A dielectric barrier discharge (DBD) system employing wastewater as one of the electrodes was applied to the degradation of an azo dye, Orange II. The main advantage of this system is that reactive species like ozone and ultraviolet (UV) light produced by the DBD can be utilized for the treatment of wastewater. This system was able to remove the chromaticity and destroy the benzene and naphthalene rings in the dye molecule effectively. The results obtained under several conditions revealed that the UV emission from the DBD reactor could enhance the degradation of the dye, particularly in the presence of titanium oxide photocatalyst. The products resulting from the destruction of the rings in the dye molecule were found to be highly recalcitrant against further oxidation to smaller molecules. The change in the initial dye concentration showed that the reaction order was around 0.8 with respect to the dye concentration. The reduction in the concentration of total organic carbon was much more efficient with oxygen than with air. (c) 2007 Elsevier B.V. All rights reserved.