Degradation of azo dyes using low iron concentration of Fenton and Fenton-like system

This study investigated Fenton and Fenton-like reactions at low iron concentration (≦10 mg l^-1) to oxidize three commercial azo dyes, namely Red MX-5B, Reactive Black 5 and Orange G. In some local cases in Taiwan, wastewater color was found to be the only problem in meeting local effluent standards. This investigation reveals that both of these methods can remove the color of these dyes completely. Moreover they only produce little sludge in wastewater that meet local effluent standards and do not need to further treat. The effects of Fe²⁺, Fe³⁺, H₂O₂ and solution pH on dye decolorization are demonstrated in detail. The optimum pH for both Fenton and Fenton-like reactions in this study are about pH 2.5-3.0. Increasing the dose of ferric nitrate enhances the dye decolorization. The optimal levels of H₂O₂ required for the process are also examined. High levels of H₂O₂ appear to reduce dye decolorization. In addition, it is also found that decolorization of azo dyes undergoes a faster reaction rate than mineralization of azo dyes.