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

Abstract

The fouling of ceramic ultrafiltration membranes by bovine serum albumin (BSA) under dynamic filtration conditions has been studied by small angle neutron scattering (SANS) combined with the monitoring of the decline of permeate 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 membrane pores and the measurement of the scattering intensity with time offers information about the gradual buildup of protein deposit inside the membrane 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 membrane in a quartz cell specially designed to allow a simultaneous experiment of permeate flux recording and small angle neutron scattering. The fouling 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 permeate flux was found to decrease with BSA concentration and the trend of decrease is entirely consistent with the thickening of the protein layer adsorbed on the surface of the membrane pores, suggesting that under this condition blockage inside the membrane pores is primarily responsible for fouling. Subsequent measurements were made at different pH values away from the BSA 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 blocked. At pH 7 the permeate flux showed a slowest decaying with time but the extent of protein deposition inside the membrane pores is intermediate, suggesting that at least at the early stage of the filtration, front blockage is insignificant and fouling mainly arises from the slow deposition of protein inside membrane pores.