Laws and Mechanisms of Inorganic Ammonia Mediates Organic NDMA Formation During Ozonation of Amines

Would the widespread ammonia nitrogen (NH4+-N) in surface water provide nitrogen sources for carcinogenic N-nitrosodimethylamine (NDMA) formation during ozonation? What about its influence laws and mechanisms? In this paper, fifteen kinds of typical amines were selected to investigate the effects of ammonia on NDMA generation during ozonation, then the anti-yellowing agent 4,4'-Hexamethylenebis (1,1-dimethylsemicarbazide) (HDMS) was chosen to further probe its influencing factors (oxidation conditions and co-existed components) as well as mechanisms. The results demonstrated that the impacts of ammonia on NDMA formation varied due to distinct structures of precursors. The inorganic ammonia promoted first then inhibited NDMA formation from HDMS with increasing ammonia dosages. No matter with or without ammonia, the increase of O-3 concentration (0-4 mg/L) promoted NDMA formation, but the increment of the former (from 0.39 to 96.61 mu g/L) was much larger than those of the latter (from 0 to 32.19 mu g/L); and the maximum value was achieved at pH 7. Co-existed components bromine (Br), carbonate (CO32-), sulphate (SO42-) and humic acid (HA) all slightly reduced NDMA production from HDMS during ozonation without ammonia, while nitrite (NO2-) and nitrate (NO3-) significantly increased its production. When ammonia was present, the co-existed components inhibited NDMA production invariably. According to the results of LC-MS/MS, GC-MS, Q-TOF and 15 N isotope labeling experiments, the influencing mechanisms of ammonia on NDMA formation during ozonation of HDMS were proposed. The results of this study would provide reference for NDMA risks control in water matrixes with combined pollution of ammonia and amines.