(410a) Protein Fouling During Normal Flow Microfiltration

Normal-flow microfiltration experiments were conducted using polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) base membranes, PTFE and PVDF membranes coated with polyvinyl alcohol (PVA), and a polycarbonate membrane coated with PVA. Feed streams consisted of lysozyme, β-lactoglobulin, ovalbumin and hemoglobin (Hb) and the pH values were set to be the isoelectric point of each of the proteins (11.0, 5.8, 4.7 and 7.2 respectively). The feed pressure values of 14 and 69 kPa were used. Lysozyme concentrations of 0.1 and 2 g L-1 were tested. For β-lactoglobulin, ovalbumin and Hb, concentrations of 0.1 and 2 g L-1 were tested. Protein fouling of the membrane was investigated by determining the variation of permeate flux with filtrate volume and by analysis of ATR-FTIR spectra and FESEM images of virgin membranes and membranes after microfiltration. Results indicate that the greatest amount of fouling occurs with Hb. The order of most to least fouling was found to be Hb>Ovalbumin> β-lactoglobulin>Lysozyme. Fouling was more severe at higher protein concentration and feed pressure. The proteins which showed significant fouling conditions were looked at more closely by pre-filtering the protein solution. By pre-filtering the feed stream, this removed protein aggregates from the solution. This pre-filtration step was observed with 0.2, 0.45 and 1 micron diameter pore sizes. A flux decline was present only when pre-filtering with the 1 micron pores. The concentration of the solution was determined before and after pre-filtration, and the protein solutions were shown to have a lower concentration after pre-filtration. Our results indicate that it is the interplay among membrane properties, protein properties and operating conditions that determine whether fouling occurs and to what extent.