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The generation of active chlorine on Ti/ Sn (1-x) Ir x O 2 anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L -1 ) and a low current density (5 mA cm -2 ) it was possible to produce up to 60 mg L -1 of active chlorine on a Ti/Sn 0.99 Ir 0.01 O 2 anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn (1-x) Ir x O 2 anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm -2 and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 · 10 -4 mol L -1 . Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.

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