Optimization of the coagulation-flocculation process for vegetable oil refinery wastewater using a full factorial design

Abstract

Vegetable oil refineries wastewater poses significant challenges to treatment techniques due to its characteristic fluctuations. In this study, a full factorial design (FFD) was applied to investigate the effect of the experimental variable (pH, coagulant dose, flocculant dose, and pollutant load) for the turbidity (Y1) and COD (Y2) removal by the coagulation-flocculation process. The results showed that the linear regression models were well suited to the experimental data, with correlation coefficients R2adj of 0.96 and 0.9 for Y1 and Y2, respectively. According to the ANOVA analysis, linear effects were detected significantly for the four factors examined on turbidity and COD removal. This study has shown that coagulation-flocculation is effective for turbidity removal, regardless of the pollutant load of wastewater. Under optimal conditions using 1 g L−1 FeCl3 and 1 mL L−1 cationic polymer at a pH = 8, the turbidity removal reaches 82% and 97.5% for a low and high pollution load, respectively. In contrast, the COD removal reaches 79.5% and 58% for low and high pollution loads, respectively. These results prove that the efficiency of physicochemical treatment in organic matter removal is more effective in less polluting industrial wastewater. This strongly suggests that a physical pretreatment is a promising option for the best efficiency of coagulation-flocculation.