Study On A New Water Treatment Technology Using Electroflocculation Combined With Nanoscale Zero-valent Iron Supported On Mesoporous Silica

With the development of modern industry and more human activities in China, the issue on drinking water micro-pollution has drawn more and more attention. Untreated industrial effluent or urban sewage is released into natural water, thus most of the drinking water sources have turned into the micro-polluted water. With the increase of the type and quantity of the pollutants in the aquatic environment, people have to research and develop the new treatment methods due to the limitations of traditional clarification processes.In this study, the research on the treatment efficiency of micro-polluted water from the Suzhou River, Shanghai by the electroflocculation method was conducted firstly. The experimental results showed that after the electrolytic time of 30 minutes, the removal efficiencies of total organic carbon(TOC), ammonia nitrogen, total phosphorus and turbidity by the single electroflocculation were 70%, 42%, 95% and 60%, respectively with current density of 3.42mA/cm2. Based on the above study, the combined electroflocculation-ultrafiltration process was then developed, and under the conditions of electrolytic time 30 minutes, current density 3.42 mA/cm2, sedimentation time 20 minutes and flow rate 20 L/h, the removal rate of TOC and ammonia nitrogen reached 80% and 51%, and the removal rate of total phosphorus and turbidity achieved 99%, which meets the Standards for Drinking Water Quality(GB5749-2006) completely.However, the removal of heavy metal by the electroflocculation process was inhibited due to the reversibility of flocs which was affected by the pH value. Therefore, in order to solve the limitation effectively, the new nanocomposite NZVIs/A10 with both adsorption and reduction properties was prepared by loading nanoscale zero-valent iron onto the surface of the modified mesoporous silica and was also appled in the electroflocculation process to remove the heavy metal Ni(II) in the micro-polluted water. First of all, the phase structure, surface morphology and composition of this new composite were characterized and analyzed by X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM) and Fourier transform infrared spectrum(FT-IR) methods. In addition, the effects of pH value and temperature on Ni(II) removal by the new composite were studied. Moreover, the reaction mechanism was further discussed through the methods of scanning electron microscope(SEM) and X-ray photoelectron spectroscopy(XPS). The results showed that the new nanocomposite NZVIs/A10 was a porous sphere uniformly loaded by the nanoscale zero-valent iron on its surface. It was also found that the removal of Ni(II) by NZVIs/A10 was much higher than that by single modified mesoporous silica or nanoscale zero-valent iron, and the removal rate increased with the increasing of pH and temperature. Finally, the electroflocculation combined with the new nanocomposite was carried out and more than 90% removal of Ni(II) was attained when the dosage, voltage and electrolytic time were 2.5g/L, 5V and 30 minutes, respectively.