There is provided a membrane module comprising a membrane package comprising at least two membrane sleeves, wherein the membrane package is configured to allow essentially free flow of a first stream inside the sleeves and essentially free flow of a second stream between each two adjacent sleeves, and a frame, configured to support the membrane package, such that part of each of four surfaces of the membrane package is affixed to predetermined areas in the frame, forming a module having separate spaces configured to facilitate separate flows of the first stream and the second stream through the membrane package. The invention further provides a multi-modular stack, comprising at least two membrane modules and at least one membrane, wherein the first stream is fully enclosed inside each module and the second stream flows through all the modules.