Water treatment method, water treatment device, slime inhibitor, and cleaning method

Abstract

The water treatment device of the present application is provided with an electrodeionization water manufacturing device (EDI device) (10) in which at least a part of ion exchangers filled in a desalination chamber (23) is an anion exchanger, and an adding unit which adds an iodine-containing oxidizing agent as a slime inhibitor to treated water supplied to the EDI device (10). The iodine-containing oxidizing agent is, for example, a solution in which iodine and iodide are dissolved in water.

Description

Technical Field

[0001] This invention relates to a water treatment method and apparatus using an electro-deionized water manufacturing device, a slime inhibitor for an electro-deionized water manufacturing device, and a cleaning method for an electro-deionized water manufacturing device. Background Technology

[0002] As one of the devices for generating deionized water from treated water, there is an electro-deionization water production device (also known as an EDI (Electro Deionization) device). An EDI device is a combination of electrophoresis and electrodialysis, having a structure in which a desalination chamber is separated by a pair of ion exchange membranes between the anode and cathode. In an EDI device, at least its desalination chamber is filled with ion exchange resin or other ion exchangers. A direct current voltage is applied between the anode and cathode, and treated water is introduced into the desalination chamber. The treated water, having had its ions removed, flows out of the desalination chamber, and the ion exchangers within the desalination chamber are regenerated. EDI devices have the advantage of not requiring the use of chemicals to regenerate the ion exchangers. In an EDI device, a concentration chamber is adjacent to the desalination chamber, separated by the ion exchange membranes that separate the desalination chamber. In the concentration chamber, due to the ions moving from the desalination chamber, the ion concentration tends to increase, easily generating slime from living bacteria. For example, as described in Patent Document 1, when slime is generated, water flow is obstructed, and therefore the pressure differential tends to increase.

[0003] Typically, in water treatment equipment, to suppress the formation of slime, a slime inhibitor, also known as a slime control agent, is added to the water supplied to the equipment. Slime inhibitors are, for example, composed of hypochlorous acid, hydrogen peroxide, ozone, etc., which have bactericidal effects. However, hypochlorous acid, hydrogen peroxide, ozone, etc., are oxidants. If these oxidants flow into the EDI device, as described in Patent Documents 1 and 2, the ion exchange resin and ion exchange membrane constituting the EDI device deteriorate, sometimes resulting in a sharp decline in the quality of the treated water and an increase in the pressure difference between the concentration chamber and the desalination chamber. Patent Document 1 discloses that when a direct current is applied between the anode and cathode of the EDI device, the deterioration of the EDI device caused by the oxidant occurs more rapidly. Therefore, when water containing an oxidizing bactericide flows through the EDI device to remove slime, the voltage applied between the anode and cathode is stopped or reduced. Patent Document 3 discloses that when the pressure difference in the EDI device increases due to slime formation, a cleaning treatment using an agent containing hydrazine monohydrate and an alkali is used to remove the slime.

[0004] Similar to EDI devices, sludge can also form in reverse osmosis membrane devices, where the membrane itself may deteriorate due to contact with the oxidant. Patent Document 4 discloses the use of a stabilizing hypobromic acid composition as a sludge inhibitor capable of suppressing the deterioration of the reverse osmosis membrane, and Patent Document 5 discloses the use of an iodine-containing oxidant comprising water, iodine, and iodides.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-51453

[0008] Patent Document 2: Japanese Patent Application Publication No. 2000-279967

[0009] Patent Document 3: Japanese Patent Application Publication No. 2004-113973

[0010] Patent Document 4: Japanese Patent Application Publication No. 2015-62889

[0011] Patent Document 5: International Publication No. 2021 / 192582 Summary of the Invention

[0012] The technical problem that the invention aims to solve

[0013] When the sludge generated in the concentration chamber of the EDI device is removed by a drug-based cleaning process as described in Patent Document 3, the cleaning process itself takes a long time, such as several days, thus creating a technical problem where the EDI device cannot be used during this period. Furthermore, the drug solution has difficulty flowing in spaces clogged by sludge, making it difficult to completely remove the sludge from those spaces. While passing water containing a sludge inhibitor as an oxidant into the EDI device can prevent clogging caused by sludge, as described in Patent Document 1, when the sludge inhibitor is supplied to the EDI device, the voltage applied to the EDI device must be stopped or reduced, during which time desalination of the treated water cannot be performed in the EDI device.

[0014] The purpose of this invention is to provide a water treatment method and apparatus that uses an EDI device, enabling the EDI device to operate without causing a decline in the quality of the treated water or an increase in the pressure differential.

[0015] Another object of the present invention is to provide a slime inhibitor and a cleaning method for an EDI device that can be used in an operating EDI device without causing a decline in the quality of the treated water in the EDI device or an increase in the pressure differential.

[0016] Technical solutions for solving technical problems

[0017] One aspect of the water treatment method of the present invention comprises: an addition step, wherein a reagent is added to water to be treated to obtain water containing iodine and having oxidizing capacity; and a treatment step, wherein the water to be treated after the addition step is supplied to an EDI (electrodeionization water production) device for treatment, wherein at least a portion of the ion exchangers filling the desalination chamber of the EDI device is anion exchangers. The reagent added in the addition step is, for example, an iodine-containing oxidant; if the water to be treated already contains an oxidant, the reagent may be an iodide; if the water to be treated already contains an iodide, the reagent may be an oxidant.

[0018] One aspect of the water treatment apparatus of the present invention comprises: an additive unit that adds a reagent to treated water to make it iodine-containing and oxidizing; and an EDI device, wherein at least a portion of the ion exchangers filling the desalination chamber of the EDI device are anion exchangers, and the treated water after the reagent has been added by the additive unit is supplied to the EDI device. The reagent added by the additive unit may be, for example, an iodine-containing oxidant; if the treated water already contains an oxidant, the reagent may be an iodide; if the treated water already contains an iodide, the reagent may be an oxidant.

[0019] One aspect of the present invention provides a slime inhibitor comprising an iodine-containing oxidant for use in an EDI device.

[0020] One aspect of the present invention is a cleaning method that involves passing a cleaning solution containing the slime inhibitor of the present invention into an EDI device to clean the EDI device.

[0021] Invention Effects

[0022] According to the present invention, the EDI device can be operated without causing a decrease in the quality of the treated water in the EDI device or an increase in the pressure differential. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating a water treatment apparatus according to one embodiment of the present invention.

[0024] Figure 2 This is a diagram illustrating an example of the structure of an EDI device.

[0025] Figure 3 This is a diagram showing another structural example of a water treatment device.

[0026] Figure 4 This is a diagram showing another structural example of a water treatment device.

[0027] Figure 5 This is another example of the structure of an EDI device.

[0028] Figure 6 This is a graph showing the change in resistivity of the treated water in Example 1.

[0029] Figure 7 This is a graph showing the change in the water pressure difference in the desalination chamber in Example 1.

[0030] Figure 8 This is a graph showing the change in the water pressure difference in the concentration chamber in Example 1.

[0031] Figure 9 This is a graph showing the change in the effective iodine concentration in the concentrated water in Example 3. Detailed Implementation

[0032] Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a diagram illustrating the structure of a water treatment apparatus according to one embodiment of the present invention. Figure 1 The water treatment apparatus shown includes an electro-deionized water production unit (EDI unit) 10, and treated water is introduced into the EDI unit 10. The EDI unit 10 performs desalination treatment on the supplied treated water, for example, and discharges the treated water. Furthermore, the water treatment apparatus includes a mechanism that adds an iodine-containing oxidant as a slime inhibitor to the treated water supplied to the EDI unit 10. Details regarding the iodine-containing oxidant used as a slime inhibitor will be described later.

[0033] Figure 2 This illustrates an example of the structure of an EDI device 10. The EDI device 10 includes a desalination chamber 23 between an anode chamber 21 and a cathode chamber 25. The anode chamber 21 has an anode 11, and the cathode chamber 25 has a cathode 12. A concentration chamber 22 is disposed on the side of the desalination chamber 23 facing the anode chamber 21, and a concentration chamber 24 is disposed on the side of the desalination chamber 23 facing the cathode chamber 25. The anode chamber 21 and the concentration chamber 22 are separated by a cation exchange membrane 31, and the concentration chamber 22 and the desalination chamber 23 are separated by an anion exchange membrane 32. The desalination chamber 23 and the concentration chamber 24 are separated by a cation exchange membrane 33, and the concentration chamber 24 and the cathode chamber 25 are separated by an anion exchange membrane 34. As a result, the desalination chamber 23 is divided 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, anion exchange resin (AER) and cation exchange resin (CER) are filled in a mixed bed (MB) configuration. Furthermore, anode chamber 21 is filled with cation exchange resin, while concentration chambers 22 and 24, and cathode chamber 25 are filled with anion exchange resin. Alternatively, concentration chambers 22 and 24 can also be filled with a mixed bed configuration of anion exchange resin (AER) and cation exchange resin (CER).

[0034] Next, regarding Figure 1 The operation of the water treatment apparatus shown will be explained. With water supplied to the anode chamber 21, concentration chamber 22, concentration chamber 24, and cathode chamber 25 of the EDI apparatus 10, and a direct current applied between the anode 11 and cathode 12, water containing an iodine-containing oxidant is passed into the desalination chamber 23. When the water is passed into the desalination chamber 23, the ionic components (i.e., anions and cations) in the water are adsorbed onto the ion exchange resin within the desalination chamber 23. At this time, in the desalination chamber 23, due to the potential difference generated at the interface of different types of ion exchange substances by the applied current, the water dissociation reaction shown in equation (1) occurs, and hydrogen ions (H+) are generated. + ) and hydroxide ions (OH) - ).

[0035] H2O→H + +OH - (1)

[0036] The hydrogen and hydroxide ions generated in this way cause the ionic components previously adsorbed on the ion exchange resin in the desalination chamber 23 to undergo ion exchange and detach from the ion exchange resin. The anions in the detached ionic components move through the anion exchange membrane 32 to the concentration chamber 22 near the anode 11, and are discharged from the concentration chamber 22 as concentrated water. Similarly, the cations move through the cation exchange membrane 33 to the concentration chamber 24 near the cathode 12, and are discharged from the concentration chamber 24 as concentrated water. As a result, the ionic components in the treated water supplied to the desalination chamber 23 move to the concentration chambers 22 and 24 and are discharged, while the ion exchange resin in the desalination chamber 23 is also regenerated. The 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 direct current can be continuous or intermittent during the flow of treated water. It should be noted that, in order to prevent the iodine component from the iodine-containing oxidant added to the treated water from leaking into the treated water, at least a portion of the ion exchangers filling the desalination chamber 23 needs to be anion exchangers, and preferably at least a portion of the ion exchangers filling the concentration chamber 24 are anion exchangers.

[0037] exist Figure 2 In the EDI device 10 shown, a basic structure 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 arranged between the anode 11 and the cathode 12. This basic structure is called a unit group. In practice, by arranging multiple such unit groups side-by-side between the electrodes, connecting multiple unit groups in series, and placing the anode 11 at one end of the series connection and the cathode 12 at the other end, the processing capacity can be increased. Figure 2In this configuration, the case of multiple unit groups arranged in parallel is marked as "×N group". In this case, since adjacent unit groups can share adjacent concentration chambers, the structure of the EDI device 10 can be set as [anode chamber|CEM|C|X|X|···|X|AEM|cathode chamber] if the repeating unit composed of [AEM|D|CEM|C] is represented by X. In this series structure, regarding 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 to set up a separate concentration chamber 22 between the desalination chamber 23 and the anode chamber 21. Similarly, regarding 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 to set up a separate concentration chamber 24 between the desalination chamber 23 and the cathode chamber 25.

[0038] Next, the iodine-containing oxidant added to the treated water will be explained. Although the EDI unit 10 typically has a structure that allows the treated water to flow at a high velocity through a space filled with ion exchangers such as granular ion exchange resins, slime originating from living bacteria may still be generated in such an EDI unit. In EDI units, clogging is prone to occur when slime is generated, and the resulting increase in water pressure differential and performance degradation due to uneven water flow tend to develop. Generally, to suppress slime generation, passing a bactericide with oxidizing properties through the water is effective as a slime inhibitor (i.e., slime control agent). However, bactericides with oxidizing properties are necessarily oxidants, and oxidants usually degrade the ion exchange resins and ion exchange membranes that constitute the EDI unit. Therefore, in the past, it was necessary to avoid supplying water containing oxidants to EDI units, especially EDI units that are operating under direct current.

[0039] The inventors of this invention have researched a method to simultaneously suppress the formation of slime in EDI devices and inhibit the deterioration of ion exchange resins and ion exchange membranes within the EDI device. They discovered that by using an iodine-containing oxidant as a slime inhibitor, the performance degradation of the EDI device can be suppressed. As will be understood from the examples described later, when the EDI device is operated by adding hypochlorous acid or hypochlorite, which is commonly used as a slime inhibitor, to the water being treated, the quality of the treated water discharged from the EDI device deteriorates in the early stages. This deterioration is believed to be caused by the degradation of the ion exchange membranes and ion exchange resins. However, when using an iodine-containing oxidant, the quality of the treated water from the EDI device is maintained well over a long period.

[0040] In this invention, an iodine-containing oxidant refers to an oxidant containing iodine as an element. It can be an iodine compound that functions as an oxidant itself, or a reaction product of an iodine compound and an oxidant. Elemental iodine (i.e., I₂) also possesses oxidizing power; therefore, solutions containing elemental iodine are also included in the category of iodine-containing oxidants. The iodine contained as an element in iodine oxides can be in any form, such as molecular iodine, iodides, polyiodides, iodic acid, hypoiodic acid, hydrogen iodide, and iodine coordinated with organic solvents such as polyvinylpyrrolidone and cyclodextrin. Furthermore, combinations of these forms are also possible. Methods for obtaining these arbitrary forms of iodine include: dissolving elemental iodine in nonpolar solvents such as benzene and carbon tetrachloride, or in alcohols; dissolving elemental iodine using an alkali and water; or dissolving elemental iodine using an iodide and water. Total iodine can also be obtained by adding an acid or oxidant to a solution containing at least one of iodides and iodide ions. Alternatively, iodine can be obtained by using povidone-iodine, which contains iodine in polyvinylpyrrolidone, iodine-cyclodextrin inclusion complexes, which contain iodine in cyclodextrin, or iodophors, which support iodine in organic polymers and surfactants.

[0041] As an iodine-containing oxidant, from the viewpoints of ease of operation and minimal impact on the quality of the treated water and the treated water, a solution containing water, iodine, and iodide is preferred, as it does not use organic matter but is prepared by dissolving elemental iodine in iodide and water. Elemental iodine alone has low solubility in water, but it becomes soluble through the coexistence of iodide or iodide ions. Furthermore, a solution prepared by dissolving elemental iodine in iodide and water yields a stable, single-liquid oxidant with a high iodine concentration, making operation easy. It should be noted that iodide refers to iodine compounds with an oxidation number of -1. Examples of iodides include potassium iodide, sodium iodide, lithium iodide, hydrogen iodide, silver iodide, copper iodide, and zinc iodide. These iodides dissolve in water and dissociate, thereby providing iodide ions.

[0042] When obtaining an iodine-containing oxidizing agent as a reactant 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 them can be used simultaneously. From a cost perspective, sodium iodide or potassium iodide is preferred as the iodine compound in this case. As the oxidizing agent reacting with the iodine compound, an oxidizing agent with a redox potential (ORP) higher than that of iodine is preferred. Examples of usable oxidizing agents include chlorine-binding and stabilized hypobromic acid compositions, and from a reaction rate perspective, oxidizing agents detected as being in the free chlorine form are preferred. Representative examples of oxidizing agents detected as being in the free chlorine form include hypochlorous acid, hypobromic acid, or their salts. It should be noted that a stabilized hypobromic acid composition refers to the reaction product of a bromine-based oxidizing agent and an aminosulfonic acid compound, or a product obtained by further reacting an aminosulfonic acid compound in a reactant of a bromine compound and a chlorine-based oxidizing agent. Examples of bromine-based oxidizing agents mentioned here include elemental bromine, bromine chloride, bromic acid, and bromates.

[0043] When the iodine-containing oxidant is a solution containing water, iodine, and iodide, from the viewpoint of iodine solubility relative to water, the molar ratio of iodide to iodine is preferably 1 or more. From the viewpoint of stability, the pH of the solution 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, there is a possibility of iodine crystallization; if it exceeds 9, there is a possibility of a significant reduction in the effective component. Considering the transportation cost of slime inhibitors, etc., it is preferable that the effective component is highly concentrated and stable. Therefore, the total iodine concentration in the iodine-containing oxidant is preferably 3% by mass or more, more preferably 3% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less. The total iodine concentration referred to here is the concentration calculated based on the total chlorine concentration, whether it is iodide or elemental iodine.

[0044] The aforementioned iodine-containing oxidant is used as a slime inhibitor for the EDI device 10, but it can also be used to clean the various chambers of the EDI device 10 (anode chamber 21, concentration chamber 22, concentration chamber 24, desalination chamber 23, and cathode chamber 25). When cleaning the EDI device 10, with the EDI device 10 stopped, the iodine-containing oxidant is dissolved in pure water to form a cleaning solution, and this cleaning solution is then introduced into each chamber of the EDI device 10.

[0045] When managing the concentration of iodine-containing oxidants in treated water, various quantitative methods related to iodine can be used. Especially when the iodine-containing oxidant is a solution containing water, iodine, and iodides, the iodine that is not iodide is the effective iodine as an oxidant. This effective iodine exhibits the same colorimetric reaction as residual chlorine when the total chlorine (or total residual chlorine) in the water is determined by the DPD method, i.e., the colorimetric method using DPD (N,N-diethyl-p-phenylenediamine). Therefore, assuming the absence of residual chlorine, the concentration of iodine effective as an oxidant can be managed using the measured value by using a total chlorine concentration meter based on the DPD method. The effective iodine concentration can also be managed by using residual chlorine quantification methods other than the DPD method or total chlorine quantification methods. For example, as a method for quantifying residual chlorine, a method for quantifying the iodine freed by the oxidation of potassium iodide through redox titration based on sodium thiosulfate is known. If this method is applied to perform a sodium thiosulfate-based redox titration on the treated water, the effective iodine concentration in the treated water can be obtained as a value converted to total chlorine concentration. In the following explanation, when referring to effective iodine concentration instead of total iodine concentration, the converted total chlorine concentration value is sometimes used. The converted total chlorine concentration value refers to the measured value obtained as the total chlorine concentration when using methods for determining total chlorine concentration to measure effective iodine concentration; it is the value obtained by converting the effective iodine concentration to total chlorine concentration. When the effective iodine concentration is expressed as a converted total chlorine concentration value, the note "(in Cl2)" is appended to clarify this.

[0046] The concentration of the iodine-containing oxidant added to the treated water needs to have sufficient bactericidal ability. From this point of view, when adding the iodine-containing oxidant to the treated water, the effective iodine concentration of the oxidant supplied to the EDI unit 10 is preferably 0.05 mg / L (as Cl2) or higher. Even though the impact of the iodine-containing oxidant on the EDI unit is slight compared to hypochlorous acid, if the concentration of the iodine-containing oxidant is too high, there is a possibility of deterioration of the EDI unit. Therefore, the effective iodine concentration supplied to the EDI unit 10 is preferably less than 10.0 mg / L (as Cl2).

[0047] The addition of iodine-containing oxidant to the treated water can be continuous or intermittent. To suppress sludge formation, a large amount of iodine-containing oxidant is preferred, but continuous addition to the treated water is not necessary; intermittent addition is possible. Intermittent addition of the iodine-containing oxidant further suppresses the deterioration of the EDI unit 10. Continuous desalination of the treated water is performed, with the period during which iodine-containing oxidant is added defined as the addition period, and the period during which no iodine-containing oxidant is added defined as the no-addition period. For example, the addition period can be set to a range of 10 seconds to 12 hours, and the no-addition period to a range of 5 seconds to 320 hours, ensuring that the addition period is within 12 hours for any given 24-hour period. When the iodine-containing oxidant is added intermittently to the treated water, it is inappropriate to evaluate the effect of the iodine-containing oxidant on the EDI unit 10 solely based on the oxidant concentration in the treated water at the time of addition. Therefore, it is preferable to set the effective iodine concentration in the treated water as an oxidant when adding iodine-containing oxidant to the treated water as C, and calculate the cumulative amount of concentration C during the period T when iodine-containing oxidant is added to the treated water, i.e., the CT value, and use the CT value as an indicator for management.

[0048] In the above description, treated water containing iodine oxidant is passed to the desalination chamber 23 of the EDI unit 10. However, treated water containing iodine oxidant can also be further supplied to the concentration chambers 22 and 24, and the electrode chamber. The anode chamber 21 and the cathode chamber 25 are collectively referred to as the electrode chamber. While there are no particular restrictions on the supply water for the concentration chambers 22 and 24, and the electrode chamber, the ion concentration in the concentration chambers 22 and 24 tends to be high, making it easy for live bacteria to multiply and creating an environment prone to slime formation. It is possible that, similarly, live bacteria may multiply and produce slime in the electrode chamber, depending on the type of supply water. Therefore, by continuously or intermittently using water containing iodine oxidant as the supply water for the concentration chambers 22 and 24, and the electrode chamber, the formation of slime and other slime in these chambers can be suppressed.

[0049] In this embodiment, as the oxidant used as a slime inhibitor in the EDI device, an iodine-containing oxidant is used instead of a chlorine-based oxidant such as hypochlorous acid or hypochlorite. Thus, without setting up an oxidant removal unit in front of the EDI device or stopping the EDI device, the EDI device can be continuously operated while preventing the deterioration of the EDI device and obtaining a sufficient sterilization effect, and the generation of slime can be suppressed.

[0050] In water treatment systems equipped with EDI devices, there are few examples of using an EDI device alone. More often, a membrane device with a separation membrane is installed before the EDI device, and the treated water that has already passed through the separation membrane is supplied to the EDI device. Figure 3 It shows in Figure 1 In the water treatment apparatus shown, a reverse osmosis membrane unit 40, equipped with a reverse osmosis membrane 41 as a separation membrane, is installed as a pre-stage water treatment unit before the EDI unit 10. Figure 3 In the water treatment apparatus shown, the water to be treated is first supplied to the reverse osmosis membrane unit 40. The permeate water that has passed through the reverse osmosis membrane 41 of the reverse osmosis membrane unit 40 is supplied as the treated water in the EDI unit 10 to the desalination chamber 23 of the EDI unit 10. The permeate water from the reverse osmosis membrane unit 40 can also be supplied to the concentration chamber 22, concentration chamber 24, and electrode chamber of the EDI unit 10. The treated water that has not passed through the reverse osmosis membrane 41 is discharged from the reverse osmosis membrane unit 40 as concentrated water. Figure 3 In the water treatment apparatus shown, the mechanism for adding an iodine-containing oxidant as a slime inhibitor to the treated water is located before the reverse osmosis membrane unit 40. Figure 3 In the water treatment device shown, since an iodine-containing oxidant is added to the water to be treated in the stage before the reverse osmosis membrane device 40, the adhesion of slime to the reverse osmosis membrane 41 can also be inhibited.

[0051] In the reverse osmosis membrane unit 40, since various organic substances are removed, the concentration of impurities in the treated water supplied to the EDI unit 10 through the reverse osmosis membrane unit 40 is lower than that in the EDI unit 10. Figure 1 The concentration of impurities in the water supplied to the EDI unit 10 in the water treatment apparatus shown. Therefore, in Figure 3 In the water treatment device shown, with Figure 1 Compared to the water treatment apparatus shown, sludge formation is less likely to occur in the EDI unit 10. Therefore, when the reverse osmosis membrane unit 40 is installed upstream of the EDI unit 10, the effective iodine concentration as an oxidant in the treated water at the inlet of the EDI unit 10 can be kept below [a certain value]. Figure 1 The effective iodine concentration in the water treatment device shown.

[0052] As a separation membrane installed in the pre-stage of the EDI device 10, besides Figure 3 In addition to the reverse osmosis membrane 41 shown in the example, other membranes such as nanofiltration (NF membrane), ultrafiltration (UF membrane), microfiltration (MF membrane), and forward osmosis (FO membrane) can also be used, or combinations of these membranes can be used. The treated water that has passed through the separation membrane is supplied to the EDI unit 10. To suppress the formation of slime in these separation membranes, it is preferable to add an iodine-containing oxidant to the treated water upstream of the separation membrane.

[0053] Figure 4This describes the structure of another water treatment device based on the present invention. Figure 4 The water treatment device shown is in Figure 3 The water treatment apparatus shown includes a total chlorine concentration meter 50 based on the DPD method connected to the permeate outlet of the reverse osmosis membrane unit 40, and piping that returns the permeate from the reverse osmosis membrane unit 40 to the upstream stage of the reverse osmosis membrane unit 40. The total chlorine concentration meter 50 is installed to determine the concentration of iodine-containing oxidant in the permeate of the reverse osmosis membrane unit 40, specifically to determine the effective iodine concentration. In this water treatment apparatus, in order to reduce the effective iodine concentration as an oxidant in the treated water supplied to the downstream EDI unit 10, control is performed so that the effective iodine concentration, which is the residual chlorine concentration, measured by the total chlorine concentration meter 50, is less than a given value. To reduce the effective iodine concentration in the permeate, for example, the amount of iodine-containing oxidant added can be controlled based on the measurement value of the total chlorine concentration meter 50. The amount of permeate discharged from the reverse osmosis membrane unit 40 returned to the front end of the reverse osmosis membrane unit 40 can be increased or decreased. Alternatively, an activated carbon device can be installed at the permeate outlet of the reverse osmosis membrane unit 40 to adjust the oxidant concentration in the treated water supplied to the EDI unit 10.

[0054] exist Figure 3 and Figure 4 In the water treatment apparatus shown, a reverse osmosis membrane unit 40 is arranged upstream of the EDI unit 10, and an iodine-containing oxidant is added to the water to be treated supplied to the reverse osmosis membrane unit 40. In these water treatment apparatuses, the addition of the iodine-containing oxidant to the water to be treated can be continuous or intermittent. In order to suppress the formation of slime while inhibiting the deterioration of the reverse osmosis membrane 41 and the EDI unit 10, and to suppress the decline in the quality of the treated water, even when the iodine-containing oxidant is added to the water to be treated upstream of the reverse osmosis membrane unit 40, it is preferable to add the iodine-containing oxidant intermittently. As a method for continuously supplying the water to the water treatment apparatus, for example, the addition period can be set to a range of 10 seconds to 12 hours, and the no-addition period can be set to a range of 5 seconds to 320 hours, so that the addition period is within 12 hours or less within any 24-hour period.

[0055] Figure 5 It shows that it is possible to Figure 1 , Figure 3 as well as Figure 4 Another example of an EDI device used in the water treatment apparatus shown. Figure 5 The EDI device shown is the following type of EDI device: [The device will...] Figure 2The desalination chamber 23 of the EDI device 10 shown is separated by an intermediate ion exchange membrane. A first small desalination chamber 27 is designated on the side closer to the anode 11 than the intermediate ion exchange membrane, and a second small desalination chamber 28 is designated on the side closer to the cathode 12 than the intermediate ion exchange membrane. An anion exchange membrane 37 is used as the intermediate ion exchange membrane. Therefore, the first small desalination chamber 27 is divided by anion exchange membranes 32 and 37, and the second small desalination chamber 28 is divided by 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 of the first small desalination chamber 27 is supplied to the second small desalination chamber 28 as is, and the treated water of the 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 is a multi-bed structure, with cation exchange resin filled on the upstream side and anion exchange resin filled on the downstream side along the flow direction of the treated water. Figure 5 In the EDI device shown, multiple sets of repeating units X can also be arranged 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. The repeating unit X is an arrangement consisting of the anion exchange membrane 32, the first small desalination chamber 27, the second small desalination chamber 28, the cation exchange membrane 33, and the concentration chamber 24.

[0056] As described above, the iodine-containing oxidant used in this embodiment refers to an oxidant containing iodine as an element. By adding an iodine-containing oxidant, the treated water becomes oxidizing. Therefore, when the treated water already contains an oxidant and has oxidizing power, simply adding an iodide to the treated water makes it the same state as when an iodine-containing oxidant was added. Similarly, when the treated water already contains an iodide, simply adding an oxidant to the treated water makes it the same state as when an iodine-containing oxidant was added. Therefore, as a reagent added to the treated water, this invention includes not only cases where the reagent is an iodine-containing oxidant, but also cases where the reagent added to the treated water is an iodide when the treated water already contains an oxidant, and cases where the reagent added to the treated water is an oxidant when the treated water already contains an iodide. Furthermore, cases where an iodine-containing reagent and an oxidant are added to the treated water separately in order to generate an iodine-containing oxidant through mixing or reaction are also included within the scope of this invention.

[0057] Example

[0058] Next, the present invention will be further described in detail through examples and comparative examples. Hereinafter, the effective iodine concentration is a value obtained by measuring the total chlorine concentration based on the DPD method. Moreover, as described above, the CT value is a value obtained as a cumulative amount, which is the cumulative amount of the effective iodine concentration C in the treated water during the period T during which the iodine-containing oxidant is added.

[0059] [Example 1]

[0060] Assembly Figure 5 The EDI device 10 shown was operated by supplying treated water containing an iodine-containing oxidant as a slime inhibitor, and the resistivity of the treated water discharged from the second small desalination chamber 28, the change in the overall water pressure difference between the first small desalination chamber 27 and the second small desalination chamber 28, and the change in the water pressure difference in the concentration chambers 22 and 24 were investigated. The overall water pressure difference between the first small desalination chamber 27 and the second small desalination chamber 28 was defined as the water pressure difference of the desalination chamber. The treated water was well water from Sagamihara City, Japan, treated by a reverse osmosis membrane device, and the effective iodine concentration in the treated water with the added iodine-containing oxidant was set to 0.75 mg / L (as Cl2). A solution containing water, iodine, and iodide was used as the iodine-containing oxide. Figure 6 The results regarding the resistivity of the treated water are shown. Figure 7 The results regarding the pressure differential of the desalination chamber are shown. Figure 8 The results regarding the differential pressure of the water in the concentration chamber are shown. The horizontal axis in these figures represents the CT value.

[0061] [Comparative Example 1, Comparative Example 2]

[0062] Assembly Figure 5 The EDI apparatus 10 shown was operated in the same manner as in Example 1, and the change in resistivity of the treated water was investigated. However, sodium hypochlorite was used as a slime inhibitor added to the treated water in Comparative Example 1, and a stabilized hypobromic acid composition was used in Comparative Example 2. Table 1 shows the resistivity of the treated water before operation and the resistivity of the treated water obtained when the CT value was 100 mg·h / L (as Cl2) after operation, together with the results in Example 1 above.

[0063] [Table 1]

[0064]

[0065] As shown in Example 1, when using an iodine-containing oxidant as a slime inhibitor, the resistivity of the treated water in the EDI unit remained high for a long period, and the pressure difference between the desalination chamber and the concentration chamber hardly changed. In contrast, in Comparative Example 1, which used sodium hypochlorite as a slime inhibitor, and Comparative Example 2, which used a stabilized hypobromic acid composition as a slime inhibitor, the resistivity decreased and the quality of the treated water deteriorated as the EDI unit's operating time increased. Regarding the trend of resistivity change, in Comparative Example 1 using sodium hypochlorite, the resistivity of the treated water decreased sharply in the early stages from the start of EDI unit operation, and then remained relatively stable. In contrast, in Comparative Example 2 using the stabilized hypobromic acid composition, the resistivity gradually decreased. These results indicate that by using an iodine-containing oxidant as a slime inhibitor, the decline in the quality of the treated water and the increase in the pressure difference in the EDI unit can be suppressed.

[0066] [Example 2, Comparative Example 3, Comparative Example 4]

[0067] The slime inhibitor was contacted with water containing live bacteria, and the number of live bacteria before and after one hour of contact with the slime inhibitor was investigated. The same iodine-containing oxidant used in Example 1 was used as the slime inhibitor in Example 2, sodium hypochlorite was used in Comparative Example 3, and a stabilized hypobromic acid composition was used in Comparative Example 4. The concentration of the slime inhibitor was 0.1 mg / L (as Cl2) in all cases. The results are shown in Table 2.

[0068] [Table 2]

[0069]

[0070] The results above show that, compared with the combination of sodium hypochlorite and stabilized hypobromic acid as a slime inhibitor, iodine-containing oxidants have stronger bactericidal activity as slime inhibitors. As mentioned above, since the use of iodine-containing oxidants as slime inhibitors can suppress the decline in treated water quality and the increase in water pressure differential in EDI units, it can be concluded that iodine-containing oxidants are also excellent slime inhibitors that can be used in operating EDI units.

[0071] [Example 3]

[0072] Assembly Figure 5The EDI unit 10 shown is operated by supplying treated water containing an iodine-containing oxidant as a slime inhibitor to the first small desalination chamber 27, concentration chamber 22, concentration chamber 24, and electrode chamber. The cumulative amount of available iodine continuously flowing into the EDI unit 10 relative to the total volume of anion exchange resin (AER) filled in the concentration chambers 22 and 24 of the EDI unit 10 was then investigated in relation to the concentration of available iodine in the concentrated water discharged from the EDI unit 10. The results are presented below. Figure 9 Before the cumulative amount of effective iodine continuously flowing into the EDI unit 10 reaches a certain value, no leakage of iodine components into the concentrated water flowing out of the concentration chambers 22 and 24 occurs, indicating that the iodine is captured by the anion exchange resin in the EDI unit 10. The iodine components mentioned here also include iodide ions, etc.

[0073] Figure reference numerals: 10 Electro-deionized water production unit (EDI unit); 40 Reverse osmosis membrane unit.

[0074] 41 Reverse Osmosis Membrane

[0075] 50 Total Chlorine Concentration Meter

[0076] 11 Anode

[0077] 12 cathodes

[0078] 21 Anode Chamber

[0079] Concentration chambers 22 and 24

[0080] 23 Desalination Chamber

[0081] 25 Cathode Chamber

[0082] Small desalination chambers 27 and 28

[0083] 31, 33 Cation exchange membranes; 32, 34, 37 Anion exchange membranes.

Claims

1. A water treatment method, comprising: The additive process involves adding chemicals to the treated water to obtain treated water containing iodine and possessing oxidizing capabilities; and The treatment process involves supplying the water, after the additive process, to an electro-deionized water manufacturing apparatus for further treatment. The drug is a solution containing water, iodine, and iodides. In the treatment process, the effective iodine concentration in the water supplied to the electro-deionized water production device, converted to a total chlorine concentration (Cl2), is less than 10.0 mg / L. At least a portion of the ion exchangers filling the desalination chamber of the electro-deionized water manufacturing apparatus are anion exchangers to prevent iodine from leaking into the treated water.

2. The water treatment method according to claim 1, wherein, Before the water to be treated after the addition process is supplied to the electro-deionized water manufacturing device in the processing step, the water to be treated after the addition process is treated by a separation membrane.

3. A water treatment device, comprising: An additive unit adds chemicals to the treated water to obtain treated water containing iodine and possessing oxidizing capabilities; and An electro-deionized water manufacturing apparatus, wherein at least a portion of the ion exchangers filling the desalination chamber of the apparatus are anion exchangers, to prevent iodine from leaking from the treated water into the treated water. The drug is a solution containing water, iodine, and iodides. The treated water, after the addition of the drug by the addition unit, with an effective iodine concentration converted to a total chlorine concentration (Cl2) of less than 10.0 mg / L, is supplied to the electro-deionized water manufacturing device.

4. The water treatment apparatus according to claim 3, wherein, A separation membrane is installed at a position after the addition unit and before the electro-deionized water manufacturing device. The treated water containing the added drug is then supplied to the electro-deionized water manufacturing apparatus after being treated by the separation membrane.

5. The water treatment apparatus according to claim 3 or 4, wherein, At least a portion of the ion exchangers filling the concentration chamber of the electro-deionized water manufacturing apparatus are anion exchangers.

6. A slime inhibitor comprising an iodine-containing oxidant, used in the operation of an electro-deionized water manufacturing apparatus to both inhibit slime formation and suppress performance degradation in the apparatus. At least a portion of the ion exchangers filling the desalination chamber of the electro-deionized water manufacturing apparatus are anion exchangers to prevent iodine from the treated water in the electro-deionized water manufacturing apparatus from leaking into the treated water. The slime inhibitor is a solution containing water, iodine, and iodides.

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