(313c) Protein Fouling in Hollow Fiber Membranes

Membrane fouling remains one of the critical factors limiting the performance of ultrafiltration and microfiltration systems for the separation and purification of high value biological products. Fouling is a complex phenomenon arising from both physical and chemical interactions between the proteins and membrane. Recent studies using flat sheet membranes with simple dead-end flow have provided important insights into the connection between membrane structure/morphology and the observed fouling characteristics. The objective of this work was to extend these results to hollow fiber membrane modules, specifically accounting for the more complex hydrodynamics in these tangential flow hollow fiber systems.

Fouling experiments were performed using solutions of human immunoglobulin (hIgG) with relatively large pore size polysulfone hollow fiber ultrafiltration membrane modules.  The filtrate flux and protein transmission both declined significantly over the course of the experiment.  For example, data obtained with 2 g/L solutions showed more than a 4-fold reduction in filtrate flux after only 60 min of constant pressure filtration, with the protein sieving coefficient decreasing from more than 95% at the start of the filtration to less than 50% at t > 60 min. The relative contributions of concentration polarization and fouling were evaluated from the difference in membrane hydraulic permeability before and after protein fouling. The extent of surface fouling was examined using streaming potential measurements. For example, the zeta potential of the membrane increased from -8 mV to -4 mV after fouling with hIgG, reflecting the coverage of the negatively-charged surface with bound protein.  The pore size characteristics of the hollow fiber membranes was examined using dextran retention measurements before and after the fouling experiment. An initial theoretical model was developed that accounts for the effects of both fouling and concentration polarization on the transmembrane pressure. These studies provide important insights into the nature of the protein fouling phenomena in hollow fiber membrane systems.