NDMA reduction mechanism of UDMH by O/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/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/PMS technology was effective on NDMA reduction, reaching an efficiency of 81% with 80 μM PMS. Higher NDMA reduction rates were achieved by O/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/PMS slightly improved from 66.3% to 70.6%. The presence of HA reduced NDMA formation in O/PMS system. The contribution of SO on NDMA reduction accounted for ~64%, which was higher than that of •OH (41.4%); however, its promotion role on conversing UDMH to NDMA was lower than O. Therefore, the technology could reduce NDMA formation effectively. In addition, the results of Gaussian calculation manifested that the N atom in -NH group of UDMH was easily attacked not only by •OH but also by O, 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.