Catalytic ozonation of 2,4-Dichlorophenoxyacetic acid using alumina in the presence of a radical scavenger

Abstract

Using a laboratory-scale mixed reactor, the performance of alumina in degrading 2,4-Dichlorophenoxyacetic acid with ozone in the presence of tert-butyl alcohol radical scavenger was studied. The operating variables investigated were the dose of alumina catalyst and solution pH. Results showed that using ozone and alumina leads to a significant increase in 2,4-D removal in comparison to non-catalytic ozonation and adsorption processes. The observed reaction rate constants (kobs ) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the kobs value increased from 19.3 to 26 M−1 s−1 and 67 M−1 s−1 when varying the alumina dose from 1 to 2 and 4 g L−1, respectively. As pH was increased, higher reaction rates were observed for both non-catalytic ozonation and catalytic ozonation processes. Thus, at pH 3 and using a catalyst dose of 8 g L−1, the kobs values for non-catalytic ozonation and catalytic ozonation processes were 3.4 and 58.9 M−1 s−1, respectively, whereas at pH 5 reaction rate constants of 6.5 and 128.5 M−1 s−1 were observed, respectively. Analysis of total organic carbon suggested that catalytic ozonation with alumina achieved a considerable level of mineralization of 2,4-D. Adsorption of 2,4-D on alumina was found to play an important role in the catalytic ozonation process.