The removal of textile dye Reactive Black 5 from aqueous solution by ozone until total decolorization using a semi-batch bubbling reactor was studied. This compound was selected because of its extended industrial application for cotton dyeing. Decomposition of that textile dye was observed by adding some chemical auxiliaries commonly used in textile dyeing processes such as sodium sulfate, sodium carbonate and sodium hydroxide, between the limits found in a normal dyehouse wastewater. The recording of UV-Vis spectra was used to evaluate the dye decomposition rate. The decomposition rate through this treatment depends on the presence of dyeing auxiliaries. Color disappears for 10 min of ozone treatment when auxiliaries are present. The treated water was then used in dyeing of cotton samples with a set of reactive dyes and direct dyes, separately, until 5 times without further salt addition, in order to evaluate the feasibility to reuse taking advantage of the present salt For short times of solution ozonation, byproducts accumulation was observed by UV-Vis spectroscopy. The influence of byproducts generated during ozonation of dye solutions on the coloration quality of the water recirculation depends on the nature of dyes used in dyeing processes. The preservation of sodium ions, responsible for the zeta potential neutralization in dyeing process, was demonstrated using atomic absorption spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.