NDMA Foration And Mechanism Study Of Ozone Promoting Chlorine/Chloramine Disinfection Of Typical Amino Compounds

NDMA is a highly carcinogenic,teratogenic,and mutagenic new disinfection by-product,therefore it has received widespread attention.Recently years,water pollution has intensified and water quality standards have been improved.Pre-ozonation can meet the requirements of removing organic matter and disinfection,and it’s been widely used worldwide.But in recent years,it has been found to promote NDMA formation during subsequent disinfection.This imposes restrictions on the use of ozone and has threatened the safety of drinking water.In this paper,10kinds of NDMA precursors with structural commonality were selected to study the effect of pre-ozonation on their NDMA formation in subsequent chlorine/chloramine disinfection processes,and to explore its mechanism.The formation of NDMA from 10 precursors by ozone,ozone-chlorine and ozone-chloramine were investigated.When the DMA group of the precursor is attached to the amide group,the reaction with ozone produces the most NDMA.For example,the NDMA formation during ozonation of DMNZD has a maximum generation of 3.63 mg/L,which is 100 times more than that of NDMA formation by chloramine disinfection.When there are two or more N atoms in the precursors,and the-NH₂ group is easily produced,the reaction with chlorine produces the largest NDMA activity.For example,the NDMA formation of DMPD during chlorination is twice as much as during ozonation,and it’s about 3 times as much as chloramination.When the linking group of DMA functional group of precursors is an electron withdrawing group,pre-ozonation promotes subsequent disinfection of chlorine or chloramine.For example,DMNZD formedd 164μg/L NDMA at 4.0 mg/L ozone dosage with post-chlorination,which is more than 2,700 times more than without pre-ozonation.When the DMA linking group is an electron donating group,pre-ozonation reduces subsequent chlorine/chloramine formation.For example,compared with direct chlorination,the NDMA formation of Metformin treated by pre-ozonation reduced over 80%.With the increase of ozone dosage,the NDMA formation of DMAPA during chlorine disinfection first decreases and then increases.During subsequent chloramine disinfection,NDMA formation first increases and then decreases.The combination of low concentration pre-ozonation and chlorine disinfection has the lowest formation of NDMA,and the NDMA removal efficiency is 34.5%comparing to the chlorination alone.The tBA promotes NDMA formation of DMAPA at low concentrations of ozone and inhibite NDMA formation at high ozone dosage.At pH7.0,the NDMA formation at 2.0 ozone dosage during chlorination is the lowest of76800 ng/L.When bromide is added,the NDMA formation of DMPhA of ozone and ozone+subsequent chlorination are significantly inhibited,but the NDMA formation during ozone+chloramine disinfection is significantly promoted.With the increase of ozone dosage,the NDMA formation of DMPhA during chlorination increased first and then decreased,and NDMA formation decreased first and then increased during chloramination.The tBA promotes the NDMA formation during post-chlorination and post-chloraminatio,especially during chloriation,the NDMA concentration increased from 64 ng/L to 630 ng/L.At pH 5.0,the NDMA formation is the lowest of 76.8 ng/L.When bromide is added,the NDMA formation of of DMPhA during ozonation and pre-ozonation with subsequent chlorine disinfection are significantly inhibited to form NDMA,but it is significantly promoted during post-chloramin disinfection.NOM in natural waters reduces the NDMA production of DMPhA during ozonation and ozone+chlorine/chloramine disinfection.Considering the structure of the precursor and the water quality parameters,appropriate pre-oxidation with subsequent disinfection process can reduce or control the NDMA formation,which can provide theoretical basis and technical support for the wider application of pre-ozonation.