A membrane distillation (MD) module includes a first MD sub-module including a first thermocouple; a second MD sub-module including a second thermocouple; and a distillation membrane sandwiched between the first MD sub-module and the second MD sub-module. A hot chamber of the first MD sub-module is closed by the distillation membrane, and a cold chamber of the second MD sub-module is closed by the distillation membrane.

A membrane separation system includes a membrane separation unit, a condensation unit, and a decompression unit. The condensation unit is disposed between the membrane separation unit and the decompression unit. The membrane separation unit has a pervaporation membrane. The pervaporation membrane separates a feed liquid containing a volatile organic compound and a gas into a permeated fluid and a non-permeated fluid. The condensation unit condenses the organic compound contained in the permeated fluid. The decompression unit decompresses an inside of a permeation space of the membrane separation unit. An operating condition of the decompression unit is controlled in such a manner that a pressure in the permeation space of the membrane separation unit has, during operation, a value larger than a minimum value of a pressure that the inside of the permeation space of the membrane separation unit can reach during rated operation of the decompression unit.

A method for purifying a liquid is described. A liquid feed is fed to a feed chamber. A carrier gas is fed through the liquid feed in the feed chamber to form a humidified carrier gas. A coolant is fed to a coolant chamber. The coolant chamber is separated from the feed chamber by a permeate gap chamber. The permeate gap chamber is separated from the feed chamber by a membrane that allows vapor to pass while blocking liquid flow across the membrane. The coolant chamber is separated from the permeate gap chamber by a thermally conductive plate. At least a portion of the vapor from the feed chamber that transported through the membrane is condensed by the coolant in the coolant chamber and the thermally conductive plate to form a first distillate. At least a portion of the humidified carrier gas is condensed to form a second distillate.