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 (O3/H2O2) and ozone/peroxymonosulfate (O3/PMS) were investigated to control NDMA formation, and O3/PMS (50-65 %) was more effective than O3/H2O2 (10-25 %) with a ratio of H2O2 or PMS to O3 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 ×105 M-1 s-1) or 2-F-DMH (1.6 ×107 M-1 s-1). The Rct value of the sulfate radical (SO4•-) showed a linear relationship with NDMA formation, indicating that SO4•- 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, O3/H2O2, and O3/PMS processes. Bromate formation was more pronounced in the O3/PMS process than in the O3/H2O2 process. Therefore, in practical applications of O3/H2O2 or O3/PMS processes, the generation of NDMA and bromate should be detected.