Regenerable draw solute for osmotically driven processes

A method of forward osmosis comprising:

• (a) introducing a first solution having a first temperature on a first side of a semi-permeable membrane and a concentrated draw solution comprising an inorganic salt having a second temperature on a second side of the semi-permeable membrane;
• (b) promoting flow of at least a portion of the first solution across the semi-permeable membrane to form a second solution on the first side of the semi-permeable membrane and a dilute draw solution on the second side of the semi-permeable membrane;
• (c) introducing at least a portion of the dilute draw solution to a first separation operation at a third temperature to recover a hydrate of the inorganic salt and a solution stream;
• (d) heating the hydrate of the inorganic salt to a fourth temperature to regenerate the concentrated draw solution;
• and
• (e) reintroducing the concentrated draw solution to the second side of the semi-permeable membrane,
• wherein:
• the inorganic salt is selected from one or more of the group selected from sodium sulfate, calcium lactate, disodium phosphate, tetrasodium pyrophosphate, and hydrates thereof;
• the first temperature and the second temperature are greater than the third temperature;
• when the solution stream comprises the inorganic salt, the solution stream is subjected to a further separation operation to provide a solvent stream and a hydrate of the inorganic salt;
• and
• the further separation operation is an organic solvent-assisted extractive crystallisation to provide the hydrate of the inorganic salt and solvent mixture that is yet further separated to provide an organic solvent and the solvent stream.