An apparatus is disclosed for separating a suspension comprising at least two types of particles which are differently sized or shaped and in which the first type of particle may be deformable at a relatively lower force or faster rate than the second type of particle. A housing is provided having a generally cylindrical inner surface in which is mounted a rotor having a generally cylindrical outer surface. The outer surface of the rotor is spaced from the inner surface of the housing to define a suspension processing gap. A filter membrane is provided on the surface of the rotor or the housing that has pores with substantially precisely dimensioned shapes and sizes to correspond substantially to the shape of the first type of particle, thus allowing passage of the first type of particle and blocking passage of the second type of particle. A suspension is directed into the processing gap for either a selected residence time in contact with the filter membrane and/or at a selected force.