| Membrane technology is widely used in drinking water treatment.With the advancement of technology and engineering operation experience,the process is becoming more and more stable.However,the membrane aging problem caused by chemical cleaning will affect the service life of the membrane and determine the operating cost.Therefore,it is necessary to further analyze the aging process of the membrane chemical cleaning.Membrane cleaning is an important part of the operation of most membrane systems,and there is an urgent need to learn more about membrane cleaning.Early research on membrane cleaning focused on membrane fouling and its control techniques.The problem of membrane aging caused by membrane cleaning and membrane cleaning still requires systematic research.This study investigated the effect of chemical cleaning on the performance of ultrafiltration membranes of different materials.Firstly,the effect of sodium hypochlorite chemical cleaning on the physicochemical properties of six different membrane materials under different aging conditions was investigated by using modern characterization techniques.The results showed that the pure water flux of PES,PSF and PVDF membranes increased,and its interception ability deteriorated.The NaOCl solution with pH 8 had the strongest oxidation capacity and the effect was more significant.The hydrophilic additive PVP is sensitive to sodium hypochlorite and is susceptible to attack degradation and release from the membrane.Based on a set of ATR-FTIR spectra we found that the sulfinate group of the PES membrane is oxidized to form a sulfonic acid group.The isopropylidene group of PSF participates in the reaction,and the PVDF membrane undergoes a significant dehydrofluorination effect.Solid three-dimensional fluorescence can be used to characterize membrane aging,and the peak intensity of the fluorescence peak position of the membrane material decreases.The integrity of the aging membrane is destroyed,pits or cracks appear on the membrane surface,and the mechanical properties are lowered.Secondly,the polyvinylidene fluoride(PVDF)membrane was selected as the research object.The three models of pollutants(HA,SA,BSA)and two kinds of actual water(Songhuajiang River water and EfOM)were investigated by aging membrane.Analysis of pollution behavior,clarifying the characteristics of aging membrane fouling behavior.Membrane pollution control of HA,irreversible pollution gradually decreases with the increase of chemical cleaning intensity,reversible pollution is gradually increased,and the total pollution resistance of the membrane is significantly reduced.The PVDF membrane fouling caused by sodium alginate is mainly reversible pollution,and reversible pollution,irreversible pollution and total pollution are gradually reduced with membrane aging.Changes in the pollution caused by BSA occurred in the early stage,and membrane fouling was significantly reduced.Membrane pollution caused by Songhua River water is mainly caused by reversible pollution.As the membrane ages,the irreversible,reversible,and total pollution resistance values gradually decrease.Membrane pollution caused by EfOM is mainly caused by reversible pollution.As the membrane aging process evolves,the resistance to reversible and total pollution gradually increases.Finally,in this study,PVDF ultrafiltration membrane was used as the base membrane,and the PVDF membrane was modified by the acetalization reaction of PVA and glutaraldehyde in dimethylacetamide solution.The modified membrane was characterized by modern characterization techniques.It was found that the modified ultrafiltration membrane was more hydrophilic,but the pure water flux decreased,and the modification formed a new coating on the membrane surface.The modified membrane was then accelerated aging,and the effects of different aging conditions on the aging properties of the modified membrane were discussed.The results show that the hydrophilicity of the modified membrane deteriorates with the increase of aging strength,the pure water flux decreases,the interception rate of the three characteristic pollutants gradually decreases,and the pore growth increases during the aging process.The phenomenon of increased porosity.The membrane flux decline curve and membrane fouling resistance distribution of PVA modified membranes under different soda immersion strengths were compared.The results showed that the membrane fouling caused by HA,BSA and SA on the modified membrane was significantly lower than that of PVDF membrane.With the evolution of the membrane aging process,the anti-pollution performance of the modified membrane after aging is improved,which is significantly smaller than the membrane contamination after the aging of the original membrane. |
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