Membrane separation device and operation method for membrane separation device

A membrane separation device comprising a unit for feeding a stream-to-be-treated, and a separation membrane unit that comprises at least one separation membrane unit component comprising at least one separation membrane module comprising one or more separation membrane elements disposed in a cylindrical pressure vessel, and a feed stream side line F1, a feed stream side line F2, and a permeate stream line P that are connected to the separation membrane unit component, wherein a stream-to-be-treated fed is separated by separation membranes into a permeate stream and a concentrate stream, wherein in the separation membrane elements, a cladding is wrapped around the outer surface of a wound laminate formed by winding the separation membranes together with a channel spacer, wherein an anti-telescoping plate is attached to at least one end of the wound laminate and the cladding, wherein a stream-to-be-treated sealing material is disposed between the perimeter of at least one of the anti-telescoping plate and the inner wall of the cylindrical pressure vessel to allow movement of the separation membrane elements substantially in either direction within the cylindrical pressure vessel, wherein when the stream-to-be-treated is fed to the separation membrane unit component through one of the feed stream side lines F1 and F2, the separation membrane unit is configured to discharge the concentrate stream from the other of the feed stream side lines, and wherein the separation membrane unit comprises a mechanism that can change the flow direction so that the stream-to-be-treated is fed to the separation membrane unit component through either of the feed stream side lines F1 and F2.