Synergistic enhancement of oxidative degradation of atrazine using combined electrolysis and ozonation

Abstract

In the current study concurrent electrolysis and ozonation was compared with the processes applied separately to degrade the herbicide atrazine in aqueous solution at pH 2, 7, and 12. Ozone containing gas was injected at a rate of 0.3 L/min into an electrolysis reactor with a boron-doped diamond anode and stainless steel cathode operating with an anodic current density of 10 mA/cm2. When electrolysis and ozonation were applied together, the rate constant of atrazine degradation could not be explained simply from considering the processes when applied separately. In particular, at pH 7, the measured first-order rate constant was 0.3441 min−1, a rate 4.78 times as large as the estimated additive rate (0.072 min−1) from electrolysis and ozonation separately in the same conditions. Across the pH range, the rate constant increased from 0.0516 min−1 at pH 2 to 0.3441 min−1 at pH 7 and 0.3065 min−1 at pH 12. Use of tert-butanol as a radical scavenger elucidated that HO contributed to a majority of the reaction at pH 7 and 12. The increasing impact of HO was due to ozone decomposition into HO through reaction with hydroxide (OH−) in both the bulk solution and at the cathode. Through LC-QTOF-MS analysis, acetamide and imine transformation of atrazine’s alkyl groups were observed at pH 7 and initial dechlorination by HO to form hydroxyatrazine was observed at pH 12.