Hardness, COD and turbidity removals from produced water by electrocoagulation pretreatment prior to Reverse Osmosis membranes

Abstract

This study refined the hardness removal (together with chemical oxygen demand (COD) and turbidity) from the produced water by a pilot-scale electrocoagulation (EC) system to mitigate the scaling and fouling of Reverse Osmosis (RO) membranes. In preliminary studies, effects of initial pH, current density and electrolysis time on pollutant removal were investigated. Response surface method (RSM) was employed further to evaluate individual/interactive influences of parameters on pollutant recovery. Analysis of Variance (ANOVA) showed a satisfactory agreement of the predicted and experimental data. The refined operating conditions were pH of 7.36, current density of 5.90mA/cm2, and reaction time of 30.94min to maximize the hardness removal at 85.81%, COD at 66.64%, and turbidity at 93.80%. The equivalent coagulant dose was 23.76mg/L (as Fe3+). The permeate flux was around 22L/(m2﹒h) and the water recovery rate reached 87.83%. The operating refinement of EC processes by RSM was a promising alternative for the pretreatment of produced water prior to RO membranes. The product water from the batch EC–RO system was suitable for reinjection or beneficial reuse.