The behavior of suspensions and macromolecular solutions in crossflow microfiltration

Although microfiltration is one of the oldest pressure-driven membrane processes, it is probably the least understood when it comes to the filtration of suspensions and macromolecules. Microfiltration is characterized by operation at low pressures, by high permeation fluxes, and by crossflow mode in flat or cylindrical geometries. The major limitation of microfiltration is membrane fouling due to the deposition and intrusion of macromolecules, colloids and particles onto and into the microporous membrane. In this review, we analyze the various components of this problem by focusing on the formation of cakes, the behavior of suspension flows and particle transport in simple geometry ducts, and on the formation and behavior of fouling layers including those resulting from macromolecules, colloids and particles. Some of the work we report on is very recent or is still in progress and needs independent verification. With this understanding, we hope that the reader will be able to use these concepts for analyzing other systems and for investigating new module designs.