Enhanced decomposition of (4-chloro-2-methylphenoxy) acetic acid by combined ultrasonic and oxidative treatment

Abstract

Combined ultrasonic (US) irradiation and sodium peroxodisulfate (Na2S2O8) treatment has been investigated for promotion of both decomposition of (4-chloro-2-methylphenoxy) acetic acid (MCPA) and mineralization of organic residues. This treatment is expected to accelerate both reactions, because the US cavitation effect promotes the production of radicals, such as SO4−· and OH·, by the decomposition of Na2S2O8 and water. In this study, decomposition experiments were performed on 100 ppm MCPA aqueous solutions in a sonoreactor at reaction temperatures of 298–333 K with US irradiation alone, Na2S2O8 treatment alone, and the combination of US and Na2S2O8 treatment. It was found that the combined treatment achieved a higher MCPA decomposition rate and total organic carbon (TOC) removal ratio than either treatment alone. The decomposition ratios of both MCPA and TOC increased with reaction temperature, and especially steep increases were observed at 333 K due to a significant promotion of thermal decomposition of Na2S2O8. The production of radical species was also promoted by the combined treatment. These results suggest that the higher MCPA decomposition rate and TOC removal ratio are due to the increased formation of sulfate and hydroxyl radicals via thermal and US decomposition of Na2S2O8.