Optimization of Removal of Cr(VI) from Wastewater by Electrocoagulation Process Using Response Surface Methodology

This study investigated the removal of hexavalent chromium [Cr(VI)] from a simulated industrial effluent that used electrocoagulation (EC) technology. Experimental runs were conducted in a laboratory-scale batch EC cell with vertically rotating cylindrical aluminum (Al) electrodes, which imparted the required velocity to avoid a concentration gradient within the treatment unit. The independent variables, current, influent pH, rotational speed (rpm), and initial Cr(VI) concentration [Cr(VI)(i)], that affected Cr removal efficiency were optimized through a central composite design (CCD) that was initiated by the response surface methodology (RSM). The ANOVA factor of the CCD indicated that the investigated independent variables had a significant impact on the responses, such as Cr(VI) removal and specific electrical energy consumption (SEEC). Four factors, which each had three levels were considered: (1) Cr(VI)(i) (15-35 mg/L); (2) applied current (1-3 A); (3) initial pH (4-6); and (4) rotational speed of the electrode (40-100 rpm). High R-2 values were observed for Cr(VI) (98.12%) and SEEC (98.09%), which validated the regression equations that were generated in this study. Optimizing the performance factors for the treatment process was targeted to achieve maximum Cr(VI) removal and minimum SEEC. Under the optimum condition, the Cr(VI) removal efficiency, SEEC, and operating cost were 89.808%, 0.14 kW center dot h/g Cr(VI) removed, and USD 0.728/m(3), respectively. The optimum values that were obtained for the selected input variables were Cr(VI)(i) of 4.99 mg/L, current of 2.189 A, initial pH 4.5, and a rotational speed of 72.46 rpm.