Among MD processes, variations exist as to the method by which the vapor is recovered once it has migrated through the membrane. MD systems can be configured in a number of ways, depending on the nature of the cold side of the membrane. But DCMD in which the membrane is in direct contact with the feed on one side and permeate on the other, and air gap
MD (AGMD) in which an air gap is interposed between the membrane and a cold condensation surface are perhaps most appropriate for desalination applications. Other configurations, such as vacuum MD (VMD) and sweeping gas MD (SGMD) methods, are typically used for stripping of volatile organics or dissolved gases. These alternatives are shown in Fig. 3.
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