Comparisons of membrane fouling and separation efficiency in protein/polysaccharide cross-flow microfiltration using membranes with different morphologies

The membrane fouling and filtration performance of Bovine serum albumin (BSA)/dextran cross-flow microfiltration using membranes with different morphologies are analyzed and compared. Three 0.1 μm hydrophilic membranes made of mixed cellulose ester (MCE), polyvinylidene fluoride (PVDF) and polycarbonate (PC) were used in these experiments. The MCE and PVDF membranes had sponge-like structures, while the PC membrane had uniform straight-through circular pores. The membrane morphology, cross-flow velocity and transmembrane pressure effects on the filtration flux; membrane fouling and solute transmissions are discussed. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. The PVDF membrane produced the highest filtration flux, while the MCE membrane exhibited the lowest. A 15-30% difference in filtration flux may be obtained due to different membrane selection. Comparing various filtration resistances, the cake resistances of PVDF and PC membranes are almost the same but much higher than that for the MCE membrane, especially under high pressure. The membrane blocking resistance sequence is MCE > PVDF > PC membrane. The membrane blocking resistance of MCE and PVDF were quite similar due to their sponge network structures. Membrane fouling was analyzed using SEM and CSLM. BSA aggregates deposited onto the membrane surfaces, while dextran molecules adsorbed on the membrane surface and the membrane pore walls. More BSA/dextran mixtures were observed on the PVDF membrane. The PC membrane fouling was due mainly to pore coverage. Dextran molecules were more likely to deposit onto PVDF and MCE membranes. Both BSA and dextran transmission decreased with increasing cross-flow velocity. Increases in transmembrane pressure lead to lower BSA but higher dextran transmission. The PVDF membrane exhibited the highest solute transmission, while the PC membrane resulted in the lowest. All membranes exhibited higher selectivity for the BSA/dextran mixture under higher pressures, especially the PC membrane.