Kinetics of catalytic ozonation of atrazine in the presence of activated carbon

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) 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 (kD) and the ratio between OH and ozone concentrations (Rct) increased from 2.43 × 10−4 to 17.0 × 10−4 s−1 and 0.21 × 10−9 to 7.40 × 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 (koverall) was observed at pH 3 and 7, whereby four-fold and two-fold increases in koverall 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 proceeds mainly in the bulk liquid phase.

Effect of catalyst dose on ozone decomposition rate constant (a), kD, and ratio between hydroxyl radicals and ozone concentrations (b), Rct, in the presence of activated carbon. [O3]0 = 1.042 × 10−4 M, [ATZ]0 = 4.64 × 10−5 M, T = 23.5 °C.Figure optionsDownload as PowerPoint slideHighlights
► Ozonation in the presence of activated carbon enhances removal rates of atrazine in water.
► Inhibition effect of radical scavengers indicates OH radical reactions in bulk liquid phase.
► Solution pH strongly affects catalytic activity of activated carbon to initiate OH radical formation.
► Complicated trend in catalytic activity at acidic pH conditions suggests the development of different initiation mechanisms.
► In the catalysts dose range of 0–1 g L−1, reaction rate constant increases linearly with mass of catalyst.