Effect of current density on groundwater arsenite removal performance using air cathode electrocoagulation

Naturally occurring arsenic enrichment in groundwater poses a huge threat to human health. Air cathode electrocoagulation (ACEC) has recently been proposed to enhance As(III) oxidation and lower energy consumption. In this study, ACEC, EC/O2 and EC/N2 were evaluated with different current densities from 1 to 8 mA/cm2 to investigate the effect on As(III) removal in different redox environments. Current density had no appreciable effect on arsenic removal efficiency given the same charge in ACEC because the concentration ratio of Fe/H2O2 under different current densities remained stable. However, in EC/O2 and EC/N2, As(III) removal was inhibited at higher current densities (4–8 mA/cm2), likely because more Fe(II) competed with As(III) for the oxidant, leading to less effective oxidation of As(III). In all EC systems, the ·OH units generated per power consumption reached the highest value at the lowest current density. Compared with other EC systems, the ACEC system showed lower energy consumption at all current densities due to the low energy consumption of the electrode reaction and more free radical generation. A lower current density saved more energy at the expense of time, showing the trade-off relationship between energy consumption and removal time. The operation costs for As(III) removal under optimal conditions were calculated as 0.028 $/m3 for ACEC, 0.030 $/m3 for EC/O2, and 0.085 $/m3 for EC/N2