Electrodialysis system, electrodialysis method, waste liquid treatment system, and waste liquid treatment method

Abstract

Provided is an electrodialysis system capable of preventing generation of scale derived from hardness components and silica in treatment of a liquid to be treated having a pH of 3 or lower or 12 or higher, and capable of efficiently performing deionization treatment. This electrodialysis system comprises: an electrodialyzer having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, and in which the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane are arranged in order from the anode side between the anode and the cathode; and a pH measurement means for measuring the pH of a treated liquid obtained after the liquid to be treated has passed through the electrodialyzer. When the value of the pH of the treated liquid measured by the pH measurement means reaches a predetermined value, the electrodialysis treatment by the electrodialyzer is terminated.

Description

Electrodialysis system, electrodialysis method, waste liquid treatment system, and waste liquid treatment method

[0001] The present invention relates to an electrodialysis system, an electrodialysis method, a waste liquid treatment system, and a waste liquid treatment method.

[0002] Ion exchangers are used in a variety of applications, including as ion removal materials in pure water production systems. Cation exchangers adsorb cationic components, and when their adsorption capacity declines, they are regenerated with acid to restore their adsorption capacity. During regeneration, a larger amount of acid than the exchange capacity of the cation exchanger is typically used, resulting in excess acid in the regeneration wastewater. Similarly, anion exchangers adsorb anionic components, and when their adsorption capacity declines, they are regenerated with alkali to restore their adsorption capacity. During regeneration of anion exchangers, a larger amount of alkali than the exchange capacity of the anion exchanger is used, resulting in excess alkali in the regeneration wastewater.

[0003] These regenerated waste liquids are usually mixed and then neutralized for treatment, but because an excess amount of acid or alkali is added, more acid or alkali is required for neutralization, which poses the problem of increased chemical usage and an increased salt concentration in the waste liquid.

[0004] Therefore, a method has been proposed in which the regenerated waste liquid is electrolyzed by electrodialysis to recover the acid and alkali.

[0005] For example, Patent Document 1 proposes a method in which regeneration wastewater from a cation exchange tower and an anion exchange tower is mixed, and then an acid and an alkali are recovered using an electrodialysis device equipped with a bipolar membrane, and the recovered acid and alkali are reused for regenerating a resin tower.

[0006] Japanese Patent Application Publication No. 9-122643

[0007] In the method described in Patent Document 1, Na in the regeneration wastewater ＋ and Cl － are separated using an ion exchange membrane, and each is separated into H ＋ and OH －By supplying NaOH and HCl, an acid or alkali is produced. ＋ and Cl － As the separation continues, the ion concentration in the supply solution decreases, making it difficult for the current to flow, resulting in the problem of a long time required for separation.

[0008] In addition, in this method, the Ca in the acidic regeneration waste liquid ２＋ and Mg ２＋ permeates the cation exchange membrane and OH － When the water is supplied, it becomes alkaline and scale is generated, and H ＋ When the pH is lowered due to the supply of sulfur dioxide, silica scale is formed.

[0009] Furthermore, if only one of the waste acid or the waste alkali needs to be reused, that is, if there is only one use for the waste acid or the waste alkali, the Na in the waste liquid ＋ and Cl － If both of these are electrolyzed to produce both NaOH and HCl, one of them will have to be discarded, which increases the cost of disposal.

[0010] An object of the present invention is to provide an electrodialysis system, an electrodialysis method, a waste liquid treatment system, and a waste liquid treatment method that can prevent the generation of scale derived from hardness components and silica and can efficiently perform deionization treatment.

[0011] As a result of extensive investigations into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by terminating electrodialysis when the pH of the treatment solution reaches a predetermined value during electrodialysis, and have thus completed the present invention.

[0012] The present invention includes the following aspects: [1] An electrodialysis system used to treat a liquid to be treated having a pH of 3 or less or a pH of 12 or more, comprising: an electrodialysis device having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, with the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode; and a pH measurement means for measuring the pH of a treated liquid obtained after the liquid to be treated has passed through the electrodialysis device, wherein the electrodialysis treatment by the electrodialysis device is terminated when the pH value of the treated liquid measured by the pH measurement means reaches a predetermined value. [2] The electrodialysis system described in [1], wherein the liquid to be treated has a pH of 3 or less and the ion exchange membrane of the electrodialysis device is an anion exchange membrane. [3] The electrodialysis system described in [1], wherein the liquid to be treated has a pH of 12 or more and the ion exchange membrane of the electrodialysis device is a cation exchange membrane. [4] The electrodialysis system according to [1], wherein the ion exchange membrane of the electrodialysis device is an anion exchange membrane, and a cation exchange membrane is provided between the anion exchange membrane and the second bipolar membrane. [5] The electrodialysis system according to [2], wherein the electrodialysis device comprises: an anode chamber defined by the anode and the first bipolar membrane, and a cathode chamber defined by the cathode and the second bipolar membrane, and an acid recovery chamber defined by the first bipolar membrane and the anion exchange membrane, which is supplied with water and produces a recovered acid solution by electrodialysis, and a deionization chamber defined by the anion exchange membrane and the second bipolar membrane, which is supplied with an acid feed solution as the liquid to be treated and produces deionized water by electrodialysis, wherein one or more cell sets each consisting of the acid recovery chamber and the deionization chamber are arranged.[6] The electrodialysis system according to [3], wherein the electrodialysis apparatus comprises: an anode chamber defined by the anode and the first bipolar membrane; and a cathode chamber defined by the cathode and the second bipolar membrane; a deionization chamber defined by the first bipolar membrane and the cation exchange membrane between the anode chamber and the cathode chamber, to which an alkaline feed solution is supplied as the liquid to be treated and which produces deionized water by electrodialysis; and an alkali recovery chamber defined by the cation exchange membrane and the second bipolar membrane, to which water is supplied and which produces a recovered alkaline solution by electrodialysis; and wherein one or more cell sets each consisting of the deionization chamber and the alkali recovery chamber are arranged in a repetitive manner. [7] The electrodialysis system according to [4], wherein the electrodialysis apparatus comprises: an anode chamber defined by the anode and the first bipolar membrane; and a cathode chamber defined by the cathode and the second bipolar membrane; an alkali recovery chamber defined by the cation exchange membrane and the second bipolar membrane between the anode chamber and the cathode chamber, which is supplied with water and produces a recovered alkaline solution by electrodialysis; an acid recovery chamber defined by the anion exchange membrane and the first bipolar membrane, which is supplied with water and produces a recovered acid solution by electrodialysis; and a deionization chamber defined by the cation exchange membrane and the anion exchange membrane, which is supplied with the liquid to be treated and produces deionized water by electrodialysis; and wherein one or more cell sets each consisting of the acid recovery chamber, the deionization chamber, and the alkali recovery chamber are arranged in a repetitive manner. [8] The electrodialysis system according to [2] or [4], wherein the pH of the liquid to be treated is less than 1, and the electrodialysis treatment by the electrodialysis device is terminated when the pH of the treated liquid reaches a range of 1 to 3. [9] The electrodialysis system according to [3] or [4], wherein the pH of the liquid to be treated is 12 or more, and the electrodialysis treatment by the electrodialysis device is terminated before the pH of the treated liquid reaches a range of less than 9.

[10] The electrodialysis system according to any of [1] to [7], wherein the liquid to be treated is regeneration wastewater from an ion exchange device.

[11] The electrodialysis system according to any one of [5] to [7], wherein the recovered acid solution or the recovered alkaline solution is used in a water treatment system other than the water treatment system from which the liquid to be treated is discharged.

[12] A waste liquid treatment system comprising: an ion exchange device filled with ion exchangers; a regenerated liquid supply device that supplies regenerated liquid for the ion exchangers to the ion exchange device; and an electrodialysis system that treats regenerated waste liquid discharged from the ion exchange device, wherein the regenerated waste liquid has a pH of 3 or less or a pH of 12 or more; the electrodialysis system comprising: an electrodialysis device having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode; and a pH measuring means that measures the pH of a treated liquid obtained after the regenerated waste liquid has passed through the electrodialysis device, wherein the electrodialysis treatment by the electrodialysis device is terminated when the pH value of the treated liquid measured by the pH measuring means reaches a predetermined value.

[13] An electrodialysis method used to treat a liquid to be treated having a pH of 3 or less or a pH of 12 or more, comprising: performing electrodialysis using an electrodialysis apparatus having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode; measuring the pH of a treated liquid obtained after the liquid to be treated passes through the electrodialysis apparatus; and terminating the electrodialysis using the electrodialysis apparatus when the measured pH value of the treated liquid reaches a predetermined value.

[14] A waste liquid treatment method comprising: a regenerated liquid supplying step of supplying a regenerated liquid of the ion exchanger to an ion exchange device filled with the ion exchanger; and an electrodialysis step of treating regenerated waste liquid discharged from the ion exchange device, wherein the regenerated waste liquid has a pH of 3 or less or a pH of 12 or more, and the electrodialysis step comprises: a step of passing the regenerated waste liquid through an electrodialysis device having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode, to perform electrodialysis treatment; and a step of measuring the pH of a treated liquid obtained after the regenerated waste liquid has passed through the electrodialysis device, wherein the electrodialysis treatment by the electrodialysis device is terminated when the pH value of the treated liquid measured in the pH measuring step reaches a predetermined value.

[0013] According to the present invention, it is possible to provide an electrodialysis system, an electrodialysis method, a waste liquid treatment system, and a waste liquid treatment method that can prevent the generation of scale derived from hardness components and silica and can perform deionization treatment efficiently.

[0014] FIG. 1 is a schematic diagram illustrating an electrodialysis device used in an electrodialysis system according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating an electrodialysis device used in an electrodialysis system according to another embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an electrodialysis device used in an electrodialysis system according to another embodiment of the present invention. FIG. 4 is a schematic diagram illustrating an electrodialysis device used in an electrodialysis system according to another embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a waste liquid treatment system for regeneration waste liquid of a cation exchanger according to another embodiment of the present invention. FIG. 6 is a schematic diagram illustrating a waste liquid treatment system for regeneration waste liquid of an anion exchanger according to another embodiment of the present invention. FIG. 7 is a diagram showing the relationship between the operation time of the electrodialysis device and the pH of the treated liquid in Example 1. FIG. 8 is a diagram showing the relationship between the operation time of the electrodialysis device in Example 1 and the current. FIG. 9 is a diagram showing the relationship between the operation time of the electrodialysis device in Example 2 and the pH of the treated liquid.

[0015] According to an embodiment of the present invention, in the electrodialysis of a liquid to be treated having a pH of 3 or less or a pH of 12 or more, a specific electrodialysis apparatus is used, and by terminating the electrodialysis when the pH of the treated liquid reaches a predetermined value, it is possible to prevent scale formation and achieve efficient deionization. In this electrodialysis, an electrodialysis apparatus is used which has at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, with the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode. When the liquid to be treated is, for example, a caustic soda regeneration waste liquid, OH present in the liquid to be treated is dissolved in the OH. － and an equivalent amount of Na ＋ When the liquid to be treated is, for example, an acidic waste liquid of hydrochloric acid, the H ＋ and an equivalent amount of Cl － can be separated and recovered as HCl. ４ ２－ Other anions and equivalent amounts of Na ＋ Ya, Ca ２＋ and Mg ２＋ Equivalent amounts of Cl and other cations － By minimizing separation of components that exist as neutral salts when considered as compounds, such as the above, it is possible to prevent the generation of scale derived from hardness components and silica.

[0016] 1 , an electrodialysis apparatus 100 used in an electrodialysis system / method according to an embodiment of the present invention includes at least an anode 1, a cathode 11, a bipolar membrane 3 (hereinafter, "bipolar membrane" may also be referred to as "BPM") (BPM 3), an ion exchange membrane 5, and a bipolar membrane 9 (BPM 9). The BPM 3, the ion exchange membrane 5, and the BPM 9 are disposed between the anode 1 and the cathode 11 in this order from the anode 1 side. The electrodialysis apparatus 100 includes an anode chamber 20 defined by the anode 1 and the BPM 3, an acid recovery chamber 22 defined by the BPM 3 and the ion exchange membrane 5, a deionization chamber 24 defined by the ion exchange membrane 5 and the BPM 9, and a cathode chamber 34 defined by the bipolar membrane 9 and the cathode 11.

[0017] Here, the bipolar membranes 3 and 9 are membranes in which a cation exchange membrane and an anion exchange membrane are integrated, and typically have a structure in which a cation exchange membrane and an anion exchange membrane are stacked. Furthermore, the bipolar membranes are configured so that the interface between the stacked cation exchange membrane and anion exchange membrane has a structure optimized for the water dissociation reaction, facilitating the water dissociation reaction. For this purpose, a substance with a catalytic effect for water dissociation (e.g., heavy metal ions or tertiary amines) is generally introduced into the interface between the stacked separate ion exchange membranes. Furthermore, the bipolar membranes are arranged with the anion exchange membrane side facing the anode and the cation exchange membrane side facing the cathode.

[0018] The bipolar membranes 3 and 9 may be any membrane effective for water dissociation, and may be not only commercially available products but also have a structure in which a cation exchange membrane and an anion exchange membrane are stacked.

[0019] The material of the ion exchange membrane 5 used in the electrodialysis device 100 of the electrodialysis system according to the embodiment of the present invention is not particularly limited, and any known material may be used as long as it is effective for separating the target ions. Examples of such a membrane include a homogeneous membrane formed by coating a paste containing styrene and divinylbenzene with polyvinyl chloride, heating the coated paste, and then introducing exchange groups thereto, and a heterogeneous membrane formed by molding an ion exchange resin powder with an appropriate film-forming binder, such as polyethylene, polystyrene, phenolic resin, or synthetic rubber.

[0020] Electrodes used in the electrochemical industry, such as for water electrolysis, can be used for the anode 1 and the cathode 11, and such electrodes can be used without any restrictions. Examples of electrodes that can be used for the anode 1 and the cathode 11 include nickel electrodes, platinum-plated titanium electrodes, and stainless steel electrodes. The anode chamber 20 and the cathode chamber 34 are each filled with an electrode solution. Examples of the electrode solution include a sodium hydroxide solution, a sodium sulfate solution, and pure water.

[0021] The anode chamber 20 accommodates the anode 1 and is provided with an acid recovery chamber 22 adjacent to the anode chamber 20 via a BPM 3. The cathode chamber 34 accommodates the cathode 11 and is provided with a deionization chamber 24 adjacent to the cathode chamber 34 via a BPM 9.

[0022] In the above configuration, the anode chamber 20 and the acid recovery chamber 22 are separated by the BPM 3, and the acid recovery chamber 22 and the deionization chamber 24 are separated by the ion exchange membrane 5. The deionization chamber 24 and the cathode chamber 34 are separated by the BPM 9. That is, the electrodialysis apparatus 100 shown in Figure 1 is a two-compartment electrodialysis apparatus in which the BPM 3, the ion exchange membrane 5, and the BPM 9 are arranged in this order from the anode 1 side, and which mainly consists of two chambers, the acid recovery chamber 22 and the deionization chamber 24.

[0023] An anion exchange membrane (hereinafter, sometimes referred to as "AEM") is used as the ion exchange membrane 5. The following describes the case where an anion exchange membrane is used as the ion exchange membrane 5.

[0024] Here, the chambers constituting the electrodialysis apparatus 100 are listed in order from the anode 1 side as follows: anode - anode chamber - (acid recovery chamber - deionization chamber) n - cathode chamber - cathode. Here, the smallest repeating unit consisting of "acid recovery chamber - deionization chamber" in the parentheses is defined as the basic configuration (i.e., cell set), and n (n is an integer of 1 or more) is the number of repeated cell sets stacked. Note that FIG. 1 shows a configuration where n = 1. The number of repeated cell sets stacked can usually be set in the range of n = 1 to 500, preferably 1 to 200.

[0025] The membranes constituting the electrodialysis device 100 are arranged in the order from the anode side as follows: anode-(BPM-AEM)n-BPM-cathode. Here, n (n is an integer of 1 or more) is the number of repeated stacks of cell sets. Note that Figure 1 shows a configuration where n=1.

[0026] In the electrodialysis apparatus 100 used in the embodiment of the present invention shown in Figure 1, water (e.g., pure water) is supplied to the acid recovery chamber 22, and water to be treated (acid feed solution) is supplied to the deionization chamber 24, and electrodialysis is performed. The water supplied to the acid recovery chamber 22 passes through the acid recovery chamber 22 and is discharged as recovered acid solution. The water to be treated supplied to the deionization chamber 24 passes through the deionization chamber 24 and is discharged as deionized water.

[0027] 2 , an electrodialysis apparatus 200 used in an electrodialysis system / method according to an embodiment of the present invention includes at least an anode 1, a cathode 11, a BPM 3, an ion exchange membrane 5, and a BPM 9, with the BPM 3, the ion exchange membrane 5, and the BPM 9 disposed between the anode 1 and the cathode 11 in this order from the anode 1 side. The electrodialysis apparatus 200 includes an anode chamber 20 defined by the anode 1 and the BPM 3, a deionization chamber 30 defined by the BPM 3 and the ion exchange membrane 5, an alkali recovery chamber 32 defined by the ion exchange membrane 5 and the BPM 9, and a cathode chamber 34 defined by the BPM 9 and the cathode 11.

[0028] The anode chamber 20 accommodates the anode 1 and is provided with a deionization chamber 30 adjacent to the anode chamber 20 via a BPM 3. The cathode chamber 34 accommodates the cathode 11 and is provided with an alkali recovery chamber 32 adjacent to the cathode chamber 34 via a BPM 9.

[0029] In the above configuration, the anode chamber 20 and the deionization chamber 30 are separated by the BPM 3, and the deionization chamber 30 and the alkali recovery chamber 32 are separated by the ion exchange membrane 5. The alkali recovery chamber 32 and the cathode chamber 34 are separated by the BPM 9. That is, the electrodialysis apparatus 200 shown in Figure 2 is a two-compartment electrodialysis apparatus in which the BPM 3, the ion exchange membrane 5, and the BPM 9 are arranged in this order from the anode 1 side, and which mainly consists of two chambers, the deionization chamber 30 and the alkali recovery chamber 32.

[0030] A cation exchange membrane (hereinafter also referred to as "CEM") is used as the ion exchange membrane 5. The following describes the case where a cation exchange membrane is used as the ion exchange membrane 5.

[0031] Here, the chambers constituting the electrodialysis device 200 are arranged in the following order from the anode side: anode - anode chamber - (deionization chamber - alkali recovery chamber) n - cathode chamber - cathode. Here, the smallest repeating unit consisting of the "deionization chamber - alkali recovery chamber" in the parentheses is defined as the basic configuration (i.e., cell set), and n (n is an integer of 1 or more) is the number of repeated cell sets stacked. Note that Figure 2 shows a configuration where n = 1.

[0032] The membranes constituting the electrodialysis device 200 are arranged in the following order from the anode side: anode-BPM-(CEM-BPM)n-cathode. Here, n (n is an integer of 1 or more) is the number of repeated stacks of cell sets. Note that FIG. 2 shows a configuration where n=1. In the configuration shown in FIG. 2, the number of repeated stacks of cell sets can also be set in the range of n=1 to 500, preferably 1 to 200.

[0033] In an electrodialysis apparatus 200 used in an embodiment of the present invention shown in Figure 2, water to be treated (alkaline feed solution) is supplied to a deionization chamber 30, and water (e.g., pure water) is supplied to an alkali recovery chamber 32, where electrodialysis is performed. The alkaline feed solution supplied to the deionization chamber 30 passes through the deionization chamber 30 and is discharged as deionized water. The water supplied to the alkali recovery chamber 32 passes through the alkali recovery chamber 32 and is discharged as recovered alkaline solution.

[0034] As shown in FIG. 3 , an electrodialysis apparatus 300 used in an electrodialysis system / method according to an embodiment of the present invention includes at least an anode 1, a cathode 11, a BPM 3, an AEM 5, a CEM 7, and a BPM 9, with the BPM 3, the AEM 5, the CEM 7, and the BPM 9 being arranged between the anode 1 and the cathode 11 in this order from the anode 1 side.

[0035] This electrodialysis apparatus 300 has an anode chamber 20 defined by the anode 1 and the BPM 3, an acid recovery chamber 22 defined by the BPM 3 and the AEM 5, a deionization chamber 24 defined by the AEM 5 and the CEM 7, an alkali recovery chamber 32 defined by the CEM 7 and the BPM 9, and a cathode chamber 34 defined by the BPM 9 and the cathode 11.

[0036] The anode chamber 20 accommodates the anode 1 and is provided with an acid recovery chamber 22 adjacent to the anode chamber 20 via the BPM 3. The cathode chamber 34 accommodates the cathode 11 and is provided with an alkali recovery chamber 32 adjacent to the cathode chamber 34 via the BPM 9.

[0037] In the above configuration, the anode chamber 20 and the acid recovery chamber 22 are separated by the BPM 3, the acid recovery chamber 22 and the deionization chamber 24 are separated by the AEM 5, and the deionization chamber 24 and the alkali recovery chamber 32 are separated by the CEM 7. The alkali recovery chamber 32 and the cathode chamber 34 are separated by the BPM 9. That is, the electrodialysis apparatus shown in Figure 3 is a three-compartment electrodialysis apparatus in which the BPM 3, AEM 5, CEM 7, and BPM 9 are arranged in this order from the anode 1 side, and which mainly consists of three chambers: the acid recovery chamber 22, the deionization chamber 24, and the alkali recovery chamber 32.

[0038] Here, the chambers constituting the electrodialysis device 300 are listed in order from the anode side as follows: anode - anode chamber - (acid recovery chamber - deionization chamber - alkali recovery chamber) n - cathode chamber - cathode. The smallest repeating unit in the parentheses consisting of "acid recovery chamber - deionization chamber - alkali recovery chamber" is defined as the basic configuration (i.e., cell set), and n (n is an integer of 1 or greater) is the number of repeated cell sets. Note that FIG. 3 shows a configuration where n = 1. Even in the configuration shown in FIG. 3, the number of repeated cell sets can usually be set in the range of n = 1 to 500, preferably 1 to 200.

[0039] The membranes constituting the electrodialysis device 300 are arranged in order from the anode side as follows: anode-BPM-(AEM-CEM-BPM)n-cathode. Here, n (n is an integer of 1 or more) is the number of repeated stacks of cell sets. Note that Figure 3 shows a configuration where n=1.

[0040] In an electrodialysis apparatus 300 used in an embodiment of the present invention shown in Figure 3, water to be treated (acid feed solution) is supplied to the deionization chamber 24, and water (e.g., pure water) is supplied to the acid recovery chamber 22 and the alkali recovery chamber 32, and electrodialysis is performed. The water to be treated supplied to the deionization chamber 24 passes through the deionization chamber 24 and is discharged as deionized water. The water supplied to the acid recovery chamber 22 passes through the acid recovery chamber 22 and is discharged as recovered acid solution. The water supplied to the alkali recovery chamber 32 passes through the alkali recovery chamber 32 and is discharged as recovered alkali solution.

[0041] As shown in FIG. 4 , an electrodialysis apparatus 400 used in an electrodialysis system / method according to an embodiment of the present invention includes at least an anode 1, a cathode 11, a BPM 3, an AEM 5, a CEM 7, and a BPM 9, with the BPM 3, the AEM 5, the CEM 7, and the BPM 9 being arranged between the anode 1 and the cathode 11 in this order from the anode 1 side.

[0042] This electrodialysis apparatus 400 has an anode chamber 20 defined by the anode 1 and the BPM 3, an acid recovery chamber 22 defined by the BPM 3 and the AEM 5, a deionization chamber 30 defined by the AEM 5 and the CEM 7, an alkali recovery chamber 32 defined by the CEM 7 and the BPM 9, and a cathode chamber 34 defined by the BPM 9 and the cathode 11.

[0043] The anode chamber 20 accommodates the anode 1 and is provided with an acid recovery chamber 22 adjacent to the anode chamber 20 via the BPM 3. The cathode chamber 34 accommodates the cathode 11 and is provided with an alkali recovery chamber 32 adjacent to the cathode chamber 34 via the BMP 9.

[0044] In the above configuration, the anode chamber 20 and the acid recovery chamber 22 are separated by the BPM 3, the acid recovery chamber 22 and the deionization chamber 30 are separated by the AEM 5, and the deionization chamber 30 and the alkali recovery chamber 32 are separated by the CEM 7. The alkali recovery chamber 32 and the cathode chamber 34 are separated by the BPM 9. That is, the electrodialysis apparatus shown in Figure 4 is a three-compartment electrodialysis apparatus in which the BPM 3, AEM 5, CEM 7, and BPM 9 are arranged in this order from the anode 1 side, and which mainly consists of three chambers: the acid recovery chamber 22, the deionization chamber 30, and the alkali recovery chamber 32.

[0045] Here, the chambers constituting the electrodialysis device 400 are listed in order from the anode side as follows: anode-anode chamber-(acid recovery chamber-deionization chamber-alkali recovery chamber) n-cathode chamber-cathode. The smallest repeating unit in the parentheses consisting of "acid recovery chamber-deionization chamber-alkali recovery chamber" is defined as the basic configuration (i.e., cell set), and n (n is an integer of 1 or greater) is the number of repeated cell sets. Note that FIG. 4 shows a configuration where n=1. In the configuration shown in FIG. 4, the number of repeated cell sets can usually be set in the range of n=1 to 500, preferably 1 to 200.

[0046] The membranes constituting the electrodialysis device 400 are arranged in the following order from the anode side: anode-BPM-(AEM-CEM-BPM)n-cathode. Here, n (n is an integer of 1 or more) is the number of repeated stacks of cell sets. Note that Figure 4 shows a configuration where n=1.

[0047] In an electrodialysis apparatus 400 used in an embodiment of the present invention shown in Figure 4, water to be treated (alkali feed solution) is supplied to the deionization chamber 30, and water (e.g., pure water) is supplied to the acid recovery chamber 22 and the alkali recovery chamber 32, and electrodialysis is performed. The water to be treated supplied to the deionization chamber 30 passes through the deionization chamber 30 and is discharged as deionized water. The water supplied to the acid recovery chamber 22 passes through the acid recovery chamber 22 and is discharged as recovered acid solution. The water supplied to the alkali recovery chamber 32 passes through the alkali recovery chamber 32 and is discharged as recovered alkali solution.

[0048] In the case of a three-compartment electrodialysis apparatus as shown in Figures 3 and 4, two types of ion exchange membranes, anion exchange membranes and cation exchange membranes, and bipolar membranes are arranged alternately. In the case of a two-compartment electrodialysis apparatus as shown in Figures 1 and 2, anion exchange membranes and bipolar membranes are arranged alternately when recovering acidic water to be treated, for example, hydrochloric acid regeneration wastewater from a cation exchange resin, and cation exchange membranes and bipolar membranes are arranged alternately when recovering alkaline water to be treated, for example, caustic soda regeneration wastewater from an anion exchange resin.

[0049] Although there are no restrictions on the flow rate or volume of the water supplied to the acid recovery chamber and the alkali recovery chamber, a lower flow rate and volume will result in a higher concentration of the recovered alkali solution. By adjusting the liquid volume and volume, the concentration can be adjusted to suit the reuse of the recovered acid solution or recovered alkali solution.

[0050] Although a three-compartment electrodialysis apparatus can recover both acid and alkali, it is more complex than a two-compartment electrodialysis apparatus, and therefore, if only one of the acid and alkali needs to be recovered, a two-compartment electrodialysis apparatus is preferable.

[0051] The regenerated wastewater from the ion exchange resin can be stored in a feed tank as the liquid to be treated and can be supplied to the electrodialysis device using a pump or other means. The feed liquid supplied to the electrodialysis device as the liquid to be treated is usually circulated and treated during electrodialysis, and the treated liquid (deionized water) after the electrodialysis is completed is discharged to a desired location. The outlet of the deionization chamber of the electrodialysis device to which the feed liquid is supplied can be equipped with a pH measuring means for measuring the pH of the treated liquid (deionized water), and the endpoint of electrodialysis can be determined based on the pH value measured by this pH measuring means.

[0052] (Waste Liquid Treatment System and Waste Liquid Treatment Method) Next, a waste liquid treatment system and a waste liquid treatment method for treating regenerated waste liquid from an ion exchanger according to an embodiment of the present invention will be described. FIG. 5 shows an example of a waste liquid treatment system for treating regenerated waste liquid from a cation exchanger (cation exchange resin). The waste liquid treatment system 500 according to an embodiment of the present invention includes a cation exchanger device 102 filled with a cation exchanger, a regenerated liquid storage tank 104 for storing a solution (regenerated liquid) for regenerating the cation exchanger, and a regenerated waste liquid storage tank 106 for storing regenerated waste liquid from the cation exchanger. The regenerated liquid storage tank 104 is provided with a regenerated liquid supply line L1 for supplying the regenerated liquid to the cation exchanger device 102. The waste liquid treatment system 500 also includes a first water storage tank 108, a second water storage tank 110, an electrode solution storage tank 112, and an electrodialysis device 300. The regenerated liquid can be supplied to the cation exchanger using a pump or other means. In the wastewater treatment system 500, a liquid to be treated, such as groundwater or industrial water, is subjected to ion exchange treatment in a cation exchanger 102 to produce cation-exchanged water. When a predetermined amount of water is passed through the cation exchanger 102, the passage of the liquid to be treated through the cation exchanger 102 is stopped, and the regenerated liquid stored in a regenerated liquid storage tank 104 is passed through a line L1 to the cation exchanger 102. The regenerated liquid that has passed through the cation exchanger 102 is stored in a regenerated liquid waste storage tank 106 as a regenerated waste liquid. After regeneration is complete, the cation exchanger 102 again passes the liquid to be treated and performs ion exchange treatment to produce cation-exchanged water. A pretreatment device such as a membrane treatment device, activated carbon filtration device, or coagulation sedimentation device may be installed upstream of the cation exchanger 102, and a posttreatment device such as an EDI (electrodeionization) device or a degassing device may be installed downstream.

[0053] The electrodialysis device 300 in the waste liquid treatment system 500 shown in Fig. 5 can be the electrodialysis device 300 shown in Fig. 3. The waste liquid treatment system 500 having the above configuration includes an acid solution circulation mechanism that connects the first water storage tank 108 and the acid recovery chamber (acid recovery chamber 22 in Fig. 3), an alkaline solution circulation mechanism that connects the second water storage tank 110 and the alkaline recovery chamber (alkali recovery chamber 32 in Fig. 3), a deionized water circulation mechanism that connects the regenerated waste liquid storage tank 106 and the deionization chamber (deionization chamber 24 in Fig. 3), an electrode solution circulation mechanism that connects the electrode solution storage tank 112, the anode chamber (anode chamber 20 in Fig. 3), and the cathode chamber (cathode chamber 34 in Fig. 3), and a recovered acid solution delivery mechanism that branches off from the acid solution circulation mechanism and connects to the regenerated liquid storage tank 104. the recovered acid solution is delivered to a regenerated solution storage tank 104 via the recovered acid solution delivery mechanism, and the recovered alkaline solution is delivered to a location outside the system via the recovered alkaline solution delivery mechanism. The recovered acid solution delivery mechanism may be a mechanism for delivering the recovered acid solution outside the system, or the recovered acid solution may be delivered to a location outside the system where the recovered acid solution is used (for example, a regenerated solution storage tank of an anion exchanger where the regenerated acid solution is used).

[0054] As the pH measuring means, a pH sensor 36 can be provided at the outlet of the deionization chamber of the electrodialysis device 300. This electrodialysis device is also equipped with a DC power supply (not shown) that supplies electricity to the electrodialysis device. The pH sensor 36 and DC power supply are connected to a control device (not shown) such as a personal computer, and the control device can control the current from the DC power supply to be applied to the cathode and anode of the electrodialysis device 300 based on the pH data of the treatment liquid transmitted from the pH sensor 36.

[0055] Figure 6 shows an example of a wastewater treatment system for treating regenerated wastewater from an anion exchanger (anion exchange resin). The wastewater treatment system 600 according to an embodiment of the present invention is similar to the wastewater treatment system shown in Figure 5 except for the following points: it includes an anion exchanger 103 instead of the cation exchanger 102 and an electrodialysis device 400 instead of the electrodialysis device 300 shown in Figure 5. The wastewater treatment system 600 according to an embodiment of the present invention includes the anion exchanger 103 filled with an anion exchanger, a regenerated liquid storage tank 104 for storing a solution (regenerated liquid) for regenerating the anion exchanger, and a regenerated liquid storage tank 106 for storing regenerated wastewater from the anion exchanger. The regenerated liquid storage tank 104 is provided with a regenerated liquid supply line L1 for supplying the regenerated liquid to the anion exchanger 103. The waste liquid treatment system 600 includes a first water tank 108 , a second water tank 110 , an electrode solution tank 112 , and an electrodialysis device 400 .

[0056] In the wastewater treatment system 600, a liquid to be treated, such as groundwater or industrial water, is subjected to ion exchange treatment in an anion exchanger 103 to produce anion-exchanged water. When a predetermined amount of water is passed through, the passage of the liquid to be treated through the anion exchanger 103 is stopped, and the regenerated liquid stored in the regenerated liquid storage tank 104 is passed through line L1 to the anion exchanger 103. The regenerated liquid that has passed through the anion exchanger 103 is stored in the regenerated liquid waste storage tank 106 as regenerated waste. After regeneration is complete, the anion exchanger 103 again passes the liquid to be treated and performs ion exchange treatment to produce anion-exchanged water. A pretreatment device such as a membrane treatment device, activated carbon filtration device, or coagulation sedimentation device may be installed upstream of the anion exchanger 103, and a posttreatment device such as an EDI (electrodeionization) device or degassing device may be installed downstream.

[0057] Here, the electrodialysis device 400 in the waste liquid treatment system 500 shown in Fig. 6 can be the electrodialysis device 400 shown in Fig. 4. The waste liquid treatment system 600 having the above configuration comprises an acid liquid circulation mechanism that connects the first water storage tank 108 and the acid recovery chamber (acid recovery chamber 22 in Fig. 4), an alkaline liquid circulation mechanism that connects the second water storage tank 110 and the alkaline recovery chamber (alkali recovery chamber 32 in Fig. 4), a deionized water circulation mechanism that connects the regenerated waste liquid storage tank 106 and the deionization chamber (deionization chamber 30 in Fig. 4), an electrode liquid circulation mechanism that connects the electrode liquid storage tank 112, the anode chamber (anode chamber 20 in Fig. 4), and the cathode chamber (cathode chamber 34 in Fig. 4), and a circulation mechanism that branches off from the alkaline liquid circulation mechanism and connects to the regenerated liquid storage tank 104. The system includes a recovered alkaline solution delivery mechanism for delivering the recovered acid solution to the outside of the system, a recovered acid solution delivery mechanism branching from the acid circulation mechanism and delivering the recovered acid solution to the outside of the system, and a pH measurement means (pH sensor 36) for measuring the pH of the treated solution obtained after the regenerated waste solution of the anion exchanger passes through the deionization chamber of the electrodialysis device 400, and when the pH value measured by the pH measurement means reaches a predetermined value, the electrodialysis treatment is terminated, the recovered alkaline solution is delivered to the regenerated solution storage tank 104 through the recovered alkaline solution delivery mechanism, and the recovered acid solution is delivered to a place outside the system where the recovered acid solution is used through the recovered acid solution delivery mechanism. The recovered alkaline solution delivery mechanism may also be a mechanism for delivering the recovered alkaline solution to the outside of the system, or the recovered alkaline solution may be delivered to a place outside the system where the recovered alkaline solution is used (for example, a regenerated solution storage tank of a cation exchange device where the regenerated alkaline solution is used).

[0058] As the pH measuring means, a pH sensor 36 can be provided at the outlet of the deionization chamber of the electrodialysis device 400, and the electrodialysis device is equipped with a DC power supply (not shown) that supplies electricity to the electrodialysis device. The pH sensor 36 and DC power supply are connected to a control device (not shown) such as a personal computer, and the control device can control the current from the DC power supply to be applied to the cathode and anode of the electrodialysis device 400 based on the pH data of the treatment liquid transmitted from the pH sensor 36.

[0059] (Controlling the end point of electrodialysis based on pH) In this way, by controlling the end point of electrodialysis based on the pH of the treatment liquid, it is possible to prevent scale components from being mixed into the recovered acid liquid and recovered alkaline liquid, and to make the liquid quality suitable for use as regeneration liquid for an ion exchange device.

[0060] For example, in a method for determining the pH by observing changes in pH, a pH meter may be installed at the outlet of the deionization chamber, in the regeneration waste liquid storage tank, in the first water storage tank, or in the second water storage tank, and measurements may be transmitted to the control device at predetermined intervals. Electrodialysis is terminated when the pH reaches a predetermined value (range) or when the pH change slope is within a predetermined range. For example, the pH of the water in the first water storage tank gradually decreases from near neutral due to the generation of an acidic solution, as described above, and stabilizes at a low value after a certain period of time. The pH of the water in the second water storage tank gradually increases from near neutral due to the generation of an alkaline solution, as described above, and stabilizes at a high value after a certain period of time. Furthermore, when the liquid in the regeneration waste liquid storage tank is cation exchanger regeneration waste, the pH of the cation exchanger regeneration waste gradually increases from the acidic side due to the migration of ions in the cation exchanger regeneration waste to a chamber adjacent to the deionization chamber, and stabilizes at the neutral or alkaline side of the initial value after a certain period of time. On the other hand, when the liquid in the regeneration waste storage tank is anion exchanger regeneration waste, the pH of the anion exchanger regeneration waste gradually decreases from the alkaline side due to the influence of ions in the anion exchanger regeneration waste moving to the chamber adjacent to the deionization chamber, and after a certain amount of time has passed, it stabilizes at a neutral or acidic side from the initial value.

[0061] When an acidic feed solution (pH≦3, preferably pH<1) is subjected to electrodialysis in a three-compartment electrodialysis apparatus (see FIG. 3), the first ions to be treated are the easily mobile ions H ＋ moves from the acid feed solution through the cation exchange membrane to the recovered alkaline solution, － The anion exchange membrane transfers to the recovered acid solution. ２ Among the ions present in dissociated neutral salts such as ＋ and Ca ２＋ is transferred to the recovered alkaline solution, and the anion Cl －moves to the recovered acid solution. ＋ The molar conductivity of Na ＋ and Ca ２＋ This phenomenon occurs because ions are larger than other cations such as H. The movement of ions occurs while maintaining the electrical neutrality of the ions in each liquid. ＋ The electrodialysis treatment is terminated when the transfer of Ca from the acid supply solution to the recovered alkaline solution is almost completed (when the pH of the treated solution from the deionization chamber is preferably about 1 to 3, more preferably 2 to 2.5). ２＋ and Mg ２＋ This suppresses the migration of hardness components such as ammonium hydroxide to the recovered alkaline solution, thereby preventing the formation of scale derived from the hardness components in the alkaline recovery chamber. By setting the end point of electrodialysis at a point when the pH of the treated solution (deionized water) from the deionization chamber is 1 or higher, separation of acid and alkali progresses sufficiently, and by setting the end point at a point when the pH is 3 or lower, migration of hardness components to the recovered alkaline solution can be suppressed, thereby reducing the risk of scale deposition in the alkaline recovery chamber.

[0062] When an acid feed solution (pH≦3, preferably pH<1) is electrodialyzed in a two-compartment electrodialysis apparatus (see FIG. 1), Cl is removed by electrodialysis of the acid feed solution. － moves from the acid feed solution to the recovered acid solution, and OH － When the pH of the treated solution of the acid supply solution reaches about 1 to 3, as in the above case, H in the acid supply solution is ＋ and an equivalent amount of Cl － Most of the hardness components have been transferred from the acid feed solution to the recovered acid solution, and by terminating the electrodialysis treatment at this point, it is possible to prevent the formation of scale derived from hardness components in the deionization chamber to which the acid feed solution is supplied.

[0063] Therefore, when the liquid to be treated supplied to the deionization chamber of the electrodialysis apparatus is an acid feed solution, the endpoint of electrodialysis is preferably the point at which the pH of the treated liquid (deionized water) from the deionization chamber reaches 1 to 3, more preferably 1.5 to 2.5, and even more preferably 2 to 2.5. The endpoint of electrodialysis can be controlled by measuring the pH of the treated liquid from the deionization chamber. Because the acid feed solution after electrolysis is roughly neutralized, the amount of neutralizing chemicals used can be reduced if the treated liquid is further neutralized. The treated liquid can also be used as cooling water for cooling equipment or utility water, or returned to an upstream stage of the water treatment equipment. The endpoint of electrodialysis can be detected by measuring the pH of the treated liquid from the deionization chamber and the pH of the recovered acid liquid from the acid recovery chamber in combination. For example, the endpoint can be determined when the pH of the treated liquid from the deionization chamber falls within a predetermined range and the pH of the recovered acid liquid is less than 0.5.

[0064] When an alkaline feed solution (pH ≥ 12, preferably pH > 13) is subjected to electrodialysis in a three-compartment electrodialysis apparatus (see FIG. 4), first, OH is － The pH of the alkaline feed solution decreases as the pH of the treated solution decreases through the anion exchange membrane. As the pH decreases, silica-derived scale tends to form. Therefore, the formation of silica scale can be prevented by terminating the electrodialysis treatment just before silica scale deposition occurs, i.e., when the pH of the treated solution (deionized water) from the deionization chamber is not too low (preferably 9 or higher, more preferably 10 or higher). Furthermore, the end point of the electrodialysis can be set to the point when the pH of the treated solution (deionized water) from the deionization chamber reaches preferably less than 12, more preferably 11.5 or lower, thereby allowing for more complete separation. The end point of the electrodialysis can be determined by measuring the pH of the treated solution from the deionization chamber and the recovered alkaline solution from the alkali recovery chamber. For example, the end point can be determined when the pH of the treated solution from the deionization chamber falls within a predetermined range and the pH of the recovered alkaline solution is greater than 13.

[0065] When an alkaline feed solution (pH ≥ 12, preferably pH > 13) is subjected to electrodialysis in a two-compartment electrodialysis apparatus (see FIG. 2), the Na in the alkaline feed solution is removed by electrodialysis. ＋ moves through the cation exchange membrane, and H ＋ As the pH decreases, silica-derived scale tends to form. Therefore, by terminating electrodialysis just before silica scale deposition, i.e., when the pH of the treated solution (deionized water) from the deionization chamber is not too low (preferably 9 or higher, more preferably 10 or higher), the formation of silica scale can be prevented, as in the case of electrodialysis of an alkaline feed solution using the above-described three-compartment electrodialysis apparatus. Furthermore, by setting the end point of this electrodialysis at the point when the pH of the treated solution (deionized water) from the deionization chamber reaches preferably less than 12, more preferably 11.5 or lower, separation can proceed more fully. Furthermore, as in the case of electrodialysis of an alkaline feed solution using the above-described three-compartment electrodialysis apparatus, the pH of the treated solution from the deionization chamber and the pH of the recovered alkaline solution from the alkaline recovery chamber may be measured in combination. For example, the end point can be set at the point when the pH of the treated solution from the deionization chamber falls within a predetermined range and the pH of the recovered alkaline solution is greater than 13.

[0066] Therefore, when the liquid to be treated supplied to the deionization compartment of the electrodialysis apparatus is an alkaline feed liquid, the endpoint of electrodialysis is preferably a time before the pH of the treated liquid (deionized water) from the deionization compartment drops from a value of 12 or more before treatment to a range of less than 9. Furthermore, the endpoint of this electrodialysis is preferably a time when the pH of the treated liquid (deionized water) from the deionization compartment drops from a value of 12 or more (preferably pH > 13) before treatment to a range of less than 12, and more preferably a time when the pH reaches 11.5 or less.

[0067] (Acid Recovery Chamber 22 and Alkali Recovery Chamber 32 of Electrodialysis Apparatus) Water is pumped by a pump or other liquid delivery means to the acid recovery chamber 22 (the cell from which the recovered acid solution flows out) or the alkali recovery chamber 32 (the cell from which the recovered alkali solution flows out) of the electrodialysis apparatus. An acid solution is recovered from the acid recovery chamber 22, and an alkali solution is recovered from the alkali recovery chamber 32. These can be reused as a regenerant for the resin tower, a neutralizer for wastewater, or the like. The recovered acid solution and alkali solution may be reused in the same water treatment system or in a different water treatment system. When used in a different water treatment system, the recovered acid solution and alkali solution can be efficiently reused. Pure water is preferably used as the water supplied to the acid recovery chamber 22 and the alkali recovery chamber 32; however, acidic or alkaline water suitable for reuse as a regenerant or neutralizer for the resin tower can also be used.

[0068] (Anode chamber 20 and cathode chamber 34 of the electrodialysis device) An electrode solution is passed through the anode chamber 20 (a cell defined by the first bipolar membrane and the anode) and the cathode chamber 34 (a cell defined by the second bipolar membrane and the cathode) of the electrodialysis device. The electrode solution is an aqueous solution of NaOH or Na ２ SO ４ An aqueous solution of a metal hydroxide or metal salt, such as an aqueous solution, can be used.

[0069] (Separation of ions in the treated liquid by the electrodialysis device) In the above-mentioned three-compartment electrodialysis device, H that was originally present in a dissociated state in the feed liquid (acid feed liquid, alkali feed liquid) is separated. ＋ or OH － This allows separation with high current efficiency and shortens the time required for separation. ＋ and Ca ２＋ Cl present in an amount equivalent to － Or, SO ４ ２－ and Cl － Na present in an amount equivalent to ＋ When the separation is carried out to the extent that the ions are neutral salts when considered as compounds, the amount of ions in the feed solution decreases, making it difficult for the current to flow, reducing the current efficiency and lengthening the time required for separation.＋ or OH － It is desirable to separate as much of the ions as possible from the feed liquid (liquid to be treated) and not separate as much as possible the other ions that will become neutral salts.

[0070] In the two-compartment electrodialysis apparatus described above, the electrical conductivity of the feed liquid (liquid to be treated) is not significantly reduced and the current efficiency is not affected because the feed liquid is replenished with ions equivalent to those that have permeated the ion exchange membrane. However, the effect of inhibiting scale can be achieved in the same way as in the three-compartment electrodialysis apparatus.

[0071] (Regeneration waste liquid) In the present invention, H originally present in a dissociated state in the feed liquid (acid feed liquid, alkali feed liquid) to the electrodialysis device is ＋ or OH － Since the regenerated acid waste liquid (acid feed liquid) of the cation exchanger and the regenerated alkaline waste liquid (alkali feed liquid) of the anion exchanger can be selectively separated, it is not necessary to mix them. If there is a place in the factory where these regenerated acid waste liquids and regenerated alkaline waste liquids can be reused in a separate system, it is possible to, for example, recover only the regenerated acid waste liquid by electrodialysis, and use the regenerated alkaline waste liquid for neutralization treatment in a separate system. In addition, by treating the regenerated acid waste liquid and the regenerated alkaline waste liquid separately without mixing them, the dissociated H contained in each waste liquid can be reduced. ＋ and OH － Therefore, the amount of acid and alkali that can be recovered by the present invention is greater than that when waste liquids are mixed. Thus, the present invention has the advantage that the regeneration waste liquid of an ion exchanger can be used without being mixed with the regeneration waste liquid of another ion exchanger.

[0072] (Electrodialysis System / Treated Object of Electrodialysis Method) The treated object (liquid to be treated) of the electrodialysis system and electrodialysis method of the present invention is not particularly limited as long as it is either an acidic liquid (acid feed liquid) having a pH of 3 or less or an alkaline liquid (alkaline feed liquid) having a pH of 12 or more, but is preferably a regenerated waste liquid discharged in the regeneration treatment of an ion exchanger, and particularly preferably a regenerated waste liquid discharged in the regeneration treatment of groundwater for producing pure water in semiconductor factories, etc., or an ion exchange resin used in industrial water treatment. Furthermore, when the treated object (liquid to be treated) is an acidic liquid (acid feed liquid), it is particularly preferred that its pH be less than 1 (pH<1), and when it is an alkaline liquid (alkaline feed liquid), it is particularly preferred that its pH be higher than 13 (pH>13).

[0073] Example 1 Regenerated wastewater from a cation exchange resin was supplied as an acid feed solution to a three-compartment electrodialysis apparatus shown in Figure 3 and subjected to electrodialysis under the following conditions to obtain a regenerated acid (treated solution): Apparatus: Bipolar membrane electrodialysis apparatus manufactured by Astom Corporation (product name: Acilyzer EX3B) Feed solution: Regenerated wastewater from a cation exchange resin tower for producing pure water The water quality is shown in the table below (Table 1) Feed solution volume and circulation flow rate: 850 ml, 1.4 L / min Recovered acid solution volume and circulation flow rate: 850 ml, 1.4 L / min Recovered alkaline solution volume and circulation flow rate: 850 ml, 1.4 L / min Voltage: 10 V The pH of the treated solution after the feed solution had passed through the electrodialysis apparatus was measured using a portable pH meter (product name: HM-40P) manufactured by DKK-TOA Corporation (glass electrode method). The ions in the feed solution and the treated solution were measured using an ion chromatograph (product name: Dionex Integration) (ion chromatography method) manufactured by Thermo Fisher Scientific Co., Ltd. The water quality (pH and component concentration) of the feed solution (regeneration wastewater) is shown in Table 1.

[0074]

[0075] The changes in component concentration, pH value, and current value of the electrodialyzed regenerated waste liquid (treated liquid) versus the operating time (dialysis time) of the electrodialysis device are shown in Figures 7 and 8. The water quality (pH and component concentration) of the regenerated waste liquid (treated liquid) during electrodialysis is shown in Table 2. The regenerated waste liquid was supplied to the electrodialysis device and electrodialysis was started, with the voltage set to 10 V. Cl was present for approximately 23 minutes after the start of operation (dialysis start). － The concentration has dropped significantly, but the cation concentration (H ＋ Excluding Na ＋ , Ca ＋ , Mg ＋ , K. ＋ The total concentration of Cl － The amount of decrease is small compared to the amount of decrease in concentration. － The gradient of the concentration and the gradient of the cation concentration should be similar, but they differ in the section about 23 minutes after the start of operation. From this, it can be seen that the cation in this section is H in HCl in the regeneration wastewater. ＋ moves, and Na in NaCl ＋ As a result, the pH of the electrodialyzed regenerated wastewater (treated liquid) increases.

[0076] After 23 minutes from the start of operation (start of dialysis), Na ＋ Concentration and Cl － The concentration of H in the regenerated wastewater was reduced by almost the same amount (Table 2). ＋ This is because the separation of NaCl has progressed due to the decrease in H ＋ was almost neutralized, and the pH rose, exceeding 2 after 43 minutes (Table 2, Figure 7).

[0077] On the other hand, as shown in Figure 8, the current value gradually decreases from around 23 minutes. This is thought to be due to the decrease in the ion concentration in the regenerated wastewater caused by electrodialysis. After around 60 minutes, the current value decreases even more rapidly.

[0078] It can be seen that the acid can be recovered in a short time by stopping the electrodialysis when the pH of the regeneration waste liquid supplied as the acid feed liquid after passing through the electrodialysis device reaches a range of 1 to 3, for example, within a range of 8 to 43 minutes (pH 1.3 to 2.1) from the start of operation (start of dialysis) in this example.

[0079] During electrodialysis, no sudden drop in current value due to scale formation was observed, and no scale material was visible on the ion exchange membrane surface after electrodialysis.

[0080]

[0081] Example 2 Regenerated waste liquid from an anion exchange resin was supplied as an alkaline feed liquid to a two-compartment electrodialysis apparatus shown in Figure 2 and subjected to electrodialysis treatment under the following conditions to obtain a regenerated alkali (treated liquid): Apparatus: Bipolar membrane electrodialysis apparatus manufactured by Astom Corporation (product name: Acilyzer EX3B) Feed liquid: Regenerated waste liquid from an anion exchange resin tower for producing pure water The water quality is shown in the table below (Table 3) Feed liquid volume and circulation flow rate: 850 ml, 1.4 L / min Recovered alkaline liquid volume and circulation flow rate: 850 ml, 1.4 L / min Voltage: 12 V The pH of the treated liquid after the feed liquid had passed through the electrodialysis apparatus was measured using a portable pH meter manufactured by DKK-TOA Corporation (product name: HM-40P (glass electrode method)). The ions in the feed solution and the treated solution were measured using an ion chromatograph (product name: Dionex Integration) (ion chromatography method) manufactured by Thermo Fisher Scientific Co., Ltd. The water quality (pH and component concentration) of the feed solution (regeneration wastewater) is shown in Table 3.

[0082]

[0083] The Na content of the electrodialyzed regenerated wastewater (treated liquid) versus the operating time of the electrodialysis device (dialysis time) ＋ The changes in concentration, pH value, and current value are shown in Figures 9 and 10. The water quality (pH and component concentration) of the regenerated waste liquid (treated liquid) during electrodialysis is shown in Table 4. The regenerated waste liquid was supplied to the electrodialysis device and dialysis was started, with the voltage set to 12 V. From the start of operation (start of dialysis), Na ＋ The concentration is decreasing. The feed liquid (recycled waste liquid) contains H＋ As the water is supplied, the pH gradually decreases.

[0084] The pH suddenly dropped around 31 minutes after the start of operation (start of dialysis). This is due to the OH in the feed liquid (regeneration waste liquid). － This is because Na is almost neutralized. ＋ Not only H ＋ Therefore, after this point, the ion migration and separation do not progress sufficiently. On the other hand, as shown in Figure 10, the current value remains almost constant after 21 minutes from the start of operation (start of dialysis).

[0085] It can be seen that alkali can be recovered in a short time by stopping electrodialysis at the point when the pH of the regenerated waste liquid (pH ≥ 12) supplied as the alkali feed liquid decreases after passing through the electrodialysis device and reaches 9, for example, 21 minutes (pH 11.1) after the start of operation (start of dialysis) in this example.

[0086] During electrodialysis, no sudden drop in current value due to scale formation was observed, and no scale material was visible on the ion exchange membrane surface after electrodialysis.

[0087]

[0088] Comparative Example 1 Electrodialysis was carried out in the same manner as in Example 1, except that the operation time (dialysis time) was set to 100 minutes. As a result, the current value was almost zero, and white scale was observed on the surface of the cation exchange membrane. This was due to Ca(OH) ２ and Mg(OH) ２ It is thought that components such as these precipitated.

[0089] Comparative Example 2 Electrodialysis was carried out in the same manner as in Example 2, except that the operation time (dialysis time) was set to 90 minutes. As a result, there was no significant change in the current value, but gel-like deposits were observed on the bipolar membrane surface. This was due to SiO ２ It is thought that this was precipitated.

[0090] REFERENCE SIGNS LIST 1 anode 3 first bipolar membrane 5 anion exchange membrane 7 cation exchange membrane 9 second bipolar membrane 11 cathode 20 anode chamber 22 acid recovery chamber 24, 30 deionization chamber 32 alkali recovery chamber 34 cathode chamber 36 pH measuring means 100 two-compartment acid recovery electrodialysis apparatus 102 cation exchange apparatus 103 anion exchange apparatus 104 regeneration liquid storage tank 106 regeneration waste liquid storage tank 108 first water storage tank 110 second water storage tank 112 electrode solution storage tank 200 two-compartment alkali recovery electrodialysis apparatus 300 three-compartment acid recovery electrodialysis apparatus 400 three-compartment alkali recovery electrodialysis apparatus 500 waste liquid treatment system for regeneration waste liquid of cation exchanger 600 waste liquid treatment system for regeneration waste liquid of anion exchanger

Claims

1. An electrodialysis system used for treating a liquid having a pH of 3 or less or a pH of 12 or more, comprising: an electrodialysis device having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, with the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode; and a pH measuring means for measuring the pH of a treated liquid obtained after the liquid to be treated passes through the electrodialysis device, and the electrodialysis treatment by the electrodialysis device is terminated when the pH value of the treated liquid measured by the pH measuring means reaches a predetermined value.

2. The electrodialysis system according to claim 1, wherein the liquid to be treated has a pH of 3 or less, and the ion exchange membrane of the electrodialysis device is an anion exchange membrane.

3. The electrodialysis system according to claim 1, wherein the liquid to be treated has a pH of 12 or more, and the ion exchange membrane of the electrodialysis device is a cation exchange membrane.

4. The electrodialysis system according to claim 1, wherein the ion exchange membrane of the electrodialysis device is an anion exchange membrane, and a cation exchange membrane is provided between the anion exchange membrane and the second bipolar membrane.

5. The electrodialysis system according to claim 2, wherein the electrodialysis apparatus comprises: an anode chamber defined by the anode and the first bipolar membrane; and a cathode chamber defined by the cathode and the second bipolar membrane; an acid recovery chamber defined by the first bipolar membrane and the anion exchange membrane between the anode chamber and the cathode chamber, to which water is supplied and which produces a recovered acid solution by electrodialysis; and a deionization chamber defined by the anion exchange membrane and the second bipolar membrane, to which an acid supply solution is supplied as the liquid to be treated and which produces deionized water by electrodialysis; and wherein one or more cell sets each composed of the acid recovery chamber and the deionization chamber are arranged.

6. The electrodialysis system according to claim 3, wherein the electrodialysis apparatus comprises an anode chamber defined by the anode and the first bipolar membrane, and a cathode chamber defined by the cathode and the second bipolar membrane, and further comprises a deionization chamber defined by the first bipolar membrane and the cation exchange membrane between the anode chamber and the cathode chamber, into which an alkaline feed liquid is supplied as the liquid to be treated and deionized water is produced by electrodialysis, and an alkali recovery chamber defined by the cation exchange membrane and the second bipolar membrane, into which water is supplied and a recovered alkaline liquid is produced by electrodialysis, and wherein one or more cell sets composed of the deionization chamber and the alkali recovery chamber are arranged in a repeated manner.

7. The electrodialysis system according to claim 4, wherein the electrodialysis apparatus comprises an anode chamber defined by the anode and the first bipolar membrane, and a cathode chamber defined by the cathode and the second bipolar membrane, and between the anode chamber and the cathode chamber, an alkali recovery chamber defined by the cation exchange membrane and the second bipolar membrane, to which water is supplied and which produces a recovered alkaline liquid by electrodialysis, an acid recovery chamber defined by the anion exchange membrane and the first bipolar membrane, to which water is supplied and which produces a recovered acid liquid by electrodialysis, and a deionization chamber defined by the cation exchange membrane and the anion exchange membrane, to which the liquid to be treated is supplied and which produces deionized water by electrodialysis, and wherein one or more cell sets each composed of the acid recovery chamber, the deionization chamber and the alkali recovery chamber are arranged in a repeated manner.

8. An electrodialysis system according to claim 2 or 4, wherein the pH of the liquid to be treated is less than 1, and when the pH of the treatment liquid reaches a range of 1 or more and 3 or less, the electrodialysis treatment by the electrodialysis device is terminated.

9. The electrodialysis system according to claim 3 or 4, wherein the pH of the liquid to be treated is 12 or more, and the electrodialysis treatment by the electrodialysis device is terminated before the pH of the treatment liquid reaches a range of less than 9.

10. The electrodialysis system according to any one of claims 1 to 7, wherein the liquid to be treated is a regenerated waste liquid from an ion exchange device.

11. The electrodialysis system according to any one of claims 5 to 7, wherein the recovered acid liquid or the recovered alkaline liquid is used in a water treatment system other than the water treatment system that discharges the liquid to be treated.

12. A waste liquid treatment system comprising: an ion exchange device filled with ion exchangers; a regenerated liquid supplying device for supplying regenerated liquid of the ion exchangers to the ion exchange device; and an electrodialysis system for treating regenerated waste liquid discharged from the ion exchange device, wherein the regenerated waste liquid has a pH of 3 or less or a pH of 12 or more; the electrodialysis system comprising: an electrodialysis device having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode; and a pH measuring means for measuring the pH of a treated liquid obtained after the regenerated waste liquid has passed through the electrodialysis device, wherein the electrodialysis treatment by the electrodialysis device is terminated when the pH value of the treated liquid measured by the pH measuring means reaches a predetermined value.

13. An electrodialysis method used for treating a liquid having a pH of 3 or less or a pH of 12 or more, comprising the steps of: performing electrodialysis using an electrodialysis apparatus having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, with the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode; measuring the pH of a treated liquid obtained after the liquid to be treated passes through the electrodialysis apparatus; and terminating the electrodialysis using the electrodialysis apparatus when the measured pH value of the treated liquid reaches a predetermined value.

14. A waste liquid treatment method comprising: a regenerated liquid supplying step of supplying a regenerated liquid of an ion exchanger to an ion exchange device filled with the ion exchanger; and an electrodialysis step of treating regenerated waste liquid discharged from the ion exchange device, wherein the regenerated waste liquid has a pH of 3 or less or a pH of 12 or more, the electrodialysis step comprising: a step of passing the regenerated waste liquid through an electrodialysis device having at least an anode, a cathode, a first bipolar membrane, an ion exchange membrane, and a second bipolar membrane, the first bipolar membrane, the ion exchange membrane, and the second bipolar membrane being arranged in this order from the anode side between the anode and the cathode, to perform electrodialysis treatment; and a step of measuring the pH of a treated liquid obtained after the regenerated waste liquid has passed through the electrodialysis device, wherein the electrodialysis treatment by the electrodialysis device is terminated when the pH value of the treated liquid measured in the pH measuring step reaches a predetermined value.

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