Dynamics of Chromium(VI) Removal from Drinking Water by Iron Electrocoagulation

The potential for new U.S. regulations for Cr­(VI) in drinking water have spurred strong interests in improving technologies for Cr­(VI) removal. This study examined iron electrocoagulation for Cr­(VI) removal at conditions directly relevant to drinking water treatment. Cr­(VI) is chemically reduced to less soluble Cr­(III) species by the Fe­(II) produced from an iron anode, and XANES spectra indicate that the Cr is entirely Cr­(III) in solid-phases produced in electrocoagulation. The dynamics of Cr­(VI) removal in electrocoagulation at pH 6 and pH 8 at both oxic and anoxic conditions can be described by a new model that incorporates Fe­(II) release from the anode and heterogeneous and homogeneous reduction of Cr­(VI) by Fe­(II). Heterogeneous Cr­(VI) reduction by adsorbed Fe­(II) was critical to interpreting Cr­(VI) removal at pH 6, and the Fe- and Cr-containing EC product was found to catalyze the redox reaction. Dissolved oxygen (DO) did not observably inhibit Cr­(VI) removal because Fe­(II) reacts with DO more slowly than it does with Cr­(VI), and Cr­(VI) removal was faster at higher pH. Even in the presence of common groundwater solutes, iron electrocoagulation lowered Cr­(VI) concentrations to levels well below California’s 10 μg/L.