Water treatment apparatus, water treatment system, water treatment method, and water treatment method for water treatment system

Abstract

To provide a water treatment apparatus capable of reducing operating costs.SOLUTION: A water treatment apparatus 1 includes a cation exchange unit 14 for removing magnesium from water containing magnesium, and a membrane filtration unit 16 for treating magnesium-containing wastewater discharged from the cation exchange unit 14, which contains the removed magnesium, by reverse osmosis membrane treatment or nanofiltration membrane treatment, thereby separating it into permeate water and magnesium-concentrated water, and is characterized by supplying the magnesium-concentrated water to a silica treatment device 12 for treating silica-containing water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for a water treatment device, a water treatment system, a water treatment method, and a water treatment method for a water treatment system. [Background technology]

[0002] Conventionally, one method for treating silica contained in wastewater is to use a magnesium salt.

[0003] For example, Patent Document 1 discloses a method of removing silica by mixing a magnesium-containing liquid in which Mg salt is dissolved at a pH of 7 or less with silica-containing water and reacting them in the pH range of 10 to 12.

[0004] Furthermore, for example, Patent Document 2 discloses a water treatment method in which silica-containing water is treated with a silica removal means, the resulting treated water is concentrated, and then the concentrated water is concentrated on the primary side of a forward osmosis membrane while an aqueous magnesium salt solution is diluted on the secondary side of the forward osmosis membrane, and the diluted aqueous magnesium salt solution is used for treatment with the silica removal means.

[0005] Furthermore, for example, Patent Document 3 discloses a water treatment method in which silica-containing water is treated with a silica removal means, the resulting treated water is concentrated, and then the concentrated water is concentrated on the primary side of a forward osmosis membrane while diluting an aqueous magnesium salt solution on the secondary side of the forward osmosis membrane, and a portion of the diluted aqueous magnesium salt solution is used for treatment with the silica removal means, and a portion of the diluted aqueous magnesium salt solution is concentrated and returned to the secondary side of the forward osmosis membrane. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-94482 [Patent Document 2] Japanese Patent Publication No. 2020-58963 [Patent Document 3] Japanese Patent Publication No. 2021-30189 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method of Patent Document 1 requires the preparation of new magnesium salts to remove silica, which results in a problem of high running costs for water treatment.Furthermore, the methods of Patent Documents 2 and 3 use an aqueous magnesium salt solution diluted on the secondary side of the forward osmosis membrane for silica removal, which increases the amount of water used for the aqueous magnesium salt solution when removing silica, which results in a problem of high running costs for water treatment due to this increase in the amount of water.

[0008] Therefore, an object of the present disclosure is to provide a water treatment device, a water treatment system, a water treatment method, and a water treatment method for a water treatment system that are capable of reducing running costs. [Means for solving the problem]

[0009] A water treatment device according to one aspect of the present disclosure comprises an Mg treatment means for removing magnesium from water to be treated that contains magnesium, and a membrane filtration treatment means for treating magnesium-containing wastewater discharged from the Mg treatment means and containing the removed magnesium through reverse osmosis membrane treatment or nanofiltration membrane treatment to separate the wastewater into permeate and magnesium-concentrated water, and is characterized in that the magnesium-concentrated water is supplied to a silica treatment means for treating silica-containing water.

[0010] In addition, in the above-mentioned water treatment device, it is preferable that the Mg treatment means is a cation exchange device filled with a cation exchanger, and the magnesium-containing wastewater discharged from the Mg treatment means is regenerated wastewater discharged when the cation exchanger that has captured the magnesium is regenerated with a regenerant.

[0011] In the water treatment device, the magnesium-containing wastewater preferably has a pH of less than 3.

[0012] In the water treatment device, the magnesium concentrated water preferably has a pH of less than 3.

[0013] The water treatment device preferably further comprises an acid recovery means for recovering acid from the permeated water.

[0014] Furthermore, a water treatment system according to one aspect of the present disclosure includes the water treatment device and the silica treatment means for treating the silica-containing water, and the silica treatment means is characterized in that it includes a reaction means for reacting a mixed liquid obtained by mixing the silica-containing water and the magnesium-enriched water in a pH range of 10 to 12.

[0015] Furthermore, a water treatment method according to one aspect of the present disclosure includes a Mg treatment step in which magnesium is removed from water to be treated containing magnesium by an Mg treatment means, and a membrane filtration treatment step in which magnesium-containing wastewater containing the removed magnesium and discharged from the Mg treatment means is treated by reverse osmosis membrane treatment or nanofiltration membrane treatment to separate the wastewater into permeate and magnesium-concentrated water, and is characterized in that the magnesium-concentrated water is supplied to a silica treatment step in which silica-containing water is treated.

[0016] In the above water treatment method, it is preferable that the Mg treatment means is a cation exchange device filled with a cation exchanger, and the magnesium-containing wastewater discharged from the Mg treatment means is regenerated wastewater discharged when the cation exchanger that has captured the magnesium is regenerated with a regenerant.

[0017] In the water treatment method, the magnesium-containing wastewater preferably has a pH of less than 3.

[0018] In the water treatment method, the magnesium-enriched water preferably has a pH of less than 3.

[0019] The water treatment method preferably further comprises an acid recovery step of recovering acid from the permeated water.

[0020] Furthermore, a water treatment method for a water treatment system that is one aspect of the present disclosure is a water treatment method for a water treatment system that carries out the water treatment method and a silica treatment step that treats the silica-containing water, and is characterized in that the silica treatment step includes a reaction step in which a mixed liquid obtained by mixing the silica-containing water and the magnesium-enriched water is reacted in a pH range of 10 to 12. [Effects of the Invention]

[0021] According to the present disclosure, it is possible to provide a water treatment device, a water treatment system, a water treatment method, and a water treatment method for a water treatment system that are capable of reducing running costs. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing another example of a water treatment system according to the present embodiment. [Figure 3] FIG. 2 is a schematic diagram showing another example of a water treatment system according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present embodiment will be described below. The present embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to the present embodiment.

[0024] 1 is a schematic diagram showing an example of a water treatment system according to this embodiment. The water treatment system 1 according to this embodiment includes a water treatment device 10 and a silica treatment device 12.

[0025] The water treatment device 10 shown in FIG. 1 includes a cation exchange device 14 as Mg treatment means for treating magnesium-containing water to be treated, and a membrane filtration device 16 as membrane filtration treatment means for treating the magnesium-containing wastewater discharged from the Mg treatment means with a reverse osmosis membrane or nanofiltration membrane to separate the magnesium-containing wastewater into permeate and concentrated water.

[0026] The cation exchange device 14 shown in FIG. 1 includes a packed tower 18 packed with a cation exchanger and pipes 20a and 20b. The pipe 20a is connected to a raw water inlet of the packed tower 18, and one end of the pipe 20b is connected to a treated water outlet of the packed tower 18. The cation exchange device 14 also includes, for example, a regenerant pipe 22a that supplies a regenerant to the packed tower 18, and a regeneration wastewater pipe 22b that supplies regeneration wastewater discharged from the packed tower 18 to the membrane filtration device 16. The regenerant pipe 22a is connected to a regenerant inlet of the packed tower 18. One end of the regeneration wastewater pipe 22b is connected to a regeneration wastewater outlet of the packed tower 18, and the other end of the regeneration wastewater pipe 22b is connected to an inlet of a membrane module 24 that constitutes the membrane filtration device 16, which will be described later. At least one of the regenerant pipe 22a and the regeneration wastewater pipe 22b may be provided with a pump for transporting liquid passing through the pipe.

[0027] The membrane filtration apparatus 16 shown in FIG. 1 includes a membrane module 24 equipped with a reverse osmosis membrane or a nanofiltration membrane, a permeate pipe 26a, concentrated water pipes 26b and 26c, and a storage tank 30. The membrane module 24 includes, for example, a membrane element formed of a reverse osmosis membrane or a nanofiltration membrane, a container for accommodating the membrane element, and the like. As described above, a reclaimed wastewater pipe 22b is installed at the inlet of the membrane module 24. The permeate pipe 26a is connected to the permeation side outlet (secondary side outlet) of the membrane module 24. One end of the concentrated water pipe 26b is connected to the concentration side outlet (primary side outlet) of the membrane module 24, and the other end of the concentrated water pipe 26b is connected to the inlet of the storage tank 30. One end of the concentrated water pipe 26c is connected to the outlet of the storage tank 30, and the other end of the concentrated water pipe 26c is connected to the concentrated water inlet of a reaction tank 34 constituting the silica treatment device 12, which will be described later, in order to supply the concentrated water to the silica treatment device 12.

[0028] The silica treatment device 12 is a silica treatment means for treating silica-containing water, and is configured to include a reaction device 32. The reaction device 32 is a reaction means for reacting a mixed liquid obtained by mixing silica-containing water and magnesium-enriched water at a pH range of 10 to 12, and is equipped with a reaction tank 34 and a pH supply device 36. The pH supply device 36 is configured to supply a pH adjuster to the reaction tank 34 to adjust the pH in the reaction tank 34 to a range of 10 to 12. Furthermore, as shown in FIG. 1, the silica treatment device 12 preferably includes a coagulation tank 38, a flocculation tank 40, and a solid-liquid separation device 42.

[0029] As described above, the other end of the concentrated water pipe 26c is connected to the concentrated water inlet of the reaction tank 34. A silica-containing water pipe 44 is connected to the raw water inlet of the reaction tank 34. One end of the treated water pipe 46a is connected to the outlet of the reaction tank 34, and the other end of the treated water pipe 46a is connected to the treated water inlet of the coagulation tank 38. One end of the treated water pipe 46b is connected to the outlet of the coagulation tank 38, and the other end of the treated water pipe 46b is connected to the treated water inlet of the flocculation tank 40. One end of the treated water pipe 46c is connected to the outlet of the flocculation tank 40, and the other end of the treated water pipe 46c is connected to the inlet of the solid-liquid separator 42. A treated water pipe 46d is connected to the treated water outlet of the solid-liquid separator 42, and a sludge pipe 48 is connected to the sludge outlet of the solid-liquid separator 42. An inorganic flocculant addition pipe 50 is connected to the flocculant inlet of the flocculation tank 38, and a polymer flocculant addition pipe 52 is connected to the flocculant inlet of the flocculation tank 40.

[0030] An example of a water treatment method for the water treatment system 1 shown in FIG. 1 will be described.

[0031] (Mg processing process) Water to be treated that contains magnesium is supplied to the packed tower 18 through the pipe 20a. The water to be treated that contains magnesium is not particularly limited as long as it contains magnesium, and examples thereof include industrial water, tap water, and well water. The water to be treated that contains magnesium comes into contact with the cation exchanger in the packed tower 18, and the magnesium in the water to be treated is removed. Then, the treated water from which the magnesium has been removed is discharged from the packed tower 18 to the pipe 20b.

[0032] (Recycling) During the cation exchanger regeneration process, the supply of magnesium-containing water to be treated is stopped, and a regenerant is supplied to the packed tower 18 through the regenerant pipe 22a. The regenerant comes into contact with the cation exchanger in the packed tower 18, removing components such as magnesium captured by the cation exchanger from the cation exchanger. The regenerated wastewater generated by the regeneration process is discharged from the packed tower 18 to the regenerated wastewater pipe 22b as magnesium-containing wastewater. The timing of the regeneration process is not particularly limited. For example, the regeneration process may be performed periodically at predetermined intervals, or when the magnesium concentration in the treated water obtained in the Mg treatment process reaches a predetermined value or higher. The magnesium concentration in the regenerated wastewater (magnesium-containing wastewater) is, for example, 10 mg / L or higher. If the magnesium concentration is less than 10 mg / L, the concentration ratio (recovery rate) of the membrane filtration device used to concentrate magnesium must be increased. This may result in excessively high concentrations of other components, potentially increasing the risk of membrane blockage. Furthermore, when the concentration ratio in the membrane filtration device is reduced, supplying magnesium of a desired concentration to the silica removal device requires a large amount of magnesium-concentrated water, which may result in an increase in pump power and discharge volume.

[0033] Examples of cation exchange resins include strong acid cation exchangers and weak acid cation exchangers. However, strong acid cation exchangers are preferred due to their high magnesium removal rate and the ability to produce recycled wastewater containing a high concentration of magnesium. Examples of cation exchangers include granular macroporous cation exchange resins, gel-type cation exchange resins, monolithic organic porous cation exchangers, ion adsorption membranes with cation exchange groups, and chelating resins. Gel-type and macroporous types can be distinguished, for example, by the following method. When irradiated ion exchange resins are observed under an optical microscope, those that transmit light are classified as "gel-type" and those that do not transmit light are classified as "macroporous." Examples of strong acid cation exchange resins include IR120B manufactured by Organo Corporation.

[0034] The pH of the magnesium-containing wastewater (reclaimed wastewater) is preferably less than 3. By adjusting the pH of the magnesium-containing wastewater to less than 3, the solubility of magnesium in the magnesium-containing wastewater is increased. In order to obtain a high silica removal rate in the downstream silica treatment device 12, it is preferable to use water with a high level of dissolved magnesium. Therefore, as described above, by adjusting the pH of the magnesium-containing water to less than 3, water with a high level of dissolved magnesium can be supplied to the downstream silica treatment device 12, thereby making it possible to increase the silica removal rate.

[0035] The regenerant is preferably an acidic agent such as hydrochloric acid or sulfuric acid, since it is easy to adjust the pH of the magnesium-containing wastewater (regenerated wastewater) to less than 3. The regenerant is not limited to an acidic agent, and may be sodium chloride, potassium chloride, or the like. If the pH of the magnesium-containing water passing through the regenerated wastewater pipe 22b exceeds 3, the pH of the magnesium-containing wastewater may be adjusted to less than 3, for example, by injecting an acidic agent into the regenerated wastewater pipe 22b and adding the acidic agent to the magnesium-containing wastewater.

[0036] (Membrane filtration process) The magnesium-containing wastewater (i.e., reclaimed wastewater) discharged from the packed tower 18 is supplied to the membrane module 24 through the reclaimed wastewater piping 22b. The reclaimed wastewater is separated into permeate, from which components such as magnesium have been removed, and magnesium-concentrated water, from which magnesium has been concentrated, by passing through the reverse osmosis membrane or nanofiltration membrane in the membrane module 24 (reverse osmosis membrane treatment or nanofiltration membrane treatment). The permeate is discharged from the membrane module 24 to the permeate piping 26a, and the magnesium-concentrated water is discharged from the membrane module 24 to the concentrate piping 26b and stored in the storage tank 30.

[0037] The membrane filtration process is preferably a nanofiltration membrane process using a nanofiltration membrane, since components other than magnesium, such as Na, can easily pass through and magnesium-enriched water can be obtained by efficiently concentrating only magnesium. The nanofiltration membrane and reverse osmosis membrane are preferably membranes with high acid resistance. Examples of nanofiltration membranes include DuPont's FilmTech NF90, NF270, and XC-N, Toray Industries' TM610 and TM620N, and Nitto Denko's NTR-7250-S4, NTR-7410-S4, NTR-7450HG-S4F, and NANO-SW MAX. Examples of reverse osmosis membranes include DuPont's BW30 series and Nitto Denko's ES15 series.

[0038] The pH of the magnesium concentrated water is preferably less than 3. If the pH of the magnesium-containing wastewater supplied to the membrane module 24 is less than 3, the pH of the magnesium concentrated water will also usually be less than 3. However, if the pH of the magnesium-containing wastewater exceeds 3, it is preferable to add an acid agent to the magnesium concentrated water, for example, by injecting an acid agent into the concentrated water pipe 26b or the storage tank 30, thereby adjusting the pH of the magnesium concentrated water to less than 3. This allows magnesium concentrated water with a high level of dissolved magnesium to be supplied to the downstream silica treatment device 12, thereby increasing the silica removal rate. Note that, considering the acid durability of nanofiltration membranes and reverse osmosis membranes, it is more preferable that the pH of the magnesium-containing wastewater supplied to the membrane module 24 be in the neutral range (for example, 4 to 8), and that the pH of the magnesium concentrated water be less than 3.

[0039] (Silica treatment process) Silica-containing water in which silica is dissolved is supplied to the reaction tank 34 from the silica-containing water pipe 44. The silica-containing water may be water containing silica, and examples thereof include wastewater from a semiconductor manufacturing factory, wastewater from a power plant, and concentrated water from a reverse osmosis membrane used in a treatment system separate from the water treatment system 1 of this embodiment. In addition, magnesium concentrated water in the storage tank 30 is supplied to the reaction tank 34 from the concentrated water pipe 26c. In the water treatment system 1 shown in FIG. 1, the magnesium concentrated water is temporarily stored in the storage tank 30 and then supplied to the reaction tank 34, but the magnesium concentrated water discharged from the membrane module 24 may be supplied directly to the reaction tank 34 without passing through the storage tank 30.

[0040] In the reaction tank 34, for example, magnesium-enriched water and silica-containing water are stirred and mixed by a stirrer (not shown). Then, a pH adjuster is added to the reaction tank 34 from a pH supply device 36, and the pH of the mixture in the reaction tank 34 is adjusted to a range of 10 to 12. The mixture reacts at a pH range of 10 to 12, thereby insolubilizing silica and other substances (reaction step). The pH of the mixture may be in the range of 10 to 12, but is preferably in the range of 10.5 to 11.5, and more preferably in the range of 11 to 11.5. If the pH of the mixture is less than 10 or more than 12, the silica removal rate may decrease. An alkaline agent such as sodium hydroxide is usually used as the pH adjuster, but an acid agent such as sulfuric acid may also be used if necessary.

[0041] The treated water containing insolubilized substances such as silica is supplied from the reaction tank 34 through a treated water pipe 46a to a coagulation tank 38. An inorganic coagulant is also supplied to the coagulation tank 38 through an inorganic coagulant addition pipe 50. Then, in the coagulation tank 38, the treated water containing insolubilized substances such as silica and the inorganic coagulant are stirred by a stirrer (not shown), for example, to coagulate the insolubilized substances such as silica (coagulation step).

[0042] Inorganic flocculants used in the flocculation process include iron-based inorganic flocculants such as iron chloride, polychlorinated aluminum, etc. Examples of suitable inorganic flocculants include aluminum-based inorganic flocculants such as PAC, etc. The pH in the flocculation step may be in the range of 3 to 11, for example, in order to prevent poor flocculation.

[0043] Treated water containing flocculates formed by the aggregation of insolubilized substances such as silica is supplied from the flocculation tank 38 through treated water pipe 46b to the flocculation tank 40. A polymer flocculant is also supplied to the flocculation tank 40 through polymer flocculant addition pipe 52. Then, in the flocculation tank 40, the treated water containing the flocculates and the polymer flocculant are agitated, for example, by an agitator (not shown), and the flocculates are flocculated (flocculation step).

[0044] Examples of polymer flocculants used in the flocculation step include cationic polymer flocculants such as polyacrylamide-based and polyacrylic acid ester-based flocculants, anionic polymer flocculants, and nonionic polymer flocculants. When attempting to form flocs with a faster settling rate, it is preferable to use at least two agents, a cationic polymer flocculant and an anionic polymer flocculant. The pH in the flocculation step may be in the range of, for example, 3 to 11, in order to suppress flocculation failure.

[0045] The treated water containing the flocculated aggregates is supplied from the flocculation tank 40 through treated water pipe 46c to solid-liquid separator 42. In solid-liquid separator 42, the flocculated aggregates are separated into solid and liquid (solid-liquid separation step). The treated water from which the flocculated aggregates have been removed, i.e., the treated water from which silica and the like have been removed, is discharged from treated water pipe 46d, and the aggregates containing silica and the like are discharged as sludge from sludge pipe 48.

[0046] The solid-liquid separator 42 may be, for example, a settling device, a pressure flotation device, a sand filter, or a membrane filter, but a sludge blanket type settling device is preferred for more stable solid-liquid separation.

[0047] In this embodiment, since reclaimed wastewater is used to treat silica-containing water, there is no need to prepare new magnesium salts, as in the past. Furthermore, in this embodiment, the reclaimed wastewater is subjected to membrane filtration to increase the magnesium concentration, so the amount of magnesium-enriched water used to treat silica-containing water is reduced compared to the conventional method of using dilution water. For these reasons, this embodiment can reduce running costs in water treatment. Furthermore, conventionally, magnesium-containing water used in silica-containing water treatment is prepared by adding an acid to dissolve Mg salts before mixing with the silica-containing water. However, in this embodiment, by using an acid as a regenerant, magnesium-containing water containing dissolved magnesium is obtained, eliminating the need to add an acid when removing silica. This also contributes to reducing running costs in water treatment.

[0048] FIG. 2 is a schematic diagram showing another example of a water treatment system according to the present embodiment. In the water treatment system 2 of FIG. 2, components similar to those of the water treatment system 1 shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The water treatment system 2 shown in FIG. 2 uses a reverse osmosis membrane treatment device 15 as Mg treatment means for treating magnesium-containing water to be treated. The reverse osmosis membrane treatment device 15 includes a membrane module 54 equipped with a reverse osmosis membrane, a permeate pipe 56a, and a concentrate pipe 56b. The membrane module 54 includes, for example, a membrane element formed of a reverse osmosis membrane and a container for accommodating the membrane element. A pipe 20a is connected to the inlet of the membrane module 54, and a permeate pipe 56a is connected to the permeate side outlet (secondary side outlet) of the membrane module 54. One end of the concentrate pipe 56b is connected to the concentrate side outlet (primary side outlet) of the membrane module 54, and the other end of the concentrate pipe 56b is connected to the inlet of the membrane module 24.

[0049] An example of a water treatment method for the water treatment system 2 shown in FIG. 2 will be described.

[0050] (Mg processing process) Water to be treated containing magnesium is supplied to the membrane module 54 through the pipe 20a. The water to be treated containing magnesium passes through the reverse osmosis membrane in the membrane module 54 and is separated into permeate, from which components such as magnesium have been removed, and concentrate, from which components such as magnesium have been concentrated. The permeate is discharged from the membrane module 24 to the permeate pipe 56a. The concentrate is discharged from the membrane module 54 to the concentrate pipe 56b as magnesium-containing wastewater containing magnesium. If the pH of the magnesium-containing wastewater (concentrated water) passing through the concentrate pipe 56b exceeds 3, for example, an acidic agent may be injected into the concentrate pipe 56b to add the acidic agent to the magnesium-containing wastewater, thereby adjusting the pH of the magnesium-containing wastewater to less than 3. The magnesium concentration in the concentrate (magnesium-containing wastewater containing magnesium) is, for example, 10 mg / L or more.

[0051] The magnesium-containing water (concentrated water) is supplied to the membrane module 24 through the concentrated water pipe 56b, where the above-mentioned membrane filtration treatment step is carried out. In addition, the magnesium-concentrated water discharged from the membrane module 24 to the concentrated water pipe 26b is supplied to the silica treatment device 12, where the above-mentioned silica treatment step is carried out.

[0052] In the water treatment system 2 shown in Figure 2, concentrated water containing magnesium is also used to treat silica-containing water, so there is no need to prepare a new magnesium salt as in the past. Furthermore, because the concentrated water is subjected to membrane filtration to increase the magnesium concentration, the amount of magnesium concentrated water used to treat silica-containing water is reduced compared to when conventional dilution water is used. Therefore, running costs for water treatment can be reduced.

[0053] FIG. 3 is a schematic diagram showing another example of a water treatment system according to the present embodiment. In the water treatment system 3 of FIG. 3, components similar to those of the water treatment system 1 shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The water treatment system 3 shown in FIG. 3 includes an acid recovery device 58. In the water treatment system 3 shown in FIG. 3, one end of the permeate pipe 26a is connected to the permeate side outlet of the membrane module 24, and the other end of the permeate pipe 26a is connected to the acid recovery device. The permeate is supplied from the permeate pipe 26a to the acid recovery device 58, where acid is recovered from the permeate (acid recovery step). The acid recovery device 58 may be, for example, an electrodialysis device. An example of the electrodialysis device is the Acilyzer EX3B manufactured by Astom Corporation. The acid recovered by the acid recovery device 58 may be used as a regenerant for regenerating the cation exchanger in the packed tower 18.

[0054] [Note] (1) a magnesium treatment means for removing magnesium from the water to be treated, the magnesium being contained therein; and a membrane filtration treatment means for treating the magnesium-containing wastewater containing the removed magnesium discharged from the Mg treatment means with a reverse osmosis membrane or a nanofiltration membrane to separate the wastewater into permeate and magnesium-concentrated water, A water treatment device characterized in that the magnesium-enriched water is supplied to a silica treatment means for treating silica-containing water. (2) the Mg treatment means is a cation exchange device filled with a cation exchanger, The water treatment device described in (1) above, characterized in that the magnesium-containing wastewater discharged from the Mg treatment means is regenerated wastewater discharged when the cation exchanger that has captured the magnesium is regenerated with a regenerant. (3) The water treatment device according to (1) or (2) above, wherein the magnesium-containing wastewater has a pH of less than 3. (4) The water treatment device according to any one of (1) to (3) above, wherein the magnesium concentrated water has a pH of less than 3. (5) The water treatment device according to (2) above, further comprising an acid recovery means for recovering acid from the permeated water. (6) The water treatment device according to any one of (1) to (5) above and the silica treatment means for treating the silica-containing water, The water treatment system is characterized in that the silica treatment means comprises a reaction means for reacting a mixed liquid obtained by mixing the silica-containing water and the magnesium-enriched water in a pH range of 10 to 12. (7) a magnesium treatment step of removing magnesium from the magnesium-containing water to be treated by a magnesium treatment means; a membrane filtration treatment step of treating the magnesium-containing wastewater containing the removed magnesium discharged from the Mg treatment means with a reverse osmosis membrane or a nanofiltration membrane to separate the wastewater into permeate and magnesium-concentrated water; A water treatment method characterized in that the magnesium-enriched water is supplied to a silica treatment step in which silica-containing water is treated. (8) the Mg treatment means is a cation exchange device filled with a cation exchanger, The water treatment method according to (7) above, wherein the magnesium-containing wastewater discharged from the Mg treatment means is regenerated wastewater discharged when the cation exchanger that has captured the magnesium is regenerated with a regenerant. (9) The water treatment method according to (7) or (8) above, wherein the magnesium-containing wastewater has a pH of less than 3. (10) 10. The water treatment method according to claim 7, wherein the magnesium-enriched water has a pH of less than 3. (11) The water treatment method according to (8) above, further comprising an acid recovery step of recovering acid from the permeated water. (12) A water treatment method for a water treatment system that carries out the water treatment method according to any one of (7) to (11) above and the silica treatment step of treating the silica-containing water, The water treatment method for a water treatment system is characterized in that the silica treatment step includes a reaction step of reacting a mixed liquid obtained by mixing the silica-containing water and the magnesium-enriched water in a pH range of 10 to 12. [Explanation of symbols]

[0055] 1 to 3 water treatment system, 10 water treatment device, 12 silica treatment device, 14 cation exchange device, 15 reverse osmosis membrane treatment device, 16 membrane filtration device, 18 packed tower, 20a, 20b piping, 22a regenerant piping, 22b regenerated wastewater piping, 24, 54 membrane module, 26a, 56a permeate piping, 26b, 26c, 56b concentrated water piping, 30 storage tank, 32 reactor, 34 reactor, 36 pH supply device, 38 coagulation tank, 40 flocculation tank, 42 ​​solid-liquid separation device, 44 silica-containing water piping, 46a to 46d treated water piping, 48 sludge piping, 50 inorganic coagulant addition piping, 52 polymer coagulant addition piping, 58 acid recovery device.

Claims

1. a magnesium treatment means for removing magnesium from the water to be treated, the magnesium being contained therein; and a membrane filtration treatment means for treating the magnesium-containing wastewater containing the removed magnesium discharged from the Mg treatment means with a reverse osmosis membrane or a nanofiltration membrane to separate the wastewater into permeate and magnesium-concentrated water, A water treatment device characterized in that the magnesium-enriched water is supplied to a silica treatment means for treating silica-containing water.

2. the Mg treatment means is a cation exchange device filled with a cation exchanger, 2. The water treatment device according to claim 1, wherein the magnesium-containing wastewater discharged from the Mg treatment means is regenerated wastewater discharged when the cation exchanger that has captured the magnesium is regenerated with a regenerant.

3. 3. The water treatment device according to claim 1, wherein the magnesium-containing wastewater has a pH of less than 3.

4. 3. The water treatment device according to claim 1, wherein the magnesium-enriched water has a pH of less than 3.

5. 3. The water treatment device according to claim 2, further comprising an acid recovery means for recovering acid from the permeated water.

6. 3. A water treatment device comprising: the water treatment device according to claim 1 or 2; and a silica treatment means for treating the silica-containing water; The water treatment system is characterized in that the silica treatment means includes a reaction means for reacting a mixed liquid obtained by mixing the silica-containing water and the magnesium-enriched water at a pH range of 10 to 12.

7. a magnesium treatment step of removing magnesium from the water to be treated containing magnesium by an magnesium treatment means; a membrane filtration treatment step of treating the magnesium-containing wastewater containing the removed magnesium discharged from the Mg treatment means with a reverse osmosis membrane or a nanofiltration membrane to separate the wastewater into permeate and magnesium-concentrated water; A water treatment method characterized in that the magnesium-enriched water is supplied to a silica treatment step in which silica-containing water is treated.

8. the Mg treatment means is a cation exchange device filled with a cation exchanger, The water treatment method according to claim 7, wherein the magnesium-containing wastewater discharged from the Mg treatment means is regenerated wastewater discharged when the cation exchanger that has captured the magnesium is regenerated with a regenerant.

9. 9. The water treatment method according to claim 7, wherein the magnesium-containing wastewater has a pH of less than 3.

10. 9. The water treatment method according to claim 7, wherein the magnesium-enriched water has a pH of less than 3.

11. 9. The water treatment method according to claim 8, further comprising an acid recovery step of recovering acid from the permeated water.

12. A water treatment method for a water treatment system that carries out the water treatment method according to claim 7 or 8 and the silica treatment step of treating the silica-containing water, The water treatment method for a water treatment system, wherein the silica treatment step includes a reaction step of reacting a mixed liquid obtained by mixing the silica-containing water and the magnesium-enriched water at a pH in the range of 10 to 12.

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