N-nitrosodimethylamine (NDMA) formation during ozonation of N,N-dimethylhydrazine compounds: Reaction kinetics, mechanisms, and implications for NDMA formation control
| Autor: | Jaedon Shin, Woongbae Lee, So-Young Na, Yunho Lee, Sungeun Lim |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Reaction mechanism
Environmental Engineering 0208 environmental biotechnology 02 engineering and technology 010501 environmental sciences Photochemistry 01 natural sciences Heterolysis Dimethylnitrosamine Unsymmetrical dimethylhydrazine Adduct Chemical kinetics chemistry.chemical_compound Ozone N-Nitrosodimethylamine Waste Management and Disposal 0105 earth and related environmental sciences Water Science and Technology Civil and Structural Engineering Dimethylhydrazines Ecological Modeling Hydrogen Peroxide Pollution 020801 environmental engineering Homolysis Kinetics chemistry Hydroxyl radical |
| Zdroj: | Water Research. 105:119-128 |
| ISSN: | 0043-1354 |
| DOI: | 10.1016/j.watres.2016.08.054 |
| Popis: | Compounds with N,N-dimethylhydrazine moieties ((CH3)2N-N-) form N-nitrosodimethylamine (NDMA) during ozonation, but the relevant reaction chemistry is hitherto poorly understood. This study investigated the reaction kinetics and mechanisms of NDMA formation during ozonation of unsymmetrical dimethylhydrazine (UDMH) and daminozide (DMZ) as structural model N,N-dimethylhydrazine compounds. The reaction of ozone with these NDMA precursor compounds was fast, and kO3 at pH 7 was 2 × 106 M−1 s−1 for UDMH and 5 × 105 M−1 s−1 for DMZ. Molar NDMA yields (i.e., Δ[NDMA]/Δ[precursor] × 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O3]0/[precursor]0) of ≥4 in the presence of tert-butanol as hydroxyl radical ( OH) scavenger. The molar NDMA yields decreased significantly in the absence of tert-butanol, indicating OH formation and its subsequent reaction with the parent precursors forming negligible NDMA. The k OH at pH 7 was 4.9 × 109 M−1 s−1 and 3.4 × 109 M−1 s−1 for UDMH and DMZ, respectively. Reaction mechanisms are proposed in which an ozone adduct is formed at the nitrogen next to N,N-dimethylamine which decomposes via homolytic and heterolytic cleavages of the –N+-O-O-O− bond, forming NDMA as a final product. The heterolytic cleavage pathway explains the significant OH formation via radical intermediates. Overall, significant NDMA formation was found to be unavoidable during ozonation or even O3/H2O2 treatment of waters containing N,N-dimethylhydrazine compounds due to their rapid reaction with ozone forming NDMA with high yield. Thus, source control or pre-treatment of N,N-dimethylhydrazine precursors and post-treatment of NDMA are proposed as the mitigation options. |
| Databáze: | OpenAIRE |
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