Water purifier and water purification method

1. A water purifier, comprising:

a diluting unit configured to bring targeted water for purification into contact with an aqueous solution containing a volatile solute and a polymer via a semi-permeable membrane so as to separate water from the targeted water by the semi-permeable membrane, and configured to dilute the aqueous solution with the separated water;

a separating unit configured to separate the volatile solute and the polymer from the diluted aqueous solution obtained by the diluting unit so as to obtain purified water; and

a dissolving unit configured to return the volatile solute separated by the separating unit to an aqueous solution containing the separated polymer, and to allow the separated volatile solute to dissolve in the aqueous solution containing the polymer;

wherein the volatile solute is either volatile anions or volatile cations;

wherein the volatile solute is volatile cations when the polymer is an anionic polymer; and

wherein the volatile solute is volatile anions when the polymer is a cationic polymer.

2. The water purifier according to claim 1 , wherein the separating unit contains a first separating unit configured to separate the diluted aqueous solution into an aqueous solution containing the volatile solute and an aqueous solution containing the polymer, and a second separating unit configured to separate the volatile solute from the aqueous solution containing the volatile solute.

3. The water purifier according to claim 2 , wherein the first separating unit is an ultrafiltration membrane.

4. The water purifier according to claim 1 , wherein the volatile solute is carbon dioxide, carbonic acid, or ammonium.

5. The water purifier according to claim 1 , wherein the polymer has a weight average molecular weight of 5,000 to 250,000.

6. The water purifier according to claim 1 , wherein the polymer has a weight average molecular weight of 5,000 to 130,000.

7. The water purifier according to claim 1 , wherein the polymer has a ratio of a molecular weight of a repeat unit therein to electric charge therein ranging from 58 to 1,000.

8. The water purifier according to claim 1 , wherein the dissolving unit is a gas absorber.

9. The water purifier according to claim 1 , wherein the semi-permeable membrane is a forward osmosis semi-permeable membrane which selectively passes water through.

10. The water purifier according to claim 1 , wherein the targeted water is sea-water.

11. A water purification method, comprising:

bringing targeted water for purification into contact with an aqueous solution containing a volatile solute and a polymer via a semi-permeable membrane so as to separate water from the targeted water by the semi-permeable membrane, and diluting the aqueous solution containing the volatile solute and the polymer with the separated water;

separating the volatile solute and the polymer from the diluted aqueous solution so as to obtain purified water; and

returning the separated volatile solute to an aqueous solution containing the separated polymer, and allowing the separated volatile solute to dissolve in the aqueous solution containing the polymer;

wherein the volatile solute is either volatile anions or volatile cations;

wherein the volatile solute is volatile cations when the polymer is an anionic polymer; and

wherein the volatile solute is volatile anions when the polymer is a cationic polymer.