Arsenic removal from groundwater by electrocoagulation in a pre-pilot-scale continuous filter press reactor

• Arsenic removal from groundwater by electrocoagulation.
• Aluminum as sacrificial anodes.
• Electrolyzes at different flow rates and current densities.
• Electrocoagulation led to 100% arsenic removal (50 μg L−1) with 3.9 kWh m−3.
• The influence of hypochlorite on arsenic removal efficiency was analyzed.

We investigated arsenic removal from groundwater by electrocoagulation (EC) using aluminum as the sacrificial anode in a pre-pilot-scale continuous filter press reactor. The groundwater was collected at a depth of 320 m in the Bajío region in central Mexico (arsenic 50 μg L–1, carbonates 40 mg L–1, hardness 80 mg L–1, pH 7.5 and conductivity 150 μS cm–1). The influence of current density, mean linear flow and hypochlorite addition on the As removal efficiency was analyzed. Poor removal of total arsenic (<60 %) in the absence of hypochlorite is due to a mixture of arsenite (HAsO2(aq) and H3AsO3(aq)) and arsenate (HAsO42−). Arsenic removal is more efficient when arsenite is oxidized to arsenate by addition of hypochlorite at a concentration typically used for disinfection (1 mg L–1). Arsenate removal by EC might involve adsorption on aluminum hydroxides generated in the process. Complete arsenate removal by EC was satisfactory at a current density of 5 mA cm–2 and mean linear flow of 0.91 cm s–1, with electrolytic energy consumption of 3.9 kWh m3.