Water treatment system

Abstract

This water treatment system comprises: an electrodialysis device that performs electrodialysis on water to be treated to generate treated water; and a recovery unit that recovers a target recovery product from the treated water. The electrodialysis device comprises an anode and a cathode provided to face each other, and a plurality of membranes disposed between the anode and the cathode. Some of the plurality of membranes include a first layer having separation performance, and a second layer that supports the first layer and does not have separation performance.

Description

Water treatment system

[0001] This disclosure relates to a water treatment system. This application claims priority to Japanese Patent Application No. 2024-170202, filed in Japan on September 30, 2024, the content of which is incorporated herein by reference.

[0002] As a method for recovering valuable substances such as metals from seawater and the like, a water treatment system using electrodialysis (ED) as shown in Patent Document 1 and Patent Document 2 is known. Patent Document 2 discloses a water treatment system including an electrodialysis device having a stack structure in which either a cation exchange membrane or an anion exchange membrane is replaced with a nanofiltration membrane, that is, an electrodialysis device incorporating a nanofiltration membrane (EDNF).

[0003] Unexamined Japanese Patent Application Publication No. 2014-161794 Unexamined Japanese Patent Application Publication No. 2023-115943

[0004] However, in the electrodialysis device incorporating a nanofiltration membrane, although the initial cost is reduced, there is a problem that the running cost cannot be reduced as expected. Therefore, there has been a demand for a technology that can recover valuable substances at a lower cost.

[0005] This disclosure provides a water treatment system capable of reducing the running cost.

[0006] When the inventor examined the reason why the running cost does not decrease, it was found that the support layer of the nanofiltration membrane does not contribute to the separation performance, but the resistance value of this support layer is high, so the electricity cost is high. The water treatment system according to this disclosure includes an electrodialysis device that performs electrodialysis on the water to be treated to generate treated water, and a recovery unit that recovers the target recovery product from the treated water. The electrodialysis device includes an anode and a cathode provided opposite to each other, and a plurality of membranes disposed between the anode and the cathode. A part of the plurality of membranes includes a first layer having separation performance and a second layer that supports the first layer and does not have separation performance.

[0007] According to the electrodialysis device and the water treatment system of this disclosure, the running cost can be reduced.

[0008] This is a schematic diagram showing the entire water treatment system according to the embodiment of this disclosure. This is an enlarged schematic diagram of a part of the water treatment system according to the embodiment of this disclosure. This is a schematic diagram of the second membrane according to the first embodiment of this disclosure. This is a schematic diagram of the second membrane according to the second embodiment of this disclosure. This is a schematic diagram of the second layer according to the third embodiment of this disclosure.

[0009] <First Embodiment> Hereinafter, the water treatment system 1 according to the first embodiment of this disclosure will be described in detail with reference to Figures 1 to 3.

[0010] <Water Treatment System> In this embodiment, the water treatment system 1 is described as a system that separates seawater (introduced water) into concentrated water (water to be treated) and fresh water using a reverse osmosis membrane (RO membrane) to produce fresh water, and further separates the concentrated water into highly concentrated water and desalinated water by electrodialysis (ED), and recovers valuable metals by evaporating the highly concentrated water and precipitating it.

[0011] As shown in Figure 1, the water treatment system 1 of this embodiment comprises a water treatment introduction section 10, a reverse osmosis membrane device 20, an electrodialysis device 30, a recovery section 70, and a flow pipe 80. The flow pipe 80 is a flow path through which various fluids can flow. The fluids to be flowed are not limited in form, but examples include concentrated water and fresh water. The flow pipe 80 includes a water supply pipe 81, a concentrated water pipe 82, a permeate water pipe 83, a highly concentrated water pipe 84, a desalination water pipe 85, a return water pipe 86, a discharge pipe 87, and an evaporation water pipe 88. Further explanation of the flow pipe 80 will be provided below as appropriate.

[0012] <Water to be treated introduction section> The water to be treated introduction section 10 is provided to allow the water to be treated by the water treatment system 1 to flow through it. The water to be treated introduction section 10 in this embodiment may include a pretreatment device (not shown). The pretreatment device is provided to suppress the deterioration of the water permeability performance of the reverse osmosis membrane device 20. The pretreatment device can remove suspended matter such as fine particles and colloids, and microorganisms such as algae and shellfish from seawater. The pretreatment device may be configured to perform other types of pretreatment. The water to be treated introduction section 10 is connected to a water supply pipe 81 through which the water to be treated flows to the reverse osmosis membrane device 20.

[0013] <Reverse Osmosis Membrane Device> The reverse osmosis membrane device 20 is configured, for example, by having multiple reverse osmosis membrane elements (reverse osmosis membrane modules) in a container. The reverse osmosis membrane device 20 is capable of treating incoming water by reverse osmosis. The reverse osmosis membrane device 20 is capable of separating incoming water into concentrated water (water to be treated) and fresh water. The reverse osmosis membrane device 20 is connected to a concentrated water pipe 82 and a permeate water pipe 83. The concentrated water pipe 82 is capable of circulating concentrated water to the electrodialysis machine 30. The permeate water pipe 83 is capable of circulating fresh water. The permeate water pipe 83 is capable of discharging fresh water to the outside of the water treatment system 1, for example.

[0014] <Electrodialysis apparatus> The electrodialysis apparatus 30 is capable of ion separation of concentrated water. As shown in Figure 2, the electrodialysis apparatus 30 comprises an electrodialysis cell 31, an anode 32, a cathode 33, and a plurality of membranes 40. The electrodialysis cell 31 has the anode 32, the cathode 33, and the plurality of membranes 40 arranged inside it. The anode 32 and the cathode 33 are arranged facing each other. A DC voltage can be applied to the inside of the electrodialysis cell 31 to the anode 32 and the cathode 33.

[0015] <Membrane> The membrane 40 is positioned between the anode 32 and the cathode 33. The membrane 40 is a membrane that has ion separation capabilities. The membrane 40 in this embodiment has a first membrane 41 and a second membrane 42. The first membrane 41 and the second membrane 42 are positioned with a gap between them. Furthermore, the first membrane 41 and the second membrane 42 are positioned alternately between the anode 32 and the cathode 33. In other words, the second membrane 42 is positioned alternately with a gap between it and the first membrane 41.

[0016] <First Membrane> The first membrane 41 in this embodiment is a cation exchange membrane. That is, the first membrane 41 allows cations to pass through regardless of their valence, but does not allow anions to pass through. The first membrane 41 may also have valence selectivity. Furthermore, the terms "permeable" (or "not permeable") in this disclosure are not limited to the fact that all of the object necessarily permeates (or does not permeate) it. That is, in this disclosure, "permeable" is used to indicate that a particular object is easily permeable, and "not permeable" is used to indicate that an object is not easily permeable. For example, the first membrane 41 in this embodiment is easily permeable to cations and not easily permeable to anions, but some anions may permeate it.

[0017] <Second Membrane> The second membrane 42 in this embodiment is a nanofiltration membrane (NF membrane). That is, the second membrane 42 is permeable only to monovalent ions. Furthermore, the second membrane 42 does not have selectivity between cations and anions. In this way, the second membrane 42 is capable of separating monovalent ions from polyvalent ions. However, the second membrane 42 may also have selectivity between cations and anions. As shown in Figure 3, the second membrane 42 in this embodiment has a first layer 43 and a second layer 44.

[0018] <First Layer> The first layer 43 has ion separation capabilities. The first layer 43 is capable of separating monovalent ions from polyvalent ions. That is, the first layer 43 is configured to permeate monovalent ions but not polyvalent ions. The first layer 43 is connected to the second layer 44 and is integrated with it. When placed inside the electrodialysis cell 31, the position of the second layer 44 relative to the first layer 43 is not limited to one side. Also, the first layer 43 is made of, for example, polyamide, but is not limited to this.

[0019] <Second Layer> The second layer 44 is provided to support the first layer 43. The second layer 44 does not have ion separation capabilities. The second layer 44 in this embodiment has a support layer 50 and a base layer 51. The support layer 50 is provided to support the first layer 43. The support layer 50 does not have ion separation capabilities. The support layer 50 is provided to allow ions, etc., that have been selectively permeated through the first layer 43 to pass through. The support layer 50 is provided so as to be sandwiched between the first layer 43 and the base layer 51. The support layer 50 is made of, for example, polysulfone, but is not limited thereto.

[0020] The base layer 51 is provided to improve the pressure resistance performance of the second film 42. The base layer 51 does not have ion separation properties. The base layer 51 is provided to allow ions selected and permeated through the first layer 43 to pass through. The base layer 51 is provided together with the first layer 43 to sandwich the support layer 50. The base layer 51 is, for example, a nonwoven fabric made of polyester, but is not limited thereto.

[0021] The second layer 44 is preferably 75 micrometers or less in thickness. That is, the combined thickness of the support layer 50 and the base layer 51 is preferably 75 micrometers or less. In other words, the second layer 44 is preferably 0 to 75 micrometers in thickness. More preferably 6 to 45 micrometers, and even more preferably 6 to 15 micrometers. The thicknesses of the support layer 50 and the base layer 51 are not limited. For example, when the thickness of the support layer 50 is 45 micrometers, the thickness of the base layer 51 is preferably 30 micrometers or less. Furthermore, the second film 42 is preferably 7 Ω·cm² or less in an aqueous sodium chloride solution of 0.5 mol / L.

[0022] <Detailed Configuration of the Electrodialysis Machine> As shown in Figure 2, the electrodialysis machine 30 has a concentration chamber 34 and a dilution chamber 35 formed by a first membrane 41 and a second membrane 42 that are arranged alternately. The concentration chamber 34 and the dilution chamber 35 are adjacent to each other via the first membrane 41 or the second membrane 42.

[0023] In the concentration chamber 34, cations that have permeated through the first membrane 41, which is a cation exchange membrane, can flow in from the adjacent dilution chamber 35. Examples of cations include sodium ions, potassium ions, calcium ions, and magnesium ions. Furthermore, ions that have permeated through the second membrane 42, which is a nanofiltration membrane, can flow into the concentration chamber 34 from the adjacent dilution chamber 35 on the opposite side. An example of an ion that flows into the concentration chamber 34 after permeating through the second membrane 42 is the monovalent ion, chloride ion.

[0024] A highly concentrated water pipe 84 is connected to the concentration chamber 34. The highly concentrated water produced by concentration in the concentration chamber 34 can be circulated to the recovery unit 70 via the highly concentrated water pipe 84. The highly concentrated water pipe 84 may also be branched to allow highly concentrated water to flow into the concentration chamber 34.

[0025] A concentrated water pipe 82 is connected to the dilution chamber 35. That is, the dilution chamber 35 is designed to allow concentrated water produced by the reverse osmosis membrane device 20 to flow into it. Various ions are permeated from the concentrated water flowing into the dilution chamber 35 to the adjacent concentration chamber 34, where it is desalinated. In other words, the concentrated water is desalinated to produce desalinated water. At this time, sulfate ions contained in the concentrated water remain in the desalinated water because they cannot permeate the second membrane 42. In addition, some ions that can permeate membrane 40 also remain in the desalinated water.

[0026] The desalination water can be discharged through the desalination water pipe 85. The desalination water pipe 85 is capable of circulating to the recovery unit 70. However, the desalination water pipe 85 may not be connected to the recovery unit 70. For example, the desalination water pipe 85 may be capable of discharging the desalination water to the outside of the water treatment system 1. In this embodiment, an example is given in which the desalination water pipe 85 is connected to the valuable material recovery unit 72, which is the recovery unit 70.

[0027] Hereinafter, the highly concentrated water and desalinated water supplied to the recovery unit 70 will be referred to as treated water. That is, the treated water generated in the electrodialysis machine 30 is distributed to the recovery unit 70.

[0028] <Recovery Unit> The recovery unit 70 is provided to recover the target substance (desired solute) from the treated water. That is, the recovery unit 70 can recover the target substance from the supplied highly concentrated water and desalinated water. The recovery unit 70 in this embodiment has a metal recovery unit 71 and a valuable substance recovery unit 72.

[0029] <Metal Recovery Section> The metal recovery section 71 is connected to a highly concentrated water pipe 84. That is, highly concentrated water can flow into the metal recovery section 71. The metal recovery section 71 can process the highly concentrated water and recover the target material. The metal recovery section 71 of this embodiment exemplifies a case where the target material is obtained by evaporating the highly concentrated water. However, the method of processing the highly concentrated water is not limited to this. The metal recovery section 71 of this embodiment evaporates the water from the highly concentrated water. The metal recovery section 71 also includes a part that recovers the target material from the highly concentrated water from which the water has been evaporated. The metal recovery section 71 of this embodiment can recover, for example, magnesium, sodium, calcium, potassium, etc.

[0030] The metal recovery section 71 is connected to an evaporation pipe 88 and a discharge pipe 87. The evaporation pipe 88 is capable of carrying water evaporated in the metal recovery section 71. The evaporation pipe 88 is connected to a permeate pipe 83. That is, the evaporation pipe 88 is capable of carrying evaporated water to the permeate pipe 83. The evaporation pipe 88 is capable of discharging the liquid from which the target material has been recovered in the metal recovery section 71 to the outside of the water treatment system 1.

[0031] <Valuable Material Recovery Unit> The valuable material recovery unit 72 is connected to the desalination water pipe 85. That is, the desalination water pipe 85 can flow into the valuable material recovery unit 72. The valuable material recovery unit 72 can process the desalination water and recover the target material. The valuable material recovery unit 72 is configured to recover the target material by means of adsorption, ion exchange, etc. In this embodiment, the valuable material recovery unit 72 can recover sulfur as sulfate ions, etc.

[0032] A return water pipe 86 is connected to the valuable materials recovery unit 72. The return water pipe 86 can circulate the liquid from which the valuable materials have been recovered in the valuable materials recovery unit 72. The return water pipe 86 is connected to the water supply pipe 81. That is, the return water pipe 86 can circulate the liquid from which the valuable materials have been recovered to the water supply pipe 81.

[0033] <Effects> In the water treatment system 1 described above, the concentrated water to be treated is treated by the electrodialysis machine 30. The electrodialysis machine 30 discharges highly concentrated water in which cations and monovalent anions are concentrated. The electrodialysis machine 30 also discharges desalinated water in which divalent or greater anions remain and cations and monovalent anions are reduced. The treated water (highly concentrated water and desalinated water) is recovered by the recovery unit 70 to recover the target material.

[0034] The electrodialysis apparatus 30 of this embodiment has a first membrane 41 which is a cation exchange membrane and a second membrane 42 which is a nanofiltration membrane. The second membrane 42 of this embodiment does not have selectivity for cations and anions, but is configured to substantially allow monovalent anions to pass through due to the balance of ions in the concentration chamber 34 and the dilution chamber 35, respectively. Since nanofiltration membranes are generally less expensive than cation exchange membranes and anion exchange membranes, this configuration can reduce the manufacturing cost of the electrodialysis apparatus 30. Therefore, the manufacturing cost of the water treatment system 1 can be reduced.

[0035] Furthermore, the second membrane 42 of this embodiment has a first layer 43 that has ion separation performance and a second layer 44 that does not have ion separation performance. The second layer 44 has a support layer 50 and a base layer 51. The second layer 44 can improve the pressure resistance performance of the second membrane 42, which is a nanofiltration membrane, and facilitate handling in the manufacture and maintenance of the electrodialysis apparatus 30. On the other hand, the second layer 44 increases the electrical resistance of the second membrane 42. According to this embodiment, the electrical resistance of the second membrane 42 can be reduced by making the second layer 44 thin (for example, 75 nanometers or less). Therefore, the power consumption of the electrodialysis apparatus 30 can be reduced. Therefore, the running cost of the water treatment system 1 can be reduced.

[0036] Furthermore, the base layer 51 in this embodiment is a nonwoven fabric made of polyester. The base layer 51 supports the first layer 43 and improves the pressure resistance performance of the second membrane 42. On the other hand, because the base layer 51 is made of a nonwoven fabric, it leaks the treated water to the outside of the electrodialysis apparatus 30. In this embodiment, by making the thickness of the second layer 44 thin (for example, 75 nanometers or less), it is possible to reduce leakage of the treated water to the outside while ensuring ease of handling of the second membrane 42. Therefore, it is possible to reduce the amount of treated water processed per unit amount of valuable material recovered. Accordingly, according to this embodiment, it is possible to reduce the processing amount per unit amount of valuable material recovered while reducing running costs.

[0037] Furthermore, the first layer 43 of this embodiment has the ability to separate monovalent ions selectively. As a result, polyvalent anions remain in the desalinated water of this embodiment. In this embodiment, for example, sulfate ions remain in the desalinated water. By treating this desalinated water, sulfate ions can be separated from other ions contained in seawater and recovered.

[0038] <Second Embodiment> Next, a second embodiment will be described with reference to Figure 4. In the second embodiment, the same reference numerals are used for components similar to those in the first embodiment, and detailed descriptions are omitted.

[0039] The water treatment system 1A and electrodialysis apparatus 30A of the second embodiment differ from the first embodiment in the configuration of the second membrane 42A. As shown in Figure 4, the second membrane 42A of the second embodiment does not include a base layer 51 in the second layer 44A. That is, the second layer 44A of the second embodiment does not have a base layer 51, but has a support layer 50. The support layer 50 of the second embodiment is the same as that of the first embodiment. The second layer 44A, i.e., the support layer 50 of the second embodiment, preferably has a thickness of 75 micrometers or less. The support layer 50 preferably has a thickness of 0 to 75 micrometers, more preferably 6 to 45 micrometers, and even more preferably 6 to 15 micrometers. Furthermore, the second membrane 42A preferably has an electrical resistance of 7 Ω・cm² ​​or less in a 0.5 mol / L aqueous sodium chloride solution.

[0040] <Effects> In the water treatment system 1A and electrodialysis apparatus 30A according to the second embodiment, the second layer 44A does not have the base material layer 51 according to the first embodiment. That is, the second layer 44A does not have a structure such as a nonwoven fabric made of polyester. Therefore, leakage of treated water to the outside can be further reduced. In addition, the electrical resistance value of the second membrane 42A can be further reduced. Therefore, the water treatment system 1A can further reduce the processing amount per unit of recovered valuable material while further reducing running costs.

[0041] <Third Embodiment> Next, a third embodiment will be described with reference to Figure 5. In the third embodiment, the same reference numerals are used for components similar to those in the first embodiment, and detailed descriptions are omitted.

[0042] The water treatment system 1B and electrodialysis apparatus 30B of the third embodiment differ from the first and second embodiments in the configuration of the second membrane 42B. In the second membrane 42B of the third embodiment, the second layer 44B has a porous body 60. Figure 5 shows the porous body 60. When the second membrane 42B is placed in the electrodialysis apparatus 30B, the porous body 60 has micropores 61 formed in the direction in which the anode 32 and cathode 33 face each other. Multiple micropores 61 are formed in the porous body 60, spaced apart in the direction in which the membrane expands.

[0043] The micropores 61 are formed to a diameter that allows a desired substance, such as an ion, to pass through. In this embodiment, monovalent ions separated and permeated in the first layer 43 can pass through the micropores 61. The diameter of the micropores 61 is, for example, 10 nanometers to 400 nanometers, but is not limited thereto. Furthermore, the second layer 44B according to the third embodiment is preferably 75 micrometers or less in thickness. The second layer 44B is preferably 0 to 75 micrometers in thickness, more preferably 6 to 45 micrometers, and even more preferably 6 to 15 micrometers. Furthermore, the second membrane 42B is preferably 7 Ω·cm² or less in an aqueous sodium chloride solution of 0.5 mol / L.

[0044] <Function and Effect> The water treatment system 1B and the electrodialysis device 30B according to the third embodiment have a second layer 44B having a porous body 60. The porous body 60 has a plurality of micropores 61 extending in the direction in which the anode 32 and the cathode 33 face each other. According to this, a substance permeable through the first layer 43 can be passed through while restricting the moving direction. Therefore, it is possible to greatly reduce the leakage of the treated water to the outside without preventing the ions passing through the first layer 43 from passing through. Further, by setting the thickness of the second layer 44B to, for example, 75 nanometers or less, the electric resistance value of the second membrane 42B can be reduced. As described above, according to the water treatment system 1B of the third embodiment, it is possible to reduce the treatment amount per amount of valuable substances recovered while further reducing the running cost.

[0045] <Other Embodiments> Although the embodiments of the present disclosure have been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present disclosure are also included.

[0046] For example, the water treatment systems 1, 1A, and 1B according to one embodiment may be in a state where the treated water introduction section 10 and the reverse osmosis membrane device 20 are not provided. That is, the water treatment systems 1, 1A, and 1B may be configured such that introduced water such as seawater can be directly introduced into the electrodialysis devices 30, 30A, and 30B. Further, the water treatment systems 1, 1A, and 1B may be in a state where either the treated water introduction section 10 or the reverse osmosis membrane device 20 is provided.

[0047] Further, the membranes 40 according to one embodiment may have different combinations. For example, for the electrodialysis device 30 according to the first embodiment, the first membrane 41 may be an NF membrane and the second membrane 42 may be an anion exchange membrane. According to such a configuration, in the concentration chamber 34, sodium ions, potassium ions, chloride ions, sulfate ions, etc. are concentrated, and in the dilution chamber 35, the above ions permeate and are reduced, and desalted water mainly remaining with magnesium ions, calcium ions, etc. is generated. In this way, the ions to be sorted may be appropriately changed.

[0048] Further, the flow pipe 80 according to an embodiment may have different branches respectively.

[0049] Further, the recovery unit 70 according to an embodiment may be in a form in which a mechanism for recovering valuable substances is not provided. That is, the recovery unit 70 may be in a form in which treated water (both or one of highly concentrated water and demineralized water) can be recovered, and the recovered treated water is treated outside the water treatment systems 1, 1A, and 1B.

[0050] Further, the membrane 40 according to an embodiment may have selectivity for different valences and selectivity for cations and anions. As an example, the first layer 43 according to the first embodiment may be permeable to ions up to divalent or may further have selectivity for cations and anions. By changing the selectivity of the membrane 40 according to the water to be treated processed in the water treatment systems 1, 1A, and 1B, the target recovery product can be appropriately changed.

[0051] Further, the second layer 44B according to the third embodiment may be composed only of the porous body 60. According to this, leakage from the second layer 44B to the outside of the electrodialysis device 30B can be further greatly reduced. However, it is not limited to this, and a form may be adopted in which a layer through which the substance that has passed through the first layer 43, such as the support layer 50 according to the first and second embodiments, can pass is further provided.

[0052] <Appendix> The water treatment systems 1, 1A, and 1B described in each embodiment are understood as follows, for example.

[0053] (1) The water treatment systems 1, 1A, and 1B according to the first aspect include an electrodialysis device 30, 30A, 30B that performs electrodialysis on the water to be treated to generate treated water, and a recovery unit 70 that recovers a target recovery product from the treated water. The electrodialysis devices 30, 30A, 30B include an anode 32 and a cathode 33 provided opposite to each other, and a plurality of membranes 40 disposed between the anode 32 and the cathode 33. A part of the plurality of membranes 40 includes a first layer 43 having separation performance, and a second layer 44, 44A, 44B that supports the first layer 43 and does not have separation performance.

[0054] According to the above configuration, the water treatment systems 1, 1A, and 1B are equipped with electrodialysis machines 30, 30A, and 30B having multiple membranes 40. Part of the multiple membranes 40 includes a first layer 43 having ion separation capabilities and second layers 44, 44A, and 44B that do not have ion separation capabilities. For example, by making the second layers 44, 44A, and 44B thinner, the electrical resistance of the membrane 40 can be reduced. This reduces the power consumption of the electrodialysis machines 30, 30A, and 30B. In addition, it is possible to suppress leakage of the treated water from the second layers 44, 44A, and 44B to the outside of the electrodialysis machines 30, 30A, and 30B. Furthermore, the recovery unit 70 makes it possible to recover desired substances. Therefore, according to the water treatment systems 1, 1A, and 1B in this configuration, it is possible to reduce the processing amount per unit of recovered valuable material while reducing running costs.

[0055] (2) The water treatment systems 1, 1A, and 1B relating to the second embodiment are the water treatment systems 1, 1A, and 1B of (1), wherein the first layer 43 has monovalent selective ion separation performance.

[0056] According to the above configuration, the first layer 43 has the ability to separate monovalent ions selectively. For example, the first layer 43 is a nanofiltration membrane. Since nanofiltration membranes are less expensive than cation exchange membranes and anion exchange membranes, the manufacturing cost of the electrodialysis machines 30, 30A, and 30B can be reduced. Therefore, the water treatment systems 1, 1A, and 1B of this type can reduce the processing volume per unit of recovered valuable material while keeping initial costs down and reducing running costs.

[0057] (3) The water treatment systems 1, 1A, 1B relating to the third embodiment are the water treatment systems 1, 1A, 1B of (1) or (2), wherein the second layer 44, 44A, 44B has a porous body 60 in which fine pores 61 are formed that extend in the direction in which the anode 32 and the cathode 33 face each other.

[0058] According to the above configuration, the second layers 44, 44A, and 44B have a porous body 60 in which fine pores 61 are formed that extend in the direction in which the anode 32 and cathode 33 face each other. Therefore, substances that can permeate the first layer 43 can pass through while restricting their direction of movement. Consequently, it is possible to significantly reduce the leakage of treated water from the second layers 44, 44A, and 44B to the outside of the electrodialysis apparatus 30, 30A, and 30B without hindering the passage of ions that permeate the first layer 43. In this way, according to this configuration, it is possible to further reduce the processing amount per unit of recovered valuable material while further reducing running costs.

[0059] (4) The water treatment systems 1, 1A, and 1B relating to the fourth aspect are any of the water treatment systems 1, 1A, and 1B described in (1) to (3), wherein the second layers 44, 44A, and 44B have a thickness of 75 micrometers or less.

[0060] According to the above configuration, the membrane 40 can be made thinner. Therefore, the electrical resistance of the membrane 40 can be reduced, and leakage of the treated water from the membrane 40 to the outside of the electrodialysis machines 30, 30A, and 30B can be suppressed. Accordingly, with the water treatment systems 1, 1A, and 1B of this type, the processing volume per unit of recovered valuable material can be reduced while reducing running costs.

[0061] (5) The water treatment systems 1, 1A, and 1B relating to the fifth aspect are any of the water treatment systems 1, 1A, and 1B described in (1) to (4), further comprising a reverse osmosis membrane device 20 that separates the incoming water introduced from the outside into the water to be treated and fresh water by reverse osmosis.

[0062] The electrodialysis apparatus and water treatment system disclosed herein can reduce running costs.

[0063] 1, 1A, 1B Water Treatment System 10 Water to be treated introduction section 20 Reverse osmosis membrane apparatus 30, 30A, 30B Electrodialysis apparatus 31 Electrodialysis tank 32 Anode 33 Cathode 34 Concentration chamber 35 Dilution chamber 40 Membrane 41 First membrane 42, 42A, 42B Second membrane 43 First layer 44, 44A, 44B Second layer 50 Support layer 51 Base layer 60 Porous body 61 Micropores 70 Recovery section 71 Metal recovery section 72 Valuable material recovery section 80 Flow pipe 81 Water supply pipe 82 Concentrated water pipe 83 Permeate water pipe 84 Highly concentrated water pipe 85 Desalination water pipe 86 Return water pipe 87 Discharge pipe 88 Evaporation water pipe

Claims

1. A water treatment system comprising: an electrodialysis apparatus that generates treated water by performing electrodialysis on water to be treated; and a recovery unit that recovers a target material from the treated water, wherein the electrodialysis apparatus comprises: an anode and a cathode provided opposite to each other; and a plurality of membranes disposed between the anode and the cathode, wherein a portion of the plurality of membranes includes: a first layer having separation performance; and a second layer that supports the first layer and does not have separation performance.

2. The water treatment system according to claim 1, wherein the first layer has the ability to separate monovalent ions selectively.

3. The water treatment system according to claim 1, wherein the second layer is a porous body having micropores formed in a direction in which the anode and the cathode face each other.

4. The water treatment system according to claim 1, wherein the second layer has a thickness of 75 micrometers or less.

5. The water treatment system according to any one of claims 1 to 4, further comprising a reverse osmosis membrane device for separating the water to be treated from fresh water by reverse osmosis.

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