Reinvestigation of the Nitrosamine-Formation Mechanism during Ozonation

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• 作者：Lei Yang ; Zhonglin Chen ; Jimin Shen ; Zhenzhen Xu ; Heng Liang ; Jiayu Tian ; Yue Ben ; Xu Zhai ; Wenxin Shi ; Guibai Li
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：July 15, 2009
• 年：2009
• 卷：43
• 期：14
• 页码：5481-5487
• 全文大小：188K
• 年卷期：v.43,no.14(July 15, 2009)
• ISSN：1520-5851

文摘

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 alternative 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.