Abstract: An apparatus for separating a feed liquid into a concentrate and a permeate fraction by membrane filtration comprises an array of cassette frames (1-5) separated by intermediate plates (10). The array is adapted to be clamped together in its longitudinal direction and loosened, as required, to remove any selected cassette frame. Each cassette frame (1-5) contains a filtration unit (6) comprising a stack of membranes, in which a first flow passage system is provided which connects two free zones (7,8) within the cassette frame, said free zones being so connected as to establish a series or parallel or combined series and parallel flow from a feed liquid inlet (25) to a concentrate outlet (25). In each stack of membranes a second system of flow passages is also provided, which is isolated from said first system and serves to conduct permeate penetrated through the membranes to at least one separate outlet (9) from each filtration unit (6).

Abstract: In the method of making a filtration unit, envelope-shaped membrane units (62) are placed in a stack, a curable liquid binder (101) is introduced between the membrane units from at least one surface of the filtration unit to a predetermined depth (a), and upon curing of the binder a layer of the binder together with the marginal portions of the edges of the membrane units embedded therein is removed, such as by surface cutting or machining, up to a depth (b) smaller than the depth (a).