The present paper deals with chemical oxygen demand (COD) reduction of a bio-digester effluent (BDE) in a batch electrocoagulation (EC) reactor using iron electrode. A central composite (CC) experimental design has been employed to evaluate the individual and interactive effects of four independent parameters on the COD removal efficiency. The parameters studied are current density (j): 44.65-223.25 A/m(2): initial pH (pH(o)): 2-8; inter-electrode distance (g): 1-3 cm and electrolysis time (t): 30-150 min. The results have been analyzed using Pareto analysis of variance (ANOVA). Analysis showed a high coefficient of determination value (R-2 =0.8547) and satisfactory prediction for second-order regression model. Graphical response Surface and contour plots have been used to locate the optimum values of studied parameters. Maximum COD and color reduction of 50.5% and 95.2%, respectively, was observed at Optimum conditions. Present study shows that EC technique can be employed in distilleries to reduce the pollution load before treatment in aerobic treatment plants to meet the discharge standards. (C) 2008 Elsevier B.V. All rights reserved.