Research On Formation And Influencing Factors Of N-Nitrosodimethylamine(NDMA) During The Dringking Water Treatment

N-nitrosodimethylamine (NDMA), a typical nitrosoamine and extremely potent carcinogen, has been discovered existing in water after chlorination or chloramination during drinking water or wastewater treatment as a new type disinfection by-product (DBP). The formation of NDMA has caused significant concern among drinking water and wastewater recycling utilities.In our country, the research on NDMA is in starting stage. The formation mechanism of NDMA was systematically studied on the basis of small scale test. An optimized process of disinfection was proposed. The method of NDMA controlling and decreasing in water was discussed.According to exist experimental condition, the synthetic method of NDMA, detection methods of NDMA and NDMA precursor, dimethylamine(DMA), were established. NDMA and DMA were detected by HPLC and spectrophotometer, respectively. Sodium sulfite was chosen as the terminator to quench the disinfection reaction.The effects of the following influencing factors on NDMA formation during disinfection were investigted: species of disinfectant, mode of disinfection, temperature, reaction time and so on. The experiment results showed that all the factors affect the formation of NDMA in some way. According to the results of orthogonal experiment, the factors can be arranged as the following sequence (effects from big to small): pH value, concentration of NH3-N, dosage of monochloramine (NH2Cl), dosage of HOCl, reaction time, concentration of bromide, concentration of nitrate, concentration of dimethylamine(DMA) and temperature of water.NDMA formation was closely dependent on the pH value, the highest NDMA formation appeared at pH 7, less NDMA was formed at pH 9, trace NDMA formed at both pH 4 and pH 12. The presence of NH3-N will lead NDMA formation through UDMH or Cl-UDMH pathway by the formation of chloramines. During the chlorination of water without NH3-N, no obvious relationship showed between the dosage of chlorine and the yield of NDMA, and all the yields of NDMA formation were under 5μg/L. Excellent linear correlations were observed between the dosage of NH2Cl and NDMA formation during chloramination. More NDMA could form by dichloramine(NHCl2) than NH2Cl. Control of the concentration of NH3-N, dosage of NH2Cl or HOCl, and the reaction time, can be an effective and simple method to limit the NDMA formation.In the presence of humic acid, nitrite or nitrate, the yield of NDMA formation would be restrained. The effect of bromide ion on NDMA formation was different between chlorination and chloramination. Other wise, the yield of NDMA formation would be changed with the variation of the order and interval between ammonia and disinfectant.During water treatment process, enhanced coagulation, enhanced filtration and disinfection condition optimization could be effect measures to control NDMA formation. In this paper, a certain amount of DMA was dosed in the water taken from Songhua River. In the experiment of coagulation optimization, three different coagulants (PAC, aluminium sulfate, ferric chloride) were compared. Control compounds, NDMA and DMA, were removed well by PAC, and the amounts of microorganism, organic matters and NDMA can be controlled effectively. Both quartzite filter media and granular activated carbon (GAC) filter media are good filters to remove control compounds, but less NDMA formed after filtration by quartzite filter media.According to the GC-MS analysis of raw water and the water after filtration by quartzite filter media, the organic matters in the water could be a factor limit the formation of NDMA. The species of nitrogenous matters were confirmed, but the N-containing heterocyclic compounds were not the effective NDMA precursors.Disinfection condition optimization is the emphasis to control the yield of NDMA, and breakpoint chlorination could be a good method to limit NDMA formation during chlorination of high ammonia containing raw water.