Decolorization of Mordant red 73 azo dye in water using H2O2/UV and photo-Fenton treatment

Decolorization of the Mordant red 73 (MR73) azo dye in water was investigated in laboratory-scale experiments using UV/H2O2 and photo-Fenton treatments. Photodegradation experiments were carried out in a stirred batch photoreactor equipped with a low-pressure mercury lamp as UV source at 254 nm. The effect of operating parameters such as pH, [H2O2], [dye] and the presence of inorganic salts (NaNO3, NaCl and Na2CO3) were also investigated. The results indicated that complete dye decolorization was obtained in less than 60 min under optimum conditions. Furthermore, results showed that dye degradation was dependent upon pH, [H2O2] and initial dye concentration. The presence of chloride ion led to large decreases in the photodegradation rate of MR73 while both nitrate and carbonate ions have a slight effect. The photo-Fenton treatment, in the presence of Fe powder as a source of Fe2+ ions, was highly efficient and resulted in 99% decolorization of the dye in 15 min. Mineralization of MR73 dye was investigated by determining chemical oxygen demand (COD). In a 3 h photoperiod “65%” of the dye was mineralized by the H2O2/UV process, while the photo-Fenton treatment was more efficient producing 85% mineralization over the same 3-h period.