Research On The Reduction Of Nitrosodimethylamine In Water With Iron And Zinc And Iron Oxides

Nitrosodimethylamine (NDMA) is the representative of nitrosamines as the pollutants. It is potentially carcinogenic to humans, and has been detected in the raw water and the effluent after disinfection. Conventional treatment methods cannot treat NDMA effectively. Thus, the enhanced processing technologies are needed to remove NDMA. Domestic and foreign researchers conducted the studies on adsorption, biological treatment, membrane separation, advanced oxidation, catalytic reduction with hydrogen, et al. However, these technologies have many issues such as incomplete degradation, long reaction time, high energy consumption, complicate operation. Therefore, there is the need to develop new effective methods to treat NDMA.In this paper, the efficiencies of the reduction of NDMA with iron oxides were explored. The efficiencies of the reduction of NDMA with zero-valent zinc and zero-valent iron were compared. Zinc was chosen to reduce NDMA. The reaction rates were investigated, the effects of the main influencing factors on the reduction were examined, the theoretical explanations for the above phenomena were conducted. For the better product analysis, the detection method for the trace unsymmetrical dimethylhydrazine (UDMH) in water, which is the intermediates during the reduction of NDMA, was established. The products of the system were analyzed and the mechanisms were deduced. To further enhance the reaction rates, the reductions of NDMA with Cu2+and iron (Fe/Cu2+) and Cu2+and zinc(Zn/Cu2+) were studied, the effects of the Cu2+loading on the reduction of NDMA were examined, the products were analyzed and the mechanisms were deduced.First of all, the reactions of the Fe2+bound to the iron oxides with NDMA, magnetite with NDMA, green rust with NDMA were explored. The results showed that Fe2+bound to goethite, hematite, lepidocrocite and ferrihydrite, magnetite and Fe2+bound to magnetite, green rust had no obvious degradation of NDMA. After the addition of Cu2+, green rust can degrade NDMA significantly, however, there were considerable differences on the NDMA removal between the reaction systems using different batches of green rust and between parallel samples.The efficiencies of the reduction of NDMA with zero-valent iron and zero-valent zinc were compared, the results showed that zero-valent zinc was more reactive than iron on the reduction of NDMA. Zero-valent zinc was used to reduce NDMA. The reaction rates were examined. The results showed that the zero-valent zinc could degrade NDMA effectively, at initial pH7.0, the reaction was divided into the lag period and the rapid reaction period, the data of the lag period obeyed the zero-order kinetic model, the data of the rapid reaction period obeyed the pseudo-first-order kinetic model. By examining the dissolved zinc ions and the pH change with and without the addition of NDMA, it was found that the addition of NDMA had little effect on the zinc corrosion. The pH effect was examined. The low pH was found to facilitate the reaction. The reduction of NDMA with zinc in aerobic and anaerobic conditions were conducted, the anaerobic condition was good for the reduction in the first8h, the aerobic condition benefited the reduction in the following6h. After comparing the phenomena of the NDMA reduction, the pH changes and the dissolved zinc ion in the above reaction systems, the zinc reactivity on the NDMA reduction was found to be consistent with the zinc corrosion rates. The differences of the removal efficiencies and kinetics of the reduction of NDMA under the different reaction conditions were related to the available amount of the H+. Through the summary of the corrosion conditions of a variety of reaction conditions, the oxygen consumption forming the passive film, localized acidification forming H+and the breakdown of passive film were regarded as the reason of the transformation from the lag period to the rapid reaction period.A high performance liquid chromatography method was developed for the determination of trace unsymmetrical dimethylhydrazine (UDMH) in water.4-nitrobenzaldehyde was used for the derivatization of UDMH, the chromatographic conditions and the derivative conditions were optimized. The method is rapid in determination, and has a low detection limit, the good linear relationship, the high precision and accuracy of determining trace UDMH in water. For the simulated water sample, the relative standard deviation was equal to or less than1.69%, the recovery of standard addition was95.7%~102.7%. Through the products analysis, we found that UDMH and DMA were formed during the reduction of NDMA. UDMH was intermediates between NDMA and DMA, some unmeasured products also existed in the process of reductions of NDMA and UDMH with zero-valent zinc. Catalytic hydrogenation was deduced as the mechanism based on the reaction phenomenon and the characters of the zero-valent zinc and NDMA.The reductions of NDMA with zero-valent iron and zinc in the presence of Cu2+ were conducted. The effect of Cu2+concentration on the efficiencies and the reaction rates of reduction of NDMA with Fe/Cu2+and Zn/Cu2+systems were studied. The Fe/Cu2+and Zn/Cu2+systems were more reactive than Fe(0) and Zn(0) systems, respectively. Through the products analysis, it was found that the presence of Cu2+did not change the type of the products. UDMH and DMA still were the products of the two reaction system. UDMH can be further reduced to DMA. There are other unmeasured products existing in the reaction system. The mechanism of the two reaction systems was deduced to be catalytic hydrogenation based on the reaction phenomenon and existing literatures. Basing on the theory calculation and the characterizations of the metal powders after reaction, Cu(OH)2was found to be the substance that enhanced the reduction of NDMA in the Fe/Cu2+system, Cu2O and Cu(OH)2were found to promote reduction of NDMA in the Zn/Cu2+system.In this research, the reaction of the iron oxides and NDMA was explored, which can fill the data gap in the natural attenuation and the attenuation in the water distribution system. The systematic studies were conducted on the reduction of NDMA with zero-valent zinc, Fe/Cu2+and Zn/Cu2+. The studies can supply the data supporting the further development of the reduction of NDMA with metals.