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 Bajio region in central Mexico (arsenic 50 mu g L-1, carbonates 40 mg L-1, hardness 80 mg L-1, pH 7.5 and conductivity 150 mu S 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 m(3). (c) 2013 Elsevier Ltd. All rights reserved.