Water treatment method and water treatment apparatus

Abstract

The present invention provides a water treatment method and water treatment apparatus that can reduce the amount of iodide used while suppressing oxidative degradation of reverse osmosis membranes. [Solution] A water treatment method comprising: a reverse osmosis membrane treatment step in which a reverse osmosis membrane feedwater to which an oxidizing agent containing at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent and a slime-suppressing aid containing iodide has been added is passed through a reverse osmosis membrane to obtain concentrated water and permeate water; and a circulation step in which a part or all of the concentrated water in the reverse osmosis membrane is circulated as circulating water to the stage preceding the reverse osmosis membrane treatment step.

Claims

1. A reverse osmosis membrane treatment step involves passing water supplied to a reverse osmosis membrane, to which an oxidizing agent containing at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent and a slime-suppressing aid containing iodide are added, through a reverse osmosis membrane to obtain concentrated water and permeate. A circulation step in which a portion or all of the concentrated water from the reverse osmosis membrane is circulated as circulating water to the stage preceding the reverse osmosis membrane treatment step, A water treatment method characterized by including [a certain component].

2. A water treatment method according to claim 1, A water treatment method characterized by the presence of the oxidizing agent and the slime-suppressing aid in the reverse osmosis membrane feedwater such that the free chlorine concentration of the permeate from the reverse osmosis membrane is less than 0.1 mg-Cl / L.

3. A water treatment method according to claim 1, A water treatment method characterized by adding the slime-suppressing aid to the reverse osmosis membrane feedwater so that the amount of iodide ions in the reverse osmosis membrane feedwater is in the range of 1 to 10 mol per 1 mol of free chlorine or free bromine, based on the concentration of iodide in the circulating water system.

4. A water treatment method according to claim 1, A water treatment method characterized by providing the oxidizing agent and the slime-suppressing aid to the reverse osmosis membrane feedwater such that, based on the residual chlorine concentration in the circulating water or the reverse osmosis membrane feedwater after the circulating water has merged, the amount of iodide ions is in the range of 1 to 10 mol per 1 mol of free chlorine or free bromine, and the CT value is in the range of 0.1 mg-Cl / L·min or more and 20 mg-Cl / L·min or less.

5. A water treatment method according to claim 4, A water treatment method characterized by adjusting the addition time of the slime-suppressing aid after the start of adding the oxidizing agent and the slime-suppressing aid so that the addition time of the slime-suppressing aid is 1 / 2 or more of the addition time of the oxidizing agent from the start of addition.

6. A water treatment method according to claim 1, A water treatment method characterized in that the point at which the oxidizing agent and slime-suppressing agent are added to the reverse osmosis membrane water supply is downstream of the destination of the circulating water in the circulation process.

7. A water treatment method according to claim 1, A water treatment method comprising at least one of an electrodeionization process and an ion exchange resin process in the subsequent steps of the reverse osmosis membrane treatment process, characterized in that when the oxidizing agent and the slime suppression aid are added to the reverse osmosis membrane water supply, the concentrated water and permeate from the reverse osmosis membrane are blown out or recirculated to the preceding steps of the reverse osmosis membrane treatment process.

8. An oxidizing agent adding means for adding an oxidizing agent containing at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent to reverse osmosis membrane water supply, A slime-suppressing agent adding means for adding a slime-suppressing agent containing iodide to the reverse osmosis membrane water supply, A reverse osmosis membrane treatment means for obtaining concentrated water and permeate by passing the reverse osmosis membrane water to which the oxidizing agent and the slime-suppressing aid have been added through a reverse osmosis membrane, A circulation means that circulates a portion or all of the concentrated water from the reverse osmosis membrane as circulating water to the stage preceding the reverse osmosis membrane treatment process, A water treatment apparatus characterized by comprising the following features.

9. A water treatment apparatus according to claim 8, A water treatment apparatus characterized by comprising an adjustment means for adjusting the amount of the oxidizing agent and the slime-suppressing aid added to the reverse osmosis membrane water supply so that the free chlorine concentration of the permeate from the reverse osmosis membrane is less than 0.1 mg-Cl / L.

10. A water treatment apparatus according to claim 8, A water treatment apparatus characterized by comprising an adjustment means for adjusting the amount of slime suppression aid added to the reverse osmosis membrane water supply, based on the concentration of iodide in the circulating water system, such that the amount of iodide ions in the reverse osmosis membrane water supply is in the range of 1 to 10 mol per 1 mol of free chlorine or free bromine.

11. A water treatment apparatus according to claim 8, A water treatment apparatus comprising an adjustment means for adjusting the amount of oxidizing agent and slime-suppressing aid added to the reverse osmosis membrane feedwater, based on the residual chlorine concentration in the circulating water or the reverse osmosis membrane feedwater after the circulating water has been combined with it, such that the amount of iodide ions is in the range of 1 to 10 mol per 1 mol of free chlorine or free bromine, and the CT value is in the range of 0.1 mg-Cl / L·min or more and 20 mg-Cl / L·min or less.

12. A water treatment apparatus according to claim 11, A water treatment apparatus characterized by comprising an adjustment means for adjusting the addition time of the slime-suppressing aid so that, after the start of addition of the oxidizing agent and the slime-suppressing aid, the addition time of the slime-suppressing aid is 1 / 2 or more of the addition time from the start of addition of the oxidizing agent.

13. A water treatment apparatus according to claim 8, A water treatment apparatus characterized in that the point at which the oxidizing agent and slime-suppressing agent are added to the reverse osmosis membrane water supply by the oxidizing agent adding means and the slime-suppressing agent adding means is downstream of the destination of the circulating water by the circulation means.

14. A water treatment apparatus according to claim 8, A water treatment apparatus comprising at least one electrodeionizing apparatus and an ion exchange resin apparatus downstream of the reverse osmosis membrane treatment means, characterized in that when the oxidizing agent and the slime suppression aid are added to the reverse osmosis membrane feedwater, the concentrated water and permeate from the reverse osmosis membrane are blown or circulated upstream of the reverse osmosis membrane treatment process.

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