Water treatment apparatus and water treatment method

Abstract

In a water treatment system that performs electro-regenerative deionization on water containing organic matter after a two-stage reverse osmosis membrane treatment, the overall operating energy of the treatment is reduced, fouling of the reverse osmosis membrane is suppressed, and leakage of slime inhibitor to the electro-regenerative deionization treatment is suppressed. [Solution] The water treatment device 1 comprises a first reverse osmosis membrane treatment device 12 that passes water to be treated containing organic matter through a first reverse osmosis membrane, a second reverse osmosis membrane treatment device 16 that passes the first RO permeate through a second reverse osmosis membrane, and an electro-regenerative deionization device 18 that performs electro-regenerative deionization on the second RO permeate, wherein the first reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 2.0 m / d / MPa or more at a water temperature of 25°C, and the second reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 1.5 m / d / MPa or less at a water temperature of 25°C, and a slime inhibitor is present in the water to be treated and the first RO permeate.

Description

Technical Field

[0001] The present invention relates to a water treatment apparatus and a water treatment method using a reverse osmosis membrane.

Background Art

[0002] Conventionally, water treatment is known in which raw water such as industrial water or municipal water is treated with a reverse osmosis membrane to obtain permeated water (treated water) and concentrated water. In such water treatment using a reverse osmosis membrane, when producing pure water, ultrapure water, etc., for example, an ion exchange resin device or an electrically regenerated deionization device (EDI (Electro Deionization) device) is arranged at the subsequent stage of two or more stages of reverse osmosis membranes.

[0003] For example, Patent Document 1 describes a water treatment system including a reverse osmosis membrane and an electro-deionized water production device, which has a protection device for removing an oxidizing agent in the permeated water supplied with the permeated water passing through the reverse osmosis membrane. The protection device includes fibrous activated carbon as a filler to which the permeated water is supplied, and the permeated water passing through the protection device is supplied to the electro-deionized water production device. It is also described that two-stage reverse osmosis membranes may be used.

[0004] Patent Document 2 describes a method for producing pharmaceutical purified water by treating raw water containing residual chlorine. After decomposing the residual chlorine in the treated water with a medium-pressure ultraviolet sterilizer equipped with a medium-pressure mercury lamp, it is treated with a reverse osmosis membrane device having a polyamide reverse osmosis membrane, and then treated with an electro-deionization device.

[0005] Patent Document 3 describes a water treatment system for removing at least boron contained in water to be treated, comprising a reverse osmosis membrane apparatus including an ultra-low pressure reverse osmosis membrane, and an EDI apparatus including a high-purity EDI stack positioned downstream of the reverse osmosis membrane apparatus, in which at least an anion-exchangeable highly toxic substance is filled in the downstream layer of the desalination chamber, and at least a cation-exchange resin is filled in the adjacent concentration chamber via a cation-exchange membrane that partitions the desalination chamber, wherein the reverse osmosis membrane apparatus is a two-stage reverse osmosis membrane apparatus, and an ultra-low pressure reverse osmosis membrane is positioned in at least one of the first and second stages. In Patent Document 3, the ultra-low pressure reverse osmosis membrane has a salt removal rate of less than 99.4% when measured under conditions in which a stock solution with a NaCl concentration of 500-2000 [mg / L], a pH of 6-8, a water temperature of 25°C, and a permeate recovery rate of 10-25% is supplied, with a supply pressure of 1 [MPa] and a membrane area of ​​1 [m²]. 2 The permeate flow rate per unit pressure and unit area is 1.3 [(m 3 / d) / (m 2 The membrane is defined as having a pressure of MPa or higher.

[0006] In water treatment using a reverse osmosis membrane for water containing organic matter, fouling can occur, where the reverse osmosis membrane becomes blocked due to slime formation. To suppress this fouling, the water treatment system in Patent Document 1 includes an oxidizing agent such as a chlorine-based or bromine-based oxidizing agent in the water being treated by the reverse osmosis membrane, and a protective device equipped with activated carbon suppresses the leakage of the oxidizing agent to the subsequent EDI device. In the method of Patent Document 2, the water to be treated is sterilized with ultraviolet light to decompose the residual chlorine in the water, then treated with a reverse osmosis membrane device, and then treated with an electrodeionizer.

[0007] However, the method described in Patent Document 1 requires careful attention to the oxidizing agent components leaking to the subsequent EDI device when sterilizing the second-stage reverse osmosis membrane. Furthermore, the method described in Patent Document 2 increases energy consumption and inflates running costs. Patent Document 3 does not describe how to suppress fouling caused by slime generation, etc. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7065723 [Patent Document 2] Japanese Patent Publication No. 2014-198292 [Patent Document 3] Brochure for International Patent Application Publication No. 2024 / 048115 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a water treatment apparatus and a water treatment method that can reduce the overall operating energy of a water treatment process in which water containing organic matter is subjected to electro-regenerative deionization in the second stage of a two-stage reverse osmosis membrane treatment, suppress fouling of the reverse osmosis membrane, and suppress leakage of slime inhibitor to the electro-regenerative deionization treatment. [Means for solving the problem]

[0010] The present invention relates to a water treatment apparatus comprising: a first reverse osmosis membrane treatment apparatus that passes water to be treated containing organic matter through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water; a second reverse osmosis membrane treatment apparatus that passes the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water; and an electro-regenerative deionization apparatus that performs electro-regenerative deionization on the second RO permeate, wherein the first reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 2.0 m / d / MPa or more at a water temperature of 25°C, and the second reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 1.5 m / d / MPa or less at a water temperature of 25°C, and a slime inhibitor is present in the water to be treated and the first RO permeate.

[0011] In the water treatment apparatus described above, it is preferable that the water to be treated contains 0.1 mg / L or more of low-molecular-weight organic substances with a molecular weight of 350 or less.

[0012] In the water treatment apparatus described above, it is preferable that the slime inhibitor includes at least one of the following: a stabilized hypobromite composition containing a brominated oxidizing agent and a sulfamic acid compound, and a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound.

[0013] Preferably, the water treatment apparatus further includes a slime inhibitor adding means for adding the slime inhibitor to the first RO permeate water, and a circulation means for circulating the second RO concentrated water to the front of the first reverse osmosis membrane treatment apparatus.

[0014] The present invention relates to a water treatment method comprising: a first reverse osmosis membrane treatment step of passing water to be treated containing organic matter through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water; a second reverse osmosis membrane treatment step of passing the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water; and an electro-regenerative deionization step of performing electro-regenerative deionization on the second RO permeate, wherein the first reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 2.0 m / d / MPa or more at a water temperature of 25°C, and the second reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 1.5 m / d / MPa or less at a water temperature of 25°C, and a slime inhibitor is present in the water to be treated and the first RO permeate.

[0015] In the water treatment method described above, it is preferable that the water to be treated contains 0.1 mg / L or more of low-molecular-weight organic matter with a molecular weight of 350 or less.

[0016] In the water treatment method described above, it is preferable that the slime inhibitor includes at least one of the following: a stabilized hypobromite composition containing a brominated oxidizing agent and a sulfamic acid compound, and a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound.

[0017] In the water treatment method described above, it is preferable to add the slime inhibitor to the first RO permeate and circulate the second RO concentrated water to the stage preceding the first reverse osmosis membrane treatment step. [Effects of the Invention]

[0018] According to the present invention, in a water treatment method in which electroregenerative deionization treatment is performed in the latter stage of two-stage reverse osmosis membrane treatment on water to be treated containing organic substances, a water treatment apparatus and a water treatment method can be provided that can suppress fouling of the reverse osmosis membrane with low energy and suppress leakage of a slime inhibitor into the electroregenerative deionization treatment.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic configuration diagram showing an example of a water treatment apparatus according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0020] Embodiments of the present invention will be described below. This embodiment is an example of carrying out the present invention, and the present invention is not limited to this embodiment.

[0021] The water treatment apparatus according to this embodiment includes a first reverse osmosis membrane treatment apparatus that passes water to be treated containing organic substances through a first reverse osmosis membrane to obtain first RO permeate water and first RO concentrate water, a second reverse osmosis membrane treatment apparatus that passes the first RO permeate water through a second reverse osmosis membrane to obtain second RO permeate water and second RO concentrate water, and an electroregenerative deionization apparatus that performs electroregenerative deionization treatment on the second RO permeate water. In the water treatment apparatus according to this embodiment, the first reverse osmosis membrane is a membrane having a permeation water volume of 2.0 m / d / MPa or more at a membrane surface effective pressure of 1 MPa and a water temperature of 25°C, the second reverse osmosis membrane is a membrane having a permeation water volume of 1.5 m / d / MPa or less at a membrane surface effective pressure of 1 MPa and a water temperature of 25°C, and a slime inhibitor is present in the water to be treated and the first RO permeate water.

[0022] An example of the schematic of the water treatment apparatus according to an embodiment of the present invention is shown in FIG. 1, and its configuration will be described.

[0023] The water treatment apparatus 1 shown in Figure 1 comprises a first reverse osmosis membrane treatment apparatus 12 that passes water to be treated containing organic matter through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water, a second reverse osmosis membrane treatment apparatus 16 that passes the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water, and an electro-regenerative deionization apparatus 18 that performs electro-regenerative deionization on the second RO permeate. The water treatment apparatus 1 may also include a water tank 10 for storing water to be treated and a first RO permeate tank 14 for storing first RO permeate.

[0024] In the water treatment device 1, a treated water pipe 24 is connected to the treated water inlet of the treated water tank 10. The treated water outlet of the treated water tank 10 and the treated water inlet of the first reverse osmosis membrane treatment device 12 are connected by a treated water pipe 26 via a pump 20. The first RO permeate outlet of the first reverse osmosis membrane treatment device 12 and the first RO permeate inlet of the first RO permeate tank 14 are connected by a first RO permeate pipe 28. The first RO concentrated water outlet of the first reverse osmosis membrane treatment device 12 is connected by a first RO concentrated water pipe 30. The first RO permeate outlet of the first RO permeate tank 14 and the first RO permeate inlet of the second reverse osmosis membrane treatment device 16 are connected by a first RO permeate pipe 32 via a pump 22. The second RO permeate outlet of the second reverse osmosis membrane treatment device 16 and the second RO permeate inlet of the electro-regenerative deionizer 18 are connected by a second RO permeate pipe 34. A treated water pipe 38 is connected to the treated water outlet of the electro-regenerative deionizer 18. The second RO concentrated water outlet of the second reverse osmosis membrane treatment device 16 and the second RO concentrated water inlet of the treated water tank 10 are connected by a second RO concentrated water pipe 36. A slime inhibitor addition pipe 40 is connected to the upstream side of the pump 22 in the first RO permeate pipe 32 as a means for adding a slime inhibitor.

[0025] The operation of the water treatment method and water treatment apparatus 1 according to this embodiment will be described.

[0026] The water to be treated, which contains organic matter, is stored in the water tank 10 as needed through the water to be treated piping 24. The water to be treated is sent to the first reverse osmosis membrane treatment device 12 through the water to be treated piping 26 by the pump 20. In the first reverse osmosis membrane treatment device 12, the water to be treated is passed through the first reverse osmosis membrane to perform a first reverse osmosis treatment to obtain first RO permeate and first RO concentrated water (first reverse osmosis treatment step). The first RO concentrated water obtained in the first reverse osmosis treatment is discharged through the first RO concentrated water piping 30. The first RO permeate obtained in the first reverse osmosis treatment is stored in the first RO permeate tank 14 as needed through the first RO permeate water piping 28. The first RO permeate is sent to the second reverse osmosis membrane treatment device 16 through the first RO permeate water piping 32 by the pump 22. Here, a slime inhibitor may be added to the first RO permeate through the slime inhibitor addition pipe 40 on the upstream side (suction side) of the pump 22 in the first RO permeate pipe 32 (slime inhibitor addition step). In the second reverse osmosis membrane treatment apparatus 16, the first RO permeate is passed through the second reverse osmosis membrane to perform a second reverse osmosis membrane treatment to obtain second RO permeate and second RO concentrated water (second reverse osmosis membrane treatment step). The second RO permeate obtained in the second reverse osmosis membrane treatment is sent through the second RO permeate pipe 34 to the electro-regenerative deionizer 18. In the electro-regenerative deionizer 18, electro-regenerative deionization treatment is performed on the second RO permeate (electro-regenerative deionization step). The treated water obtained by the electro-regenerative deionization treatment is discharged through the treated water pipe 38. At least a portion of the second RO concentrated water obtained in the second reverse osmosis membrane treatment may be circulated through the second RO concentrated water piping 36, which is a circulation means, to the supply water of the first reverse osmosis membrane treatment device 12 preceding the second reverse osmosis membrane treatment device 16, for example, to the water tank to be treated 10. At least a portion of the second RO concentrated water may be circulated to the water to be treated piping 24 or to the water to be treated piping 26. The slime inhibitor may be added in the first RO permeate water piping 28, in the first RO permeate water tank 14, or downstream (discharge) of the pump 22 in the first RO permeate water piping 32.

[0027] The inventors have found that in a water treatment process in which water containing organic matter is subjected to electro-regenerative deionization in the second stage of a two-stage reverse osmosis membrane treatment, by using a membrane with a permeate flow rate of 2.0 m / d / MPa or more as the first reverse osmosis membrane and a membrane with a permeate flow rate of 1.5 m / d / MPa or less as the second reverse osmosis membrane, and by including a slime inhibitor in the water to be treated and the first RO permeate, the overall operating energy of the treatment can be reduced, and fouling of the reverse osmosis membrane can be suppressed using the slime inhibitor.

[0028] By using a membrane with a relatively large permeate flow rate of 2.0 m / d / MPa or higher in the first reverse osmosis membrane treatment device 12, which has a high osmotic pressure and a large water volume, a relatively low-pressure pump can be used as the pump 20 for supplying the water to be treated to the first reverse osmosis membrane treatment device 12, thus saving energy for the overall operation of the treatment. However, because the first reverse osmosis membrane treatment device 12 uses a membrane with a relatively low blocking rate and a large permeate flow rate of 2.0 m / d / MPa or higher, organic matter such as low-molecular-weight organic matter derived from the water to be treated is more likely to leak into the first RO permeate, increasing the risk of slime generation in the second reverse osmosis membrane treatment device 16. It is conceivable to suppress slime generation by making the first RO permeate alkaline and thus creating alkaline conditions for the second reverse osmosis membrane, but making the first RO permeate alkaline would reduce the blocking rate of the second reverse osmosis membrane in the second reverse osmosis membrane treatment device 16. Therefore, it is desirable to operate the second reverse osmosis membrane treatment device 16 in a neutral state to maintain the blocking rate. Therefore, the inventors considered that slime generation in the first reverse osmosis membrane treatment device 12 and the second reverse osmosis membrane treatment device 16 could be suppressed by adding a slime inhibitor to the treated water and the first RO permeate. On the other hand, slime countermeasures such as making the second osmosis membrane alkaline would reduce the blocking rate of the second reverse osmosis membrane, which is undesirable for the subsequent electro-regenerative deionizer 18 from the standpoint of both ion load and residual chlorine management. For the treated water of the electro-regenerative deionizer 18, in order to maintain a guaranteed water supply (for example, a residual chlorine concentration of 0.02 mg-Cl / L or less), it is desirable for the blocking rate of the second reverse osmosis membrane to be high (for example, a blocking rate of 99% or more), and it is undesirable to use a membrane with a permeate volume of 2.0 m / d / MPa or more, like the first reverse osmosis membrane, for the second reverse osmosis membrane. Therefore, the inventors considered that it would be sufficient to use a membrane with a relatively high blocking rate and a small permeate volume of 1.5 m / d / MPa or less as the second reverse osmosis membrane.

[0029] The first reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeability of pure water of 2.0 m / d / MPa or more at a water temperature of 25°C. The rejection rate of the first reverse osmosis membrane is, for example, about 93-97%.

[0030] The second reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeation rate of pure water of 1.5 m / d / MPa or less at a water temperature of 25°C. The rejection rate of the second reverse osmosis membrane is, for example, about 99-99.8%.

[0031] The first and second reverse osmosis membranes can be neutral-charged membranes, anion-charged membranes, or cationic-charged membranes, and any of these may be used.

[0032] The membrane shapes of the first and second reverse osmosis membranes are not particularly limited and include, for example, annular, flat, spiral, and hollow fiber types.

[0033] There are no particular restrictions on the method of introducing the slime inhibitor into the treated water and the first RO permeate. Examples include adding the slime inhibitor to the treated water, adding the slime inhibitor to both the treated water and the first RO permeate, or adding the slime inhibitor to the first RO permeate and circulating the second RO concentrated water containing the slime inhibitor to the first reverse osmosis membrane treatment device 12. When adding the slime inhibitor to the treated water, the slime inhibitor may be added, for example, in the treated water tank 10, in the treated water piping 24, or in the treated water piping 26. Since most of the slime inhibitor added to the second reverse osmosis membrane remains in the second RO concentrated water, it is preferable to add the slime inhibitor to the first reverse osmosis membrane by circulating the second RO concentrated water to the first reverse osmosis membrane treatment device 12, as this reduces the amount of slime inhibitor added to the first reverse osmosis membrane.

[0034] The water to be treated can be any water containing organic matter, and there are no particular restrictions, but examples include industrial water, municipal water, groundwater, and wastewater recovery water.

[0035] Organic substances contained in the treated water include organic substances with a molecular weight exceeding 350 and low molecular weight organic substances with a molecular weight of 350 or less. Examples of organic substances with a molecular weight exceeding 350 include humic substances and proteins such as albumin. Examples of low molecular weight organic substances with a molecular weight of 350 or less include alcohol compounds such as methanol, ethanol, and isopropyl alcohol (IPA), amine compounds such as monoethanolamine and urea, and tetraalkylammonium salts such as tetramethylammonium hydroxide.

[0036] The water treatment method and water treatment apparatus according to this embodiment can be suitably applied when the water to be treated contains, for example, 0.1 mg / L or more of low-molecular-weight organic substances with a molecular weight of 350 or less, preferably 0.1 mg / L to 5 mg / L.

[0037] The pH of the water to be treated is, for example, in the range of 5.5 to 9.0, and preferably in the range of 6.5 to 8.0. If the pH of the water to be treated is less than 5.5, the amount of water permeate through the reverse osmosis membrane may decrease due to the effect of the slime inhibitor, and if it exceeds 9.0, the rejection rate of the reverse osmosis membrane may decrease significantly.

[0038] The pH of the first RO permeate is, for example, in the range of 5.5 to 9.0, and preferably in the range of 6.5 to 8.0. If the pH of the first RO permeate is less than 5.5, the amount of water permeating through the reverse osmosis membrane may decrease due to the effect of the slime inhibitor, and if it exceeds 9.0, the rejection rate of the reverse osmosis membrane may decrease significantly.

[0039] If the pH of the treated water or the first RO permeate is not within the above range, the pH of the treated water or the first RO permeate may be adjusted. pH adjustment of the treated water can be done using pH adjusting agents such as acids such as hydrochloric acid, sulfuric acid, or nitric acid, or alkalis such as sodium hydroxide aqueous solution or potassium hydroxide aqueous solution.

[0040] There are no particular limitations on slime inhibitors, but examples include chlorine-based oxidizing agents, bromine-based oxidizing agents, stabilized hypochlorous acid compositions containing a chlorine-based oxidizing agent and a sulfamic acid compound, and stabilized hypobromous acid compositions containing a bromine-based oxidizing agent and a sulfamic acid compound. As slime inhibitors, stabilized hypochlorous acid compositions and stabilized hypobromous acid compositions are preferred, and stabilized hypobromous acid compositions are more preferred, from the viewpoint of suppressing the deterioration of reverse osmosis membranes.

[0041] Examples of chlorine-based oxidizing agents include chlorine gas, chlorine dioxide, hypochlorous acid or its salts, chlorous acid or its salts, chloric acid or its salts, perchloric acid or its salts, chlorinated isocyanuric acid or its salts, and chloramine. Among these, examples of salts include alkali metal hypochlorite salts such as sodium hypochlorite and potassium hypochlorite, alkaline earth metal hypochlorite salts such as calcium hypochlorite and barium hypochlorite, alkali metal hypochlorite salts such as sodium chlorite and potassium chlorite, alkaline earth metal hypochlorite salts such as barium chlorite, other metal hypochlorite salts such as nickel chlorite, alkali metal chlorite salts such as ammonium chlorate, sodium chlorate, and potassium chlorate, and alkaline earth metal chlorite salts such as calcium chlorate and barium chlorate. These chlorine-based oxidizing agents may be used individually or in combination of two or more. From the standpoint of ease of handling, sodium hypochlorite is preferred as the chlorine-based oxidizing agent.

[0042] Examples of bromine-based oxidizing agents include bromine (liquid bromine), bromine chloride, bromate, bromate salts, and hypobromous acid. Hypobromous acid may also be produced by reacting a bromine compound such as sodium bromide with a chlorine-based oxidizing agent such as hypochlorous acid.

[0043] Examples of bromine compounds include sodium bromide, potassium bromide, lithium bromide, ammonium bromide, and hydrobromic acid. Of these, sodium bromide is preferred from the standpoint of formulation costs and other factors.

[0044] A "stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound" may be a stabilized hypochlorous acid composition containing a mixture of a "chlorine-based oxidizing agent" and a "sulfamic acid compound," or it may be a stabilized hypochlorous acid composition containing the "reaction product of a chlorine-based oxidizing agent and a sulfamic acid compound." A "stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound" may be a stabilized hypobromous acid composition containing a mixture of a "bromine-based oxidizing agent" and a "sulfamic acid compound," or it may be a stabilized hypobromous acid composition containing the "reaction product of a bromine-based oxidizing agent and a sulfamic acid compound."

[0045] Sulfamic acid compounds are compounds represented by the following general formula (1). R2NSO3H (1) (In the formula, R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

[0046] Examples of sulfamic acid compounds include sulfamic acid (amidosulfuric acid), in which both R groups are hydrogen atoms; sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, such as N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N-isopropylsulfamic acid, and N-butylsulfamic acid; sulfamic acid compounds in which both of the two R groups are alkyl groups having 1 to 8 carbon atoms, such as N,N-dimethylsulfamic acid, N,N-diethylsulfamic acid, N,N-dipropylsulfamic acid, N,N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid, and N-methyl-N-propylsulfamic acid; sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-phenylsulfamic acid; or salts thereof. Examples of sulfamate salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts, strontium salts and barium salts, other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts and nickel salts, ammonium salts and guanidine salts, and so on. Sulfamate compounds and their salts may be used individually or in combination of two or more. From the standpoint of environmental impact, sulfamic acid (amidosulfate) is preferred as the sulfamate compound.

[0047] The stabilized hypobromite composition may further contain an alkali. Examples of alkalis include sodium hydroxide and potassium hydroxide. Sodium hydroxide and potassium hydroxide may be used in combination, considering factors such as product stability at low temperatures. The alkali may also be used as an aqueous solution rather than a solid.

[0048] As a stabilized hypobromite composition, in order to further degrade the reverse osmosis membrane, it is preferable to have one that contains bromine and a sulfamic acid compound, or a mixture of bromine and a sulfamic acid compound, for example, a mixture of bromine, a sulfamic acid compound, an alkali, and water, or one that contains a reaction product of bromine and a sulfamic acid compound, for example, a mixture of a reaction product of bromine and a sulfamic acid compound, an alkali, and water.

[0049] Because the stabilized hypobromite composition can be measured on-site, similar to hypochlorous acid, more accurate concentration control is possible.

[0050] The pH of the stabilized hypobromite composition is, for example, greater than 13.0, and more preferably greater than 13.2. If the pH of the stabilized hypobromite composition is 13.0 or lower, the effective halogen in the stabilized hypobromite composition may become unstable.

[0051] The bromate concentration in the stabilized hypobromous acid composition is preferably less than 5 mg / kg. If the bromate concentration in the stabilized hypobromous acid composition is 5 mg / kg or higher, the bromate ion concentration in the treated water may increase.

[0052] The concentration of the slime inhibitor in the treated water and the first RO permeate is, for example, in the range of 0.1 to 2.0 mg-Cl / L as a total chlorine concentration, and preferably in the range of 0.2 to 1.0 mg-Cl / L. If the concentration of the slime inhibitor in the treated water and the first RO permeate is less than 0.1 mg-Cl / L as a total chlorine concentration, the slime inhibitory effect may be insufficient, and if it exceeds 2.0 mg-Cl / L, it may cause deterioration of the reverse osmosis membrane or corrosion of piping, etc.

[0053] The concentration of slime inhibitors in the treated water and the first RO permeate can be expressed as total chlorine concentration. For example, the "concentration in terms of total chlorine" of the "stabilized hypobromite composition" is the value (mg / L as Cl2) measured using the total chlorine measurement method (DPD (diethyl-p-phenylenediamine) method) with a HACH DR / 4000 multi-parameter water quality analyzer. Although the concentration of the "stabilized hypobromite composition" can also be expressed as bromine concentration (mg / L as Br2), here we use the "concentration in terms of total chlorine" (mg / L as Cl2), which is the value measured using the total chlorine measurement method, in order to compare it with the concentration of the "chlorine-based oxidizing agent" using the same units.

[0054] The electroregenerative deionization (EDI) apparatus 18 is located downstream of the second reverse osmosis membrane treatment apparatus 16. The EDI apparatus is a device that combines electrophoresis and electrodialysis. The configuration of the EDI apparatus is such that a desalination chamber, partitioned by a pair of ion exchange membranes, is placed between the anode and the cathode. In the EDI apparatus, at least the desalination chamber is filled with ion exchange resin. The second RO permeate is passed through the desalination chamber with a DC voltage applied between the anode and the cathode. As a result, desalination treatment is performed on the second RO permeate in the desalination chamber, and treated water from which ionic components have been removed flows out of the desalination chamber.

[0055] The residual chlorine concentration of the treated water obtained from the electro-regenerative deionizer 18 is, for example, 0.02 mg-Cl / L or less.

[0056] The water treatment device 1 may be equipped with a pH measuring device as a means for measuring the pH of the water to be treated, the first RO permeate, the second RO permeate, etc. The water treatment device 1 may be equipped with a total chlorine concentration measuring device as a means for measuring the total chlorine concentration of the water to be treated, the first RO permeate, the second RO permeate, etc. The water treatment device 1 may be equipped with a flow rate measuring device as a means for measuring the flow rate of the water to be treated, the first RO permeate, the second RO permeate, etc. The water treatment device 1 may further be equipped with a pump, a safety filter, a pressure measuring device, a temperature measuring device, an oxidation-reduction potential (ORP) measuring device, a residual chlorine measuring device, an electrical conductivity measuring device, an energy recovery device, etc., as needed.

[0057] A degassing membrane device may be provided between the first reverse osmosis membrane treatment apparatus 12 and the second reverse osmosis membrane treatment apparatus 16 as a degassing means, and the first RO permeate may be degassed.

[0058] Prior to the first reverse osmosis membrane treatment apparatus 12, a pretreatment apparatus may be provided, such as a biological treatment apparatus, a flocculation treatment apparatus, a flocculation and sedimentation treatment apparatus, a pressurized flotation treatment apparatus, a filtration treatment apparatus, a membrane separation treatment apparatus, an activated carbon treatment apparatus, an ozone treatment apparatus, an ultraviolet irradiation treatment apparatus, a softening treatment apparatus, a decarboxylation treatment apparatus, and the like. The pretreatment steps may include biological, physical, or chemical pretreatments such as biological treatment, flocculation treatment, flocculation and sedimentation treatment, pressurized flotation treatment, filtration treatment, membrane separation treatment, activated carbon treatment, ozone treatment, ultraviolet irradiation treatment, softening treatment, and decarboxylation treatment, as well as combinations of two or more of these pretreatments as needed.

[0059] In the downstream of the second reverse osmosis membrane treatment apparatus 16 or the electroregenerative deionization apparatus 18, a post-treatment apparatus may be provided, such as a regenerative ion exchange resin apparatus, a non-regenerative ion exchange resin apparatus, a degassing membrane apparatus, an ultraviolet sterilization apparatus, an ultraviolet oxidation apparatus, a heating apparatus, an ultrafiltration apparatus, etc., and as a post-treatment step, regenerative ion exchange treatment, non-regenerative ion exchange treatment, degassing membrane treatment, ultraviolet sterilization treatment, ultraviolet oxidation treatment, heating treatment, ultrafiltration treatment, and any combination of two or more of these post-treatments may be performed as needed.

[0060] This specification includes the following embodiments. (1) A first reverse osmosis membrane apparatus that passes water to be treated containing organic matter through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water, A second reverse osmosis membrane apparatus for passing the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water, An electroregenerative deionizer is used to perform electroregenerative deionization on the aforementioned second RO permeate, Equipped with, The first reverse osmosis membrane is a membrane with a membrane surface effective pressure of 1 MPa and a permeate rate of 2.0 m / d / MPa or more at a water temperature of 25°C. The second reverse osmosis membrane is a membrane with a membrane surface effective pressure of 1 MPa and a permeate rate of 1.5 m / d / MPa or less at a water temperature of 25°C. A water treatment apparatus that provides a slime inhibitor to the treated water and the first RO permeate.

[0061] (2) The water treatment apparatus described in (1), The water treatment apparatus contains 0.1 mg / L or more of low-molecular-weight organic substances with a molecular weight of 350 or less in the water to be treated.

[0062] (3) A water treatment apparatus as described in (1) or (2), The slime inhibitor comprises at least one of a stabilized hypobromite composition containing a brominated oxidizing agent and a sulfamic acid compound, and a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound, in a water treatment apparatus.

[0063] (4) A water treatment apparatus described in any one of (1) to (3), A slime inhibitor adding means for adding the slime inhibitor to the first RO permeate, A circulation means for circulating the second RO concentrated water to the front of the first reverse osmosis membrane treatment device, A water treatment device that is further equipped with these features.

[0064] (5) A first reverse osmosis membrane treatment step in which the water to be treated containing organic matter is passed through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water, A second reverse osmosis membrane treatment step is performed by passing the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water, The process involves electroregenerative deionization of the second RO permeate, Includes, The first reverse osmosis membrane is a membrane with a membrane surface effective pressure of 1 MPa and a permeate rate of 2.0 m / d / MPa or more at a water temperature of 25°C. The second reverse osmosis membrane is a membrane with a membrane surface effective pressure of 1 MPa and a permeate rate of 1.5 m / d / MPa or less at a water temperature of 25°C. A water treatment method comprising the presence of a slime inhibitor in the water to be treated and the first RO permeate.

[0065] (6)(5) The water treatment method described above, The water to be treated contains 0.1 mg / L or more of low-molecular-weight organic matter with a molecular weight of 350 or less, in a water treatment method.

[0066] A water treatment method as described in (7)(5) or (6), A water treatment method comprising, as the slime inhibitor, at least one of a stabilized hypobromite composition containing a brominated oxidizing agent and a sulfamic acid compound, and a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound.

[0067] (8)(5)~(7) A water treatment method described in any one of the above, A water treatment method comprising adding the slime inhibitor to the first RO permeate and circulating the second RO concentrated water to the stage preceding the first reverse osmosis membrane treatment process. [Explanation of symbols]

[0068] 1 Water treatment device, 10 Treatment tanks, 12 First reverse osmosis membrane treatment device, 14 First RO permeate tank, 16 Second reverse osmosis membrane treatment device, 18 EDI device, 20, 22 Pumps, 24, 26 Treatment water piping, 28, 32 First RO permeate water piping, 30 First RO concentrated water piping, 34 Second RO permeate water piping, 36 Second RO concentrated water piping, 38 Treated water piping, 40 Slime inhibitor addition piping.

Claims

1. A first reverse osmosis membrane treatment apparatus that passes water to be treated containing organic matter through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water, A second reverse osmosis membrane apparatus for passing the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water, An electroregenerative deionizer is used to perform electroregenerative deionization on the second RO permeate, Equipped with, The first reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeation rate of pure water of 2.0 m / d / MPa or more at a water temperature of 25°C. The second reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeation rate of pure water of 1.5 m / d / MPa or less at a water temperature of 25°C. A water treatment apparatus characterized by the presence of a slime inhibitor in the treated water and the first RO permeate.

2. A water treatment apparatus according to claim 1, The water treatment apparatus is characterized in that the treated water contains 0.1 mg / L or more of low-molecular-weight organic matter with a molecular weight of 350 or less.

3. A water treatment apparatus according to claim 1, The water treatment apparatus is characterized in that the slime inhibitor comprises at least one of a stabilized hypobromite composition comprising a brominated oxidizing agent and a sulfamic acid compound, and a stabilized hypochlorous acid composition comprising a chlorine-based oxidizing agent and a sulfamic acid compound.

4. A water treatment apparatus according to claim 1, A slime inhibitor adding means for adding the slime inhibitor to the first RO permeate, A circulation means for circulating the second RO concentrated water to the front of the first reverse osmosis membrane treatment device, A water treatment apparatus characterized by further comprising the following features.

5. A first reverse osmosis membrane treatment step involves passing water to be treated containing organic matter through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrated water, A second reverse osmosis membrane treatment step is performed by passing the first RO permeate through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrated water, The process involves electroregenerative deionization of the second RO permeate, Includes, The first reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeable water flow rate of 2.0 m / d / MPa or more at a water temperature of 25°C. The second reverse osmosis membrane is a membrane with an effective membrane pressure of 1 MPa and a permeate rate of 1.5 m / d / MPa or less at a water temperature of 25°C. A water treatment method characterized by the presence of a slime inhibitor in the water to be treated and the first RO permeate.

6. A water treatment method according to claim 5, A water treatment method characterized in that the water to be treated contains 0.1 mg / L or more of low-molecular-weight organic matter with a molecular weight of 350 or less.

7. A water treatment method according to claim 5, The water treatment method is characterized in that the slime inhibitor comprises at least one of a stabilized hypobromite composition containing a brominated oxidizing agent and a sulfamic acid compound, and a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound.

8. A water treatment method according to claim 5, A water treatment method characterized by adding the slime inhibitor to the first RO permeate and circulating the second RO concentrated water to the stage preceding the first reverse osmosis membrane treatment process.

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