Determination of the Reaction Rate Constants and Decomposition Mechanisms of Ozone with Two Model Emerging Contaminants: DEET and Nortriptyline

Two representative substances of the so-called emerging compounds group (ECs), N,N-diethyl-m-toluamide (DEET) and nortriptyline hydrochloride, were selected to be subjected to ozonation processes, which constitute promising technologies for the removal of hazardous pollutants. The kinetic study provided ozonation rate constants, with an average value of 0.123 +/- 0.003 L.mol(-1).s(-1) for DEET, which remained almost unaffected with the pH; while values varying from 2.40 x 10(3) to 472 x 10(3) L.mol(-1).s(-1) for nortriptyline were deduced in the pH range 2-11. Because of the ionic nature of nortriptyline, the specific rate constants of the protonated and neutral species were determined, the values obtained being 2.1 x 10(3) and 4.3 x 10(5) L.mol(-1).s(-1), respectively. By means of liquid chromatography time-of-flight mass spectrometry analysis, the main byproducts formed in the ozonation reactions were identified (14 for DEET and 27 for nortriptyline), and the evolution of their concentrations with reaction time were established. According to these compounds and their concentration profiles, the reaction mechanisms for the ozonation of both emerging contaminants were proposed and discussed. A decrease in the toxicity was also observed during ozonation of nortriptyline.