Local permeate flux-sheer-pressure relationships in a rotating disk microfiltration module: implications for global performance

This paper investigates first the performance of a rotating disk microfiltration system, described by the mean permeate flux as a function of particle concentration, disk rotation speed and peripheral transmembrane pressure (TMP), using suspensions of calcium carbonate particles. The second part presents the radial distribution of permeate flux and filtration resistance obtained by using concentric membrane rings and their relationship with local shear stress and TMP. Our data confirm that high shear stresses induced by the disk rotation prevent the formation of a cake on the membrane except in the central part at low speed. Consequently, this system is capable of maintaining high permeate fluxes (200 l h(-1) m(-2)) at large particle concentrations (700 kg m(-3)). At speeds above 1100 rpm, the permeate flux increases with radius above 4 cm and fouling disappears almost completely in the peripheral zone. The local flux in the central zone reaches a plateau when TMP is increased above 35 kPa, while it keeps increasing with pressure in other zones. The filtration resistance was found to increase linearly with local TMP in all zones, but at a lesser rate in peripheral ones. Fouling irreversibility was observed when reducing rotation speed, especially at high TMP. We conclude that this system is very efficient in case of external fouling when used at disk tip velocities above 12 m s(-1). (C) 2000 Elsevier Science B.V. All rights reserved.