Tradeoff between groundwater arsenite removal efficiency and current production in the self-powered air cathode electrocoagulation with different oxygen reduction pathways

Abstract

Naturally occurring arsenic enrichment in aquifers posts a huge threat to drinking water safety. To achieve energy-efficient arsenite [As(III)] removal, a self-powered iron electrocoagulation was developed that coupled iron corrosion anode with oxygen reduction air cathode for simultaneous As(III) oxidation and removal. Activated carbon (AC), which favored the four-electron oxygen reduction reaction (ORR, O2+4e−+4H+→2H2O, E0′ = 0.816 V), and carbon black (CB), which favored two-electron ORR (O2+2e−+2H+→H2O2, E0′ = 0.283 V), were evaluated for As(III) removal efficiency and current production performance. The comparison showed a tradeoff between higher current (i.e., higher iron corrosion rate) attributed to the higher reduction potential with four-electron ORR, and higher H2O2 production for improved As(III) oxidation with two-electron ORR yet the lower reduction potential The CB cathode that favored H2O2 production had the best As(III) removal of 99.2 ± 0.4% and the lowest maximum power density of 60 ± 0.3 mW m–2, while the AC cathode showed the opposite trend. These results suggested that cathode catalysts need to be carefully evaluated for the balance of As(III) removal and current production to provide a sustainable and effective solution for groundwater As(III) removal.