Author(s)

E. KWEINOR TETTEH & S. RATHILAL

Abstract

Recovery of oil and water from industrial mineral oil wastewater for reuse is a means of conserving water and energy for economic growth and sustainability. The effluent generated from a local South African oil refinery is characterized by a high content of four water parameters, namely chemical oxidation demand (COD), soap oil and grease (SOG), turbidity (NTU) and total suspended solids (TSS). The goal of this study is to optimize the coagulation floatation process using a polymeric coagulant for the efficient reduction of contaminant concentrations. The response surface methodology (RSM) coupled with the box–behnken design (bbD) was adapted to evaluate the effects and interactions of three factors: pH, coagulant dosage and floatation time to maximize the efficiency of the coagulant to the response of the four water qualities. A standard jar test procedure of coagulation floatation was adapted to improve the water quality. Quadratic and linear models were generated for COD with SOG and NTU with TSS as the responding variables, respectively. In addition, analysis of variance (ANOVA) shows that the model was significant with a 95% confidence level. The desirability from the experiment shows that at the optimum coagulant dosage of 50 mg/L, about 70% of the initial wastewater contaminants were removed as compared with RSM at an optimum dose of 40 mg/L and 80% removal. This helps reduce chemical costs and upgrade the water quality. The bbD-RSM serves as a statistical tool for evaluation, verification and decision-making for the response feedback and helps identify the most important factor to control in order to enhance the treatment efficiency of the process.

Keywords

Coagulation, floatation, response surface methodology, soap oil and grease