Decolorization kinetics of Procion H-exl dyes from textile dyeing using Fenton-like reactions

The decolorization kinetics of three commercially used Procion H-exl dyes was studied using a Fenton-like reagent. The effect of the major system parameters (pH, concentration of H2O2 and Fe3+ and initial dye concentration) on the kinetics was determined. For comparison, the effect of the use of UV irradiated Fenton-like reagent and of Fenton reagent on the kinetics was also examined. In addition, mineralization rates and the biodegradability improvement as well as the effect of the addition of Cl−, CO32− or HCO3− on the decolorization rates was studied. The reactions were carried out in a 300 ml stirred cylindrical reactor with the capability of UV irradiation. The dye half-life time goes through a minimum with respect to the solution pH between 3 and 4. It also exhibits a broad minimum with respect to Fe3+ and H2O2 at molar ratios of H2O2/Fe3+ from about 100 to 10. The addition of CO32− and HCO3− substantially reduces the decolorization rates, while this effect is significantly less pronounced with Cl−. At an optimum range of parameters, the mineralization rate (TOC reduction) is very slow for the Fenton-like process (TOC decrease from an initial 49.5 to 41.1 mg/l after 30 min and to only 35.2 mg/l after 600 min), but it increases significantly for the photo-Fenton-like process (to TOC values of 39.7 and 11.4 mg/l, respectively). The biodegradability, as expressed by the BOD/COD ratio, increases significantly from an initial value of 0.11–0.55 for the Fenton-like and to 0.72 for the photo-Fenton-like processes.