In the paper the electro-oxidation of a spent dyeing bath, mediated by the Cl-/Cl-2 redox couple, was studied and proposed for the treatment of textile wastewater as a technology alternative to hypochlorite oxidation. The work focused on the optimization of the electrochemical reactor. Particular attention was paid to the dependence of transport mechanisms and reaction rates on temperature, applied current, and hydrodynamic conditions in the reactor. The simultaneous production of H2O2 from the cathodic reduction of O-2, which could also react with the dye, was also assessed. The regime which controlled the reaction was determined from the Hatta number.