Water treatment apparatus, water treatment method, and method of starting water treatment apparatus

A water treatment method comprising:

• allowing a diluted draw solution to flow out, the diluted draw solution being obtained by causing water to move to a draw solution having a cloud point from a water-containing solution containing water as a solvent via a semipermeable membrane to dilute the draw solution, and discharge the water-containing solution as a concentrated water-containing solution that is concentrated;
• heating the diluted draw solution to a temperature equal to or higher than the cloud point;
• separating the heated diluted draw solution into a water-rich solution and the draw solution having water content lower than that of the water-rich solution;
• cooling a liquid to generate a coolant;
• performing heat exchange between the coolant and the draw solution having water content lower than that of the water-rich solution;
• and
• performing heat exchange between the diluted draw solution and the water-rich solution.

A method of starting a water treatment apparatus, the water treatment apparatus including:

• a forward osmosis device configured to allow a diluted draw solution to flow out, the diluted draw solution being obtained by causing water to move to a draw solution having a cloud point from a water-containing solution containing water as a solvent via a semipermeable membrane to dilute the draw solution, and configured to discharge the water-containing solution as a concentrated water-containing solution that is concentrated;
• a heater configured to heat the diluted draw solution to a temperature equal to or higher than the cloud point;
• a water separator configured to separate the diluted draw solution heated by the heater into a water-rich solution and the draw solution having water content lower than that of the water-rich solution;
• a cooler configured to cool a liquid and allow the liquid to flow out as a coolant;
• an inflow side heat exchanger configured to perform heat exchange between the coolant flowed out from the cooler and the draw solution flowed out from the water separator;
• and
• an outflow side heat exchanger configured to perform heat exchange between the diluted draw solution flowed out from the forward osmosis device and the water-rich solution flowed out from the water separator,
• the method comprising:
• supplying the draw solution stored in the water separator to the heater to be heated to a temperature equal to or higher than the cloud point through a circulation flow passage that causes a downstream side of the water separator and an upstream side of the forward osmosis device along a flowing direction of the draw solution to communicate with an upstream side of the heater and a downstream side of the forward osmosis device along a flowing direction of the diluted draw solution.