Fouling of ceramic membranes by albumins under dynamic filtration conditions

The fouling of ceramic ultrafiltration membranes by bovine serum albumin (BSA) and human serum albumin (HSA) has been followed by means of small angle neutron scattering (SANS) and simultaneous monitoring of the decline of permeate flux with time under cross-flow conditions. SANS is primarily sensitive to the gradual buildup of the protein layer deposited inside the membrane pores while the permeate flux is a measure of the overall blockage of the membrane. The combined measurement allows the determination of the location of protein fouling. The effect of solution pH on the fouling by the two albumins was characterised at a fixed protein concentration of 1 g dm-3 on alumina membranes with nominal pore diameter of 200 Å. The filtration results show that the pattern of fouling is similar for both BSA and HSA, that there is a rapid permeate flux decline at pH 3 and 5, and a slower decline at pH 7. The simultaneous SANS experiment shows that at pH 5 there is strong deposition of protein layer inside the membrane pores, suggesting that at this pH blockage inside the membrane pores is primarily responsible for fouling. However, at pH 3, SANS showed that amount of BSA and HSA deposition inside the pores was at its smallest, suggesting that, in this case, the permeate flux decline is caused by the blockage of the front surface of the membrane. At pH 7 the extent of protein deposition inside the membrane is intermediate between the values for the other two pH, suggesting that the blockage at this pH mainly arises from the slow deposition of protein inside the membrane pores. Similar pH effects were observed on alumina membranes with a nominal pore diameter of 2000 Å. Although there is a general similarity in the fouling pattern of the two proteins, HSA causes less blockage with time at the pH conditions away from the isoelectric point of the albumins. The effect of cross-flow velocity on the fouling was also examined. It was found that permeate flux dropped faster at an elevated cross-flow velocity, although the extent of protein deposition inside the membrane pores was found to be similar, indicating that blockage at the front, outer surface of the membrane is intensified by a higher flow velocity. (C) 2000 Elsevier Science B.V.