Patent ID: 8075776

Claim:
A process for withdrawing filtered permeate from a substrate comprising the steps of: providing a reservoir containing non-pressurized substrate; providing an assembly having, an upper solid body and a lower solid body, an upper face of the lower solid body being separated from a lower face of the upper solid body by a vertical distance; a plurality of hollow fiber filtering membranes disposed generally vertically between the solid bodies, the ends of the membranes secured in the solid bodies, the membranes sealed in the solid bodies in a manner that prevents non-pressurized substrate from contaminating the permeate, the membranes each having a length between the solid bodies at least 1.001 times the vertical distance but not longer than 1.05 times the vertical distance, the membranes secured in the solid bodies such that each of the membranes may move against one or more others of the membranes; an enclosure sealed to the upper solid body in a manner that the enclosure and the upper solid body define a cavity and prevent non-pressurized substrate from entering the cavity, the enclosure being immersible in the non-pressurized substrate; a permeate port in communication with the cavity; the lumen of each membrane in fluid communication with the port via the cavity; a structure having holes through an upper part and open to a bubble discharge zone near the lower solid body and walls extending downwards from the upper part below the lower solid body; and, applying a suction to lumens of the membranes via the permeate port to withdraw permeate from the non-pressurized substrate in the reservoir; directing a gas to flow into the structure and through the holes to provide bubbles in the non-pressurized substrate in the reservoir above the structure during the step of applying the suction; and, adding feed water to the reservoir so that the membranes are immersed in non-pressurized substrate in the reservoir during the step of applying the suction wherein the substrate comprises a biomass containing live and growing microorganisms and the gas consists essentially of air.