Electro-Fenton process for the removal of Direct Red 23 using BDD anode in chloride and sulfate media

Abstract This paper aims to study the degradation and mineralization of the dye Direct Red 23 (DR23) by electro-Fenton (EF) process for the first time using BDD and DSA anode and carbon graphite (CG) cathode in NaCl and Na2SO4 media. The effect of different parameters such as the nature, concentration, and combination of the supporting electrolyte, the nature of the anode, the concentration of the catalyst and DR23 and the current density on H2O2 generation and mineralization rate was investigated. The best treatment efficiencies were achieved by BDD/CG cell. The degradation of DR23 solution was faster in NaCl medium. The mineralization was more efficient in Na2SO4, where the main oxidizing species were the hydroxyl radicals, generated both in the bulk solution (•OH) and at the anode surface (M(•OH)). The TOC removal, the energy consumption, and electrical cost per m3 were 90%, 2.41 kWh g−1 TOC, and 3.21 US $ m−3, respectively, after 6 h of electrolysis in sulfate medium while lower mineralization rate (83%) and higher energy consumption (2.86) and electrical cost per m3 (3.27 US $ m−3) were achieved in chloride medium. As the textile wastewater contain generally sulfate and chloride ions, experiences were also performed in a medium formed of Na2SO4 and NaCl. The following combination of these salts (75% Na2SO4 + 25% NaCl) as supporting electrolyte was beneficial to further increase the mineralization rate of DR23 solution, current efficiency and reduce the energy consumption. Degradation of DR23 in the presence of different scavengers (methanol, 2-propanol, and tert-butanol) asserted that the elimination of DR23 is mainly attributed to the action of •OH/M(•OH) on the target pollutant.