Arsenic (As) removal from groundwater (GW) was carried out by electrocoagulation (EC). To define the effects of the main factors involved in As removal by EC on the energy consumption of the treatment, an experimental design based on an orthogonal array (OA) L-9(3(4)) proposed by Taguchi was used. Four factors at three different levels were considered for the optimisation. namely the interelectrode distance, the current density, the electrode area-reactor volume ratio and the liquid motion driving mode. The response variable was the energy consumption for the treatment time necessary for reducing the residual As concentration in GW to 10 mu g L-1, which is the maximum contaminant level (MCL) established by the World Health Organisation (WHO) for drinking water. Based on the signal-to-noise ratio (S/N) and the analysis of variance (ANOVA), the results indicated that the interelectrode distance is the most significant process parameter, and the second most significant factor is the liquid motion driving mode. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.