Optimization of the coagulation-flocculation process using response surface methodology for wastewater pretreatment generated by vegetable oil refineries: A path towards environmental sustainability

Treating complex and variable wastewater, mainly from refineries with diverse pollutants, presents multifaceted challenges. However, through diligent management and the implementation of efficient treatment strategies, the effectiveness of wastewater treatment can be maintained, ensuring the protection of the environment and public health. This study aims to enhance the coagulation-flocculation process for pretreated wastewater from vegetable oil refineries (VORW). Findings reveal that pretreatment through gravity separation influences coagulation-flocculation efficiency for oil-containing wastewater. Employing a central composite design (CCD), the study examines the effects of pH, coagulant/flocculant dosage, and settling time on turbidity and chemical oxygen demand removal (COD). Each factor significantly impacts results, with pH exerting the most substantial influence. ANOVA results validate the statistical significance of the selected models, aligning with experimental data for each response. The study demonstrates a satisfactory model fit, supported by high adjusted coefficients of determination (R²_Adj = 96.59 % for turbidity and R²_Adj = 93.61 % for COD). Optimal parameters—pH 7.5, coagulant dose 110 mg/L, flocculant dose 0.55 ml/L, and settling time 15 min—yield a 96 % reduction in turbidity and a 95 % reduction in COD. Furthermore, the combined treatment of flotation followed by coagulation-flocculation proves highly effective in achieving significant pollutant removal, showcasing the practical application of the design of experiments (DOE) in optimizing wastewater treatment processes.