Kinetics and mechanisms of nitrate and ammonium formation during ozonation of dissolved organic nitrogen.

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 (NO) and ammonium (NH). In batch ozonation experiments, the formation of NO and NH was investigated for natural organic matter standards, surface water, and wastewater effluent samples. A good correlation was found between NO formation and the O exposure (R > 0.82) during ozonation of both model DON solutions and real water samples. To determine the main precursor of NO, solutions composed of tannic acid and model compounds with amine functional groups were ozonated. The NO yield during ozonation was significantly higher for glycine than for trimethylamine and dimethylamine. Experiments with glycine also showed that NO was formed via an intermediate with a second-order rate constant of 7.7 ± 0.1 Ms while NH was formed by an electron-transfer mechanism with O as confirmed from a hydroxyl radical (OH) yield of 24.7 ± 1.9%. The NH concentrations, however, were lower than the OH yield (0.03 mol NH/mol OH) suggesting other OH-producing reactions that compete with NH formation. This study concludes that NO formation during ozonation of DON is induced by an oxygen-transfer to nitrogen forming hydroxylamine and oxime, while NH formation is induced by electron-transfer reactions involving C-centered radicals and imine intermediates.