Research On N-nitrosamines Formation During A Dissolved Ozone Flotation

N-nitrosamines are common disinfection by-products in the water.Due ot the high careinogenci and teratogenicity,N-nitrosamine have been attracted much attention.This paper focuses on three nitrosamines formation characteristics(NDMA,NDEA,NPIP)during a dissolved ozone flotation.Based on the determination of conventional indicators,TOC,excitation-emission matrix(EEM)and molecular weight distribution(MWD),the effect of different coagulant dosage and ozone concentration on the formation of three nitrosamines were investigated.By comparing dual-step ozone induced flotation(DOIF)treatment effect in coagulant dosage(80mg/L,120mg/L and 160mg/L),the removal efficiency of UV254,chroma,turbidity and NH3-N were 45%,54%,58% and 36% respectively,and more than 87% of total Escherichia coli could be removed.With the increasing of PAC dosage,the concentration of three types of nitrosamines were significantly increased,and,however,the growth rate of those were decreased,this was because the coagulation effect the nitrosamines precursor substances content in the water.With the increasing of ozone concentration,the promotion of nitrosamines precursor substance was oxidized to generate nitrosamines,the concentration and growth rate of nitrosamines also increased.Through the analysis of the TOC and EEM,the humic acid substance in the process has been effectively removed.However,it had little effect on TOC removal,which indicatd that the amount of total organic matter in water changed not obviously.The analysis of the MWD proved that the ozone could oxidized the large molecular organics into organics with small molecular,but for the amount of total organic matter in water did not change significantly.This paper also studied HPLC detection methods for three kinds of nitrosamines.Through the comparison experiment,a coconut Charcoal column was selected as pre-treatment SPE column,and CH3 OH water solution(10:90,v/v)were used as mobile phases.The linear correlation coefficient of NDMA NDEA NPIP were 0.9997,0.999 and 0.9999.The method recoveries were in the range of 77.23%~81.8%.