Formation And Influencing Factors Of NDMA In Drinking Water

N-nitrosodimethylamine(NDMA),a extremely potent carcinogen,has been discovered after chloramination during drinking water as a disinfection by-product(DBP).Polyamine and polyDADMAC that water treatment polymers used as coagulants and flocculants are NDMA precursor.Considering the toxicity of NDMA and the widespread use of the flocculants,the effect of water treatment processes on NDMA formation from amine-based water treatment polymers(polyamine and polyDADMAC)was investigated.The study is meaningful for reducing the risk of drinking water.The analytical procedure to detect NDMA in water consists of SPE and analysis by GC-MS.The analytical procedure to detect low-level NDMA in water consists of LLE and analysis by GC-FID.The effect of Cl/N ratio,chlorine and ammonia addition sequence on NDMA formation were investigated.The results showed that NDMA formation from amine-based water treatment polymers decreased significantly after the breakpoint of chlorination.The highest NDMA formation was observed when ammonium chloride was added first followed by free chlorine.When free chlorine was added first followed by ammonium chloride,NDMA formation from the polyamine and polyDADMAC decreased as the time interval between free chlorine and ammonium chloride additions was increased.The NDMA formation potential(NDMAFP)followed the trend polyamine > polyDADMAC.Dichloramine and DMA formation were the critical factor affecting NDMA formation.The effect of pre-chlorination prior to chloramination on NDMA formation from polyamine and polyDADMAC was investigated.Pre-chlorination increased the NDMAFP of both polyamine and polyDADMAC,and NDMA formation potential of polyamine increased significantly.During pre-chlorination,pH was an important factor in NDMA formation from polyamine.At near-neutral pH,the yield of NDMA from polyamine was higher.At low or high pH,the yield of NDMA from polyamine was lower.The chlorinated UDMH mechanism was responsible for NDMA formation.The effect of pre-oxidation with potassium permanganate prior to chloramination on NDMA formation from polyamine and polyDADMAC was investigated.Pre-oxidation with potassium permanganate increased NDMA formation potential bothpolyamine and polyDADMAC.During pre-oxidation with potassium permanganate,pH was an important factor on NDMA formation from polyamine and polyDADMAC,the NDMA formation potential of polyamine and polyDADMAC were increased with increasing pre-oxidation pH.The radical mechanism were responsible for NDMA formation from polyamine.The chlorinated UDMH mechanism were responsible for NDMA formation from polyDADMAC.