Abstract: Stack assembly comprising a hollow external housing having a central axis, the external housing extending from a first end to a second end and enclosing a housing space, and a membrane stack comprising a plurality of membranes, wherein the membrane slack is positionable inside the external housing and a number of side plates extending substantially parallel to the central axis, wherein each side plate of the number of side plates is associated with a side of the membrane stack and extending along the associated side and a number of sealing connectors that extend substantially parallel to the central axis and adjacent with an inner surface of the external housing, wherein each sealing connector of the number of sealing connectors is configured to connect two side plates to each other, wherein the sealing connectors and the side plates cooperate to form an enclosing structure, and wherein, in use of the stack assembly, the enclosing structure encloses the membrane stack.