Mechanisms of polarization and fouling of ultrafiltration membranes by proteins

• Published in: Journal of membrane science 1983, Vol.16, p.237-258
• Main Authors: Reihanian, H., Robertson, C.R., Michaels, A.S.
• Format: Article
• Language: English
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/S0376-7388(00)81313-7

Unstirred, constant-pressure, batch-cell ultrafiltration of dilute (0-6 g/l) aqueous bovine serum albumin (BSA) solutions through high permeability, asymmetric ultrafiltration membranes yields the classical linear dependence of permeate volume with (time) 1/2, as predicted by osmotic (Vilker and Colton) and “gel-polarization” (Trettin and Doshi) models of the solute polarization process. However, step-changes in pressure during ultrafiltration reveal a linear dependence of flux on pressure, which is inconsistent with either of these models. A simple particle filtration model, based on the build-up of a BSA filter cake of constant hydraulic permeability, adequately correlates the observed results Of particular importance is the surprising observation that, following interruption of flow for extended time-periods (up to 16 hr), there is relatively little rebound of flux on repressurization, indicating only slight diffusional relaxation of the polarization layer. This implicates the existence of strong intermolecular attractive interactions within the BSA gel. Stirring of the solution overlying the polarized membrane (under zero-permeation conditions) is accompanied by a rapid removal of the BSA gel-layer (as evidenced by a rapid increase in pure-solvent permeability of the membrane with agitation time). For hydrophobic membranes which display strong adsorptivity of BSA from solution (e.g., polysulfone), the rate of BSA-layer removal by agitation is much slower than that observed with non BSA-sorbing, hydrophilic membranes (regenerated cellulose). This finding indicates that molecular interactions between BSA and the membrane surface are of central importance to membrane-fouling by this (and undoubtedly other) macrosolutes, and suggests that surface treatments to minimize solute adsorption should be highly beneficial to the reduction of fouling during ultrafiltration.