A fluidized membrane bioreactor comprising a bioreactor including biochemically active organisms; fluidized particles which is a support media to be attached by the organisms; and membranes which permit treated water to pass through except the organisms, wherein the fluidized particles are in direct contact with the membranes. The membranes are installed internally or externally to the bioreactor. The particles may be granular activated carbon or other suitable materials. The fluidized particles serve not only as support media for microorganisms, but also as media for sorption or otherwise retention of matter that can cause membrane fouling and as an abrasive material for cleaning the membrane surface.