Assessment of the kinetics of oxidation of some steroids and pharmaceutical compounds in water using ozone

Emerging contaminants are present in surface and ground water, generating a potential risk for the public health of surrounding populations that consume contaminated water. However, their elimination using conventional treatment methods has not been an easy task. The aim of this research was the assessment of the kinetics of oxidation of four emerging contaminants in water two steroids: estradiol (E2) and ethynilestradiol (EE2) and two pharmaceutical drugs: naproxen (NPX) and ibuprofen (IBP) – by using an ozonation process. The stoichiometry and the second order rate constants for the four compounds were obtained. The method of competitive kinetics was established to assess the kinetics of oxidation of steroids and NPX and the absolute rate constant under pseudo-first-order conditions method for IBP. The second order rate constants for E2, EE2, NPX were in the order of 104 to 105 L/(mol s) and for IBP the value was 101 L/(mol s). An oxidation kinetic model for the steroids and pharmaceutical drugs at different doses of ozone was obtained from the rate constants, and validated with the experimental values. In addition, the half-life of the selected compounds for each experimental ozone dose was obtained, which serves to predict the behavior of oxidation of emerging contaminants, knowing the initial concentration of ozone. This research is focused toward a project for water treatment with the presence of emerging contaminants on a semi-pilot scale in continuous operation.