Patent ID: 8728314

Claim:
A membrane module that is immersed in a liquid to be treated and performs filtration, comprising: a pair of water collecting cases; and at least one membrane element provided between the pair of water collecting cases, wherein water collecting spaces in which permeate having permeated through the membrane element is collected are formed in the water collecting cases, the water collecting cases can be coupled via coupling portions to water collecting cases of another membrane module adjacent to the membrane module in a predetermined arrangement direction, the coupling portions including tubular members having fitting holes, fitting projections that can be detachably fit into fitting holes in the predetermined arrangement direction, flow holes formed on the fitting projections, and holding mechanisms for holding the fitting projections to be displaceable within a predetermined range in a direction orthogonal to the predetermined arrangement direction are provided on end surfaces in the predetermined arrangement direction of the water collecting cases, the water collecting spaces communicate with water collecting spaces of the water collecting cases of the other membrane module via the flow holes of the coupling portions, the holding mechanisms include tubular circumferential wall portions provided in the water collecting cases, holding grooves and inserting grooves formed in the circumferential wall portions, annular brim portions provided in the fitting projections and projected to an outer side in the radial direction, and holding pawls provided in outer circumferential portions of the annular brim portions, the inserting grooves are formed in the predetermined arrangement direction, the holding grooves are formed in a circumferential direction and communicate with lower end portions of the inserting grooves, the fitting projections are inserted into inner sides of the circumferential wall portions, by insertion of the holding pawls from the inserting grooves to the holding grooves, the fitting projections are restrained in the predetermined arrangement direction, a seal members directly contact the annular brim portions of the fitting projections and the water collecting cases while being provided between the water collecting cases and the annular brim portions of the fitting projections in the predetermined arrangement direction and thereby water tightness is maintained, the outer diameters of the annular brim portion are set smaller than the inner diameters of the circumferential wall portions, the fitting projections are displaceable to the direction orthogonal to the predetermined arrangement direction to the circumferential wall portions by means of the annular brim portions sliding in a plane orthogonal to the predetermined arrangement direction via the seal members, and displacement amounts of the fitting projections are regulated to a range obtained by subtracting the outer diameter of the annular brim portions from the inner diameter of the circumferential wall portions.