Fouling of ceramic membranes by albumins under dynamic filtration conditions

The fouling of ceramic ultrafiltration membranes by bovine serum albumin (B SA) and human serum albumin (HSA) has been followed by means of small angle neutron scattering (SANS) and simultaneous monitoring of the decline of pe rmeate flux with time under cross-flow conditions. SANS is primarily sensit ive to the gradual buildup of the protein layer deposited inside the membra ne pores while the permeate flux is a measure of the overall blockage of th e membrane. The combined measurement allows the determination of the locati on of protein fouling. The effect of solution pH on the fouling by the two albumins was characterised at a fixed protein concentration of Ig dm(-3) on alumina membranes with nominal pore diameter of 200 Angstrom. The filtrati on 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 d ecline at pH 7. The simultaneous SANS experiment shows that at pH 5 there i s 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 depo sition 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 o f the membrane. At pH 7 the extent of protein deposition inside the membran e 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 i nside the membrane ports. Similar pH effects were observed on alumina membr anes with a nominal pore diameter of 2000 Angstrom. Although there is a gen eral 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 ex amined. It was found that permeate flux dropped faster at an elevated cross -how velocity, although the extent of protein deposition inside the membran e pores was found to be similar, indicating that blockage at the front, out er surface of the membrane is intensified by a higher how velocity. (C) 200 0 Elsevier Science B.V. All rights reserved.