Journal of Water Process Engineering 4 (2014) 25–30 Contents lists available at ScienceDirect Journal of Water Process Engineering journal h om epage: www.elsevier.com/locate/jwpe An electrocoagulation column (ECC) for groundwater purification Shaima S. Hamdan, Muftah H. El-Naas ∗ Chemical and Petroleum Engineering Department, UAE University, P.O. Box 15551, Al-Ain, United Arab Emirates a r t i c l e i n f o Article history: Received 7 May 2014 Received in revised form 7 August 2014 Accepted 16 August 2014 Keywords: Electrocoagulation column Chromium (VI) Brackish groundwater Heavy metals a b s t r a c t A novel electrocoagulation column (ECC) has been evaluated for the treatment of brackish groundwater to reduce the concentrations of Cr(VI) and other ions to be within drinking water limits. The ECC was fabricated from Plexiglas and had a rod anode and helical cathode; both electrodes were made from iron. The effect of influent flow rate, applied current density, initial concentration, pH and air mixing were studied at a temperature of 25 ◦ C. The results showed that Cr(VI) removal rate was inversely proportional to the inlet flow rate and directly proportional to applied current density, reaching 100% chromium removal for initial chromium concentration of 5 mg/L at inlet flow rate of 30 mL/min with lowest energy consumption of 0.75 kWh/m 3 and dissolved iron of 0.185 mg/L with an electrical cost of 0.03 US $/m 3 of treated groundwater. The EC column could also reduce other contaminants and metals ions such as Mg, Zn and Sr. Overall, the study affirmed that electrocoagulation is a reliable and environmentally compatible technique for the purification of groundwater. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, there is a growing environmental concern for the quality of re-used water sources in irrigation, agricultures or even industrial purposes. These concerns are attributed to the presence of pollutants, such as carcinogenic chemicals, organic matter, dyes and oils, which have adverse impacts once the contaminated water is discharged into the environment. Chromium compounds that have harmful effects on all living forms are extensively used in chrome plating, leather tanning, wood preserving, and manufac- turing of cement, dye and paper [1–3]. Chromium occurs primarily in two states: hexavalent Cr(VI) and trivalent Cr(III); hexavalent chromium is certainly more harmful to humans and animals. It has severe risks in terms of toxicity, including skin irritation, kidney failure, and gastric damage, in addition to the carcinogenic effect [4]. Researchers have been striving to develop advanced technolo- gies for the removal of toxic chromium species from wastewater. Various methods have been proposed and applied toward the attainment of this goal, including chemical precipitations [5,6], adsorption [7–9], biological reduction via bacteria [10], reverse osmoses [11], ion-exchange [12], electrodialysis [13] and photo- catalysis [14]. As a non-conventional technique, electrocoagulation (EC) presents important advantages over others including low ∗ Corresponding author. Tel.: +971 3 713 5188. E-mail address: Muftah@uaeu.ac.ae (M.H. El-Naas). operating cost, low occurrence of secondary pollution, and low sludge generation [15]. In wastewater treatment, electrocoagulation (EC) process works through destabilizing suspended or dissolved contaminants in an aqueous medium by introducing a current into the medium and generating coagulant in situ by electrolytic oxidation of an appro- priate anode material [16]. The EC technique used in the this work focuses on the removal of chromium from groundwater, while simultaneously converting Cr(VI) to Cr(III), which is less toxic and soluble in aqueous media; the aim is to reduce the chromium con- centration to be within the maximum allowable drinking water limit of 0.05 mg/L. The reactions taking place in an electrochemi- cal cell when iron metal (Fe) used as “sacrificial electrode” can be described by the following equations: Anode reaction: Fe (s) → Fe 2+ (aq) + 2e - (1) Cathode reactions: Cr 2 O 2- 7 + 6e - + 7H 2 O → 2Cr 3+ (aq) + 14OH - (2) Cr 2 O 2- 7 + 6Fe 2+ + 7H 2 O → 2Cr 3+ (aq) + 6Fe 3+ + 14OH - (3) In site reactions: Cr 3+ (aq) + 3OH - (aq) → Cr(OH) 3(s) (4) Fe 3+ (aq) + 3OH - (aq) → Fe(OH) 3(s) (5) During the past few years, considerable amount of research has been focused on the development of new and more efficient continuous EC processes. Recently the performance of vertical http://dx.doi.org/10.1016/j.jwpe.2014.08.004 2214-7144/© 2014 Elsevier Ltd. All rights reserved.