Effect And Mechanism Of Bromine Ion On The Formation Of NDMA By Ozonation Of Amino Compounds

Br^-is commonly found in groundwater,surface water,and inland water in coastal areas,and the Br^-concentration in in China’s source water is high.In recent years,researchers have found that ozone can react with precursors to directly generate N-nitrosodimethylamine（NDMA）.The presence of Br^-may promote the risk of ozone oxidizing certain amine compounds to form NDMA,preventing the wider application of ozone,leading to an increase in the health risks of nitrogen-containing disinfection by-products and a potential safety risk to drinking water,but its influencing factors and formation mechanisms are unclear.Therefore,in this study,ten typical amino compounds with different structures were selected for experiments,and the effects and conversion pathways of Br^-on the ozonation of amino compounds to NDMA under different oxidation conditions and different components in water were investigated.In this study,ten kinds of amino compounds with different structures were selected to investigate the effect of Br^-concentration on the formation of NDMA by comparing the formation of NDMA by ozonation at different Br^-concentration.It is found that low concentration of Br^-mainly affects the production of NDMA by consuming hydroxyl radicals and catalysis in solution,and high concentration of Br^-mainly affects the production of NDMA by competing with amino compounds for ozone molecules.At the same time,three kinds of water sources from different water plants were selected for research.The experimental results showed that the presence of NDMA had a significant positive correlation with ammonia nitrogen（NH₄⁺）and nitrate ions（NO₃^-）.Compared with the water without Br^-,the amount of NDMA produced by the three types of source water increased after adding Br^-.After adding0.1μM Br^-to the source water of G water supplier,the amount of NDMA in the water suddenly increased from 54.44ng/L to 73.11ng/L.The addition of low concentration Br^-to some amino compounds will promote the formation of NDMA,but with high concentration of Br^-it will show the opposite rule,inhibiting the formation of NDMA.Taking daminozide（DMNZD）as an example,the study found that when the dosage of Br^-increased from 0 to 1μM,the concentration of NDMA increased from 138 to 195.5μg/L;but when the amount of Br^-added was 100μM,the production of NDMA decreased to 80μg/L.Faintly acidic or alkaline conditions（pH=9）and other components in water（HCO₃^-,NOM,high concentration of HA）can inhibit the ozonation of DMNZD to form NDMA.SO₄^2-and low concentrations of HA can promote its formation.The addition of low concentration Br^-to some amino compounds will also promote the formation of NDMA,while the addition of high concentration Br^-will still increase the amount of NDMA.Taking 1,1-dimethylhydrazine（UDMH）as an example,the study found that when the amount of Br^-was increased from 0 to 100μM,the concentration of NDMA continued to increase from 142.5 to 327.5μg/L.And whether Br^-is contained or not,the increase of O₃ concentration will lead to the increase of NDMA production.When the ozone dosage increased from 0 to 4 mg/L,the highest molar yield of NDMA was 17.8%.When 0.1μM Br^-was present in the solution,the highest molar yield of NDMA was 20.9%.Based on the results of LC/MS/MS and GC/MS,the conversion pathways of Br^-influencing the ozonation of DMNZD and UDMH to NDMA were proposed.This achievement explores the effect of Br^-on the formation of NDMA from typical amino compounds during ozonation,providing theoretical basis and technical support for avoiding or reducing Br^-promoting the ozonation of some amino compounds to form NDMA and prospected the future research direction.