The effect of varying transmembrane pressure and crossflow velocity on the microfiltration fouling of a model beer

Abstract

Experiments were conducted to determine the fouling propensity during crossflow filtration of a model beer, primarily composed of dextrin and protein. The Carbosep™ filters of nominal pore size 0.45 μm were fouled over a range of transmembrane pressures and crossflow velocities at a constant temperature of 20 °C. After each experiment, the membrane was cleaned and re-used in order to replicate industrial filtration conditions. For each experiment, the flux decline data were obtained, together with the concentrations of the dextrin and protein in the permeate and retentate streams. Further data manipulation enabled retention ratios to be calculated for each component. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was established, the permeate flux became constant for a given set of experimental conditions. The steady-state flux increased with increasing transmembrane pressure and with increasing crossflow velocity. For a given crossflow velocity, an increase in transmembrane pressure resulted in a reduction in transmission of both the BSA protein and dextrin components of the model beer. This is attributed to an increase in the fouling layer thickness due to higher permeate fluxes, coupled with a decrease in fouling layer voidage at higher transmembrane pressures. The retention data suggest that higher transmembrane pressures lead to an increase in the proportion of BSA present in the fouling layer. For a given transmembrane pressure, an increase in crossflow velocity led to increased transmission of both the BSA and dextrin through the membrane. This is due to the inhibition of fouling layer development through the larger wall shear stress and thinner laminar sub-layer that are associated with an increase in crossflow velocity.