Ultra-pure water production system and ultra-pure water production method

Abstract

The present application provides a kind of ultra-pure water manufacturing system and manufacturing method, the ultra-pure water manufacturing system in the ultra-pure water manufacturing of the used ultra-pure water containing hydrogen peroxide after using ultra-pure water as the treated water of ultra-pure water manufacturing, by simple structure, can help the cleaning of device and treated water.A kind of ultra-pure water manufacturing system (1), it is with pretreatment unit (2), primary pure water manufacturing unit (3) and secondary pure water manufacturing unit (4), and for manufacturing ultra-pure water, it has: storage part (5), the storage part (5) is set to the front stage of pretreatment unit (2) or between pretreatment unit (2) and primary pure water manufacturing unit (3), can store raw water or treated water;Recycling processing unit (6), the recycling processing unit (6) is obtained after the use of ultra-pure water containing hydrogen peroxide in the used ultra-pure water, remove the impurities mixed in the used ultra-pure water, and make part or all of hydrogen peroxide to be made into recycled water;And circulating mechanism (7), the circulating mechanism (7) is obtained by the recycled water of recycling processing unit (6) and is sent back to storage part (5) and is circulated.

Description

Technical Field

[0001] This invention relates to an ultrapure water manufacturing system and method that reuses treated water as ultrapure water in ultrapure water production. Background Technology

[0002] Ultrapure water is generally produced by removing impurities from raw water through a pretreatment unit and a primary pure water production unit. This pure water is then further purified through a secondary pure water production unit, and the ultrapure water produced is supplied to the point of use (POU).

[0003] Generally, the pretreatment unit is composed of several treatment devices such as coagulation sedimentation, sand filtration, activated carbon adsorption, and pH adjustment. The primary pure water production unit is composed of a combination of filtration and separation treatment devices, adsorption treatment devices, reverse osmosis (RO) membrane devices, ultraviolet oxidation devices, degassing devices, and ion exchange treatment devices. The secondary pure water production unit is composed of a combination of ultraviolet oxidation devices, ion exchange treatment devices, and ultrafiltration devices.

[0004] In addition, if there is no large amount of chemicals or other contaminants mixed in with the ultrapure water after use at the point of use, it is sometimes recycled for reuse in ultrapure water production. In this case, impurities are removed from the used ultrapure water, and it is cleaned and recycled to produce recycled water, which is then sent back to the primary pure water production department.

[0005] For example, in semiconductor manufacturing systems, SC-2, SPM, FPM, and other chemicals are added to the ultrapure water used for washing semiconductor wafers. Therefore, the used ultrapure water contains acids such as sulfuric acid, phosphoric acid, and hydrofluoric acid, as well as hydrogen peroxide. Therefore, in cases where the ultrapure water used in semiconductor washing is recycled, it is treated by a removal device that removes impurities from the washing chemicals that have been introduced during use.

[0006] As a device for removing impurities used in such recycling processes, an ultrapure water production system is known, which has activated carbon for removing hydrogen peroxide and an ion exchange device for removing acid components, etc., wherein, as activated carbon, two types of activated carbon with high and low decomposition capacity relative to hydrogen peroxide are used in combination to completely remove hydrogen peroxide (see, for example, Patent Document 1).

[0007] This removal device consists of activated carbon installed in the recovery and treatment section before the ion exchange unit. This is because the ion exchange unit has low tolerance to hydrogen peroxide, and because the oxygen generated from the decomposition of hydrogen peroxide in the water flowing through the ion exchange unit can cause malfunctions, it is essential to install activated carbon to remove hydrogen peroxide before the ion exchange unit in order to maintain the lifespan of the unit and to effectively carry out ion exchange treatment.

[0008] If such activated carbon recovery treatment is performed, impurities including hydrogen peroxide are basically removed from the recovered water recycled to the primary pure water production unit. When the treated water is used again as the treated water for ultrapure water production, ultrapure water can be produced without considering the impact of impurities mixed in during use, which is preferable.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2004-181364 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, when such recycled water is reused, it is generally temporarily stored in a storage unit for mixing with the pretreated water obtained in the pretreatment unit. The mixed water obtained in this storage unit is used as the treated water. However, since the mixed water remains in such a storage unit for a certain period of time, it sometimes becomes contaminated with microorganisms or organic matter. Generally, sodium hypochlorite is added to the storage unit or any part upstream of it to address this, but due to the presence of recycled water, the amount added increases.

[0014] Furthermore, as a different issue from the above, sodium hypochlorite can cause malfunctions in downstream reverse osmosis or ion exchange resin units regardless of the presence or absence of recycled water. Therefore, it must be removed before reaching these units. However, if this removal is insufficient, it will lead to malfunctions in the downstream units. As one of these reasons, the appropriate amount of sodium hypochlorite can sometimes vary due to changes in the amount of recycled water.

[0015] Furthermore, the path from the removed portion to the reverse osmosis membrane unit, etc., becomes an environment that can cause the proliferation of microorganisms. Therefore, for example, malfunctions often occur in reverse osmosis membrane units or their pre-filters due to microbial proliferation.

[0016] The inventors conducted in-depth research to solve the aforementioned problems, resulting in the present invention. Specifically, the purpose of this invention is to provide an ultrapure water manufacturing system and method. This ultrapure water manufacturing system, after using ultrapure water, recovers it in a state containing hydrogen peroxide, and its simple structure contributes to the cleanliness of the device.

[0017] Methods for solving problems

[0018] The ultrapure water manufacturing system of the present invention is characterized in that it is an ultrapure water manufacturing system having a pretreatment unit, a primary pure water manufacturing unit, and a secondary pure water manufacturing unit, and is used to manufacture ultrapure water. It includes: a storage unit disposed in front of the pretreatment unit or between the pretreatment unit and the primary pure water manufacturing unit, capable of storing raw water or water to be treated; a recovery treatment unit that removes impurities from used ultrapure water containing hydrogen peroxide obtained after the use of the ultrapure water, and allows part or all of the hydrogen peroxide to permeate to produce recovered water; and a circulation mechanism that returns the recovered water obtained from the recovery treatment unit to the storage unit for circulation.

[0019] The ultrapure water manufacturing method of the present invention is characterized in that it is an ultrapure water manufacturing method that processes raw water through a pretreatment unit, a primary pure water manufacturing unit, and a secondary pure water manufacturing unit to produce ultrapure water. The method includes a storage unit provided in front of the pretreatment unit or between the pretreatment unit and the primary pure water manufacturing unit, which is capable of storing raw water or water to be treated. The used ultrapure water containing hydrogen peroxide obtained after the use of the ultrapure water is processed by a recycling unit to remove impurities mixed in the used ultrapure water and to make recycled water by permeating part or all of the hydrogen peroxide. The recycled water is then sent back to the storage unit for recycling.

[0020] Invention Effects

[0021] According to the present invention, used ultrapure water used in semiconductor manufacturing and the like is recycled in a state containing hydrogen peroxide, and then recycled and reused in the production of ultrapure water. Thus, in the ultrapure water production process, the generation or proliferation of bacteria can be inhibited and the content of organic matter can be reduced by simplifying the device configuration.

[0022] Furthermore, this eliminates the need to install the activated carbon device previously used in recycling within the recycling and processing department, reduces the installation space required for the device, and also allows for cost reduction in this area. Attached Figure Description

[0023] Figure 1This is a diagram showing the schematic configuration of an ultrapure water production system as one embodiment of the present invention. Detailed Implementation

[0024] Hereinafter, embodiments of the ultrapure water manufacturing system and ultrapure water manufacturing method of the present invention will be described with reference to the accompanying drawings.

[0025] (Ultrapure water production system)

[0026] The ultrapure water production system of this embodiment is as follows: Figure 1 The ultrapure water production system 1 shown comprises a pretreatment unit 2, a primary pure water production unit 3, a secondary pure water production unit 4, a storage unit 5, a recycling unit 6, and a circulation mechanism 7. Each component will be described in detail below.

[0027] In this embodiment, the pretreatment device 2 can have the same configuration as the pretreatment device used in conventional ultrapure water production systems, and there are no particular limitations.

[0028] The pretreatment unit 2 removes suspended solids from the raw water to generate pretreated water, which is then supplied to the primary pure water production unit 3. The pretreatment unit 2 can be configured using, for example, a sand filter or a precision filter to remove suspended solids from the raw water, and may further be equipped with a heat exchanger for adjusting the temperature of the raw water, depending on the requirements. It should be noted that, depending on the quality of the raw water, the pretreatment unit 2 may be omitted.

[0029] In this embodiment, the primary pure water production unit 3 can have the same configuration as the primary pure water production unit used in conventional ultrapure water production systems, and there are no particular limitations.

[0030] The primary pure water production unit 3 removes impurities from the pretreated water to produce pure water. This primary pure water production unit 3 is configured by appropriately combining one or more of the following: a reverse osmosis membrane device, a degassing device (such as decarbonation, vacuum degassing, or degassing membrane device), an ion exchange device (such as a cation exchange resin device, an anion exchange resin device, a mixed-bed ion exchange resin device, or an electro-deionization device), and an ultraviolet oxidation device. The primary pure water production unit 12 removes ionic and non-ionic components and dissolved gases from the pretreated water to produce primary pure water, and supplies this primary pure water to the secondary pure water production unit 4.

[0031] As a primary pure water production unit 3, examples include strongly basic anion exchange resin units, 2B3T type units (strong acid cation exchange resin units, decarbonation towers, and basic anion exchange units), reverse osmosis membrane units, ultraviolet oxidation units, mixed bed ion exchange resin units, and degassing membrane units, etc., which can be appropriately selected to construct the unit. Furthermore, heat exchangers for adjusting the temperature of the treated water can be added as needed.

[0032] In this embodiment, the secondary pure water production unit 4 can have the same configuration as the secondary pure water production unit used in conventional ultrapure water production systems, and there are no particular limitations.

[0033] The secondary pure water production unit 4 removes trace impurities from the primary pure water to produce ultrapure water. This secondary pure water production unit 4 can be configured with, for example, an ultrafiltration membrane device, a heat exchanger, an ultraviolet oxidation device, a hydrogen peroxide removal device, a degassing membrane device, and a non-regenerating mixed-bed ion exchange resin device (Polisher), etc., selected appropriately. It may also be further equipped with a heat exchanger for adjusting the temperature of the water being treated, as needed.

[0034] In this embodiment, the storage unit 5 is a tank or trough located between the pretreatment unit 2 and the primary pure water production unit 3. It is supplied with pretreated water that has been treated in the pretreatment unit 2 and recycled water obtained in the recycling unit 6 (described later), and the two are mixed together to store the water treated after the primary pure water production unit.

[0035] It should be noted that storage section 5 is in Figure 1 The example shown is located between the pretreatment unit 2 and the primary pure water production unit 3, but it can also be located in front of the pretreatment unit 2, where raw water is temporarily supplied to the storage unit 5 and mixed with the recycled water obtained in the recycling treatment unit 6.

[0036] In this embodiment, the recycling unit 6 removes impurities that have been introduced into the used ultrapure water containing hydrogen peroxide, and allows hydrogen peroxide to pass through, so as to recycle the treated water for the regeneration of ultrapure water.

[0037] The used ultrapure water used here can be exemplified by ultrapure water used in semiconductor manufacturing plants for washing semiconductor wafers, which may contain chemicals used in this process. During semiconductor wafer washing, chemicals such as SC-2, SPM, and FPM are added as cleaning agents. Therefore, used ultrapure water contains acids such as sulfuric acid, phosphoric acid, and hydrofluoric acid, as well as hydrogen peroxide.

[0038] In this case, the recycling unit 6 can be configured to remove acids such as sulfuric acid, phosphoric acid, and hydrofluoric acid from the used ultrapure water and allow hydrogen peroxide to pass through. An example of such a recycling unit 6 is... Figure 1 The membrane treatment unit 61 and the reverse osmosis membrane unit 62 (first reverse osmosis membrane unit) are arranged sequentially as shown in the diagram.

[0039] Here, the membrane treatment device 61 can be exemplified by a precision filtration membrane (MF) or an ultrafiltration membrane (UF), which removes particulates contained in the used ultrapure water and is installed upstream of the reverse osmosis membrane device 62. It should be noted that the membrane treatment device is not an essential element.

[0040] Furthermore, as the reverse osmosis membrane device 62, any known reverse osmosis membrane device used in water treatment can be listed, without particular limitation. Since this reverse osmosis membrane device 62 can remove acid-derived ionic components and allows hydrogen peroxide to pass through without removal, it is a suitable device for the recovery treatment unit of this embodiment.

[0041] In prior art document 1, an ion exchange resin device was used. However, since hydrogen peroxide is also decomposed and removed to a certain extent through the ion exchange resin device, it is preferable not to install an ion exchange resin device in the recycling processing unit of this embodiment.

[0042] In this recycling and processing unit 6, it is preferable that there is no device capable of removing hydrogen peroxide, such as a catalyst resin supported on activated carbon, palladium, or platinum. However, even if a device is capable of partially removing hydrogen peroxide, it can be installed as long as the remaining portion can pass through.

[0043] Therefore, the activated carbon device is preferably not used in the recovery and treatment unit 6. However, if the activated carbon device is used, the used ultrapure water is allowed to pass through the activated carbon device at a space velocity SV = 40hr. -1 The above process can also result in hydrogen peroxide being present in the recycled water.

[0044] It should be noted that in the past, the removal of hydrogen peroxide was also required in such recycling operations. Usually, an activated carbon device is installed in the recycling processing unit. However, as described in the preferred embodiment of this invention, the installation area of ​​this part of the device can be reduced without the activated carbon device, and the overall device can be simplified, which is preferred in this respect.

[0045] The recycled water obtained in the aforementioned recycling treatment unit 6 is circulated to the storage unit 5 through the circulation mechanism 7. The circulation mechanism 7 is composed of piping that allows the recycled water to flow to the storage unit 5.

[0046] Here, the circulation mechanism 7 may also include a flow adjustment mechanism to regulate the flow rate of the recycled water supplied to the storage unit 5. For example, a flow adjustment mechanism such as... Figure 1As shown, valve V1 is installed in this manner, allowing adjustment of the amount of treated water supplied from the pretreatment unit 2 and the amount of recycled water supplied from the circulation mechanism 7, thereby also adjusting the hydrogen peroxide concentration in the mixed water. Any valve known to the public, such as V1, can be used as long as it allows for flow rate adjustment.

[0047] (Method for producing ultrapure water)

[0048] Next, regarding the ultrapure water manufacturing method as one embodiment of the present invention, it is described that... Figure 1 The ultrapure water production system shown in the figure will be used as an example for explanation.

[0049] First, raw water is supplied to pretreatment unit 2 to remove suspended solids and obtain pretreated water. At this time, municipal water, well water, groundwater, industrial water, etc., are used as raw water. This pretreated water is then supplied to storage unit 5.

[0050] Next, the pretreated water is sent from storage unit 5 to primary pure water production unit, where the total organic carbon (TOC) and ion components in the pretreated water are removed using a reverse osmosis membrane device or an ion exchange device to produce primary pure water. Then, the obtained primary pure water is sent to secondary pure water production unit, where trace amounts of impurities in the primary pure water are removed to produce ultrapure water (secondary pure water).

[0051] At this point, the resistivity of the primary purified water obtained is, for example, 17 MΩ·cm or higher, and the resistivity of the ultrapure water (secondary purified water) obtained is, for example, 18 MΩ·cm or higher.

[0052] The obtained ultrapure water is supplied to the point of use (POU) for use according to various purposes. Furthermore, as described above, in the case of washing semiconductor wafers, the used ultrapure water contains hydrogen peroxide, which is subject to recycling in this embodiment. This used ultrapure water is sent to the recycling treatment unit of the ultrapure water manufacturing apparatus of this embodiment, where acid components or other impurities are removed, becoming recycled water. This recycled water contains hydrogen peroxide.

[0053] The recycled water is sent to the storage unit 5 through the circulation mechanism 7 for circulation. The recycled water supplied to the storage unit 5 in this manner is mixed with the pretreated water and reused again as treated water in the production of ultrapure water. It should be noted that, as described above, since the recycled water in this embodiment contains hydrogen peroxide, the sterilization effect in the storage unit where it is circulated can effectively inhibit the generation and proliferation of bacteria.

[0054] Furthermore, in this embodiment, pretreatment water and recycled water are mixed in the storage unit 5. However, the pretreatment water usually contains hypochlorite (such as sodium hypochlorite (NaClO)) for sterilization, and the recycled water contains hydrogen peroxide (H2O2). Both contain components with bactericidal effects, and the storage unit 5 is in a state that can inhibit the generation or proliferation of bacteria.

[0055] However, the hypochlorite contained in the pretreated water is a residual component that has already been utilized for sterilization during pretreatment, and hydrogen peroxide has a weaker bactericidal effect compared to hypochlorite. Furthermore, since the pretreated water is mixed with the recycled water, their respective concentrations decrease depending on the amount mixed.

[0056] However, the inventors have discovered that, as in this embodiment, when the pretreated water and the recycled water are mixed, a superior bactericidal effect can be obtained that exceeds the effect of simply adding these components together. The reasons for this improved bactericidal effect are as follows.

[0057] As described above, in storage section 5, pretreated water and recycled water are mixed. In this mixed water, hypochlorite and hydrogen peroxide coexist, and these compounds react to produce singlet oxygen. 1 O2) or OH radicals (·OH). Due to singlet oxygen ( 1 Both O2 and OH radicals (·OH) are highly active and have the function of decomposing organic matter. Therefore, the sterilization treatment in the storage section 5 is significantly improved compared with hypochlorite alone and hydrogen peroxide alone, and can exhibit the preferred sterilization effect.

[0058] Furthermore, the singlet oxygen produced ( 1 O2) or OH radicals (·OH) partially react with organic matter (TOC components) in water. As a result, they are transformed into forms that are easily removed by reverse osmosis membrane devices or ion exchange devices, thus a reduction in TOC in the treated water can be expected.

[0059] It should be noted that the concentration of hydrogen peroxide in the recycled water is preferably 2–50 ppm, more preferably 4–20 ppm. If the concentration is within this range, singlet oxygen or OH radicals can be effectively generated through reaction with hypochlorite in the pretreated water. In this case, the concentration of hypochlorite in the pretreated water is preferably 0.05–10 ppm, more preferably 0.1–2 ppm. Even at this level, hypochlorite is essentially eliminated due to the reaction with hydrogen peroxide. It should be noted that the amount of hypochlorite added should be appropriately adjusted to a level where hypochlorous acid remains due to the decomposition of hydrogen peroxide.

[0060] Furthermore, the supply rates of pretreated water and recycled water in storage unit 5 are preferably set such that the hydrogen peroxide concentration of the mixed water is 1 to 10 ppm (this hydrogen peroxide concentration can be calculated from the mixing ratio of pretreated water and recycled water). To set such a concentration, for example, the ratio of recycled water supply to pretreated water supply (recycled water supply / pretreated water supply) is preferably set to 10 / 90 to 50 / 50, more preferably to 20 / 80 to 40 / 60.

[0061] By using the ultrapure water manufacturing apparatus and method described above, the hydrogen peroxide contained in used ultrapure water can be used for sterilization, and it can also be reused as treated water for manufacturing ultrapure water, which is preferable. Furthermore, due to these advantages, compared to conventional ultrapure water manufacturing apparatuses that reuse used ultrapure water, for example, an activated carbon unit can be omitted, simplifying the configuration of the recovery treatment unit.

[0062] (Modified Example)

[0063] It should be noted that the above mentions the case where hypochlorite is basically eliminated through the reaction with hydrogen peroxide, but depending on the conditions or adverse circumstances, the case where hypochlorite remains in the primary pure water production unit is also considered.

[0064] Therefore, in the first embodiment described above, an activated carbon device is preferably provided in the primary pure water production unit to remove hypochlorite. At this time, a reverse osmosis membrane unit (hereinafter referred to as a second reverse osmosis membrane unit) is typically provided in the primary pure water production unit, and the activated carbon device is provided upstream of this second reverse osmosis membrane unit. By configuring it in this way, the deterioration of the second reverse osmosis membrane unit caused by hypochlorite in the treated water supplied from the storage unit 5 to the primary pure water production unit can be suppressed.

[0065] As the activated carbon device, known activated carbon used in water treatment can be used, such as coconut shell activated carbon, coal-based activated carbon, etc. These activated carbons have countless [structures / materials] formed inside. Left and right (most of them are) The pores are fine, ranging from 500 to 1500 μm. 2 The specific surface area is approximately [value missing]. To achieve high decomposition capacity, decomposition catalysts such as platinum, palladium, or silver can also be supported. It should be noted that the pore distribution and specific surface area of ​​the activated carbon in this specification are values ​​obtained by adsorption methods using nitrogen (N2), argon (Ar), or mercury intrusion methods.

[0066] It should be noted that, regarding the primary pure water production section, as long as hypochlorite can be removed, hydrogen peroxide can also be passed through in this activated carbon device to remove it. Most of the hypochlorite reacts with hydrogen peroxide and disappears in storage section 5 and its downstream section; only the slight residual hypochlorite needs to be removed, which is easily achieved using an activated carbon device. Therefore, the space velocity in this activated carbon device can be SV = 5 to 40 hr. -1 Use within the range. Typically, SV = 5–10hr. -1 In this condition, hydrogen peroxide is also effectively removed along with hypochlorite at high flow rates (SV = 10–40 hr). -1 In this case, hypochlorite is removed, while hydrogen peroxide becomes more readily permeable. Therefore, by changing the treatment conditions in the activated carbon unit, the concentration of hydrogen peroxide in the downstream treated water can also be adjusted. By setting the concentration of hydrogen peroxide in the downstream treated water to 0.1 to 1 ppm, the generation or proliferation of bacteria between the activated carbon unit and the downstream reverse osmosis membrane unit can be inhibited, thus ensuring stable operation of the downstream reverse osmosis membrane unit.

[0067] In this activated carbon device, at a high flow rate SV = 10–40hr -1 In the case of processing, the activated carbon device used is preferably […]. The proportion of fine pores is increased to 10% by volume or more, preferably 20% by volume or more, or it is made into activated carbon with high decomposition capacity supported by decomposition catalysts such as platinum, palladium or silver.

[0068] Activated carbon that improves the decomposition ability relative to hydrogen peroxide by altering the pore distribution can be exemplified by, for example, CENTAUR (trade name) sold by Calgon Carbon Japan. Furthermore, T-SB (trade name) manufactured by Kuraray Chemical Co., Ltd. can be exemplified as an activated carbon supporting a high-decomposition catalyst for hydrogen peroxide.

[0069] It should be noted that, in order to adjust the hydrogen peroxide concentration, a hydrogen peroxide removal device other than activated carbon (H2O2 removal device) can also be installed. This hydrogen peroxide removal device is a device that decomposes and removes hydrogen peroxide from water. Examples include metal catalyst supported resin devices that decompose and remove hydrogen peroxide by using palladium (Pd) or platinum (Pt) supported resin, and reducing resin devices filled with reducing resin having sulfite groups and / or bisulfite groups on the surface.

[0070] In addition, if there is virtually no hypochlorous acid in the water flowing into the activated carbon device, a bypass line can be installed in the activated carbon device to adjust the hydrogen peroxide concentration.

[0071] The residual hydrogen peroxide can be removed by further using a hydrogen peroxide removal mechanism downstream of the reverse osmosis membrane unit, etc. Examples of such hydrogen peroxide removal mechanisms include metal catalyst supported resin devices that decompose and remove hydrogen peroxide by palladium (Pd) or platinum (Pt) supported resin, reducing resin devices filled with reducing resin having sulfite groups and / or bisulfite groups on the surface, or activated carbon devices described in the above-mentioned recovery treatment unit and primary pure water production unit, etc.

[0072] Example

[0073] The present invention will now be described with reference to embodiments and comparative examples. It should be noted that the present invention is not to be interpreted in a limiting manner by these embodiments.

[0074] (Example 1)

[0075] use Figure 1 The ultrapure water manufacturing apparatus shown produces ultrapure water for use in the washing (SPM washing) of semiconductor wafers in a semiconductor manufacturing facility. The used ultrapure water after washing contains sulfuric acid, phosphoric acid, hydrogen peroxide, etc., and is treated in a recycling unit to obtain recycled water. It should be noted that the apparatus used in the recycling unit is as follows.

[0076] <Recycling Department>

[0077] Membrane treatment device 61: 3M bag filter, 1μm

[0078] Reverse osmosis membrane unit 62: Low-pressure RO (manufactured by Toray Corporation, trade name: TM720D)

[0079] Operating pressure 0.6MPa

[0080] The hydrogen peroxide concentration in the recovered water obtained by sequentially processing the membrane treatment unit 61 and the reverse osmosis membrane unit 62 (first reverse osmosis membrane unit) is 20 ppm. This recovered water is then circulated and supplied to the storage unit 5. In the storage unit 5, the pretreated water obtained in the pretreatment unit is mixed with the recovered water and used as the treated water for further production of ultrapure water. The mixing ratio is pretreated water:recovered water = 4:1.

[0081] It should be noted that the sodium hypochlorite concentration of the pretreated water and the hydrogen peroxide concentration of the recycled water at this time are shown in Table 1. In addition, the viable bacteria count at the inlet of the mixed water in the storage tank 5 and the reverse osmosis membrane unit (second reverse osmosis membrane unit) installed in the primary pure water production unit, as well as the TOC concentration at the outlet of the raw water and the second reverse osmosis membrane unit, were measured and are shown in Table 1.

[0082] Determination of sodium hypochlorite concentration: For pretreated water, residual chlorine was determined using a residual chlorine meter (DPD (diethyl-p-phenylenediamine method), manufactured by Shibata Scientific Co., Ltd., simplified water quality reagent kit).

[0083] Hydrogen peroxide concentration: For recycled water, the concentration was measured using an online hydrogen peroxide measuring device (NOXIA) (manufactured by Nomura MicroScience Co., Ltd.).

[0084] Viable bacteria count was determined using raw water and samples collected at the inlet of the second reverse osmosis membrane unit, and the count was determined using a culture method (standard agar medium, 32 degrees Celsius for 7 days).

[0085] TOC determination: The determination was performed at the outlet of the raw water and the second reverse osmosis membrane unit using a Sievers M9e (manufactured by Suez).

[0086] (Comparative Example 1)

[0087] Compared to Example 1, the recycling treatment unit is configured as a device consisting of a combined activated carbon unit (manufactured by Mitsubishi Chemical, trade name: DIAHOPE 006 and manufactured by Calgon Carbon Japan, trade name: CENTAUR, volume ratio 2:1) and a weakly alkaline anion exchange unit (manufactured by DowDuPont, trade name: A368D) connected in sequence. Otherwise, the recycled water is mixed to produce ultrapure water in the same manner as in Example 1.

[0088] The water quality was measured in the same manner as in Example 1, and the results are shown in Table 1.

[0089] (Comparative Example 2)

[0090] Sulfite was added to the pretreatment water to remove sodium hypochlorite. Otherwise, the recycled water was mixed in the same manner as in Example 1 to produce ultrapure water.

[0091] The water quality was measured in the same manner as in Example 1, and the results are shown in Table 1.

[0092] Table 1

[0093]

[0094] As can be seen from the above, in an ultrapure water production device that recycles and reuses used ultrapure water containing hydrogen peroxide, during the recycling process, the water is circulated in a state where it contains hydrogen peroxide and is then processed into treated water. This process inhibits the number of viable bacteria and TOC after mixing with the raw water or pre-treated water.

[0095] At this point, the activated carbon unit that is usually installed during recycling can be omitted, which simplifies the equipment and reduces the installation area.

[0096] Explanation of symbols

[0097] 1…Ultrapure water production system, 2…Pretreatment unit, 3…Primary pure water production unit, 4…Secondary pure water production unit, 5…Storage unit, 6…Recovery and treatment unit, 7…Circulation mechanism, 61…Membrane treatment unit, 62…First reverse osmosis membrane unit

Claims

1. An ultrapure water producing system characterized by comprising: An ultrapure water production system for producing ultrapure water, which has a pretreatment section, a primary pure water production section, and a secondary pure water production section, and which has: a storage section provided in a front stage of the pretreatment section or between the pretreatment section and the primary pure water production section, and capable of storing raw water or treated water; a recovery treatment section which, for used ultrapure water containing hydrogen peroxide obtained after use of the ultrapure water, removes impurities mixed in the used ultrapure water and allows a part or all of the hydrogen peroxide to permeate to produce recovered water; and a circulation mechanism which sends the recovered water obtained by the recovery treatment section back to the storage section and circulates it, the hydrogen peroxide concentration of the recovered water being 2 to 50 ppm.

2. The ultrapure water producing system according to claim 1, wherein The recovery treatment section has a first reverse osmosis membrane device.

3. The ultrapure water producing system according to claim 1 or 2, characterized by, The recovery treatment section does not have an activated carbon device.

4. The ultrapure water producing system according to claim 1 or 2, wherein The primary pure water production section has a second reverse osmosis membrane device, and a hypochlorous acid removal device in a front stage of the second reverse osmosis membrane device.

5. The ultrapure water producing system according to claim 4, wherein The hypochlorous acid removal device is an activated carbon device.

6. The ultrapure water producing system according to claim 5, wherein The activated carbon device is a high decomposition type activated carbon device.

7. The ultrapure water producing system according to claim 1 or 2, wherein In the storage section, there is a flow rate adjustment mechanism capable of adjusting the supply amount of the recovered water to the supply amount of the raw water or treated water to 10 / 90 to 50 / 50.

8. A method for producing ultrapure water, characterized by, An ultrapure water production method for producing ultrapure water by treating raw water with a pretreatment section, a primary pure water production section, and a secondary pure water production section, wherein there is a storage section provided in a front stage of the pretreatment section or between the pretreatment section and the primary pure water production section, and capable of storing raw water or treated water, used ultrapure water containing hydrogen peroxide obtained after use of the ultrapure water is treated by a recovery treatment section, impurities mixed in the used ultrapure water are removed, and a part or all of the hydrogen peroxide is allowed to permeate to produce recovered water, the recovered water is sent back to the storage section and circulated, the hydrogen peroxide concentration of the recovered water is 2 to 50 ppm.

9. The method of producing ultra-pure water according to claim 8, wherein The recovery treatment section has a first reverse osmosis membrane device.

10. The method of producing ultra-pure water according to claim 8 or 9, wherein In the storage section, the hydrogen peroxide concentration of mixed water obtained by mixing pretreated water obtained by treating with the pretreatment section and the recovered water is 1 to 10 ppm.

11. The method of producing ultra-pure water according to claim 8 or 9, wherein The primary pure water production section has a second reverse osmosis membrane device and a hypochlorous acid removal device in a front stage thereof, by the hypochlorous acid removal device, hypochlorite contained in the recovered water is removed.

12. The method of producing ultra-pure water according to claim 11, wherein The hypochlorous acid removal device is an activated carbon device.

13. The method of producing ultra-pure water according to claim 12, wherein In the activated carbon device, the water to be treated is passed at SV = 5 ~ 40 h -1 water is passed.

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