Predicting Hydroxyl Radical Activity and Trace Contaminants Removal in Ozonated Water

There is a renewed interest in predicting R_CT following growing evidence that AOP is effective against many emerging contaminants. Five surface waters were investigated to evaluate the OH-radical activity using the R_CT concept, predict R_CT using traditional water quality characteristics and predict contaminants removal by ozonation and peroxone. It was shown that R_CT was dependent on water quality characteristics and could be modeled (R² = 0.92), using water characteristics and treatment conditions. Predictions of MIB oxidation closely matched the published data of Kawamura (2000 Kawamura, S. 2000. Integrated Design and Operation of Water Treatment Facilities, 2nd, New York: John Wiley & Sons, Inc.  [Google Scholar]) and bench-scale assays performed on one of the water under investigation.     

Novel real-time method using the stopped-flow for evaluating bisphenol A degradation kinetics by molecular ozone and radical mechanisms

A novel real-time method was developed to evaluate the bisphenol A degradation kinetics by molecular ozone and radical pathway using the stopped-flow technique. The second-order kinetics was determined under pseudo-first-order conditions for the molecular pathway by the absolute rate constant method and for the radical pathway by the R_ct concept involving the hydroxyl radical and ozone ratio. Bisphenol A degradation by ozone was performed and evaluated at a pH ranging from 2 to 10. At pH?4?M^?1?s^?1 and for the radical pathway at pH?>?10, the constant was 3.43?×?10⁹?M^?1?s^?1. To validate the method, ciprofloxacin degradation kinetics was determined at pH 8 by radical pathway, in 4.55?×?10⁹?M^?1?s^?1. The method permits the determination of kinetic parameters for the design of chemical reactors; avoiding the generation of undesirable reactions and by-products in the degradation of emerging compounds.     

Catalytic decomposition of ozone and para-Chlorobenzoic acid (pCBA) in the presence of nanosized ZnO

This research forwards the evaluating of the efficiency of nanosized ZnO in the application of the catalytic ozonation, determines the reaction kinetics of ozone with the nanosized ZnO, and delineates the characteristics of the decomposition of para-Chlorobenzoic acid (pCBA) and ozone in catalytic ozonation using the nanosized ZnO particles. It was found that the nanosized ZnO enhanced the degradation of ozone and the catalytic ozonation on the surface of the nanosized ZnO significantly enhanced the degradation of pCBA. In catalytic reactions the degradation of pCBA followed two-stage kinetics, initial rapid removal phase (Phase I) and a slower decomposition phase (Phase II). The total degradation rate of pCBA was well matched with the initial removal of pCBA in Phase I. The R_ct values representing the ratio of hydroxyl radicals [OH] and ozone [O₃] were found to increase with an increased concentration of the nanosized ZnO indicating the enhanced transformation of ozone into OH.