Characteristics And Kinetics Study Of Chloramines And NDMA Formation Under The Condition Of Chlorination And Congulation For The Raw Water

N-Nitrosodimethylamine (NDMA) is a probable human carcinogen that has been indentified as an emerging disinfection byproduct. The ammonia-N, chloride (chloramines) and PDMDAAC all exist under the condition of chlorination and enhanced coagulation for the slightly-polluted raw water. However, the current research in this area is lack of reference for NDMA formation and related precursors. Therefore, the kinetics and characteristics of chloramines (oxidant) and NDMA formation will be studied.The characteristics of chloramines formation from the reactions of chlorine with ammonia, urea, glycine, phenylalanine, glutamic acid, asparagine and histidine were firstly studied under the condition of chlorination treatment for slightly-polluted raw water. The results show that ether ammonia, urea or amino acid could generate chloramines through the reaction with chlorine in normal temperature and neutral water, and the better conditions of chloramines formation are that of 5:1 of Cl2:N (mass ratio) for NH2Cl, urea, glycine and asparagine, but 8:1 for NHCl2, phenylalanine, glutamic acid, and histidine,30min of contact time and not more than 25℃ of temperature. The generation of chloramines will reduce when the Cl2:N ratio is greater or less than 5:1 or 8:1. The temperature rise is unfavorable for the formation of urea-chloramine and amino acid-chloramine, and it makes no difference for the formation of inorganic chloramine. pH> 5 and pH< 4, respectively, are favorable for amino acid and urea chloramines generation, chlorine and ammonia produce mainly NH2CI in pH> 5. The influence of Cl2:N ratio on the generation of inorganic chloramines is agreement with the breakpoint-chlorination reaction rule. The kinetics and its parameters of chloramines formation were also explored using initial concentration method. The rate equation of chloramines formation is agreement with v=kC1αC1β(R2> 0.99). The reaction order is close to 2nd order in overall, and the rate constants are ranked in size as glycine-chloramine> NH2CI > NHCl2> urea-chloramines.Then, the characteristics of NDMA formation from the reactions of monochloramine with DMA by high performance liquid detection method were studied:The normal temperature, alkaline conditions and long-time contact are favorable for NDMA formation; NDMA formation will increase with monochloramine’s increase, and increase with DMA when DMA/NH2Cl (molar ratio) is nearly less than 1:1, and reduce with the DMA/NH2Cl greater than 1:1. The degradation of DMA and monochloramine conforms to the first order reaction, and the reaction order is close to 1, and the rate constants increase with pH.Finally, the characteristics of NDMA formation of PAC/PDMDAAC, PDMDAAC and DMDAAC was studied. The result showes that PDMDAAC, DMDAAC and PAC/PDMDAAC can generate NDMA when reacting with monochloramine, and the potential ability is:PDMDAAC> PAC/PDMDAAC> DMDAAC. And the NDMA formation increase with coagulants’increase; and increase firstly then reduce with monochloramine’s increase; long-time contect and higher temperature are favorable for NDMA formation; and NDMA formation increase with pH when pH is 4 to 8, and reduce in pH 9.