Performance of a commercial activated carbon in removing atrazine with ozone in a laboratory-scale mixed reactor was studied. The operating variables were the presence of radical scavenger, solution pH, and dose of activated carbon catalyst. Results show that activated carbon significantly enhances the degradation rate of atrazine through increasing production rate of hydroxyl radicals ((OH)-O-center dot) resulting from the ozone decomposition initiated on the carbon surface. At pH level of 3, using 1 g L-1 activated carbon; pseudo first-order ozone decomposition rate constant k(D) and the ratio between (OH)-O-center dot and ozone concentrations (R-ct) increased from 2.43 x 10(-4) to 17.0 x 10(-4) s(-1) and 0.21 x 10(-9) to 7.40 x 10(-9), respectively. The overall reaction rate was enhanced by the presence of activated carbon at pH 3, 5, and 7; however, the most significant improvement in the overall rate constants (k(overall)) was observed at pH 3 and 7, whereby four-fold and two-fold increases in k(overall) values were observed. The notable decrease of atrazine removal rate observed in the presence of radical scavenger tert-butyl alcohol indicates that the reaction between atrazine and both molecular ozone and (OH)-O-center dot proceeds mainly in the bulk liquid phase. (C) 2011 Elsevier B.V. All rights reserved.