The treatment of C.I. Acid Blue 5 solution by electrochemical process was studied under recirculation mode with a cathode containing multi walled carbon nanotubes in the presence of sodium sulfate electrolyte. Comparison of electro-Fenton and photoelectro-Fenton processes at pH 3.0 revealed that 23.04 and 98.25% of the dye was decolorized at 60 min, respectively. The kinetic of dye removal by photoelectro-Fenton process was studied with nonlinear regression analysis. A kinetic model was developed for estimation of pseudo-first order rate constant (k(app)) as a function of operational parameters including initial concentration of the dye (10-50 mg/L), flow rate (5-20 L/h), pH (3-9), initial concentration of Fe3+ (0.05-0.2 mM) and applied current (0.05-0.45 A). The calculated results, which were obtained from kinetic model, were in consistent with the experimental data (R-2 = 0.9934). The calculated and experimental data were applied for prediction of the electricity consumption in decolorization processes. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.