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 μM 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 SO 4 •− 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 3 . Therefore, the technology could reduce NDMA formation effectively. In addition, the results of Gaussian calculation manifested that the N atom in -NH 2 group of UDMH was easily attacked not only by •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.