Apparatus and method for liquid treatment by forward osmosis

A method of recovering draw agent utilised in a forward osmosis membrane cell used for desalination or water purification, the method comprising the steps of:

• passing diluted draw agent to a vapour-liquid separator;
• using the vapour-liquid separator to separate the diluted draw agent into draw agent vapour and solvent;
• and
• condensing the draw agent vapour, thereby recovering the draw agent as a liquid,
• wherein the method utilizes the forward osmosis membrane cell, in which cell a membrane separates a feed solution side and a draw solution side, a draw solution exit line providing a fluid connection between the draw solution side of the membrane and a feed line for the vapour-liquid separator, a fluid connection for recirculating the draw agent separated by the vapour-liquid separator to an entry line of the draw solution side of the membrane cell, and wherein the draw solution side, the vapour liquid separator, the draw solution exit line, the feed line, the fluid connection and the entry line together form a draw solution fluid circuit,
• whereby a pressure of the draw solution fluid circuit is elevated to and maintained at greater than atmospheric pressure so that the draw agent vapour is condensed to thereby recover the draw agent as a liquid;
• and
• whereby the method does not use a compressor for compressing draw agent in a gas phase.