Patent ID: 7534353

Claim:
A process for withdrawing filtered permeate from activated sludge at ambient pressure comprising the steps of: providing a tank; providing an assembly in the tank, the 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 the activated sludge at ambient pressure 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 the activated sludge at ambient pressure from entering the cavity, the enclosure being immersible in the activated sludge at ambient pressure; a permeate port in communication with the cavity; and, the lumen of each membrane in fluid communication with the port via the cavity; feeding activated sludge into the tank to immerse the membranes in the activated sludge at ambient pressure; applying a suction to lumens of the membranes via the permeate port to withdraw permeate at an essentially constant flux from the activated sludge at ambient pressure in the tank; blowing air into the activated sludge at ambient pressure to provide bubbles in the activated sludge at ambient pressure in the tank which bubbles contact the membranes as the bubbles rise through the activated sludge at ambient pressure; and, withdrawing retentate sludge from the tank wherein the steps of blowing air and withdrawing the retentate sludge occur during the step of applying the suction.