Membrane bioseparations: Cellulase recovery, particle deposition, and second osmotic virial coefficients

Membrane separations have numerous applications in the bioprocess industries, including enzyme recovery, cell capture and harvesting, and buffer exchange. This dissertation represents both a broadening of these applications and an extension of fundamental science surrounding foulant transport at the membrane surface.; To improve a biomass-to-ethanol process design, an ultrafiltration separation was experimentally characterized as a method of recovering and recycling expensive cellulase enzymes during the saccharification of pretreated yellow poplar or corn stover. Vacuum filtration or inclined settling were used as solid-liquid separations, and the filtrate or overflow was sent to an ultrafilter for enzyme recovery and concentration. Experimental results and an economic analysis show that reuse of cellulase can reduce glucose production costs, especially when the enzyme price is high.; Direct visual observation was used to measure the transport and deposition of latex particles onto aluminum oxide microfiltration membranes during tangential flow filtration. The fractional deposition of foulant particles was defined and measured across a range of operating conditions. This parameter was shown to grow from zero to unity with increasing permeate flux or decreasing shear flow. A surface transport model was developed to predict the fractional deposition as well as the speed of foulant particles rolling over the membrane surface.; Ultrafiltration experiments were conducted to assess the effects of solution conditions on protein ultrafiltration permeate fluxes. This work was conducted with the goal of identifying a correlation between second osmotic virial coefficients (B22) and permeate flux. Lysozyme was used as a model protein in solutions of various pH, ionic strength, and anion type. Under the conditions tested, permeate fluxes were generally smaller for small or negative values of B22, indicative of attractive interactions between protein molecules, though a direct correlation between B22 and the permeate flux that is general for all solution conditions could not be identified. Instead, it was found that B 22 was indirectly linked to the permeate flux because solution conditions resulting in small or negative values of B22 often resulted in protein aggregation or precipitation. These aggregates or precipitates collect on the membrane surface, form a filter cake, and thereby reduce the permeate flux.