Kinetics of the Chemical Oxidation of the Pharmaceuticals Primidone, Ketoprofen, and Diatrizoate in Ultrapure and Natural Waters

Oxidation of three pharmaceuticals (primidone, ketoprofen, and diatrizoate sodium) by means of several advanced oxidation processes including such as ozonation, UV radiation, and Fenton's reagent has been studied. The influence of operating variables was established, and first-order rate constants were determined in most of the oxidation systems. Specifically, for the reactions with ozone, the following rate constants were obtained by means of a competition kinetic model: 1.0 +/- 0.1, 0.40 +/- 0.07, and 0.05 +/- 0.01 M(-1).s(-1), for primidone, ketoprofen, and diatrizoate, respectively. The results showed that reaction with OH radicals was the major pathway for the oxidative transformation of these compounds. In the photodegradation experiments by 254 nm radiation, the quantum yields were also determined for every compound at different pH and temperatures. Additionally, the competition kinetic model, which was also used in Fenton's reagent experiments, allowed to evaluate the rate constants for the reaction with hydroxyl radicals whose values were the following: (6.7 +/- 0.2) x 10(9) M(-1).s(-1) for primidone, (8.4 +/- 0.3) x 10(9) M(-1).s(-1) for ketoprofen, and (5.4 +/- 0.3) x 10(8) M(-1).s(-1) for diatrizoate. Furthermore, the simultaneous oxidation of these selected pharmaceuticals in some natural water systems (a commercial mineral water, a groundwater, and surface water from a reservoir) was studied. The influence of the operating conditions on the removal efficiency was established. Finally, a kinetic model was proposed for the prediction of the elimination of the selected pharmaceuticals by ozone in these natural waters, with theoretical results that agreed well with the experimental ones.