A systematic study of the effect of design and operation conditions of an electrochemical reactor on the treatment time for arsenic (As) electro-removal from underground water (GW) was carried out to analyse the energy and electrode consumption. The effects of four factors-current density, interelectrode distance, electrode area-volume ratio, and liquid motion driving mode-were evaluated. The response variables were the energy and the electrode consumption and the treatment time to reduce the GW residual As concentration to 10 mu g L-1, which is the maximum contaminant level (MCL) established by the World Health Organization (WHO) in drinking water. The results obtained in this study showed that the factor that had the greatest effect on most of the response variables was the liquid motion driving mode. The best residence time was 20 s. which favoured low energy consumption (58.78 Wh m(-3)) and low electrode material loss (9.59 g m(-3)). (C) 2009 Elsevier B.V. All rights reserved.