Flux Kinetics, Limit and Critical F 1 luxes for Low Pressure Dead-end Microfiltration. 2 The case of BSA Filtration through a Positively Charged Membrane

Abstract

The influence of the applied pressure on the flux decay mechanism during Bovine Serum Albumin (BSA) dead-end microfiltration (MF) has been investigated for a polyethersulfone, positively charged, membrane (SB-6407) from Pall®11 . BSA solutions, at pH values of 4, 5 (very close to the protein isoelectric point, IEP) and 6, were micro-filtered through the membrane at different low applied transmembrane pressures. Although filtration was done in dead-end configuration, limit fluxes appeared for all pressures and pH values studied. The concepts of (long time) limit and critical fluxes and their correlation have been clarified and analysed too. The usual blocking filtration laws have been included in a common frame and both the cases with zero or non-zero limit fluxes have been incorporated. Within this frame, the standard model, that assumes an internal pore deposition, has been included as well; although, in our case, the acting mechanism seems to be mainly the so called complete blocking. Protein adsorption has been analysed in terms of the protein-protein and protein-membrane electrostatic interactions. There is a faster flux-decay for the protein isoelectric point with a slightly slower decline in flux when there are both membrane-to-protein and protein-protein repulsion. The slowest kinetics appears for membrane-to-protein attraction with protein-protein repulsion. Moreover, adsorption is stronger, and the limit flux smaller, when the protein is attracted towards the membrane and there is protein-protein repulsion.