Patent ID: 8480886

Claim:
A multistage immersion type membrane separator in which an air diffuser is disposed under a filtration part immersed in a treatment tank, the filtration part having a plurality of plate-like membrane cartridges arranged in a vertically parallel multistage fashion and spaced at intervals for forming a cross flow passage of a predetermined width; the plate-like membrane cartridges have a filter supporting plate having rigidity on which a permeated water passage is formed, and a permeated water outlet disposed at an upper portion on one side end surface of the filter supporting plate such that it is communicated to the permeated water passage and connected to a collecting means; and the air diffuser has a diffuser tube disposed sidewardly that has plural blowholes, a flushing pipe that has at its tip an opening serving as an outlet above the diffuser tube, and a flushing valve disposed in the flushing pipe wherein the diffuser tube is communicated at its basal end to an air supply source and at its front-end to the flushing pipe, a control means communicating with said flushing valve and said air supply source, and configured such that the flushing valve is opened while supplying air to the diffuser tube, thereby to cause the air supplied to the diffuser tube to pass through the flushing to be exhausted; a mixed liquor inside a treatment tank is caused to flow backward from the blowholes into the diffuser tube; the flowed mixed liquor is caused to be exhausted after passing through the flushing pipe together with the air as an air-liquid mixed flow, said flushing pipe exhaust depositing the air and liquid stream into the atmosphere above the liquid surface of the treatment tank, said flushing pipe tip including a liquid air separator comprising: a cylindrical outlet tube having a outlet tube diameter, and an inlet pipe have an inlet pipe diameter of less than said outlet tube diameter, said inlet pipe being attached to and in communication with said outlet tube so that a mixed flow of air and liquid passing through the inlet tube is introduced into the outlet tube and flows circumferentially around the inside of said outlet tube.