| The membrane water treatment technology has been large-scale applied in the field of water treatment. But on the other hand, it also has some defects, such as the existence of the membrane fouling when used in practice, which will reduce the membrane flux. Generally, in order to get the membrane flux recovered, we need to clean the membrane fouling, with the p Hysical or chemical cleaning operation. Due to the limit of the p Hysical cleaning in flux recovery, it is necessary to adopt further chemical cleaning to recover its flux. So this paper mainly studied on the impact of the characteristics upon the Polyvinylidene Fluoride(PVDF) membrane which caused by the chemical cleaning.The PVDF hollow fiber ultrafiltration membrane was choosed as the research object.It was investigated under the mode of constant flow run effect on the quality of the output water,the flux of the output water.And sodium hypochlorite, sodium hydroxide, citric acid was studied as the representative of the chemical cleaning agent and so was the combination of two kinds of cleaning agent(sodium hypochlorite and sodium hydroxide) which focus on the influence of the membrane integrity and cleaning effect. Using the transmembrane pressure, and the three-dimensional fluorescence spectrum, TOC detector, which was used to analysis and estimate the membrane performance caused by different cleaning agents.Through the tensile test, scanning electron microscope(sem), Fourier infrared(FTIR) and BET specific surface area analysis characterization methods, the change mechanism of membrane materials which caused by chemical cleaning is discussed in this paper.In this study, it was found that, all of the sodium hydroxide, sodium hypochlorite, citric acid chemical cleaning can cause the increase of the flux of PVDF membrane. Among them, the flux of the PVDF membrane which was cleaned by sodium hydroxide increased significantly.And the flux of the membrane cleaned with sodium hypochlorite increases in a good correlation with the increasing of the time.and the concentration and flux changes has good predictability with the degree of aged.Citric acid cleaning also increases PVDF membrane flux, but when the accumulative of cleaning reached to a certain extent, the membrane flux turn to a declining trend.When consider the removal rate wewillfound that after a certain amount of chemical cleaning, several kinds of cleaning agents will decrease the rate of interception of PVDF membrane of pollutants, and which one reduces largest is the combination of sodium hydroxide and sodium hypochlorite cleaning, then followed by sodium hydroxide, sodium hypochlorite and citric acid cleaning cleaning.Experimental results show that the tensile test can effectively reflect the aging degree of membrane, and the tensile strength will be increased with the increase of aging degree;while the tensile elongation will not necessarily increase or decrease; Contact Angle is an effective aging degree evaluation tool, which can accurately assess the aging degree of PVDF ultrafiltration membrane, but some other factors in the practical application may interfere the measurement results of contact Angle; Although the chemical PVDF membrane performance after cleaning and other materials has obvious changes, but changes in membrane surface FTIR spectra before and after cleaning is not significant, the mechanism of chemical cleaning aging of the PVDF membrane remains as a matter to research; BET can effectively characterize the microstructure changes on the surface of the PVDF membrane, the changes of the specific surface area and pore volume indicate the changes made by the chemical cleaning, but the membrane pore size did not change significantly. |
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