Removal of arsenic from a deep well by electrocoagulation in a continuous filter press reactor

Abstract

We investigated arsenic removal from groundwater by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter press reactor. The groundwater was collected at a depth of 200 m in the plateau region, in Central Mexico, (As 134 μg L−1, Fe 0.3 mg L−1, Cd 0.7 mg L−1, Na 58 mg L−1, pH 6.8). The influence of current density (J) and mean linear flow rate (u) on As removal was analyzed. EC revealed that u of 0.91 cm s−1 (which gives a retention time of 53.4 s) at J of 6 and 8 mA cm−2 yielded samples that met the Mexican standard for arsenic (≤25 μg L−1). EC at 10 mA cm−2 did not improve results any further owing to massive generation of gases and anode passivation. The partial EC removal of arsenic can be attributed to the mixture of HAsO2, H3AsO3 and HAsO42−. HAsO42− is more susceptible to removal by adsorption on Al(OH)3 and Al2O3 flocs. The best EC result was obtained at 6 mA cm−2 and 0.91 cm s−1, with energy consumption of 0.89 kWh m−3, which decreased arsenic from 134 to 14 μg L−1.