A full-wave rectified alternating current wireless electrocoagulation strategy for the oxidative remediation of As(III) in simulated anoxic groundwater

Abstract

The application of conventional DC electrocoagulation for remedying the anoxic As(III)-contaminated groundwater normally suffers from the external introduction of O2 and the vulnerability of the ohmic contact between iron electrode and conductive wire. To address these limitations, a novel full-wave rectified alternating current wireless electrocoagulation (FWAC-WEC) technology for the oxidative immobilization of As(III) from anoxic groundwater was developed in this study. The FWAC-WEC process produced Fe(II) and O2 simultaneously when utilizing iron bipolar electrodes (Fe-BPEs) and two Ti plate coated mixed IrO2/Ta2O5 (MMO) driving electrodes. The increase in Fe-BPEs number (1–3) and outage time (0–6 s) and the decrease in the angle for Fe-BPEs to electric field line separately benefited As(tot) removal. Besides, As(tot) removal was enhanced with increasing pH value but deteriorated by the presence of HCO3− and PO43−. In the FWAC-WEC process, As(III) was initially oxidized to ionic As(V) by intermediate Fe(IV) species. Thus, As(tot) removal was significantly promoted by adsorption and/or co-precipitation of As(V) with the fresh Fe(III) (oxyhydr)oxides, which appreciably obeyed the Langmuir isotherm and the second-order kinetics. Notably, the FWAC-WEC technology can effectively eliminate the passivation of Fe-BPEs and thereby increase the utilization of Fe-BPEs due to the periodic exchange of driving electrodes polarity. This strategy could remarkably reduce the energy consumption to 0.101 kW·h/m3 for As(III) removal, which was much less than 0.167 KW·h/m3 in the DC counterpart. Generally, the FWAC-WEC technology is energy-efficient and has the potential of being a sustainable treatment option to improve access to safe groundwater for millions of people.