Mechanisms for protein fouling during microfiltration

Although protein fouling is one of the critical factors governing the effectiveness of many microfiltration processes, the underlying chemical and physical mechanisms that influence the initiation and growth of the fouling layer have not yet been clearly established. The objectives of this thesis were (1) to obtain a detailed understanding of the effects of protein aggregates on the fouling of microfiltration membranes by bovine serum albumin (BSA), (2) to determine the role of intermolecular chemical reactions on the formation of these protein aggregates and on the continued addition of BSA to the growing deposit, and (3) to quantify these effects by developing a simple mathematical model for the flux decline during the microfiltration of a variety of proteins having different physical and chemical characteristics.;The rapid initial flux decline observed during the filtration of BSA solutions was due to blockage of the membrane pores caused by the convective deposition of large BSA aggregates onto the membrane surface. Native (non-aggregated) BSA is able to add to the growing deposit via the intermolecular thiol-disulfide interchange reaction between the free thiol group on the bulk BSA and the internal disulfide linkages of the protein within the deposit. The rate of this protein reaction was dependent on the accessibility of the free thiol as well as the presence of divalent metal cations and reducing agents like dithiothreitol.;A mathematical model was developed for the flux based on the above physical picture. The flux decline was assumed to be due to pore blockage, with the rate of pore blockage governed by both aggregate deposition and chemical addition of native protein. This fouling model was in good agreement with the rate of pore blockage governed by both aggregate deposition and chemical addition of native protein. This fouling model was in good agreement with the flux decline data for a number of proteins with significantly different physical and chemical characteristics (e.g., pepsin, ovalbumin,...