A. Ould-dris et al., Analysis of cake build-up and removal in cross-flow microfiltration of CaCO3 suspensions under varying conditions, J MEMBR SCI, 175(2), 2000, pp. 267-283
This paper investigates the effect of cyclic variations of transmembrane pr
essure (TMP), velocity and concentration on the particle cake formed on an
organic membrane during the microfiltration of CaCO3 suspension. The steady
-state permeate Bur was measured in a series of tests in which the TMP was
varied between 0.25 and 3 bar, the velocity was changed between 0.25 and 2
m/s and the particle concentration was successively raised and diluted betw
een 1 and 700 g/l. In these tests, the permeate flux was observed to exhibi
t an important hysteresis due to the irreversibility of the cake formed. Wh
en the change in operating conditions resulted in cake growth (TMP or conce
ntration increase, velocity decrease), the permeate flux was found to be go
verned simultaneously by the resistance of the cake layer and concentration
polarization with shear-induced diffusion. When the TMP or concentration w
ere reduced, the cake thickness remained constant because of particle cohes
ion. When the velocity was increased, the cake thickness also remained cons
tant until a critical velocity corresponding to the erosion shear stress fo
r the cake was reached. Above this critical velocity, the cake was progress
ively eroded, starting from the membrane outlet, and completely removed if
the velocity became high enough. This critical velocity decreased when the
concentration rose because the suspension viscosity and density increased.
The erosion shear stress was found to be a linear function of the normal st
ress on the cake surface. The main conclusion is that, when a cake has been
formed, the permeate Aux is governed not only by the present operating con
ditions but also by the previous ones. (C) 2000 Elsevier Science B.V. All r
ights reserved.