Comparative study of the removal of direct red 23 by anodic oxidation, electro-Fenton, photo-anodic oxidation and photoelectro-Fenton in chloride and sulfate media

Abstract

This study aims to compare the efficiency of anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and their association with UV irradiation (photo anodic oxidation (PAO), and photo electro-Fenton (PEF) for the removal of Direct Red 23 from wastewater using a BDD/carbon felt cell in chloride and sulfate medium and in their combination. The effect of the supporting electrolyte was investigated in AO-H2O2 and EF processes. High discoloration efficiency was obtained in chloride media while a higher mineralization rate was achieved in sulfate media. The EF process reached higher total organic carbon (TOC) removal efficiency than AO-H2O2. 90% TOC removal rate was achieved by the EF against 82% by AO-H2O2 in sulfate media. The influence of using the mixt supporting electrolyte formed of 75% Na2SO4 + 25% NaCl was found to have beneficial effect on TOC removal, achieving 89% and 97% by AO-H2O2 and EF, respectively. High currents led to higher mineralization rates while low currents yielded to a higher mineralization current efficiency (MCE%) and lower energy consumption (EC). UV irradiation enhanced process efficiency. Mineralization efficiency followed the sequence: AO-H2O2 < PAO < EF < PEF. The PEF process was able to remove TOC completely at 5 mA cm−2 current density and 6 h of electrolysis with a MCE% value of 16.57% and EC value of 1.29 kWh g−1 TOC removed.