NDMA reduction mechanism of UDMH by O3/PMS technology

Carcinogenic N, N-Dimethylnitrosamine (NDMA) has been reported to generate significantly during ozonation of fuel additive unsymmetrical dimethylhydrazine (UDMH), the combined ozone/Peroxy-Monosulfate (O-3/PMS) technology was tried for reducing its formation in this study. The influence of PMS dosages, ozone concentrations, pH, Br- and humic acid (HA) on NDMA formation from UDMH were investigated. In addition, the reduction mechanisms were explored by intermediates identification and Gaussian calculation. The results demonstrated that O-3/PMS technology was effective on NDMA reduction, reaching an efficiency of 81% with 80 mu M PMS. Higher NDMA reduction rates were achieved by O-3/PMS with increasing pH within the scope of research (from 5 to 9), achieving a maximum of 69.9% at pH 9. The presence of bromide ion facilitated NDMA generation during ozonation, but the reduction efficiency by O-3/PMS slightly improved from 66.3% to 70.6%. The presence of HA reduced NDMA formation in O-3/PMS system. The contribution of SO4 center dot- on NDMA reduction accounted for similar to 64%, which was higher than that of center dot OH (41.4%); however, its promotion role on conversing UDMH to NDMA was lower than O-3. Therefore, the technology could reduce NDMA formation effectively. In addition, the results of Gaussian calculation manifested that the Natom in -NH2 group of UDMH was easily attacked not only by center dot OH but also by O-3, so it is the key path that determines final NDMA formation. This study would provide reference for reducing NDMA formation during ozonation of UDMH-containing water matrixes. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this study, the O-3/PMS technology was effective in reducing the formation of the carcinogen NDMA during ozonation of UDMH. Increasing pH levels led to higher NDMA reduction rates, while the presence of humic acid helped decrease NDMA formation.