Patent ID: 8741141

Claim:
A membrane separator comprising: a plurality of vertically-stacked membrane modules, each of the membrane modules includes a plurality of membrane elements arranged in parallel and along a vertical direction of the membrane separator; channels for a liquid to be treated formed in the vertical direction of the membrane separator between the membrane elements; and a water collecting case which keeps water-tight both sides of the membrane elements along the channels for the liquid to be treated, and has therein a water collecting space with which permeate channels of the membrane elements communicate, wherein the water collecting case having an outer wall that surrounds the water collecting space and that forms a channel that extends along the flowing direction of the liquid to be treated, a portion of the outer wall opposed to side ends of the membrane elements via the water collecting space being contoured to form a projecting portion projecting to an outer side and a recessed portion recessed to an inner side, wherein both the projecting portion and the recessed portion extend from a lower end of the water collecting case to an upper end of the water case and wherein a cross-sectional shape of the channel of the water collecting space corresponds to the contours of the projecting portion and the recessed portion in a transverse section of the water collecting case.