Kinetics Study of Imidacloprid Degradation by Ozonation

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Kinetics tests in ozonation of imidacloprid in water were performed. The kinetics for reactions between imidacloprid with molecular ozone and hydroxyl radicals were investigated. An indirect competition method was used to determine the second-orderrate constant for hydroxyl radicaloxidationof imidacloprid (k·OH-Imid) in the presence of p-chlorobenzoic acid(pCBA) as the reference compound. The results demonstrate that the ozonation is an effective method to remove imidacloprid from water. The pseudo first-order rate constants of imidacloprid degradation increases from 0.079 min-1 to 0.326 min-1 with the increase of pH from 6.0 to 8.7 at an average ozone dose of 1.15 mg/L. When the alkalinity (CaCO3) increases from 0 mg/L to 250 mg/L at pH 7.0 and an average ozone dose of 1.41 mg/L, the pseudo first order rate constant decreases from 0.121 to 0.034 min-1. The second-order rate constant ((10.92±0.12) (mol/L)-1∙s-1 for the reaction of imidacloprid and molecular ozone is determined at pH 2.0 and in the presence of 50 mmol/L tert-butyl alcohol. The rate constant is 2.92×109 (mol/L)-1∙s-1 at pH 7.0. The rate constants are estimated to range at 2.65×109-3.79×109 (mol/L)-1∙s-1 at pH 6.0-8.6.

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