| The ultrafiltration(UF) technology is widely used in water plant for drinking watertreatment. Chemical cleaning is an important means to maintain the normal operation of theUF membrane modules. Meanwhile chemical cleaning could cause dirreparable damages,threatening water security. The hollow fiber polyvinyl chloride(PVC) UF membrane wasselected for the study in this paper. The effects of effluent quality by various constant fluxwere studied, as well as chemical cleaning including sodium hypochlorite, sodium hydroxide,citric acid. The changes brought about by the sodium hypochlorite--sodium hydroxide,sodium hypochlorite--citric acid were also studied. The characteristics of the membrane andthe cleaning effect were analyzed by combination of transmembrane pressure (TMP), thebovine serum albumin(BSA) retention rate and membrane effluent particle size distribution.Reasons of membrane properties changes were evaluated and analyzed by scanning electronmicroscopy and Fourier transform infrared analysis techniques. The possibility of particle sizeanalysis applied to the detection of membrane integrity was suggested.It was found that the higher the flux of membrane run, the higher the TMP, the faster theTMP growth rate, the worse the retention capacity of the BSA.30L/(m~2h) was the optimumoperating flux to ensure operational stability.When cleaning agents were used alone, sodium hydroxide and sodium hypochlorite hadhigh pollutant removal efficiency, both of which make the membrane pore expansion andfracture phenomena.1%concentration of sodium hypochlorite and0.02mol/L sodiumhydroxide caused the most serious membrane damages, which threaten the safety of theeffluent and should be avoided in practical applications. No matter what concentration ofcitric acid, extending the cleaning time had bad removal of organic pollution on membrane.Citric acid should not be used.When cleaned by combination of sodium hypochlorite and other two cleaners, thecontribution of sodium hypochlorite was always greater than the other. Combination ofsodium hydroxide and sodium hypochlorite has a good effect on the removal of organicpollutions, and was better than citric acid—sodium hypochlorite. The former caused worsedamage than the latter, even greater than they were used alone. The reaction mechanism wasnot yet clear. Citric acid had smaller contribution to the process of cleaning, or evencounterproductive. Therefore, in practical applications, a combination of citric acid andsodium hypochlorite was not appropriate to take.Particle size distribution of effluent could reflect the situation of pore size and membrane damage. It was useful in detecting membrane integrity and water quality, which could beapplied and utilized. |
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