Water treatment methods

Abstract

To enable operation of an electric type deionized water production apparatus (EDI apparatus) without causing degradation of treatment water quality in the EDI apparatus and elevation of water passing differential pressure in a water treatment device of the EDI apparatus.SOLUTION: An EDI apparatus 10 in which at least a part of ion exchangers filled in a desalting chamber 23 is an anion exchanger is employed, and water to be treated added with iodine-containing oxidant as slime inhibitor is supplied to the EDI apparatus 10. The iodine-containing oxidant is, e.g., a solution obtained by dissolving iodine and iodide in water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water treatment method using an electric deionized water production device. In the law It relates thereto.

Background Art

[0002] As one of the devices for generating deionized water from treated water, there is an electric deionized water production device (also referred to as an EDI (Electro Deionization) device. Hereinafter, the electric deionized water production device will also be referred to as an EDI device). The EDI device is a device that combines electrophoresis and electrodialysis, and has a configuration in which a desalination chamber partitioned by a pair of ion exchange membranes is arranged between an anode and a cathode. In the EDI device, at least the desalination chamber is filled with an ion exchanger such as an ion exchange resin, a DC voltage is applied between the anode and the cathode, and the treated water is passed through the desalination chamber, whereby the treated water from which the ion components have been removed flows out of the desalination chamber and the regeneration treatment of the ion exchanger in the desalination chamber proceeds. The EDI device has the advantage of eliminating the need for the treatment of regenerating the ion exchanger with chemicals. In the EDI device, a concentration chamber is adjacent to the desalination chamber across the ion exchange membrane partitioning the desalination chamber. However, in the concentration chamber, the ion concentration tends to increase due to the ion components that have moved from the desalination chamber, and slime derived from live bacteria is likely to occur. When slime occurs, the water flow is inhibited, so the water passing differential pressure tends to increase (see, for example, Patent Document 1).

[0003] In general, to suppress slime formation in water treatment equipment, one method is to add a slime inhibitor (also called a slime control agent) to the water supplied to the equipment. Slime inhibitors are composed of, for example, hypochlorous acid, hydrogen peroxide, and ozone, which have bactericidal properties. However, hypochlorous acid, hydrogen peroxide, and ozone are oxidizing agents, and when these oxidizing agents flow into an EDI device, as described in Patent Documents 1 and 2, the ion exchange resins and ion exchange membranes that make up the EDI device deteriorate, which can lead to a rapid decrease in the quality of the treated water and an increase in the differential pressure of the water flow in the concentration chamber and desalination chamber. Patent Document 1 discloses that the deterioration of the EDI device by oxidizing agents proceeds more rapidly when a direct current is applied between the anode and cathode of the EDI device, and therefore, when water containing an oxidizing disinfectant is flowing through the EDI device to remove slime, the voltage application between the anode and cathode should be stopped or weakened. Patent Document 3 discloses that when the water pressure difference increases due to slime generation in an EDI device, a cleaning treatment is performed using a chemical agent containing hydrazine monohydrate and alkali to remove the slime.

[0004] Similar to EDI devices, reverse osmosis membrane devices equipped with reverse osmosis membranes are also susceptible to slime formation, but membranes such as reverse osmosis membranes also deteriorate upon contact with oxidizing agents. As slime inhibitors that can suppress the deterioration of reverse osmosis membranes, Patent Document 4 discloses the use of a stabilized hypobromous acid composition, and Patent Document 5 discloses the use of an iodine-based oxidizing agent containing water, iodine, and iodide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-51453 [Patent Document 2] Japanese Patent Publication No. 2000-279967 [Patent Document 3] Japanese Patent Publication No. 2004-113973 [Patent Document 4] Japanese Patent Publication No. 2015-62889 [Patent Document 5] International Publication No. 2021 / 192582 [Overview of the project] [Problems that the invention aims to solve]

[0006] When removing slime generated in the concentration chamber of an EDI device by chemical cleaning as described in Patent Document 3, the cleaning process itself takes a long time (for example, several days), which presents the problem that the EDI device cannot be used during that time. In addition, the chemical solution does not flow easily into spaces blocked by slime, and as a result, it is difficult to completely remove the slime from those spaces. When water containing a slime inhibitor, which is an oxidizing agent, is passed through the EDI device, blockage by slime can be prevented, but when a slime inhibitor is supplied to the EDI device as described in Patent Document 1, the voltage applied to the EDI device must be stopped or reduced, and during that time, desalination treatment of the water to be treated cannot be performed in the EDI device.

[0007] The objective of the present invention is a water treatment method using an EDI device. by law A water treatment method that allows the EDI device to operate without causing a decrease in treated water quality or an increase in differential water pressure in the EDI device. Law The purpose is to provide. [Means for solving the problem]

[0009] The present invention relates to a water treatment method comprising: an addition step of adding chemicals to the water to be treated to obtain water containing iodine and possessing oxidizing power; and supplying the water that has undergone the addition step to an EDI device (electrodeionized water production device) for treatment in the EDI device. and obtain treated water It has a processing step, The chemical is a solution containing water, iodine, and iodide. In the treatment process, the iodine concentration in the treated water supplied to the electrolytic deionized water production device is 0.01 mg / L as Cl, converted to a total chlorine concentration. 2 More than 10.0 mg / L as Cl 2 It is less than, Electric deionized water production device The ion exchanger is packed in Desalination room It is divided into a first small desalination chamber and a second small desalination chamber by an intermediate ion exchange membrane, and the first small desalination chamber contains Anion exchanger The container is filled with a special material, and in the processing step, the water to be treated is supplied to the first small desalination chamber, the water from the first small desalination chamber is supplied to the second small desalination chamber, and the water from the second small desalination chamber is treated water. That is 。 [Effects of the Invention]

[0013] According to the present invention, it becomes possible to operate the EDI device without causing a decrease in the treated water quality and an increase in the flow-through differential pressure in the EDI device.

Brief Description of the Drawings

[0014] [Figure 1] It is a diagram showing a water treatment device according to an embodiment of the present invention. [Figure 2] It is a diagram showing an example of the configuration of an EDI device. [Figure 3] It is a diagram showing another configuration example of the water treatment device. [Figure 4] It is a diagram showing yet another configuration example of the water treatment device. [Figure 5] It is a diagram showing another example of the configuration of an EDI device. [Figure 6] It is a graph showing the change in the specific resistance of the treated water in Example 1. [Figure 7] It is a graph showing the change in the flow-through differential pressure in the desalination chamber in Example 1. [Figure 8] It is a graph showing the change in the flow-through differential pressure in the concentration chamber in Example 1. [Figure 9] It is a graph showing the change in the iodine concentration in the concentrated water in Example 3.

Embodiments for Carrying Out the Invention

[0015] Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of a water treatment device according to an embodiment of the present invention. The water treatment device shown in FIG. 1 includes an electro-deionization water production device (EDI device) 10, and raw water to be treated is passed through the EDI device 10. The EDI device 10 performs, for example, desalination treatment on the supplied raw water to be treated and discharges the treated water. Further, the water treatment device includes a mechanism for adding an iodine-containing oxidant as a slime inhibitor to the raw water to be treated supplied to the EDI device 10. Details of the iodine-containing oxidant used as the slime inhibitor will be described later.

[0016] Figure 2 shows an example of the configuration of the EDI device 10. The EDI device 10 includes a desalination chamber 23 between an anode chamber 21 having an anode 11 and a cathode chamber 25 having a cathode 12. A concentration chamber 22 is arranged on the anode chamber 21 side of the desalination chamber 23, and a concentration chamber 24 is arranged on the cathode chamber 25 side of the desalination chamber 23. The anode chamber 21 and the concentration chamber 22 are partitioned by a cation exchange membrane 31, and the concentration chamber 22 and the desalination chamber 23 are partitioned by an anion exchange membrane 32. The desalination chamber 23 and the concentration chamber 24 are partitioned by a cation exchange membrane 33, and the concentration chamber 24 and the cathode chamber 25 are partitioned by an anion exchange membrane 34. Eventually, the desalination chamber 23 is partitioned by the anion exchange membrane 32 located on the anode 11 side and the cation exchange membrane 33 located on the cathode 12 side. The desalination chamber 23 is filled with ion exchange resin. In the illustrated example, an anion exchange resin (AER) and a cation exchange resin (CER) are filled in a mixed bed form (MB). Also, the anode chamber 21 is filled with a cation exchange resin, and the concentration chambers 22, 24 and the cathode chamber 25 are filled with an anion exchange resin. The concentration chambers 22, 24 may be filled with an anion exchange resin (AER) and a cation exchange resin (CER) in a mixed bed form.

[0017] Next, the operation of the water treatment device shown in FIG. 1 will be described. Feed water is passed through the anode chamber 21, the concentration chambers 22, 24 and the cathode chamber 25 of the EDI device 10 respectively, and in a state where a direct current is applied between the anode 11 and the cathode 12, the water to be treated to which an iodine-containing oxidizing agent is added is passed through the desalination chamber 23. When the water to be treated is passed through the desalination chamber 23, the ionic components (anions and cations) in the water to be treated are adsorbed by the ion exchange resin in the desalination chamber 23. At this time, in the desalination chamber 23, due to the potential difference generated at the interface of different ion exchange substances by the applied current, a water dissociation reaction (H2O → H + + OH - ) occurs, and hydrogen ions (H + ) and hydroxide ions (OH -) are generated. The hydrogen ions and hydroxide ions generated in this way exchange ions with the ionic components that were previously adsorbed on the ion exchange resin in the desalination chamber 23, causing them to desorb from the ion exchange resin. Of the desorbed ionic components, anions move to the concentration chamber 22 closer to the anode 11 via the anion exchange membrane 32, and are discharged from this concentration chamber 22 as concentrated water. Similarly, cations move to the concentration chamber 24 closer to the cathode 12 via the cation exchange membrane 33, and are discharged from this concentration chamber 24 as concentrated water. In short, the ionic components in the water to be treated supplied to the desalination chamber 23 move to the concentration chambers 22 and 24 and are discharged, and at the same time, the ion exchange resin in the desalination chamber 23 is regenerated. Treated water, i.e., deionized water, from which the ionic components have been removed, is discharged from the desalination chamber 23. Electrode water is discharged from the anode chamber 21 and the cathode chamber 25, respectively. The application of DC current may be continuous or intermittent when the water to be treated is passed through. Furthermore, in order to prevent iodine components derived from the iodine-containing oxidizing agent added to the treated water from leaking into the treated water, it is necessary to make at least a portion of the ion exchanger packed in the desalination chamber 23 an anion exchanger, and it is preferable to make at least a portion of the ion exchanger packed in the concentration chamber 24 an anion exchanger.

[0018] In the EDI device 10 shown in Figure 2, a basic configuration consisting of [concentration chamber (C) 22 | anion exchange membrane (AEM) 32 | desalination chamber (D) 23 | cation exchange membrane (CEM) 33 | concentration chamber (C) 24] is placed between the anode 11 and the cathode 12. This basic configuration is called a cell set. In practice, multiple such cell sets (referred to as "N sets" in Figure 2) are placed side by side between the electrodes, and the processing capacity can be increased by electrically connecting multiple cell sets in series, with one end as the anode 11 and the other end as the cathode 12. In this case, adjacent concentration chambers can be shared between adjacent cell sets, so the configuration of the EDI device 10 can be [anode chamber | CEM | C | X | X | ... | X | AEM | cathode chamber], where X represents a repeating unit consisting of [AEM | D | CEM | C]. In this series structure, with respect to the desalination chamber 23 closest to the anode chamber 21, the anode chamber 21 itself can function as a concentration chamber 22 without the need for an independent concentration chamber 22 to be interposed between it and the anode chamber 21. Similarly, with respect to the desalination chamber 23 closest to the cathode chamber 25, the cathode chamber 25 itself can function as a concentration chamber 24 without the need for an independent concentration chamber 24 to be interposed between it and the cathode chamber 25.

[0019] Next, we will explain the iodine-containing oxidizing agent added to the water to be treated. Generally, the EDI device 10 has a configuration in which the water to be treated is passed through a space filled with ion exchange materials such as granular ion exchange resin at a high flow rate. However, even in such an EDI device, slime derived from live bacteria may be generated. In EDI devices, blockage is likely to occur when slime is generated, and this tends to lead to an increase in the differential pressure of the water flow and a deterioration in performance due to uneven water flow. Generally, to suppress the generation of slime, it is effective to pass an oxidizing disinfectant through the water as a slime inhibitor (slime control agent). However, an oxidizing disinfectant is nothing more than an oxidizing agent, and generally, oxidizing agents degrade the ion exchange resin and ion exchange membrane that make up the EDI device. For this reason, it has been conventionally considered necessary to avoid supplying water containing an oxidizing agent to an EDI device, especially an EDI device that is operating with a DC current applied. The inventors investigated a method to suppress both the generation of slime in an EDI device and the deterioration of ion exchange resins and ion exchange membranes in the EDI device. They found that by using an iodine-containing oxidizing agent as a slime inhibitor, the deterioration of the performance of the EDI device could be suppressed, thus completing the present invention. As will become clear from the examples described below, when hypochlorous acid or hypochlorite salts, which are commonly used as slime inhibitors, were added to the water to be treated and the EDI device was operated, the water quality of the treated water deteriorated rapidly. This deterioration in water quality is thought to be due to the deterioration of ion exchange membranes and ion exchange resins. However, when an iodine-containing oxidizing agent was used, the water quality of the treated water was maintained at a good level for a long period of time.

[0020] In the present invention, an iodine-containing oxidizing agent refers to an oxidizing agent that contains iodine as an element, and may be an iodine compound that functions as an oxidizing agent itself, or a reaction product of an iodine compound and an oxidizing agent. Since elemental iodine (i.e., I2) also has oxidizing power, a solution containing elemental iodine is also included in the category of iodine-containing oxidizing agents. The iodine contained as an element in an iodine-containing oxide may be in any form, for example, molecular iodine, iodide, polyiodide, iodic acid, hypoiodic acid, hydrogen iodide, or iodine coordinated to an organic solvent such as polyvinylpyrrolidone or cyclodextrin, or a combination of these forms may be present. Methods for obtaining iodine in any of these forms include dissolving elemental iodine in nonpolar solvents such as benzene or carbon tetrachloride or alcohols, dissolving elemental iodine using an alkaline agent and water, or dissolving elemental iodine using iodide and water. Total iodine may also be obtained by adding an acid or oxidizing agent to a solution containing at least one of iodide and iodide ions. Alternatively, iodine coordinated to organic solvents such as polyvinylpyrrolidone or cyclodextrin may be obtained using povidone-iodine, which is obtained by coordinating iodine to polyvinylpyrrolidone; iodine-clad cyclodextrin, which is obtained by encapsulating iodine in cyclodextrin; or iodole, which is obtained by supporting iodine on organic polymers and surfactants.

[0021] As an iodine-containing oxidizing agent, a solution containing water, iodide, and elemental iodine dissolved in water without the use of organic matter is preferred, from the viewpoint of ease of handling and minimal impact on the treated water and the water quality of the treated water. Elemental iodine alone has low solubility in water, but it becomes soluble in water when iodide or iodide ions are present. Dissolving elemental iodine in water with iodide yields a relatively high-concentration and stable one-component oxidizing agent that is easy to handle. Iodide refers to iodine compounds with an oxidation state of -1. Examples of iodides include potassium iodide, sodium iodide, lithium iodide, hydrogen iodide, silver iodide, copper iodide, and zinc iodide. These iodides dissociate in water to yield iodide ions.

[0022] When obtaining an iodine-containing oxidizing agent, which is a reaction product of an iodine compound and an oxidizing agent, the iodine compound can be, for example, potassium iodide, sodium iodide, lithium iodide, hydrogen iodide, silver iodide, copper iodide, zinc iodide, etc., and two or more of these may be used simultaneously. In this case, from the viewpoint of cost and other factors, sodium iodide or potassium iodide is preferred as the iodine compound. As the oxidizing agent to react with the iodine compound, an oxidizing agent with a higher oxidation-reduction potential (ORP) than iodine can be used. Examples of oxidizing agents that can be used include bound chlorine and stabilized hypobromous acid compositions, but from the viewpoint of reaction speed and other factors, an oxidizing agent that is detected as free chlorine is preferred. Typical examples of oxidizing agents that are detected as free chlorine include hypochlorous acid, hypobromous acid, or salts thereof. A stabilized hypobromous acid composition is a product obtained by reacting a brominated oxidizing agent with a sulfamic acid compound, or by further reacting a sulfamic acid compound with a reaction product of a brominated compound with a chlorine-based oxidizing agent. Examples of brominated oxidizing agents include elemental bromine, bromine chloride, bromate, and bromate salts.

[0023] When the iodine-containing oxidizing agent is a solution containing water, iodine, and iodide, the molar ratio of iodide to iodine is preferably 1 or greater from the viewpoint of iodine solubility in water, and from the viewpoint of stability, the pH is preferably 3 to 9, more preferably 3 to 7, and even more preferably 4 to 6.5. If the pH is less than 3, iodine crystals may precipitate, and if it exceeds 9, the amount of active ingredients may decrease significantly. Considering the transportation costs of the slime inhibitor, it is preferable that the active ingredients be highly concentrated and stable, so the total iodine concentration in the iodine-containing oxidizing agent is preferably 3% by mass or more, more preferably in the range of 3% to 40% by mass, and even more preferably 10% to 25% by mass. The total iodine concentration referred to here is the concentration calculated based on the total amount of iodine in all forms contained in the iodine-containing oxidizing agent, regardless of whether it is iodide or elemental iodine.

[0024] The iodine-containing oxidizing agent described above is used as a slime inhibitor for the EDI device 10, but it can also be used to clean each chamber of the EDI device 10 (anode chamber 21, concentration chambers 22, 24, desalination chamber 23, and cathode chamber 25). When cleaning the EDI device 10, the EDI device 10 should be stopped, the iodine-containing oxidizing agent should be dissolved in pure water to make a cleaning solution, and this cleaning solution should be passed through each chamber of the EDI device 10.

[0025] When controlling the concentration of iodine-containing oxidizing agents in treated water, various quantitative methods for iodine can be used. In particular, when the iodine-containing oxidizing agent is a solution containing water, iodine, and iodide, the iodine that is not iodide is the iodine that is effective as an oxidizing agent. This effective iodine shows a similar color reaction to residual chlorine when measuring total chlorine (total residual chlorine) in water using a colorimetric method (i.e., the DPD method) with DPD (N,N-diethyl-paraphenylenediamine). Therefore, assuming that residual chlorine is not present, the concentration of iodine effective as an oxidizing agent can be controlled by measuring it using a total chlorine concentration meter based on the DPD method. The effective iodine concentration can also be controlled by using residual chlorine quantitative methods or total chlorine quantitative methods other than the DPD method. For example, as a quantitative method for residual chlorine, a method is known in which iodine liberated by the oxidation of potassium iodide by residual chlorine is quantified by redox titration with sodium thiosulfate. By applying this method and performing a redox titration with sodium thiosulfate on the water to be treated, the effective iodine concentration in the water can be determined as a value converted to the total chlorine concentration. In the following explanation, when referring to the effective iodine concentration rather than the total iodine concentration, the concentration may be expressed as the measured value when the total chlorine concentration was measured (i.e., the value converted to the total chlorine concentration). When expressed as a value converted to the total chlorine concentration, "as Cl2" is added to indicate this.

[0026] The concentration of the iodine-containing oxidizing agent added to the water to be treated must be such that it has sufficient bactericidal ability. From this perspective, when adding the iodine-containing oxidizing agent to the water to be treated, it is preferable that the effective iodine concentration in the water to be treated supplied to the EDI device 10 be 0.01 mg / L as Cl2 or higher. Even if the effect of the iodine-containing oxidizing agent on the EDI device is minor compared to hypochlorous acid, etc., if the concentration of the iodine-containing oxidizing agent is excessively high, it may cause deterioration of the EDI device. Therefore, it is preferable that the effective iodine concentration in the water to be treated supplied to the EDI device 10 be less than 10.0 mg / L as Cl2. The addition of the iodine-containing oxidizing agent to the water to be treated may be continuous or intermittent. A larger amount of iodine-containing oxidizing agent is better to suppress slime generation, but it is not necessary to continuously add the iodine-containing oxidizing agent to the water to be treated, and the addition of the iodine-containing oxidizing agent to the water to be treated can be done intermittently. By intermittently adding the iodine-containing oxidizing agent, the deterioration of the EDI device 10 can be further suppressed. Alternatively, the desalination treatment of the water to be treated can be performed continuously. The period during which the iodine-containing oxide is added to the water to be treated can be defined as the addition period, and the period during which it is not added can be defined as the no-addition period. For example, the addition period can be set to a range of 0.01 to 12 hours, and the no-addition period to a range of 1 to 320 hours, so that the addition period is within 12 hours in any given 24-hour period. When the iodine-containing oxidizing agent is added to the water to be treated intermittently, it is not appropriate to evaluate the effect of the iodine-containing oxidizing agent on the EDI device 10 based solely on the concentration of the oxidizing agent in the water to be treated while the iodine-containing oxidizing agent is being added. Therefore, it is preferable to calculate the cumulative amount of concentration C during the period T in which the iodine-containing oxidizing agent is added to the treated water, i.e., the CT value, by taking the effective iodine concentration in the treated water converted to the total chlorine concentration as C, and using the CT value as a management indicator.

[0027] In the above explanation, the water to be treated to which the iodine-containing oxidizing agent has been added is passed through the desalination chamber 23 of the EDI device 10. However, the water to be treated to which the iodine-containing oxidizing agent has been added may also be further supplied to the concentration chambers 22, 24 and the electrode chambers (i.e., the anode chamber 21 and the cathode chamber 25). There are no particular restrictions on the type of water supplied to the concentration chambers 22, 24 and the electrode chambers, but the concentration chambers 22 and 24 tend to have high ion concentrations, making them environments where viable bacteria can easily proliferate and slime is likely to form. In the electrode chambers as well, depending on the type of water supplied, there is a risk that viable bacteria will proliferate and slime will form. Therefore, by continuously or intermittently using water to which the iodine-containing oxidizing agent has been added as the water supplied to the concentration chambers 22, 24 and the electrode chambers, the generation of slime and other substances in the concentration chambers 22, 24 and the electrode chambers can be suppressed.

[0028] In this embodiment, by using an iodine-containing oxidizing agent instead of a chlorine-based oxidizing agent such as hypochlorous acid or hypochlorite as the oxidizing agent used as a slime inhibitor in the EDI device, it is possible to obtain a sufficient sterilization effect while preventing deterioration of the EDI device and suppressing slime generation, without providing an oxidizing agent removal means upstream of the EDI device or controlling the shutdown of the EDI device, while continuously operating the EDI device.

[0029] In water treatment systems equipped with an EDI device, the EDI device is rarely used alone. Instead, a membrane device with a separation membrane is typically placed before the EDI device, and the water that has permeated the separation membrane is supplied to the EDI device. Figure 3 shows a water treatment system, similar to the one shown in Figure 1, in which a reverse osmosis membrane device 40, equipped with a reverse osmosis membrane 41 (which acts as a separation membrane), is placed before the EDI device 10. In the water treatment system shown in Figure 3, the water to be treated is first supplied to the reverse osmosis membrane device 40. The water that has permeated the reverse osmosis membrane 41 of the reverse osmosis membrane device 40 (i.e., the permeate) is then supplied to the desalination chamber 23 of the EDI device 10. The permeate from the reverse osmosis membrane device 40 may also be supplied to the concentration chambers 22, 24 or the electrode chamber of the EDI device 10. The water that has not permeated the reverse osmosis membrane 41 is discharged from the reverse osmosis membrane device 40 as concentrated water. In the water treatment apparatus shown in Figure 3, the mechanism for adding an iodine-containing oxidizing agent, which acts as a slime inhibitor, to the water to be treated is located upstream of the reverse osmosis membrane apparatus 40. Since the iodine-containing oxidizing agent is added to the water to be treated upstream of the reverse osmosis membrane apparatus 40, it is also possible to suppress the adhesion of slime to the reverse osmosis membrane 41.

[0030] In the reverse osmosis membrane device 40, various organic substances are removed, so the impurity concentration in the treated water supplied to the EDI device 10 after passing through the reverse osmosis membrane device 40 is lower than the impurity concentration in the treated water supplied to the EDI device 10 in the water treatment device shown in Figure 1. Therefore, in the water treatment device shown in Figure 3, slime generation in the EDI device 10 is less likely to occur compared to the water treatment device shown in Figure 1. Thus, when the reverse osmosis membrane device 40 is installed upstream of the EDI device 10, it is possible to lower the iodine concentration, which is effective as an oxidizing agent, in the treated water at the inlet of the EDI device 10 to a lower level than the concentration in the water treatment device shown in Figure 1.

[0031] In addition to the reverse osmosis membrane 41 shown in the example in Figure 3, other types of separation membranes can be used as the upstream membrane of the EDI device 10, such as nanofiltration membranes (NF membranes), microfiltration membranes (MF membranes), ultrafiltration membranes (UF membranes), and forward osmosis membranes (FO membranes), and these membranes can also be combined. The water to be treated that has permeated through the separation membrane is supplied to the EDI device 10. To suppress the generation of slime in these separation membranes, it is preferable to add an iodine-containing oxidizing agent to the water to be treated upstream of the separation membrane.

[0032] Figure 4 shows the configuration of another water treatment apparatus based on the present invention. The water treatment apparatus shown in Figure 4 is the same as the water treatment apparatus shown in Figure 3, but is equipped with a total chlorine concentration meter 50 using the DPD method connected to the permeate outlet of the reverse osmosis membrane apparatus 40, and piping that returns the permeate from the reverse osmosis membrane apparatus 40 to the upstream stage of the reverse osmosis membrane apparatus 40. The total chlorine concentration meter 50 is provided to determine the concentration of the iodine-containing oxidizing agent in the permeate from the reverse osmosis membrane apparatus 40, specifically the effective iodine concentration. In this water treatment apparatus, in order to reduce the effective iodine concentration, which is the oxidizing agent in the water to be treated supplied to the downstream EDI apparatus 10, control is performed so that the effective iodine concentration measured as residual chlorine concentration by the total chlorine concentration meter 50 is below a predetermined value. To reduce the effective iodine concentration in the permeate, for example, the amount of iodine-containing oxidizing agent added can be controlled based on the measurement value of the total chlorine concentration meter 50, or the amount of permeate discharged from the reverse osmosis membrane device 40 returned to the upstream side of the reverse osmosis membrane device 40 can be increased or decreased, or an activated carbon device can be installed at the permeate outlet of the reverse osmosis membrane device 40 to adjust the oxidizing agent concentration in the water to be treated supplied to the EDI device 10.

[0033] The water treatment apparatus shown in Figures 3 and 4 has a reverse osmosis membrane apparatus 40 placed before the EDI apparatus 10, and an iodine-containing oxidizing agent is added to the water to be treated supplied to the reverse osmosis membrane apparatus 40. In these water treatment apparatuses as well, the addition of the iodine-containing oxidizing agent to the water to be treated may be continuous or intermittent. In order to suppress the deterioration of the reverse osmosis membrane 41 and the EDI apparatus 10 while suppressing the generation of slime, and to suppress the deterioration of the water quality in the treated water, it is preferable to add the iodine-containing oxidizing agent to the water to be treated intermittently, even when the iodine-containing oxidizing agent is added to the water to be treated before the reverse osmosis membrane apparatus 40. Assuming that the water to be treated is continuously supplied to the water treatment apparatus, for example, the iodine-containing oxidizing agent can be added to the water to be treated supplied to the reverse osmosis membrane apparatus 40 with an addition period of 0.01 to 12 hours and a no-addition period of 1 to 320 hours, so that the addition period is 12 hours or less in any given 24-hour period.

[0034] Figure 5 shows another example of an EDI device that can be used in each of the water treatment devices shown in Figures 1, 3, and 4. The EDI device shown in Figure 5 divides the desalination chamber 23 of the EDI device 10 shown in Figure 2 with an intermediate ion exchange membrane, designating the side of the intermediate ion exchange membrane closer to the anode 11 as the first small desalination chamber 27 and the side of the intermediate ion exchange membrane closer to the cathode 12 as the second small desalination chamber 28. An anion exchange membrane 37 is used as the intermediate ion exchange membrane. Therefore, the first small desalination chamber 27 is partitioned by an anion exchange membrane 32 and an anion exchange membrane 37, and the second small desalination chamber 28 is partitioned by an anion exchange membrane 37 and a cation exchange membrane 33. In this EDI device, the water to be treated is first supplied to the first small desalination chamber 27, the outlet water from the first small desalination chamber 27 is supplied directly to the second small desalination chamber 28, and the treated water of this EDI device is discharged from the second small desalination chamber 28. In the example shown here, the first small desalination chamber 27 is filled with anion exchange resin. The second small desalination chamber 28 has a double-bed configuration, with cation exchange resin filled on the upstream side and anion exchange resin filled on the downstream side, along the direction of the flow of the treated water. In the EDI apparatus shown in Figure 5, a repeating unit X can be set up in series between the concentration chamber 22 adjacent to the anode chamber 21 and the anion exchange membrane 34 in contact with the cathode chamber 25, with the arrangement consisting of the anion exchange membrane 32, the first small desalination chamber 27, the anion exchange membrane 37, the second small desalination chamber 28, the cation exchange membrane 33, and the concentration chamber 24 being the repeating unit X.

[0035] As described above, the iodine-containing oxidizing agent used in this embodiment is an oxidizing agent that contains iodine as an element, and by adding the iodine-containing oxidizing agent, the water to be treated becomes oxidizing. Therefore, if the water to be treated already contains an oxidizing agent and has oxidizing power, simply adding iodide to the water to be treated will bring it to the same state as when an iodine-containing oxidizing agent is added. Similarly, if the water to be treated already contains iodide, simply adding an oxidizing agent to the water to be treated will bring it to the same state as when an iodine-containing oxidizing agent is added. Therefore, the present invention encompasses not only cases where an iodine-containing oxidizing agent is added to the water to be treated, but also cases where iodide is added to the water to be treated when the water to be treated already contains an oxidizing agent, and cases where an oxidizing agent is added to the water to be treated when the water to be treated already contains iodide. Furthermore, the present invention also includes cases in which an iodine-containing chemical and an oxidizing agent are added separately to the water to be treated, such that an iodine-containing oxidizing agent is generated by mixing or reaction in the water to be treated. [Examples]

[0036] Next, the present invention will be described in more detail with reference to examples. In the following, the effective iodine concentration is a value obtained by measuring the total chlorine concentration by the DPD method. The CT value is, as described above, a value obtained as the cumulative amount of the effective iodine concentration C in the treated water during the period T in which the iodine-containing oxidizing agent is added.

[0037] [Example 1] The EDI apparatus 10 shown in Figure 5 was assembled, and the EDI apparatus 10 was operated by supplying treated water to which an iodine-containing oxidizing agent had been added as a slime inhibitor. The resistivity of the treated water discharged from the second small desalination chamber 28, the change in the overall water flow differential pressure in the first small desalination chamber 27 and the second small desalination chamber 28 (referred to as the water flow differential pressure in the desalination chambers), and the change in the water flow differential pressure in the concentration chambers 22 and 24 were investigated. Well water from Sagamihara City was used as the treated water, and the effective iodine concentration in the treated water when the iodine-containing oxidizing agent was added was set to 0.75 mg / L as Cl2. A solution containing water, iodine, and iodide was used as the iodine-containing oxide. The results are shown in Figure 6 (resistivity of treated water), Figure 7 (water flow differential pressure in the desalination chambers), and Figure 8 (water flow differential pressure in the concentration chambers). The horizontal axis in these figures represents the CT value.

[0038] [Comparative Examples 1, 2] The EDI device 10 shown in Figure 5 was assembled and operated in the same manner as in Example 1. However, sodium hypochlorite (Comparative Example 1) and a stabilized hypobromous acid composition (Comparative Example 2) were used as slime inhibitors added to the treated water, and the change in resistivity of the treated water was investigated. Table 1 shows the resistivity of the treated water obtained before the start of operation and when the CT value became 100 mg·h / L as Cl2 after the start of operation, along with the results for Example 1 described above.

[0039] [Table 1]

[0040] As shown in Example 1, when an iodine-containing oxidizing agent was used as a slime inhibitor, the resistivity of the treated water in the EDI system remained high over a long period, and the differential pressure between the desalination and concentration chambers hardly changed. In contrast, when sodium hypochlorite was used as a slime inhibitor (Comparative Example 1) and when a stabilized hypobromite composition was used (Comparative Example 2), it was found that the resistivity decreased as the operating time of the EDI system increased, and the water quality of the treated water deteriorated. Regarding the trend of the change in resistivity, in Comparative Example 1, which used sodium hypochlorite, the resistivity of the treated water decreased rapidly early after the start of operation of the EDI system, and thereafter the resistivity did not change much. In contrast, in Comparative Example 2, which used a stabilized hypobromite composition, the resistivity decreased gradually. From these results, it was found that using an iodine-containing oxidizing agent as a slime inhibitor can suppress the deterioration of treated water quality and the increase in differential pressure in the EDI system.

[0041] [Example 2, Comparative Examples 3, 4] Water containing viable bacteria was contacted with the same iodine-containing oxidizing agent used in Example 1 (Example 2), sodium hypochlorite (Comparative Example 3), and stabilized hypobromous acid composition (Comparative Example 4) as slime inhibitors. The number of viable bacteria before contact with the slime inhibitor and the number of viable bacteria after contact with the slime inhibitor for 1 hour were examined. The concentration of the slime inhibitor was 1 mg / L as Cl2 in all cases. The results are shown in Table 2.

[0042] [Table 2]

[0043] From the above results, it was found that iodine-containing oxidizing agents have stronger bactericidal activity as slime inhibitors compared to sodium hypochlorite and stabilized hypobromite compositions. As mentioned above, by using iodine-containing oxidizing agents as slime inhibitors, the deterioration of treated water quality and the increase in differential water flow pressure in EDI equipment can be suppressed. Therefore, it was found that iodine-containing oxidizing agents are excellent slime inhibitors that can be used even in operational EDI equipment.

[0044] [Example 3] The EDI device 10 shown in Figure 5 was assembled, and the water to be treated, to which an iodine-containing oxidizing agent had been added as a slime inhibitor, was supplied to the first small desalination chamber 27 of the EDI device 10 and the EDI device 10 was operated. The relationship between the ratio of the cumulative amount of available iodine continuously flowing into the EDI device 10 to the total volume of anion exchange resin (AER) filling the concentration chambers 22 and 24 of the EDI device 10, and the available iodine concentration in the concentrated water discharged from the EDI device 10 was investigated. The results are shown in Figure 9. It was found that until the cumulative amount of available iodine continuously flowing into the EDI device 10 reached a certain value, no leakage of iodine components (including iodide ions, etc.) into the concentrated water flowing out of the concentration chambers 22 and 24 occurred, and that iodine was captured by the anion exchange resin in the EDI device 10. [Explanation of Symbols]

[0045] 10. Electrical deionized water production system (EDI system) 40 Reverse osmosis membrane equipment 41 Reverse osmosis membrane 50 Total Chlorine Concentration Meter 11 Anode 12 Cathode 21 Anode chamber 22,24 Concentration chamber 23 Desalination room 25 Cathode Chamber 27, 28 Small desalination chamber 31,33 Cation exchange membrane 32,34,37 Anion exchange membrane

Claims

1. An addition step in which chemicals are added to the water to be treated to obtain water that contains iodine and has oxidizing power, A processing step comprising supplying the water to be treated after the addition step to an electrolytic deionized water production apparatus, and processing it in the electrolytic deionized water production apparatus to obtain treated water, It has, The aforementioned chemical is a solution containing water, iodine, and iodide. In the aforementioned processing step, the iodine concentration in the water to be treated supplied to the electrolytic deionized water production apparatus is 0.01 mg / L as Cl₂ or more and less than 10.0 mg / L as Cl₂ when converted to a total chlorine concentration. In the aforementioned electro-type deionized water production apparatus, the desalination chamber filled with an ion exchanger is divided into a first small desalination chamber and a second small desalination chamber by an intermediate ion exchange membrane, and the first small desalination chamber is filled with an anion exchanger. A water treatment method comprising the above-mentioned processing step, wherein the water to be treated is supplied to the first small desalination chamber, the outlet water from the first small desalination chamber is supplied to the second small desalination chamber, and the outlet water from the second small desalination chamber is the treated water.

2. The water treatment method according to claim 1, wherein, in the processing step, the water to be treated after the addition step is treated with a separation membrane before being supplied to the electrolytic deionized water production apparatus.

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