Gas sparging to enhance permeate flux in ultrafiltration using hollow fibre membranes

This study focuses on the use of gas-liquid two-phase crossflow to overcome concentration polarisation in the ultrafiltration of macromolecular solutions as applied to hollow fibre membrane systems. The experimental work was conducted on a purpose built pilot-plant scale rig with albumin and dextran as the test media, The effect of gas injection on the permeate flux and membrane sieving coefficient was examined experimentally at different transmembrane pressures, feed concentrations and gas to liquid flow ratios. The results were encouraging, with flux enhancements of 20-50% obtained for dextran and 10-60% for albumin, when air was injected into the system over the range of process variables examined, The sieving coefficient of albumin was considerably reduced when gas-liquid two-phase cross-flow was used. These results were compared to those obtained with tubular membrane systems, and an additional mechanism, based on physical displacement of the concentration polarisation boundary layer is proposed, The operational difficulty related to protein foaming is also discussed.