The N-Nitrosodimethylamine Formation As A Disinfection By-Product During The Enhanced Coagulation Treatment Of Micro-polluted Waters

N-Nitrosodimethylamine (NDMA) is an emerging disinfection byproduct (DBP) that has been identified as a probable human carcinogen since its occurrence in drinking water supplies. The ammonia nitrogen concentration is higher in China than that in other countries, which can generate chloramines when react with chlorine. NDMA can be formed by the reaction of chloramines and NDMA precursors (dimethylamine, small molecular containing dimethylamine groups, high-molecular polymers containing dimethylamine groups).When poly(dimethyldiallylammonium chloride) (PDMDAAC) was used as the coagulant, ammonia nitrogen, chlorine and high polymers containing dimethylamine groups constitude the formation conditions of NDMA, which will pose a huge threat to human health.Methods were developed for the analysis of reactants firstly. A HPLC-Pre-Column derivatization method was established for the determination of inorganic monochloramine (NH2Cl) in water samples because of the interference of organic nitrogen compounds. A fine linear relationship of NH2Cl could be obtained within concentration ranges from 0.10mg/L to 10.00mg/L, whose linear correlation coefficient (R2) was 0.999. The method detection limit (MDL) of NH2Cl in water was 0.013mg/L and relative standard deviations (RSDs) were 2.5%-3.4%. The recoveries of 0.26mg/L water sample and real water sample were 93.5%-113.4% and 92.6%-106.0%, respectively. The HPLC method of NDMA detection was also developped, followed by solid phase extraction using cocoanuts as filler.The influences of organic nitrogen compounds on chloramines formation were researched. Three organic nitrogen compounds (urea, glycine and phenylalanine) were selected in this experiment. Almost none inorganic chloramines formed in the reaction of organic nitrogen compounds and chlorine. The varieties and concentractions of organic nitrogen compounds would not change the peak number of chloramines, but the Cl:N ratio would increase. The chloramines concentration at fixed Cl:N ratio decreased as the increasing concentration of organic nitrogen compounds.As the basic precursor of NDMA and the basic group of PDMDAAC, dimethylamine (DMA) was used in this experiment. Reaction conditions such as reaction time, temperature, pH, concentraction were investigated. The NDMA formation was closely depended on the pH value and the C1:N ratio. NDMA formation was maximized at pH 7 and Cl:N 7 when chloramines were monochloramine and dichloramine. Organic nitrogen compounds would inhibit the reaction, which was the reason of the decreasion of NDMA. The reaction of PDMDAAC and chloramines was researched in the end. DMA was released from the degradation of PDMDAAC because of the breakout of teriary amine chain. The released DMA reacted with monochloramine, which lead to NDMA formation.