An apparatus and method are disclosed for filtering or separating particles. The apparatus has a centrifuge rotor rotatable about an axis of rotation. A fluid chamber rotates with the rotor. A substance is supplied to the inlet of the chamber. A saturated fluidized bed of first particles forms within the fluid chamber and obstructs flow of second particles through the chamber. Additive substances alter sedimentation velocity of the first particles to modify the filtration characteristics of the saturated fluidized bed.