Response surface optimization of pH and coagulant dosage for pharmaceutical wastewater pretreatment using alum and bentonite

Abstract

Selection of an appropriate coagulant for removal of chemical oxygen demand (COD) and turbidity from wastewater generated in a pharmaceutical industry was demonstrated. The standard jar test procedure was adopted to determine the optimum pH and coagulant dosage needed for enhanced COD and turbidity removal. Alum and bentonite (montmorillonite) were chosen as coagulant and coagulant aid, respectively. Based on the results obtained from experiments, COD removal (CODRE, %) and turbidity removal (TRE, %) were optimized using response surface methodology. Under the optimum conditions, the model predicted a CODRE of 67% and TRE of 90% and CODRE of 55% and TRE of 70% using alum (coagulant dosage = 0.79 g/L, pH 5.91) and bentonite (coagulant dosage = 0.58 g/L, pH 5.61), respectively. Confirmatory experiments conducted on the optimized condition showed experimental findings within 5% of the projected values. Though alum resulted in higher CODRE and TRE as compared to bentonite, bentonite can have the advantage of being environmentally benign when compared to the conventionally used coagulant, alum.