Water treatment method and water treatment device

Abstract

To provide a method that, when water treatment is performed by using an electro-deionization (EDI) apparatus for producing deionized water, enables the EDI apparatus to be operated at all times without requiring special control of the EDI or a protective device installed in a front stage of the EDI, while suppressing the generation of slime and other substances, and deterioration of the EDI due to oxidizing agents.SOLUTION: A water treatment method which is characterized in that a brominated oxidizing agent that containing hypobromous acid and / or a hypobromite is added to water to be treated at the time when the water to be treated is passed through a desalination chamber 23 of an EDI apparatus 10 to obtain treated water. The brominated oxidizing agent is preferably a stable hypobromous acid composition containing hypobromous acid or its salt and a sulfamic acid compound.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method and a water treatment apparatus that uses an electrodeionization water production apparatus (EDI apparatus). [Background technology]

[0002] One type of device that produces deionized water (demineralized water) from water to be treated is the electrodeionization (EDI) device. The EDI device combines electrophoresis and electrodialysis and includes a demineralization compartment separated by an ion exchange membrane between an anode and a cathode. In the EDI device, at least the demineralization compartment is filled with an ion exchange resin. By applying a direct current between the anode and the cathode and passing the water to be treated through the demineralization compartment, treated water from which ionic components have been removed flows out of the demineralization compartment. The EDI device has the advantage of eliminating the need for chemical regeneration of the ion exchange resin. However, as described in Patent Document 1, it is known that the ion exchange resin and ion exchange membrane deteriorate when oxidizing agents such as hypochlorous acid and chlorine gas flow into the EDI device, resulting in a rapid deterioration in the quality of the treated water and an increase in the differential pressure across the water flow. When this phenomenon occurs, the EDI device may need to be replaced.

[0003] In EDI devices, the concentration compartment is adjacent to the deionization compartment, separated by an ion exchange membrane, but the concentration compartment is prone to high ion concentrations due to ionic components that have migrated from the deionization compartment, making it easy for slime derived from live bacteria to form. Patent Document 2 therefore discloses that in an EDI device, an oxidizing disinfectant such as sodium hypochlorite is added to the water supplied to the concentration compartment, and that the application of current between the anode and cathode is stopped or weakened when the oxidizing disinfectant is being used to prevent deterioration of the ion exchange resin and ion exchange membrane.

[0004] When an EDI system is used to produce pure water, a reverse osmosis (RO) system equipped with a reverse osmosis membrane is often installed upstream of the EDI system. To prevent slime from adhering to the RO membrane, an oxidant is injected into the treated water supplied to the RO system as a slime control agent. If the oxidant does not permeate the RO membrane, it will not flow into the downstream EDI system. However, the RO cannot completely remove the oxidant, and a certain amount of oxidant leaks into the permeate side of the RO system. Furthermore, oxidant leakage through the RO system can occur due to deterioration of the RO system over time caused by repeated cleaning-in-place (CIP) or when raw water leaks through the RO system. Patent Document 3 discloses a water treatment system in which a protective device using activated carbon is installed between the RO system and the EDI system to prevent oxidant leaking through the RO system from entering the EDI system.

[0005] When an oxidizing agent is used as a slime control agent for a reverse osmosis membrane device, the reverse osmosis membrane itself is also deteriorated by the oxidizing agent. Patent Document 4 discloses the use of a stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound as a slime control agent to suppress oxidative deterioration of the reverse osmosis membrane. The bromine-based oxidizing agent referred to in Patent Document 4 includes, for example, bromine, bromine chloride, and hypobromous acid, as well as a reaction product of sodium bromide and hypochlorous acid. Patent Document 5 discloses an example of a method for producing a stabilized hypobromous acid composition. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-165176 [Patent Document 2] Japanese Patent Application Publication No. 2018-51453 [Patent Document 3] Japanese Patent Publication No. 2020-18970 [Patent Document 4] Japanese Patent Application Publication No. 2018-15679 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-101251 Summary of the Invention [Problem to be solved by the invention]

[0007] The EDI device described in Patent Document 2 requires an additional control process to stop the electrical regeneration of the ion exchange resin in the demineralization compartment when an oxidizing bactericide is supplied to the concentration compartment, making it impossible to perform continuous demineralization of the water to be treated. Furthermore, the water treatment system shown in Patent Document 3 includes a protective device using activated carbon installed upstream of the EDI device to prevent deterioration of the EDI device due to the inflow of oxidizing agents such as slime control agents. However, this configuration requires the addition of a new piece of equipment, the protective device, and the effort required to replace the activated carbon, a consumable item.

[0008] The object of the present invention is to provide a water treatment method and water treatment apparatus that uses an EDI device, which does not require special control in the EDI device, and does not require a protective device to be installed upstream of the EDI device, and which can operate the EDI device continuously while suppressing the generation of slime and deterioration of the EDI device due to oxidizing agents. [Means for solving the problem]

[0009] The present inventors have investigated the phenomenon of deterioration of EDI devices due to oxidizing agents and have found that by using a bromine-based oxidizing agent containing hypobromous acid or hypobromite instead of the chlorine-based oxidizing agents such as hypochlorous acid or hypochlorite that have been conventionally used as slime control agents, it is possible to reduce the deterioration of EDI devices while still achieving a sufficient bactericidal effect. Therefore, the water treatment method of the present invention is a method for reducing the deterioration of EDI devices by using a bromine-based oxidizing agent containing hypobromous acid or hypobromite instead of the chlorine-based oxidizing agent such as hypochlorous acid or hypochlorite that has conventionally been used as a slime control agent. The concentration room adjacent to the desalination room and A desalination chamber is provided between the anode and the cathode. and concentration chamberA water treatment method for obtaining treated water by passing water to be treated through a deionization compartment using an EDI device in which a bromine-based oxidizing agent containing hypobromous acid and / or hypobromite is added to the water to be treated in a stage upstream of the EDI device. Both the deionization compartment and the concentration compartment are filled with anion exchange resin and cation exchange resin in a mixed bed form, and the concentration of hypobromous acid contained in the treated water at the inlet of the EDI device is 0.02 mg / L as Cl, which is the value obtained when measuring the total chlorine concentration of the treated water. 2 More than 0.5mg / L as Cl 2 Less than do.

[0010] The water treatment device of the present invention comprises an anode, a cathode, and a deionization compartment. The concentration room adjacent to the desalination room and A desalination chamber is provided between the anode and the cathode. and concentration chamber and an EDI device in which the water to be treated is passed through a desalination chamber; and an addition means provided upstream of the EDI device for adding a bromine-based oxidizing agent containing hypobromous acid and / or hypobromite to the water to be treated, Both the deionization compartment and the concentration compartment are filled with anion exchange resin and cation exchange resin in a mixed bed form, and the concentration of hypobromous acid contained in the water to be treated at the inlet of the EDI device is 0.02 mg / L as Cl, which is the value obtained when measuring the total chlorine concentration of the water to be treated. 2 More than 0.5mg / L as Cl 2 is less than While the water to be treated is flowing through the deionization compartment, a DC voltage is applied continuously or intermittently between the anode and the cathode. [Effects of the Invention]

[0011] According to the present invention, when water to be treated is passed through an EDI device to obtain treated water, no special control of the EDI device is required, and no protective device is required to be installed upstream of the EDI device.This makes it possible to operate the EDI device continuously while suppressing the generation of slime and deterioration of the EDI device due to oxidizing agents. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a water treatment device according to an embodiment of the present invention; [Figure 2] FIG. 1 illustrates an example of the configuration of an EDI device. [Figure 3] FIG. 10 is a diagram illustrating another configuration example of a water treatment device. [Figure 4] FIG. 10 is a diagram illustrating another configuration example of a water treatment device. [Figure 5]FIG. 1 is a diagram showing an example of the configuration of an EDI device having a deionization compartment divided into two small deionization compartments via an intermediate ion exchange membrane. [Figure 6] FIG. 1 is a diagram illustrating the results of Example 1. [Figure 7] 1 is a graph showing the results of Example 3. [Figure 8] 1 is a graph showing the results of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 one embodiment of the present invention. The water treatment device shown in FIG. 1 includes an electrodeionized water production device (EDI device) 10, through which water to be treated is passed. The EDI device 10 performs, for example, desalination treatment on the water to be treated and discharges the treated water. The water treatment device also includes a mechanism for supplying a bromine-based oxidizing agent to the water to be treated that is supplied to the EDI device 10 in order to suppress slime generation.

[0014] FIG. 2 shows an example of the configuration of an EDI device 10. The EDI device 10 includes a deionization compartment 23 between an anode compartment 21 equipped with an anode 11 and a cathode compartment 25 equipped with a cathode 12. A concentration compartment 22 is disposed on the anode compartment 21 side of the deionization compartment 23, and a concentration compartment 24 is disposed on the cathode compartment 25 side of the deionization compartment 23. The anode compartment 21 and the concentration compartment 22 are separated by a cation exchange membrane 31, and the concentration compartment 22 and the deionization compartment 23 are separated by an anion exchange membrane 32. The deionization compartment 23 and the concentration compartment 24 are separated by a cation exchange membrane 33, and the concentration compartment 24 and the cathode compartment 25 are separated by an anion exchange membrane 34. In summary, the deionization compartment 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 deionization compartment 23 is filled with an ion exchange resin. In the illustrated example, anion exchange resin (AER) and cation exchange resin (CER) are packed in a mixed bed (MB). The anode chamber 21 is packed with a cation exchange resin, the concentration chambers 22 and 24 are packed with anion exchange resin and cation exchange resin in a mixed bed, and the cathode chamber 25 is packed with anion exchange resin.

[0015] Next, the operation of the water treatment device shown in Figure 1 will be described. Feed water is passed through the anode chamber 21, concentration chambers 22 and 24, and cathode chamber 25 of the EDI device 10, and water to be treated, to which a bromine-based oxidant has been added, is passed through the deionization chamber 23 with a direct current applied between the anode 11 and the cathode 12. When the water to be treated is passed through the deionization chamber 23, ionic components (anions and cations) in the water to be treated are adsorbed onto the ion exchange resin in the deionization chamber 23. At this time, in the deionization chamber 23, a potential difference generated at the interface between different ion exchange materials due to the applied current causes a water dissociation reaction (H2O → H + +OH - ) occurs simultaneously, and hydrogen ions (H + ) and hydroxide ions (OH -) is generated. The hydrogen ions and hydroxide ions thus generated exchange ions that had previously been adsorbed on the ion exchange resin in deionization chamber 23, causing them to be desorbed from the ion exchange resin. Of the desorbed ion components, anions migrate through anion exchange membrane 32 to concentration chamber 22 closer to anode 11 and are discharged from this concentration chamber 22 as concentrated water. Similarly, cations migrate through cation exchange membrane 33 to concentration chamber 24 closer to cathode 12 and are discharged from this concentration chamber 24 as concentrated water. Ultimately, the ion components in the water to be treated that was supplied to deionization chamber 23 migrate to concentration chambers 22 and 24 and are discharged, and at the same time, the ion exchange resin in deionization chamber 23 is regenerated. Treated water from which the ion components have been removed, i.e., deionized water, is discharged from deionization chamber 23. Electrode water is discharged from anode chamber 21 and cathode chamber 25, respectively. Note that the application of a direct current may be performed continuously or intermittently while the water to be treated is passing through.

[0016] In the EDI device 10 shown in FIG. 2, a basic configuration consisting of [concentration compartment (C) 22 | anion exchange membrane (AEM) 32 | deionization compartment (D) 23 | cation exchange membrane (CEM) 33 | concentration compartment (C) 24] is arranged between an anode 11 and a cathode 12. This basic configuration is called a cell set. In practice, multiple such cell sets (referred to as "N sets" in FIG. 2) can be juxtaposed between the electrodes, and the multiple cell sets can be electrically connected in series with one end serving as the anode 11 and the other end as the cathode 12, thereby increasing processing capacity. In this case, adjacent cell sets can share adjacent concentration compartments. Therefore, the configuration of the EDI device 10 can be [anode compartment|CEM|C|X|X|···|X|AEM|cathode compartment], where X represents the repeating unit consisting of [AEM|D|CEM|C]. In such a series structure, for the deionization compartment 23 closest to the anode compartment 21, the anode compartment 21 itself can function as the concentration compartment 22 without an independent concentration compartment 22 interposed between the anode compartment 21 and the anode compartment 21. Similarly, for the deionization compartment 23 closest to the cathode compartment 25, the cathode compartment 25 itself can function as the concentration compartment 24 without an independent concentration compartment 24 interposed between the cathode compartment 25 and the anode compartment 21.

[0017] Next, we will explain the bromine-based oxidizing agent added to the water being treated. The EDI device 10 is configured to pass water being treated at a high flow rate through a space filled with granular ion exchange resin. Slime derived from live bacteria can also occur in EDI devices. Slime formation in EDI devices is prone to blockage, which can lead to increased differential pressure through the water passage and uneven water flow, leading to performance degradation. In general, passing an oxidizing bactericide through the water as a slime control agent (slime inhibitor) is effective in suppressing slime formation. However, oxidizing bactericides are essentially oxidizing agents, and oxidizing agents generally deteriorate the ion exchange resins and ion exchange membranes that make up EDI devices. For this reason, it has traditionally been considered necessary to avoid supplying water containing oxidizing agents to EDI devices, especially those operating under DC current. The present inventors have investigated ways to simultaneously suppress the generation of slime in an EDI device and the deterioration of the ion exchange resins and ion exchange membranes in the EDI device, and have found that the deterioration of the characteristics of the EDI device can be suppressed by using a bromine-based oxidizing agent as a slime control agent, thereby completing the present invention. As will be apparent from the examples described below, when an EDI device is operated after adding hypochlorous acid or hypochlorite, which are commonly used as slime control agents, to the water to be treated, the quality of the treated water deteriorates early, and this deterioration in water quality is thought to be due to the deterioration of the ion exchange membranes and ion exchange resins. However, when a bromine-based oxidizing agent is used, the quality of the treated water is maintained at a good level for a long period of time.

[0018] The term "bromine-based oxidizing agent" as used herein refers to an oxidizing agent containing hypobromous acid and / or hypobromite and having oxidizing properties. A liquid composition (hypobromous acid-stabilized composition) containing hypobromous acid and / or hypobromite and a sulfamic acid compound can also be used as the bromine-based oxidizing agent. Hypobromous acid and its salts are relatively unstable compounds and are generally generated each time they are used. However, a hypobromous acid-stabilized composition containing hypobromous acid or its salt and a sulfamic acid compound is a stable composition that can withstand long-term storage. Therefore, it is preferable to use a hypobromous acid-stabilized composition as the bromine-based oxidizing agent. The term "sulfamic acid compound" as used herein refers to a compound represented by the following general formula (1): R2NSO3H (1) (In the formula, R is independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aryl group having 6 to 10 carbon atoms.)

[0019] Examples of sulfamic acid compounds include sulfamic acid (also called amidosulfuric acid) in which both R groups are hydrogen atoms, as well as sulfamic acid compounds in which one of the R groups is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, such as N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N-isopropylsulfamic acid, and N-butylsulfamic acid; sulfamic acid compounds in which both of the R groups are alkyl groups having 1 to 8 carbon atoms, such as N,N-dimethylsulfamic acid, N,N-diethylsulfamic acid, N,N-dipropylsulfamic acid, N,N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid, and N-methyl-N-propylsulfamic acid; sulfamic acid compounds in which one of the R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-phenylsulfamic acid; and salts thereof. Examples of sulfamic acid salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts, strontium salts and barium salts, other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts and nickel salts, ammonium salts and guanidine salts. The sulfamic acid compounds and their salts may be used alone or in combination of two or more. As the sulfamic acid compound, it is preferable to use sulfamic acid from the viewpoint of environmental load, etc.

[0020] When managing the concentration of bromine-based oxidants in treated water, it is sometimes necessary to know the concentration of hypobromous acid in the water. Hypobromous acid exhibits a similar color reaction to residual chlorine when measuring total chlorine (total residual chlorine) in water using a colorimetric method using DPD (N,N-diethylparaphenylenediamine) (i.e., the DPD method). Therefore, assuming the absence of residual chlorine, measurements can be performed using a DPD total chlorine concentration meter, and the resulting measurements can be used to manage the hypobromous acid concentration. Hypobromous acid concentration can also be managed using residual chlorine determination methods other than the DPD method, such as redox titration with sodium thiosulfate to quantify the iodine liberated by hypobromous acid oxidizing potassium iodide. The hypobromous acid concentration can be calculated as a value converted to total chlorine concentration by measuring the iodine liberated by hypobromous acid oxidizing potassium iodide. Therefore, assuming the absence of residual chlorine, measurements of total chlorine concentration using iodometric titration can be used to manage the hypobromous acid concentration. In the following description, the concentration of hypobromous acid is expressed as the measured value when the total chlorine concentration is measured (i.e., the total chlorine concentration equivalent value), and "as Cl2" is added to make this clear.

[0021] The concentration of the bromine-based oxidizing agent added to the water to be treated must be sufficient to provide sufficient bactericidal activity. From this perspective, when adding a bromine-based oxidizing agent to the water to be treated, it is preferable to set the hypobromous acid concentration in the water to be treated supplied to the EDI device 10 to 0.02 mg / L as Cl2 or higher. Although the impact of bromine-based oxidizing agents on the EDI device is minor compared to hypochlorous acid, an excessively high bromine-based oxidizing agent concentration may cause deterioration of the EDI device. Therefore, it is preferable to set the hypobromous acid concentration in the water to be treated supplied to the EDI device 10 to less than 0.5 mg / L as Cl2. The bromine-based bactericide may be added to the water to be treated continuously or intermittently. To suppress slime formation, it is preferable to add a large amount of bromine-based oxidizing agent, but it is not necessary to continuously add the bromine-based oxidizing agent to the water to be treated; the bromine-based oxidizing agent can be added intermittently. Intermittent addition of the bromine-based oxidizing agent can further suppress deterioration of the EDI device 10. The treatment of the water to be treated is performed continuously, with the period during which the bromine-based oxidizing agent is added to the water being treated being designated the addition period and the period during which the bromine-based oxidizing agent is not added being designated the non-addition period. For example, the addition period can be set to 0.25 to 12 hours, and the non-addition period can be set to 3 to 320 hours, so that the addition period is 12 hours or less within any 24-hour period. The hypobromous acid concentration in the water being treated during the addition of the bromine-based oxidizing agent to the water being treated is defined as C, converted into the total chlorine concentration. It is preferable that the cumulative amount of concentration C, i.e., the CT value, during the period T during which the bromine-based oxidizing agent is added to the water being treated be 550 mg·h / L or less.

[0022] In the above description, the water to be treated, to which a bromine-based oxidizing agent has been added, is passed through the deionization chamber 23 of the EDI device 10. However, the water to be treated, to which a bromine-based oxidizing agent has been added, may also be 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 limitations on the feed water passed through the concentration chambers 22, 24 and the electrode chambers. However, the concentration chambers 22, 24 tend to have high ion concentrations, which makes them an environment where live bacteria can easily grow and slime can easily form. Depending on the type of feed water, live bacteria can also grow in the electrode chambers, which can cause slime to form. Therefore, by continuously or intermittently using water to which a bromine-based oxidizing agent has been added as feed water to the concentration chambers 22, 24 and the electrode chambers, the formation of slime and other contaminants in the concentration chambers 22, 24 and the electrode chambers can be suppressed. The preferred values ​​for the bromine-based oxidizing agent concentration and CT value in the feed water supplied to the concentration chambers 22, 24 and the electrode chambers are the same as those for the water to be treated supplied to the deionization chamber 23.

[0023] In this embodiment, the oxidizing agent used as a slime control agent in the EDI device is a bromine-based oxidizing agent rather than a chlorine-based oxidizing agent such as hypochlorous acid or hypochlorite. This allows the EDI device to be operated continuously without installing an oxidizing agent removal means in front of the EDI device or performing shutdown control of the EDI device, thereby preventing deterioration of the EDI device and achieving a sufficient sterilization effect.

[0024] In water treatment devices equipped with an EDI device, there are few cases in which the EDI device is used alone, and a reverse osmosis membrane device is often provided upstream of the EDI device. FIG. 3 shows a water treatment device in which a reverse osmosis membrane device 40 equipped with a reverse osmosis membrane 41 is provided upstream of the EDI device 10 in the water treatment device shown in FIG. 1. In the water treatment device shown in FIG. 3, the water to be treated is first supplied to the reverse osmosis membrane device 40, and the water to be treated that has permeated the reverse osmosis membrane 41 of the reverse osmosis membrane device 40 (i.e., permeated water) is supplied to the deionization chamber 23 of the EDI device 10. The permeated water from the reverse osmosis membrane device 40 may be supplied to the concentration chambers 22, 24 or the electrode chambers of the EDI device 10. The water to be treated 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 device shown in FIG. 3, a mechanism for adding a bromine-based oxidant to the water to be treated is provided upstream of the reverse osmosis membrane device 40. Since a bromine-based oxidizing agent is added to the water to be treated in the upstream stage of the reverse osmosis membrane device 40, adhesion of slime to the reverse osmosis membrane 41 can also be suppressed.

[0025] Because the reverse osmosis membrane device 40 removes various organic substances, the impurity concentration in the water to be treated that passes through the reverse osmosis membrane device 40 and is supplied to the EDI device 10 is lower than the impurity concentration in the water to be treated that is supplied to the EDI device 10 in the water treatment device shown in FIG. 1. Therefore, the water treatment device shown in FIG. 3 is less susceptible to slime generation in the EDI device 10 than the water treatment device shown in FIG. 1. Therefore, when the reverse osmosis membrane device 40 is provided upstream of the EDI device 10, the hypobromous acid concentration in the water to be treated at the inlet of the EDI device 10 can be made lower than the concentration in the water treatment device shown in FIG. 1. For example, the hypobromous acid concentration in the water to be treated at the inlet of the EDI device 10 can be made less than 0.5 mg / L as Cl2. Furthermore, bromine-based oxidizing agents themselves are less likely to pass through the reverse osmosis membrane device 40. For example, the hypobromous acid concentration in the water being treated at the inlet of the reverse osmosis membrane device 40 can be set to less than 2 mg / L as Cl2, while the hypobromous acid concentration in the water being treated at the inlet of the EDI device 10 can be set to less than 0.5 mg / L as Cl2. In particular, a stabilized hypobromous acid composition containing hypobromous acid or its salt and a sulfamic acid compound has reduced permeation through the reverse osmosis membrane 41 compared to sodium hypochlorite, etc., so when the reverse osmosis membrane device 40 is installed upstream of the EDI device 10, it is more preferable to use a stabilized hypobromous acid composition as a bromine-based oxidant. Note that, as will be apparent from the examples described below, when a stabilized hypobromous acid composition is added as a bromine-based oxidant upstream of the reverse osmosis membrane device 40, sulfamic acid compounds hardly permeate the reverse osmosis membrane 41, so that hypobromous acid is contained in the permeate of the reverse osmosis membrane device 40 as a bromine-based oxidant.

[0026] Depending on the type and source of the water to be treated, the water may contain ammonia. When a bromine-based oxidizing agent is added to the water to be treated that contains ammonia, as disclosed in Japanese Patent Application Laid-Open No. 2018-30061, ammonium ions (NH4 + ) by the presence of hypobromite ions (HBrO - ) easily permeates the reverse osmosis membrane. Therefore, in the water treatment device shown in FIG. 3, when the water to be treated contains ammonia, the bromate oxidizing agent easily permeates the reverse osmosis membrane 41.

[0027] Figure 4 shows the configuration of another water treatment device according to the present invention. The water treatment device shown in Figure 4 is the same as the water treatment device shown in Figure 3, except that a DPD-based total chlorine concentration meter 50 is connected to the permeate outlet of the reverse osmosis membrane device 40, and a pipe is added to return the permeate from the reverse osmosis membrane device 40 to a stage upstream of the reverse osmosis membrane device 40. The total chlorine concentration meter 50 is provided to determine the concentration of bromine-based oxidizing agents in the permeate from the reverse osmosis membrane device 40, specifically the hypobromous acid concentration. In this water treatment device, in order to reduce the hypobromous acid concentration in the water to be treated that is supplied to the downstream EDI device 10, the hypobromous acid concentration measured as the residual chlorine concentration by the total chlorine concentration meter 50 is controlled to be less than 0.5 mg / L as Cl2. In order to reduce the concentration of hypobromous acid in the permeate, for example, the amount of bromine-based 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 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 provided at the permeate outlet of the reverse osmosis membrane device 40, thereby adjusting the oxidant concentration in the treated water supplied to the EDI device 10.

[0028] The water treatment devices shown in FIGS. 3 and 4 have a reverse osmosis membrane device 40 disposed upstream of the EDI device 10, and a bromine-based oxidant is added to the water to be treated that is supplied to the reverse osmosis membrane device 40. In these water treatment devices, the bromine-based oxidant may be added continuously or intermittently to the water to be treated. To prevent the generation of slime while suppressing deterioration of the reverse osmosis membrane 41 and the EDI device 10 and to suppress deterioration in the quality of the treated water, it is preferable to add the bromine-based oxidant intermittently, even when adding the bromine-based oxidant to the water to be treated upstream of the reverse osmosis membrane device 40. When the water to be treated is continuously supplied to the water treatment device, the bromine-based oxidant may be added to the water to be treated that is supplied to the reverse osmosis membrane device 40 at a concentration of 0.2 to 2 mg / L as Cl2, with the addition period set to 0.25 to 12 hours and the non-addition period set to 3 to 320 hours, so that the addition period is 12 hours or less in any 24-hour period.

[0029] 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 desalting compartment 23 of the EDI device 10 shown in Figure 2 with an intermediate ion exchange membrane, with the first small desalting compartment 27 located closer to the anode 11 than the intermediate ion exchange membrane and the second small desalting compartment 28 located 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 desalting compartment 27 is divided by the anion exchange membrane 32 and the anion exchange membrane 37, and the second small desalting compartment 28 is divided by the anion exchange membrane 37 and the cation exchange membrane 33. In this EDI device, the water to be treated is first supplied to the first small desalting compartment 27, and the outlet water from the first small desalting compartment 27 is directly supplied to the second small desalting compartment 28, from which the treated water is discharged. In the example shown here, the first small deionization compartment 27 is filled with anion exchange resin. The second small deionization compartment 28 has a double-bed configuration, with a cation exchange resin packed on the upstream side along the direction of flow of the water to be treated and an anion exchange resin packed on the downstream side. In the EDI device shown in Figure 5, too, an arrangement consisting of anion exchange membrane 32, first small deionization compartment 27, anion exchange membrane 37, second small deionization compartment 28, cation exchange membrane 33, and concentrating compartment 23 is defined as repeating unit X, and multiple sets of repeating unit X can be provided in series between concentrating compartment 22 adjacent to anode chamber 21 and anion exchange membrane 34 in contact with cathode chamber 25. [Example]

[0030] Next, the present invention will be described in more detail with reference to examples. In the following, the concentration of hypobromous acid is expressed as a total chlorine concentration equivalent value obtained by measuring the total chlorine concentration by the DPD method.

[0031] [Example 1] Using the EDI device shown in Figure 5, we investigated the deterioration behavior of the EDI device by examining the changes in the water quality of the treated water discharged from the second small desalination compartment of the EDI device when sodium hypochlorite, a chlorine-based oxidant, and sodium hypobromite, a bromine-based oxidant, were introduced as slime control agents. The feed water to the EDI device was water permeated through a two-stage reverse osmosis membrane device in a standard water treatment facility, with a conductivity of 2-3 μS / cm and a pH of 6. Test water containing sodium hypochlorite was obtained by adding sodium hypochlorite to the permeate from the two-stage reverse osmosis membrane device. The hypochlorous acid concentration in this test water was 0.05 mg / L as Cl2 in terms of total chlorine concentration. The test water containing sodium hypobromite was permeate obtained by adding a stabilized hypobromous acid composition to the feed water from the two-stage reverse osmosis membrane device in series. The hypobromous acid concentration in this test water was 0.14 mg / L as Cl2. All test waters were supplied directly to the first small demineralization chamber of the EDI device. The temperature of the test water was 25°C. The resistivity of the treated water discharged from the second small demineralization chamber of the EDI device was determined and used as the quality of the treated water. The results are shown in Figure 6. In Figure 6, the horizontal axis represents the CT value, which is the value obtained by measuring the total chlorine concentration in the test water integrated over the water flow time.

[0032] As shown in Figure 6, when a chlorine-based oxidant was introduced into the EDI device, a rapid deterioration in the quality of the treated water occurred after only a few dozen hours of water flow. In contrast, when a bromine-based oxidant was used, no significant deterioration in water quality was observed, and deterioration of the EDI device was suppressed.

[0033] [Example 2] Test water containing the stabilized hypobromous acid composition was passed through a reverse osmosis membrane device, and the sulfamic acid concentration was measured at the inlet of the reverse osmosis membrane device and in the permeated water. The total chlorine concentration of the permeated water was also measured using the DPD method. The test water was prepared by adding a stabilized hypobromous acid composition containing hypobromous acid and sulfamic acid to pure water, and then adjusting the pH to 7 by adding a buffer. The results are shown in Table 1.

[0034] [Table 1]

[0035] As shown in Table 1, when a composition containing hypobromous acid and sulfamic acid was added to the water to be treated in a reverse osmosis membrane device, sulfamic acid was not detected in the permeate water from the reverse osmosis membrane device, but components that were detected by measuring the total chlorine concentration using the DPD method were contained. This shows that hypobromous acid is contained in the permeate water from the reverse osmosis membrane.

[0036] [Example 3] The water treatment device shown in Figure 3 was assembled, and changes in the behavior of water quality degradation of treated water due to differences in the structure of the EDI device 10 used were investigated. The EDI device 10 used was the EDI device shown in Figure 2 (structure 1), in which the desalination compartment is not divided into two small desalination compartments, and the EDI device shown in Figure 5 (structure 2), in which the desalination compartment is divided into two small desalination compartments by an intermediate ion exchange membrane. Water containing a stabilized hypobromous acid composition was passed through a reverse osmosis membrane device 40 as the water to be treated, and the permeate from the reverse osmosis membrane device 40 was passed through the EDI device 10. The hypobromous acid concentration in the water to be treated at the inlet of the EDI device 10 was 0.14 mg / L as Cl2. The temperature of the water to be treated was 25°C. The results are shown in Figure 7. The EDI device with structure 1 (Figure 2), in which the desalination compartment is not divided into small desalination compartments but is filled with a mixed bed of anion exchange resin and cation exchange resin, experienced less water quality degradation due to hypobromous acid than the EDI device with structure 2 (Figure 5), in which the desalination compartment is divided into two small desalination compartments by an intermediate ion exchange membrane, and the resistivity of the treated water remained at 16 MΩ cm even when the CT value reached 100 mg h / L.

[0037] If the CT value in mg·h / L is x and the resistivity of the treated water in MΩ·cm is y, the linear regression equation for Structure 1 (Figure 2) is y = -0.0128x + 17.33, and for Structure 2 (Figure 5) is y = -0.0233x + 15.634. One criterion for determining EDI system degradation is when the resistivity of the treated water drops to 10 MΩ·cm. The CT value until the resistivity of the treated water drops to 10 MΩ·cm is estimated from the linear regression equation obtained from the graph in Figure 7 to be approximately 572 for Structure 1 and approximately 242 for Structure 2. This is approximately 2.4 times larger for Structure 1 than for Structure 2, indicating that Structure 1 suppresses EDI system degradation for a longer period. Specifically, Structure 1 was found to function well as an EDI system until the CT value reached at least 550 mg·h / L.

[0038] [Example 4] Using a water treatment device similar to that used in Example 3, a bromine-based oxidizing agent was intermittently added to the treated water upstream of the reverse osmosis membrane device 40, and changes in the quality of the treated water were examined. In Example 4, the same water as in Example 3 was used, except that the hypobromous acid concentration in the treated water at the inlet of the EDI device 10 during the addition of the bromine-based oxidizing agent was adjusted to 0.07 mg / L as Cl2. The intermittent addition conditions were 3 hours of bromine-based oxidizing agent addition per day. The results are shown in Figure 8. As shown in Figure 8, the quality of the treated water temporarily deteriorated when the bromine-based oxidizing agent was added, but recovered after the addition was stopped. Furthermore, repeated intermittent addition did not decrease the resistivity when the water quality deteriorated due to the addition of the bromine-based oxidizing agent. These results demonstrate that the intermittent addition of a bromine-based oxidizing agent significantly suppresses deterioration of the EDI device. [Explanation of symbols]

[0039] 10. Electrodeionized water production equipment (EDI equipment) 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 room 31,33 Cation exchange membrane 32,24,37 Anion exchange membrane

Claims

1. A water treatment method using an electrodeionization water production apparatus comprising an anode, a cathode, a deionization compartment, and a concentration compartment adjacent to the deionization compartment, the deionization compartment and the concentration compartment being disposed between the anode and the cathode, wherein treated water is obtained by passing water to be treated through the deionization compartment, applying a DC voltage continuously or intermittently between the anode and the cathode while the water to be treated is flowing through the deionization compartment; an addition step of adding a bromine-based oxidizing agent containing hypobromous acid and / or hypobromite to the water to be treated upstream of the electrodeionized water production apparatus; and Both the deionization compartment and the concentration compartment are filled with an anion exchange resin and a cation exchange resin in a mixed bed form, The water treatment method, wherein the concentration of hypobromous acid contained in the water to be treated at the inlet of the electrodeionized water production apparatus is 0.02 mg / L as Cl 2 or more and less than 0.5 mg / L as Cl 2 as a value obtained by measuring the total chlorine concentration of the water to be treated.

2. 2. The water treatment method according to claim 1, wherein the bromine-based oxidizing agent is a stabilized hypobromous acid composition containing hypobromous acid and / or a hypobromite salt and a sulfamic acid compound.

3. 3. The water treatment method according to claim 1, wherein the water to be treated, to which the bromine-based oxidant has been added, is supplied to a reverse osmosis membrane device, and the permeate from the reverse osmosis membrane device is supplied to the electrodeionized water production device.

4. a measuring step of measuring the total chlorine concentration of the permeated water from the reverse osmosis membrane device; The concentration of hypobromous acid in the permeated water is 0.5 mg / L as Cl as the value obtained by the measurement step. ２ an adjusting step of adjusting the concentration of the bromine-based oxidizing agent contained in the permeated water when the concentration is above; The water treatment method of claim 3 further comprising:

5. The water treatment method according to claim 1 , wherein the bromine-based oxidizing agent is intermittently added to the water to be treated in the adding step.

6. 6. A water treatment method according to claim 1, wherein the product of the value representing the concentration of hypobromous acid contained in the treated water at the inlet of the electrodeionized water production device as a value measured for the total chlorine concentration of the treated water and the time the treated water is passed through the electrodeionized water production device is 550 mg h / L or less.

7. an electrodeionization water production apparatus comprising an anode, a cathode, a deionization compartment, and a concentration compartment adjacent to the deionization compartment, the deionization compartment and the concentration compartment being disposed between the anode and the cathode, wherein water to be treated is passed through the deionization compartment and treated water is discharged; an adding means provided upstream of the electrodeionized water production apparatus for adding a bromine-based oxidizing agent containing hypobromous acid and / or hypobromite to the water to be treated; Equipped with Both the deionization compartment and the concentration compartment are filled with an anion exchange resin and a cation exchange resin in a mixed bed form, the concentration of hypobromous acid contained in the water to be treated at the inlet of the electrodeionized water production apparatus is equal to or greater than 0.02 mg / L as Cl 2 and less than 0.5 mg / L as Cl 2 as a value obtained by measuring the total chlorine concentration of the water to be treated; A water treatment device, wherein a DC voltage is applied continuously or intermittently between the anode and the cathode while the water to be treated is flowing through the deionization compartment.

8. a reverse osmosis membrane device is provided in front of the electrodeionized water production device; 8. The water treatment device according to claim 7, wherein the adding means is provided upstream of the reverse osmosis membrane device, and the water to be treated that has permeated the reverse osmosis membrane of the reverse osmosis membrane device is supplied to the electrodeionized water production device.

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