Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device, capable of effectively utilizing a slime control agent for a reverse osmosis membrane on treatment of ammonia-containing water to be treated by using a reverse osmosis membrane 51 and an electric type deionization water production apparatus (EDI apparatus) 10 provided in a latter part thereof while preventing degradation of the reverse osmosis membrane and the EDI apparatus.SOLUTION: By adding hypochlorous acid and / or a salt thereof to water to be treated, then adding a slime control agent to the water to be treated, the water to be treated with reduced ammonia concentration is designed to be supplied to the reverse osmosis membrane 51. The slime control agent comprises a joint chlorine-based oxidant or a stabilized bromine oxidant.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment method and a water treatment device in which ammonia-containing water to be treated is successively treated by a reverse osmosis membrane (RO membrane) and an electrodeionized water production apparatus (EDI apparatus). [Background technology]

[0002] In the field of water treatment, water to be treated is often treated with a reverse osmosis membrane. Since biofouling caused by live bacteria can occur in reverse osmosis membranes, a slime control agent (slime inhibitor) for reverse osmosis membranes is added to the water supplied to the reverse osmosis membrane for sterilization. For example, an oxidizing agent containing a halogen (chlorine or bromine), i.e., a halogen-based oxidizing agent, is widely used as the slime control agent. Patent Document 1 discloses that when ammonia is contained in the water supplied to a reverse osmosis membrane device equipped with a reverse osmosis membrane, the halogen-based oxidizing agent added to the water is more likely to permeate the reverse osmosis membrane.

[0003] It is often the case that an electric deionized water producing device (EDI (Electrodeionization) device) is provided at the permeate outlet of the reverse osmosis membrane device to perform a desalination process on the permeate of the reverse osmosis membrane. The EDI device is a device that combines electrophoresis and electrodialysis, and is provided with a desalination compartment partitioned by an ion exchange membrane between an anode and a cathode. In the EDI device, at least the desalination compartment is filled with an ion exchange resin, and by applying a direct current between the anode and the cathode and passing the water to be treated through the desalination compartment, the treated water from which ion components have been removed flows out from the desalination compartment. The EDI device has the advantage of eliminating the need for a process to regenerate the ion exchange resin with a chemical. However, as described in Patent Document 2, it is known that when an oxidizing agent flows into the EDI device, the ion exchange resin and ion exchange membrane in the EDI device deteriorate, causing a sudden decrease in the water quality of the treated water and an increase in the water flow differential pressure. When such a phenomenon occurs, the EDI device may need to be replaced. Therefore, when an EDI device is provided downstream of a reverse osmosis membrane device, it is necessary to control the EDI device so that the slime control agent for the reverse osmosis membrane does not flow into the EDI device. If ammonia is contained in the feed water supplied to the reverse osmosis membrane device, the oxidizing agent, which is the slime control agent, is likely to permeate the reverse osmosis membrane as described above, which may cause deterioration of the EDI device.

[0004] Incidentally, Patent Document 3 discloses intermittently adding a slime control agent to the water supplied to a reverse osmosis membrane device. However, when a tank is provided for temporarily storing the water supplied to the reverse osmosis membrane device and the slime control agent is intermittently added to the tank, the slime control agent is diluted in the tank, so that the target concentration may not be reached or the agent may not be added according to a predetermined time schedule, and there is a risk that accurate control cannot be performed and sufficient sterilization effect cannot be obtained.

[0005] Hypochlorous acid is included in the category of halogen-based oxidizing agents, but it is known to deteriorate reverse osmosis membranes. Therefore, it is necessary to suppress the inflow of hypochlorous acid into reverse osmosis membrane devices. From the viewpoint of suppressing deterioration of reverse osmosis membranes, combined chlorine-based oxidizing agents or stabilized bromine-based oxidizing agents are preferably used as slime control agents for reverse osmosis membranes. Combined chlorine-based oxidizing agents are compounds of chlorine-based oxidizing agents such as hypochlorous acid and sulfamic acid compounds, and a representative example is chlorosulfamic acid. Stabilized bromine-based oxidizing agents are, for example, compounds of bromine-based oxidizing agents and sulfamic acid compounds, as described in Patent Document 4 and the like, and are also called stabilized hypobromous acid compositions. The bromine-based oxidizing agents referred to here include, for example, bromine, bromine chloride, and hypobromous acid, and further include reaction products of sodium bromide and hypochlorous acid. Patent Document 5 discloses an example of a method for producing a stabilized hypobromous acid composition.

[0006] On the other hand, hypochlorous acid has a great effect in suppressing biofouling and is frequently used for sterilization in pipes and tanks. Therefore, when hypochlorous acid is used as a sterilizing agent for pipes and tanks, it is necessary to take measures such as controlling the addition or adding a reducing agent to the feed water of the reverse osmosis membrane at the inlet side of the reverse osmosis membrane device to decompose and remove hypochlorous acid. When adding a reducing agent, it is necessary to add an excess of the reducing agent to completely suppress the inflow of hypochlorous acid into the reverse osmosis membrane device, but the slime control agent for the reverse osmosis membrane is consumed by the excess reducing agent. In particular, when the reducing agent is added continuously, it is necessary to constantly add an excess of the slime control agent for the reverse osmosis membrane. Patent Documents 6-8 disclose that when a tank for temporarily storing the feed water to the reverse osmosis membrane device is provided and sodium hypochlorite is added to the feed water in the tank or in the preceding stage, a reducing agent, for example, sodium hydrogen sulfite, is changed to the feed water in the pipe leading from the tank to the reverse osmosis membrane device, and then a slime control agent for the reverse osmosis membrane is added. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-30061 A [Patent Document 2] Japanese Patent Application Publication No. 11-165176 [Patent Document 3] JP 2020-142211 A [Patent Document 4] JP 2018-15679 A [Patent Document 5] JP 2014-101251 A [Patent Document 6] International Publication No. 2016 / 158633 [Patent Document 7] JP 2010-201313 A [Patent Document 8] JP 2016-221500 A Summary of the Invention [Problem to be solved by the invention]

[0008] When treating water using a reverse osmosis membrane and an EDI device placed behind it, if the water contains ammonia or its dissociated form, ammonium ions, the slime control agent, which is an oxidizing agent, will easily pass through the reverse osmosis membrane and reach the EDI device, which may cause the EDI device to deteriorate. In addition, since the reverse osmosis membrane itself is deteriorated by hypochlorous acid, a reducing agent may be added to the water before the reverse osmosis membrane to remove hypochlorous acid, but in that case, the slime control agent for the reverse osmosis membrane is also consumed by the reducing agent, which causes a problem.

[0009] An object of the present invention is to provide a water treatment method and water treatment device that can effectively utilize a slime control agent for reverse osmosis membranes while preventing deterioration of the reverse osmosis membrane and the EDI device when treating water containing ammonia using a reverse osmosis membrane and an EDI device arranged downstream of the reverse osmosis membrane. [Means for solving the problem]

[0010] The water treatment method of the present invention is directed to ammonia-containing water to be treated, Two stages arranged in series The treated water is passed through a reverse osmosis membrane. Sequential After passing through Later The permeated water from the reverse osmosis membrane is fed to an electrical deionization device. formula A water treatment method for obtaining treated water from a deionized water production apparatus, in which hypochlorous acid and / or its salt are added to the water to be treated, and then a slime control agent is added to the water to be treated, thereby producing water to be treated with a reduced ammonia concentration. The first To be fed to reverse osmosis membrane At least a part of the concentrated water from the reverse osmosis membrane in the latter stage is returned to the inlet side of the reverse osmosis membrane in the former stage. Slime control agents are combined chlorine-based oxidizers or stabilized bromine-based oxidizers.

[0011] The water treatment device of the present invention is a water treatment device for treating water containing ammonia, 1. Equipped with reverse osmosis membrane 1. A reverse osmosis membrane device; a second reverse osmosis membrane device provided with a second osmosis membrane and supplied with permeated water from the first reverse osmosis membrane device; The permeate from the reverse osmosis membrane device is supplied to the desalination chamber, and the treated water is discharged from the desalination chamber. formula The deionized water production apparatus includes a first adding means for adding hypochlorous acid and / or its salt to the water to be treated, and a second adding means for adding a slime control agent to the water to be treated to which the hypochlorous acid and / or its salt has been added by the first adding means, and the water to be treated to which the slime control agent has been added by the second adding means is 1. It is fed to a reverse osmosis membrane device, At least a portion of the concentrated water from the second reverse osmosis membrane device is returned to the upstream stage of the first reverse osmosis membrane device. Slime control agents are combined chlorine-based oxidizers or stabilized bromine-based oxidizers. Effect of the Invention

[0012] According to the present invention, when treating water containing ammonia using a reverse osmosis membrane and an EDI device arranged downstream of the membrane, it is possible to effectively utilize a slime control agent for the reverse osmosis membrane while preventing deterioration of the reverse osmosis membrane and the EDI device. [Brief description of the drawings]

[0013] [Figure 1]1 is a diagram showing a water treatment device according to an embodiment of the present invention; [Diagram 2] FIG. 1 illustrates an example of a configuration of an EDI device. [Diagram 3] FIG. 13 is a diagram showing another configuration example of the water treatment device. [Figure 4] FIG. 13 is a diagram showing another configuration example of the water treatment device. [Diagram 5] FIG. 13 is a diagram showing another configuration example of the water treatment device. [Figure 6] FIG. 13 is a diagram illustrating another example of the configuration of an EDI device. [Figure 7] FIG. 1 is a diagram illustrating the results of Example 1. [Figure 8] 1 is a graph showing the results of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of a water treatment device according to an embodiment of the present invention. The water treatment device shown in FIG. 1 is a device for treating ammonia (NH 3 As is well known, ammonia is converted into ammonium ions (NH 4 + ) between NH 3 +H 2 O ⇔ NH 4 + +OH - In the acid-base equilibrium state represented by the formula (1) above, ammonia and ammonium ions coexist in the water to be treated unless the water to be treated is extremely acidic or extremely basic. In the following explanation, water to be treated that contains ammonia and / or ammonium ions is also called ammonia-containing water to be treated. Even when the water to be treated is called ammonia-containing water to be treated, the water to be treated usually contains ammonium ions in addition to ammonia.

[0015] The water treatment device includes an electrodeionized water production device (EDI device) 10, a supply tank 40 for storing water to be treated, and a reverse osmosis membrane device 50 provided with a reverse osmosis membrane 51. Hypochlorous acid is added to the water to be treated upstream of the supply tank 40 in the form of, for example, an aqueous sodium hypochlorite solution. The hypochlorous acid is added for sterilization and the like in the supply tank 40. Instead of adding hypochlorous acid to the water to be treated upstream of the supply tank 40, hypochlorous acid may be introduced into the supply tank 40 independently of the water to be treated, as shown by the dashed line in FIG. 1.

[0016] A pipe 42 is connected to the outlet of the supply tank 40, and a reverse osmosis membrane device 50 is connected to the tip of the pipe 42. A pump 44 is provided in the pipe 42 to pump the water to be treated in the supply tank 40 toward the reverse osmosis membrane device 50. A slime control agent is added to the water to be treated flowing through the pipe 42 at a position between the outlet of the supply tank 40 and the primary side of the pump 44. The slime control agent may be added to the water to be treated continuously, but it is preferable to add it intermittently. When the slime control agent is added intermittently, the water to be treated steadily flows toward the reverse osmosis membrane device 50 in the pipe 42, and the period during which the slime control agent is added to the water to be treated is defined as an addition period, and the period during which the slime control agent is not added is defined as a non-addition period. For example, the addition period is within 12 hours in any 24-hour period, and the addition period is within 0.25 to 12 hours, and the non-addition period is within 3 to 320 hours, so that the slime control agent can be added to the water to be treated. In this embodiment, the slime control agent added to the treated water flowing through pipe 42 is a slime control agent for reverse osmosis membranes, such as a slime cottontole agent containing a combined chlorine-based oxidant, or a slime control agent containing a stabilized bromine-based oxidant, and in particular, a slime control agent containing a stabilized bromine-based oxidant is preferred.

[0017] Furthermore, a reducing agent may be added to the water to be treated flowing through the pipe 42 between the outlet of the supply tank 40 and the addition position of the slime control agent as a means for removing hypochlorous acid. The reducing agent may be added continuously or intermittently, but since the reducing agent is intended to suppress deterioration of the reverse osmosis membrane, it is preferable to add the reducing agent continuously from that viewpoint. In addition, the reducing agent is often added in excess to prevent deterioration of the reverse osmosis membrane, but in that case, there is a risk that the slime control agent will be consumed by the excess reducing agent. When adding the slime control agent, adding it intermittently rather than continuously can suppress the consumption of the slime control agent by the reducing agent. The reducing agent added to the water to be treated to remove hypochlorous acid is, for example, sodium hydrogen sulfite. The water to be treated that did not pass through the reverse osmosis membrane 51 in the reverse osmosis membrane device 50, i.e., concentrated water, is discharged from the concentrated water outlet of the reverse osmosis membrane device 50. On the other hand, the water to be treated that has permeated the reverse osmosis membrane 51, ie, the permeate, is supplied to the deionization chamber 23 of the EDI device 10 (see FIG. 2).

[0018] FIG. 2 shows an example of the configuration of the EDI device 10. The EDI device 10 is provided with a deionization chamber 23 between an anode chamber 21 equipped with an anode 11 and a cathode chamber 25 equipped with a cathode 12. A concentration chamber 22 is disposed on the anode chamber 21 side of the deionization chamber 23, and a concentration chamber 24 is disposed on the cathode chamber 25 side of the deionization chamber 23. The anode chamber 21 and the concentration chamber 22 are separated by a cation exchange membrane 31, and the concentration chamber 22 and the deionization chamber 23 are separated by an anion exchange membrane 32. The deionization 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. In the end, the deionization chamber 23 is partitioned by the anion exchange membrane 32 located on the anode 11 side and the cation exchange membrane 33 located on the cathode 12 side. The deionization chamber 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 form, and the cathode chamber 25 is packed with anion exchange resin.

[0019] In the EDI device 10, feed water is passed through the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25, respectively, and the water to be treated is passed through the deionization chamber 23 while a direct current is applied between the anode 11 and the cathode 12. As a result, the water to be treated is desalted in the deionization chamber 23, and treated water from which ionic components have been removed, i.e., deionized water, is discharged from the deionization chamber 23. In this embodiment, the water to be treated supplied to the deionization chamber 13 is the permeate of the reverse osmosis membrane 51. Concentrated water containing ionic components migrated from the water to be treated is discharged from the concentration chambers 22 and 24, and electrode water is discharged from the anode chamber 21 and the cathode chamber 25. The direct current may be applied continuously or intermittently while the water to be treated is passed through the deionization chamber 23.

[0020] 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 the anode 11 and the cathode 12. This basic configuration is called a cell set. In practice, a plurality of such cell sets ("N sets" in FIG. 2) are arranged in parallel between the electrodes, and the plurality of cell sets are electrically connected in series with one end serving as the anode 11 and the other end serving as the cathode 12, thereby increasing the processing capacity. In this case, adjacent concentration compartments can be shared between adjacent cell sets, so that the configuration of the EDI device 10 can be [anode compartment|CEM|C|X|X|···|X|AEM|cathode compartment], where X represents a 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 between 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 between the cathode compartment 25.

[0021] Next, the operation of the water treatment device shown in Fig. 1 will be described. Hypochlorous acid is added to the water to be treated, which is ammonia-containing water to be treated, for example, for sterilization inside the tank, and the water is temporarily stored in the supply tank 40. Hypochlorous acid ions (ClO - ) reacts with ammonium ion to form monochloramine (NH 2Cl) is produced (this is equivalent to sodium hypochlorite reacting with ammonia to produce monochloramine), so the ammonium ion concentration in the water to be treated is reduced. In addition, the hypochlorous acid concentration in the water to be treated is also reduced with the production of monochloramine. The water to be treated is then supplied from the supply tank 40 to the reverse osmosis membrane device 50 via the pipe 42, and a slime control agent is added at that time. However, since the ammonia concentration in the water to be treated is reduced, the slime control agent, which is an oxidizing agent, is less likely to permeate the reverse osmosis membrane 51. As a result, the reverse osmosis membrane device 50 supplies the desalting chamber 23 of the EDI device 10 with water to be treated that contains almost no hypochlorous acid and in which the leakage of the slime control agent, which is an oxidizing agent, is suppressed, so that the ion exchange resin and ion exchange membrane contained in the EDI device 10 are prevented from being deteriorated by the oxidizing agent, and deterioration of the EDI device 10 can be prevented.

[0022] In the water treatment device of this embodiment, the ammonium ion concentration in the water to be treated is reduced by adding hypochlorous acid and reacting it with ammonium ions. If hypochlorous acid is added in an amount greater than the equivalent of the ammonium ions contained in the water to be treated, the hypochlorous acid not consumed in the reaction will deteriorate the reverse osmosis membrane 51. On the other hand, if hypochlorous acid is added in an amount less than the equivalent of the ammonium ions in the water to be treated, ammonium ions will remain, and as a result, the slime control agent may permeate the reverse osmosis membrane 51 and deteriorate the EDI device 10. As will be clear from the examples described later, when ammonium ions remain, the degree of deterioration of the EDI device 10 can be suppressed by intermittently adding the slime control agent. In addition, in this embodiment, the slime control agent is added to the water to be treated not in the supply tank 40 but at a position downstream of the supply tank 40 where the water to be treated steadily flows in one direction, so that the slime control agent can be intermittently added to provide more accurate and effective sterilization without being affected by the dilution of the slime control agent in the tank.

[0023] In the water treatment device shown in FIG. 1, as described above, a reducing agent can be added to the water to be treated at a position before the slime control agent is added in the pipe 42, and excess hypochlorous acid can be removed. Here, a means other than adding a reducing agent can be used as a removal means for removing hypochlorous acid. FIG. 3 shows another configuration example of a water treatment device based on the present invention. In the water treatment device shown in FIG. 3, instead of adding a reducing agent in the water treatment device shown in FIG. 1, an activated carbon tower 43 is arranged at the adding position of the reducing agent in the pipe 42. The inside of the activated carbon tower 43 is filled with activated carbon that adsorbs and removes hypochlorous acid, and the water to be treated passes through the activated carbon tower 43. In the water treatment device based on the present invention, a means other than a reducing agent or activated carbon can be used as a removal means for removing hypochlorous acid from the water to be treated.

[0024] In the water treatment device of this embodiment, hypochlorous acid and a slime control agent are added to the ammonia-containing water to be treated as described above, thereby preventing oxidants such as slime control agents from permeating the reverse osmosis membrane 51 and flowing into the EDI device 10. However, in case the oxidant does permeate the reverse osmosis membrane 51, an activated carbon filter can be installed between the permeate outlet of the reverse osmosis membrane device 50 and the inlet of the EDI device 10, and the oxidant can be captured in the activated carbon filter to prevent the oxidant from flowing into the EDI device 10. In that case, since the amount of oxidant to be captured is considered to be small, it is preferable to use a fibrous activated carbon filter such as that disclosed in JP 2020-18970 A as the activated carbon filter.

[0025] FIG. 4 shows another example of the configuration of a water treatment device according to the present invention. The water treatment device shown in FIG. 4 is configured by disposing another reverse osmosis membrane device 55 between the reverse osmosis membrane device 50 and the EDI device 10 in the water treatment device shown in FIG. 1. The reverse osmosis membrane device 55 is provided with a reverse osmosis membrane 56. Permeated water from the reverse osmosis membrane device 50 in the front stage is supplied to the reverse osmosis membrane device 55 in the rear stage, and the permeated water from this reverse osmosis membrane device 55 is supplied to the desalting chamber 23 of the EDI device 10. The concentrated water from the reverse osmosis membrane device 50 in the front stage is discharged to the outside, as in the case of the water treatment device shown in FIG. 1. In contrast, at least a portion of the concentrated water from the reverse osmosis membrane device 55 in the rear stage is circulated to the supply tank 40. In this water treatment device, the water to be treated in the supply tank 40 is diluted by concentrated water circulating from the downstream reverse osmosis membrane device 55, so that the ammonium ion concentration in the water to be treated in the supply tank 40 decreases and the contact concentration and contact time between the slime control agent and ammonium ions are reduced.As a result, the permeation of the slime control agent through the reverse osmosis membranes 51, 56 is further suppressed, and deterioration of the EDI device 10 can be further suppressed.

[0026] The water treatment device according to the present invention may be configured to add hypochlorous acid and / or its salt to the ammonia-containing water to be treated, and then add a slime control agent to the water to be treated, and then treat the water to be treated by the reverse osmosis membrane device 50 and the EDI device 10 in sequence. Therefore, the water treatment device according to the present invention is not limited to the configurations shown in Figs. 1, 3, and 4. Fig. 5 shows another configuration example of the water treatment device according to the present invention. The water treatment device shown in Fig. 5 is configured such that an activated carbon tower 43 is provided in front of the supply tank 40 that temporarily stores the water to be treated in the water treatment device shown in Fig. 1, and the ammonia-containing water to be treated to which hypochlorous acid has been added is passed through the activated carbon tower 43 and then supplied to the supply tank 40. The slime control agent is added to the water to be treated in the supply tank 40, but the slime control agent may be added to the water to be treated in the rear of the supply tank 40, for example, in the piping 42. Since the activated carbon tower 43 is provided as a means for removing hypochlorous acid, a reducing agent is not added to the water to be treated in this water treatment device. The water treatment device shown in FIG. 5 is configured so that hypochlorous acid does not flow into supply tank 40. However, hypochlorous acid has the ability to not only remove ammonia or ammonium ions but also to sterilize. Considering the characteristics of supply tank 40, in which water tends to stagnate and live bacteria tend to grow, a configuration that allows hypochlorous acid to flow into supply tank 40 and sterilize supply tank 40 is preferable.

[0027] FIG. 6 shows another example of an EDI device that can be used in each of the above-mentioned water treatment devices. In the EDI device shown in FIG. 6, the desalting compartment 23 of the EDI device 10 shown in FIG. 2 is divided by an intermediate ion exchange membrane, with the anode 11 side of the intermediate ion exchange membrane being the first small desalting compartment 27, and the cathode 12 side of the intermediate ion exchange membrane being the second small desalting compartment 28. 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 of the first small desalting compartment 27 is directly supplied to the second small desalting compartment 28, and the treated water of this EDI device is discharged from the second small desalting compartment 28. In the example shown here, the first small deionization chamber 27 is filled with anion exchange resin. The second small deionization chamber 28 has a double-bed structure, with a cation exchange resin filled on the upstream side along the direction of flow of the water to be treated and anion exchange resin filled on the downstream side. In the EDI device shown in Fig. 6, the arrangement of the anion exchange membrane 32, the first small deionization chamber 27, the anion exchange membrane 37, the second small deionization chamber 28, the cation exchange membrane 33 and the concentration chamber 23 is defined as a repeating unit X, and multiple sets of the repeating unit X can be provided 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.

[0028] The EDI device 10 used in the water treatment device according to the present invention may be, for example, an EDI device as shown in Fig. 2 having one deionization compartment 23 between two adjacent concentration compartments 22, 24, or may be, for example, an EDI device as shown in Fig. 6 having two small deionization compartments 27, 28 separated by an intermediate ion exchange membrane (e.g., anion exchange membrane 37) between two adjacent concentration compartments 22, 24. In each deionization compartment 23 or each small deionization compartment 27, 28, the ion exchange resin may be packed in any of a single bed form, a mixed bed form, or a multiple bed form.

[0029] When operating a water treatment device based on the present invention, it may be desirable to measure and manage the oxidant concentration in the water to be treated or the treated water at various locations in the device. Hypochlorous acid, combined chlorine-based oxidants used as slime control agents, and stabilized bromine-based oxidants all show values ​​corresponding to their concentrations when a commonly used total chlorine concentration measurement is performed. For example, all of these oxidants show a color change corresponding to the oxidant concentration when measured by a colorimetric method (i.e., the DPD method) using DPD (N,N-diethylparaphenylenediamine), which is known as a method for measuring total chlorine concentration. In addition to the DPD method, a total chlorine concentration measurement method in which iodine liberated by the oxidant oxidizing potassium iodide is quantified by oxidation-reduction titration using sodium thiosulfate can be used to manage the concentration of the oxidant. Therefore, when managing the oxidant concentration regardless of the type of oxidant, the total chlorine concentration is measured, and the measured value can be used to manage the concentration of the oxidant. In that case, the concentration of the oxidant is expressed as a total chlorine concentration equivalent value. In the following explanation, the oxidant concentration is expressed as the measured value when the total chlorine concentration was measured (i.e., the total chlorine concentration equivalent value). To clarify this, the oxidant concentration is expressed as "as Cl 2 " is added.

[0030] An example of measuring the oxidant concentration and controlling the water treatment device based on the measured value will be described. In the water treatment device shown in FIG. 1, a stabilized bromine-based oxidant is used as a slime control agent. The concentration of the stabilized bromine-based oxidant in the permeate of the reverse osmosis membrane device 50, i.e., the supply water to the EDI device 10, is determined by measuring the total chlorine concentration by the DPD method, and the measured value is, for example, 0.02 mg / L as Cl. 2 or more, the measured value is 0.02 mg / L as Cl 2 In the case of the water treatment device shown in FIG. 4, the measured value of the concentration of stabilized bromine-based oxides in the permeate of the downstream reverse osmosis membrane device 55 is, for example, 0.02 mg / L as Cl. 2 or more, the measured value is 0.02 mg / L as Cl 2As described below, control can be performed to change the amount of concentrated water from the downstream reverse osmosis membrane device 55 that is returned to the supply tank 40.

[0031] As described above, in the water treatment method and water treatment device according to the present invention, in order to suppress the inflow of the slime control agent into the EDI device 10 when the water to be treated contains ammonia, hypochlorous acid is added to the water to be treated to reduce the ammonium ion concentration. By intermittently adding the slime control agent for the reverse osmosis membrane to the water to be treated, deterioration of the EDI device 10 is suppressed regardless of the configuration of the desalting compartment in the EDI device 10 or the filling form of the ion exchange resin in the desalting compartment. Furthermore, when a reducing agent is added to the water to be treated to remove hypochlorous acid, the consumption of the slime control agent by the excess reducing agent is greatly suppressed. By adding the reducing agent and the slime control agent to the water to be treated in this order in the rear stage of the supply tank 40, the slime control agent can be added intermittently to bring about accurate and effective sterilization. Furthermore, when reverse osmosis membrane devices 50, 55 are provided in two series, concentrated water from the reverse osmosis membrane device 55 in the latter stage is returned to the former stage to dilute the ammonia in the water to be treated, thereby suppressing the slime control agent from permeating the reverse osmosis membranes 51, 56. The EDI device used in the present invention may be one in which a single desalting chamber 23 is provided between adjacent concentration chambers 22, 24 as shown in FIG. 2, or one in which two small desalting chambers 27, 28 separated by an intermediate ion exchange membrane are provided between adjacent concentration chambers 22, 24 as shown in FIG. 6. The ion exchange resin filling form for the desalting chamber or small desalting chamber may be a single bed or a mixed bed. However, as the configuration of the EDI device, it is preferable to have two small desalting chambers separated by an intermediate ion exchange membrane rather than a single desalting chamber provided between adjacent concentration chambers. As the filling form of the ion exchange resin, it is preferable to have the ion exchange resin filled in a single bed in at least a part of the desalting chamber or small desalting chamber rather than a mixed bed form. EXAMPLES

[0032] Next, the present invention will be described in more detail with reference to examples and reference examples.

[0033] [Example 1] When treating ammonia-containing water to be treated, the presence or absence of deterioration in the quality of the treated water from the EDI device at the rear stage was examined for cases where a treatment to reduce ammonium ions by adding hypochlorous acid was performed and cases where ammonia-containing water to be treated was not performed. The water treatment device shown in FIG. 1 was assembled, and ammonia-containing water to be treated was passed through the water treatment device as test water. Then, the change in resistivity of the treated water discharged from the EDI device 10 was examined for cases where hypochlorous acid was added to the test water at the front stage of the supply tank 40 and cases where it was not added. No reducing agent was added. As the EDI device 10, an EDI device shown in FIG. 2 (structure 1) in which the desalting compartment is not divided into two small desalting compartments, and an EDI device shown in FIG. 6 (structure 2) in which the desalting compartment is divided into two small desalting compartments by an intermediate ion exchange membrane were used. The test water was pure water to which an ammonium salt was added, the water temperature was 25° C., and the pH was 7. Stabilized hypobromous acid was used as a slime control agent. The results are shown in FIG. 7. In FIG. 7, “NH 4 + "Treated" indicates the result for test water in which ammonium ions were reduced by adding hypochlorous acid, and "NH 4 + "Untreated" indicates the result for test water to which hypochlorous acid was not added. In addition, the ammonium ion concentration at the inlet of the reverse osmosis membrane device 50 for the test water to which hypochlorous acid was not added was 1 mg / L. When the total chlorine concentration of the permeated water obtained by passing this test water through the reverse osmosis membrane device 50 was measured, it was 0.14 mg / L as Cl 2 On the other hand, in the test water to which hypochlorous acid was added, no ammonium ions were detected at the inlet of the reverse osmosis membrane device 50, and when the total chlorine concentration of the permeated water obtained by passing this test water through the reverse osmosis membrane device 50 was measured, it was 0.02 mg / L as Cl 2 It was less than.

[0034] As shown in FIG. 7, when the water supplied to the reverse osmosis membrane device 50 contains ammonium ions (NH4 + In the case of "untreated", deterioration of water quality was confirmed regardless of whether the EDI device 10 was of structure 1 or structure 2. 4 + From the results of "Treated," it was found that the water quality (electrical conductivity) of the treated water from the EDI device 10 could be maintained at 18 MΩ·cm by removing ammonium ions with hypochlorous acid.

[0035] [Reference example 1] The effect of intermittently adding a slime control agent was investigated. The water treatment device shown in FIG. 1 was assembled using the EDI device of structure 1 (FIG. 2) as the EDI device 10, and ammonia-containing water to be treated was passed through the water treatment device as test water. The slime control agent was intermittently added to the test water flowing through the pipe 42, and the change in the resistivity of the treated water discharged from the EDI device 10 was investigated. Hypochlorous acid and reducing agents were not added. Pure water to which ammonium salt was added so that the ammonium ion concentration was 1 mg / L was used as the test water. The temperature of the test water was 25° C. and the pH was 7. Stabilized hypobromous acid was used as the slime control agent, and the concentration in the reverse osmosis membrane concentrated water at the time of addition was 2 mg / L as Cl. 2 The slime control agent was added intermittently so that the water quality was maintained at a constant level even when the agent was added repeatedly. In other words, even under conditions where the slime control agent, which is an oxidizing agent, would leak through the reverse osmosis membrane, the water quality could be maintained and the deterioration of the EDI device could be prevented by adding the slime control agent intermittently. The results are shown in Figure 8. As shown in Figure 8, it was found that by adding the slime control agent intermittently, the water quality was quickly restored to the level it was when the agent was not added, and the water quality was maintained at a constant level even when the agent was added repeatedly. In other words, even under conditions where the slime control agent, which is an oxidizing agent, would leak through the reverse osmosis membrane, the water quality could be maintained and the deterioration of the EDI device could be prevented by adding the slime control agent intermittently. [Explanation of symbols]

[0036] 10. Electrodeionized water production equipment (EDI equipment) 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 40 Supply Tank 43 Activated carbon tower 50,55 Reverse osmosis membrane equipment 51,56 reverse osmosis membrane

Claims

1. A water treatment method for treating water containing ammonia, comprising the steps of: passing the water through two reverse osmosis membranes in series; supplying the permeate through the reverse osmosis membrane in the latter stage to an electrodeionized water production apparatus; and obtaining treated water from the electrodeionized water production apparatus, comprising: Hypochlorous acid and / or its salt is added to the water to be treated, and then a slime control agent is added to the water to be treated, so that the water to be treated with a reduced ammonia concentration is supplied to the reverse osmosis membrane in the previous stage; At least a portion of the concentrated water from the reverse osmosis membrane in the latter stage is returned to the inlet side of the reverse osmosis membrane in the former stage; The slime control agent is a combined chlorine-based oxidant or a stabilized bromine-based oxidant.

2. The water treatment method according to claim 1 , wherein the slime control agent is added to the water to be treated intermittently.

3. The water treatment method according to claim 1 or 2, wherein the hypochlorous acid and / or its salt added to the water to be treated is removed before the slime control agent is added to the water to be treated.

4. The total chlorine concentration of the permeated water of the reverse osmosis membrane in the latter stage is measured; The measured total chlorine concentration is 0.02 mg / L as Cl ２ The water treatment method according to any one of claims 1 to 3, wherein the amount of slime control agent added is controlled when the above condition is met.

5. A water treatment device for treating water containing ammonia, a first reverse osmosis membrane device including a first reverse osmosis membrane; a second reverse osmosis membrane device having a second osmosis membrane and receiving permeated water from the first reverse osmosis membrane device; an electrodeionization water production apparatus in which permeate from the second reverse osmosis membrane device is supplied to a deionization compartment and treated water is discharged from the deionization compartment; A first adding means for adding hypochlorous acid and / or a salt thereof to the water to be treated; A second adding means for adding a slime control agent to the water to be treated to which the hypochlorous acid and / or its salt has been added by the first adding means, The water to be treated to which the slime control agent has been added by the second adding means is supplied to the first reverse osmosis membrane device, At least a portion of the concentrated water from the second reverse osmosis membrane device is returned to a stage upstream of the first reverse osmosis membrane device; The slime control agent is a combined chlorine-based oxidant or a stabilized bromine-based oxidant.

6. A supply tank for storing the water to be treated that is to be supplied to the first reverse osmosis membrane device; A removal means for removing the hypochlorous acid and / or its salt is provided between the supply tank and the second adding means in a line connecting the supply tank and the first reverse osmosis membrane device; Further equipped with The water treatment device according to claim 5 , wherein the first adding means is provided in the supply tank or at a position upstream of the supply tank.

7. The system further includes a supply tank for storing the water to be treated, the water being supplied to the first reverse osmosis membrane device. The water treatment device according to claim 5 , wherein the second adding means is provided in a line connecting the supply tank and the first reverse osmosis membrane device.

8. 8. The water treatment device according to claim 5, wherein at least a portion of the deionization compartment of the electrodeionization water production device is filled with an ion exchange resin in a mixed bed form.

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