Control of N-nitrosodimethylamine (NDMA) formation from N,N-dimethylhydrazine compounds by ozone-based advanced oxidation processes

N-nitrosodimethylamine (NDMA) is formed during ozonation of model compounds with dimethylhydrazine groups, such as daminozide (DMZ) and 2-furaldehyde 2,2-dimethylhydrazone (2-F-DMH) at pH 7 with yields of 100 % and 87 %, respectively. In this study, ozone/hydrogen peroxide (O-3/H2O2) and ozone/peroxymonosulfate (O-3/PMS) were investigated to control NDMA formation, and O-3/PMS (50-65 %) was more effective than O-3/H2O2 (10-25 %) with a ratio of H2O2 or PMS to O-3 of 8:1. The reaction of PMS or H2O2 to decompose ozone could not compete with the ozonation of model compound because of the high second-order rate constants of the ozonation of DMZ (5 x 10(5) M-1 s(-1)) or 2-F-DMH (1.6 x 10(7) M-1 s(-1)). The R-ct value of the sulfate radical (SO4 center dot-) showed a linear relationship with NDMA formation, indicating that SO4 center dot- significantly contributed to its control. NDMA formation could be further controlled by injecting small quantities of ozone numerous times to minimize the dissolved ozone concentration. The effects of tannic acid, bromide and bicarbonate on NDMA formation were also investigated during ozonation, O-3/H2O2, and O-3/PMS processes. Bromate formation was more pronounced in the O-3/PMS process than in the O-3/H2O2 process. Therefore, in practical applications of O-3/H2O2 or O-3/PMS processes, the generation of NDMA and bromate should be detected.