Evaluating electrocoagulation pretreatment prior to reverse osmosis system for simultaneous scaling and colloidal fouling mitigation: Application of RSM in performance and cost optimization

Abstract

In the present research, electrocoagulation (EC) process was applied as a selected pretreatment to evaluate its effectiveness and operating cost regarding simultaneous calcium and turbidity removal in order to mitigate the scaling and colloidal fouling potential of reverse osmosis (RO) technology. The effects of the main parameters, namely, initial calcium concentration, initial turbidity, time, and current density, on EC process were assessed and optimized by employing response surface methodology (RSM). A reasonable correlation between the experimental and predicted data was found through analysis of variance (ANOVA). The highest calcium and turbidity removal efficiencies of 36 % and 93.5 %, respectively, and the minimal operating cost of 1.58 US$/m3 were obtained at the optimum time of 35.5 min and current density of 3.85 mA/cm2 with the selected constant initial calcium concentration of 250 mg/L and initial turbidity of 85 NTU. In the present study, the applicability of two pretreatments, including hybrid EC-filtration and filtration-only to RO membrane fouling was also compared. The RO recovery of the hybrid EC-filtration pretreatment improved about 25 % in comparison to that of the filtration-only pretreatment, which demonstrated the effective capability of the EC process in scaling and colloidal fouling mitigation.