Patent ID: 8496825

Claim:
A spiral wound module comprising: a permeate collection tube, at least one membrane envelope wound about collection tube and defining a first and second scroll face, wherein the membrane envelope comprises a section of membrane sheet having an active membrane area, a length corresponding to the distance between the first and second scroll faces, a width extending in a direction perpendicular to the length, at least one longitudinal axis extending along the length of the sheet and dividing the sheet into an inner and outer region with the inner region located adjacent to the permeate collection tube, and at least one latitudinal axis extending along the width of the sheet and dividing the sheet into an inlet and outlet region with the inlet region located adjacent to the first scroll face, wherein the membrane sheet comprises a semi-permeable membrane layer and a support layer, and wherein in the spiral wound module is characterized by the membrane sheets being prepared such that the active membrane area of the membrane sheet has an average water permeability or average solute permeability that varies by at least 10% between at least one of: i) the inner and outer regions and ii) the inlet and outlet regions.