Electrocoagulation (EC) has been employed for the reduction of chemical oxygen demand (COD) of industrial wastewater in batch EC reactor using aluminium electrodes. Sedimentation step with different sludge settling velocities (SSV) followed the EC step which has been used for the removal of turbidity (NTU) and total sludge concentration (TS). The individual and interactive effects of the three main independent parameters, which have been studied using central composite experimental design parameters, are current density (I): 60-140 A m(-2), initial pH (pH(0)): 3-11; and electrolysis time (t): 30-90 min. The coupled electrochemical and sedimentation processes have been optimized by Box-Behnken design of surface response analysis. It was employed to derive a statistical model from the effect of parameters studied on the COD, turbidity, TS removal efficiency and the sludge settling velocity (SSV) using aluminium electrodes and optimizing the operating conditions. The graphical representation of this model enabled the optimum conditions for these parameters to be defined. An optimal region characterized with low values of COD. TS and turbidity can be found, and the effects of these three parameters on the sludge settling velocity (SSV) have been discussed. This statistical analysis has been compared to the physical interpretation reported previously. (C) 2010 Elsevier B.V. All rights reserved.