Research Of NDEA Formation During Water Treatment And Removal Of Its Precursor(DEA)

Nitrosamines are a class of strong carcinogen, distributed in drinking water, groundwater and other water environments. At present, nitrosodimethylamine(NDMA) is used as a representative of nitrosamines in most research. But, compared with NDMA, nitrosodiethylamine(NDEA) has a highly function of mutagenic, carcinogenic and mutagenic, and its typical precursors, diethylamine, which is widely existed in human environment, can produce NDEA easily during drinking water disinfection. Therefore, it is necessary to explore the formation discipline of NDEA and to find effective ways to remove DEA.In the exploration of NDEA formation, in this paper, using different disinfection method to study the effect of the following factors on NDEA formation: time of disinfection, concentration of DEA, temperature and coexisting ions. The results of single factor experiments show that dichloramine(NHCl2) has a higher potential of NDEA formation; the production of NDEA is lower when using hypochlorous acid(HCl O) as disinfectant and it is affected by the amount of ammonium ion(NH4+) and nitrite ion(NO2-) in water; when using monochloramine(NH2Cl) as disinfectant, the production of NDEA has a liner relationship with the dosage of NH2 Cl and reaction time, it can achieve the maximum production with molar ratio at 1:1 during the content of DEA and NH2 Cl, p H=7.0, and the temperature at 25℃; and it is affected by the amount of NO2- in water.The results of orthogonal test show that when using NH2 Cl as disinfectant, according to the effects descending order, influencing factors of NDEA formation can be arranged as the following sequence: reaction time, concentration of DEA, p H, concentration of NO3-, temperature, concentration of NH2 Cl, concentration of NH4+, concentration of NO2- and organic ammonia.In exploring effective ways to remove DEA, in this paper, an effective adsorbent is synthesized by loading Fe on activated carbon with the method of impregnation-calcination. The best way for preparing the activated carbon loaded with Fe(Fe/AC) which has best adsorption properties is that: calcination temperature at 500℃; the concentration of Fe2(SO4)3 loaded on AC is 0.1 mol/L; roasting time is 4h. The properties of Fe/AC are characterized by scanning electron microscopy(SEM), energy dispersive spectrometer(EDS), X-ray diffraction(XRD) and specific surface area analysis(BET) in order to reveal possible mechanism. Compared with the original activated carbon, in modified activated carbon, atomic percentage of Fe increases 3.87 times, and atomic percentage of S increases 1.23 times; after modification, Fe(Ⅲ) gathered in the Fe/AC carrier, new crystal phase generated in Fe/AC; compared with AC, specific surface area of Fe/AC increased, adsorption performance of Fe/AC enhanced; surface area of Fe/AC has increased, iron oxide adhered in Fe/AC obviously, and the internal porosity of Fe/AC increased clearly.According to the best way to prepare Fe/AC, its absorption properties were studied in the process of removing DEA. The results indicate that adsorption capacity of Fe/AC is 10 times of AC, the maximum adsorption capacity of 3.55 mg/g. At 25℃, the optimum static adsorption conditions of Fe/AC to remove DEA are that: p H=13, reacting 240 min, dosing 0.3g Fe/AC in 50 m L DEA solution, the removal rate of 10 mg/L DEA solution is 91.60%. The adsorption follows pseudo-second order kinetics. The equilibrium data fit the Langmuir equation well,with the maximum adsorption capacity being 427.72 μg/g. The adsorption is a spontaneous process, the higher the temperature is, the more beneficial to adsorption is.