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We assessed the potentiality of reducing concentration polarization and enhancing ultrafiltration of macromolecules via gas sparging (gas bubbles supplied to the UF system with the feed solution). Consideration was given to the problem of how the quantity of the gas sparged and the duration of the process affect the transport and separation properties of hollow-fibre UF modules. Ultrafiltration tests were carried out with model solutions containing macroparticles either organic (dye) or mineral (kaolin). Gas sparging was found to increase the permeability of the module by approximately 25%, but there was a slight deterioration of selectivity. The rate of gas flow seems to be of negligible importance.

1. The entrainment of a gas bubbles in the feed solution may reduce the concentration polarization effect, thus increasing the efficiency of macroparticle separation from aqueous solutions in the UF process. 2. The increase of permeate volume flux due to gas sparging is smaller than was anticipated (in the experiments it ranged between 15% and 25%, the effect of the gas flow rate being negligible). 3. The application of the gas–liquid twophase flow slightly deteriorates the separation efficiency of the hollow-fibre module. This adverse effect becomes more pronounced when the gas flow rate increases. The separation of particles (dye, kaolin) by UF, which are retained almost completely (100%), seems to be only slightly affected by the increased gas flow rate. 4. The entrainment of gas bubbles into the UF system increases the stability of UF module operation.