title: Reinvestigation of the nitrosamine-formation mechanism during ozonation.
abstract: Previous studies have linked nitrosamine formation during ozonation to a nitrosation process in which nitrosation is catalyzed by formaldehyde, a normal byproduct of ozonation. This mechanism cannot explain the increase in N-nitrosodimethylamine (NDMA) formation with an increase of pH. This study reinvestigates the pathway of N-nitrosamine formation during ozonation. Our observations demonstrated the critical importance of some reactive inorganic nitrogenous intermediates, such as hydroxylamine and dinitrogen tetroxide (N2O4). We report two altemative pathways that possibly explain nitrosamine formation during ozonation at neutral and alkaline pH: (i) secondary amine precursors reacting with hydroxylamine to form unsymmetrical dialkylhydrazine intermediates, which are further oxidized to their relevant nitrosamines; and (ii) a nitrosation pathway in which N2O4 acts as the nitrosating reagent. The key variables of pathway (i) (including reaction time, pH, dissolved oxygen) were investigated. Since hydroxylamine is a common intermediate of dimethylamine oxidation, it is reasonable to assume that hydroxylamine is a possible inorganic precursor for NDMA formation during oxidation processes using strong oxidants. With an improved understanding of the pathway of nitrosamine formation, it should be apparent that the reactive nitrogenous intermediates play an important role in the N-nitrosamine-formation, so future studies of N-nitrosamine-formation control should be focused on the transformation of nitrogen in water treatment
authors.affiliation: State Key Laboratory of Urban Water Resources and Environment, School of Municipal & Environmental Engineering, Harbin Institute of Technology, Harbin, 150090, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.forename: Zhonglin
authors.initials: Z
authors.lastname: Chen
authors.forename: Jimin
authors.initials: J
authors.lastname: Shen
authors.forename: Zhenzhen
authors.initials: Z
authors.lastname: Xu
authors.forename: Heng
authors.initials: H
authors.lastname: Liang
authors.forename: Jiayu
authors.initials: J
authors.lastname: Tian
authors.forename: Yue
authors.initials: Y
authors.lastname: Ben
authors.forename: Xu
authors.initials: X
authors.lastname: Zhai
authors.forename: Wenxin
authors.initials: W
authors.lastname: Shi
authors.forename: Guibai
authors.initials: G
authors.lastname: Li
mesh_terms: D006801:Humans; D019811:Hydroxylamine / Q000737:chemistry; D009602:Nitrosamines / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010126:Ozone / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D009602:Nitrosamines; D014874:Water Pollutants, Chemical; D019811:Hydroxylamine; D010126:Ozone; D010100:Oxygen