Stability of latex crossflow filtration:: cake properties and critical conditions of deposition

The critical permeation flux is the flux at which cake deposition starts to be detectable. The variations of the critical flux (determined simultaneously by a mass balance and successive variations of transmembrane pressures) during sub-micron latex particles filtration were studied under various operating conditions (membrane pore diameter, shear stress at the membrane surface, latex concentration, surfactant content). These variations were explained taking into account the properties of the suspension and of the fouling deposit (reversibility, specific resistance, thickness, porosity) formed beyond the critical threshold. It was shown that the critical parameter, J(crit)/tau(w), which defines the conditions required for stable filtration performance was more appropriate than DeltaP(crit)/tau(w), previously suggested in the literature since J(crit) was actually independent of the clean hydraulic resistance of the membrane, and consequently of the membrane pore size. This indicates that there is no need to work with the largest pore size membrane: larger pores will not induce higher critical flux and will not improve the area of the stability zone of the filtration. This work also points out the major impact of surfactants on fouling phenomena and J(crit), observations rarely reported in the literature: the higher the surfactant content, the higher the deposited mass and the lower J(crit). (C) 2002 Elsevier Science B.V. All rights reserved.