Treatment of petroleum refinery wastewater by chemical coagulation method: determination of optimum removal conditions using experimental design

Wastewater minimization is very important in the production process of petroleum industries due to they have large water demands in their operations. In this study, optimum treatment conditions of petroleum industry wastewater were obtained with the chemical coagulation method. Analyses of the obtained wastewater was carried out and pollution values were determined before the treatment process. The best coagulant is selected for optimization experiments between the Al-2(SO4)(3).18H(2)O, FeCl3.6H(2)O and FeSO4.7H(2)O coagulants. The best removal efficiency was obtained with Al-2(SO4) coagulant and Central Composite Design (CCD) was performed for optimization procedure. pH, coagulant dosage and mixing speed were choosen as the independent parameters and the results of COD, TSS, turbidity and color analyses were used as responses. The three dimensional plots and ANOVA tables, which are the outputs of CCD, were mainly evaluated for their removal efficiency of wastewater treatment. The obtained model equations using the coefficients were solved and the optimum values of the variables were determined. The optimum values of treatment parameters were obtained as pH 9.43, coagulant dosage 36.14 mg/L, mixing speed 145.93 rpm. The highest removal efficiency values at the optimum treatment conditions were obtained as (%) 78.75, 91.21, 72.89 and 98.10 for COD, TSS, color and turbidity, respectively.