Evolution Of Membrane Fouling In Micellar-enhanced Ultrafiltration

In micellar-enhanced ultrafiltration (MEUF), surfactants are added to wastewaterto promote the removal of micropollutants. MEUF shows high efficiency for removalof single metal ions or for simultaneous removal of several types of metal ion(s), suchas cadmium and zinc. As with most membrane filtration methods, the application ofMEUF in water and wastewater treatment requires good control of fouling to preventsignificant flux decline, increased operating costs, decreased membrane lifetime, andreduced removal efficiency.In this study, micellar-enhanced ultrafiltration was used to remove Cd2+fromsynthetic wastewater using polysulfone spiral wound ultrafiltration membrane andSDS as surfactant. It was observed in the experiments that gelatinoids formed by SDSdissolve easily which have interference effect to distinguish different membraneresistances. The effect of some important parameters about membrane fouling inMEUF was investigated, including transmembrane pressures, SDS concentrations.The permeate flux declined with the increase of SDS feed concentration which washigher than1CMC (7.8mM). However, according to the two cases in which SDS feedconcentration were both near to1CMC, higher SDS concentration showed higher flux.It can be explained by a concentration polarization mechanism. During the process ofconcentration polarization, the SDS molecules were rejected by the membrane. Theserejected SDS molecules deposited on the membrane surface gradually and formed thegel layer near the membrane surface. According to the SDS feed concentration whichwas larger than1CMC, higher one would led to more serious fouling than lower one.Permeate flux followed the sequence0.25>0.20>0.15>0.10>0.05MPa, but itdidn’t increase with equidistance like pure permeate flux. What’s more, higher TMPfiltered caused a faster initial flux decline. The decline order of Rf,0.10<0.15<0.20MPa, was constant during whole period, while0.05MPa and0.25MPa presentdifferently. One of reasons underlying those different results were their specificmeasure that no backwashing and stop for12h after each unit, which led to variety ofdifferent permeate flux and fouling resistance. At the beginning of MEUF, it showedthat the membrane fouling caused by high TMP like0.25MPa had less pollution onmembrane, and low TMP like0.05MPa had more serious pollution due to colloid gel.Particle aggregation in MEUF was found to play an important role duringmembrane filtration. Different SDS concentration had different influence onmembrane fouling, not always the higher values led to more serious fouling, the paper showed that when the SDS concentration reached a value higher than3CMC, thedegree of fouling got more serious with the increasing of permeate volume. Eachresearch is proposed for practical aspect, this study will offer more assistance tomeasure the resistance on foul in practical aspect of MEUF.