Water treatment system and cleaning method thereof

Abstract

A water treatment system 100 includes: a first electrodialysis device 1A for generating an acidic liquid and a concentrated alkali waste liquid from the acid regeneration waste liquid of a cation exchange resin tower 40; a second electrodialysis device 1B for generating an alkali liquid and a concentrated acid waste liquid from the alkali regeneration waste liquid of an anion exchange resin tower 41; and a cleaning mechanism 20 for cleaning one electrodialysis device of the first and second electrodialysis devices 1A, 1B using cleaning water containing the concentrated waste liquid generated by the other of the electrodialysis devices 1A, 1B.

Description

Water treatment system and cleaning method thereof

[0001] The present invention relates to a water treatment system and a method for cleaning the same.

[0002] A recovery system is known that recovers acidic or alkaline solutions from wastewater from ion-exchange resin towers using an electrodialysis device. In this recovery system, the electrodialysis device must be cleaned to prevent clogging due to scale formation.

[0003] As an example of a method for cleaning an electrodialysis apparatus, Patent Document 1 describes a method for cleaning an alkaline compartment with an acidic aqueous solution in an electrodialysis apparatus that produces an acidic solution and an alkaline solution from a salt solution by electrodialysis. Patent Document 2 describes a method for desalting and alkali treating water glass using an electrodialysis apparatus, in which precipitates composed mainly of silicates adhere to the desalting compartments, and the precipitates are removed by cleaning the desalting compartments with an alkaline aqueous solution. The alkaline aqueous solution used for cleaning can be an alkaline solution produced by electrodialysis or an alkaline solution to which a new alkaline agent has been added.

[0004] Patent No. 7356200 Patent No. 3967586

[0005] However, when the cleaning method described in Patent Document 1 is applied to an acid recovery facility, the amount of recovered acid solution decreases by the amount of acid solution used for cleaning, resulting in a problem of reduced acid solution recovery efficiency.When the cleaning method described in Patent Document 2 is applied to an alkali recovery facility, the amount of recovered alkaline solution decreases by the amount of alkaline solution used for cleaning, resulting in a problem of reduced alkaline solution recovery efficiency.

[0006] An object of the present invention is to provide a water treatment system and a cleaning method thereof that can suppress a decrease in the amount of recovered acid solution and alkaline solution and prevent clogging due to scale.

[0007] In order to achieve the above object, one aspect of the present invention provides a water treatment system comprising: a first electrodialysis device that produces a concentrated acid solution and alkaline waste liquid from an acid regeneration waste liquid of a cation exchange resin tower; a second electrodialysis device that produces a concentrated alkaline solution and acid waste liquid from an alkaline regeneration waste liquid of an anion exchange resin tower; and a cleaning mechanism that cleans the other of the first and second electrodialysis devices with cleaning water containing the concentrated waste liquid produced by one of the first and second electrodialysis devices.

[0008] Another aspect of the present invention provides a method for cleaning a water treatment system having a first electrodialysis device that produces a concentrated acid solution and alkaline waste liquid from the acid regeneration waste liquid of a cation exchange resin tower, and a second electrodialysis device that produces a concentrated alkaline solution and acid waste liquid from the alkaline regeneration waste liquid of an anion exchange resin tower, characterized in that the other of the first and second electrodialysis devices is cleaned with cleaning water containing the concentrated waste liquid produced by one of the first and second electrodialysis devices.

[0009] According to the present invention, it is possible to suppress a decrease in the amount of recovered acid solution and alkaline solution, and to prevent clogging due to scale.

[0010] Fig. 1 is a schematic diagram showing the configuration of a water treatment system according to a first embodiment of the present invention. Fig. 2 is a schematic diagram showing the configuration of an electrodialysis device on the acid recovery side of the water treatment system shown in Fig. 1. Fig. 3 is a schematic diagram showing the configuration of an electrodialysis device on the alkali recovery side of the water treatment system shown in Fig. 1. Fig. 4 is a schematic diagram showing the configuration of an electrodialysis device on the acid recovery side of the water treatment system shown in Fig. 4. Fig. 5 is a schematic diagram showing the configuration of an electrodialysis device on the alkali recovery side of the water treatment system shown in Fig. 4.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiments are merely examples and are not intended to limit the scope of the present invention.

[0012] (First Embodiment) Fig. 1 is a schematic diagram showing the configuration of a water treatment system according to a first embodiment of the present invention. Fig. 1 shows a primary pure water production apparatus 200 equipped with a water treatment system 100 according to this embodiment. In Fig. 1, solid arrows indicate pipes (or flow paths). The intersection of two pipes indicates that they are not connected, but intersect while being separated from each other.

[0013] In addition to the water treatment system 100, the primary pure water production apparatus 200 includes a K tower 40, an A tower 41, a regenerated wastewater tank 42, and a wastewater treatment facility 43. The K tower 40 is a cation exchange resin tower packed with a cation exchange resin (e.g., a strongly acidic cation exchange resin), and the A tower 41 is an anion exchange resin tower packed with an anion exchange resin (e.g., a strongly basic anion exchange resin).

[0014] Raw water such as industrial water or groundwater is subjected to pretreatment such as clarification as necessary, and then passed through K tower 40 and A tower 41. K tower 40 removes cation components, and A tower 41 removes anion components, thereby producing primary pure water.

[0015] The K tower 40 is regenerated with an acid such as hydrochloric acid. Here, for example, hydrochloric acid with a concentration of about 4% by mass is produced from hydrochloric acid with a concentration of 35% by mass. The K tower 40 is regenerated using hydrochloric acid with a concentration of about 4% by mass as a regenerant. The K tower 40 discharges acid regeneration waste liquid. Here, the acid regeneration waste liquid is ＋ , Na ＋ , Ca ２＋ , Mg ２＋ , Cl － The acid used to regenerate the K column 40 may be sulfuric acid.

[0016] The A tower 41 is regenerated with an alkali such as sodium hydroxide. Here, for example, sodium hydroxide with a concentration of about 3% by mass is produced from sodium hydroxide with a concentration of 25% by mass. The A tower 41 is regenerated using sodium hydroxide with a concentration of about 3% by mass as a regenerant. The A tower 41 discharges alkali regeneration waste liquid. Here, the alkali regeneration waste liquid contains NO ３ － , S.O. ４ ２－, SiO ２ , Na ＋ The ionic components are as follows:

[0017] The water treatment system 100 includes two electrodialysis apparatuses 1A and 1B and a cleaning mechanism 20. The electrodialysis apparatus 1A can be referred to as the first electrodialysis apparatus, and the electrodialysis apparatus 1B can be referred to as the second electrodialysis apparatus. The electrodialysis apparatus 1A constitutes an acid recovery system and produces a concentrated acid solution and alkaline waste solution from the acid regeneration waste solution in the K tower 40 by electrodialysis. The electrodialysis apparatus 1B constitutes an alkali recovery system and produces a concentrated alkaline solution and acid waste solution from the alkaline regeneration waste solution in the A tower 41 by electrodialysis. The cleaning mechanism 20 cleans one of the electrodialysis apparatuses 1A and 1B with cleaning water containing the concentrated waste solution produced by the other electrodialysis apparatus.

[0018] Here, the electrodialysis devices 1A and 1B each have an acid chamber 8 for producing an acid solution and an alkaline chamber 7 for producing an alkaline solution. The electrodialysis device 1A constitutes an acid recovery facility, and the electrodialysis device 1B constitutes an alkaline recovery facility. In the acid recovery facility including the electrodialysis device 1A, the acid regeneration waste liquid is supplied to a raw water tank 12. The acid solution (here, hydrochloric acid with a concentration of 4% by mass) produced in the acid chamber 8 by electrodialysis is recovered and reused as a regenerant. The alkaline solution (sometimes referred to as concentrated alkaline waste liquid) produced in the alkaline chamber 7 is discharged from the electrodialysis device 1A and used to clean the electrodialysis device 1B of the alkaline recovery facility. Meanwhile, in the alkaline recovery facility including the electrodialysis device 1B, the alkaline regeneration waste liquid is supplied to a raw water tank 32. The alkaline solution (here, sodium hydroxide with a concentration of 3% by mass) produced in the alkaline chamber 7 by electrodialysis is recovered and reused as a regenerant. The acid solution produced in the acid chamber 8 (sometimes referred to as concentrated acid waste solution) is discharged from the electrodialysis device 1B and used to clean the electrodialysis device 1A of the acid recovery facility.

[0019] In the electrodialysis apparatus 1A of the acid recovery facility, scale, mainly consisting of hardness components, is generated in the alkaline chamber 7 during electrodialysis. To prevent clogging of the alkaline chamber 7 due to the generation of hardness components, the cleaning mechanism 20 cleans the alkaline chamber 7 of the electrodialysis apparatus 1A with the acid solution (concentrated acid waste liquid) discharged from the electrodialysis apparatus 1B of the alkali recovery facility. In the electrodialysis apparatus 1B of the alkali recovery facility, silica scale is generated in the acid chamber 8 during electrodialysis. To prevent clogging of the acid chamber 8 due to the generation of silica scale, the cleaning mechanism 20 cleans the acid chamber 8 of the electrodialysis apparatus 1B with the alkaline solution (concentrated alkali waste liquid) discharged from the electrodialysis apparatus 1A of the acid recovery facility. Note that the cleaning mechanism 20 may clean only one of the acid chamber 8 of the electrodialysis apparatus 1B or the alkaline chamber 7 of the electrodialysis apparatus 1A.

[0020] The waste cleaning liquid used to clean the alkaline chamber 7 of the electrodialysis apparatus 1A and the waste cleaning liquid used to clean the acid chamber 8 of the electrodialysis apparatus 1B are each discharged into a regenerated wastewater tank 42. In the regenerated wastewater tank 42, the waste cleaning liquids from the electrodialysis apparatuses 1A and 1B are mixed and supplied to a wastewater treatment facility 43.

[0021] 1 is configured to treat the same raw water by arranging K tower 40 and A tower 41 in series, but this is not limiting. In the primary pure water production system 200, A tower 41 and K tower 40 may be arranged in series with other K towers and A towers, respectively, to form two series (e.g., series 1 in which K tower 40 and A tower 41' are arranged in series, and series 2 in which K tower 40' and A tower 41 are arranged in series), and different raw waters may be treated in each series. Alternatively, K tower 40 and A tower 41 may be arranged in parallel, and the same raw water may be supplied to K tower 40 and A tower 41 respectively for treatment, or different raw waters may be supplied to K tower 40 and A tower 41 separately for treatment. If the K tower 40 and the A tower 41 are arranged in series to treat the same raw water, the acid component in the acid regeneration waste liquid discharged from the K tower 40 and the alkali component in the alkali regeneration waste liquid discharged from the A tower 41 are roughly equivalent in amount, making it easy to mix and neutralize the concentrated acid and alkali waste liquids discharged from the electrodialysis devices 1A and 1B. In addition, because the discharge cycle of the acid regeneration waste liquid from the K tower 40 and the discharge cycle of the alkali regeneration waste liquid from the A tower 41 are the same, the timing of operation and cleaning of the electrodialysis devices 1A and 1B can be easily adjusted.

[0022] Next, the configuration of the water treatment system 100 of this embodiment will be described in detail. First, the configuration of the electrodialysis device 1A will be described in detail. FIG. 2 is a schematic diagram showing the configuration of the electrodialysis device 1A. In FIG. 2, solid and dashed arrows indicate pipes (or flow paths), and solid open arrows indicate signal lines for transmitting control signals and the like. The intersection of two pipes indicates that they are not connected and intersect while being separated from each other. The dotted arrow A indicates the direction (or path) of flow of cleaning water.

[0023] Referring to Fig. 2, the electrodialysis apparatus 1A includes anion exchange membranes 5 and ion exchange partition walls 4a, each having an anion exchange function on one side and a cation exchange function on the other side, alternately arranged between an anode 3a and a cathode 3b. A plurality of chambers are provided, each partitioned by the ion exchange partition walls 4a and the anion exchange membranes 5. A power supply 11 applies current between the anode 3a and the cathode 3b. A control device 10 controls the electrodialysis operation, including the current application operation (such as the start and end of current application), and the cleaning operation (such as the start and end of cleaning). The application of current and the start and end of cleaning may be performed manually.

[0024] When the alkaline chamber 7 and the acid chamber 8 of the electrodialysis apparatus 1A are not filled with an ion exchanger, the ion exchange partition wall 4a may have any configuration as long as it is capable of dissociating water. For example, the ion exchange partition wall 4a may be a bipolar membrane, a membrane in which a cation exchange membrane is superimposed with a separate anion exchange membrane, or a membrane in which a cation exchange membrane and a separate anion exchange membrane are superimposed with a polyvalent metal adsorbed on at least one of the membranes.

[0025] When the alkaline chamber 7 and the acid chamber 8 of the electrodialysis apparatus 1A are filled with ion exchangers (in this case, the electrodialysis apparatus is also called an electrodeionization apparatus, or EDI), the ion exchange partition wall 4a may have any configuration as long as it is capable of water dissociation by contact between the ion exchange partition wall alone or the filled ion exchanger. Examples of the ion exchange partition wall 4a include a bipolar membrane, a membrane in which a cation exchange membrane is stacked with a separate anion exchange membrane, a membrane in which a cation exchange membrane and a separate anion exchange membrane are stacked with a polyvalent metal adsorbed on at least one of the membranes, a cation exchange membrane, an anion exchange membrane, a cation exchange membrane adsorbed with a polyvalent metal, and an anion exchange membrane adsorbed with a polyvalent metal. When a cation exchange membrane, an anion exchange membrane, a cation exchange membrane adsorbed with a polyvalent metal, or an anion exchange membrane adsorbed with a polyvalent metal is used, water dissociation is possible by filling the membrane with an ion exchanger having a counterpart ion exchange function. For example, the combination of a cation exchange membrane and an anion exchanger allows for water dissociation.

[0026] The bipolar membrane may have a structure in which, for example, an anion exchange membrane and a cation exchange membrane are laminated together, with an intermediate layer (catalyst) formed between the two exchange membranes. As the ion exchange membrane (or ion exchange resin) having a polyvalent metal adsorbed thereon, one having particles containing a polyvalent metal (at least one of aluminum silicate, magnesium silicate, calcium silicate, calcium magnesium silicate, aluminosilicate, and silicate mineral) adsorbed thereon can be used.

[0027] The multiple chambers provided between the anode 3a and the cathode 3b include an anode chamber 6a, a cathode chamber 6b, an alkaline chamber 7, and an acid chamber 8. The anode chamber 6a is partitioned by the anode 3a and the ion exchange partition wall 4a. The cathode chamber 6b is partitioned by the cathode 3b and the ion exchange partition wall 4a. The alkaline chamber 7 is partitioned by the ion exchange partition wall 4a and the anion exchange membrane 5. The acid chamber 8 is adjacent to the alkaline chamber 7 on the anode side, with the anion exchange membrane 5 sandwiched between them. Two pairs of an acid chamber 8 and an alkaline chamber 7 are disposed between the anode chamber 6a and the cathode chamber 6b, but this is not limiting. The number of pairs of an acid chamber 8 and an alkaline chamber 7 may be one or three or more.

[0028] The acid recovery system including the electrodialysis apparatus 1A includes a raw water tank 12, a wastewater tank 13, and a recovered water tank 14. The raw water tank 12 stores the raw water, which is the liquid to be treated. The raw water tank 12 is connected to a pipe 12c for supplying the raw water, and this pipe 12c is provided with a valve 2b. The supply of the raw water to the raw water tank 12 can be controlled by opening and closing the valve 2b. Specifically, the acid regeneration wastewater from the K tower 40 shown in FIG. 1 can be supplied from the pipe 12c to the raw water tank 12 at a predetermined timing. Note that the valve 2b is not an essential component. For example, a pump may be provided upstream of the valve 2b, and the raw water may be supplied to the raw water tank 12 by controlling the on / off operation of the pump.

[0029] The raw water tank 12 is connected to the alkaline chamber 7 via a pipe 12a, allowing the liquid to be treated stored in the raw water tank 12 to be supplied to the alkaline chamber 7. Although not shown, a pump is provided in the pipe 12a, allowing the treated liquid from the alkaline chamber 7 to circulate between the raw water tank 12 and the alkaline chamber 7. In this embodiment, circulating the treated liquid allows an alkaline liquid of a predetermined concentration to be obtained. This alkaline liquid of a predetermined concentration can be referred to as a concentrated alkaline waste liquid. While there are no particular restrictions on the predetermined concentration, a concentration of 0.04% by mass or more is preferable from the viewpoint of cleanability. This concentrated alkaline waste liquid is used to clean the acid chamber 8 of the electrodialysis apparatus 1B. The raw water tank 12 may also be composed of a storage tank for storing acid regeneration waste liquid and a storage tank for storing raw water for electrodialysis.

[0030] The drainage tank 13 stores and discharges the alkaline liquid (concentrated alkaline waste liquid) produced in the alkaline chamber 7 and the cleaning waste liquid used to clean the alkaline chamber 7. The drainage tank 13 may be composed of a storage tank for storing concentrated alkaline waste liquid and a storage tank for storing cleaning waste liquid. A discharge pipe 12b is connected to the portion of the pipe 12a on the outlet side of the alkaline chamber 7. The pipe 12b communicates with the drainage tank 13, and the alkaline liquid (or cleaning waste liquid) flowing through the pipe 12a can be supplied from the pipe 12b to the drainage tank 13. A valve 2c is provided in the pipe 12b, and by opening and closing this valve 2c, the alkaline liquid (or cleaning waste liquid) can be supplied to the drainage tank 13 at a predetermined timing.

[0031] The recovery water tank 14 is used to recover the acid solution generated in the acid chamber 8. The recovery water tank 14 is connected to the acid chamber 8 via a pipe 14a. Although not shown, a pump is provided in the pipe 14a, which circulates the acid solution generated in the acid chamber 8 between the recovery water tank 14 and the acid chamber 8. The recovery water tank 14 is also connected to a pipe 14b, through which pure water (PW) can be supplied to the recovery water tank 14. A valve 2d is provided in the pipe 14b, and pure water can be supplied to the recovery water tank 14 at predetermined times by opening and closing the valve 2d. In this embodiment, an acid solution of a predetermined concentration can be obtained by supplying and circulating pure water.

[0032] The cleaning mechanism 20 has a pipe 21 for supplying cleaning water containing concentrated acid waste liquid discharged from the electrodialysis apparatus 1B. The pipe 21 is connected to a portion of the pipe 12a on the inlet side of the alkaline chamber 7. The cleaning water is supplied to the alkaline chamber 7 via the pipe 21 and a portion of the pipe 12a. The cleaning waste liquid used to clean the alkaline chamber 7 is supplied to the drainage tank 13 via the pipe 12b. The pipe 21 is provided with a valve 2a. The supply of cleaning water to the alkaline chamber 7 can be controlled using this valve 2a and a valve 2c provided on the pipe 12b. Although not shown, a pump is provided on the pipe 21, which can supply cleaning water to the alkaline chamber 7 at a predetermined space velocity. The portion of the pipe 12a, the pipe 12b, and the valves 2a and 2c constitute part of the cleaning mechanism 20.

[0033] A so-called EDI structure can be applied, in which the alkaline chamber 7 and the acid chamber 8 are each filled with an ion exchanger. In the EDI, the alkaline chamber 7 is preferably filled with an ion exchanger having at least an anion exchange function to transfer chloride (Cl), a type of electrolyte component. On the other hand, the acid chamber 8 may be filled with any ion exchanger, such as a cation exchange resin or an anion exchange resin. The ion exchanger may be treated to adsorb a polyvalent metal.

[0034] An electrode solution flows through the anode chamber 6a and the cathode chamber 6b. The anode chamber 6a and the cathode chamber 6b are configured so that the electrode solution circulates. Depending on the electrode material, sodium hydroxide, saline solution, or the like is used as the electrode solution. In the case of EDI, pure water is preferably used as the electrode solution.

[0035] Next, the configuration of the electrodialysis device 1B will be described in detail. Figure 3 is a schematic diagram showing the configuration of the electrodialysis device 1B. In Figure 3, solid and dashed arrows indicate pipes (or flow paths), and solid open arrows indicate signal lines for transmitting control signals and the like. The intersection of two pipes indicates that they are not connected and intersect while being separated from each other. Dotted arrow A indicates the direction (or path) in which the wash water flows.

[0036] The electrodialysis apparatus 1B shown in Figure 3 differs from the electrodialysis apparatus 1A in that the electrodialysis section is partially different in configuration and further in that the concentrated alkaline waste liquid discharged from the electrodialysis apparatus 1A is used as cleaning water. The same components as those in the electrodialysis apparatus 1A are designated by the same reference numerals, and detailed descriptions thereof will be omitted.

[0037] Ion exchange partition walls 4b and cation exchange membranes 30 are alternately arranged between the anode 3a and the cathode 3b. A plurality of chambers are provided, each partitioned by the ion exchange partition walls 4b and the cation exchange membranes 30. The ion exchange partition wall 4b basically has the same configuration as the ion exchange partition wall 4a. However, while the surface of the ion exchange partition wall 4a that has an anion exchange function is arranged on the anode 3a side, the surface of the ion exchange partition wall 4b that has an anion exchange function is arranged on the cathode 3b side.

[0038] The multiple chambers provided between the anode 3a and the cathode 3b include an anode chamber 6a, a cathode chamber 6b, an alkaline chamber 7, and an acid chamber 8. The anode chamber 6a is partitioned by the anode 3a and the ion exchange partition wall 4b. The cathode chamber 6b is partitioned by the cathode 3b and the ion exchange partition wall 4b. The alkaline chamber 7 is partitioned by the ion exchange partition wall 4b and the cation exchange membrane 30. The acid chamber 8 is adjacent to the alkaline chamber 7 on the cathode side, with the cation exchange membrane 30 sandwiched between them. Two pairs of an acid chamber 8 and an alkaline chamber 7 are disposed between the anode chamber 6a and the cathode chamber 6b, but this is not limiting. The number of pairs of an acid chamber 8 and an alkaline chamber 7 may be one or three or more.

[0039] The alkali recovery facility including the electrodialysis apparatus 1B has a raw water tank 32, a wastewater tank 33, and a recovered water tank 34. The raw water tank 32 stores the raw liquid, which is the liquid to be treated. The raw water tank 32 is connected to a pipe 32c for supplying the raw liquid, and this pipe 32c is provided with a valve 2f. The supply of the raw liquid to the raw water tank 32 can be controlled by opening and closing the valve 2f. Specifically, the alkaline regenerated waste liquid from the A tower 41 shown in FIG. 1 can be supplied to the raw water tank 32 from the pipe 32c at a predetermined timing. The raw water tank 32 may be composed of a storage tank for storing the alkaline regenerated waste liquid and a storage tank for storing raw water for electrodialysis.

[0040] The raw water tank 32 is connected to the acid chamber 8 via a pipe 32a, allowing the liquid to be treated stored in the raw water tank 32 to be supplied to the acid chamber 8. Although not shown, a pump is provided in the pipe 32a, allowing the treated liquid from the acid chamber 8 to circulate between the raw water tank 32 and the acid chamber 8. In this embodiment, circulating the treated liquid allows an acid solution of a predetermined concentration to be obtained. This acid solution of a predetermined concentration can be referred to as a concentrated acid waste liquid. While there are no particular restrictions on the predetermined concentration, a concentration of 0.04% by mass or more is preferable from the viewpoint of cleanability. This concentrated acid waste liquid is used to clean the alkaline chamber 7 of the electrodialysis apparatus 1A.

[0041] The drainage tank 33 stores and discharges the acid solution (concentrated acid waste solution) produced in the acid chamber 8 and the cleaning waste solution used to clean the acid chamber 8. The drainage tank 33 may be composed of a storage tank for storing concentrated acid waste solution and a storage tank for storing cleaning waste solution. A discharge pipe 32b is connected to the portion of the pipe 32a on the outlet side of the acid chamber 8. The pipe 32b communicates with the drainage tank 33, so that the acid solution (or cleaning waste solution) flowing through the pipe 32a can be supplied from the pipe 32b to the drainage tank 33. A valve 2g is provided in the pipe 32b, and by opening and closing this valve 2g, the acid solution (or cleaning waste solution) can be supplied to the drainage tank 33 at predetermined times.

[0042] The recovered water tank 34 is used to recover the alkaline solution produced in the alkaline chamber 7. The recovered water tank 34 is in communication with the alkaline chamber 7 via a pipe 34a. Although not shown, a pump is provided in the pipe 34a, and the alkaline solution produced in the alkaline chamber 7 is configured to circulate between the recovered water tank 34 and the alkaline chamber 7. The recovered water tank 34 is also in communication with a pipe 34b, and pure water (PW) can be supplied to the recovered water tank 34 via this pipe 34b. In this embodiment, an alkaline solution of a predetermined concentration can be obtained by supplying and circulating pure water.

[0043] The cleaning mechanism 20 includes a pipe 22 for supplying cleaning water containing concentrated alkaline waste liquid discharged from the electrodialysis apparatus 1A. The pipe 22 is connected to a portion of the pipe 32a on the inlet side of the acid chamber 8. The cleaning water is supplied to the acid chamber 8 via the pipe 22 and a portion of the pipe 32a. The cleaning waste liquid used to clean the acid chamber 8 is supplied to the drain tank 33 via the pipe 32b. The pipe 22 is provided with a valve 2e. The supply of cleaning water to the acid chamber 8 can be controlled using the valve 2e and a valve 2g provided on the pipe 32b. Although not shown, a pump is provided on the pipe 22, which allows the cleaning water to be supplied to the acid chamber 8 at a predetermined space velocity. The portion of the pipe 32a, the pipe 32b, and the valves 2e and 2g constitute a part of the cleaning mechanism 20.

[0044] The electrodialysis apparatus 1B can also have an EDI structure, as in the electrodialysis apparatus 1A. In the EDI, the alkaline chamber 7 and the acid chamber 8 are each filled with an ion exchanger, and the ion exchanger filled in the acid chamber 8 preferably contains at least a large amount of a cation exchange resin. On the other hand, the alkaline chamber 7 may be filled with an ion exchanger containing any resin, such as an anion exchange resin.

[0045] Next, the operation of the water treatment system 100 of this embodiment will be described in detail with reference to Figures 1 to 3. Below, the operating steps for batch operation will be described as an example. In batch operation, a certain amount of stock solution is received, and circulation and electrodialysis are performed. When the concentration of the acid solution (or alkaline solution) reaches a predetermined value, the acid solution (or alkaline solution) is discharged and new stock solution is received again.

[0046] The acid regeneration waste liquid from the K tower 40 and the alkali regeneration waste liquid from the A tower 41 are both periodically discharged, and the discharge periods are basically the same. Batch operation of the electrodialysis apparatus 1A is performed in accordance with the discharge period of the acid regeneration waste liquid from the K tower 40, and batch operation of the electrodialysis apparatus 1B is performed in accordance with the discharge period of the alkali regeneration waste liquid from the A tower 41.

[0047] First, the operating steps of the electrodialysis apparatus 1A will be described. The operating steps of the electrodialysis apparatus 1A include a stock solution charging step, a first circulation dialysis step, an intermediate cleaning step, a second circulation dialysis step, a discharge step, and a cleaning step.

[0048] (Stock solution introduction step) The control device 10 controls the valves 2b and 2d to be open and the valves 2a and 2c to be closed. A predetermined amount of stock solution is supplied from the pipe 12c to the stock water tank 12, and a predetermined amount of pure water is supplied from the pipe 14b to the recovery water tank 14.

[0049] (First circulating dialysis step) The control device 10 closes all of the valves 2a to 2d and passes the liquid to be treated stored in the raw water tank 12 through the alkaline chamber 7. The control device 10 also applies electricity to the power supply device 11 to perform electrodialysis.

[0050] Electrodialysis is initiated by energizing the anode 3a and the cathode 3b. In the alkaline compartment 7, anions adsorbed on the anion exchange resin move to the anode 3a side, permeate the anion exchange membrane 5, and move to the acid compartment 8. Water dissociation occurs in the ion exchange partition 4a, and H ＋ moves from the ion exchange partition 4 a to the acid chamber 8 .

[0051] Pure water is supplied to the acid chamber 8 and circulated, and an acid solution is produced in the acid chamber 8 by electrodialysis. The acid solution produced in the acid chamber 8 is, for example, hydrochloric acid, sulfuric acid, etc. (sometimes both hydrochloric acid and sulfuric acid are mixed). Here, as the electrodialysis proceeds in the acid chamber 8, H ＋ and Cl － is supplied to generate hydrochloric acid, and when the concentration reaches a predetermined value (for example, 4 mass %), the hydrochloric acid is recovered.

[0052] On the other hand, in the alkaline chamber 7, the acid in the circulating treatment liquid is gradually removed as the electrodialysis progresses, and the OH generated by water dissociation is gradually removed. － As a result, the pH of the treatment liquid in the alkaline chamber 7 increases and becomes alkaline. For example, the liquid to be treated (e.g., acid regeneration waste liquid) supplied to the alkaline chamber 7 contains cations (H ＋ , Na ＋ , Ca ２＋ , Mg ２＋etc.) and anions (Cl － , S.O. ４ ２－ As the electrodialysis proceeds, the OH ions supplied from the ion exchange partition 4 are mixed in the alkaline chamber 7. － By H ＋ is neutralized, and then OH － As the pH of the treatment solution in the alkaline chamber 7 increases, the pH of the treatment solution in the alkaline chamber 7 increases. If the pH of the treatment solution in the alkaline chamber 7 exceeds 7 and reaches the alkaline region, there is a high risk of scale such as calcium hydroxide or magnesium hydroxide being generated.

[0053] Here, it is assumed that scale forms in the alkaline chamber 7 before the hydrochloric acid circulating between the recovered water tank 14 and the acid chamber 8 reaches a predetermined concentration. The control device 10 also opens the valve 2c to supply the alkaline solution circulating between the alkaline chamber 7 and the raw water tank 12 to the wastewater tank 13. This alkaline solution stored in the wastewater tank 13 can be used as concentrated alkaline waste liquid in the intermediate cleaning step for cleaning the acid chamber 8 of the electrodialysis apparatus 1B, which will be described later.

[0054] (Intermediate Cleaning Step) The control device 10 stops the supply of electricity to the power supply device 11 and controls the valves 2a and 2c to be in an open state and the valves 2b and 2d to be in a closed state. After the supply of electricity is stopped, the cleaning mechanism 20 passes the concentrated acid waste liquid supplied from the pipe 21 through the alkaline chamber 7 to clean it. The cleaning waste liquid used to clean the alkaline chamber 7 is supplied to the drainage tank 13 via the pipe 12b. The cleaning waste liquid stored in the drainage tank 13 is drained to any location outside the system.

[0055] The space velocity of the water passing through the alkaline chamber 7 is 400 h -1 That's it, 1000h -1 The following is preferable: Within this range of space velocity, the alkaline chamber 7 can be washed at a flow rate that washes away scale and does not excessively increase the differential pressure between the inlet and outlet of the alkaline chamber 7.

[0056] If the cleaning time is too short, sufficient cleaning effect may not be obtained. On the other hand, if the cleaning time is extended, the electrodialysis time per batch operation period will be shortened accordingly, resulting in a decrease in the amount of acid recovered. In addition, if the cleaning time is extended, a large amount of cleaning water will be used. In consideration of these points, the cleaning time is preferably in the range of 1 minute to 60 minutes, and more preferably in the range of 2 minutes to 10 minutes.

[0057] (Second circulating dialysis step) After the cleaning waste liquid is discharged, the control device 10 closes all of the valves 2a to 2d, passes the liquid to be treated stored in the raw water tank 12 through the alkaline chamber 7, and applies electricity to the power supply device 11. The operation of the alkaline chamber 7 and the acid chamber 8 during electrodialysis is as described in the first circulating dialysis step.

[0058] Here, it is assumed that scale is generated in the alkaline chamber 7 and the hydrochloric acid circulating between the recovered water tank 14 and the acid chamber 8 reaches a predetermined concentration (for example, 4% by mass).

[0059] (Discharge Step) When the hydrochloric acid reaches a predetermined concentration, the control device 10 controls the power supply 11 to stop powering on, the valve 2c to be opened, and the valves 2a, 2b, and 2d to be closed. The alkaline solution (cation-enriched water) circulating between the raw water tank 12 and the alkaline chamber 7 is supplied to the wastewater tank 13 via the pipe 12c. The alkaline solution stored in the wastewater tank 13 can be used as concentrated alkaline waste liquid in the cleaning step for cleaning the acid chamber 8 of the electrodialysis apparatus 1B, which will be described later.

[0060] The hydrochloric acid circulating between the recovery water tank 14 and the acid chamber 8 is stored in the recovery water tank 14. The hydrochloric acid stored in the recovery water tank 14 is discharged to a recovery destination outside the system. Here, the recovered hydrochloric acid is reused as a regenerant for the K tower 40, etc.

[0061] (Cleaning step) After recovering the hydrochloric acid, the control device 10 controls the valves 2a and 2c to be open and the valves 2b and 2d to be closed. Thereafter, the cleaning mechanism 20 passes the concentrated acid waste liquid supplied from the pipe 22 through the alkaline chamber 7 to clean it. The cleaning waste liquid used to clean the alkaline chamber 7 is supplied to the drainage tank 13 via the pipe 12b. The cleaning waste liquid stored in the drainage tank 13 is drained to any location outside the system. The space velocity and cleaning time are as described in the intermediate cleaning step.

[0062] Next, the operating steps of the electrodialysis apparatus 1B will be described. Similar to the operating steps of the electrodialysis apparatus 1A, the operating steps of the electrodialysis apparatus 1B also include a stock solution charging step, a first circulation dialysis step, an intermediate cleaning step, a second circulation dialysis step, a discharge step, and a cleaning step.

[0063] (Stock solution introduction step) The control device 10 controls the valves 2f and 2h to be open and the valves 2e and 2g to be closed. A predetermined amount of stock solution is supplied from the pipe 32c to the stock water tank 32, and a predetermined amount of pure water is supplied from the pipe 34b to the recovery water tank 34.

[0064] (First circulating dialysis step) The control device 10 closes all of the valves 2e to 2h and passes the liquid to be treated stored in the raw water tank 32 through the acid chamber 8. The control device 10 also energizes the power supply device 11 to perform electrodialysis.

[0065] Electrodialysis is initiated by energizing the anode 3a and the cathode 3b. In the acid chamber 8, cations (mainly Na) adsorbed on the cation exchange resin are separated. ＋ ) moves to the cathode 3b side, permeates the cation exchange membrane 30, and moves to the alkaline chamber 7. Water dissociation occurs in the ion exchange partition wall 4b, and OH － moves from the ion exchange partition 4b to the alkaline chamber 7.

[0066] In the alkaline chamber 7, pure water is supplied and electrodialysis is carried out while circulating the pure water. As the electrodialysis progresses, OH is gradually added. － and Na ＋is supplied to generate sodium hydroxide (alkaline solution), and the pH of the treatment solution flowing through the alkaline chamber 7 increases. When the sodium hydroxide reaches a predetermined concentration (for example, 3 mass %), the sodium hydroxide is recovered.

[0067] On the other hand, in the acid chamber 8, as the electrodialysis progresses, the alkali in the circulating treatment solution gradually disappears, and the H generated by water dissociation is released. ＋ As a result, the pH of the treatment solution in the acid chamber 8 decreases, and the amount of silica (SiO ２ ) scale is generated.

[0068] Here, it is assumed that scale forms in the acid chamber 8 before the concentration of sodium hydroxide in the treatment solution circulating between the recovered water tank 34 and the alkaline chamber 7 reaches a predetermined concentration. The control device 10 also opens the valve 2g to supply the acid solution circulating between the acid chamber 8 and the raw water tank 32 to the wastewater tank 33. The acid solution stored in the wastewater tank 33 can be used as concentrated acid waste liquid in the intermediate cleaning step for cleaning the alkaline chamber 7 of the electrodialysis apparatus 1A described above.

[0069] (Intermediate Cleaning Step) The control device 10 stops power supply to the power supply device 11 and controls the valves 2e and 2g to be open and the valves 2f and 2h to be closed. After power supply is stopped, the cleaning mechanism 20 passes concentrated alkaline waste liquid supplied from the pipe 22 through the acid chamber 8 to clean it. The cleaning waste liquid used to clean the acid chamber 8 is supplied to the drainage tank 33 via the pipe 32b. The cleaning waste liquid stored in the drainage tank 33 is drained to any location outside the system.

[0070] The space velocity of the washing water passing through the acid chamber 8 is 400 h -1 That's it, 1000h -1 This range of space velocity allows the acid chamber 8 to be washed at a flow rate that washes away scale and does not excessively increase the pressure difference between the pressure (water pressure) at the inlet and the pressure (water pressure) at the outlet of the acid chamber 8.

[0071] If the cleaning time is too short, sufficient cleaning effect may not be obtained. On the other hand, if the cleaning time is extended, the electrodialysis time per batch operation period will be shortened accordingly, resulting in a decrease in the amount of alkali recovered. In addition, if the cleaning time is extended, a large amount of cleaning water will be used. In consideration of these points, the cleaning time is preferably in the range of 1 minute to 60 minutes, and more preferably in the range of 2 minutes to 10 minutes.

[0072] (Second circulating dialysis step) After the cleaning waste liquid is discharged, the control device 10 closes all of the valves 2e to 2h, passes the liquid to be treated stored in the raw water tank 32 through the acid chamber 8, and applies electricity to the power supply device 11. The operation of the alkaline chamber 7 and the acid chamber 8 during electrodialysis is as described in the first circulating dialysis step.

[0073] Here, it is assumed that scale is formed in the acid chamber 8 and the concentration of sodium hydroxide in the treatment liquid circulating between the recovered water tank 34 and the alkaline chamber 7 reaches a predetermined concentration (for example, 3% by mass).

[0074] (Discharge Step) When the concentration of sodium hydroxide reaches a predetermined concentration, the control device 10 controls the power supply 11 to stop powering on, and controls the valve 2g to open and the valves 2e, 2f, and 2h to close. The acid solution circulating between the raw water tank 32 and the acid chamber 8 is supplied to the wastewater tank 33 via the pipe 32c. The acid solution stored in the wastewater tank 33 can be used as concentrated acid waste liquid in the cleaning step for cleaning the alkali chamber 7 of the electrodialysis apparatus 1A described above.

[0075] The alkaline solution (sodium hydroxide) circulating between the recovered water tank 34 and the alkaline chamber 7 is stored in the recovered water tank 34. The alkaline solution stored in the recovered water tank 14 is discharged to a recovery destination outside the system. Here, the recovered alkaline solution is reused as a regenerant for the A tower 41, etc.

[0076] (Cleaning Step) After recovering the alkaline solution, the control device 10 controls the valves 2e and 2g to be open and the valves 2f and 2h to be closed. Thereafter, the cleaning mechanism 20 passes the concentrated alkaline waste solution supplied from the pipe 22 through the acid chamber 8 to clean it. The cleaning waste solution used to clean the acid chamber 8 is supplied to the drainage tank 33 via the pipe 32b. The cleaning waste solution stored in the drainage tank 33 is drained to any location outside the system. The space velocity and cleaning time are as described in the intermediate cleaning step.

[0077] According to the operating steps of the electrodialysis devices 1A and 1B of the water treatment system 100 of this embodiment described above, the following operational effects are achieved.

[0078] By cleaning the alkaline chamber 7 of the electrodialysis device 1A constituting the acid recovery system with concentrated acid waste liquid discharged from the electrodialysis device 1B constituting the alkali recovery system, clogging of the alkaline chamber 7 due to scale formation can be prevented. In this case, the concentrated acid waste liquid no longer needed on the alkali recovery system side is used to clean the alkaline chamber 7, so the amount of acid solution recovered in the acid recovery system is not reduced, and a decrease in the acid solution recovery efficiency can be suppressed. Furthermore, by preventing clogging of the alkaline chamber 7, the electrodialysis device 1A can be operated stably. Furthermore, using concentrated acid waste liquid no longer needed on the alkali recovery system side is more cost-effective than adding new acid to the wash water.

[0079] Furthermore, by cleaning the acid chamber 8 of the electrodialysis device 1B constituting the alkali recovery system with concentrated alkali waste liquid discharged from the electrodialysis device 1A constituting the acid recovery system, clogging of the acid chamber 8 due to scale formation can be prevented. In this case, the concentrated alkali waste liquid no longer needed on the acid recovery system side is used to clean the acid chamber 8, so the amount of alkali solution recovered by the alkali recovery system is not reduced, and a decrease in the alkali solution recovery efficiency can be suppressed. Furthermore, by preventing clogging of the acid chamber 8, the electrodialysis device 1B can be operated stably. Furthermore, using concentrated alkali waste liquid no longer needed on the acid recovery system side is more cost-effective than adding new alkali to the wash water.

[0080] Furthermore, batch operation allows the liquid to be treated (waste liquid) to be circulated and electrodialysis to be performed repeatedly, so the maximum current value applied at one time between the anode 3a and the cathode 3b can be kept low, allowing for the miniaturization of the device.

[0081] In the operation of the electrodialysis apparatuses 1A and 1B, cleaning is performed twice, in an intermediate cleaning step and a cleaning step, but this is not limited to this. If clogging due to scale can be prevented and a decrease in the recovery efficiency of the acid solution and the alkaline solution can be suppressed, the intermediate cleaning step may be omitted or may be performed two or more times.

[0082] The power supply unit 11 may be energized at either a constant current or a constant voltage. A constant current allows for easy treatment of the wastewater to a predetermined concentration in one batch operation before discharging it. On the other hand, a constant voltage may prevent the wastewater from being treated to the predetermined concentration if the resistance (membrane resistance) between the anode 3a and the cathode 3b increases. For this reason, it is preferable to energize the power supply unit 11 at a constant current.

[0083] If the back pressure on the outlet side of electrodialysis apparatus 1A hardly changes, a pressure gauge may be provided at the inlet of electrodialysis apparatus 1A, and when the measured value of the pressure gauge exceeds a predetermined value, cleaning mechanism 20 may clean alkaline chamber 7 of electrodialysis apparatus 1A. Similarly, if the back pressure on the outlet side of electrodialysis apparatus 1B hardly changes, a pressure gauge may be provided at the inlet of acid chamber 8, and when the measured value of the pressure gauge exceeds a predetermined value, cleaning mechanism 20 may clean acid chamber 8 of electrodialysis apparatus 1B. Note that, in order to more accurately capture pressure changes in alkaline chamber 7 and acid chamber 8, pressure gauges may be provided at the inlet and outlet, respectively, and when the difference between the measured values ​​of these pressure gauges (differential pressure) exceeds a predetermined value, cleaning mechanism 20 may clean alkaline chamber 7 and acid chamber 8.

[0084] The cleaning mechanism 20 may clean the alkaline chamber 7 of the electrodialysis apparatus 1A with pure water before cleaning the alkaline chamber 7 with concentrated acid waste liquid. Furthermore, a step in which the cleaning mechanism 20 immerses the alkaline chamber 7 in concentrated acid waste liquid may be provided before the intermediate cleaning step and the cleaning step. Furthermore, the cleaning mechanism 20 may clean the acid chamber 8 of the electrodialysis apparatus 1B with pure water before cleaning the acid chamber 8 with concentrated alkaline waste liquid. Furthermore, a step in which the cleaning mechanism 20 immerses the acid chamber 8 in concentrated alkaline waste liquid may be provided before the intermediate cleaning step and the cleaning step.

[0085] The frequency of cleaning the electrodialysis apparatus 1A is preferably set to approximately once every 12 to 48 hours, in accordance with one cycle of the discharge of acid regeneration waste liquid from the K tower 40. Similarly, the frequency of cleaning the electrodialysis apparatus 1B is preferably set to approximately once every 12 to 48 hours, in accordance with one cycle of the discharge of alkali regeneration waste liquid from the A tower 41. If the cleaning interval is short, the amount of cleaning water used increases, reducing the operating time of the electrodialysis apparatuses 1A and 1B. Conversely, if the cleaning interval is long, the risk of scaling increases. It is preferable to set the cleaning interval taking these points into consideration.

[0086] If the concentration of hardness components in the acid regeneration waste liquid from the K tower 40 is higher than 1000 mg / L, the alkaline chamber 7 of the electrodialysis apparatus 1A will need to be cleaned more frequently and for longer periods of time, resulting in a decrease in the acid recovery efficiency. Taking this into consideration, the concentration of hardness components in the acid regeneration waste liquid from the K tower 40 is preferably about 100 to 1000 mg / L. Meanwhile, the concentration of silica components in the alkaline regeneration waste liquid is preferably about 100 to 500 mg / L.

[0087] In the electrodialysis apparatus 1A, the timing of collecting the acid solution may be determined using the pH, conductivity, or current value of the acid solution, a timer, etc. In the electrodialysis apparatus 1B, the timing of collecting the alkaline solution may be determined using the pH, conductivity, or current value of the alkaline solution, a timer, etc.

[0088] Although the electrodialysis devices 1A and 1B have an EDI structure in which the alkaline chamber 7 and the acid chamber 8 are filled with ion exchange resin, the present invention is not limited to this. The electrodialysis devices 1A and 1B may also have an ED (electrodialysis) structure in which the alkaline chamber 7 and the acid chamber 8 are not filled with ion exchange resin. The ED structure can also perform the same operations as the EDI structure, and its effects are basically the same.

[0089] In the ED structure, scale is generated over the entire surface of the ion exchange membrane. In this case, the scale is deposited thickly on the surface of the ion exchange membrane, which may increase the voltage applied between the anode 3a and the cathode 3b. In contrast, in the EDI structure, scale is also generated on the surface of the filled ion exchanger (resin), so the scale is deposited thinly and widely. Therefore, the surface area on which scale is generated can be increased compared to the ED structure, and the increase in voltage applied between the anode 3a and the cathode 3b can be suppressed. From the viewpoint of suppressing the increase in voltage, it is preferable to use the EDI structure.

[0090] Second Embodiment Figure 4 is a schematic diagram showing the configuration of a water treatment system according to a second embodiment of the present invention. Figure 4 shows a primary pure water production system 200 equipped with a water treatment system 101 according to this embodiment. In Figure 4, solid arrows indicate pipes (or flow paths). The intersection of two pipes indicates that they are not connected, but intersect while being separated from each other. The primary pure water production system 200 shown in Figure 4 is the same as that shown in Figure 1 except for the water treatment system 101. The same components are designated by the same reference numerals, and detailed descriptions thereof will be omitted.

[0091] The water treatment system 101 includes two electrodialysis apparatuses 1C and 1D and a cleaning mechanism 20. The electrodialysis apparatus 1C can be referred to as the first electrodialysis apparatus, and the electrodialysis apparatus 1D can be referred to as the second electrodialysis apparatus. The electrodialysis apparatus 1C constitutes an acid recovery system and produces a concentrated acid solution and alkaline waste solution from the acid regeneration waste solution in the K tower 40 by electrodialysis. The electrodialysis apparatus 1D constitutes an alkali recovery system and produces a concentrated alkaline solution and acid waste solution from the alkaline regeneration waste solution in the A tower 41 by electrodialysis. The cleaning mechanism 20 cleans the other of the electrodialysis apparatuses 1C and 1D with cleaning water containing the concentrated waste solution produced by one of the electrodialysis apparatuses 1A and 1B.

[0092] Here, electrodialysis devices 1C and 1D each have an acid chamber 8 for producing an acid solution, an alkaline chamber 7 for producing an alkaline solution, and a deionization chamber 9. In an acid recovery facility including electrodialysis device 1C, acid regeneration waste liquid is supplied to the deionization chamber 9. The acid solution (here, hydrochloric acid with a concentration of 4% by mass) produced in the acid chamber 8 by electrodialysis is recovered and reused as a regenerant. To prevent clogging of the alkaline chamber 7 due to scale formation, a cleaning mechanism 20 cleans the alkaline chamber 7 of electrodialysis device 1C with concentrated acid waste liquid discharged from electrodialysis device 1D.

[0093] Meanwhile, in an alkali recovery facility including electrodialysis apparatus 1D, alkali regeneration waste liquid is supplied to deionization chamber 9. The alkaline solution (here, sodium hydroxide with a concentration of 3% by mass) produced in alkali chamber 7 by electrodialysis is recovered and reused as a regenerant. To prevent clogging of acid chamber 8 due to scale formation, cleaning mechanism 20 cleans acid chamber 8 of electrodialysis apparatus 1D with concentrated alkali waste liquid discharged from electrodialysis apparatus 1C. Note that cleaning mechanism 20 may clean only one of alkali chamber 7 of electrodialysis apparatus 1C and acid chamber 8 of electrodialysis apparatus 1D.

[0094] The waste cleaning liquid used to clean the alkaline chamber 7 of the electrodialysis apparatus 1C and the waste cleaning liquid used to clean the acid chamber 8 of the electrodialysis apparatus 1D are each discharged into a regenerated wastewater tank 42. In the regenerated wastewater tank 42, the waste cleaning liquids from the electrodialysis apparatuses 1C and 1D are mixed and supplied to a wastewater treatment facility 43.

[0095] Next, the configuration of the water treatment system 101 of this embodiment will be described in detail. First, the configuration of the electrodialysis device 1C will be described in detail. FIG. 5 is a schematic diagram showing the configuration of the electrodialysis device 1C. In FIG. 5, solid and dashed arrows indicate pipes (or flow paths), and solid open arrows indicate signal lines for transmitting control signals and the like. The intersection of two pipes indicates that they are not connected and intersect while being separated from each other. The dotted arrow A indicates the direction (or path) of flow of cleaning water.

[0096] The electrodialysis apparatus 1C shown in Figure 5 differs from the electrodialysis apparatus 1A in the structure of the portion where electrodialysis is performed and the arrangement of piping and valves. An ion exchange partition wall 4a, an anion exchange membrane 5, and a cation exchange membrane 30 are arranged between the anode 3a and the cathode 3b, in this order from the anode 3a side. The electrodialysis apparatus 1C has multiple chambers partitioned by the ion exchange partition wall 4a, the anion exchange membrane 5, and the cation exchange membrane 30. The multiple chambers include an alkaline chamber 7, an acid chamber 8, and a deionization chamber 9 to which the liquid to be treated is supplied.

[0097] The deionization compartment 9 is partitioned by an anion exchange membrane 5 and a cation exchange membrane 30. The acid compartment 8 is disposed adjacent to the anode side of the deionization compartment 9, with the anion exchange membrane 5 sandwiched therebetween. The alkaline compartment 7 is disposed adjacent to the cathode side of the deionization compartment 9, with the cation exchange membrane 30 sandwiched therebetween. An ion exchange partition 4a is disposed on the anode side of the acid compartment 8 and the cathode side of the alkaline compartment 7, respectively. In this embodiment, two pairs of an acid compartment 8, a deionization compartment 9, and an alkaline compartment 7 are disposed between the anode compartment 6a and the cathode compartment 6b, but this is not limited thereto. The number of pairs of an acid compartment 8, a deionization compartment 9, and an alkaline compartment 7 may be one or three or more. The ion exchange partition 4a, the anion exchange membrane 5, the cation exchange membrane 30, the alkaline compartment 7, and the acid compartment 8 are basically the same as those described in the first embodiment.

[0098] Raw water tank 12 communicates with pipe 12c, which is provided with valve 2b. Raw water tank 12 communicates with deionization chamber 9 via pipe 12a, so that the liquid to be treated stored in raw water tank 12 can be supplied to deionization chamber 9. Although not shown, pipe 12a is provided with a pump, which is configured to circulate deionized water produced in deionization chamber 9 between raw water tank 12 and deionization chamber 9. Pipe 12a is connected to pipe 24 for recovering or discharging pure water produced in deionization chamber 9. Pipe 24 is provided with valve 2i, which can be used to control the recovery or discharge of pure water.

[0099] The alkaline chamber 7 is connected to the wastewater tank 13 via a pipe 23. Although not shown, a pump is provided in the pipe 23, and the treated liquid from the alkaline chamber 7 is circulated between the wastewater tank 13 and the alkaline chamber 7. A valve 2c is provided at the outlet of the wastewater tank 13 in the pipe 23. The valve 2c can be used to control the circulation and discharge of the treated liquid (alkaline liquid). By circulating the treated liquid while undergoing electrodialysis, an alkaline liquid of a predetermined concentration can be obtained. This alkaline liquid of a predetermined concentration can be called concentrated alkaline waste liquid. This concentrated alkaline waste liquid is used to clean the acid chamber 8 of the electrodialysis device 1D.

[0100] The recovered water tank 14 is connected to the acid chamber 8 via a pipe 14a. Although not shown, a pump is provided in the pipe 14a, so that the acid solution produced in the acid chamber 8 circulates between the recovered water tank 14 and the acid chamber 8. The recovered water tank 14 is also connected to a pipe 14b, and pure water (PW) can be supplied to the recovered water tank 14 via this pipe 14b. The raw water tank 12, wastewater tank 13, and recovered water tank 14 are the same as those described in the first embodiment.

[0101] In this embodiment, the pipe 21, a portion of the pipe 23, and the valves 2a and 2c constitute the cleaning mechanism 20. The pipe 21 is connected to a portion of the pipe 23 on the inlet side of the alkaline chamber 7. Cleaning water is supplied to the alkaline chamber 7 via the pipe 21 and a portion of the pipe 23. Waste cleaning liquid used to clean the alkaline chamber 7 is supplied to the drainage tank 13 via a portion of the pipe 23. The supply and discharge of cleaning water to and from the alkaline chamber 7 can be controlled using the valves 2a and 2c. Cleaning water can be supplied to the alkaline chamber 7 at a predetermined space velocity using a pump (not shown).

[0102] The electrodialysis apparatus 1C preferably has an EDI structure in which the alkaline chamber 7, acid chamber 8, and deionization chamber 9 are each filled with an ion exchanger. The deionization chamber 9 is required to transfer anions and cations. For this reason, the deionization chamber 9 is preferably filled with an ion exchanger containing a mixed-bed resin of an anion resin and a cation resin. On the other hand, the alkaline chamber 7 and the acid chamber 8 can be filled with ion exchangers containing any resin. In this embodiment, the alkaline chamber 7 is filled with an anion exchange resin, and the acid chamber 8 is filled with a cation resin. The electrodialysis apparatus 1C may also have an ED structure.

[0103] Next, the configuration of the electrodialysis device 1D will be described in detail. Figure 6 is a schematic diagram showing the configuration of the electrodialysis device 1D. In Figure 6, solid and dashed arrows indicate pipes (or flow paths), and solid open arrows indicate signal lines for transmitting control signals and the like. The intersection of two pipes indicates that they are not connected and intersect while being separated from each other. Dotted arrow A indicates the direction (or path) in which the wash water flows.

[0104] The electrodialysis apparatus 1D shown in Figure 6 differs from the electrodialysis apparatus 1B in that it is partially different in the configuration of the electrodialysis section and is further configured to use the concentrated alkaline waste liquid discharged from the electrodialysis apparatus 1C as cleaning water. The same components as those in the electrodialysis apparatus 1B are designated by the same reference numerals, and detailed descriptions thereof will be omitted.

[0105] Between the anode 3a and the cathode 3b, an ion exchange partition wall 4b, a cation exchange membrane 30, and an anion exchange membrane 5 are disposed in this order from the anode 3a side. The device has a plurality of chambers partitioned by the ion exchange partition wall 4b, the cation exchange membrane 30, and the anion exchange membrane 5. The plurality of chambers includes an alkaline chamber 7, an acid chamber 8, and a deionization chamber 9 to which the liquid to be treated (alkaline regenerated waste liquid) is supplied.

[0106] The deionization compartment 9 is partitioned by a cation exchange membrane 30 and an anion exchange membrane 5. The acid compartment 8 is disposed adjacent to the cathode side of the deionization compartment 9, with the anion exchange membrane 5 sandwiched therebetween. The alkaline compartment 7 is disposed adjacent to the anode side of the deionization compartment 9, with the cation exchange membrane 30 sandwiched therebetween. An ion exchange partition 4b is disposed on the cathode side of the acid compartment 8 and on the anode side of the alkaline compartment 7. In this embodiment, two pairs of an alkaline compartment 7, a deionization compartment 9, and an acid compartment 8 are disposed between the anode compartment 6a and the cathode compartment 6b, but this is not limited to this. The number of pairs of an alkaline compartment 7, a deionization compartment 9, and an acid compartment 8 may be one or three or more. The ion exchange partition 4b, the anion exchange membrane 5, the cation exchange membrane 30, the alkaline compartment 7, and the acid compartment 8 are basically the same as those described in the first embodiment.

[0107] Raw water tank 32 communicates with pipe 32c, which is provided with valve 2f. Raw water tank 32 communicates with deionization chamber 9 via pipe 32a, allowing the liquid to be treated stored in raw water tank 32 to be supplied to deionization chamber 9. Although not shown, pipe 32a is provided with a pump, which is configured to circulate deionized water (pure water) produced in deionization chamber 9 between raw water tank 32 and deionization chamber 9. Pipe 32a is connected to pipe 26 for recovering or discharging the pure water produced in deionization chamber 9. Pipe 26 is provided with valve 2j, which can be used to control the recovery or discharge of pure water.

[0108] The acid chamber 8 is connected to the drainage tank 33 via piping 25. Although not shown, a pump is provided in piping 25, allowing the treated liquid (acid solution) from the acid chamber 8 to circulate between the drainage tank 33 and the acid chamber 8. A valve 2g is provided at the outlet of the drainage tank 33 in piping 25. The valve 2g can be used to control the circulation and discharge of the treated liquid (acid solution). By circulating the treated liquid while undergoing electrodialysis, an acid solution of a predetermined concentration can be obtained. This acid solution of a predetermined concentration can be called concentrated acid waste. This concentrated acid waste can be used to clean the alkaline chamber 7 of the electrodialysis apparatus 1C.

[0109] The recovered water tank 34 is in communication with the alkaline chamber 7 via a pipe 34a. Although not shown, a pump is provided in the pipe 34a, and the alkaline solution produced in the alkaline chamber 7 is circulated between the recovered water tank 34 and the alkaline chamber 7. The recovered water tank 34 is also in communication with a pipe 34b, and pure water (PW) can be supplied to the recovered water tank 34 via this pipe 34b. The raw water tank 32, the wastewater tank 33, and the recovered water tank 34 are the same as those described in the first embodiment.

[0110] In this embodiment, pipe 22, a portion of pipe 25, and valves 2e and 2g constitute cleaning mechanism 20. Pipe 22 is connected to the portion of pipe 25 on the inlet side of acid chamber 8. Cleaning water is supplied to acid chamber 8 via pipe 22 and a portion of pipe 25. Waste cleaning liquid used to clean acid chamber 8 is supplied to drainage tank 33 via a portion of pipe 25. Valves 2e and 2g can be used to control the supply and discharge of cleaning water to and from acid chamber 8. Cleaning water can be supplied to acid chamber 8 at a predetermined space velocity using a pump (not shown).

[0111] The electrodialysis apparatus 1D preferably has an EDI structure in which the alkaline chamber 7, acid chamber 8, and deionization chamber 9 are each filled with an ion exchanger. The deionization chamber 9 is required to transfer anions and cations. For this reason, the deionization chamber 9 is preferably filled with an ion exchanger containing a mixed-bed resin of an anion resin and a cation resin. On the other hand, the alkaline chamber 7 and the acid chamber 8 can be filled with ion exchangers containing any resin. In this embodiment, the alkaline chamber 7 is filled with an anion exchange resin, and the acid chamber 8 is filled with a cation resin. The electrodialysis apparatus 1D may also have an ED structure.

[0112] Next, the operation of the water treatment system 101 of this embodiment will be described in detail with reference to Figures 4 to 6. Below, the operating steps for batch operation will be described as an example. The batch operation is as described in the first embodiment. The batch operation of the electrodialysis device 1C is performed in accordance with the discharge cycle of the acid regeneration waste liquid from the K tower 40, and the batch operation of the electrodialysis device 1D is performed in accordance with the discharge cycle of the alkali regeneration waste liquid from the A tower 41.

[0113] First, the operating steps of the electrodialysis apparatus 1C will be described. The operating steps of the electrodialysis apparatus 1C include a stock solution charging step, a first circulation dialysis step, an intermediate cleaning step, a second circulation dialysis step, a discharge step, and a cleaning step.

[0114] (Stock solution introduction step) The control device 10 controls the valves 2b and 2d to be open and the valves 2a, 2c, and 2i to be closed. A predetermined amount of stock solution (acid regeneration waste liquid) is supplied from the pipe 12c to the stock water tank 12, and a predetermined amount of pure water is supplied from the pipe 14b to the recovered water tank 14.

[0115] (First circulation dialysis step) The control device 10 opens the valve 2c and closes the valves 2a, 2b, 2d, and 2i, and passes the liquid to be treated stored in the raw water tank 12 through the deionization chamber 9. The control device 10 also applies electricity to the power supply device 11 to perform electrodialysis. Here, the liquid to be treated contains cations (H ＋ , Na ＋ , Ca ２＋ , Mg ２＋ etc.) and anions (Cl －etc.)

[0116] Electrodialysis is initiated by energizing the anode 3a and the cathode 3b. In the deionization chamber 9, anions (anions (Cl － )) moves through the anion exchange membrane 5 to the acid chamber 8 adjacent to the anode side, and cations (cations (Na ＋ , Ca 2＋ , Mg 2＋ ) moves through the cation exchange membrane 30 to the alkaline compartment 7 adjacent to the cathode side. The deionization compartment 9 produces deionized water (pure water).

[0117] In the acid chamber 8, pure water is supplied and electrodialysis is carried out while circulating the pure water. ＋ and Cl － is supplied to generate hydrochloric acid (acid solution), and the pH of the treatment solution flowing through the acid chamber 8 decreases. When the hydrochloric acid reaches a predetermined concentration (for example, 4% by mass), the hydrochloric acid is recovered.

[0118] In the alkaline chamber 7, as the electrodialysis progresses, OH generated by water dissociation － As the electrodialysis progresses, the OH supplied from the ion exchange partition 4a increases. － By H ＋ is neutralized, and then OH － As the pH of the treatment solution in the alkaline chamber 7 increases, the pH of the treatment solution in the alkaline chamber 7 increases. When the pH of the treatment solution in the alkaline chamber 7 exceeds approximately 12, hydroxides of calcium (Ca) or magnesium (Mg) precipitate, i.e., scale is produced.

[0119] Here, it is assumed that scale forms in the alkaline chamber 7 before the hydrochloric acid circulating between the recovered water tank 14 and the acid chamber 8 reaches a predetermined concentration. The alkaline solution circulating through the alkaline chamber 7 is stored in the wastewater tank 13. This alkaline solution stored in the wastewater tank 13 can be used as concentrated alkaline waste liquid in the intermediate cleaning step for cleaning the acid chamber 8 of the electrodialysis apparatus 1D, which will be described later.

[0120] (Intermediate Cleaning Step) The control device 10 stops the supply of electricity to the power supply device 11 and controls the valve 2a to be in an open state and the valves 2b, 2c, 2d, and 2i to be in a closed state. After the supply of electricity is stopped, the cleaning mechanism 20 passes concentrated acid waste liquid supplied from the pipe 21 through the alkaline chamber 7 to clean it. The cleaning waste liquid used to clean the alkaline chamber 7 is supplied to the drainage tank 13 via a part of the pipe 23. The cleaning waste liquid stored in the drainage tank 13 is drained to any location outside the system.

[0121] In the electrodialysis apparatus 1C, as in the electrodialysis apparatus 1A, the space velocity of the water passing through the alkaline chamber 7 is 400 h -1 That's it, 1000h -1 The following is preferred: The cleaning time is preferably in the range of 1 to 60 minutes, more preferably in the range of 2 to 10 minutes.

[0122] (Second circulating dialysis step) After the cleaning waste liquid is discharged, the control device 10 opens valve 2c and closes valves 2a, 2b, 2d, and 2i, passes the liquid to be treated stored in raw water tank 12 through deionization chamber 9, and applies electricity to power supply 11. The operations of alkaline chamber 7, acid chamber 8, and deionization chamber 9 during electrodialysis are as described in the first circulating dialysis step.

[0123] Here, it is assumed that scale is generated in the alkaline chamber 7 and the hydrochloric acid circulating between the recovered water tank 14 and the acid chamber 8 reaches a predetermined concentration (for example, 4% by mass).

[0124] (Discharge Step) When the hydrochloric acid reaches a predetermined concentration, the control device 10 controls the power supply 11 to stop powering on, open the valve 2i, and close the valves 2a to 2d. The alkaline solution circulating through the alkaline chamber 7 is supplied to the drainage tank 13 via the pipe 23. The alkaline solution stored in the drainage tank 13 can be used as concentrated alkaline waste liquid in a cleaning step for cleaning the acid chamber 8 of the electrodialysis apparatus 1D, which will be described later.

[0125] The hydrochloric acid circulating between the recovered water tank 14 and the acid chamber 8 is stored in the recovered water tank 14. The hydrochloric acid stored in the recovered water tank 14 is discharged to a recovery destination outside the system. Here, the recovered hydrochloric acid is reused as a regenerant for the K tower 40, etc. The demineralized water (pure water) produced in the deionization chamber 9 is recovered or discharged via piping 26.

[0126] (Cleaning step) After recovering the hydrochloric acid, the control device 10 controls the valve 2a to be in an open state and the valves 2b, 2c, 2d, and 2i to be in a closed state. The cleaning mechanism 20 cleans the alkaline chamber 7 by passing the concentrated acid waste liquid supplied from the pipe 21 through the alkaline chamber 7. The cleaning waste liquid used to clean the alkaline chamber 7 is supplied to the drainage tank 13 via a part of the pipe 23. The cleaning waste liquid stored in the drainage tank 13 is discharged to any location outside the system. The space velocity and cleaning time are as explained in the intermediate cleaning step.

[0127] Next, the operating steps of the electrodialysis apparatus 1D will be described. Similar to the electrodialysis apparatus 1C, the operating steps of the electrodialysis apparatus 1D also include a stock solution introduction step, a first circulation dialysis step, an intermediate cleaning step, a second circulation dialysis step, a discharge step, and a cleaning step.

[0128] (Stock solution introduction step) The control device 10 controls the valves 2f and 2h to be open and the valves 2e, 2g, and 2j to be closed. A predetermined amount of stock solution (alkaline regenerated waste liquid) is supplied from the pipe 32c to the stock water tank 32, and a predetermined amount of pure water is supplied from the pipe 34b to the recovered water tank 34.

[0129] (First circulation dialysis step) The control device 10 opens the valve 2g and closes the valves 2e, 2f, 2h, and 2j, and passes the liquid to be treated stored in the raw water tank 32 through the deionization chamber 9. The control device 10 also applies electricity to the power supply device 11 to perform electrodialysis. Here, the liquid to be treated contains Na ＋ , O.H. － , NO ３ － , S.O. ４ ２－ , SiO ２ , Cl － This includes the following:

[0130] Electrodialysis is initiated by energizing the anode 3a and the cathode 3b. In the deionization chamber 9, anions (OH － , NO ３ － , S.O. ４ ２－ , Cl － ) moves through the anion exchange membrane 5 to the acid chamber 8 adjacent to the cathode side, and the cation (Na ＋ ) moves through the cation exchange membrane 30 to the alkaline compartment 7 adjacent to the anode side. The deionization compartment 9 produces deionized water (pure water).

[0131] In the alkaline chamber 7, pure water is supplied and electrodialysis is carried out while circulating the pure water. As the electrodialysis progresses, OH is gradually added. － and Na ＋ is supplied to generate sodium hydroxide (alkaline solution), and the pH of the treatment solution flowing through the alkaline chamber 7 increases. When the sodium hydroxide reaches a predetermined concentration (for example, 3 mass %), the sodium hydroxide is recovered.

[0132] On the other hand, in the acid chamber 8, as the electrodialysis progresses, the alkali in the circulating treatment solution gradually disappears, and the H generated by water dissociation is released. ＋ As a result, the pH of the treatment liquid in the acid chamber 8 decreases, and scale is produced.

[0133] Here, it is assumed that scale forms in the acid chamber 8 before the concentration of sodium hydroxide in the treatment solution circulating between the recovered water tank 34 and the alkaline chamber 7 reaches a predetermined concentration. The control device 10 also closes the valve 2g, supplying the acid solution circulating between the acid chamber 8 and the raw water tank 32 to the wastewater tank 33. The acid solution stored in the wastewater tank 33 can be used as concentrated acid waste liquid in the intermediate cleaning step for cleaning the alkaline chamber 7 of the electrodialysis apparatus 1C described above.

[0134] (Intermediate Cleaning Step) The control device 10 stops power supply to the power supply device 11 and controls the valve 2e to be open and the valves 2f, 2g, 2h, and 2j to be closed. After power supply is stopped, the cleaning mechanism 20 passes concentrated alkaline waste liquid supplied from the pipe 22 through the acid chamber 8 to clean it. The cleaning waste liquid used to clean the acid chamber 8 is supplied to the drainage tank 33 via the pipe 25. The cleaning waste liquid stored in the drainage tank 33 is drained to any location outside the system.

[0135] In the electrodialysis apparatus 1D, as in the electrodialysis apparatus 1B, the space velocity of water passing through the acid chamber 8 is 400 h -1 That's it, 1000h -1 The following is preferred: The cleaning time is preferably in the range of 1 to 60 minutes, more preferably in the range of 2 to 10 minutes.

[0136] (Second circulating dialysis step) After the cleaning waste liquid is discharged, the control device 10 opens valve 2g and closes valves 2e, 2f, 2h, and 2j, passes the liquid to be treated stored in raw water tank 12 through deionization chamber 9, and applies electricity to power supply 11. The operations of alkaline chamber 7, acid chamber 8, and deionization chamber 9 during electrodialysis are as described in the first circulating dialysis step.

[0137] Here, it is assumed that scale is formed in the acid chamber 8 and the concentration of sodium hydroxide in the treatment liquid circulating between the recovered water tank 34 and the alkaline chamber 7 reaches a predetermined concentration (for example, 3% by mass).

[0138] (Discharge Step) When the sodium hydroxide reaches a predetermined concentration, the control device 10 controls the power supply 11 to stop powering on, open the valve 2j, and close the valves 2e to 2h. The acid solution circulating through the acid chamber 8 is supplied to the drainage tank 33 via the pipe 25. The acid solution stored in the drainage tank 33 can be used as concentrated acid waste liquid in the cleaning step for cleaning the alkali chamber 7 of the electrodialysis apparatus 1C described above.

[0139] The alkaline solution (sodium hydroxide) circulating between the recovered water tank 34 and the alkaline chamber 7 is stored in the recovered water tank 34. The sodium hydroxide stored in the recovered water tank 34 is discharged to a recovery destination outside the system. Here, the recovered sodium hydroxide is reused as a regenerant for the A tower 41, etc. The demineralized water (pure water) produced in the demineralization chamber 9 is recovered or discharged via piping 26.

[0140] (Cleaning Step) After the sodium hydroxide is recovered, the control device 10 controls the valve 2e to be open and the valves 2f, 2g, 2h, and 2j to be closed. The cleaning mechanism 20 passes concentrated alkaline waste liquid supplied from the pipe 22 through the acid chamber 8 to clean it. The cleaning waste liquid used to clean the acid chamber 8 is supplied to the drainage tank 33 via the pipe 25. The cleaning waste liquid stored in the drainage tank 33 is drained to any location outside the system. The space velocity and cleaning time are as described in the intermediate cleaning step.

[0141] The operation steps of the electrodialysis devices 1C and 1D of the water treatment system 101 of this embodiment described above also achieve the same effects as those of the water treatment system 100 of the first embodiment. In the water treatment system 101 of this embodiment, the intermediate cleaning step may be omitted or may be performed two or more times as long as it is possible to prevent clogging due to scale and suppress a decrease in the recovery amounts of the acid solution and the alkaline solution.

[0142] Furthermore, the configurations and modifications described in the operational effects of the electrodialysis devices 1A and 1B can be applied to the electrodialysis devices 1C and 1D, as long as they do not impair operation. For example, both the EDI structure and the ED structure can be applied to the electrodialysis devices 1C and 1D. However, in the ED structure, as the desalination progresses in the desalination compartment 9, the water approaches pure water, which may make it difficult for current to flow. In contrast, in the EDI structure, the desalination compartment 9 is filled with an ion exchanger (resin), so current flows through the ion exchanger (resin) even when the water approaches pure water as desalination progresses. From the perspective of electrodialysis stability, the EDI structure is preferable. The electrodialysis devices 1C and 1D can be called pure water production systems because the desalination compartment 9 produces desalination water (pure water).

[0143] In the above-described electrodialysis devices 1A, 1B, 1C, and 1D, the flow direction in each chamber between the anode 3a and the cathode 3b is not limited to the direction shown in the drawings. For example, in the electrodialysis device 1A shown in FIG. 2, the flow direction of the treated solution in the alkaline chamber 7 and the flow direction of the acid solution in the acid chamber 8 during electrodialysis are the same, but this is not limiting. The flow directions of the treated solution in the alkaline chamber 7 and the acid chamber 8 during electrodialysis may be countercurrent. Similarly, in the electrodialysis device 1B shown in FIG. 3, the flow directions of the treated solution in the alkaline chamber 7 and the acid chamber 8 during electrodialysis may be countercurrent.

[0144] In the electrodialysis apparatus 1C shown in Fig. 5, the flow direction of the deionized water in the deionization compartment 9, the flow direction of the treated solution in the alkaline compartment 7, and the flow direction of the treated solution in the acid compartment 8 during electrodialysis are the same, but this is not limited to this. For example, the flow direction of the deionized water in the deionization compartment 9 and the flow direction of the treated solution in the alkaline compartment 7 during electrodialysis may be countercurrent, or the flow direction of the deionized water in the deionization compartment 9 and the flow direction of the treated solution in the acid compartment 8 during electrodialysis may be countercurrent. Similarly, in the electrodialysis apparatus 1D shown in Fig. 6, the flow direction of the deionized water in the deionization compartment 9 and the flow direction of the treated solution in the alkaline compartment 7 may be countercurrent, or the flow direction of the deionized water in the deionization compartment 9 and the flow direction of the treated solution in the acid compartment 8 may be countercurrent.

[0145] By using countercurrent flow in the electrodialysis devices 1A, 1B, 1C, and 1D, for example, the residence time of highly charged components (hardness components) in the alkaline chamber 7 is shortened, thereby suppressing scale formation. For example, in the electrodialysis device 1C, hardness components (divalent calcium ions and magnesium ions) move to the alkaline chamber 7 before monovalent ions. When the flow directions of the deionization chamber 9 and the alkaline chamber 7 are countercurrent, the hardness components move to the alkaline chamber 7 near the inlet side of the deionization chamber 9. Because the inlet side of the deionization chamber 9 is adjacent to the outlet side of the alkaline chamber 7, the hardness components are discharged from the alkaline chamber 7 immediately after moving to the alkaline chamber 7. This shortens the residence time of the hardness components in the alkaline chamber 7. In the water treatment system 100 of the first embodiment or the water treatment system 101 of the second embodiment, EDIs with different numbers of chambers may be used in the alkali recovery equipment and the acid recovery equipment. For example, in the water treatment system 100 of the first embodiment, the electrodialysis device 1B shown in FIG. 3 may be replaced with the electrodialysis device 1D shown in FIG.

[0146] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0147] This application claims priority based on Japanese Patent Application No. 2024-106310, filed July 1, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0148] 1A, 1B, 1C, 1D Electrodialysis device 2a to 2j Valves 3a Anode 3b Cathode 4a, 4b Ion exchange partition 5 Anion exchange membrane 6a Anode chamber 6b Cathode chamber 7 Alkaline chamber 8 Acid chamber 9 Deionization chamber 10 Control unit 11 Electrical supply unit 20 Cleaning mechanism 30 Cation exchange membrane

Claims

1. A water treatment system comprising: a first electrodialysis device that produces concentrated acid and alkaline waste liquid from the acid regeneration waste liquid of a cation exchange resin tower; a second electrodialysis device that produces concentrated alkaline and acid waste liquid from the alkaline regeneration waste liquid of an anion exchange resin tower; and a cleaning mechanism that cleans the other of the first and second electrodialysis devices with cleaning water containing the concentrated waste liquid produced by one of the first and second electrodialysis devices.

2. The water treatment system according to claim 1, wherein the first and second electrodialysis devices each have an acid chamber for producing the acid solution and an alkaline chamber for producing the alkaline solution, and the cleaning mechanism cleans the acid chamber of the second electrodialysis device with the alkaline solution produced in the alkaline chamber of the first electrodialysis device, and cleans the alkaline chamber of the first electrodialysis device with the acid solution produced in the acid chamber of the second electrodialysis device.

3. The water treatment system according to claim 2, further comprising a pressure gauge at the inlet of the alkaline chamber of the first electrodialysis device or the acid chamber of the second electrodialysis device, and wherein the cleaning mechanism cleans the alkaline chamber of the first electrodialysis device or the acid chamber of the second electrodialysis device when the measured value of the pressure gauge exceeds a predetermined value.

4. The water treatment system of claim 2, wherein the first electrodialysis device is configured to receive a fixed amount of the acid regeneration waste liquid, perform electrodialysis while circulating the received acid regeneration waste liquid, and recover the acid liquid when the concentration of the acid liquid produced in the acid chamber reaches a predetermined value, and the cleaning mechanism cleans the alkaline chamber of the first electrodialysis device with the concentrated acid waste liquid discharged from the second electrodialysis device after the acid liquid is recovered.

5. The water treatment system of claim 2, wherein the second electrodialysis device is configured to receive a fixed amount of the alkaline regeneration waste liquid, perform electrodialysis while circulating the received alkaline regeneration waste liquid, and recover the alkaline liquid when the concentration of the alkaline liquid produced in the alkaline chamber reaches a predetermined value, and the cleaning mechanism cleans the acid chamber of the second electrodialysis device with the concentrated alkaline waste liquid discharged from the first electrodialysis device after recovering the alkaline liquid.

6. The water treatment system according to any one of claims 2 to 5, wherein the first electrodialysis device has an alkaline chamber partitioned by the ion exchange partition wall and the anion exchange membrane and supplied with the acid regeneration waste liquid, and an acid chamber partitioned by the ion exchange partition wall and the anion exchange membrane and adjacent to the anode side of the alkaline chamber via the anion exchange membrane; and the second electrodialysis device has an ion exchange partition wall and a cation exchange membrane partitioned by the anode and the cathode, and an acid chamber partitioned by the ion exchange partition wall and the cation exchange membrane and supplied with the alkaline regeneration waste liquid, and an alkaline chamber partitioned by the ion exchange partition wall and the cation exchange membrane and adjacent to the anode side of the acid chamber via the cation exchange membrane.

7. The water treatment system according to claim 6, wherein the alkaline chamber and the acid chamber of the first electrodialysis device are each filled with an ion exchanger, and the alkaline chamber and the acid chamber of the second electrodialysis device are each filled with an ion exchanger.

8. The water treatment system according to any one of claims 2 to 5, wherein the first electrodialysis device has a deionization compartment to which the acid regeneration waste liquid is supplied, the deionization compartment being partitioned by the anion exchange membrane and the cation exchange membrane, the alkaline compartment adjacent to the cathode side of the deionization compartment across the cation exchange membrane, and the acid compartment adjacent to the anode side of the deionization compartment across the anion exchange membrane; and the second electrodialysis device has an ion exchange partition, the cation exchange membrane, and the anion exchange membrane arranged in this order from the anode side between the anode and the cathode, the deionization compartment being partitioned by the cation exchange membrane and the anion exchange membrane, the alkaline regeneration waste liquid being supplied, the acid compartment adjacent to the cathode side of the deionization compartment across the anion exchange membrane, and the alkaline compartment adjacent to the anode side of the deionization compartment across the cation exchange membrane.

9. The water treatment system according to claim 8, wherein the alkaline compartment, the acid compartment, and the deionization compartment of the first electrodialysis device are each filled with an ion exchanger, and the alkaline compartment, the acid compartment, and the deionization compartment of the second electrodialysis device are each filled with an ion exchanger.

10. A method for cleaning a water treatment system having a first electrodialysis device that produces concentrated acid and alkaline waste liquid from acid regeneration waste liquid of a cation exchange resin tower, and a second electrodialysis device that produces concentrated alkaline and acid waste liquid from alkaline regeneration waste liquid of an anion exchange resin tower, characterized in that the other of the first and second electrodialysis devices is cleaned with cleaning water containing the concentrated waste liquid produced by one of the first and second electrodialysis devices.

Images