Effect of system parameters and of inorganic salts on the decolorization and degradation of Procion H-exl dyes. Comparison of H 2O 2/UV, Fenton, UV/Fenton, TiO 2/UV and TiO 2/UV/H 2O 2 processes

Abstract

Reactive dyes are extensively used in the last years due to their superior performance, but they are environmentally hazardous. In the present work, the decolorization and degradation of commercial reactive azo dyes (Procion Navy H-exl, Procion Crimson H-exl and Procion Yellow H-exl) were studied using five advanced oxidation processes (AOPs): H 2O 2/UV, Fenton, UV/Fenton, TiO 2/UV and TiO 2/UV/H 2O 2. The dependence of the decolorization on the system parameters (solution pH, dye and reactants initial concentrations, and TiO 2 loading) and on the presence of salts (NaCl, Na 2CO 3, NaHCO 3, Na 2SO 4, NaNO 3 and Na 3PO 4) was investigated. The decolorization (determined by spectrophotometric analysis) and the degradation (determined as TOC reduction) were compared for the different processes examined. The decolorization of the Procion H-exl solutions considered was found to strongly depend on the system parameters in all five AOPs. Although decolorization is very fast for the Fenton process and becomes even faster for the UV/Fenton process, degradation rates are relatively low for these two methods. Addition of H 2O 2 increases the decolorization and especially the degradation rates for the TiO 2/UV process. The H 2O 2/UV and TiO 2/UV/H 2O 2 processes result in the fastest dye degradation. The addition of the salts examined has in general an adverse effect on the decolorization rates, but to a varying degree depending on the salt used.