JP6629383B2 - Ultrapure water production method - Google Patents

Description

  The present invention relates to an ultrapure water production system, and more particularly to an ultrapure water production method and an ultrapure water production system with an improved urea removal rate.

  Conventionally, ultrapure water used in a semiconductor manufacturing process and the like is generally produced by an ultrapure water production system using city water, well water, industrial water, used ultrapure water recovered from a semiconductor factory, etc. as raw water. . The ultrapure water production system includes a pretreatment system, a primary pure water system, and a secondary pure water system, and the processing in each system is performed as follows.

  The pretreatment system treats raw water by combining a coagulation sedimentation device, a sand filtration device, an activated carbon adsorption device (AC), and a pH adjustment device to produce pretreatment water. The primary pure water system combines the filtration / separation device, activated carbon adsorption device, reverse osmosis membrane (RO) device, ultraviolet oxidation device (TOC-UV), deaerator, ion exchange device, etc. Organic matter is removed to produce primary pure water. The secondary pure water system is composed of an ultraviolet oxidation device (TOC-UV), an ion exchange device, an ultrafiltration device (UF), etc., and performs a final finish of primary pure water to produce ultrapure water.

  In recent years, with respect to ultrapure water used in a semiconductor manufacturing process, the demand for further purification has become severe. For example, a specific resistance of 18 MΩ · cm or more and a total organic carbon (TOC) concentration of 1 μgC / L or less are required. Have been

  By the way, in recent years, while many attempts have been made to further reduce the TOC concentration of ultrapure water, a conventional ultrapure water production system does not have a sufficient removal rate of urea contained in raw water and remains in treated water. It has been found that urea is preventing the reduction of the TOC concentration. Therefore, it is required to efficiently remove urea at a high removal rate. In response to such a demand, an ultrapure water production system including a biological treatment means in a pretreatment system has been proposed (for example, Patent Reference 1). Further, a method of adding hypobromous acid to water to be treated has been proposed (for example, see Patent Document 2).

  However, the pure water production system using the biological treatment means has a problem that a high urea removal rate cannot be stably obtained. In addition, in the method of adding hypobromous acid, since a highly reactive chemical is used, an apparatus for storing and adding the chemical is required, and it is necessary to treat the remaining chemical. There have been problems such as complicated configuration and operation. As described above, the conventional method has a problem that the urea removal rate and the efficient removal of urea have not been sufficiently performed yet.

JP 2012-196588 A JP 2010-53724 A

  The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to improve the urea removal rate in a reverse osmosis membrane device without using a chemical, and to produce ultrapure water having an extremely low TOC concentration. It is an object of the present invention to provide an ultrapure water production method and an ultrapure water production system that can be used.

The ultrapure water production method according to the embodiment includes a pressurizing step of pressurizing the water to be treated having a urea concentration of 10 to 100 μg / L to 2.0 to 4.0 MPa, and treating the pressurized water to be treated by a reverse osmosis membrane. And a first reverse osmosis membrane treatment step.
Further, the ultrapure water production method according to another embodiment includes a pressurizing step of pressurizing water to be treated having a urea concentration of 10 to 100 μg / L to 2.0 to 4.0 MPa within a standard operating pressure of the reverse osmosis membrane. And a first reverse osmosis membrane treatment step of treating pressurized water to be treated with the reverse osmosis membrane. In the above embodiment, the urea removal rate in the reverse osmosis membrane is 60% or more. Further, the pressing force in the pressing step is preferably 3.0 MPa or more.

The ultrapure water production system according to the embodiment includes a pump for pressurizing the water to be treated having a urea concentration of 10 to 100 μg / L to 2.0 to 4.0 MPa, and a pump for treating the pressurized water to be treated by a reverse osmosis membrane. 1 reverse osmosis membrane device.
Further, the ultrapure water production system according to another embodiment includes a pump that pressurizes the water to be treated having a urea concentration of 10 to 100 μg / L to 2.0 to 4.0 MPa within a standard operating pressure of the reverse osmosis membrane, A first reverse osmosis membrane treatment device for treating pressurized water to be treated with the reverse osmosis membrane at a urea removal rate of 60% or more. In the above embodiment, the urea removal rate in the reverse osmosis membrane is 60% or more. Further, the pressing force in the pressing step is preferably 3.0 MPa or more.

  According to the ultrapure water production method and the ultrapure water production system of the embodiment, the urea removal rate in the reverse osmosis membrane device can be improved, and ultrapure water having an extremely low TOC concentration can be obtained.

It is a block diagram showing the ultrapure water production system of a 1st embodiment. It is a block diagram which shows the ultrapure water production system of 2nd Embodiment. It is a block diagram which shows the ultrapure water production system of 3rd Embodiment. It is a block diagram showing an ultrapure water production system of a fourth embodiment. It is a graph which shows the relationship between the water recovery rate and the urea removal rate in an Example. It is a graph which shows the relationship between the urea concentration and the urea removal rate in an Example and a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the drawings, devices having common functions are denoted by the same reference numerals, and redundant description will be omitted. Further, the present invention is not limited to the following embodiments.

(First embodiment)
FIG. 1 is a block diagram of an ultrapure water production system 1 according to the first embodiment. The ultrapure water production system 1 includes a pretreatment system 10, a primary pure water system 20, and a secondary pure water system 30 in this order. The secondary pure water system 30 is connected to a point of use (POU) 40 to supply the produced ultrapure water to the POU.

  In the ultrapure water production system 1, raw water is not particularly limited, and city water, well water, industrial water, used ultrapure water collected from the use point 40, and the like can be used.

  The pretreatment system 10 removes raw water, adjusts the temperature with a heat exchanger or the like as necessary, and produces pretreatment water. The pretreatment system 10, for example, is configured by appropriately selecting a sand filtration device, a microfiltration device, and the like, and mainly performs turbidity in order to suppress the influence of impurities in raw water on each device of the subsequent primary pure water system. . The pretreatment system 10 temporarily stores the produced pretreatment water in the pretreatment water tank 11, and the pretreatment water is sent to the primary pure water system 20. If the quality of the raw water is sufficient to supply the primary purified water system 20, the pretreatment system 10 may be omitted.

  The primary pure water system 20 of the present embodiment produces primary pure water by removing organic substances, ionic components, and dissolved gases from pretreated water. The primary pure water system 20 includes an activated carbon device (AC) 21, an auxiliary reverse osmosis membrane device (Sub-RO) 23, a reverse osmosis membrane device (RO) 25, an ultraviolet oxidation device (TOC-UV) 26, and a mixed-bed ion exchange. The device (MB) 27 is provided in this order. Immediately before the auxiliary reverse osmosis membrane device 23 and the reverse osmosis membrane device 25, pumps 22 and 24 are provided to supply the auxiliary reverse osmosis membrane device 23 and the reverse osmosis membrane device 25 with water to be treated at a predetermined supply pressure. I have. The pumps 22 and 24 are, for example, water supply pumps whose discharge pressure can be adjusted.

  Here, the reverse osmosis membrane treatment in the conventional ultrapure water production system did not remove low molecular weight organic substances, and in particular, the urea removal rate was extremely low. This is considered to be because urea has a low molecular weight of 60 and is a polar molecule, and thus has a high affinity for water and passes through a reverse osmosis membrane together with water. Further, in the conventional ultrapure water production system, part of the urea that has passed through the reverse osmosis membrane device is not decomposed by the ultraviolet oxidizing device, and further passes through the secondary pure water system, so that the TOC at the terminal ends. In some cases.

  In particular, when the urea concentration of the water to be treated is extremely low, it has been difficult to remove urea by the reverse osmosis membrane treatment in the conventional ultrapure water production system. On the other hand, according to the ultrapure water production system 1 of the present embodiment, when the water to be treated having a low urea concentration is treated with the reverse osmosis membrane, the supply pressure is equal to or higher than a predetermined supply pressure, so that the urea removal rate is dramatically increased. It is possible to improve.

  In the primary pure water system 20 of the present embodiment, first, the activated carbon device 21 removes impurities such as hydrogen peroxide and chlorine mixed in the pretreatment water, which cause film deterioration. Next, the auxiliary reverse osmosis membrane device 23 desalinates the treated water of the activated carbon device 21. At this time, the activated carbon device 21 and the auxiliary reverse osmosis membrane device 23 remove a part of the urea to make the urea concentration of the deionized water 10 to 100 μg / L, preferably 30 to 50 μg / L.

In the primary pure water system 20 of the present embodiment, the urea removal rate in the activated carbon device 21 is preferably about 40 to 60%. Therefore, the space velocity (SV) of the water to be treated in the activated carbon device 21 is preferably 5 to 20 hr ^-1 , more preferably 7 to 15 hr ^-1 . Further, by setting the space velocity SV in the activated carbon device 21 to be smaller than the above value, for example, setting the SV to 2 to 7 hr ^-1 , the amount of urea removed in the activated carbon device 21 can be increased.

  The auxiliary reverse osmosis membrane device 23 can desalinate the treated water of the activated carbon device 21 and remove a part of the urea in the treated water of the activated carbon device 21. In the auxiliary reverse osmosis membrane 23, the urea removal rate is preferably 20 to 40%. Therefore, although depending on the quality of the pretreatment water, the water recovery rate in the auxiliary reverse osmosis membrane device 23 is preferably set to 50 to 80%. In addition, from the viewpoint of desalination ability, the pump 22 pressurizes the activated carbon treated water to preferably 0.5 to 1.5 MPa, more preferably 0.7 to 1.3 MPa, and supplies it to the auxiliary reverse osmosis membrane device 23. Is desirable.

  As the auxiliary reverse osmosis membrane device 23, a membrane module in which a cellulose triacetate-based asymmetric membrane, a polyamide-based composite membrane is used as a sheet flat membrane, a spiral membrane, a tubular membrane, a hollow fiber membrane, or the like can be used without particular limitation. . The auxiliary reverse osmosis membrane device 23 is preferably a polyamide-based composite membrane in order to improve the urea removal rate and desalination rate, and the membrane shape is preferably a spiral membrane.

  In addition, it is possible to increase the removal amount of urea by connecting the auxiliary reverse osmosis membrane 23 in two stages in series to form a two-stage auxiliary reverse osmosis membrane device.

  The reverse osmosis membrane device 25 removes urea in the water to be treated having a urea concentration of 10 to 100 μg / L, preferably 30 to 50 μg / L. As a two-stage reverse osmosis membrane device in which the two-stage reverse osmosis membrane devices 25 are connected in series, the urea concentration of the water to be treated in the second-stage reverse osmosis membrane device may be the above-mentioned value. At this time, the pump 24 pressurizes the water to be treated, and sets the supply pressure in the reverse osmosis membrane device 25 to 2.0 to 4.0 MPa, preferably 2.5 to 3.5 MPa. As a result, the reverse osmosis membrane device 25 can remove urea at a high removal rate. Specifically, the removal rate of urea can be preferably 60% or more, more preferably 65% or more. Can be set to about 85%, more preferably about 90%. At this time, the urea can be removed at a high removal rate when the supply pressure of the water to be treated pressurized by the pump 24 is 2.0 MPa or more, and the power consumption is increased when the supply pressure is 4.0 MPa or less. Can be suppressed.

  The water recovery rate in the reverse osmosis membrane device 25 is preferably 50 to 95%, more preferably 60 to 90%, and more preferably 65 to 85% in order to improve the urea removal rate. More preferred. The water recovery rate is adjusted by providing a variable opening valve in the concentrated water pipe and the permeated water pipe of the reverse osmosis membrane device 25, and adjusting the opening of the valve to change the flow rates of the concentrated water and the permeated water, respectively. That can be achieved. Prior to passing the water through the reverse osmosis device 25, an acid agent such as hydrochloric acid or an alkaline agent such as sodium hydroxide may be added to the water to be treated to adjust the pH to an arbitrary value. In this case, for example, by adding sodium hydroxide to the water to be treated to adjust the pH to 10 to 11, the generation of scale on the reverse osmosis membrane surface in the reverse osmosis device 25 can be suppressed, and the water recovery rate can be improved. .

  As the reverse osmosis membrane device 25, a membrane module using a cellulose triacetate-based asymmetric membrane or a polyamide-based composite membrane as a sheet flat membrane, a spiral membrane, a tubular membrane, or a hollow fiber membrane can be used. Above all, in order to remove urea at a high removal rate, a membrane module in which a polyamide composite membrane in which an ultrathin polyamide film is formed on a polysulfone support membrane, for example, by an interfacial polymerization method as a spiral membrane, or a cellulose triacetate-based asymmetric membrane Is preferably used as a hollow fiber membrane, and from the viewpoint of improving the urea removal rate, a polyamide-based composite membrane is more preferable, and the membrane shape is more preferably a spiral membrane.

  Examples of the reverse osmosis membrane device 25 include SW-30 (manufactured by Dow Filmtec, maximum operating pressure of 8.2 MPa), SU820 (manufactured by Toray Industries, Inc.), TM820 (manufactured by Toray Industries, Inc.), and NTR-SWC (manufactured by Toray Industries, Inc.) Commercial products such as Denko Corporation can be used. The maximum operating pressure of SU820, TM820, and NTR-SWC is the same as that of SW-30.

  The ultraviolet oxidation device 26 has, for example, an ultraviolet lamp capable of irradiating ultraviolet light having a wavelength of about 185 nm, and irradiates ultraviolet light to the water to be treated from the ultraviolet lamp to oxidize and decompose TOC in the water to be treated. The ultraviolet lamp used in the ultraviolet oxidation device 26 does not need to be a lamp that generates only ultraviolet light having a wavelength of about 185 nm, and in the present embodiment, for example, emits ultraviolet light of about 254 nm together with ultraviolet light of about 185 nm. Low pressure mercury lamps can be used.

The ultraviolet oxidizer 26 decomposes water with ultraviolet rays having a wavelength of about 185 nm to generate OH radicals, and oxidatively decomposes organic substances in the water to be treated into organic acids by the OH radicals. The irradiation amount of the ultraviolet light in the ultraviolet oxidizing device 26 of the primary pure water system 20 can be appropriately changed depending on the quality of the water to be treated. For example, urea can be further removed by setting the ultraviolet irradiation amount to 0.2 to 0.7 kW · h / m ³ . It is preferable that the amount of ultraviolet irradiation is adjusted in the above range according to a desired urea concentration required for the treated water. For example, from the viewpoint of suppressing the irradiation amount of ultraviolet rays, it is preferable to set the irradiation amount to about 0.2 to 0.4 kW · h / m ^3. By doing so, the amount of urea removed can be increased. At that time, if the UV irradiation amount is about 0.7 kW · h / m ³ , a sufficient urea removal rate can be obtained.

  As the mixed bed type ion exchange device 27, a device in which a cation exchange resin and an anion exchange resin are mixed and filled can be used, and any of a regeneration type and a non-regeneration type may be used. The mixed-bed ion exchange device 27 adsorbs and removes low-molecular-weight ion components generated by oxidative decomposition of organic substances in the ultraviolet oxidizer 26 in the preceding stage. The removal rate of urea in the combination of the ultraviolet oxidation device 26 and the mixed bed type ion exchange device 27 of the present embodiment is preferably 40 to 60%, whereby the urea remaining in the water to be treated is removed and the TOC is reduced. Primary purified water with a reduced concentration can be obtained. The primary pure water is, for example, ultrapure water having a specific resistance of 17 MΩ · cm or more and a TOC concentration of 10 μgC / L or less.

  According to this embodiment, the reverse osmosis membrane device 25 removes urea at a high removal rate, and further removes urea by a combination of the ultraviolet oxidation device 26 and the mixed-bed ion exchange device 27 downstream of the reverse osmosis membrane device 25. Therefore, urea can be removed at a high removal rate. Note that a membrane deaerator may be provided downstream of the mixed-bed ion exchange device 27, whereby the dissolved carbon dioxide and dissolved oxygen in the water to be treated can be removed.

  As described above, in the primary pure water system 20 of the present embodiment, first, the activated carbon device 21 and the auxiliary reverse osmosis membrane device 23 generate the water to be treated having a urea concentration of 10 to 100 μg / L from the pretreated water, and the pump 24 Since the reverse osmosis membrane device 25 performs the reverse osmosis membrane treatment on the water to be treated while the supply pressure of the water to be treated to the reverse osmosis membrane device 25 is increased to 2.0 to 4.0 MPa, urea is removed at a high removal rate. can do. The combination of the ultraviolet oxidation device 26 and the mixed-bed ion exchange device 27 on the downstream side decomposes and removes a small amount of organic substances in the permeated water of the reverse osmosis membrane device 25, so that higher-purity primary pure water can be obtained. Can be manufactured. In addition, since the reverse osmosis membrane device 25 removes urea at a high removal rate, an oxidizing agent for decomposing urea is not required. Therefore, when the oxidizing agent is used, a reduction for reducing the remaining oxidizing agent is performed. The agent can be omitted. Further, a device for adding an oxidizing agent or a reducing agent to the water to be treated for urea decomposition is not required.

  Next, the primary pure water is once stored in a primary pure water tank 31 and then sent to a secondary pure water system 30. The secondary pure water system 30 includes an ultraviolet oxidizer (TOC-UV) 32, a non-regenerative polisher (Polisher) 33, a membrane deaerator (MDG) 34, and an ultrafiltration unit (UF) 35, Ultrapure water is produced in which the organic matter in the primary pure water whose (TOC) concentration has been reduced to about 5 μg C / L is further reduced to about 1 μg C / L.

The configuration of the ultraviolet oxidizer 32 in the secondary pure water system 30 is the same as that of the ultraviolet oxidizer 26 in the primary pure water system 20. The ultraviolet oxidation device 32 oxidizes and decomposes organic matter in the water to be treated by irradiating the water to be treated with ultraviolet light having a wavelength of about 185 nm. The irradiation amount of the ultraviolet light in the ultraviolet oxidizing device 32 can be appropriately changed depending on the quality of the water to be treated. For example, urea can be further removed by setting the ultraviolet irradiation amount to 0.2 to 0.7 kW · h / m ³ . It is preferable that the amount of ultraviolet irradiation is adjusted in the above range according to a desired urea concentration required for the treated water. For example, from the viewpoint of suppressing the irradiation amount of ultraviolet rays, it is preferable to set the irradiation amount to about 0.2 to 0.4 kW · h / m ^3. By doing so, the amount of urea removed can be increased. At that time, if the UV irradiation amount is about 0.7 kW · h / m ³ , a sufficient urea removal rate can be obtained.

  The non-regenerative polisher 33 adsorbs and removes ionic components generated by the ultraviolet oxidation device 32 decomposing organic substances.

  The non-regenerative polisher 33 is of a type 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 cylinder. The membrane deaerator 34 removes a trace amount of dissolved oxygen in the primary purified water to reduce the dissolved oxygen concentration to about 1 μg / L or less. The ultrafiltration membrane device 35 removes trace elutes and fine particle components from the ion exchange resin on the upstream side to reduce the number of fine particles of 0.05 μm or more to 250 Psc. / L or less.

  In addition, in order to process primary pure water with extremely few impurities and produce ultrapure water of ultra-high quality, each water treatment device of the secondary pure water system 30 is of an exchange type that does not perform chemical regeneration or the like. Preferably, it is used.

  As described above, the secondary pure water system 30 processes the primary pure water to produce ultrapure water with higher purity. This ultrapure water is supplied to the use point 40.

  According to the ultrapure water production system 1 of the present embodiment described above, the urea removal rate in the reverse osmosis membrane device 25 is extremely high, and it is possible to efficiently produce ultrapure water having an extremely low TOC concentration.

(Second embodiment)
Next, a second embodiment will be described with reference to FIG. The ultrapure water production system 2 according to the present embodiment uses an auxiliary reverse osmosis membrane device 23 and a reverse osmosis membrane device 25 in combination with an ultraviolet oxidizing device 26 and a mixed-bed ion exchange device 27 disposed downstream of the reverse osmosis membrane device 25. The second embodiment differs from the first embodiment in that the first embodiment is disposed between the first and second embodiments. Therefore, common elements are denoted by common reference numerals, and redundant description will be omitted.

  In the present embodiment, in the primary pure water system 20, first, the activated carbon device 21 and the auxiliary reverse osmosis membrane device 23 generate water to be treated having a urea concentration of 10 to 100 μg / L from the pretreated water, and the pump 24 operates in the reverse osmosis membrane device. Since the reverse osmosis membrane device 25 performs the reverse osmosis membrane treatment on the water to be treated in a state where the supply pressure of the water to be treated to 25 is increased to 2.0 to 4.0 MPa, urea can be removed at a high removal rate. . Further, since the combination of the ultraviolet oxidation device 26 and the mixed-bed ion exchange device 27 removes organic matter from the permeated water of the auxiliary reverse osmosis membrane device 23, the treated water is processed by the reverse osmosis membrane device 25. By increasing the water recovery rate in the device 25, the urea removal rate can be improved. In addition, since the reverse osmosis membrane device 25 removes urea at a high removal rate, an oxidizing agent for decomposing urea is not required. Therefore, when the oxidizing agent is used, a reduction for reducing the remaining oxidizing agent is performed. The agent can be omitted. Further, a device for adding an oxidizing agent or a reducing agent to the water to be treated for urea decomposition is not required.

(Third embodiment)
Next, a third embodiment will be described with reference to FIG. The ultrapure water production system 3 of the present embodiment differs from the first embodiment in that the primary pure water system 20 is provided with a two-bed, three-tower type device 28 instead of the pump 22 and the reverse osmosis membrane device 23. Therefore, common elements are denoted by common reference numerals, and redundant description will be omitted.

  FIG. 3 is a block diagram of the ultrapure water production system 3 of the present embodiment. The primary pure water system 20 of the present embodiment includes a two-bed three-tower (2B3T) device 28, a pump 24, a reverse osmosis membrane device (RO) 25, an ultraviolet oxidation device (TOC-UV) 26, and a mixed-bed ion exchange device. (MB) 27 are provided in this order. In the primary pure water system 20 of the present embodiment, first, the activated carbon device 21 and the combination of the ion exchange device and the decarbonation device in the two-bed three-column device 28 desalinate the pretreated water and remove a part of the urea. As a result, water to be treated having a urea concentration of 10 to 100 μg / L is generated. Next, after the reverse osmosis membrane device 25 removes the colloid, urea and most of the other organic substances, the combination of the ultraviolet oxidizer 26 and the mixed-bed ion exchanger 27 decomposes the organic substances having a small molecular weight remaining in the water to be treated. ,Remove.

  The auxiliary reverse osmosis membrane device 23 may be installed at any position between the activated carbon device 21 and the reverse osmosis membrane device 25. In this case, the urea concentration of the water to be treated in the reverse osmosis membrane device 25 can be reduced to preferably 50 μg / L or less, more preferably 30 μg / L or less, by further removing the urea of the water to be treated. In addition, the urea removal rate can be further improved.

  The primary pure water system 20 of the present embodiment can reduce the salt concentration of the water to be treated in the reverse osmosis membrane device 25 by desalting in the two-bed, three-tower type device 28. , The urea removal rate in the reverse osmosis membrane device 25 can be improved. As the two-bed three-column apparatus 28, it is preferable to use an apparatus having a cation exchange resin apparatus, a decarbonation tower and an anion exchange resin apparatus in that order. The two-bed, three-tower type apparatus 28 can remove salts and dissolved carbonic acid in the pretreatment water. Further, the two-bed, three-tower type apparatus 28 has an advantage that it is hardly affected by the turbid matter because it is a countercurrent regeneration type. When the raw water contains a large amount of mineral acids and salts, a three-bed four-column apparatus or the like can be used instead of the two-bed three-column apparatus 28. The three-bed, four-column apparatus is composed of a cation exchange resin apparatus, a decarboxylation apparatus, a weakly basic anion exchange resin, and a strongly basic ion exchange apparatus.

  In the ultrapure water production system 3 of the third embodiment, first, the activated carbon device 21 and the two-bed three-tower type device 28 generate water to be treated having a urea concentration of 10 to 100 μg / L from the pretreated water, and the pump 24 Since the reverse osmosis membrane device 25 performs the reverse osmosis membrane treatment on the water to be treated while the supply pressure of the water to be treated to the reverse osmosis membrane device 25 is increased to 2.0 to 4.0 MPa, urea is removed at a high removal rate. can do. The combination of the ultraviolet oxidation device 26 and the mixed-bed ion exchange device 27 on the downstream side decomposes and removes a small amount of organic substances in the permeated water of the reverse osmosis membrane device 25, so that higher-purity primary pure water can be obtained. Can be manufactured. In addition, since the reverse osmosis membrane device 25 removes urea at a high removal rate, an oxidizing agent for decomposing urea is not required. Therefore, when the oxidizing agent is used, a reduction for reducing the remaining oxidizing agent is performed. The agent can be omitted. Further, a device for adding an oxidizing agent or a reducing agent to the water to be treated for urea decomposition is not required.

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to FIG. The ultrapure water production system 4 of the present embodiment comprises a combination of an ultraviolet oxidation device 26 and a mixed-bed ion exchange device 27 arranged at the subsequent stage of a reverse osmosis membrane device, a two-bed three-column device 28 and a reverse osmosis membrane device 25. The third embodiment is different from the third embodiment in that the second embodiment is disposed therebetween. Therefore, common elements are denoted by common reference numerals, and redundant description will be omitted.

  In the ultrapure water production system 3 of the fourth embodiment, first, the activated carbon device 21 and the two-bed three-tower device 28 generate water to be treated having a urea concentration of 10 to 100 μg / L from the pretreated water, and the pump 24 Since the reverse osmosis membrane device 25 performs the reverse osmosis membrane treatment on the water to be treated while the supply pressure of the water to be treated to the reverse osmosis membrane device 25 is increased to 2.0 to 4.0 MPa, urea is removed at a high removal rate. can do. Further, the combination of the ultraviolet oxidizer 26 and the mixed bed ion exchanger 27 removes organic matter from the permeated water of the two-bed three-column apparatus 28, and then the treated water is treated by the reverse osmosis membrane apparatus 25. The water recovery rate in the membrane device 25 can be improved, and thereby the urea removal rate in the reverse osmosis membrane device 25 can be improved. In addition, since the reverse osmosis membrane device 25 removes urea at a high removal rate, an oxidizing agent for decomposing urea is not required. Therefore, when the oxidizing agent is used, a reduction for reducing the remaining oxidizing agent is performed. The agent can be omitted. Further, a device for adding an oxidizing agent or a reducing agent to the water to be treated for urea decomposition is not required.

Next, the present invention will be described in more detail with reference to examples.
(Example 1)
Reverse osmosis membrane at a supply pressure of 3.0 MPa while adding urea to ultrapure water (specific resistance 18.2 MΩ · cm, TOC concentration 2 μg C / L) using a quantitative pump so that the urea concentration becomes 100 μg / L. Water was passed through module A (SW30, manufactured by Dow Filmtec). Experiments were performed with water recovery rates of 50%, 70%, 80%, and 90%. The urea concentration in the permeated water was measured, and the urea removal rate represented by the following formula (1) was measured.

  Urea removal rate (%) = [(supply water urea concentration−permeate urea concentration) / supply water urea concentration] × 100 (1)

The relationship between the water recovery rate and the urea removal rate in Example 1 is shown in the graph of FIG. 5 by a triangular black point with the water recovery rate on the horizontal axis and the urea removal rate on the vertical axis.

(Example 2)
In Example 1, the urea removal rate was measured using the same apparatus and under the same conditions as in Example 1, except that the urea concentration of the RO feed water was adjusted to 30 μg / L. Shown together with Example 1 in the graph of FIG. 5 the relationship between the urea removal rate and the water recovery rate in Example 2 by a square black dots.

(Experimental example 1)
In Experimental Example 1, water to be treated having a water recovery rate of 90%, a supply pressure of 3.0 MPa, and urea concentrations of 30 μg / L, 50 μg / L, 100 μg / L, and 10 g / L was subjected to reverse osmosis membrane module A. The same procedure was used as in 1. The relationship between the urea concentration and the urea removal rate at this time is shown in the graph of FIG. 6 by white circles with the urea concentration on the horizontal axis and the urea removal rate on the vertical axis.

(Experimental example 2)
In Experimental Example 1, the same experiment was performed under the same conditions as in Experimental Example 1 except that the water recovery rate was 50%. The relationship between the urea concentration and the urea removal rate at this time is shown in the graph of FIG.

(Experimental example 3)
In Experimental Example 1, the same experiment was performed under the same conditions as in Experimental Example 1 with the supply pressure set to 2.0 MPa. The relationship between the urea concentration and the urea removal rate at this time is shown in the graph of FIG.

(Comparative Example 1)
In Experimental Example 1, a reverse osmosis membrane module B (SU720, manufactured by Dow Filmtech) was used instead of the reverse osmosis membrane module A, the water recovery rate was 50%, and the supply pressure was 1.5 MPa. A similar experiment was performed. The relationship between the urea concentration and the urea removal rate at this time is shown in the graph of FIG.

  From FIG. 5, at a supply pressure of 3.0 MPa, when the urea concentration is 100 μg / L, the urea removal rate decreases as the water recovery rate increases, but when the urea concentration is 30 μg / L, the water recovery rate decreases. It can be understood that the urea removal rate is improved as the value is increased. Although not shown in FIG. 5, the tendency of the urea removal rate to increase when the water recovery rate was increased was confirmed under the condition that the urea concentration was 50 μg / L or less.

  Further, from FIG. 6, comparing the experimental example 2 with the comparative example 1, when the water recovery rate is 50%, in the comparative example 1 in which the supply pressure and the supply pressure are set to 1.5 MPa, the lower the urea concentration of the water to be treated, the lower the urea concentration. The urea removal rate was low, and it was found that the urea removal rate was less than 30% when the urea concentration was 100 μg / L or less. On the other hand, in Experimental Example 2 in which the supply pressure was 3.0 MPa, it was found that the urea removal rate gradually decreased as the urea concentration became lower than 100 μg / L. Furthermore, in Experimental Example 1 in which the water recovery rate was increased to 90% under the same conditions as in Experimental Example 2, the urea removal rate gradually increased from 100 μ / L as the urea concentration became smaller. It turned out to be.

  From the above, it was found that the urea removal rate was improved by performing the reverse osmosis membrane treatment with the urea concentration of the water to be treated being 100 μg / L or less and the supply pressure of the water being treated being 3.0 MPa or more.

(Example 3)
In the ultrapure water production system 1 shown in FIG. 1, when activated water is supplied to the activated carbon device 21 with a urea concentration of 100 μg / L, the activated carbon device 21, the auxiliary reverse osmosis membrane device 23, the reverse osmosis membrane device 25, Table 1 shows the urea concentration in the treated water of the bed type ion exchange device 27 and the polisher 33. The urea concentration (0.8 μg / L) of the treated water of the polisher 33 in this embodiment corresponds to a TOC concentration of 0.16 μg C / L.

The specifications and water flow conditions of each device in this embodiment are as follows.
Raw water: City water Activated carbon device (AC) 21: Filled with activated carbon F400 (manufactured by Mitsubishi Chemical Calgon), space velocity (SV) 10 hr ^-1
Auxiliary reverse osmosis membrane device (Sub-RO) 23: Reverse osmosis membrane module SU720 (manufactured by Dow Filmtec), supply pressure 1.5 MPa, water recovery rate 75%
Reverse osmosis membrane device (RO) 25: Reverse osmosis membrane module SW30 (manufactured by Dow Filmtech), supply pressure 2.0 MPa, water recovery rate 85%
UV oxidation devices (TOC-UV) 26, 32: AUV-8000 TOC (manufactured by Japan Photo Science Co., Ltd.), UV irradiation dose 0.3 kW · h / m ³
Mixed bed type ion exchange device (MB) 27: Anion exchange resin: Strongly basic anion exchange resin Duolite A-113plus (manufactured by Rohm & Haas) and cation exchange resin: Strongly acidic cation exchange resin Duolite C -20 (manufactured by Rohm & Haas Co.) is preliminarily regenerated and converted into H-form and OH-form and then mixed and filled, space velocity (SV) 40 hr ^-1
Polisher 33: Anion exchange resin: Strongly basic anion exchange resin Duolite A-113plus (manufactured by Rohm & Haas) and cation exchange resin: Strongly acidic cation exchange resin Duolite C-20 (Rohm & Haas) Haas Co., Ltd.) was previously regenerated and converted into H-form and OH-form and then mixed and filled, space velocity (SV) 40 hr ^-1

(Example 4)
In the ultrapure water production system 2 shown in FIG. 2, the activated carbon device 21, the auxiliary reverse osmosis membrane device 23, and the mixed-bed ion exchange device 27 when the water to be treated having a urea concentration of 100 μg / L is supplied to the activated carbon device 21. Table 2 shows the urea concentrations in the treated water of the reverse osmosis membrane device 25 and the polisher 33. The urea concentration (0.5 μg / L) of the treated water of the polisher 33 in this embodiment corresponds to a TOC concentration of 0.16 μg C / L.
The specifications and water flow conditions of each device used in the fourth embodiment are the same as those in the third embodiment.

(Example 5)
In the ultrapure water production system 3 shown in FIG. 3, when activated water is supplied to the activated carbon device 21 with a urea concentration of 100 μg / L, the activated carbon device 21, the two-bed three-column device 28, the reverse osmosis membrane device 25, Table 3 shows the urea concentrations in the treated water of the mixed bed ion exchange device 27 and the polisher 33. The urea concentration (0.9 μg / L) of the treated water of the polisher 33 in this embodiment corresponds to a TOC concentration of 0.18 μg C / L.

The specifications of the two-bed, three-column apparatus 28 used in Example 5 are such that the following cation exchange resin tower, atmospheric degassing tower, and anion exchange resin tower are connected in this order. In addition, the conditions for passing water through each water treatment tower are also shown.
Two-bed, three-column apparatus 28: Cation exchange resin tower: Packed with strongly acidic cation exchange resin Duolite C-20 (manufactured by Rohm & Haas), space velocity (SV) = 10 hr ^-1
Atmospheric pressure degassing tower (manufactured by Nomura Micro Science Co., Ltd.),
Anion exchange resin tower: packed with strong basic anion exchange resin Duolite A-113plus (manufactured by Rohm & Haas), space velocity (SV) = 10 hr ^-1 ,
Further, the specifications of the activated carbon device 21, the reverse osmosis membrane device 25, and the ultraviolet oxidizing device 26 in the fifth embodiment and the conditions for water passage are the same as those in the third embodiment.

(Example 6)
In the ultrapure water production system 4 shown in FIG. 4, when activated water is supplied to the activated carbon unit 21 with water to be treated having a urea concentration of 100 μg / L, a two-bed three-column unit 28, a mixed-bed ion exchange unit Table 4 shows the urea concentrations in the treated water of the reverse osmosis membrane device 25 and the polisher 33. The urea concentration (0.7 μg / L) of the treated water of the polisher 33 in this embodiment corresponds to a TOC concentration of 0.14 μg C / L. The specifications and water flow conditions of each device used in the sixth embodiment are the same as those in the fifth embodiment.

  As described above, according to the ultrapure water production system 1 to the ultrapure water production system 4 of the third to sixth embodiments, in the reverse osmosis membrane device 25, the water to be treated having a urea concentration of 50 μg / L is It can be seen that since the treatment is performed under a pressure of at least 0.0 MPa, the removal rate of urea is extremely high, and ultrapure water having a TOC concentration of 1 μgC / L or less can be produced. Further, it can be seen that by combining the unit devices of the conventional water treatment apparatus, ultrapure water having an extremely low TOC concentration can be obtained from the water to be treated containing urea at about 100 μg / L or less.

  1, 2, 3, 4 ... ultrapure water production system, 10 ... pretreatment system, 11 ... pretreatment water tank, 20 ... primary pure water system, 21 ... activated carbon device, 22, 24 ... pump, 23 ... auxiliary reverse osmosis Membrane device, 25 reverse osmosis membrane device, 26 ultraviolet ray oxidation device, 27 mixed-bed ion exchange device, 28 two-bed three-column device, 30 secondary water system, 31 primary water tank, 32 ... Ultraviolet oxidation device, 33 ... Non-regenerative polisher, 34 ... Membrane deaerator, 35 ... Ultrafiltration membrane device.

Claims (6)

A pressure step of pressurizing the water to be treated having a urea concentration of 10 to 100 μg / L to 2.0 to 4.0 MPa;
A first reverse osmosis membrane treatment step in which pressurized water to be treated is treated by a reverse osmosis membrane device having a reverse osmosis membrane at a removal rate of urea per stage of the reverse osmosis membrane device of 60% or more and less than 65%. and,
A method for producing ultrapure water, comprising: The method for producing ultrapure water according to claim 1, wherein the pressing force in the pressurizing step is 3.0 MPa or more. The ultrapure water production method according to claim 1 or 2, wherein a water recovery rate in the first reverse osmosis membrane treatment step is 60 to 90%. The ultrapure water production method according to any one of claims 1 to 3 , further comprising a first removal step of generating the water to be treated from raw water. The first removing step includes:
An activated carbon treatment step of bringing raw water into contact with activated carbon,
A second reverse osmosis membrane treatment step of treating the activated carbon treated water with a reverse osmosis membrane;
A second removal step of decomposing and removing organic matter in the permeated water obtained in the second reverse osmosis membrane treatment step by a combination of an ultraviolet oxidation treatment and a mixed bed ion exchange treatment ;
The ultrapure water production method according to claim 4, comprising : The first removing step includes:
An activated carbon treatment step of bringing raw water into contact with activated carbon,
A two-bed three-column processing step or a three-bed four-column processing step of treating activated carbon treated water by a combination of a cation exchange treatment, a decarboxylation treatment, and an anion exchange treatment;
A second removal step of decomposing and removing organic substances in the permeated water obtained in the two-bed three-column treatment step or the three-bed four-column treatment step using a combination of ultraviolet oxidation treatment and mixed-bed ion exchange treatment. and,
The ultrapure water production method according to claim 4, comprising :

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