title: Competitive kinetics versus stopped flow method for determining the degradation rate constants of steroids by ozonation.
abstract: Steroids are classified as endocrine disrupting chemicals; they are persistent with low biodegradability and are hardly degraded by conventional methods. Ozonation process has been effective for steroids degradation and the determination of the kinetics is a fundamental aspect for the design and operation of the reactor. This study assessed two methods: competitive kinetics and stopped flow, for determining the degradation kinetics of two steroids, estradiol (E2) and ethinylestradiol (EE2) in spiked water. Experiments were performed at pH 6, 21 °C, and using tertbutyl alcohol as scavenger of hydroxyl radicals; competitive kinetics method used sodium phenolate as reference compound. For the stopped flow, the experiments were performed in a BioLogic SFM-3000/S equipment. For both methods, the second order rate constants were in the order of 10(6) and 10(5) M(-1) s(-1) for E2 and EE2 respectively. The competitive kinetics can be applied with assurance and reliability but needing an additional analysis method to measure the residual concentrations. Stopped flow method allows the evaluation of the degradation kinetics in milliseconds and avoids the use of additional analytical methodologies; this method allows determining the reaction times on line. The methods are applicable for degradation of other emerging contaminants or other steroids and could be applied in water treatment at industrial level. Finally, it is important to consider the resources available to implement the most appropriate method, either competitive kinetics or the stopped-flow method.
authors.affiliation: Department of Environmental Technology, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A. C., Av. Normalistas 800, Colinas de la Normal, 44270 Guadalajara, Jalisco Mexico.
authors.forename: Alberto
authors.initials: A
authors.lastname: López-López
authors.affiliation: Department of Environmental Technology, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A. C., Av. Normalistas 800, Colinas de la Normal, 44270 Guadalajara, Jalisco Mexico.
authors.forename: Valentín
authors.initials: V
authors.lastname: Flores-Payán
authors.affiliation: Department of Environmental Technology, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A. C., Av. Normalistas 800, Colinas de la Normal, 44270 Guadalajara, Jalisco Mexico.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: León-Becerril
authors.affiliation: Department of Environmental Technology, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A. C., Av. Normalistas 800, Colinas de la Normal, 44270 Guadalajara, Jalisco Mexico.
authors.forename: Leonel
authors.initials: L
authors.lastname: Hernández-Mena
authors.affiliation: Department of Environmental Technology, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A. C., Av. Normalistas 800, Colinas de la Normal, 44270 Guadalajara, Jalisco Mexico.
authors.forename: Ramiro
authors.initials: R
authors.lastname: Vallejo-Rodríguez
keywords: Competitive kinetics; Second order constant; Steroids; Stopped flow