Boron-removed pure water production method, pure water production device, and ultrapure water production system

Abstract

The invention provides a pure water manufacturing device and a pure water manufacturing method, which can stably and efficiently manufacture pure water for a long time by inhibiting scale clogging of a reverse osmosis membrane. A pure water production method for obtaining boron-removed pure water by sequentially passing raw water through two or more stages of reverse osmosis membranes, the pure water production method comprising, in a prescribed order: an alkali treatment step for passing alkaline water to be treated through a first stage of reverse osmosis membrane; and an acid treatment step in which the acidic water to be treated is passed through the other stage of reverse osmosis membrane and the first reverse osmosis membrane and the second reverse osmosis membrane are exchanged, and the following treatment periods are repeated at predetermined intervals: a first treatment period in which the first reverse osmosis membrane is used in the alkali treatment step and the second reverse osmosis membrane is used in the acid treatment step; and during the second treatment, the second reverse osmosis membrane is used in the alkali treatment step, and the first reverse osmosis membrane is used in the acid treatment step.

Description

Technical Field

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS)

[0002] This application claims the priority of Japanese Patent Application No. 2022-160066, filed on October 4, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present invention relates to a method for producing pure water from which boron has been removed, a pure water production device, and an ultrapure water production system using the pure water production device. Background Art

[0005] As a method for producing pure water by treating raw water containing boron, there is known a method for producing pure water in which an alkali is added to raw water to adjust the pH to 9.2 or higher and then a reverse osmosis membrane treatment is performed. In this method, an acid is added to the permeated water from which boron has been removed and then a reverse osmosis membrane treatment is performed to increase the resistivity of the treated water (for example, see Patent Documents 1 and 2).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 11-128921

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 11-128922 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] Although the boron removal rate is improved by increasing the pH of water to 10 or more, the higher the pH, the more easily scale clogging will occur in the reverse osmosis membrane due to hardness such as calcium and magnesium. Therefore, in the conventional method of producing pure water with boron removed, a hardness removal mechanism and a degassing device with high decarbonation function are provided in the front stage to suppress scale clogging. In contrast, when the pH of the feed water of the reverse osmosis membrane is adjusted to 5 or less, although the generation of hardness scale is suppressed, silica scale is easily generated.

[0012] When hardness scale clogging occurs, the scale is cleaned by passing an acidic cleaning agent with a pH of about 1 to 3 through the reverse osmosis membrane. When silica scale clogging occurs, the scale is cleaned by passing an alkaline cleaning agent with a pH of about 11.5 to 13 through the reverse osmosis membrane.

[0013] In either case of hardness scale clogging or silica scale clogging, it is difficult to completely prevent scale clogging, and scale clogging may occur during short-term operation depending on the quality of raw water and operating conditions. When scale clogging progresses, the device has to be stopped for backwashing or cleaning of the reverse osmosis membrane, installation of cleaning equipment, and membrane replacement, and the efficiency of pure water production decreases. Therefore, for example, it is necessary to avoid cleaning the reverse osmosis membrane as much as possible and continue to operate for a period of six months to more than one year. For example, when it is difficult to continue to operate due to a significant decrease in the permeate flow rate or a significant increase in the pressure difference between the supply side and the permeate side, cleaning is mostly required. However, in such an operating method, solid crystals of scale components sometimes grow on the surface of the reverse osmosis membrane when it is difficult to continue to operate, and during the crystal growth period, the physical properties of the membrane surface change and deteriorate.

[0014] When such hard scale is formed on the surface of the reverse osmosis membrane, the reverse osmosis membrane is easily deteriorated by the chemical due to long-term cleaning using a high-concentration chemical. In addition, even if cleaning is performed, the deterioration of the membrane surface caused by crystal growth during water flow will not be restored, so it is inevitable that the quality of the water treated by the reverse osmosis membrane after cleaning will deteriorate.

[0015] In order to prevent the formation of hard scale, frequent repeated cleaning may be required. However, this method is not only necessary to stop the operation frequently, but also causes excessive drainage due to repeated cleaning, and it is difficult to reuse the drainage, so it is not practical. That is, from the perspective of suppressing the degradation of the reverse osmosis membrane and reducing the amount of reagents used, a method for producing pure water with a high water recovery rate without cleaning the scale and stopping the pure water production device is also desired.

[0016] The present invention has been made to solve the above-mentioned problems, and its object is to provide a pure water production device and a pure water production method which can produce pure water stably and efficiently for a long period of time without cleaning the reverse osmosis membrane by suppressing scale clogging of the reverse osmosis membrane.

[0017] Technical Solution

[0018] The pure water production method of the embodiment is characterized in that raw water is passed through two or more reverse osmosis membranes in sequence to obtain pure water with boron removed. In the pure water production method, the following processes are performed in a prescribed order: an alkali treatment process, in which alkaline treated water is passed through one reverse osmosis membrane among the reverse osmosis membranes; and an acid treatment process, in which acidic treated water is passed through another reverse osmosis membrane among the reverse osmosis membranes, and the first reverse osmosis membrane and the second reverse osmosis membrane are replaced, thereby repeating the following treatment periods at prescribed intervals: during the first treatment period, the first reverse osmosis membrane is used in the alkali treatment process, and the second reverse osmosis membrane is used in the acid treatment process; and during the second treatment period, the second reverse osmosis membrane is used in the alkali treatment process, and the first reverse osmosis membrane is used in the acid treatment process.

[0019] Preferably, in the pure water production method of the embodiment, during the first treatment, alkaline treated water is passed through the first reverse osmosis membrane to perform an alkali treatment process, the permeate water of the first reverse osmosis membrane is adjusted to acidity, and the generated acidic treated water is passed through the second reverse osmosis membrane to perform the acid treatment process, and during the second treatment, alkaline treated water is passed through the second reverse osmosis membrane to perform an alkali treatment process, the permeate water of the second reverse osmosis membrane is adjusted to acidity, and the generated acidic treated water is passed through the first reverse osmosis membrane to perform the acid treatment process, the pH of the alkaline treated water is greater than 9.0 and less than 11.0, and the pH of the acidic treated water is less than 5.0.

[0020] Preferably, the pure water production method of the embodiment further comprises a step of passing raw water having a pH of 5.0 to 7.5 through a third reverse osmosis membrane before the alkali treatment step.

[0021] Preferably, in the pure water production method of the embodiment, during the first treatment, the acidic treated water is passed through the second reverse osmosis membrane to perform the acid treatment process, the permeate water of the second reverse osmosis membrane is adjusted to alkaline, and the generated alkaline treated water is passed through the first reverse osmosis membrane to perform the alkali treatment process, and during the second treatment, the acidic treated water is passed through the first reverse osmosis membrane to perform the acid treatment process, the permeate water of the first reverse osmosis membrane is adjusted to alkaline, and the generated alkaline treated water is passed through the second reverse osmosis membrane to perform the alkali treatment process, the pH of the alkaline treated water is greater than 9.0 and less than 11.0, and the pH of the acidic treated water is greater than 5.0 and less than 6.0.

[0022] The pure water manufacturing device of the embodiment is characterized in that it has two or more reverse osmosis membrane devices connected in series to manufacture pure water with boron removed, and the pure water manufacturing device has: a raw water supply pipe for supplying raw water; a first reverse osmosis membrane device and a second reverse osmosis membrane device; a first adjustment mechanism for adjusting the treated water to alkalinity or acidity; a second adjustment mechanism for adjusting the treated water to a liquid property different from that of the first adjustment mechanism, one of acidity and alkalinity; a first treatment path for causing the raw water to flow through the first adjustment mechanism, the first reverse osmosis membrane device, the second adjustment mechanism, and the second reverse osmosis membrane device in sequence; a second treatment path for causing the raw water to flow through the first adjustment mechanism, the second reverse osmosis membrane device, the second adjustment mechanism, and the first reverse osmosis membrane device in sequence; a switching mechanism for switching between the first treatment path and the second treatment path; and a control mechanism for controlling the switching mechanism to switch between the first treatment path and the second treatment path after each specified treatment period.

[0023] Preferably, in the pure water production apparatus of the embodiment, the first adjustment mechanism is an alkali adjustment mechanism that adjusts raw water to be alkaline, and the second adjustment mechanism is an acid adjustment mechanism that adjusts treated water to be acidic.

[0024] Preferably, in the pure water manufacturing device of the embodiment, the first treatment path comprises: a first supply pipe for supplying raw water to the supply side of the first reverse osmosis membrane device; a second supply pipe for supplying permeated water of the first reverse osmosis membrane device to the second adjustment mechanism; a third supply pipe for supplying treated water that has passed through the second adjustment mechanism to the supply side of the second reverse osmosis membrane device; a fourth supply pipe for conveying the permeated water of the second reverse osmosis membrane device to the rear section; and four switching valves respectively mounted on the first supply pipe to the fourth supply pipe, wherein the first adjustment mechanism is arranged on the upstream side of the switching valve of the first supply pipe, and the second treatment The path includes: a fifth supply pipe, which supplies raw water to the supply side of the second reverse osmosis membrane device; a sixth supply pipe, which supplies permeate water of the second reverse osmosis membrane device to the second adjustment mechanism; a seventh supply pipe, which supplies treated water that has passed through the second adjustment mechanism to the supply side of the first reverse osmosis membrane device; an eighth supply pipe, which transports permeate water of the first reverse osmosis membrane device to the rear section; and four switching valves, which are respectively clamped on the fifth supply pipe to the eighth supply pipe, wherein the first adjustment mechanism is arranged on the upstream side of the switching valve of the sixth supply pipe, and the control mechanism controls the eight switching valves to switch the first treatment path and the second treatment path.

[0025] Preferably, in the pure water production apparatus of the embodiment, the first adjustment mechanism is an acid adjustment mechanism that adjusts raw water to be weakly acidic, and the second adjustment mechanism is an alkali adjustment mechanism that adjusts treated water to be alkaline.

[0026] The ultrapure water production system of the embodiment is an ultrapure water production system that sequentially comprises a primary pure water system and a secondary pure water system, and the ultrapure water production system is characterized in that the primary pure water system comprises a pure water production device of the embodiment, and an ultraviolet oxidation device and an electric deionization device at its subsequent stage, and the secondary pure water system sequentially comprises an ultraviolet oxidation device, a non-regenerative ion exchange device for producing ultrapure water, a membrane degassing device and an ultrafiltration device, and 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 apparatus and pure water production method of the present invention, by suppressing scale clogging of the reverse osmosis membrane for a long period of time, pure water can be produced stably and efficiently for a long period of time without cleaning the reverse osmosis membrane.

[0030] According to the pure water production system of the present invention, by suppressing scale clogging of the reverse osmosis membrane provided on the front stage side of the ultrapure water production system for a long period of time, ultrapure water can be produced stably and efficiently for a long period of time without cleaning the reverse osmosis membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a block diagram schematically showing the pure water production method according to the first embodiment.

[0032] Figure 2 This is a block diagram schematically showing the pure water production method according to the second embodiment.

[0033] Figure 3 It is a block diagram schematically showing a pure water production apparatus according to a third embodiment.

[0034] Figure 4 It is a block diagram schematically showing a pure water production apparatus according to a first modified example of the third embodiment.

[0035] Figure 5 It is a block diagram schematically showing a pure water production apparatus according to a fourth embodiment.

[0036] Figure 6 It is a diagram for explaining a first processing path in the pure water production apparatus according to the fourth embodiment.

[0037] Figure 7 It is a diagram for explaining a second processing path in the pure water production apparatus according to the fourth embodiment.

[0038] Figure 8 It is a diagram schematically showing a processing path in the first processing period when a four-way valve is used.

[0039] Fig. 9 It is a diagram schematically showing a processing path in the second processing period when a four-way valve is used.

[0040] Fig.10 It is a block diagram schematically showing a pure water production apparatus according to a first modified example of the fourth embodiment.

[0041] Fig.11 It is a diagram schematically showing the arrangement of the fourth reverse osmosis membrane device when a four-way valve is used.

[0042] Fig.12 This is a block diagram schematically showing the configuration of the ultrapure water production system according to the embodiment.

[0043] Fig.13 This is a graph showing the relationship between the pH of water to be treated by the reverse osmosis membrane device, the boron removal rate, and the resistivity of the treated water.

[0044] Fig.14 This is a graph showing the relationship between the pH of water to be treated and the resistivity of the treated water in a reverse osmosis membrane device.

[0045] Fig.15 This is a graph showing changes in water flow time and permeate flow rate when the pH of the water to be treated in the reverse osmosis membrane device is adjusted to 9, 10.5, and 11.

[0046] Fig.16 This is a graph showing changes in the permeate flow rate immediately after the treatment of the reverse osmosis membrane device was started after the pH of the water to be treated was adjusted to 3, 4, and 6.

[0047] Fig.17 This is a graph showing changes in the treated water flow rate when two reverse osmosis membrane devices are replaced before and after every 90 days.

[0048] Fig.18 It means in Fig.17 A graph showing changes in permeate quality of the second and third stage reverse osmosis membrane devices under the operating conditions shown. DETAILED DESCRIPTION

[0049] The following is an explanation of an embodiment of the present invention. The pure water production method of the present embodiment is a method for producing pure water for use in the electronic industry such as semiconductor manufacturing and medical water. The pure water production method of the present embodiment is a method for producing pure water from which boron has been removed by passing raw water through two or more reverse osmosis membranes in sequence, and comprises: an alkali treatment process, in which alkaline treated water passes through one reverse osmosis membrane; and an acid treatment process, in which acidic treated water passes through another reverse osmosis membrane. The alkali treatment process and the acid treatment process are performed in a prescribed order, and the acid treatment process may be performed after the alkali treatment process, or after the acid treatment process. In the pure water production method of the present embodiment, it is characterized in that the first reverse osmosis membrane and the second reverse osmosis membrane are replaced, so that the following treatment periods are repeated at prescribed intervals: during the first treatment period, the first reverse osmosis membrane is used in the alkali treatment process, and the second reverse osmosis membrane is used in the acid treatment process; and during the second treatment period, the second reverse osmosis membrane is used in the alkali treatment process, and the first reverse osmosis membrane is used in the acid treatment process. The order of the alkali treatment process and the acid treatment process in the first treatment period and the second treatment period is set to be the same. The following uses a specific example to describe the method in detail.

[0050] Figure 1 FIG. 1 is a block diagram schematically showing the method for producing pure water according to the first embodiment. Figure 1 As shown, the pure water production method of the first embodiment includes: step 101, performing reverse osmosis membrane treatment on raw water to remove hardness components; step 102, adjusting the treated water from which the hardness components have been removed to alkalinity, and then performing reverse osmosis membrane treatment to remove boron; and step 103, adjusting the treated water from which the boron has been removed to acidity, and then performing reverse osmosis membrane treatment to remove ion components.

[0051] exist Figure 1 In the pure water manufacturing method of the first embodiment shown, process 102 is equivalent to an alkali treatment process, and process 103 is equivalent to an acid treatment process. In terms of improving the removal rate of boron, the pH of the alkaline treated water in process 102 is 9.0 or more and 11.0 or less, more preferably 9.2 or more and 10.5 or less. In terms of improving the removal rate of ion components, the pH of the acidic treated water in process 103 is preferably 5.0 or less, more preferably 4.5 or less, and preferably 2.0 or more, more preferably 3.0 or more. That is, the pH is preferably 2.0 or more and 5.0 or less, more preferably 3.0 or more and 4.5 or less. It should be noted that between process 102 and process 103 and between process 202 and process 203 or after two processes, in order to remove ion components, a process of passing water to one or more reverse osmosis membranes may also be provided. As needed, a booster pump, a degasser, and a tank may be provided between each reverse osmosis membrane.

[0052] In the pure water production method of the present embodiment, after the hardness component removal step 101, the boron removal step 102, and the ion component removal step 103 are sequentially continued for a predetermined period, the reverse osmosis membrane device (first reverse osmosis membrane device (first RO)) used in the boron removal step 102 and the reverse osmosis membrane device (second reverse osmosis membrane device (second RO)) used in the ion component removal step 103 are replaced, and the boron removal step 202 is performed by the second reverse osmosis membrane device, and the ion component removal step 203 is performed by the first reverse osmosis membrane device. Then, the treatment period 100 (first treatment period) and the treatment period 200 (second treatment period) are alternately repeated every predetermined period, and the treatment period 100 (first treatment period) is sequentially performed for the hardness component removal step 101, the boron removal step 102, and the ion component removal step 103, and the treatment period 200 (second treatment period) is sequentially performed for the hardness component removal step 101, the boron removal step 202, and the ion component removal step 203. The exchange of the first reverse osmosis membrane device and the second reverse osmosis membrane device is realized by combining valves and piping in a manner that can switch the flow path of the treated water. In addition, instead of setting piping for flow path switching, it can also be realized by extracting two reverse osmosis membranes or even reverse osmosis membrane modules and exchanging their positions.

[0053] In the pure water production method of the present embodiment, during the treatment period 100, the hardness component is removed in the process 101, but depending on the water quality and the operation period, the hardness component will leak into the permeated water of the reverse osmosis membrane device. In the first reverse osmosis membrane device, alkaline treated water is treated, so when the treated water contains hardness components, hardness scale clogging is easy to progress. In addition, in the second reverse osmosis membrane device that treats acidic treated water, scale clogging caused by silica is easy to progress. Therefore, before the scale clogging of the first reverse osmosis membrane device and the second reverse osmosis membrane device deteriorates the water recovery rate, the first reverse osmosis membrane device and the second reverse osmosis membrane device are replaced to perform the treatment period 200. During the treatment period 200, the first reverse osmosis membrane device treats the treated water adjusted to acidity in the process 203, and in this process, the hardness component is dissolved by the acid and the scale clogging is improved. In addition, in the second reverse osmosis membrane device where scale clogging due to silica is progressing, in step 202, by treating the treated water adjusted to be alkaline, the silica scale is dissolved by the alkali, and the scale clogging is improved. In the treatment period 200, the hardness scale clogging of the second reverse osmosis membrane device that occurred in step 202 and the silica scale clogging of the first reverse osmosis membrane device that occurred in step 203 progress, but by replacing the first reverse osmosis membrane device and the second reverse osmosis membrane device again before the water recovery rate decreases, the treatment period 100 is performed, and the scale clogging of the first reverse osmosis membrane device and the second reverse osmosis membrane device is improved in the same manner as in the treatment period 200. As a result, the progress of scale clogging in the first reverse osmosis membrane device and the second reverse osmosis membrane device can be suppressed for a long time, so that pure water can be produced stably and efficiently for a long time. Moreover, the acid conditions and alkaline conditions used in step 102 (step 202) and step 103 (step 203) are milder acid / alkaline conditions than ordinary scale cleaning agents, and therefore can also inhibit the deterioration of the reverse osmosis membrane. As a result, high-quality pure water can be produced stably for a long time.

[0054] Figure 2 FIG. 2 is a block diagram schematically showing a method for producing pure water according to a second embodiment. Figure 2 As shown, the pure water production method of the second embodiment includes: step 301, after adjusting the raw water to weak acidity, performing reverse osmosis membrane treatment to remove hardness components; step 302, after adjusting the treated water from which the hardness components have been removed to alkalinity, performing reverse osmosis membrane treatment to remove boron; and step 303, after adjusting the treated water from which the boron has been removed to acidity, performing reverse osmosis membrane treatment to remove ion components.

[0055] exist Figure 2In the pure water production method of the second embodiment shown, step 302 is equivalent to the alkali treatment step, and step 301 is equivalent to the acid treatment step. In terms of improving the removal rate of hardness components, the pH of the acidic treated water in step 301 is preferably above 5 and below 6. In terms of improving the removal rate of boron, the pH of the alkaline treated water in step 302 is above 9.0 and below 11.0, and more preferably above 9.2 and below 10.5. It should be noted that between step 302 and step 30 and between step 402 and step 403 or thereafter, in order to remove ion components, a step of passing water through one or more reverse osmosis membranes may also be provided. As needed, a booster pump, a degassing device, and a tank may be provided between each reverse osmosis membrane.

[0056] In the pure water production method of the present embodiment, after the hardness component removal step 301, the boron removal step 302, and the ion component removal step 303 are sequentially continued for a predetermined period, the reverse osmosis membrane device (third reverse osmosis membrane device (third RO)) used in the hardness component removal step 301 and the reverse osmosis membrane device (first reverse osmosis membrane device) used in the boron removal step 302 are replaced, and the hardness component removal step 401 is performed using the first reverse osmosis membrane device, and the boron removal step 402 is performed using the third reverse osmosis membrane device. Then, the treatment period 300 (first treatment period) and the treatment period 400 (second treatment period) are alternately repeated every predetermined period, and the treatment period 300 (first treatment period) is sequentially performed for the hardness component removal step 301, the boron removal step 302, and the ion component removal step 303, and the treatment period 400 (second treatment period) is sequentially performed for the hardness component removal step 401, the boron removal step 402, and the ion component removal step 303. The exchange of the first reverse osmosis membrane device and the third reverse osmosis membrane device is realized by combining valves and piping in a manner that can switch the flow path of the treated water. In this case, instead of setting piping for flow path switching, it can also be realized by extracting two reverse osmosis membranes or even reverse osmosis membrane modules and exchanging their positions.

[0057] In the pure water production method of this embodiment, during the treatment period 300, the hardness component is removed in the process 301, but depending on the water quality and the operation period, the hardness component will leak into the permeated water of the third reverse osmosis membrane device, and the scale clogging of the first reverse osmosis membrane device in the later stage will progress. In addition, in the third reverse osmosis membrane device that treats weakly acidic treated water, the scale clogging caused by silica is easy to progress. Therefore, before the scale clogging of the first reverse osmosis membrane device and the third reverse osmosis membrane device deteriorates the water recovery rate, the first reverse osmosis membrane device and the third reverse osmosis membrane device are replaced to perform the treatment period 400. During the treatment period 400, the first reverse osmosis membrane device treats the treated water adjusted to weak acidity in the process 401, and in this process, the hardness scale is dissolved by the acid, and the scale clogging is improved. In addition, the third reverse osmosis membrane device where the scale clogging caused by silica progresses is treated by treating the treated water adjusted to alkaline in the process 402, and the silica scale is dissolved by the alkali, and the scale clogging is improved. In the treatment period 400, the hardness scale clogging of the third reverse osmosis membrane device in the process 402 and the silica scale clogging of the first reverse osmosis membrane device in the process 401 progress, but by replacing the first reverse osmosis membrane device and the third reverse osmosis membrane device again before the water recovery rate decreases, the scale clogging of the first reverse osmosis membrane device and the third reverse osmosis membrane device is improved as in the treatment period 400. As a result, the progress of the scale clogging in the first reverse osmosis membrane device and the third reverse osmosis membrane device can be suppressed for a long time, so that pure water can be produced stably and efficiently for a long time. In addition, the acidic and alkaline conditions used in the process 301 (process 401) and the process 302 (process 402) are milder acidic / alkaline conditions than the ordinary scale cleaning agent, so the deterioration of the reverse osmosis membrane can be suppressed, and as a result, high-quality pure water can be produced stably for a long time.

[0058] It should be noted that, specifically, scale components include calcium (Ca) compounds such as calcium carbonate, calcium fluoride, calcium hydroxide, calcium sulfate, calcium phosphate, and magnesium (Mg) compounds such as magnesium carbonate, magnesium fluoride, magnesium hydroxide, magnesium sulfate, and magnesium phosphate, which are insoluble in water, and mainly silicon dioxide, aluminum, etc. Scale clogging refers to the phenomenon that these scale components adhere to the membrane surface, causing a part or all of the membrane to be blocked, thereby reducing the amount of permeable water. In addition, scale clogging caused by hardness components is easy to occur under alkaline conditions, and scale clogging caused by silicon dioxide is easy to occur under acidic conditions.

[0059] The replacement timing of the reverse osmosis membrane device in the first embodiment and the second embodiment can be, for example, performed when the treated water flow rate at the most downstream is measured and the treated water flow rate is reduced from the initial to a specified ratio. It is also possible to pre-calculate the period from the initial reduction of the treated water flow rate at the most downstream to the specified ratio in consideration of the water recovery rate, and perform the replacement every such period. In addition, it is also possible to perform the replacement when the supply water pressure and the permeate water pressure of each reverse osmosis membrane device are measured and their difference becomes a specified value, or to pre-calculate the period when the difference between the supply water pressure and the permeate water pressure of the reverse osmosis membrane device becomes a specified value in consideration of the water recovery rate, and perform the replacement every such period. In addition, it is also possible to obtain the pressure difference that causes irreversible degradation of the membrane in advance through preliminary experiments, and perform the switch before reaching this pressure difference.

[0060] Next, refer to Figure 3 , a pure water production apparatus for realizing the pure water production method of the first embodiment is described. Figure 3 : is a block diagram schematically showing a pure water production device 1 of the third embodiment. The pure water production device 1 of the third embodiment has two reverse osmosis membrane devices (reverse osmosis membrane device 11 and reverse osmosis membrane device 12) connected in series. The pure water production device 1 also includes: a supply pipe 13 connected to the supply side of the reverse osmosis membrane device 11, for supplying the treated water to the reverse osmosis membrane device 11; and an alkali adjustment mechanism 14, which is provided in the path of the supply pipe 13 and adjusts the treated water of the reverse osmosis membrane device 11 to be alkaline. The pure water production device 1 also includes: a supply pipe 15 connecting the permeate side of the reverse osmosis membrane device 11 and the supply side of the reverse osmosis membrane device 12, for supplying the permeate water of the reverse osmosis membrane device 11 to the supply side of the reverse osmosis membrane device 12; and an acid adjustment mechanism 16, which is provided in the path of the supply pipe 15 and adjusts the treated water of the reverse osmosis membrane device 12 to be acidic. A supply pipe 17 is connected to the permeate side of the reverse osmosis membrane device 12 , and the pure water produced in the pure water production device 1 is sent to the subsequent stage through the supply pipe 17 .

[0061] The reverse osmosis membrane devices 11 and 12 are, for example, provided with one or more reverse osmosis membrane modules, which are composed of reverse osmosis membranes and flow path materials for passing treated water through the reverse osmosis membranes in a housing. As reverse osmosis membranes, various organic polymer membranes or ceramic membranes composed of cellulose acetate, aliphatic polyamide systems or aromatic polyamide systems or their composite systems can be used. The shape of the reverse osmosis membrane is hollow linear, spiral, flat, tubular, etc. From the perspective of improving pressure resistance and improving treatment efficiency, the reverse osmosis membrane of the present embodiment is preferably spiral. In addition, the reverse osmosis membrane devices 11 and 12 are ultra-low pressure type, low pressure type, medium pressure type or high pressure type reverse osmosis membrane devices, and the two reverse osmosis membrane devices are of the same type. For example, when the reverse osmosis membrane device 11 is an ultra-low pressure type, the reverse osmosis membrane device 12 is also an ultra-low pressure type, when the reverse osmosis membrane device 11 is a low pressure type, the reverse osmosis membrane device 12 is also a low pressure type, when the reverse osmosis membrane device 11 is a medium pressure type, the reverse osmosis membrane device 12 is also a medium pressure type, and when the reverse osmosis membrane device 11 is a high pressure type, the reverse osmosis membrane device 12 is also a high pressure type.

[0062] The alkali adjustment mechanism 14 and the acid adjustment mechanisms 16 and 21 are constituted by, for example, a tank storing an acid adjustment agent or an alkali adjustment agent and a drug injection pump that measures a predetermined amount of the agent in the tank and adds the agent to each supply pipe.

[0063] A supply pipe 18 is connected to a branch point B11 on the downstream side of the alkali adjustment mechanism 14 of the supply pipe 13. Another branch point B14 is located downstream of the branch point B11. The supply pipe 18 is connected to the supply pipe 15 at a branch point B12 located on the downstream side of the acid adjustment mechanism 16 of the supply pipe 15 on the opposite side of the connection portion with the branch point B11. The treated water adjusted to alkalinity by the alkali adjustment mechanism 14 passes through the branch point B11 and is supplied to the supply side of the reverse osmosis membrane device 12 via the supply pipe 18.

[0064] A supply pipe 19 is connected to a branch point B13 located in the path of the supply pipe 17. The end of the supply pipe 19 on the opposite side of the connection portion with the branch point B13 is connected to the supply pipe 13 at a branch point B14. The permeated water of the reverse osmosis membrane device 12 passes through the branch point B13 from the supply pipe 17, flows in the supply pipe 19, and is supplied to the supply side of the reverse osmosis membrane device 11 from the branch point B14 via the path on the downstream side of the supply pipe 13. An acid adjustment mechanism 21 for adjusting the permeated water of the reverse osmosis membrane device 12 to be acidic is provided in the path of the supply pipe 19. A supply pipe 20 is connected to the branch point B15 of the supply pipe 15 on the permeation side of the reverse osmosis membrane device 11, and the pure water produced in the pure water production device 1 is transported to the rear stage via the supply pipe 20.

[0065] In the pure water manufacturing device 1, the flow path composed of the supply pipe 13, the reverse osmosis membrane device 11, the supply pipe 15, the reverse osmosis membrane device 12, and the supply pipe 17, and treating the water to be treated in the order of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 is the first treatment path. In addition, starting from the path on the upstream side of the branch point B11 of the supply pipe 13, passing through the supply pipe 18, the path on the downstream side of the branch point B12 of the supply pipe 15, the reverse osmosis membrane device 12, the path on the upstream side of the branch point B13 of the supply pipe 17, the supply pipe 19, and then passing through the path on the downstream side of the branch point B14 of the supply pipe 13, and treating the water to be treated in the order of the reverse osmosis membrane device 12 and the reverse osmosis membrane device 11 is the second treatment path.

[0066] In the pure water manufacturing device 1, valves V11 to V16 are respectively installed in the paths of the supply pipes 13, 15, 17, 18, 19, and 20 so as to be able to switch between the first processing path and the second processing path. These valves V11 to V16 function as a switching mechanism. For example, the valve V11 is installed between the branch point B11 and the branch point B14 of the path of the supply pipe 13, and the valve V14 is installed on the downstream side near the branch point B11 of the path of the supply pipe 18. The valve V12 is installed on the upstream side (reverse osmosis membrane device 11 side) of the branch point B12 of the path of the supply pipe 15 and the downstream side (reverse osmosis membrane device 12 side) of the branch point B15, and the valve V16 is installed in the path of the supply pipe 20. The valve V13 is mounted on the downstream side of the branch point B13 of the path of the supply pipe 17, and the valve V15 is mounted on the downstream side of the branch point B13 of the path of the supply pipe 19 and the upstream side (the reverse osmosis membrane device 12 side) of the acid adjustment mechanism 21. The valves V11 to V16 are, for example, on-off valves that can be opened and closed, and may be automatic on-off valves that automatically control opening and closing by receiving a control signal output by the control device 22. In addition, two valves provided at the branch, such as the valve V11 and the valve V14, the valve V12 and the valve V16, and the valve V13 and the valve V15, may be respectively integrated and replaced by a three-way valve so as to have the same switching function.

[0067] The pure water production device 1 is optionally provided with a pump P1, a reverse osmosis membrane device 23, a tank TK, a pump P2, and a supply pipe 24 that connects them and transports raw water from the pump P1 to the supply pipe 13 through the reverse osmosis membrane device 23 and the tank TK at the front section of the supply pipe 13. The most downstream side of the supply pipe 24 is connected to the supply pipe 13 via the pump P2. The preferred structure of the reverse osmosis membrane device 23 is the same as that of the reverse osmosis membrane devices 11 and 12. In addition, the reverse osmosis membrane device 23 is an ultra-low pressure type, a low pressure type, or a high pressure type reverse osmosis membrane device, and is preferably the same type as the reverse osmosis membrane devices 11 and 12. The pumps P1 and P2 are, for example, water supply pumps capable of adjusting the discharge pressure.

[0068] Furthermore, a water pressure gauge for measuring the water pressure of the treated water or the permeated water may be provided on the supply side and the permeate side of the reverse osmosis membrane devices 11, 12, 23. Furthermore, a flow meter for measuring the flow rate of the treated water or the permeated water may be provided in addition to or instead of the water pressure gauge.

[0069] The concentrated water discharge pipes 25 and 26 are connected to the concentration sides of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12, respectively. The concentrated water can be discharged to the outside of the system of the pure water production device 1 through the discharge pipes 25 and 26, or returned to the front stage of the reverse osmosis membrane device 23 for reprocessing. The concentrated water discharge pipe 27 is connected to the concentration side of the reverse osmosis membrane device 23, and the concentrated water of the reverse osmosis membrane device 23 is discharged to the outside of the system of the pure water production device 1 through the discharge pipe 27.

[0070] The pure water production apparatus 1 includes a control device 22 for controlling the opening and closing of the valves V11 to V16 according to a program input in advance. Hereinafter, a method of switching between the first processing period and the second processing period using the control device 22 will be described.

[0071] First, the control device 22 outputs a control signal to open valves V11, V12, and V13, and to close valves V14, V15, and V16. Thus, the first treatment path is opened. Raw water is supplied to the reverse osmosis membrane device 23 from a raw water tank (not shown) through a pump P1. Raw water is, for example, city water, well water, industrial water, etc. In addition, raw water may also be used and recovered at a place where ultrapure water is used, and then used recycled water that has been subjected to reagent removal treatment as needed. For example, in raw water, as ions that can form water-insoluble inorganic salts and generate scale components, hardness components such as calcium and magnesium and dissolved carbon dioxide gas contain 10 mg / L to 300 mg / L in total in terms of calcium carbonate. In addition, in raw water, for example, silicon dioxide (Si) is contained in an amount of about 1 mg / L to 50 mg / L, chlorine is contained in an amount of about 0.1 mg / L to 0.6 mg / L in terms of Cl, and boron is contained in an amount of about 5 μg / L to 100 μg / L. The pH of raw water is about 5 to 7.5.

[0072] The supply pressure of raw water to the reverse osmosis membrane device 23 is, for example, 0.4 MPa to 8.0 MPa, preferably 0.5 MPa to 3.0 MPa. By subjecting raw water to reverse osmosis membrane treatment in the reverse osmosis membrane device 23, hardness components in the raw water are removed ( Figure 1 In step 101), an acid adjustment mechanism may be provided on the upstream side of the reverse osmosis membrane device 23 of the supply pipe 24, and the raw water may be adjusted to be acidic before being treated by the reverse osmosis membrane device 23. In this case, the pH of the raw water adjusted to be acidic is preferably 5.0 or more and 6.0 or less, thereby improving the removal rate of the hardness component in the raw water.

[0073] The permeated water of the reverse osmosis membrane device 23 is temporarily stored in the tank TK. The permeated water stored in the tank TK is supplied to the reverse osmosis membrane device 11 as treated water via the supply pipe 13 of the first treatment path by the pump P2. In the process of the treated water circulating in the supply pipe 13, an alkaline adjusting agent is added to the treated water by the alkali adjusting mechanism 14, thereby adjusting the treated water to be alkaline. As the alkali adjusting agent, for example, a potassium hydroxide aqueous solution, a sodium hydroxide aqueous solution, etc., a sodium hydroxide aqueous solution is generally used. In addition, in order to improve the removal rate of boron in the reverse osmosis membrane device 11, the pH of the permeated water adjusted to be alkaline is greater than 9.0 and less than 11.0, preferably greater than 9.2 and less than 10.5.

[0074] The treated water is treated in the reverse osmosis membrane device 11, and in addition to boron in the treated water, silica, carbonate ions, and anions are also removed ( Figure 1 Step 102). The conductivity of the permeate water of the reverse osmosis membrane device 11 from which boron has been removed is, for example, 1μS / cm to 15μS / cm, the boron concentration is, for example, 0.3ppb (μg / L) to 10ppb (μg / L), and the boron removal rate in the reverse osmosis membrane device 11 is 50% to 95%. The permeate water of the reverse osmosis membrane device 11 from which boron has been removed is then supplied to the supply side of the reverse osmosis membrane device 12 as treated water via the supply pipe 15 of the first treatment path. During the circulation of the treated water in the supply pipe 15, an acid adjusting agent is added to the treated water by the acid adjusting mechanism 16, thereby adjusting the treated water to be acidic. As the acid adjusting agent, for example, an aqueous solution of hydrochloric acid, an aqueous solution of sulfuric acid, etc., an aqueous solution of sulfuric acid is generally used. In addition, in order to improve the removal rate of the ion components in the reverse osmosis membrane device 12, the pH of the permeate water adjusted to be acidic is preferably below 5.0, more preferably below 4.5, and preferably above 2.0, more preferably above 3.0. Furthermore, the pH of the permeated water is preferably 2.0 or more and 5.0 or less, and more preferably 3.0 or more and 4.5 or less.

[0075] The treated water is treated in the reverse osmosis membrane device 12, and the ion components in the treated water are removed ( Figure 1Process 103). The ion components removed in the reverse osmosis membrane device 12 are mainly chloride ions, sulfate ions, nitrate ions, fluoride ions, anionic components such as ionized bicarbonate ions, cationic components such as sodium ions and calcium ions, and weak electrolytes such as silicon dioxide. The resistivity (resistivity) of the permeate water of the reverse osmosis membrane device 12 from which the ion components have been removed is, for example, 0.5MΩμcm to 10MΩμcm, and the boron concentration is, for example, 0.1ppb (μg / L) to 5ppb (μg / L). The permeate water of the reverse osmosis membrane device 12 is transported to the rear section via the supply pipe 17. The concentrated water of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 is discharged to the outside of the system of the pure water manufacturing device 1, or returned to the front section side of the reverse osmosis membrane device 23 for reprocessing.

[0076] As described above, the treated water in the tank TK is treated by passing through the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 in sequence via the first treatment path. The prescribed period for performing this treatment is the first treatment period. After the first treatment period, the control device 22 outputs a control signal to close the valves V11, V12, and V13 and open the valves V14, V15, and V16. Thus, the second treatment path is opened and the second treatment period begins.

[0077] In the second treatment period, the treated water stored in the tank TK is supplied to the reverse osmosis membrane device 12 from the branch point B11 of the supply pipe 13 of the second treatment path via the supply pipe 18 by the pump P2. While the treated water is flowing through the supply pipe 13, an alkali adjusting agent is added to the treated water by the alkali adjusting mechanism 14, thereby adjusting the treated water to be alkaline. The type of the alkali adjusting agent and the preferred embodiment of the pH of the treated water are the same as those in the first treatment period.

[0078] The treated water is in the reverse osmosis membrane device 12 ( Figure 1 In the process 202 of the present invention, boron, silicon dioxide, carbonate ions and anions in the treated water are removed in the same manner as in the first treatment period. The water quality of the permeated water of the reverse osmosis membrane device 11 from which boron has been removed is the same as in the first treatment period.

[0079] The permeated water of the reverse osmosis membrane device 12 then flows from the branch point B13 of the supply pipe 17 of the second treatment path through the supply pipe 19 and the downstream side of the branch point B14 of the supply pipe 13 in sequence and is supplied to the supply side of the reverse osmosis membrane device 11 as treated water. While the treated water flows through the supply pipe 19, an acid regulator is added to the treated water by the acid regulator 16, thereby adjusting the treated water to be acidic. The preferred embodiment of the type of the acid regulator and the pH of the treated water is the same as that during the first treatment.

[0080] The treated water is treated in the reverse osmosis membrane device 11, and the ion components in the treated water are removed in the same manner as in the first treatment period ( Figure 1 The water quality of the permeate water of the reverse osmosis membrane device 11 from which the ion components have been removed is the same as that during the first treatment. The permeate water of the reverse osmosis membrane device 11 is sequentially transported to the rear section via the supply pipe 15, the branch point B15, and the supply pipe 20. The concentrated water of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 is discharged to the outside of the system of the pure water manufacturing device 1, or returned to the front section side of the reverse osmosis membrane device 23 for reprocessing.

[0081] As described above, during the second treatment period, the treated water in the tank TK is treated by the reverse osmosis membrane device 12 and the reverse osmosis membrane device 11 in sequence via the second treatment path. After the second treatment period, the control device 22 outputs a control signal to open the valves V11, V12, and V13 and close the valves V14, V15, and V16. Thus, the first treatment path is opened and the first treatment period is restarted. By repeating these operations, the first treatment period and the second treatment period are repeated alternately.

[0082] In the pure water production device 1 of the present embodiment, during the first treatment period, the hardness component is removed in the reverse osmosis membrane device 11, but depending on the water quality and the operation period, the hardness component leaks into the permeate water of the reverse osmosis membrane device, and the scale clogging of the reverse osmosis membrane device 11 progresses. In addition, in the second reverse osmosis membrane device that treats acidic treated water, the scale clogging caused by silica is easy to progress. Therefore, before the scale clogging of the reverse osmosis membrane devices 11 and 12 deteriorates the water recovery rate, the order of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 is reversed to perform the second treatment period. During the second treatment period, the reverse osmosis membrane device 11 treats the treated water adjusted to acidity, and in this process, the hardness component is dissolved by the acid, and the scale clogging is improved. In addition, in the second reverse osmosis membrane device 12 where the scale clogging caused by silica progresses, by treating the treated water adjusted to alkaline, the silica scale is dissolved by the alkali, and the scale clogging is improved. In the second treatment period, the scale clogging of the reverse osmosis membrane device 12 arranged on the front side will progress in the same way as described above, but by switching the flow order of the treated water to the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 again before the water recovery rate decreases, the scale clogging of the reverse osmosis membrane devices 11 and 12 is improved in the same way as in the second treatment period. As a result, the progress of scale clogging in the reverse osmosis membrane devices 11 and 12 can be suppressed for a long time, so that pure water can be produced stably and efficiently for a long time. In addition, the acidic and alkaline conditions used in the pure water production device 1 are milder acidic / alkaline conditions than ordinary scale cleaning agents, so the deterioration of the reverse osmosis membrane can be suppressed, and as a result, high-quality pure water can be produced stably for a long time.

[0083] The timing of switching between the first treatment period and the second treatment period can be determined as follows. The first switching method is a method performed when the treated water flow rate at the most downstream is measured and the treated water flow rate is reduced from the initial to a specified ratio. Specifically, it can be performed as follows. A flow meter is connected to the most downstream side of the piping, and a calculation unit is set in the control device 22, and the flow meter inputs the measured value into the calculation unit. The flow meter is set at, for example, near the ends of the supply pipe 17 and the supply pipe 20, near the connection between the supply pipe 17 and the supply side of the second reverse osmosis membrane device 12, and near the connection between the supply pipe 20 and the permeation side of the first reverse osmosis membrane device. The calculation unit calculates the reduction ratio of the flow rate from the initial stage of water flow. When the calculated reduction ratio of the flow rate exceeds a predetermined threshold value, the control device 22 outputs a control signal for controlling the switching mechanism to open and close the valve. The threshold value of the flow rate reduction ratio during switching in the first switching method is, for example, in the range of 0.05 to 0.5 when the initial flow rate is set to 1, that is, the flow rate is set to a specified value in the range of 50% to 95% relative to the initial flow rate 100%, so that the reverse osmosis membrane treatment can be continued for a long time without performing scale cleaning of the reverse osmosis membrane devices 11 and 12. The threshold value of the flow rate reduction ratio during switching is preferably in the range of 0.05 to 0.2 when the initial flow rate is set to 1, that is, the flow rate is set to a range of 80% to 95% relative to the initial flow rate 100%, so that membrane degradation can be suppressed, water quality can be stabilized, and reverse osmosis membrane treatment can be continued. It is also possible to pre-calculate the period during which the downstream treated water flow rate is reduced from the initial to the specified ratio in consideration of the water recovery rate, and switch every this period.

[0084] The second switching method is as follows: a water pressure gauge is arranged on the supply side and the permeate side of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12, respectively. During the first treatment period, when the pressure difference between the supply water of the reverse osmosis membrane device 11 and the permeate water of the reverse osmosis membrane device 12 becomes a specified value, during the second treatment period, when the pressure difference between the supply water of the reverse osmosis membrane device 12 and the permeate water of the reverse osmosis membrane device 11 becomes a specified value, the first treatment path and the second treatment path are switched by the control device. This method can also be performed in the following manner in the same manner as the above-mentioned first switching method. An operation unit is set in the control device 22, and each water pressure gauge inputs the measured value into the operation unit, and the operation unit calculates the pressure difference. When the calculated pressure difference exceeds a predetermined threshold value, the control device 22 outputs a control signal for controlling the switching mechanism to open and close the valve. The threshold value of the pressure difference during switching in the second switching method is preferably a specified value in the range of 105% or more and 200% or less relative to the water flow pressure difference at the beginning of water flow, and preferably a specified value in the range of 105% or more and 125% or less. This allows long-term reverse osmosis membrane treatment without cleaning the scale of the reverse osmosis membrane devices 11 and 12. The water flow pressure difference refers to the difference obtained by subtracting the average value of the supply water pressure and the concentrated water pressure from the permeate water pressure.

[0085] The third switching method is as follows: considering the raw water quality, the amount of alkali adjuster added by the alkali adjustment mechanism 14, the amount of acid adjuster added by the acid adjustment mechanism 16, 21, the specifications of the reverse osmosis membrane devices 11, 12 and the water recovery rate, the duration of the first treatment period and the second treatment period is predetermined, and the control device 22 controls the switching mechanism according to the duration. In this case, it is implemented as follows. A timer unit is set in the control device 22, and the timer unit measures the time and outputs a switching signal at a preset time. When the timer unit outputs a switching signal at a preset time, the switching signal is input to the control device 22. Through the input of the switching signal, the control device 22 outputs a control signal to control the switching mechanism (valves V11~V16). The progress rate of scale blockage can be investigated by preliminary experiments, and the duration of the first treatment period and the second treatment period can be determined based on the progress rate.

[0086] Next, refer to Figure 4 , a pure water production apparatus 2 which is a first modified example of the pure water production apparatus 1 according to the third embodiment will be described. Figure 4 2 is a block diagram schematically showing a pure water production device 2 of this modification. The pure water production device 2 is different from the pure water production device 1 in that a reverse osmosis membrane device 28 is further provided between two reverse osmosis membrane devices (reverse osmosis membrane device 11 and reverse osmosis membrane device 12) connected in series. Figure 4 In the realization and Figure 3The same functional components are marked with the same reference numerals and detailed descriptions are omitted. Figure 4 Arbitrary configurations are shown with part thereof omitted.

[0087] The reverse osmosis membrane device 28 is mounted on the upstream side (reverse osmosis membrane device 11 side) of the supply pipe 15, for example, the branch point B15. A concentrated water discharge pipe 29 is provided on the concentrated side of the reverse osmosis membrane device 28, and the concentrated water is discharged to the outside of the system of the pure water production device 2 through the discharge pipe 29, or returned to the front section of the reverse osmosis membrane device 23 for reprocessing. The reverse osmosis membrane device 28 is an ultra-low pressure type, low pressure type, or high pressure type reverse osmosis membrane device, and can be connected to the reverse osmosis membrane device 11, 12, or Figure 3 The reverse osmosis membrane devices 23 shown are of the same type or of different types. In addition, a water pressure gauge for measuring the water pressure of the treated water or the permeated water may be provided on the supply side and the permeation side of the reverse osmosis membrane device 28. In addition, in addition to the water pressure gauge, or in place of the water pressure gauge, a flow meter for measuring the flow rate of the treated water or the permeated water may also be provided.

[0088] In the pure water manufacturing device 2, during the first treatment period, the treated water is sequentially passed through the first treatment path, that is, the supply pipe 13, the reverse osmosis membrane device 11, the reverse osmosis membrane device 28, the supply pipe 15, and the reverse osmosis membrane device 12 for treatment. The conductivity of the permeated water of the reverse osmosis membrane device 28 during the first treatment period is, for example, 1μS / cm to 15μS / cm, and the boron concentration is, for example, 0.1ppb (μg / L) to 5ppb (μg / L), and the resistivity of the permeated water of the reverse osmosis membrane device 12 is, for example, 0.5MΩ to 10MΩ, and the boron concentration is, for example, 0.1ppb (μg / L) to 3ppb (μg / L). In this way, by having the reverse osmosis membrane device 28, the removal rate of boron and silicon dioxide in the produced pure water can be improved, and the removal rate of boron in the pure water manufacturing device 2 can reach 60% to 98%.

[0089] In the pure water production device 2, during the second treatment period, the treated water is treated by sequentially flowing through the second treatment path, that is, the upstream side of the branch point B11 of the supply pipe 13, the branch point B11, the supply pipe 18, the branch point B12, the reverse osmosis membrane device 12, the upstream side of the branch point B13 of the supply pipe 17, the supply pipe 19, the downstream side of the branch point B14 of the supply pipe 13, the reverse osmosis membrane device 11, the supply pipe 15, the reverse osmosis membrane device 28, and the supply pipe 20. The water quality of the permeated water of the reverse osmosis membrane device 11 during the second treatment period is the same as that during the first treatment period.

[0090] In the pure water production device 2 , similarly to the above-described pure water production device 1 , the switching between the first treatment period and the second treatment period is repeated, and pure water production can be continued stably for a long period of time without cleaning the scale of the reverse osmosis membrane devices 11 and 12 .

[0091] In addition, as a second modification of the pure water production device 1, a configuration in which the water flow order of the reverse osmosis membrane device 23 and the reverse osmosis membrane device 11 is reversed can be adopted. In this modification, a first treatment period in which the reverse osmosis membrane device 23 is used in the front stage and the reverse osmosis membrane device 11 is used in the rear stage and a second treatment period in which the reverse osmosis membrane device 11 is used in the front stage and the reverse osmosis membrane device 23 is used in the rear stage can be repeated. In this modification, a switching mechanism is provided by providing piping and valves as in the pure water production device 1 of the above-mentioned embodiment, and a first treatment path in which raw water flows through the reverse osmosis membrane device 23, the alkali adjustment mechanism 14, and the reverse osmosis membrane device 11 in sequence and a second treatment path in which raw water flows through the reverse osmosis membrane device 11, the alkali adjustment mechanism 14, and the reverse osmosis membrane device 23 in sequence are configured. Thus, the control device 22 can control the switching mechanism every time a predetermined treatment period passes, switch the first treatment path and the second treatment path, and alternately repeat the first treatment period in which the first treatment path is used and the second treatment period in which the second treatment path is used. In addition, in this modification, the reverse osmosis membrane device 23 is an ultra-low pressure type, low pressure type or high pressure type reverse osmosis membrane device, and is the same type as the reverse osmosis membrane device 11. An acid adjustment mechanism can be provided immediately after the pump P1 in the path of the supply pipe 24, and the treated water can be adjusted to acidity and supplied to the first stage reverse osmosis membrane device. Thereby, the removal rate of the hardness component in the first stage reverse osmosis membrane device can be improved. The acid adjustment agent in this case is the same as that described above, but the pH of the treated water is preferably adjusted to 5.0 to 6.0.

[0092] In this modification, during the first treatment period, the hardness component is removed in the reverse osmosis membrane device 23, but depending on the water quality and the operation period, the hardness component leaks into the permeated water of the reverse osmosis membrane device 23, and the scale clogging of the reverse osmosis membrane device 11 in the rear stage progresses. In addition, in the reverse osmosis membrane device 23 that treats weakly acidic treated water, the scale clogging caused by silica is easy to progress. Therefore, before the scale clogging of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 23 deteriorates the water recovery rate, the water flow order of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 23 is exchanged to perform the second treatment period. During the second treatment period, the reverse osmosis membrane device 11 treats the treated water adjusted to be weakly acidic, and in this process, the hardness scale is dissolved by the acid, and the scale clogging is improved. In addition, in the reverse osmosis membrane device 23 where the scale clogging caused by silica progresses, by treating the treated water adjusted to be alkaline, the silica scale is dissolved by the alkali, and the scale clogging is improved. During the second treatment period, the silica scale clogging of the reverse osmosis membrane device 23 treating alkaline treated water and the hardness scale clogging of the reverse osmosis membrane device 11 treating weakly acidic treated water progress, but by replacing the reverse osmosis membrane device 11 and the reverse osmosis membrane device 23 again before the water recovery rate decreases, the scale clogging of the reverse osmosis membrane devices 11 and 23 is improved in the same manner as in the second treatment period. As a result, the progress of scale clogging in the reverse osmosis membrane devices 23 and 11 can be suppressed for a long time, so that pure water can be produced stably and efficiently for a long time. In addition, the acidic and alkaline conditions used in this modification are milder acidic / alkaline conditions than ordinary scale cleaning agents, so the deterioration of the reverse osmosis membrane can be suppressed, and as a result, high-quality pure water can be produced stably for a long time.

[0093] Next, refer to Figure 5 , a pure water production apparatus 3 according to a fourth embodiment will be described. Figure 5 It is a block diagram schematically showing a pure water production apparatus 3 according to a fourth embodiment. Figure 5 The pure water manufacturing device 3 shown in the figure is different from the pure water manufacturing device 1 in that the acid adjustment mechanism is concentrated in one place. As a result, the arrangement scheme of the piping (supply pipe) and the valve is also different. Therefore, the piping method of the pure water manufacturing device 3 is mainly described below. Figure 5 In the realization and Figure 3 The same functional components are denoted by the same reference numerals and detailed descriptions are omitted. Figure 3 The description of the same methods and effects as those of the pure water production apparatus 1 shown will also be partially omitted.

[0094] The pure water manufacturing device 3 of the fourth embodiment has two reverse osmosis membrane devices (reverse osmosis membrane device 11 and reverse osmosis membrane device 12) connected in series, similarly to the pure water manufacturing device 1 of the third embodiment. The pure water manufacturing device 1 also includes: a supply pipe 13 connected to the supply side of the reverse osmosis membrane device 11, for supplying treated water to the reverse osmosis membrane device 11; and an alkali adjustment mechanism 14, which is provided in the path of the supply pipe 13 and adjusts the treated water of the reverse osmosis membrane device 11 to be alkaline. A pump P2 is arranged at the end of the supply pipe 13 on the opposite side of the connection point with the reverse osmosis membrane device 11, and the treated water is transported from the tank TK to the reverse osmosis membrane device 11 by the pump P2. The supply pipe 13 has two branching points on its path, namely, branching points B1 and B7 in sequence from the upstream side. Moreover, a valve V31 is sandwiched between the branching point B1 and the branching point B7 of the path of the supply pipe 13.

[0095] The pure water production device 3 is also provided with a supply pipe 35 connected to the permeation side of the reverse osmosis membrane device 11 to transport the treated water to the rear stage. Branch points B2, B3, B6, and B4 are located in the path of the supply pipe 35 in order from the upstream side (the permeation side of the reverse osmosis membrane device 11). An acid adjustment mechanism 16 for adjusting the treated water of the reverse osmosis membrane device 12 to acidity is provided between the branch point B3 and the branch point B6 of the path of the supply pipe 35. A valve V32 is interposed between the branch point B2 and the branch point B3 of the supply pipe 35, and a valve V33 is interposed between the branch points B6 and B4.

[0096] A supply pipe 36 is connected to the branch point B4 of the supply pipe 35. The end of the supply pipe 36 on the opposite side of the branch point B4 is connected to the supply side of the reverse osmosis membrane device 12. Thus, the treated water adjusted to acidity by the acid adjustment mechanism 16 is supplied from the supply side of the reverse osmosis membrane device 12 via the supply pipe 36.

[0097] A supply pipe 18 is connected to the branch point B1 between the alkali adjustment mechanism 14 and the valve V31 of the supply pipe 13. The treated water adjusted to alkalinity by the alkali adjustment mechanism 14 is transported to the supply pipe 18 through the branch point B1. The supply pipe 18 is connected to the supply pipe 36 at the branch point B4, and the treated water is supplied to the supply side of the reverse osmosis membrane device 12 through the supply pipe 13, the branch point B1, the supply pipe 18, the branch point B4 and the supply pipe 36 in sequence. The pure water manufacturing device 3 also has a supply pipe 37 connected between the branch point B5 of the supply pipe 17 and the branch point B3 of the supply pipe 35. A valve V36 is clamped in the supply pipe 37. The pure water manufacturing device 3 has a supply pipe 39 connected between the branch point B6 of the supply pipe 35 and the supply pipe 13. A valve V37 is clamped in the supply pipe 39. The supply pipe 17 is connected to the branch point B5 of the supply pipe 37, and the pure water produced in the pure water manufacturing device 1 is transported to the rear section via the supply pipe 17. A valve V34 is interposed in the path of the supply pipe 17 .

[0098] The permeated water of the reverse osmosis membrane device 12 is adjusted to acidity by the acid adjustment mechanism 16 provided in the path of the supply pipe 35 while passing through the supply pipe 17, the branch point B5, the supply pipe 37, the branch point B3, and the supply pipe 35 in sequence. Thereafter, the treated water adjusted to acidity flows into the supply pipe 13 through the branch point B6, the supply pipe 39, and the branch point B7, and is then supplied to the supply side of the first reverse osmosis membrane device 11. The supply pipe 20 is connected to the branch point B2 of the supply pipe 35 connected to the permeation side of the reverse osmosis membrane device 11, and the pure water produced in the pure water production device 1 is transported to the rear stage via the supply pipe 20. A valve V38 is interposed in the path of the supply pipe 20.

[0099] Preferred embodiments of the valves V31 to V38 and the pumps P1 and P2 are the same as those of the pure water production apparatus 1 according to the third embodiment.

[0100] In the pure water production device 3, the flow path composed of the supply pipe 13, the reverse osmosis membrane device 11, the supply pipe 35, the supply pipe 36, the reverse osmosis membrane device 12 and the supply pipe 17, and the flow path for treating the treated water in the order of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 is the first treatment path. Figure 6 In the figure, the solid line represents the first treatment path, and the dotted line represents the path where the treated water does not flow. In addition, starting from the upstream side of the branch point B1 of the supply pipe 13, the path is composed of the path from the supply pipe 18 to the branch point B4, the supply pipe 36, the reverse osmosis membrane device 12, the path from the permeate side of the reverse osmosis membrane device 12 to the branch point B5 of the supply pipe 17, the supply pipe 37, the path from the branch point B3 of the supply pipe 35 to the branch point B6, the supply pipe 39, the flow path downstream of the branch point B7 of the supply pipe 13, the reverse osmosis membrane device 11, the path from the permeate side of the reverse osmosis membrane device 11 of the supply pipe 35 to the branch point B2, and the supply pipe 20, and the flow path that treats the treated water in the order of the reverse osmosis membrane device 12 and the reverse osmosis membrane device 11 is the second treatment path. Figure 7 In FIG. 1 , the second treatment path is indicated by a solid line, and the path through which the treated water does not flow is indicated by a dotted line.

[0101] In the pure water production apparatus 3 , the water to be treated stored in the tank TK flows through the first treatment path during the first treatment period, and flows through the second treatment path during the second treatment period.

[0102] The pure water production apparatus 3 includes a control device 22 for controlling the opening and closing of the valves V31 to V38 according to a program input in advance. Hereinafter, a method of switching between the first processing period and the second processing period using the control device 22 will be described.

[0103] First, the control device 22 outputs a control signal to open valves V31, V32, V33 and V34, and close valves V35, V36, V37 and V38. Thus, the first processing path is opened, and the first processing period is started by operating the pump P2. After the first processing period has been carried out for a specified period, the control device 22 outputs a control signal to close valves V31, V32, V33 and V34, and open valves V35, V36, V37 and V38. Thus, the second processing path is opened, and the second processing period is started. After the second processing period, the control device 22 outputs a control signal to open valves V31, V32, V33 and V34, and close valves V35, V36, V37 and V38. Thus, the first processing path is opened, and the first processing period is restarted. By repeatedly performing these operations, the first processing period and the second processing period are repeated alternately.

[0104] In the pure water production device 3 of the present embodiment, during the first treatment period, the hardness component is removed in the reverse osmosis membrane device 23, but depending on the water quality and the operation period, the hardness component leaks into the permeated water of the reverse osmosis membrane device 23, and the scale clogging of the reverse osmosis membrane device 11 progresses. In addition, in the reverse osmosis membrane device 12 that treats acidic treated water, the scale clogging caused by silica is easy to progress. Therefore, before the scale clogging of the reverse osmosis membrane devices 11 and 12 deteriorates the water recovery rate, the order of the reverse osmosis membrane device 11 and the reverse osmosis membrane device 12 is reversed to perform the second treatment period. During the second treatment period, the reverse osmosis membrane device 11 treats the treated water adjusted to acidity, and in this process, the hardness scale is dissolved by the acid, and the scale clogging is improved. In addition, in the reverse osmosis membrane device 12 where the scale clogging caused by silica progresses, by treating the treated water adjusted to alkaline, the silica scale is dissolved by the alkali, and the scale clogging is improved. In the second treatment period, the scale clogging of the reverse osmosis membrane devices 11 and 12 progresses in the same manner as described above, but the first treatment period is performed by switching the flow order of the treated water to the reverse osmosis membrane devices 11 and 12 again before the water recovery rate decreases, and the scale clogging of the reverse osmosis membrane devices 11 and 12 is improved in the same manner as in the second treatment period. As a result, the progress of scale clogging in the reverse osmosis membrane devices 11 and 12 can be suppressed for a long time, so that pure water can be produced stably and efficiently for a long time. In addition, the acidic and alkaline conditions used in the pure water production device 3 are milder acidic / alkaline conditions than ordinary scale cleaning agents, so the deterioration of the reverse osmosis membrane can be suppressed, and as a result, high-quality pure water can be produced stably for a long time.

[0105] It should be noted that a set of two valves in each branch of valves V31 to V38, such as valve V31 and valve V35, valve V32 and valve V38, valve V33 and valve V37, valve V34 and valve V36, can also be integrated and replaced by a three-way valve to have the same flow path switching function. In addition, valves V31, V33, V35, and V37 can be integrated into a four-way valve, and valves V32, V34, V36, and V38 can be integrated into another four-way valve to have the same flow path switching function.

[0106] exist Figure 8 and Fig. 9 Schematically shows a pure water manufacturing device 4 having a piping structure in the case of using valves V41 and V42 as two four-way valves. The pure water manufacturing device 4 includes: valves V41 and V42 as four-way valves; a supply pipe 13; a supply pipe 131 connected to the supply side of the reverse osmosis membrane device 11; a supply pipe 141 connected to the permeation side of the reverse osmosis membrane device 11; a supply pipe 132 connected to the supply side of the reverse osmosis membrane device 12; a supply pipe 142 connected to the permeation side of the reverse osmosis membrane device 12; a piping 143 connecting the valve V41 and the valve V42; and a supply pipe 150 for conveying treated water (permeated water) to the rear stage. In the pure water manufacturing device 4, the supply pipe 131, the supply pipe 132, and the piping 143 are connected to the supply pipe 13 via the valve V41. The side of the piping 143 opposite to the side connected to the valve V41 is connected to the valve V42. Furthermore, the supply pipe 141 , the supply pipe 142 , and the pipe 143 are connected to the supply pipe 150 via a valve V42 .

[0107] Figure 8 FIG. 2 is a diagram schematically showing a processing path during the first processing period when a four-way valve is used. Figure 8 As shown, during the first treatment period, the flow path of valve V41 is switched to a flow path where supply pipe 13 is connected to supply pipe 131, and pipe 143 is connected to supply pipe 132. The flow path of valve V42 is switched to a flow path where supply pipe 141 is connected to pipe 143, and supply pipe 142 is connected to supply pipe 150. Figure 8 In the example, the four-way valve can be replaced with multiple two-way valves.

[0108] Fig. 9 FIG. 2 is a diagram schematically showing a processing path during the second processing period when a four-way valve is used. Fig. 9 As shown, during the second treatment period, the flow path of valve V41 is switched to a flow path where supply pipe 13 is connected to supply pipe 132, and pipe 143 is connected to supply pipe 131. The flow path of valve V42 is switched to a flow path where supply pipe 141 is connected to supply pipe 150, and supply pipe 142 is connected to pipe 143. Fig. 9 In the example, the four-way valve can be replaced with multiple two-way valves.

[0109] Next, refer to Fig.10 ,right Figure 5 A first modified example of the pure water production apparatus 3 shown will be described. Fig.10 1 is a block diagram schematically showing a pure water production device 5 according to a first modification. A reverse osmosis membrane device 40 is interposed downstream of a branch point B3 of the route of the supply pipe 35 and upstream of the acid adjustment mechanism 16. The pure water production device 5 is similar to the pure water production device 5 in that the reverse osmosis membrane device 40 performs the third stage of reverse osmosis membrane treatment. Figure 5 The pure water production device 3 shown is different. The rest is the same as the pure water production device 3. Therefore, the same reference numerals are attached to the components that achieve the same effects, and detailed descriptions are omitted.

[0110] In the pure water production device 5, during the first treatment period, the permeated water of the reverse osmosis membrane device 11 is supplied to the supply side of the fourth reverse osmosis membrane device 40 via the supply pipe 35. The alkaline treated water is treated in the reverse osmosis membrane device 40, thereby removing boron and silica, and then the permeated water of the reverse osmosis membrane device 40 is adjusted to acidity by the acid adjustment mechanism 16, and flows into the supply pipe 36 through the branch points B6 and B4. The acidic treated water flowing through the supply pipe 36 is treated in the reverse osmosis membrane device 12.

[0111] In addition, in the pure water production device 5, during the second treatment period, the permeated water of the reverse osmosis membrane device 12 is transported to the branch point B3 via the supply pipe 37, and is supplied from the branch point B3 to the supply side of the fourth reverse osmosis membrane device 40 via the supply pipe 35. The alkaline treated water is treated in the reverse osmosis membrane device 40, thereby also removing boron and silica. Thereafter, the permeated water of the reverse osmosis membrane device 40 is adjusted to acidity by the acid adjustment mechanism 16, and flows into the supply pipe 39 through the branch point B6. The acidic treated water flowing through the supply pipe 39 is supplied from the supply pipe 13 to the supply side of the reverse osmosis membrane device 11 through the branch point B7 and is treated.

[0112] By using the pure water production apparatus 5 , pure water having a lower boron concentration, for example, 0.1 ppb (μg / L) or less, can be obtained.

[0113] Fig.11 It is a schematic representation of the use of a four-way valve as Fig.10 FIG. 6 is a diagram of a pure water production device 6 with a valve of the pure water production device 5 shown. Fig.11In the pure water manufacturing device 6 shown, the reverse osmosis membrane device 40 is clamped on the path of the piping 143 in such a manner that the upstream side (valve V42 side) of the piping 143 becomes the supply side and the downstream side (valve V41 side) of the piping 143 becomes the permeation side. In addition, the reverse osmosis membrane device 40 is arranged on the upstream side of the acid adjustment mechanism 16. Thus, a first treatment path in which the treated water passes through the reverse osmosis membrane device 11, the reverse osmosis membrane device 40, and the reverse osmosis membrane device 12 in sequence and a second treatment path in which the treated water passes through the reverse osmosis membrane device 12, the reverse osmosis membrane device 40, and the reverse osmosis membrane device 11 in sequence can be formed. In addition, in the pure water manufacturing device 6, by switching the flow paths of the valves V41 and V42 in the same manner as in the above-mentioned pure water manufacturing device 4, the first treatment period and the second treatment period can be repeated alternately. It should be noted that in Fig.11 In the embodiment, the four-way valve may be replaced with a plurality of (for example, two) two-way valves.

[0114] Next, the second modification of the pure water manufacturing device 3 is described. This modification adopts the structure of switching the water flow order to the reverse osmosis membrane device 23 and the reverse osmosis membrane device 11 to perform the first treatment period and the second treatment period in the same manner as the first modification of the pure water manufacturing device 1. This modification is provided with a switching mechanism that can switch the flow order of the treated water to the reverse osmosis membrane device 23 and the reverse osmosis membrane device 11 by using piping and valves, and constitutes a first treatment path in which raw water flows through the reverse osmosis membrane device 23, the alkali adjustment mechanism 14, and the reverse osmosis membrane device 11 in sequence, and a second treatment path in which raw water flows through the reverse osmosis membrane device 11, the alkali adjustment mechanism 14, and the reverse osmosis membrane device 23 in sequence. Thus, the control device 22 can control the switching mechanism every time a specified treatment period passes, switch the first treatment path and the second treatment path, and alternately repeat the first treatment period using the first treatment path and the second treatment period using the second treatment path. In this case, instead of providing a pipe for switching the flow path, the switching may be achieved by extracting two reverse osmosis membranes or even reverse osmosis membrane modules and exchanging their positions.

[0115] In this variation, an acid adjustment mechanism may be provided immediately after the pump P1 in the path of the supply pipe 24, and the treated water may be adjusted to be acidic and supplied to the first reverse osmosis membrane device. In this way, the removal rate of the hardness component in the first reverse osmosis membrane device can be improved. The acid adjustment agent in this case is the same as that described above, but the pH of the treated water is preferably adjusted to 5.0 to 6.0. In the pure water manufacturing device of this variation, scale clogging can be improved by replacing the reverse osmosis membrane device 23 and the reverse osmosis membrane device 11 in the same manner as in the first variation of the pure water manufacturing device 1, so that the progress of scale clogging in the reverse osmosis membrane devices 23 and 11 can be suppressed for a long time, and as a result, pure water can be manufactured stably and efficiently for a long time.

[0116] Next, refer to Fig.12 , an ultrapure water production system 7 according to the present embodiment using the above-described pure water production apparatus 1 will be described. Fig.12 It is a block diagram schematically showing the configuration of the ultrapure water production system 7 .

[0117] like Fig.12 As shown, the ultrapure water production system 7 sequentially includes a pretreatment system 70, a primary pure water system 71, and a secondary pure water system (subsystem) 72. The secondary pure water system 72 is connected to a point of use (POU) 73 via piping, so that the ultrapure water produced by the ultrapure water production system 7 is supplied to the POU 73.

[0118] The pre-treatment system 70 performs treatments such as coagulation, filtration, and membrane separation, 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, for example, the pre-treatment system 70 is equipped with a coagulation sedimentation device, a pressurized flotation device, a sand filtration device, a precision filtration device, an ultrafiltration device, a heat exchanger, etc. in an appropriate combination. It should be noted that the pre-treatment system 70 can be omitted when the quality of the raw water is sufficient to be supplied to the primary pure water system 71.

[0119] The ultrapure water production system 7 includes a tank TK1 at the rear stage of the pretreatment system 70. The treated water pretreated by the pretreatment system 70 is introduced into the tank TK1 and temporarily stored. The treated water in the tank TK1 is supplied to the primary pure water system 71 by a pump P3.

[0120] The primary pure water system 71 removes organic matter, ion components and dissolved gases from pre-treated water to produce primary pure water. The primary pure water system 71 is equipped with a pump P3, an activated carbon device (AC) 711, a degassing device 712, the pure water manufacturing device 1 of the above-mentioned embodiment, an ultraviolet oxidation device (TOC-UV) 713 and an electrodeionization device (EDI) 714 in sequence. It should be noted that the pure water manufacturing device 1 used in the primary pure water system 71 is preferably equipped with three reverse osmosis membrane devices, namely reverse osmosis membrane devices 23, 11, and 12, as a water treatment device. In addition, the primary pure water system 71 can also be equipped with the pure water manufacturing devices 2 to 6 of the above-mentioned embodiment or their modified examples instead of the pure water manufacturing device 1.

[0121] In the primary pure water system 71, first, the activated carbon device (AC) 711 removes impurities such as hydrogen peroxide and chlorine mixed in the pre-treated water that may cause membrane degradation.

[0122] Next, the degassing device 712 removes carbon dioxide gas in the treated water. The degassing device 712 is a membrane degassing device that removes dissolved gas in water under vacuum via a vacuum degassing tower and a degassing membrane. After that, the pure water production device 1 removes ion components and boron in the treated water of the degassing device 712.

[0123] The ultraviolet oxidizing device 713 has, for example, an ultraviolet lamp that can irradiate ultraviolet rays having a wavelength of about 185 nm, and by irradiating the water to be treated with ultraviolet rays from the ultraviolet lamp, the total organic carbon component (TOC) in the water to be treated is oxidized and decomposed. The ultraviolet lamp used in the ultraviolet oxidizing device 713 can use a lamp that generates ultraviolet rays having a wavelength of about 185 nm, or a low-pressure mercury lamp that radiates ultraviolet rays having a wavelength of about 254 nm together with ultraviolet rays having a wavelength of about 185 nm. The ultraviolet rays irradiated by the ultraviolet oxidizing device 713 decompose water to generate OH radicals, and organic matter in the water to be treated is oxidized and decomposed into organic acids by the OH radicals. The amount of ultraviolet irradiation in the ultraviolet oxidizing device 713 of the primary pure water system can be appropriately changed according to the water quality of the water to be treated.

[0124] The electrodeionization device (EDI) 714 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 removed ion components flows. 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.

[0125] In the electrodeionization device 714, 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.

[0126] The electrodeionization device 714 can continuously remove ion components without using any reagents such as acid or alkali for regenerating the ion exchange resin, thereby improving safety, reducing manufacturing costs, and miniaturizing the device in ultrapure water production, thereby improving manufacturing efficiency.

[0127] In addition, in the ultrapure water production system 7 of the present embodiment, the pure water production device 1 of the above-mentioned embodiment having two or more stages of reverse osmosis membrane devices connected in series is used, so the water quality of the water supplied to the electrodeionization device 714 is improved. As a result, the burden on the electrodeionization device 714 and the like is reduced, and the water quality of the obtained ultrapure water can be expected to be improved.

[0128] The primary pure water obtained in this manner has, for example, a resistivity of 17 MΩμcm or more and a TOC concentration of 10 μgC / L or less.

[0129] The ultrapure water production system of this embodiment is provided with a primary pure water tank TK2 for storing primary pure water, a pump P4, and a secondary pure water system 72 in the rear section of the primary pure water system 71. The primary pure water produced in the primary pure water system is temporarily stored in the primary pure water tank TK2 and then transported to the secondary pure water system 72 by the pump P4. The secondary pure water system 72 is provided with an ultraviolet oxidizing device (TOC-UV) 721, an ion exchange device (Polisher) 722 for non-regenerative ultrapure water production, a membrane degassing device (MDG) 723, and an ultrafiltration device (UF) 724.

[0130] The structure of the ultraviolet oxidation device 721 in the secondary pure water system 72 is the same as that of the ultraviolet oxidation device 721 in the primary pure water system 71. The non-regenerative ultrapure water production ion exchange device 722 is a mixed bed ion exchange resin device in which a strongly acidic cation exchange resin and a strongly basic anion exchange resin are mixed and filled in a container such as a gas cylinder. The non-regenerative ultrapure water production ion exchange device 722 adsorbs and removes ion components generated by decomposing organic matter by the ultraviolet oxidation device 721.

[0131] The membrane degassing device 723 removes dissolved gas via a degassing membrane. The membrane degassing device 723 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 device 724 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 larger than 0.05 μm to about 250 Pcs. / L or less.

[0132] In this way, the secondary pure water system 72 processes the primary pure water to produce ultrapure water with higher purity. As for the quality of the ultrapure water, for example, the total organic carbon (TOC) concentration is less than 1 μgC / L, the resistivity is more than 18 MΩ·cm, and the boron concentration is less than 0.1 ppb (μg / L). The ultrapure water produced by the secondary pure water system is supplied to the use point 73.

[0133] It should be noted that, in each of the above-mentioned embodiments, the water quality of raw water, pre-treated water, pure water or ultrapure water can be measured by the following methods or devices, respectively.

[0134] pH: electrode method.

[0135] Boron concentration: ICP emission spectrometry / ICP-MS method.

[0136] Hardness component: ICP-MS method.

[0137] Dissolved carbon dioxide gas (calcium carbonate equivalent): Sievers M9e manufactured by SUEZ Corporation.

[0138] Silicon dioxide (Si): atomic absorption spectrophotometry / absorption spectrophotometry.

[0139] Chlorine (Cl conversion): DPD method.

[0140] Electrical conductivity: Electrical conductivity meter (HE-960CW manufactured by Horiba, Ltd.).

[0141] Resistivity (specific resistance): resistivity meter (HE-960RW manufactured by Horiba, Ltd.).

[0142] Total organic carbon (TOC) concentration: TOC meter (other than ultrapure water: Sievers M9e manufactured by SUEZ, ultrapure water: Anatel A-1000XP manufactured by BECKMANCOULTER).

[0143] Number of particles of 0.05 μm or larger: Particle counter (UDI-50 manufactured by Particle Measuring Systems).

[0144] [Example]

[0145] Next, experimental examples and working examples are described. The present invention is not limited to the following working examples.

[0146] [Experimental Example 1]

[0147] Use with Figure 5 The pure water production device of the three-stage reverse osmosis membrane device shown in the figure was used to investigate the relationship between the pH of the treated water of the second stage reverse osmosis membrane device, the boron removal rate, and the resistivity of the treated water. The pH of the treated water of the third stage reverse osmosis membrane device was fixed to 4, and the pH of the treated water of the second stage reverse osmosis membrane device was changed. The treated water was treated and the boron concentration and resistivity in the permeated water of the third stage reverse osmosis membrane device were measured. The water of Atsugi City was used as raw water, and the raw water was degassed and treated with activated carbon in sequence to obtain treated water. The treated water was supplied to the first stage reverse osmosis membrane device without being adjusted.

[0148] It should be noted that in this experimental example, with regard to the water quality of the supply water of the first-stage reverse osmosis membrane device, the total content of hardness components such as calcium and magnesium and dissolved carbon dioxide gas is 10 mg / L to 300 mg / L when converted to calcium carbonate, the content of silicon dioxide (Si) is about 1 mg / L to 50 mg / L, the content of chlorine is about 0.1 mg / L to 0.6 mg / L when converted to Cl, and the pH is about 7.2.

[0149] The above results are shown in Fig.13 .like Fig.13 As shown, it can be seen that when the pH of the treated water of the second-stage reverse osmosis membrane device is around 9.0-10.5, the resistivity of the treated water is the largest, and when the pH is 9.0, the boron removal rate is improved.

[0150] It should be noted that in Figure 13 to Figure 18 In the figure, "reverse osmosis membrane-2" represents the second stage reverse osmosis membrane device, and "reverse osmosis membrane-3" represents the third stage reverse osmosis membrane device.

[0151] [Experimental Example 2]

[0152] In Experimental Example 1, the pH of the treated water of the second reverse osmosis membrane device was adjusted to 10.5, the pH of the treated water of the third reverse osmosis membrane device was changed, and the resistivity of the permeated water of the third reverse osmosis membrane device was measured. Thus, the relationship between the pH of the treated water of the third reverse osmosis membrane device and the resistivity of the treated water was investigated. The results are shown in Fig.14 .

[0153] like Fig.14 As shown, it can be seen that when the pH of the water to be treated by the third-stage reverse osmosis membrane device is around 4 to 5.5, the resistivity of the treated water is the largest.

[0154] [Experimental Example 3]

[0155] Use alone Figure 5 The second reverse osmosis membrane device shown was used to investigate the changes in water flow time and permeate flow rate when the pH of the treated water was adjusted to 9, 10.5, and 11. Other conditions were the same as those in Experimental Example 1. The results are shown in Fig.15 .

[0156] like Fig.15 As shown, it can be seen that on the 90th day of water flow, the flow rate decreased by about 1% at pH = 9, the flow rate decreased by 7.5% at pH = 10.5, and the flow rate decreased by 11% at pH = 11.

[0157] It should be noted that in Fig.15 In the figure, “RO” refers to reverse osmosis membrane, and “RO-2” refers to the second reverse osmosis membrane.

[0158] [Experimental Example 4]

[0159] In Experimental Example 3, the pH of the treated water was 10.5 and the permeate flow rate was reduced for 90 days. The reverse osmosis membrane device was set as the third stage reverse osmosis membrane device, and the pH of the treated water was adjusted to 3, 4, and 6, and the change in the permeate flow rate immediately after the treatment was started was investigated. Other conditions were the same as in Experimental Example 1. The results are shown in Fig.16 .

[0160] like Fig.16 As shown, at pH=6, the flow rate recovered by about 2-3% after three days. In contrast, at pH=4, the flow rate recovered to the initial value after two days, and at pH=3, the flow rate recovered to the initial value after one day.

[0161] [Example 1]

[0162] Based on the above results, use Figure 5 The pure water production device shown has three reverse osmosis membrane devices, in which a reverse osmosis membrane device B is set in the second reverse osmosis membrane device, and a reverse osmosis membrane device C is set in the third reverse osmosis membrane device. The treatment period is set to 90 days, and the order of the reverse osmosis membrane devices B and C is switched by opening and closing the valve every 90 days to treat the treated water. The change in the treated water flow rate (the permeate water flow rate of the third reverse osmosis membrane device) when the pH of the treated water of the second reverse osmosis membrane device is set to 10.5 and the pH of the treated water of the third reverse osmosis membrane device is set to 4 is investigated. The results are shown in Fig.17 .

[0163] like Fig.17 As shown, it can be seen that the flow rate of the reverse osmosis membrane B, which was configured to be located in the second section at the beginning of water flow, decreased by about 7.5% after 90 days of water flow. After 90 days of water flow, the flow path was switched so that the reverse osmosis membrane B was configured to be located in the third section and the reverse osmosis membrane C was configured to be located in the second section, so that after the switch, the reverse osmosis membrane B returned to the initial flow rate in about 2 days. After that, the flow rate of the reverse osmosis membrane C decreased, and it was switched again after 180 days of water flow.

[0164] exist Fig.18 The changes in the conductivity of the treated water (permeated water) of the second stage reverse osmosis membrane device and the specific resistance of the treated water (permeated water) of the third stage reverse osmosis membrane device in Example 1 are shown in FIG. Fig.18 As shown, it can be seen that: just before the flow path is switched, the permeate water quality of the second stage reverse osmosis membrane device and the third stage reverse osmosis membrane device is slightly reduced, but the water quality is restored by switching.

[0165] According to the pure water production device of the embodiment described above, by exchanging the water flow order of the reverse osmosis membrane device on the front side for treating alkaline treated water and the reverse osmosis membrane device on the rear side for treating acidic treated water every predetermined treatment period (here, 90 days), it is possible to improve scale clogging caused by long-term use during the water treatment process without performing a cleaning operation. Therefore, pure water can be produced stably and efficiently for a long time.

[0166] Description of Reference Numerals

[0167] 1-6: Pure water manufacturing device; 7: Ultrapure water manufacturing system;

[0168] 11, 12, 23, 28, 40: reverse osmosis membrane device;

[0169] 13, 15, 17-20, 35-37, 39, 131, 132, 141, 142, 150: supply pipe;

[0170] 143: Piping;

[0171] 14: Alkali adjustment mechanism;

[0172] 16, 21: acid adjustment mechanism;

[0173] 25-27, 29: discharge pipe;

[0174] 22: Control device;

[0175] B1~B7, B11~B15: branching points;

[0176] V11~V16, V31~V38, V41, V42: valve;

[0177] P1~P4: pump;

[0178] TK, TK1, TK2: tank;

[0179] 70: Pre-treatment system;

[0180] 71: primary pure water system;

[0181] 72: Secondary pure water system (subsystem);

[0182] 73: Point of Use (POU);

[0183] 711: Activated carbon device (AC);

[0184] 712: degassing device;

[0185] 713: Ultraviolet oxidation device (TOC-UV);

[0186] 714: Electrodeionization device (EDI);

[0187] 721: Ultraviolet oxidation device (TOC-UV);

[0188] 722: Non-regenerative ion exchange device for producing ultrapure water (Polisher);

[0189] 723: Membrane degasser (MDG);

[0190] 724: Ultrafiltration device (UF).

Claims

1. A method for producing pure water, characterized in that: The raw water is passed through two or more reverse osmosis membranes to obtain pure water with boron removed. In the pure water production method, Carry out the following steps in the prescribed order: an alkali treatment step, wherein the alkaline treated water passes through a section of the reverse osmosis membrane; as well as The acid treatment step is to pass the acidic treated water through another reverse osmosis membrane in the reverse osmosis membrane. The first reverse osmosis membrane and the second reverse osmosis membrane are exchanged to repeat the following treatment period at predetermined intervals: During the first treatment, a first reverse osmosis membrane is used in an alkali treatment step, and a second reverse osmosis membrane is used in an acid treatment step; as well as During the second treatment, the second reverse osmosis membrane is used in the alkali treatment process, and the first reverse osmosis membrane is used in the acid treatment process.

2. The method for producing pure water according to claim 1, wherein: During the first treatment, alkaline treated water is passed through the first reverse osmosis membrane to perform an alkali treatment step, permeated water of the first reverse osmosis membrane is adjusted to be acidic, and the generated acidic treated water is passed through the second reverse osmosis membrane to perform the acid treatment step, During the second treatment, alkaline treated water is passed through the second reverse osmosis membrane to perform an alkali treatment step, water permeated through the second reverse osmosis membrane is adjusted to be acidic, and the resulting acidic treated water is passed through the first reverse osmosis membrane to perform the acid treatment step. The pH of the alkaline treated water is 9.0 or more and 11.0 or less. The pH of the acidic water to be treated is 5.0 or less.

3. The method for producing pure water according to claim 2, wherein: The pure water production method further comprises the following steps before the alkali treatment step: Raw water having a pH of 5.0 or more and 7.5 or less is passed through the third reverse osmosis membrane.

4. The method for producing pure water according to claim 1, wherein: During the first treatment, the acid treatment step is performed by passing the acidic treated water through the second reverse osmosis membrane, the permeated water of the second reverse osmosis membrane is adjusted to be alkaline, and the generated alkaline treated water is passed through the first reverse osmosis membrane to perform the alkaline treatment step, During the second treatment, the acid treatment step is performed by passing the acidic treated water through the first reverse osmosis membrane, the permeated water of the first reverse osmosis membrane is adjusted to be alkaline, and the generated alkaline treated water is passed through the second reverse osmosis membrane to perform the alkaline treatment step. The pH of the alkaline treated water is 9.0 or more and 11.0 or less. The pH of the acidic water to be treated is 5.0 or more and 6.0 or less.

5. A pure water production device, characterized in that: A device for producing pure water from which boron has been removed is provided, wherein the device comprises: A raw water supply pipe for supplying raw water; a first reverse osmosis membrane device and a second reverse osmosis membrane device; The first adjustment mechanism adjusts the treated water to be alkaline or acidic; The second adjustment mechanism adjusts the treated water to a different liquid property from that of the first adjustment mechanism, either acidic or alkaline; The first treatment path causes the raw water to flow through the first adjustment mechanism, the first reverse osmosis membrane device, the second adjustment mechanism, and the second reverse osmosis membrane device in sequence; The second treatment path causes the raw water to flow through the first adjustment mechanism, the second reverse osmosis membrane device, the second adjustment mechanism, and the first reverse osmosis membrane device in sequence; A switching mechanism capable of switching between a first processing path and a second processing path; as well as The control means controls the switching means to switch between the first processing path and the second processing path every time a predetermined processing period elapses.

6. The pure water production device according to claim 5, wherein: The first adjustment mechanism is an alkaline adjustment mechanism for adjusting the raw water to be alkaline. The second adjustment mechanism is an acid adjustment mechanism for adjusting the treated water to be acidic.

7. The pure water production device according to claim 5 or 6, wherein: The first processing path has: a first supply pipe for supplying raw water to a supply side of the first reverse osmosis membrane device; a second supply pipe for supplying permeated water of the first reverse osmosis membrane device to the second adjustment mechanism; a third supply pipe for supplying the treated water having passed through the second adjustment mechanism to a supply side of the second reverse osmosis membrane device; a fourth supply pipe for conveying the permeated water of the second reverse osmosis membrane device to the rear section; as well as Four switching valves are respectively mounted on the first supply pipe to the fourth supply pipe, wherein the first adjustment mechanism is arranged on the upstream side of the switching valve of the first supply pipe, The second processing path has: a fifth supply pipe for supplying raw water to a supply side of the second reverse osmosis membrane device; a sixth supply pipe for supplying permeated water of the second reverse osmosis membrane device to the second adjustment mechanism; a seventh supply pipe for supplying the treated water having passed through the second adjustment mechanism to a supply side of the first reverse osmosis membrane device; An eighth supply pipe for conveying the permeated water of the first reverse osmosis membrane device to a subsequent stage; and Four switching valves are respectively mounted on the fifth supply pipe to the eighth supply pipe, wherein the first adjustment mechanism is arranged on the upstream side of the switching valve of the sixth supply pipe, The control mechanism controls the eight switching valves to switch between the first processing path and the second processing path.

8. The pure water production device according to claim 5, wherein: The first adjustment mechanism is an acid adjustment mechanism for adjusting the raw water to be weakly acidic. The second adjustment mechanism is an alkali adjustment mechanism for adjusting the water to be treated to be alkaline.

9. An ultrapure water production system, which comprises a primary pure water system and a secondary pure water system in sequence, wherein in the ultrapure water production system, The primary pure water system comprises a pure water production device according to claim 5 or 6, and an ultraviolet oxidation device and an electrodeionization device in the subsequent stage thereof. The secondary pure water system 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. Produce ultrapure water with a boron concentration of 0.1 μg / L or less.

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