Identification of the location of protein fouling on ceramic membranes under dynamic filtration conditions

The fouling of ceramic ultrafiltration membranes by bovine serum albumin (B SA) under dynamic filtration conditions has been studied by small angle neu tron scattering (SANS) combined with the monitoring of the decline of perme ate flux with time under the crossflow condition. Although the dropping of permeate flux is indicative of the blockage of the membrane pores it offers no information about the location of the protein deposition. In comparison , neutron scattering is sensitive to the structural composition of the memb rane pores and the measurement of the scattering intensity with time offers information about the gradual buildup of protein deposit inside the membra ne pores. The combined experiment of the SANS and permeate flux measurement thus allows a reliable determination of the location of protein fouling. BSA solution was pumped through a thin flat sheet of commercial alumina mem brane in a quartz cell specially designed to allow a simultaneous experimen t of permeate flux recording and small angle neutron scattering. The foulin g experiment was first made at pH 5, close to the isoelectric point (IP) of 4.8 for BSA at the BSA concentration ranged from 0.1 to 1 g dm(-3) The per meate flux was found to decrease with BSA concentration and the trend of de crease is entirely consistent with the thickening of the protein layer adso rbed on the surface of the membrane pores, suggesting that under this condi tion blockage inside the membrane pores is primarily responsible for foulin g. Subsequent measurements were made at different pH values away from the B SA isoelectric point and at a fixed BSA concentration of 1 g dm(-3). At pH 3 the permeate flux showed a fastest decaying with time while SANS showed a least amount of BSA deposition inside the membrane pores. This observation clearly indicates that it is the front surface of the membrane that is blo cked. At pH 7 the permeate flux showed a slowest decaying with time but the extent of protein deposition inside the membrane pores is intermediate, su ggesting that at least at the early stage of the filtration, front blockage is insignificant and fouling mainly arises from the slow deposition of pro tein inside membrane pores. (C) 1999 Elsevier Science B.V. All rights reser ved.