Pure water production method, pure water production device, and ultrapure water production system

Abstract

By reducing the treatment load of the three-stage reverse osmosis membrane device on the front stage side, the use amount of a chemical agent can be reduced, and purified water having a reduced boron concentration can be efficiently produced. A method and apparatus for producing pure water in which raw water is treated by at least three stages of ultra-low pressure reverse osmosis membrane devices, each reverse osmosis membrane being a negatively charged membrane having a skin layer formed from a crosslinked aromatic polyamide, the raw water containing 1-100 mg / L of carbonic acid and 150 [mu] g / L or less of boron, the method for producing pure water comprises: a step for treating raw water by means of a first-stage reverse osmosis membrane device; a step for obtaining alkaline water to be treated; a step for treating the alkaline water to be treated by means of a second-stage reverse osmosis membrane device; and a step for treating the permeated water with a third-stage reverse osmosis membrane device to obtain pure water having a boron concentration of 3 [mu] g / L to 20 [mu] g / L and an electrical conductivity of 0.3 [mu] S / cm to 40 [mu] S / cm.

Description

Technical Field

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0002] This application claims the benefit of priority based on Japanese Patent Application No. 2022-171509, filed on October 26, 2022, the entirety of which is incorporated herein by reference. (Technical field)

[0004] The present invention relates to a pure water production method and a pure water production device capable of removing boron contained in raw water to significantly reduce the boron concentration, and an ultrapure water production system capable of obtaining ultrapure water of high water quality using the same. Background Art

[0005] As a method for treating raw water containing boron to produce pure water, there is known a method for producing pure water by adding alkali to the raw water to adjust the pH to 9.2 or above, and then performing reverse osmosis membrane treatment. In this method, a non-regenerative ion exchange device that does not perform chemical regeneration is arranged in the rear section. In order to reduce the load of the non-regenerative ion exchange device, acid is added to the permeated water from which boron has been removed, and then reverse osmosis membrane treatment is performed using a special reverse osmosis membrane such as a positively charged reverse osmosis membrane device, thereby increasing the resistivity of the treated water to, for example, 5.0 MΩ·cm. In addition, in a reverse osmosis membrane device that treats alkaline treated water, scale clogging caused by hardness is likely to occur. Therefore, a hardness removal mechanism and a degassing device with a strong decarbonation function are provided in the front section of the reverse osmosis membrane device to suppress scale clogging (for example, refer to patent documents 1 and 2).

[0006] In addition, the following method has been proposed: instead of performing decarbonation using an acid, a membrane degassing device and a three-stage reverse osmosis membrane device are combined, a scale inhibitor and an alkali are added to the raw water, water is passed through the first-stage reverse osmosis membrane separation device, and a reverse osmosis membrane with a high salt rejection rate in a low salt concentration range is used as the reverse osmosis membrane of the third-stage reverse osmosis membrane separation device, thereby producing high-purity pure water such as 15 MΩ·cm (for example, refer to Patent Document 3).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 11-128921

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 11-128922

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2000-061465 Summary of the invention

[0012] Problem that the invention aims to solve

[0013] However, in the above-mentioned conventional pure water production method, although the load of ion removal on the rear section side of the reverse osmosis membrane is reduced, the load of ion removal on the multiple reverse osmosis membranes on the front section side is significantly high. For example, in the positively charged reverse osmosis membrane that treats acidic treated water, scale and particle adhesion caused by silicon dioxide are easily generated. Therefore, there are the following problems: the higher the ion removal load, the more frequently backwashing, cleaning, installation of cleaning equipment, and membrane replacement are performed, and the device has to be stopped every time, which reduces the efficiency of pure water production. In addition, since a hardness removal mechanism, a degassing device, and a membrane degassing device are configured on the front section side, there is also a problem of a larger scale of the device and a vast land required for installation. Moreover, the amount of chemicals used, such as acids added for degassing and removing ion components, and cleaning agents used for frequently cleaning / backwashing of reverse osmosis membrane devices, is large, so there is a problem of high environmental load.

[0014] In addition, the pure water produced by the above-mentioned existing method using three-stage reverse osmosis membrane is not enough to be directly used for the manufacture of semiconductors, liquid crystals, etc. The water quality. Therefore, in order to obtain water quality that can be used for the manufacture of semiconductors, liquid crystals, etc., it is necessary to further perform deionization treatment in the later stage by, for example, a mixed bed ion exchange resin tower, an electric deionization device, etc. In the device for performing these deionization treatments, if the required water quality on the specifications of the device is met, it can be treated, but in the treatment of the front section of the device, high water quality such as that obtained by the existing method is not necessary, so there is also a problem of excess and waste of equipment related to the treatment of the front section. For example, if a degassing device (degassing tower) is set at the front section of the three-stage reverse osmosis membrane in order to remove carbonic acid, it is necessary to supply the treated water of the degassing tower to the pump of the later section, so the device becomes larger. In addition, the water quality can also be improved by using a high-pressure reverse osmosis membrane, but in this case, there is a problem of high power consumption due to the need to operate under high pressure.

[0015] The present invention aims to provide a method and apparatus for producing pure water using an ultra-low pressure reverse osmosis membrane device to produce pure water that can be supplied to a regenerative deionization device such as a mixed bed ion exchange resin device and an electrodeionization device, thereby seeking to improve the production efficiency of pure water from which boron has been removed.

[0016] In summary, the present invention is completed to solve the above-mentioned problems, and its purpose is to provide a pure water production method, a pure water production device and an ultrapure water production system using the pure water production device, which can reduce the amount of reagents used by reducing the processing load of the reverse osmosis membrane device on the front side, and can efficiently produce pure water from which boron is removed.

[0017] Solutions for solving problems

[0018] The pure water production method of the present invention is characterized in that it is a pure water production method for removing boron in raw water by treating raw water with at least three stages of ultra-low pressure reverse osmosis membrane devices, the reverse osmosis membranes of the three stages of reverse osmosis membrane devices are all negatively charged membranes having an epidermal layer formed by cross-linked aromatic polyamide, the raw water contains carbonic acid of 1 mg / L or more and 100 mg / L or less, and boron of 150 μg / L or less, and the pure water production method has the following steps: a step of treating the raw water with a first stage of reverse osmosis membrane device to obtain a first permeate water; a step of adjusting the first permeate water to alkaline to obtain alkaline treated water; a step of treating the alkaline treated water with a second stage of reverse osmosis membrane device to obtain a second permeate water; and a step of treating the second permeate water with a third stage of reverse osmosis membrane device to obtain pure water having a boron concentration of 3 μg / L or more and 20 μg / L or less and an electrical conductivity of 0.3 μS / cm or more and 40 μS / cm or less.

[0019] In the method for producing pure water of the present invention, the pH of the alkaline water to be treated is preferably 9.0 or more and 10.0 or less.

[0020] Preferably, the method for producing pure water of the present invention further comprises a step of adding an acid to the second permeated water to obtain second treated water, and the second treated water is treated by a third-stage reverse osmosis membrane device.

[0021] Preferably, in the pure water production method of the present invention, the raw water contains chlorine, and in the step of obtaining the second treated water, aminosulfonic acid is added to the second permeate water, and the concentrated water of the third reverse osmosis membrane device is mixed with the raw water and treated by the first reverse osmosis membrane device.

[0022] Preferably, in the method for producing pure water of the present invention, the pH of the second treated water is 5.5 or more and 7.5 or less.

[0023] Preferably, in the method for producing pure water of the present invention, the pure water obtained as permeate water of the third-stage reverse osmosis membrane device is further treated by an electrodeionization device.

[0024] The pure water manufacturing device of the present invention is characterized in that it is a pure water manufacturing device for removing boron, which has a first reverse osmosis membrane device, a second reverse osmosis membrane device and a third reverse osmosis membrane device connected in series, wherein the first reverse osmosis membrane device, the second reverse osmosis membrane device and the third reverse osmosis membrane device are ultra-low pressure reverse osmosis membrane devices, and the reverse osmosis membranes of the first reverse osmosis membrane device, the second reverse osmosis membrane device and the third reverse osmosis membrane device are negatively charged membranes having a skin layer formed of cross-linked aromatic polyamide, and the pure water manufacturing device has: a raw water supply mechanism, which supplies the first reverse osmosis membrane device with a raw water containing 1 mg / L or more and 100 The invention relates to a method for treating a raw water comprising: a first reverse osmosis membrane device and a second reverse osmosis membrane device, wherein the raw water contains less than 100 μg / L of carbonic acid and less than 150 μg / L of boron; a first supply pipe for delivering the permeate water of the first reverse osmosis membrane device to the second reverse osmosis membrane device; an alkali adjustment mechanism, which is arranged on the path of the first supply pipe and adjusts the treated water flowing in the first supply pipe to be alkaline; and a second supply pipe for delivering the permeate water of the second reverse osmosis membrane device to the third reverse osmosis membrane device, so as to obtain pure water with a boron concentration of not less than 3 μg / L and not more than 20 μg / L and an electrical conductivity of not less than 0.3 μS / cm and not more than 40 μS / cm.

[0025] Preferably, the pure water production apparatus of the present invention includes an electrodeionization device at a subsequent stage of the third reverse osmosis membrane device.

[0026] The ultrapure water production system of the present invention is an ultrapure water production system which is sequentially equipped with a primary pure water device and a secondary pure water device, wherein the primary pure water device comprises the pure water production device of the present invention and an electrodeionization device arranged at the rear section of the pure water production device, and the secondary pure water device comprises an ultraviolet oxidation device, a non-regenerative ion exchange device for producing ultrapure water, a membrane degassing device and an ultrafiltration device in sequence, and the ultrapure water production system produces ultrapure water with a boron concentration of less than 0.1 μg / L.

[0027] In addition, in this specification, the symbol "to" represents a numerical range that is greater than or equal to a value on the left side of the symbol and less than or equal to a value on the right side.

[0028] Effects of the Invention

[0029] According to the pure water production method and pure water production device of the present invention, by using three-stage reverse osmosis membrane devices on the front side and reducing the processing load of these reverse osmosis membrane devices on the front side, the amount of chemicals used can be reduced, and pure water with a reduced boron concentration can be efficiently produced.

[0030] According to the ultrapure water production system of the present invention, the amount of chemicals used in the pure water production apparatus using the three-stage reverse osmosis membrane apparatus on the front stage can be reduced, so that ultrapure water of high quality can be produced efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart schematically showing the pure water production method according to the embodiment.

[0032] Figure 2 is a schematic diagram showing the Figure 1 Flow chart of a pure water production method in which pure water obtained by the pure water production method shown is further treated.

[0033] Figure 3 This is a flow chart schematically showing a method for producing pure water according to a modified example.

[0034] Figure 4 1 is a block diagram schematically showing a pure water production system according to an embodiment.

[0035] Figure 5 This is a block diagram schematically showing a pure water production system according to another embodiment.

[0036] Figure 6 1 is a block diagram schematically showing an ultrapure water production system according to an embodiment.

[0037] Figure 7 : is a block diagram schematically showing a pure water production system used in the embodiment.

[0038] Figure 8 It is a graph showing the carbonic acid concentration in the feed water and the treated water of the reverse osmosis membrane device of each stage in the method of the Example and the Comparative Example.

[0039] Fig. 9 It is a graph showing the boron concentration in the feed water and the treated water of each stage of the reverse osmosis membrane device in the method of the Example and the Comparative Example.

[0040] Fig.10 It is a graph showing the electrical conductivity of the feed water and the treated water of the reverse osmosis membrane device of each stage in the method of the Example and the Comparative Example. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 FIG. 1 is a flow chart schematically showing a pure water production method 100 according to an embodiment of the present invention. Figure 1 In the pure water production method 100 shown, raw water is treated by at least three stages of ultra-low pressure reverse osmosis membrane devices. The pure water production method 100 is suitable for producing pure water supplied to an electrodeionization device or a regenerative ion exchange resin device, for example.

[0042] The pure water production method 100 comprises: a reverse osmosis membrane treatment step 101, in which raw water is treated by a first-stage reverse osmosis membrane device to obtain permeate water W10 (first permeate water); an alkali adjustment step 102, in which the permeate water W10 is adjusted to be alkaline to obtain alkaline treated water W11; a reverse osmosis membrane treatment step 103, in which the alkaline treated water W11 is treated by a second-stage reverse osmosis membrane device to obtain permeate water W20 (second permeate water); and a reverse osmosis membrane treatment step 104, in which the permeate water W20 is subjected to a third-stage reverse osmosis membrane treatment as treated water to obtain permeate water W30. The permeate water W30 is pure water produced by the pure water production method 100.

[0043] The raw water used in the pure water production method 100 of the present embodiment is, for example, city tap water, well water, industrial water, etc. In addition, the raw water may also be used recycled water that has been used and recycled at the place where ultrapure water is used, and then subjected to chemical removal treatment as needed. The raw water (or pre-treated water described later) supplied to the reverse osmosis membrane treatment process 101 contains 1 mg / L to 100 mg / L of carbonic acid and 150 μg / L or less of boron. The boron concentration in the raw water is preferably 5 μg / L or more. If it is within this range, it is easy to significantly obtain the effect of the present invention. In addition, the raw water may also contain hardness components such as calcium and magnesium in a total of 10 mg / L to 300 mg / L after conversion to calcium carbonate. In addition, the raw water may also contain, for example, silicon dioxide (Si) of about 1 mg / L to 50 mg / L and chlorine of about 0.1 mg / L to 0.6 mg / L in terms of Cl. The pH of the raw water is, for example, about 5.0 to 7.5. It should be noted that carbonic acid contains carbon dioxide, bicarbonate ions and carbonate ions. The carbonic acid concentration is the total carbonic acid (CO 2 +HCO 3 - +CO 3 2- ) concentration is converted into CO 2 The value obtained by concentration.

[0044] In addition to the raw water supplied to the reverse osmosis membrane treatment process 101, or on the basis of the raw water, pretreated water obtained by pre-treating the raw water in advance can also be used instead of the raw water, and the pre-treated water must be prepared before use in the pure water manufacturing method 100. As pretreatment, for example, coagulation sedimentation treatment, pressure flotation treatment, sand filtration treatment, precision filtration treatment, these treatments are used to remove turbid components such as suspended matter and colloidal matter in the raw water. In the pretreatment, activated carbon treatment can also be implemented to remove chlorine in the water. In addition, in the pretreatment, the water temperature can be adjusted within the range of 15°C to 30°C by a heat exchanger.

[0045] The three-stage reverse osmosis membrane devices used in the pure water production method 100 are all ultra-low pressure reverse osmosis membrane devices. The operating pressure of the ultra-low pressure reverse osmosis membrane is, for example, 0.4 MPa to 1.1 MPa, preferably 0.6 MPa to 0.7 MPa. It should be noted that the operating pressure of the reverse osmosis membrane device is the design pressure when each reverse osmosis membrane is manufactured, and in fact, it is sometimes operated at a pressure outside the above range.

[0046] In the pure water production method 100, the supply pressure to the first reverse osmosis membrane device is adjusted so that the treated water is supplied to the first reverse osmosis membrane device to the third reverse osmosis membrane device at a supply pressure of preferably 0.4MPa to 1.1MPa, more preferably 0.6MPa to 0.7MPa. The supply pressure is expressed by the pressure difference obtained by subtracting the permeate water pressure from the pressure on the supply side of the reverse osmosis membrane device (the average of the supply water pressure and the concentrated water pressure). In the reverse osmosis membrane treatment process 101, the raw water is subjected to reverse osmosis membrane treatment, and hardness components such as calcium and magnesium in the raw water are removed. The concentrated water of the first reverse osmosis membrane device is discharged to the outside of the system, and the permeate water W10 is sent to the rear stage. The removal rate of the hardness components in the reverse osmosis membrane treatment process 101 can be obtained at 99% to 99.9%. For the water quality of the permeate water W10, for example, the hardness components such as calcium and magnesium can be obtained in total of 0.1mg / L to 3mg / L after conversion to calcium carbonate. In addition, regarding the water quality of the permeated water W10, for example, the carbonic acid concentration is 0.5 mg / L to 50 mg / L, the boron concentration is 3 μg / L to 120 μg / L, and the electrical conductivity is 2 μS / cm to 10 μS / cm.

[0047] In the alkali adjustment step 102, the permeate water W10 obtained in the reverse osmosis membrane treatment step 101 is adjusted to alkaline to obtain alkaline treated water W11. For example, in the alkali adjustment step 102, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution, preferably an aqueous sodium hydroxide solution, is added to the permeate water W10 to generate the treated water W11. The pH of the treated water W11 is preferably 9.0 to 10.0, and the conductivity is preferably 10 μS / cm to 50 μS / cm. In addition, the carbonic acid concentration and boron concentration of the treated water W11 are the same as those of the above-mentioned permeate water W10. By making the pH of the treated water W11 above 9.0, the removal rate of boron in the subsequent reverse osmosis membrane treatment step 103 can be improved. In addition, by making the pH of the treated water W11 below 10.0, the amount of chemicals used can be suppressed, and the ion components can be fully removed in the pure water manufacturing method 100. Furthermore, by setting the pH of the treated water W11 to 10.0 or less, the amount of chemicals (alkali) used can be reduced, thereby reducing sodium leakage to the downstream stage (leaking of sodium into the permeated water W20).

[0048] In the reverse osmosis membrane treatment process 103, the treated water W11 is supplied to the second reverse osmosis membrane device for reverse osmosis membrane treatment. The concentrated water of the second reverse osmosis membrane device is discharged to the outside of the system or returned to the front side of the first reverse osmosis membrane device. The permeated water W20 of the second reverse osmosis membrane device is sent to the rear side.

[0049] In the reverse osmosis membrane treatment process 103, as described above, the treated water adjusted to alkalinity is treated, so the boron removal rate can be improved, and the boron removal rate in the reverse osmosis membrane treatment process 103 can reach 50% to 90%. In addition, in the reverse osmosis membrane treatment process 103, the removal rate of carbonic acid can also be improved, and the removal rate of carbonic acid can reach 95% to 98%. For the water quality of the permeated water W20, for example, the carbonic acid concentration is 0.025 mg / L to 2.5 mg / L, the boron concentration is 3 μg / L to 40 μg / L, the conductivity is 1 μS / cm to 40 μS / cm, and the pH is about 8.5 to 10. It should be noted that the boron removal rate is a value calculated by [1-(boron concentration in permeated water W20 / boron concentration in treated water W11)]×100(%). The carbonic acid removal rate is a value calculated by [1-(carbonic acid concentration in permeated water W20 / carbonic acid concentration in treated water W11)]×100(%).

[0050] In the reverse osmosis membrane treatment process 104, as described above, the permeate water W20 from which boron and carbonic acid have been removed is supplied as treated water to the third reverse osmosis membrane device for reverse osmosis membrane treatment. The concentrated water of the third reverse osmosis membrane device is discharged to the outside of the system or returned to the front side of the first reverse osmosis membrane device. The permeate water W30 of the third reverse osmosis membrane device is sent to the back stage as pure water for treatment or directly supplied to the point of use (POU).

[0051] In the reverse osmosis membrane treatment step 104, ion components in the treated water (permeated water W20), for example, anion components such as chloride ions, sulfate ions, nitrate ions, fluoride ions, bicarbonate ions, cation components such as sodium ions, potassium ions, and weak electrolytes such as boron and silicon dioxide are removed. The water quality of the permeated water (pure water) W30 obtained in the reverse osmosis membrane treatment step 104 is as follows: the boron concentration is 3 μg / L to 20 μg / L, preferably 5 μg / L to 10 μg / L, the carbonic acid concentration is, for example, 0.005 mg / L to 0.5 mg / L, and the conductivity is 0.3 μS / cm to 40 μS / cm, preferably 1 μS / cm to 20 μS / cm, and more preferably 1 μS / cm to 10 μS / cm.

[0052] From the perspective of obtaining pure water of the above-mentioned water quality, it is preferred that the water recovery rate in the three-stage reverse osmosis membrane device is 50% to 80% for the reverse osmosis membrane treatment process 101, 70% to 90% for the reverse osmosis membrane process 103, and 80% to 95% for the reverse osmosis membrane process 104.

[0053] Furthermore, the total boron removal rate through the three-stage reverse osmosis membrane device (steps 101, 103, and 104) can be 40% to 95%.

[0054] Above, the method of performing only three-stage reverse osmosis membrane treatment is described, but the reverse osmosis membrane treatment can also be more than four stages. In this case, a method of further performing reverse osmosis membrane treatment on the upstream side of the first reverse osmosis membrane device, a method of further performing reverse osmosis membrane treatment between the first reverse osmosis membrane device and the second reverse osmosis membrane device, a method of further performing reverse osmosis membrane treatment between the second reverse osmosis membrane device and the third reverse osmosis membrane device, a method of further performing reverse osmosis membrane treatment on the downstream side of the third reverse osmosis membrane device, or any combination thereof can be used. In the additional reverse osmosis membrane treatment, any one of the ultra-low pressure type, low pressure type, and high pressure type reverse osmosis membrane devices can be used. Among them, it is preferred to further perform reverse osmosis membrane treatment by ultra-low pressure type between the second reverse osmosis membrane device and the third reverse osmosis membrane device, by which the boron concentration can be further reduced.

[0055] It should be noted that the operating pressure of the low-pressure reverse osmosis membrane is, for example, greater than 0.8 MPa and less than 2.5 MPa, preferably 1 MPa to 1.6 MPa. The operating pressure of the high-pressure reverse osmosis membrane is, for example, greater than 2.5 MPa and less than 8 MPa. It should be noted that the operating pressure of the above-mentioned ultra-low pressure, low pressure, and high pressure reverse osmosis membrane devices is the design pressure when manufacturing each reverse osmosis membrane. In fact, it is sometimes operated at a pressure outside the above range.

[0056] According to the pure water manufacturing method 100 of the embodiment described above, in the reverse osmosis membrane treatment process 103 performed by the second stage reverse osmosis membrane device, an excellent carbonic acid removal rate is achieved, so the hardness removal mechanism on the front stage side and the degassing device for removing carbonic acid can be omitted. Therefore, the amount of reagents used can be reduced, and the device can be simplified, so pure water can be manufactured efficiently at low cost. Moreover, if the water supply pressure in the three-stage reverse osmosis membrane treatment process is set to an ultra-low pressure as described above, the number and output of the water supply pump can be reduced, thereby further simplifying the device, reducing the pure water manufacturing cost, and improving the manufacturing efficiency.

[0057] Next, a preferred method for treating the permeated water W30 will be described. Figure 21 is a flowchart schematically showing a pure water production method 110 of an embodiment. The pure water production method 110 is an example of a method for further producing high-purity pure water by treating permeated water W30. The pure water production method 110 comprises: an electrodeionization treatment step 111, in which the permeated water W30 is treated by an electrodeionization device; an ultraviolet oxidation treatment step 112, in which the desalted water W40 obtained in the electrodeionization treatment step 111 is subjected to ultraviolet oxidation treatment as treated water; and a non-regenerative ion exchange resin (Primary / Polisher) treatment step 113, in which the ion components in the treated water W41 of the ultraviolet oxidation treatment step 112 are removed.

[0058] In the electrodeionization treatment process 111, the permeate water W30 is supplied to an electrodeionization device (EDI), and the ion components in the permeate water W30 are removed. The electrodeionization device, for example, alternately has a desalination chamber separated by an anion exchange membrane and a cation exchange membrane, and a concentration chamber into which concentrated water containing the removed ion components flows. The electrodeionization device also has a mixture of anion exchange resin and cation exchange resin filled in the desalination chamber, and electrodes for applying a DC voltage.

[0059] In the electrodeionization device, direct current is applied to the electrodes, and the ions in the treated water are adsorbed by the ion exchange resins by passing the treated water through anion exchange resins and cation exchange resins. The adsorbed ions migrate to the surface of the ion exchange membranes through electrophoresis, and are transferred to the concentration chamber by electrodialysis in the ion exchange membranes and discharged into the concentrated water. In the desalination chamber, the water dissociation reaction proceeds to generate H + and OH - , thereby the ion exchange resin in the desalination chamber is continuously regenerated. The desalted water W40 collected in the desalination chamber is sent to the back stage, and the concentrated water in the concentration chamber is discharged to the outside of the system.

[0060] As the treatment condition in the electrodeionization treatment step 111, the current density in the desalination chamber is preferably 0.2 A / dm 2 ~1.0A / dm 2 , thereby, the regeneration efficiency of the ion exchange resin in the desalination chamber can be improved, and the ion removal efficiency can be improved. The current density of the desalination chamber can be adjusted by the voltage between the anode and the cathode of the electrodeionization device. In addition, the water quality of the desalted water obtained in the electrodeionization process, for example, has a resistivity of 15MΩ·cm to 18MΩ·cm.

[0061] Examples of the electrodeionization apparatus (EDI) used in the electrodeionization treatment step 111 include VNX series such as model IP-VNX-MAX (manufactured by EVOQUA), E-Cell series such as model SUEZMK3-27EU (manufactured by SUEZ), and MDI series such as model UX5015 (manufactured by ECORBIT).

[0062] In the pure water production method 110 of the present embodiment, the water quality of the pure water obtained in the pure water production method 100 can obtain water quality acceptable to the electrodeionization treatment step 111, so the deionization treatment in the electrodeionization treatment step 111 can be appropriately performed. As the water quality acceptable to the electrodeionization treatment step 111, specifically, for example, a boron concentration of 3 μg / L to 20 μg / L, an electrical conductivity of 0.3 μS / cm to 40 μS / cm, and a carbonic acid concentration of 0.001 mg / L to 3 mg / L.

[0063] Next, the desalted water W40 obtained in the electrodeionization treatment process 111 is supplied to the ultraviolet oxidation device in the ultraviolet oxidation treatment process 112. The ultraviolet oxidation device, for example, has an ultraviolet lamp that can irradiate ultraviolet rays having a wavelength of about 185 nm, and by irradiating the treated water with ultraviolet rays from the ultraviolet lamp, the total organic carbon component (TOC) in the treated water is oxidized and decomposed. The ultraviolet lamp used in the ultraviolet oxidation device can use a lamp that generates ultraviolet rays with a wavelength of about 185 nm. The ultraviolet lamp can also use a low-pressure mercury lamp that radiates ultraviolet rays with a wavelength of about 254 nm together with ultraviolet rays with a wavelength of about 185 nm. The ultraviolet rays radiated by the ultraviolet oxidation device decompose water to generate OH radicals, and the organic matter in the treated water (the desalted water W40) is oxidized and decomposed into organic acids by the OH radicals. The amount of ultraviolet irradiation in the ultraviolet oxidation treatment process 112 can be appropriately changed according to the water quality of the treated water.

[0064] The treated water W41 generated in the ultraviolet oxidation treatment process 112 is then supplied to a non-regenerative ion exchange resin device (Primary / Polisher) in a non-regenerative ion exchange resin treatment process 113. The non-regenerative ion exchange resin device is formed by mixing and filling a strong acid cation exchange resin and a strong basic anion exchange resin in a resin tower, and the non-regenerative ion exchange resin device removes ion components in the treated water W41. Here, the ion components removed are mainly trace amounts of organic acids generated by the decomposition of organic matter in the ultraviolet oxidation treatment process 112.

[0065] The resistivity of the treated water W42 generated by the non-regenerative ion exchange resin treatment step 113 can be obtained to be above 18MΩ·cm, and the TOC concentration can be reduced to, for example, below 10μgC / L. It should be noted that the non-regenerative ion exchange resin treatment step 113 may not be performed. In this case, the ultraviolet oxidation treatment step 112 may be performed before the electrodeionization treatment step 111, and the permeated water W30 may be treated in sequence by the ultraviolet oxidation treatment step 112 and the electrodeionization treatment step 111.

[0066] According to the pure water manufacturing method 110 described above, the electrodeionization treatment process 111 is adopted, so that the ion components can be continuously removed without using any reagents such as acids and alkalis that are usually used in the regeneration of ion exchange resins. Therefore, it is possible to achieve a reduction in the pure water manufacturing cost, miniaturization of the device, reduction of the environmental load, etc., thereby improving the manufacturing efficiency. In addition, in the electrodeionization treatment process 111, most of the ion components can be removed, so that the processing load of the three-stage reverse osmosis membrane device in the front section can be reduced, thereby achieving a reduction in the pure water manufacturing cost, miniaturization of the device, reduction of the environmental load, etc.

[0067] Next, refer to Figure 3 A pure water production method 120 as a modified example of the pure water production method 100 of the embodiment is described. The pure water production method of this modified example has an acid adjustment step of adding an acid to the permeated water W20 to generate a second treated water having a pH lower than that of the alkaline treated water in the pure water production method 100. Figure 1 The pure water production method 100 shown is different. That is, the pure water production method 120 of the modified example has: a reverse osmosis membrane treatment step 101, in which raw water is treated by a first-stage reverse osmosis membrane device to obtain permeate water W10 (first permeate water); an alkali adjustment step 102, in which the permeate water W10 is adjusted to be alkaline to obtain alkaline treated water W11; a reverse osmosis membrane treatment step 103, in which the alkaline treated water W11 is treated by a second-stage reverse osmosis membrane device to obtain permeate water W20 (second permeate water); an acid adjustment step 121, in which acid is added to the permeate water W20 to obtain second treated water W21; and a reverse osmosis membrane treatment step 122, in which the second treated water W21 is treated by a third-stage reverse osmosis membrane device to obtain permeate water W31. The permeate water W31 is pure water produced by the pure water production method 120.

[0068] In the acid adjustment step 121, an acid is added to the permeated water W20 obtained in the reverse osmosis membrane treatment step 103 to obtain the second treated water W21. For example, in the acid adjustment step 121, hydrochloric acid, sulfuric acid, aminosulfonic acid aqueous solution, etc. are added to the permeated water W20 to generate the treated water W21. From the viewpoint of reducing the environmental load, the liquid property of the treated water W21 is preferably weakly acidic to weakly alkaline. Specifically, the pH of the treated water W21 is preferably 5.5 to 7.5, and more preferably 6.5 to 7.5. By making the pH of the second treated water W21 above 5.5, the removal rate of the cationic components in the subsequent reverse osmosis membrane treatment step 122 can be improved. In addition, since the acid is not added excessively, the treated water quality can be improved. When the salts (ion components) that permeate in trace amounts in the reverse osmosis membrane treatment process 103 are present in the permeated water W20 of the reverse osmosis membrane treatment process 103 in the form of hydroxide salts such as sodium hydroxide, by making the pH of the treated water W21 below 7.5, the hydroxide salts are converted into the form of aminosulfonates such as sodium aminosulfonate, so that the salts are easily removed in the reverse osmosis membrane treatment process 122. In addition, by making the pH of the treated water W21 above 5.5, the processing load in the reverse osmosis membrane treatment process 122 can be reduced. In addition, for the acid added in the acid adjustment process 121, from the viewpoint of reducing the amount of reagents used and reducing the environmental load, it is preferred to use an aqueous solution of aminosulfonic acid in the above.

[0069] When aminosulfonic acid is used in the acid adjustment process 121, it is preferred that the raw water is not treated with activated carbon and the chlorine concentration in the raw water is 0.1μg / L to 0.4μg / L. By circulating the concentrated water generated in the reverse osmosis membrane treatment process 122 to the supply side of the first-stage reverse osmosis membrane device, the chlorine in the raw water reacts with the aminosulfonic acid in the concentrated water to produce a bactericidal force, and the effect of suppressing biofouling in the three-stage reverse osmosis membrane device can be obtained. In particular, biofouling in the first-stage reverse osmosis membrane where biofouling is most likely to occur violently can be prevented. As a result, the amount of bactericide usually added to the treated water for sterilization can be reduced, thereby reducing the environmental load. In addition, by adding aminosulfonic acid, the free chlorine in the treated water that deteriorates the reverse osmosis membrane can be converted into combined chlorine, thereby also having the effect of reducing the load on the reverse osmosis membrane. Thus, in the pure water production method 120 of this modification, by adding sulfamic acid in the acid adjustment step 121, two effects can be obtained: improving the removal rate of weak electrolytes in the reverse osmosis membrane treatment step 122 and suppressing biofouling in the three-stage reverse osmosis membrane. Therefore, in the conventional pure water production method, two acids need to be added at two places, namely, the feed water of the first stage reverse osmosis membrane and the feed water of the third stage reverse osmosis membrane. However, in the pure water production method 120 of this modification, it can be reduced to adding one acid at the acid adjustment step 121.

[0070] When aminosulfonic acid is used in the acid adjustment process 121, the amount of aminosulfonic acid added is preferably in a balance between the reduction amount of the above-mentioned bactericide and the addition amount of aminosulfonic acid, and is within the range that can reduce the total amount of chemicals used in the pure water manufacturing method 120, for example, 1 mg / L to 10 mg / L relative to the treated water.

[0071] Next, the pure water production apparatus 200 according to the embodiment of the present invention will be described. Figure 4 1 is a block diagram schematically showing a pure water production system 4 including a pure water production device 200 according to an embodiment. The pure water production device 200 includes three stages of ultra-low pressure reverse osmosis membrane devices 201 , 202 , and 203 .

[0072] A pretreatment device 210 is provided as a raw water supply mechanism at the front stage of the pure water production device 200. The pretreatment device 210 is provided with an activated carbon device (AC) 211, a storage tank TK, a pump P1, a heat exchanger (HEX) 212, and a precision filter device (PF) 213 in order. The configuration of the pretreatment device 210 can be appropriately changed according to the quality of the raw water. For example, the pretreatment device 210 may not include the activated carbon device (AC) 211, the heat exchanger (HEX) 212, and the precision filter device (PF) 213, or may be configured by combining a coagulation sedimentation device, a pressure flotation device, a sand filter device, and the like in addition to the above-mentioned activated carbon device (AC) 211, the storage tank TK, the heat exchanger (HEX) 212, and the precision filter device (PF) 213.

[0073] In the rear section of the pure water production device 200, an electrodeionization device (EDI) 221, an ultraviolet oxidation device (TOC-UV) 222, and a non-regenerative ion exchange resin device (Primary / Polisher) 223 are sequentially arranged. The electrodeionization device (EDI) 221, the ultraviolet oxidation device (TOC-UV) 222, and the non-regenerative ion exchange resin device (Primary / Polisher) 223 can be appropriately arranged according to the desired water quality.

[0074] The pure water production device 200 has a supply pipe L1 (first supply pipe) for sending the permeated water of the reverse osmosis membrane device 201 to the reverse osmosis membrane device 202 and a supply pipe L2 (second supply pipe) for sending the permeated water of the reverse osmosis membrane device 202 to the reverse osmosis membrane device 203. In addition, discharge pipes L3, L4, and L5 are connected to the concentration sides of the reverse osmosis membrane devices 201, 202, and 203, respectively. The pure water production device 200 has a circulation pipe L6. One end of the circulation pipe L6 is connected to the tank TK, and the other end is connected to the discharge pipes L4 and L5, whereby the circulation pipe L6 circulates the concentrated water of the reverse osmosis membrane devices 202 and 203 to the tank TK.

[0075] Reverse osmosis membrane devices 201, 202, 203, for example, are provided with one or more reverse osmosis membrane modules, which are formed by accommodating reverse osmosis membranes and flow path materials for passing treated water through reverse osmosis membranes in a shell. The reverse osmosis membranes provided by reverse osmosis membrane devices 201, 202, 203 are negatively charged membranes having a skin layer formed by cross-linked aromatic polyamide. Preferably, these reverse osmosis membranes are asymmetric membranes or composite membranes, which are formed by polyarylethersulfones, polyimides, polyvinylidene fluoride, etc. such as polysulfone and polyethersulfone, and have a support layer with fine porous, and a composite membrane having the above-mentioned skin layer on the support layer. It should be noted that the negatively charged membrane refers to a membrane in which a membrane formed by a skin layer shows a negative charge when pH is 7. The shape of the reverse osmosis membrane is hollow fiber, spiral, flat, tubular, etc. From the viewpoint of improving pressure resistance and improving treatment efficiency, these reverse osmosis membranes are preferably spiral.

[0076] The salt rejection rate (salt removal rate) of the reverse osmosis membrane used in the reverse osmosis membrane devices 201, 202, and 203 is preferably 99.0% or more, more preferably 99.2% or more, further preferably 99.5% or more, and further preferably 99.6% or more. It should be noted that the salt rejection rate is expressed by the removal rate of sodium chloride when a sodium chloride aqueous solution with a pH of 7 and a concentration of 500 ppm or 1500 ppm is supplied at a water temperature of 25°C, a water recovery rate of 15%, and a supply pressure of 1.03 MPa or 0.69 to 0.7 MPa.

[0077] Examples of the ultra-low pressure type reverse osmosis membrane devices using ultra-low pressure type membranes as the reverse osmosis membrane devices 201 , 202 , and 203 include the ESPA series manufactured by Nitto Denko Corporation and the TBW series / TMHA series manufactured by Toray Industries, Inc.

[0078] The supply pipe L1 is provided with an alkali adjustment mechanism 204 for adjusting the treated water flowing in the supply pipe L1 to be alkaline. The alkali adjustment mechanism 204 is composed of, for example, a tank storing an alkali adjustment agent such as an aqueous sodium hydroxide solution or potassium hydroxide, and an injection pump that measures a predetermined amount of the alkali adjustment agent in the tank and adds the alkali adjustment agent to the supply pipe L1.

[0079] Used Figure 4 The production of pure water by the pure water production apparatus 200 shown in the figure is similar to the pure water production method 100 ( Figure 1 ) is the same. First, raw water consisting of city tap water, well water, industrial water, used recycled water, etc. is supplied to the pretreatment device 210. The raw water passes through the pretreatment device, thereby removing turbid components and chlorine in the water, and then the water temperature is adjusted to 15°C to 30°C to generate pretreated water.

[0080] The pretreated water thus obtained contains 1 mg / L to 100 mg / L of carbonic acid and 150 μg / L or less of boron, and the boron concentration is preferably 5 μg / L or more. The pH of the pretreated water is, for example, about 5.0 to 7.5.

[0081] The pre-treated water is pressurized by pump P1 and supplied to the reverse osmosis membrane device 201. The pre-treated water is subjected to reverse osmosis membrane treatment in the reverse osmosis membrane device 201, and the hardness components in the water are removed to generate permeate water W10 ( Figure 1 The concentrated water of the reverse osmosis membrane device 201 is discharged to the outside of the system through the discharge pipe L3. The permeated water W10 is sent to the subsequent stage through the supply pipe L1.

[0082] The permeated water W10 is adjusted to be alkaline ( Figure 1 Specifically, the alkali adjusting mechanism 204 quantitatively injects an alkali adjusting agent into the supply pipe L1, thereby mixing the alkali adjusting agent with the permeated water W10 to generate the treated water W11 adjusted to alkalinity. The pH of the treated water W11 is preferably 9.0 to 10.0.

[0083] The alkaline treated water W11 is then supplied to the reverse osmosis membrane device 202. The treated water W11 is subjected to reverse osmosis membrane treatment in the reverse osmosis membrane device 202, and boron and carbonic acid in the water are removed to generate permeate water W20 ( Figure 1 The reverse osmosis membrane treatment process 103). As described above, the treated water W11 is alkaline, so the boron removal rate in the reverse osmosis membrane device 202 can reach 50% to 90%, and the carbonic acid removal rate can reach 95% to 98%. The concentrated water of the reverse osmosis membrane device 202 is circulated to the tank TK via the discharge pipe L4 and the circulation pipe L6. The permeated water W20 is sent to the rear stage via the supply pipe L2.

[0084] The permeated water W20 is then supplied to the reverse osmosis membrane device 203. The permeated water W20 is subjected to reverse osmosis membrane treatment in the reverse osmosis membrane device 203, and the ion components in the water are removed to generate permeated water W30 ( Figure 1 The concentrated water of the reverse osmosis membrane device 203 is circulated to the tank TK via the discharge pipe L5 and the circulation pipe L6. The permeated water (pure water) W30 is sent to the subsequent stage.

[0085] For the water quality of the permeate water (pure water) W30 obtained in the reverse osmosis membrane treatment process 104, for example, the boron concentration is 3μg / L~20μg / L, preferably 5μg / L~10μg / L, the carbonic acid concentration is 0.005mg / L~0.5mg / L, the conductivity is 0.3μS / cm~40μS / cm, preferably 1μS / cm~20μS / cm, and more preferably 1μS / cm~10μS / cm.

[0086] In addition, from the perspective of obtaining pure water of the above-mentioned water quality (permeated water W30), it is preferred that the water recovery rate in the three-stage reverse osmosis membrane device is 50% to 80% for reverse osmosis membrane device 201, 70% to 90% for reverse osmosis membrane device 202, and 80% to 95% for reverse osmosis membrane device 203.

[0087] After that, the permeated water W30 is sequentially supplied to the electrodeionization device (EDI) 221, the ultraviolet oxidation device 222, and the non-regenerative ion exchange resin device 223. Figure 2 The pure water production method 110 shown in FIG. 1 is as follows. First, the permeated water W30 is supplied to the electrodeionization device 221 to remove the ion components ( Figure 2 Electrodeionization treatment process 111). In the electrodeionization device 221, the ion components in the treated water are adsorbed by the ion exchange resin by passing the treated water through the anion exchange resin and the cation exchange resin while applying a direct current to the electrodes. The adsorbed ion components migrate to the surface of the ion exchange membrane by electrophoresis, are electrodialyzed in the ion exchange membrane, and are transferred to the concentration chamber and discharged into the concentrated water. The deionized water W40 from which the ion components have been removed is sent to the rear section, and the concentrated water in the concentration chamber is discharged out of the system.

[0088] The desalted water W40 is supplied to the ultraviolet oxidizing device 222, and the desalted water W40 is irradiated with ultraviolet rays ( Figure 2 The ultraviolet ray oxidation treatment step 112 is performed. Thus, the total organic carbon content (TOC) in the desalted water W40 is oxidatively decomposed. The ultraviolet ray irradiated is preferably an ultraviolet ray having a wavelength of about 185 nm, and more preferably an ultraviolet ray having a wavelength of about 185 nm and an ultraviolet ray having a wavelength of about 254 nm.

[0089] The treated water W41 generated by the ultraviolet oxidation device 222 is then supplied to the non-regeneration type ion exchange resin device 223, and the ion components in the treated water W41 are removed ( Figure 2 The resistivity of the treated water W42 generated by the non-regenerative ion exchange resin device 223 can be obtained to be 18 MΩ·cm or more, and the TOC concentration can be reduced to, for example, 10 μgC / L or less.

[0090] It should be noted that the non-regenerative ion exchange resin device (Primary / Polisher) 223 may not be provided. In this case, the ultraviolet oxidation device 222 may be arranged before the electrodeionization device (EDI) 221, and the permeated water W30 may be treated in sequence by the ultraviolet oxidation device 222 and the electrodeionization device (EDI) 221.

[0091] According to the pure water manufacturing device 200 described above, in the reverse osmosis membrane device 202, an excellent carbonic acid removal rate can be achieved, so the hardness removal mechanism on the front side and the degassing device for removing carbonic acid can be omitted. In addition, on the basis of being able to omit the hardness removal mechanism and the degassing device, the processing load of the pure water manufacturing device 200 is reduced, so the amount of reagents used can be reduced, and the device can be simplified. As a result, pure water can be manufactured efficiently at low cost. Moreover, if the water supply pressure in the three-stage reverse osmosis membrane treatment process is set to ultra-low pressure as described above, the number and output of the water supply pump can be reduced, so the device can be further simplified, the pure water manufacturing cost can be reduced, and the manufacturing efficiency can be improved.

[0092] Next, a pure water production apparatus 300 which is a modified example of the pure water production apparatus 200 of the embodiment will be described. Figure 5 1 is a block diagram schematically showing a pure water production system 5 including a pure water production device 300. The pure water production device 300 is a device for realizing the pure water production method 120 of the above-mentioned embodiment, and is similar to the above-mentioned embodiment in that an acid adjustment mechanism 205 is provided in the path of the supply pipe L2. Figure 4 The pure water production system 4 shown is different, and as a result, the treatment method in the third stage reverse osmosis membrane device is different, and the other structures and effects are the same as the pure water production device 200. Therefore, the structures having the same functions as the pure water production device 200 are denoted by the same reference numerals and detailed descriptions are omitted.

[0093] The pure water production system 5 includes a pretreatment device 310 disposed at the front end of the pure water production device 300. The pretreatment device 310 includes a storage tank TK, a pump P1, a heat exchanger (HEX) 212, and a precision filter device (PF) 213 in sequence. An electrodeionization device (EDI) 221, an ultraviolet oxidation device (TOC-UV) 222, and a non-regenerative ion exchange resin device (Primary / Polisher) 223 are disposed in sequence at the rear end of the pure water production device 300.

[0094] The pure water production device 300 includes three stages of reverse osmosis membrane devices 201, 202, and 303. In addition, the pure water production device 300 includes a supply pipe L1 (first supply pipe) for sending permeated water from the reverse osmosis membrane device 201 to the reverse osmosis membrane device 202 and a supply pipe L2 (second supply pipe) for sending permeated water from the reverse osmosis membrane device 202 to the reverse osmosis membrane device 303. In addition, discharge pipes L3, L4, and L35 are connected to the concentration sides of the reverse osmosis membrane devices 201, 202, and 303, respectively. The pure water production device 300 includes a circulation pipe L6, one end of which is connected to the tank TK, and the other end is connected to the discharge pipes L4 and L35, and the circulation pipe L6 circulates the concentrated water from the reverse osmosis membrane devices 202 and 303 to the tank TK.

[0095] The reverse osmosis membrane device 303 has the same structure as the reverse osmosis membrane devices 201 and 202 described above, and is an ultra-low pressure type reverse osmosis membrane device.

[0096] The supply pipe L1 is provided with an alkali adjustment mechanism 204 for adjusting the treated water flowing in the supply pipe L1 to be alkaline. The alkali adjustment mechanism 204 is composed of, for example, a tank storing an alkali adjustment agent such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution, and an injection pump that measures a predetermined amount of the alkali adjustment agent in the tank and adds the alkali adjustment agent to the supply pipe L1.

[0097] The supply pipe L2 is provided with an acid adjustment mechanism 205 for adding acid to the treated water flowing in the supply pipe L2. The acid adjustment mechanism 205 is composed of, for example, a tank storing an acid adjustment agent such as hydrochloric acid, sulfuric acid, or aminosulfonic acid, and a drug injection pump that measures a predetermined amount of the acid adjustment agent in the tank and adds the acid to the supply pipe L2. The acid added in the acid adjustment mechanism 205 is preferably aminosulfonic acid among the above.

[0098] Used Figure 5 The production of pure water by the pure water production apparatus 300 shown in the figure is similar to the pure water production method 120 ( Figure 3 ). First, raw water consisting of city tap water, well water, industrial water, used recycled water, etc. is supplied to the pretreatment device 310. The raw water passes through the pretreatment device 310, thereby removing turbid components in the water, and then the water temperature is adjusted to 15°C to 30°C to generate pretreated water.

[0099] The pretreated water thus obtained contains 1 mg / L to 100 mg / L of carbonic acid and 150 μg / L or less of boron. In addition, the pretreated water contains, for example, about 0.1 mg / L to 0.4 mg / L of chlorine in terms of Cl. The pH of the pretreated water is, for example, about 5.0 to 7.5.

[0100] The pre-treated water is pressurized by pump P1 and supplied to the reverse osmosis membrane device 201 at a water supply pressure of preferably 0.4 MPa to 1.1 MPa, more preferably 0.6 MPa to 0.7 MPa, and the hardness components in the water are removed to generate permeate water W10 ( Figure 3 The concentrated water of the reverse osmosis membrane device 201 is discharged to the outside of the system through the discharge pipe L3. The permeated water W10 is sent to the subsequent stage through the supply pipe L1.

[0101] The permeated water W10 is adjusted to be alkaline ( Figure 3 Specifically, the alkali adjusting mechanism 204 quantitatively injects an alkali adjusting agent into the supply pipe L1, thereby mixing the alkali adjusting agent with the permeate water W10 to generate the treated water W11 adjusted to alkalinity. When aminosulfonic acid is used in the acid adjusting mechanism 205, the pH of the treated water W11 is preferably 9.0 to 10.0.

[0102] The alkaline treated water W11 is then supplied to the reverse osmosis membrane device 202. The treated water W11 is subjected to reverse osmosis membrane treatment in the reverse osmosis membrane device 202, and boron and carbonic acid in the water are removed to generate permeate water W20 ( Figure 3 The concentrated water of the reverse osmosis membrane device 202 is circulated to the tank TK via the discharge pipe L4 and the circulation pipe L6. The permeated water W20 is sent to the subsequent stage via the supply pipe L2.

[0103] In the process of the permeate water W20 flowing through the supply pipe L2, acid is added by the acid adjustment mechanism 205 ( Figure 3 Acid adjustment step 121). Specifically, an acid adjusting agent is quantitatively injected into the supply pipe L2 by the acid adjusting mechanism 205, and the acid adjusting agent, preferably aminosulfonic acid, is mixed into the permeated water W20 to generate treated water W21 having a lower pH than the treated water W11. When aminosulfonic acid is used in the acid adjusting mechanism 205, the pH of the treated water W21 is preferably 5.5 to 7.5, and more preferably 6.5 to 7.5.

[0104] The treated water W21 is then supplied to the reverse osmosis membrane device 303, where the ion components in the water are removed to generate permeate water W30 ( Figure 3 The concentrated water of the reverse osmosis membrane device 303 is circulated to the tank TK via the discharge pipe L35 and the circulation pipe L6. The permeated water (pure water) W31 is sent to the rear stage. By adding acid to the treated water W21, the removal rate of ion components in the reverse osmosis membrane device 303 can be improved.

[0105] Regarding the water quality of the permeate water (pure water) W31 obtained through the reverse osmosis membrane device 303, the boron concentration is 3μg / L~20μg / L, preferably 5μg / L~10μg / L, the carbonic acid concentration is, for example, 0.1mg / L~1mg / L, preferably 0.2mg / L~0.5mg / L, and the electrical conductivity is 0.3μS / cm~40μS / cm, preferably 1μS / cm~20μS / cm, and more preferably 1μS / cm~10μS / cm.

[0106] Afterwards, the permeated water W31 is sequentially supplied to the electrodeionization device (EDI) 221, the ultraviolet oxidation device 222, and the non-regenerative ion exchange resin device 223. In the electrodeionization device 221, the ion components in the permeated water W31 are removed. The desalted water from which the ion components have been removed is sent to the rear section, and the concentrated water in the concentration chamber is discharged out of the system. In the ultraviolet oxidation device 222, the desalted water is irradiated with ultraviolet rays as described above, and the total organic carbon component (TOC) in the desalted water is oxidized and decomposed. The treated water generated by the irradiation with ultraviolet rays is then supplied to the non-regenerative ion exchange resin device 223, and the ion components in the treated water are removed. The resistivity of the treated water generated by the non-regenerative ion exchange resin device 223 can be obtained to be above 18MΩ·cm, and the TOC concentration is reduced to, for example, below 10μgC / L.

[0107] It should be noted that in this variant, the non-regenerative ion exchange resin device (Primary / Polisher) 223 may not be provided. In this case, the ultraviolet oxidation device 222 may be arranged before the electrodeionization device (EDI) 221, and the permeated water W30 may be treated sequentially by the ultraviolet oxidation device 222 and the electrodeionization device (EDI) 221.

[0108] When sulfamic acid is used in the acid adjustment mechanism 205, the concentrated water generated by the reverse osmosis membrane device 303 is circulated to the tank TK of the front section of the reverse osmosis membrane device 201, thereby, the chlorine in the raw water reacts with the sulfamic acid in the concentrated water to produce a bactericidal force, and the effect of suppressing the biofouling in the three-stage reverse osmosis membrane device can be obtained. In particular, the biofouling in the first section of the reverse osmosis membrane where biofouling is most likely to be produced violently can be prevented. Thus, the amount of bactericides usually added to the treated water for sterilization can be reduced, so the environmental load can be reduced. In addition, by adding sulfamic acid, the free chlorine in the treated water that deteriorates the reverse osmosis membrane can be changed into combined chlorine, thereby, it also has the effect of reducing the load of the reverse osmosis membrane. By adding sulfamic acid through the acid adjustment mechanism 205, the two effects of improving the removal rate of weak electrolytes in the reverse osmosis membrane device 202 and suppressing the biofouling in the three-stage reverse osmosis membrane device 303 can be obtained. In the conventional pure water production method, two kinds of acids need to be added to the feed water of the first reverse osmosis membrane and the feed water of the third reverse osmosis membrane. However, in the pure water production apparatus 200 , this can be reduced to adding one kind of acid at the acid adjustment mechanism 205 .

[0109] When aminosulfonic acid is used in the acid adjustment mechanism 205, the amount of aminosulfonic acid added is preferably within a range that can balance the amount of the bactericide reduced and the amount of aminosulfonic acid added and can reduce the total amount of the used agent.

[0110] Next, refer to Figure 6 , an ultrapure water production system 6 using an embodiment of the above-mentioned pure water production apparatus 200 will be described. Figure 6 It is a block diagram schematically showing the configuration of the ultrapure water production system 6 .

[0111] like Figure 6 As shown, the ultrapure water production system 6 sequentially includes a pretreatment device 60, a primary pure water device 61, and a secondary pure water device (subsystem) 62. The secondary pure water device 62 is connected to a point of use (POU) 63 via piping, so that the ultrapure water produced by the ultrapure water production system 6 is supplied to the POU 63.

[0112] The pretreatment device 60 performs coagulation, filtration, membrane separation and other treatments, and adjusts the temperature through a heat exchanger or the like as needed to remove turbid components such as suspended matter and colloidal matter contained in the treated water (raw water). Specifically, the pretreatment device 60 is appropriately combined with an activated carbon device, a coagulation and sedimentation device, a pressurized flotation device, a sand filtration device, a precision filtration device, an ultrafiltration device, a heat exchanger, etc. In addition, the pretreatment device 60 can also be combined with the above-mentioned pretreatment device 210 ( Figure 4 ) or pre-processing device 310 ( Figure 5It should be noted that, when the quality of the raw water is sufficient to be supplied to the primary pure water device 61, the pretreatment device 60 may be omitted.

[0113] The ultrapure water production system 6 includes a tank TK1 after the pretreatment device 60. The treated water pretreated by the pretreatment device 60 is introduced into the tank TK1 and temporarily stored. The treated water in the tank TK1 is supplied to the primary pure water device 61 by a pump P2.

[0114] The primary pure water device 61 removes organic matter, ion components and dissolved gases from pre-treated water to produce primary pure water. The primary pure water device 61 includes a pump P2, the pure water manufacturing device 200 of the above-mentioned embodiment, an electrodeionization device (EDI) 611, an ultraviolet oxidation device (TOC-UV) 612, and a non-regenerative ion exchange resin device (Primary / Polisher) 613. It should be noted that the primary pure water device 61 may also include the pure water manufacturing device 300 of the above-mentioned embodiment or a pure water manufacturing device as a modified example thereof instead of the pure water manufacturing device 200.

[0115] In the primary pure water device 61 , first, hardness components, carbonic acid, and boron in pre-treated water are removed in the pure water production device 200 .

[0116] Next, the treated water is supplied to an electrodeionization device (EDI) 611. The electrodeionization device 611 has, for example, an anion exchange membrane and a cation exchange membrane alternately arranged between an anode and a cathode, and alternately has a desalination chamber separated by the anion exchange membrane and the cation exchange membrane and a concentration chamber into which concentrated water containing ion components to be removed flows. In addition, the electrodeionization device has a mixture of anion exchange resin and cation exchange resin filled in the desalination chamber, and electrodes for applying a DC voltage.

[0117] In the electrodeionization device 611, for example, the treated water is supplied to the desalination chamber and the concentration chamber in parallel, and the mixture of the anion exchange resin and the cation exchange resin in the desalination chamber adsorbs the ion components in the treated water. The adsorbed ion components are transferred to the concentration chamber by the action of the direct current, and the concentrated water in the concentration chamber is discharged to the outside of the system.

[0118] The electrodeionization device 611 can continuously remove ion components without using any chemicals such as acid and alkali for regenerating ion exchange resins, thereby improving safety in ultrapure water production, reducing production costs, miniaturizing the device, etc., and thus improving production efficiency.

[0119] Next, the desalted water generated by the electrodeionization device 611 is supplied to the ultraviolet oxidation device 612. The ultraviolet oxidation device 612 has, for example, an ultraviolet lamp that can irradiate ultraviolet rays having a wavelength of about 185 nm, and by irradiating the treated water with ultraviolet rays from the ultraviolet lamp, the total organic carbon component (TOC) in the treated water is oxidized and decomposed. The ultraviolet lamp used in the ultraviolet oxidation device 612 can use a lamp that generates ultraviolet rays with a wavelength of about 185 nm. As the ultraviolet lamp, a low-pressure mercury lamp that radiates ultraviolet rays with a wavelength of about 254 nm together with ultraviolet rays with a wavelength of about 185 nm can also be used. The ultraviolet rays radiated by the ultraviolet oxidation device 612 decompose water to generate OH radicals, and the organic matter in the treated water is oxidized and decomposed into organic acids by the OH radicals. The amount of ultraviolet irradiation in the ultraviolet oxidation device 612 of the primary pure water device 61 can be appropriately changed according to the water quality of the treated water.

[0120] The treated water of the ultraviolet oxidation device 612 is treated by a non-regenerative ion exchange resin device (Primary / Polisher) 613. The non-regenerative ion exchange resin device 613 mainly removes trace organic acid plasma components generated by decomposing organic matter by the ultraviolet oxidation device 612.

[0121] The primary pure water obtained in this way has, for example, a resistivity of 18 MΩ·cm or more and a TOC concentration of 10 μgC / L or less.

[0122] The ultrapure water production system of this embodiment is provided with a primary pure water tank TK2 for storing primary pure water, a pump P3, and a secondary pure water device 62 in sequence at the rear stage of the primary pure water device 61. The primary pure water produced by the primary pure water device is temporarily stored in the primary pure water tank TK2, and then sent to the secondary pure water device 62 by the pump P3. The secondary pure water device 62 is provided with an ultraviolet oxidation device (TOC-UV) 621, an ion exchange device (Polisher) 622 for non-regenerative ultrapure water production, a membrane degasser (MDG) 623, and an ultrafiltration device (UF) 624.

[0123] The structure of the ultraviolet oxidation device 621 in the secondary pure water device 62 is the same as that of the ultraviolet oxidation device 612 in the primary pure water device 61. The non-regenerative ultrapure water manufacturing ion exchange device 622 is a mixed bed ion exchange resin device formed by mixing and filling a container such as a gas cylinder with a strongly acidic cation exchange resin and a strongly basic anion exchange resin. In addition, the non-regenerative ultrapure water manufacturing ion exchange device 622 does not regenerate the ion exchange resin in the container, and replaces it with another device when the ion exchange capacity decreases. The non-regenerative ultrapure water manufacturing ion exchange device 622 adsorbs and removes the ion components generated by the decomposition of organic matter by the ultraviolet oxidation device 621.

[0124] The membrane degassing device 623 removes dissolved gas via a degassing membrane. The membrane degassing device 623 removes trace dissolved oxygen in the primary pure water, reducing the dissolved oxygen concentration to, for example, about 1 μg / L or less. The ultrafiltration membrane device 624 performs filtration processing through an ultrafiltration membrane to remove trace elutions and particulate components from the ion exchange resin on the upstream side, for example, reducing the number of particles above 0.05 μm to about 250 Pcs. / L or less.

[0125] In the ultrapure water manufacturing system 6 of the present embodiment, an excellent carbonic acid removal rate is achieved in the pure water manufacturing device 200, so the hardness removal mechanism on the front side and the degassing device for removing carbonic acid can be omitted. In addition, on the basis of being able to omit the hardness removal mechanism and the degassing device, the processing load of the pure water manufacturing device 200 is reduced, so the amount of reagents used can be reduced, and the device can be simplified. As a result, pure water can be manufactured efficiently at low cost. Moreover, if the water supply pressure in the three-stage reverse osmosis membrane treatment process in the pure water manufacturing device 200 is set to ultra-low pressure, the number and output of the water supply pump can be reduced, so the device can be further simplified, the pure water manufacturing cost can be reduced, and the manufacturing efficiency can be improved.

[0126] It should be noted that, in each of the above-mentioned embodiments, the water quality of raw water, pretreated water, pure water or ultrapure water can be measured by the following methods or devices, respectively.

[0127] pH: electrode method.

[0128] Boron concentration: ICP (high frequency inductively coupled plasma) emission spectrometry or ICP-MS (inductively coupled plasma mass spectrometry) method.

[0129] Hardness component: ICP-MS method.

[0130] Dissolved carbon dioxide gas (calcium carbonate equivalent): Sievers M9e manufactured by SUEZ Corporation.

[0131] Silicon dioxide (Si): atomic absorption spectrophotometry / absorption spectrophotometry.

[0132] Chlorine (Cl conversion): DPD (diethyl-p-phenylenediamine) method.

[0133] Conductivity: Conductivity meter (HE-960CW manufactured by Horiba, Ltd.).

[0134] Resistivity (specific resistance): resistivity meter (HE-960RW manufactured by Horiba, Ltd.).

[0135] Total organic carbon (TOC) concentration: TOC meter (other than ultrapure water: Sievers M9e manufactured by SUEZ, ultrapure water: Anatel A-1000XP manufactured by BECKMAN COULTER).

[0136] Number of particles of 0.05 μm or larger: Particle counter (UDI-50 manufactured by Particle Measuring Systems).

[0137] Example

[0138] Next, examples will be described. The present invention is not limited to the following examples.

[0139] (Example 1)

[0140] use Figure 7 The pure water production system 7 shown produces pure water. Figure 7 The pure water production system 7 shown is a Figure 5 The pretreatment device 310 shown in the figure is combined with the pure water production device 300. The city tap water of Atsugi City is treated with activated carbon and then supplied to the pretreatment device 310. The pretreated water W1 (raw water with pH = 7.2, boron concentration of 150 ppb, and carbonic acid concentration of 30 ppm) generated by the pretreatment device 310 is subjected to reverse osmosis membrane treatment in sequence through the reverse osmosis membrane devices 201, 202, and 303. Sodium hydroxide aqueous solution is added to the supply water of the reverse osmosis membrane device 202 by the alkali adjustment mechanism 204 so that the pH of the supply water becomes 9.5. The concentrated water of the reverse osmosis membrane devices 202 and 303 is refluxed to the tank TK.

[0141] (Example 2)

[0142] use Figure 7 The pure water production system 7 shown in the figure produces pure water. Pre-treated water (raw water with pH = 7.2, boron concentration of 50 ppb, and carbonic acid concentration of 15 ppm) is produced by the pre-treatment device 310, and the obtained pre-treated water is sequentially subjected to reverse osmosis membrane treatment by the reverse osmosis membrane devices 201, 202, and 303. Sodium hydroxide aqueous solution is added to the feed water of the reverse osmosis membrane device 202 by the alkali adjustment mechanism 204 so that the pH of the feed water becomes 9.5. The concentrated water of the reverse osmosis membrane devices 202 and 303 is refluxed to the tank TK.

[0143] (Example 3)

[0144] Pretreated water W1 was obtained in the same manner as in Example 1, and reverse osmosis membrane treatment was sequentially performed on the pretreated water W1 by reverse osmosis membrane devices 201, 202, and 303. Sodium hydroxide aqueous solution was added to the feed water of the reverse osmosis membrane device 202 by the alkali adjustment mechanism 204 so that the pH of the feed water was changed to 9.0. Aminosulfonic acid aqueous solution was added to the feed water of the reverse osmosis membrane device 303 so that the pH of the feed water was changed to 6.5. The concentrated water of the reverse osmosis membrane devices 202 and 303 was refluxed to the tank TK.

[0145] (Comparative Example 1)

[0146] Pre-treated water W1 was obtained in the same manner as in Example 1 and passed through a two-stage reverse osmosis membrane device (equivalent to Figure 7 The reverse osmosis membrane devices 201 and 202 of the second stage reverse osmosis membrane device are used to perform reverse osmosis membrane treatment on the pretreated water W1 in sequence. Sodium hydroxide aqueous solution is added to the feed water of the second stage reverse osmosis membrane device so that the pH of the feed water becomes 9.5. The concentrated water of the second stage reverse osmosis membrane device is refluxed to the tank TK in the same manner as in Example 1.

[0147] (Comparative Example 2)

[0148] Pre-treated water W1 was obtained in the same manner as in Example 1 and passed through a three-stage reverse osmosis membrane device (equivalent to Figure 7 The reverse osmosis membrane devices 201, 202, and 303 of the first stage reverse osmosis membrane device sequentially perform reverse osmosis membrane treatment on the pretreated water W1. Sulfuric acid is added to the feed water of the first stage reverse osmosis membrane device so that the pH of the feed water becomes 6.0. In addition, an aqueous sodium hydroxide solution is added to the feed water of the second stage reverse osmosis membrane device so that the pH of the feed water becomes 9.0. An aqueous sulfamic acid solution is added to the feed water of the third stage reverse osmosis membrane device so that the pH of the feed water becomes 4.7. The concentrated water of the second stage reverse osmosis membrane device and the third stage reverse osmosis membrane device is refluxed to the tank TK in the same manner as in Example 1.

[0149] (Comparative Example 3)

[0150] Pretreated water W1 was obtained in the same manner as in Example 1. After adding acid to the pretreated water W1, it was treated in a degassing tower (not shown) to obtain degassed water. The degassed water was used as raw water and passed through a three-stage reverse osmosis membrane device (equivalent to Figure 7 The reverse osmosis membrane treatment was performed in sequence by the reverse osmosis membrane devices 201, 202, and 303. A sodium hydroxide aqueous solution was added to the feed water of the second reverse osmosis membrane device so that the pH of the feed water became 9.0. Furthermore, sulfuric acid was added to the feed water of the third reverse osmosis membrane device so that the pH of the feed water became 4.7. The concentrated water of the second reverse osmosis membrane device and the third reverse osmosis membrane device was refluxed to the tank TK in the same manner as in Example 1.

[0151] In the above-described Examples and Comparative Examples, the discharge pressure of the pump P1 was set to 1.6 MPa, and TBW-HR (manufactured by Toray Industries, Inc.), which is an ultra-low pressure type reverse osmosis membrane, was used as the reverse osmosis membrane device.

[0152] (Comparative Example 4)

[0153] Pretreated water W1 was obtained in the same manner as in Example 1, and reverse osmosis membrane treatment was performed on the pretreated water W1 using a high-pressure reverse osmosis membrane device. In the comparative example, the discharge pressure of the pump P1 was set to 1.6 MPa, and TM820K-400 (manufactured by Toray Industries, Ltd.) as a high-pressure reverse osmosis membrane was used as the reverse osmosis membrane device.

[0154] The quality of pretreated water in the above-mentioned embodiments and comparative examples, the quality of water supplied to the reverse osmosis membrane device 202 (second-stage reverse osmosis membrane device), the quality of water supplied to the reverse osmosis membrane device 303 (third-stage reverse osmosis membrane device), and the quality of treated water in each example (the quality of permeated water in the final-stage reverse osmosis membrane device) were measured. The results are shown in Table 1. In addition, the removal rate of each component in the embodiments and comparative examples and the total amount of reagents (sodium hydroxide, aminosulfonic acid, sulfuric acid) used were measured. Regarding the amount of reagents used, in Example 1, the amount used (g) was calculated as 1. It should be noted that the amount of reagents used varies greatly depending on the operating conditions, so it is expressed as an approximate estimate based on the results of 100 days of operation. The results are shown in Table 2. In Tables 1 and 2, "DG" refers to a degassing tower, and "RO2" refers to a second-stage reverse osmosis membrane device (equivalent to Figure 7 RO3 refers to the third reverse osmosis membrane device (equivalent to Figure 7 Reverse osmosis membrane device 303).

[0155] In the examples and comparative examples, each water quality was measured by the following apparatuses or methods.

[0156] pH: HP-200 manufactured by Horiba, Ltd.

[0157] Boron concentration: ICP (high frequency inductively coupled plasma) emission spectrometry.

[0158] Carbonic acid concentration: Sievers M9e manufactured by SUEZ Corporation.

[0159] [Table 1]

[0160]

[0161]

[0162] [Table 2]

[0163]

[0164] As shown in Table 1 and Table 2, in the pure water production methods of Examples 1 to 3, pure water with a sufficiently reduced boron concentration and appropriate water quality was obtained. In the method of Comparative Example 1, since the reverse osmosis membrane is only two stages, the sufficient reduction in boron concentration cannot be achieved. In the method of Comparative Example 2, although pure water with high water quality can be obtained, the conductivity is too low, the water quality is excessive, and the amount of chemicals used increases. In addition, in the method of Comparative Example 2, no degassing treatment is performed in the front stage, so the carbonic acid concentration of the treated water is also slightly high. The method of Comparative Example 3 can also obtain pure water with high water quality, but the conductivity is too low and the water quality is excessive. In addition, the method of Comparative Example 3 performs treatment using a degassing tower in the front stage, so there are problems of increased use of chemicals and large-scale equipment. In the method of Comparative Example 4, a high-pressure reverse osmosis membrane is used, and the power consumption is the same as that of Example 1, but a sufficient reduction in boron concentration cannot be achieved.

[0165] In addition, the carbonic acid concentration, boron concentration and conductivity of the pretreated water, the feed water and the treated water of each stage of the reverse osmosis membrane device of Example 1 and Comparative Example 3 are shown in Figure 8 to Figure 10 . Figure 8 Express the carbonic acid concentration in logarithm, Fig. 9 represents the boron concentration, Fig.10 represents the conductivity. In addition, Figure 8 to Figure 10 In the figure, “RO1” refers to the first reverse osmosis membrane device.

[0166] like Figure 8 As shown, in the method of Example 1, carbonic acid is removed in the first stage reverse osmosis membrane device and the second stage reverse osmosis membrane device. In contrast, in the method of Comparative Example 3, carbonic acid is removed in the degassing tower, and the treated water (degassed water) from which carbonic acid is removed is supplied to the first stage reverse osmosis membrane device, thereby obtaining treated water with high conductivity (conductivity 0.125 μS / cm).

[0167] In addition, if Fig. 9 As shown, in the method of Example 1, most of the boron is removed in the second reverse osmosis membrane device, and part of the boron is removed in the third reverse osmosis membrane device. In contrast, in the method of Comparative Example 3, most of the boron is removed in the second reverse osmosis membrane.

[0168] Moreover, if Fig.10 As shown, in the method of Example 1, the conductive components (ion components, etc.) are removed through the first stage reverse osmosis membrane device to the third stage reverse osmosis membrane device. In contrast, in the method of Comparative Example 3, most of the conductive components (ion components, etc.) are removed in the degassing tower and the first stage reverse osmosis membrane device.

[0169] As can be seen from the above, the method of Example 1 and the method of Comparative Example 3 share the same three-stage reverse osmosis membrane device and part of the reagents used, but the effects of the reverse osmosis membrane devices are different.

[0170] Description of Reference Numerals

[0171] 100, 110, 120: pure water production method; 101, 103, 104, 122: reverse osmosis membrane treatment process; 102: alkali adjustment process; 111: electrodeionization treatment process; 112: ultraviolet oxidation treatment process; 113: non-regenerative ion exchange resin (primary / polisher) treatment process; 121: acid adjustment process; W10, W20: permeated water; W30, W31: permeated water (pure water); W11, W21: treated water; W40: desalted water; W41, W42: treated water; 200, 300: pure water production device; 210, 310: pretreatment device ; 211: activated carbon device (AC); TK: storage tank; 212: heat exchanger (HEX); 213: precision filtration device (PF); 221, 611: electrodeionization device (EDI); 222, 612: ultraviolet oxidation device (TOC-UV); 223, 613: non-regenerative ion exchange resin device (Primary / Polisher); 201, 202, 203, 303: reverse osmosis membrane device; 204: alkali adjustment mechanism; 205: acid adjustment mechanism; 4, 5, 6: pure water manufacturing system; L1, L2: supply pipe; L3~L5: discharge pipe; L6: circulation piping.

Claims

1. A method for producing pure water, It is characterized in that This is a method for producing pure water by treating raw water with at least three stages of ultra-low pressure reverse osmosis membrane devices to remove boron from raw water. The reverse osmosis membranes of the three-stage reverse osmosis membrane device are all negatively charged membranes having a skin layer formed of cross-linked aromatic polyamide. The raw water contains carbonic acid in an amount of 1 mg / L or more and 100 mg / L or less, and boron in an amount of 150 μg / L or less. The pure water production method comprises the following steps: The step of treating the raw water by a first-stage reverse osmosis membrane device to obtain first permeated water; The step of adjusting the first permeated water to be alkaline to obtain alkaline treated water; The step of treating the alkaline treated water by a second reverse osmosis membrane device to obtain second permeate water; as well as The step of treating the second permeated water with a third-stage reverse osmosis membrane device to obtain pure water having a boron concentration of 3 μg / L to 20 μg / L and an electrical conductivity of 0.3 μS / cm to 40 μS / cm.

2. The method for producing pure water according to claim 1, in, The pH of the alkaline water to be treated is 9.0 or more and 10.0 or less.

3. The method for producing pure water according to claim 1 or 2, in, The pure water production method further comprises a step of adding an acid to the second permeated water to obtain second treated water, and the second treated water is treated by a third-stage reverse osmosis membrane device.

4. The method for producing pure water according to claim 3, in, The raw water contains chlorine, In the step of obtaining the second treated water, aminosulfonic acid is added to the second permeated water. The concentrated water from the third-stage reverse osmosis membrane device is mixed with the raw water and processed by the first-stage reverse osmosis membrane device.

5. The method for producing pure water according to claim 3, in, The pH of the second treated water is 5.5 or more and 7.5 or less.

6. The method for producing pure water according to claim 1 or 2, in, The pure water obtained as permeate water of the third-stage reverse osmosis membrane device is further treated by an electrodeionization device.

7. A pure water production device, It is characterized in that A pure water production device for removing boron, comprising a first reverse osmosis membrane device, a second reverse osmosis membrane device and a third reverse osmosis membrane device connected in series, The first reverse osmosis membrane device, the second reverse osmosis membrane device and the third reverse osmosis membrane device are ultra-low pressure reverse osmosis membrane devices. The reverse osmosis membranes of the first reverse osmosis membrane device, the second reverse osmosis membrane device, and the third reverse osmosis membrane device are negatively charged membranes having a skin layer formed of cross-linked aromatic polyamide. The pure water production device comprises: a raw water supply mechanism for supplying raw water containing 1 mg / L or more and 100 mg / L or less of carbonic acid and 150 μg / L or less of boron to the first reverse osmosis membrane device; a first supply pipe for delivering permeate water from the first reverse osmosis membrane device to the second reverse osmosis membrane device; an alkali adjustment mechanism provided in the path of the first supply pipe, the alkali adjustment mechanism adjusting the water to be treated flowing in the first supply pipe to be alkaline; as well as a second supply pipe for delivering the permeated water of the second reverse osmosis membrane device to the third reverse osmosis membrane device; As permeate water of the third reverse osmosis membrane device, pure water having a boron concentration of 3 μg / L to 20 μg / L and an electrical conductivity of 0.3 μS / cm to 40 μS / cm was obtained.

8. The pure water production device according to claim 7, in, An electrodeionization device is provided at the rear section of the third reverse osmosis membrane device.

9. An ultrapure water production system, which is an ultrapure water production system comprising a primary pure water device and a secondary pure water device in sequence, The primary pure water device comprises the pure water production device according to claim 7 or 8 and an electrodeionization device arranged at a subsequent stage of the pure water production device. The secondary pure water device is equipped with an ultraviolet oxidation device, a non-regenerative ion exchange device for producing ultrapure water, a membrane degassing device and an ultrafiltration device in sequence. The ultrapure water production system produces ultrapure water having a boron concentration of 0.1 μg / L or less.

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