This study makes a comparison between UV/Nano-TiO2, Fenton, Fenton-like, electro-Fenton (EF) and electrocoagulation (EC) treatment methods to investigate the removal of C.I. Acid Blue 9 (AB9), which was chosen as the model organic contaminant. Results indicated that the decolorization efficiency was in order of Fenton > EC > UV/Nano-TiO2 > Fenton-like > EF. Desired concentrations of Fe2+. and H2O2 for the abatement of AB9 in the Fenton-based processes were found to be 10(-4) M and 2 x 10(-3) M, respectively. In the case of UV/Nano-TiO2 process, we have studied the influence of the basic photocatalytic parameters such as the irradiation time, pH of the solution and amount of TiO2 nanoparticles on the photocatalytic decolorization efficiency of AB9. Accordingly, it could be stated that the complete removal of color, after selecting desired operational parameters could be achieved in a relatively short time, about 25 min. Our results also revealed that the most effective decomposition of AB9 was observed with 150 mg/l of TiO2 nanoparticles in acidic condition. The effect of operational parameters including current density, initial pH and time of electrolysis were studied in electrocoagulation process. The results indicated that for a solution of 20 mg/l AB9, almost 98% color were removed, when the pH was about 6, the time of electrolysis was 8 min and the current density was approximately 25 A/m(2) in electrocoagulation process. (C) 2008 Elsevier B.V. All rights reserved.