Patent ID: 8728316

Claim:
A membrane filter unit applied to an activated sludge treatment method comprising an anaerobic tank and an aerobic tank, with a membrane filter unit immersed in the aerobic tank, to sequentially biologically treat wastewater to separate into activated sludge and treated water, the membrane filter unit comprising: a hollow fiber membrane module in which a plurality of sheet-like hollow fiber membrane elements, each element obtained by arranging a great number of porous hollow fiber membranes in parallel, are arrayed in parallel with the porous hollow fibers oriented in a vertical direction; and a minute bubble generating unit arranged below the hollow fiber membrane module for releasing minute bubbles toward a lower end of the module to generate a gas-liquid mixed flow vertically swirling between an inner space and an outer space of the hollow fiber membrane module when the membrane filter unit is applied to the activated sludge treatment method, wherein individual porous hollow fiber membranes within each hollow fiber membrane element are spaced apart from each other by a first area defining a narrow gap, a group of said porous hollow fiber membranes in each hollow fiber membrane element is spaced apart from adjoining group of said porous hollow fiber membranes in the same hollow fiber membrane element by second area that defines a wider gap than the narrow gap defined by the first area, a plurality of element groups are arranged in a parallel direction of the hollow fiber membrane module, wherein each element group comprises a plurality of spaced apart but adjacent hollow fiber membrane elements, and these element groups are spaced apart from each other at an interval that is wider than the spacing between individual hollow fiber membrane elements within an element group, and an interrupting member is arranged on a lower end entrance of the part of the intervals between the adjacent element groups for gas-liquid mixed flow, wherein the interrupting member sorts the gas-liquid mixed flow which flows upward from below the hollow fiber membrane module toward a lower surface of the hollow fiber membrane module to move toward an adjacent hollow fiber membrane element group.