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Kinetic studies on ozone decomposition in water were performed over a range of temperatures from 10 to 40 °C and pH rangp from 2.5 to 9. The ozone decomposition rate was determined in eq 24. This expression is supported by a reaction mechanism. The second term is negligible, at pH values below 3, leading to a first-order kinetic expression. The direct ozone-water reaction and the hydroxide ion initiation step are the main causes of ozone decomposition. Experimental and calculated ozone concentrations agree within ±10% for 95% of the experiments.

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The oxidation of some chlorophenols: 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, tetrachlorocatechol (3,4,5,6-tetrachloro-2-hydroxy phenol) and 4-chloroguaiacol (4-chloro-2-methoxy phenol) has been studied via single photodecomposition produced by polychromatic UV irradiation, oxidation by hydroxyl radicals generated by Fenton's reagent (hydrogen peroxide plus ferrous ions), and degradation by hydroxyl radicals produced by combinations of UV irradiation plus hydrogen peroxide, and UV irradiation plus hydrogen peroxide and ferrous ions (photo-Fenton system). These organics have been selected as models of chlorophenolic derivative pollutants present in wastewaters and groundwaters. The degradation levels obtained in each process are reported. The quantum yields in the single photodecomposition reaction and the rate constants between the chlorophenols and the hydroxyl radicals in the reaction with Fenton's reagent are determined. Finally, the additional contributions to the photodecomposition promoted by the radical reaction in the combined UV/H 2 O 2 and photo-Fenton systems are also evaluated.

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