Effect of the electrolyte on the electrolysis and photoelectrolysis of synthetic methyl paraben polluted wastewater

Abstract

Abstract In this work, the electrochemical oxidation of methyl paraben (MeP) with diamond electrodes is studied. Results point out that this preservative can be easily removed from wastewater, either in sulfate or chloride media. Pollutant removal is faster in chloride media due to the chlorination of the molecule. However, mineralization is faster in sulfate media. Current density does not have a clear influence on the efficiency, explained by a mediated oxidation control of the process. Irradiation by UV light produces a synergistic effect on the process, which is greater in sulfate than in chloride media, a behavior that could be initially understood in terms of the formation of sulfate and chloride radicals. However, chemical tests showed that persulfate is not active for the oxidation of MeP neither in dark conditions nor under UV irradiation and that hypochlorite is active in the chlorination of the MeP molecule but not in the mineralization. Consequently, these results can be better explained considering the oxidizing effect of ozone and hydrogen peroxide, which are produced during the electrolysis on the surface of diamond, and that within the reaction conditions undertaken, are unstable and decompose to hydroxyl radicals. Regarding electrolysis in chloride media, although chlorates or perchlorates are produced, UV light significantly delays the appearance of both species.