Fenton and Fenton-like processes for the mineralization of Ponceau S in aqueous solution: Assessment of eco-toxicological effect of post treated solutions

This study reports the influence of various operational parameters on the decolorization and mineralization of Ponceau S (PS) by HO and SO4- radicals, generated by the activation of oxidants like H2O2 (HP) and (NH4)2S2O8 (APS) by three transition metal ion catalysts viz. Fe2+, Ag+ and Co2+ in the so called Fenton and Fenton-like processes. The most effective catalyst for the activation of both the oxidants is found to be Fe2+, although its effect is more for HP than APS. Further, Co2+ inhibits mineralization completely when used with HP. The ideal systems for mineralization are Fe2+/HP operating at pHs 3 and 6.6, and Fe2+/APS operating at pH 3. The most significant result of this study is that Fe2+/APS system is applicable at all pH, which is important for real scale applications. As the treated solutions have to be released into the water bodies, the eco-toxicological effect of these solutions on a model microorganism, Escherichia coli were examined based on their metabolic inhibition assay. The treated solutions were found to be more biotoxic than the pure dye solution, the magnitude being more in Fe2+/HP system than in Fe2+/APS system. Thus, metal ion assisted treatment processes are not environmentally benign.