Comparative mineralization of textile dye indigo by photo-Fenton process and anodic oxidation using boron-doped diamond anode

In the present study, we applied two advanced oxidation processes (AOPs); photo-Fenton and anodic oxidation (using a boron doped diamond (BDD) anode) processes, to oxidative degradation and mineralization of the textile dye Indigo in sodium dithionite aqueous media. The effect of key parameters, such as H2O2 dosage for photo-Fenton process and initial pH for anodic oxidation, on the degradation and mineralization kinetics of dye Indigo was investigated. The highest mineralization rates were observed at pH 3.0 for anodic oxidation process, and for a ratio R:[H2O2]/[Fe2+] = 40 for photo-Fenton process. Under optimal operating conditions a complete mineralization of Indigo dye was achieved after 7 h treatment by anodic oxidation whereas only 63% of TOC removal was obtained after 10 h treatment by photo-Fenton process. The carboxylic acids (glyoxylic, malonic, oxalic, acetic and formic) formed as oxidation by-products were identified and their evolution was followed by ion-exclusion chromatography. The evolution of NO3- and NH4+ ions released to the solution during the treatment was followed by ion chromatography. These results show that anodic oxidation using a BDD anode is an efficient environmentally friendly technology for the remediation of wastewaters containing textile dye Indigo.