Influencing factors and kinetic studies of imidacloprid degradation by ozonation

Batch kinetic tests in ozonation of imidacloprid from water were performed in this study. The pseudo-first-order rate constant of imidacloprid degradation was increased from 0.079 to 0.326 min(-1) with the increasing pH from 6.02 to 8.64 at an average ozone dose of 1.149 mg L-1. When the alkalinity was increased from 0 to 250 mg L-1 NaHCO3, the pseudo-first-order rate constants decreased from 0.121 to 0.034 min(-1). These results suggested that the predominant oxidant gradually switched from ozone to hydroxyl radicals () with the increase in solution pH. The secondary rate constant (10.92 +/- 0.12 M(-1)s(-1)) for the reaction of imidacloprid and molecular ozone was determined at pH 2.0 and in the presence of 50 mM ter-butyl alcohol (p-chlorobenzoic acid, pCBA), respectively. An indirect competition method was used to determine the secondary rate constant for oxidation of imidacloprid in the presence of pCBA as the reference compound. The rate constants were estimated to range 2.65-3.79 M(-1)s(-1) at pH 6.02-8.64. Results obtained from this study demonstrate that ozonation appears to be an effective method to remove imidacloprid from water.