Kinetics of oxidation of ponceau 4R in aqueous solutions by Fenton and photo-Fenton processes

A 2(2) factorial design of experiments complemented with a central point assayed in triplicate was proposed to investigate the influence of initial Fenton's reagent (H2O2 and Fe2+)concentration on the maximum oxidation of the Ponceau 4R dye in aqueous solution. The reactions took place in batch reactors without (Fenton process) and with (photo-Fenton process) UV irradiation under well-stirred conditions at approximately 25 degrees C. Based on these preliminary results, the kinetics of color degradation, removal of total organic carbon and consumption of reactants was experimentally investigated for 7200 s at optimal initial concentration of H2O2 and Fe2+. The results show that the Fenton and photo-Fenton process caused approximately 95% of decoloration after only 300 s of reaction and complete color degradation at 7200 s. At this final time of reaction, TOC removals of 97% and approximately 100% were observed when applying Fenton and photo-Fenton conditions, respectively. A toxicity assay revealed that A. salina was not sensitive to the synthetic effluent treated by the photo-Fenton process and diluted with aqueous nutritive solution at 25, 12.5, 10 and 5%. A suggested simplified mechanism involving three elementary reactions was able to reproduce the experimental kinetic results of Fe2+, H2O2 consumption, Fe3+ formation and azo dye degradation. On the whole, the results obtained at the investigated conditions show that the photo-Fenton and Fenton processes are effective processes to achieve TOC reduction and color degradation of Ponceau 4R dye typically found in liquid effluents from the Brazilian confectionary industries.