Characterization and reduction of membrane fouling in crossflow microfiltration.

摘要

Despite its wide application, membrane technology remains limited in large part due to fouling. The goal of the research for this dissertation is to better understand how foulants deposit on microfiltration membrane surfaces, how they are removed using different cleaning techniques, and how to optimize these techniques to minimize fouling and maximize transmembrane flux.; A model of rapid backpulsing for fouling control in crossflow microfiltration is described for solid-liquid separations where only a portion of the foulant is reversibly deposited on the membrane. This model was used to predict optimum backpulse durations and frequencies which maximize the net flux through the membrane, showing good agreement with experiments.; Direct visual observation (DVO) of yeast deposition and subsequent removal in clumps via single backpulses was made using microvideo photography. The recovered fluxes increase with increasing shear rate, backpulse pressure, and backpulse duration. A model for flux recovery based on the fraction of the membrane surface cleaned is in good agreement with experiment results.; In rapid backpulsing experiments, DVO pictures show that membranes are more effectively cleaned by longer backpulse durations and higher backpulse pressures, though net fluxes may be decreased due to greater permeate loss during each backpulse. Shorter, stronger backpulses result in higher net fluxes than do weaker, longer backpulses. The sizes of the foulant blockages increase with filtration time due to cell aggregation, while yeast cell rupture caused by reverse filtration may lead to greater irreversible fouling.; A novel cleaning technique termed infrasonic pulsing was developed which consists of applying pressure pulses on the permeate side which rapidly vibrate the membrane and lift a portion of the foulant cake off its surface. A model of the infrasonic pulsing process provides a good fit of experiments.; A combined sedimentation and membrane filtration process is presented for recycling cellulase enzymes in the biomass-to-ethanol process. In the first stage, lignocellulose particles longer than approximately 50 mum are removed via sedimentation in an inclined settler. Microfiltration is then used to remove the remaining suspended solids. Finally, the soluble cellulase enzymes are recovered by ultrafiltration. A preliminary economic analysis indicates that enzyme recycling is feasible.