title: Kinetics and mechanisms of nitrate and ammonium formation during ozonation of dissolved organic nitrogen.
abstract: Dissolved organic nitrogen (DON) is an emerging concern in oxidative water treatment because it exerts oxidant demand and may form nitrogenous oxidation/disinfection by-products. In this study, we investigated the reactions of ozone with DON with a special emphasis on the formation of nitrate (NO3-) and ammonium (NH4+). In batch ozonation experiments, the formation of NO3-and NH4+was investigated for natural organic matter standards, surface water, and wastewater effluent samples. A good correlation was found between NO3-formation and the O3exposure (R2> 0.82) during ozonation of both model DON solutions and real water samples. To determine the main precursor of NO3-, solutions composed of tannic acid and model compounds with amine functional groups were ozonated. The NO3-yield during ozonation was significantly higher for glycine than for trimethylamine and dimethylamine. Experiments with glycine also showed that NO3-was formed via an intermediate with a second-order rate constant of 7.7 ± 0.1 M-1s-1while NH4+was formed by an electron-transfer mechanism with O3as confirmed from a hydroxyl radical (OH) yield of 24.7 ± 1.9%. The NH4+concentrations, however, were lower than the OH yield (0.03 mol NH4+/mol OH) suggesting other OH-producing reactions that compete with NH4+formation. This study concludes that NO3-formation during ozonation of DON is induced by an oxygen-transfer to nitrogen forming hydroxylamine and oxime, while NH4+formation is induced by electron-transfer reactions involving C-centered radicals and imine intermediates.
authors.affiliation: The University of Queensland (UQ), Advanced Water Management Centre, Queensland 4072, Australia; School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland.
authors.forename: Glen Andrew
authors.initials: GA
authors.lastname: de Vera
authors.affiliation: The University of Queensland (UQ), Advanced Water Management Centre, Queensland 4072, Australia; ICRA, Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona, H(2)O Building, Emili Grahit 101, 17003 Girona, Spain; ICREA, Catalan Institute for Research and Advanced Studies, 08010 Barcelona, Spain.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gernjak
authors.affiliation: University of North Carolina at Chapel Hill, Department of Environmental Sciences and Engineering, 146A Rosenau Hall, Chapel Hill, NC 27599, United States.
authors.forename: Howard
authors.initials: H
authors.lastname: Weinberg
authors.affiliation: The University of Queensland (UQ), Advanced Water Management Centre, Queensland 4072, Australia; ICRA, Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona, H(2)O Building, Emili Grahit 101, 17003 Girona, Spain.
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Farré
authors.affiliation: The University of Queensland (UQ), Advanced Water Management Centre, Queensland 4072, Australia. Electronic address: j.keller@uq.edu.au.
authors.forename: Jurg
authors.initials: J
authors.lastname: Keller
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland; Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland. Electronic address: vongunten@eawag.ch.
authors.forename: Urs
authors.initials: U
authors.lastname: von Gunten
mesh_terms: D064751:Ammonium Compounds; D007700:Kinetics; D009584:Nitrogen; D010126:Ozone; D014874:Water Pollutants, Chemical; D018508:Water Purification
chemical_list: D064751:Ammonium Compounds; D014874:Water Pollutants, Chemical; D010126:Ozone; D009584:Nitrogen
keywords: Ammonium; Dissolved organic nitrogen; Nitrate; O(3) exposure; Ozonation