Degradation of Contaminants of Emerging Concern by Electrochemical Oxidation: Coupling of Ultraviolet and Ultrasound Radiations

Abstract

In this work, we study the electrochemical oxidation of methyl red, a dye present in textile industrial effluents, which is selected as the model for the degradation of Contaminants of Emerging Concern. The influence of the initial pollutant concentration (1–5 mg dm−3), applied current density (2–15 mA cm−2), and the coupling of ultraviolet or ultrasound radiation have been studied using a titanium plate as anode. The results show that electrochemical oxidation is able to efficiently remove methyl red, and the process efficiency decreases with the initial pollutant concentration. At high applied current densities, efficiency drastically decreases due to a less effective mass transfer of the pollutant on the anodic surface. On one hand, the coupling of ultrasound entails an antagonistic effect on the process efficiency, which is probably due to a massive formation of oxidant radicals followed by a fast recombination process. On the other hand, the coupling of ultraviolet radiation increases the process efficiency. Concomitantly to the oxidation processes, titanium electrode produces rising TiO2–anatase nanoparticles, boosting the mineralization process. This new finding sets up a significant improvement over conventional photocatalysis treatments using TiO2–anatase as a catalyst due to synergistic effects coming from the coupling of the electrochemical oxidation and photocatalysis process with Ti anode.