| N-nitrosodimethylamine（NDMA）,a disinfecting by-product with a high life cancer risk,was found to generated in ozonated drinking water containing amine compounds.Pre-ozonation can meet the requirements of removing organic matter and disinfection,and it’s been widely used worldwide.Formation of NDMA imposes restrictions on the use of ozone and has threatened the safety of drinking water.In this paper,ozone/persulfate oxidation technology was used to study the effect on the NDMA formation from typical NDMA precursors and natural organic matter,and to explore its mechanism.Unsymmetrical dimethylhydrazine（UDMH）was selected as the representative compound to investigated the cause of NDMA reduction during O3/PMS system.It was found that the system can achieve 66%reduction in NDMA when pH=7,O3=2.0mg/L,PMS=40μM;The result of t BA capture experiment showed that a large amount of·OH was generated in the system and contributes greatly to the reduction of NDMA.The molar ratio of ozone to persulfate affects the efficiency of the system.Alkaline conditions and the presence of bromide ions can promote the reduction efficiency.The existence of HA and NOM reduced the efficiency of system reduction due to competition.1,1,1’,1’-Tetramethyl-4,4’-（methylenedi-p-phenylene）disemicarbazid（TMDS）was selected as the representative compound to study the mechanism of NDMA formation from TMDS during O3/PMS oxidation.The study found that when the amount of persulfate was increased from 0 to 100μM,the concentration of NDMA continued to increase from 1.32 to 3.04μg/L.Moreover,the increase of O3concentration will lead to the increase of NDMA production whether O3 alone or O3/PMS oxidation.When the ozone dosage increased from 0 to 4 mg/L,the highest molar yield of NDMA was 1.02%.Faintly acidic or alkaline conditions（pH=9）can inhibit NDMA formation from TMDS during oxidation.Low concentrations of HA and bromide ions can promote its formation,however inhibition was observed at high concentration.Three actual water were selected as the research objects to investigate the effect of O3/PMS oxidation on the NDMA generation potential of different NOMs.O3/PMS pre-oxidation can reduce the generation potential of NDMA in source water to a certain extent,such as 33.2%and 41.6%reduction on NDMA FP-Cl2 and FP-NH2Cl in reservoir water,17.2%and 8.4%reduction in reuse water,and NDMAFP in river water.NDMAFP appears to promote the formation in river water.Based on the results of frontier electron densities and NPA charges on UDMH and TMDS,the conversion pathways of NDMA formation from UDMH and TMDS were proposed.This achievement explores the effect of O3/PMS oxidation on the conversion of typical amine compounds to NDMA,which provides a theoretical basis for further regulation of the generation of NDMA.NOM experiments provide theoretical basis and technical support for application.By comprehensively considering the influence of precursor structure and water quality parameters,establishing the structure-effect relationship of the system,and then selecting appropriate pre-oxidation conditions and subsequent disinfection methods to reduce or control NDMA generation. |
