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 (k_obs ) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the k_obs 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 k_obs 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.

Keywords:

• Ozone
• catalytic ozonation
• alumina
• 2
• 4-D
• water treatment

Acknowledgments

The authors are grateful for the financial support provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), the University of Saskatchewan, and the Communities of Tomorrow.