using a mixed natural-synthetic coagulant in Design-Expert version 13. For turbidity and suspended solids, maximum removal of 90 and 91% was achieved at an optimal pH of 5.5 and a coagulant dosage of 70 mg/L for hydrated lime with watermelon and rockmelon seeds, respectively. The findings show that combined natural-synthetic coagulants are effective for the pretreatment of large-scale sewage wastewater.