Ultrapure water production apparatus

Abstract

To decrease a ratio of potable water in raw water used in ultrapure water production.SOLUTION: An ultrapure water production method includes a pretreatment for obtaining pretreatment water by removing suspended substances in raw water containing potable water, a primary treatment of manufacturing primary pure water by removing total organic carbon components and ion components in the pretreatment water, and a secondary treatment of producing ultrapure water by removing impurities in the primary pure water, wherein secondary raw water containing sewerage treatment water is allowed to be merged with the raw water or pretreatment water on an upstream side than the primary treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ultrapure water production system. [Background technology]

[0002] In an ultrapure water production apparatus that supplies ultrapure water to semiconductor manufacturing facilities, etc., a technology has been disclosed that uses tap water as raw water and wastewater (sometimes called recovered water) of ultrapure water used in semiconductor manufacturing, etc. (see Patent Documents 1-7). Generally, recovered water is originally ultrapure water mixed with substances used in semiconductor manufacturing, such as acids, alkalis, IPA (isopropyl alcohol), surfactants, CMP abrasives, etc. Therefore, the components are relatively clear, and it is relatively easy to treat it and mix it with raw water for use. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-233997 [Patent Document 2] Japanese Patent Application Publication No. 7-313994 [Patent Document 3] Japanese Patent Application Publication No. 10-272465 [Patent Document 4] Japanese Patent Application Publication No. 11-226569 [Patent Document 5] JP 2000-189760 A [Patent Document 6] JP 2006-61779 A [Patent Document 7] JP 2013-202587 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, because a large amount of ultrapure water is used in the manufacture of semiconductors, etc., the amount of tap water used to produce ultrapure water is also increasing. Because the supply of tap water is limited, measures are being sought to reduce the amount of tap water used in the manufacture of ultrapure water so that there is no shortage of tap water for other uses. In addition, there is a limit to the use of the above-mentioned recycled water, so although it is effective in reducing the use of raw water, it is not sufficient to meet the current demand for larger semiconductor manufacturing factories. Furthermore, due to the current environmental and climate change issues, the supply of drinking water is becoming unstable, creating a need to secure new raw water sources.

[0005] In general, sewage or treated sewage water has poorer water quality than drinking water, and contains particularly difficult-to-decompose substances such as urea, as well as a large amount and variety of other substances. Removal equipment for difficult-to-decompose substances such as urea tends to be large-scale, making it difficult to put into practical use, and even a small amount may reach the end of the pure water system. In addition, the water quality fluctuates widely, and the amount of water is not stable. Therefore, it has not been common to use sewage or treated sewage water as raw water for ultrapure water for manufacturing semiconductors, etc.

[0006] An object of the present invention is to reduce the proportion of clean water in the raw water used for producing ultrapure water. [Means for solving the problem]

[0007] The ultrapure water production method according to the first aspect includes a pretreatment step of removing suspended matter from raw water, including drinking water, to obtain pretreated water, a primary treatment step of removing total organic carbon components and ionic components from the pretreated water to produce primary pure water, and a secondary treatment step of removing impurities from the primary pure water to produce ultrapure water, in which a second raw water, including sewage treatment water, is merged with the raw water or the pretreated water upstream of the primary treatment step.

[0008] In this ultrapure water production method, ultrapure water is produced using second raw water containing wastewater from a sewage treatment plant in addition to raw water made from tap water, so the proportion of tap water in the raw water used to produce ultrapure water can be reduced.

[0009] In a second aspect, in the ultrapure water manufacturing method according to the first aspect, the amount of the second raw water to be merged with the raw water or the pretreated water is set so that the weighted average of the urea concentration in the raw water or the pretreated water and the urea concentration in the second raw water is equal to or lower than a urea concentration determined from the urea concentration required for the ultrapure water.

[0010] In this method for producing ultrapure water, the amount of second raw water to be mixed with the raw water is set according to the urea concentration required in the ultrapure water, so that the urea concentration in the ultrapure water can be suppressed to a standard or lower.

[0011] In a third aspect, in the ultrapure water manufacturing method according to the first or second aspect, when the urea concentration of the second raw water exceeds an allowable value determined based on a urea concentration required for the ultrapure water, the second raw water is passed through a urea decomposition device to reduce the urea concentration to below the allowable value.

[0012] In this method for producing ultrapure water, when the urea concentration of the second raw water exceeds an allowable value required by the urea concentration required for the ultrapure water, the second raw water is passed through a urea decomposition device to reduce the urea concentration to below the allowable value, and then the second raw water is merged with the raw water using clean water, thereby making it possible to more effectively use sewage.

[0013] The ultrapure water manufacturing apparatus of the fourth aspect comprises a pretreatment section which removes suspended matter from raw water, including drinking water, to obtain pretreated water, a primary treatment section which removes total organic carbon components and ionic components from the pretreated water to produce primary pure water, a secondary treatment section which removes impurities from the primary pure water to produce ultrapure water, and a urea meter which measures the urea concentration of second raw water, including sewage treatment plant water, and merges the second raw water, the urea concentration of which is below an allowable value, into the raw water or the pretreated water upstream of the primary treatment section.

[0014] This ultrapure water production system produces ultrapure water using, in addition to raw water made from tap water, a second raw water that contains wastewater from a sewage treatment plant and has a urea concentration below the allowable value, so that the proportion of tap water in the raw water used to produce ultrapure water can be reduced.

[0015] In a fifth aspect, in the ultrapure water producing apparatus according to the fourth aspect, the apparatus further comprises a urea decomposition device that decomposes urea in the second raw water, and a urea decomposition section that passes the second raw water through the urea decomposition device to reduce the urea concentration when the urea concentration exceeds an allowable value determined by a urea concentration required for the ultrapure water.

[0016] In this ultrapure water production system, when the urea concentration of the second raw water exceeds an allowable value required by the urea concentration required for the ultrapure water, the second raw water is passed through a urea decomposition device to reduce the urea concentration to below the allowable value, and then the second raw water is merged with the raw water made from clean water. Therefore, sewage can be used more effectively.

[0017] In a sixth aspect, in the ultrapure water manufacturing apparatus of the fourth aspect, the amount of the second raw water to be merged with the raw water or the pretreated water is set so that the weighted average of the urea concentration in the raw water or the pretreated water and the urea concentration of the second raw water is equal to or less than an allowable value determined by the urea concentration required for the ultrapure water.

[0018] In this ultrapure water production system, the amount of second raw water to be mixed with the raw water is set according to the urea concentration required in the ultrapure water, so that the urea concentration in the ultrapure water can be suppressed to a standard or lower. Effect of the Invention

[0019] According to the present invention, the proportion of clean water in the raw water used for producing ultrapure water can be reduced. [Brief description of the drawings]

[0020] [Figure 1] 1 is a block diagram showing an overview of an ultrapure water production apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a block diagram showing an overview of an ultrapure water production system according to a modified example of the present embodiment. [Diagram 3] FIG. 1 is a block diagram showing an example of the configuration of a urea meter. [Figure 4]6 is a diagram showing a change in urea concentration of second raw water over time and an example of the receiving conditions for the second raw water. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Components indicated by the same reference numerals in each drawing are the same or similar components. Note that duplicated descriptions and reference numerals in the embodiments described below may be omitted. In addition, all drawings used in the following description are schematic, and the dimensional relationship of each element, the ratio of each element, etc. shown in the drawings do not necessarily match the actual ones. In addition, the dimensional relationship of each element, the ratio of each element, etc. between multiple drawings do not necessarily match.

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] 1, an ultrapure water producing apparatus 100 according to this embodiment can produce ultrapure water by receiving raw water derived from natural water, i.e., city water, industrial water, etc., as well as second raw water derived from sewage. This ultrapure water producing apparatus 100 has a pretreatment section 10, a primary treatment section 11, a secondary treatment section 12, and a urea meter 30. The ultrapure water producing apparatus 100 may further include a urea decomposition section 13.

[0024] The pretreatment unit 10 is a device that removes suspended solids from raw water (first raw water) including drinking water to obtain pretreated water. For example, impurities such as residual chlorine and large debris in the raw water are filtered by a sand filter filled with media such as filter sand, a packed tank filter tower such as an MMF (multimedia filter tower), a membrane filter using a filter such as an MF (microfilter) or an UF (ultrafiltration membrane), and / or a granular activated carbon tower. The raw water including drinking water is so-called tap water obtained by subjecting natural water 14, such as river water, lake water, and well water, to a coagulation and sedimentation process 17 and a filtration process 18 in a drinking water treatment plant 16. The raw water is stored in a raw water tank 20, for example, and used to produce ultrapure water.

[0025] The primary treatment unit 11 is a device that produces primary pure water by removing total organic carbon (TOC) components and ionic components from the pretreated water. As an example, the primary pure water is purified by combining a reverse osmosis membrane device that uses a semipermeable membrane to perform reverse osmosis of the pretreated water, an ion exchange resin device filled with ion exchange resin, an electrodeionization device (EDI), an ultraviolet irradiation device that decomposes organic matter, and a degassing membrane device that degasses dissolved gas. The primary treatment unit 11 may be provided with a urea decomposition device such as a high-pressure reverse osmosis membrane device or an oxidation reaction tank that decomposes urea by adding hypobromous acid or the like, as necessary. The produced primary pure water is supplied to a pure water tank 22.

[0026] The secondary treatment unit 12 is a device that further removes impurities from the primary pure water to produce ultrapure water, and for example, removes trace amounts of inorganic ions contained in the primary pure water using, for example, a non-regenerative ion exchange tower (polisher). In addition, an ultraviolet ray irradiation unit, a hydrogen peroxide decomposition unit, a degassing unit, etc. are combined. An ultrafiltration membrane is installed at the end of the secondary treatment unit 12 to remove fine particles. The produced ultrapure water is supplied to a POU (point of use) 19 and used for semiconductor manufacturing, etc., and a portion is circulated to a pure water tank 22 via a circulation line 28.

[0027] The second raw water is water including treated sewage water obtained by subjecting sewage 24 to, for example, a biological treatment process 27 in a sewage treatment plant 26. The second raw water, whose urea concentration is equal to or lower than an allowable value determined by the urea concentration required for ultrapure water, merges with raw water or pretreated water upstream of the primary treatment unit 11. In the example shown in FIG. 1, the second raw water merges with the raw water and is stored in the raw water tank 20. In the modified example shown in FIG. 2, the second raw water merges with the pretreated water between the pretreatment unit 10 and the primary treatment unit 11. The pretreatment unit 10 is not a device intended for removing urea, and the removal of suspended solids performed in the pretreatment unit 10 has already been performed in the sewage treatment plant, so the raw water and the second raw water may be merged at the position of the modified example 2.

[0028] The urea meter 30 measures the urea concentration of the second raw water including sewage treatment water, and for example, the one illustrated in FIG. 3 can be used. Here, the urea meter 30 is composed of a pretreatment device 36 and a TOC meter 54. The pretreatment device 36 is composed of, for example, an ultraviolet irradiation device, a reverse osmosis membrane device, or an ion exchange device, and since, for example, the second raw water contains urea and TOC components other than urea, the TOC components other than urea are removed. The TOC meter 54 has a decarbonation device 56, an ultraviolet oxidation device 58, a CO2 detection device 60, and a CO2 detection device 62. The TOC meter 54 is a device that measures the concentration of urea in the second raw water from which TOC components other than urea have been removed as TOC. In addition, the liquid to be measured is not limited to the second raw water which is sewage treatment water, and the second raw water treated by the urea decomposition device 32, the ultrapure water obtained by the secondary treatment device 12, and other liquids obtained in each intermediate process of the ultrapure water production device 100 can be used as the liquid to be measured.

[0029] The decarbonation device 56 of the TOC meter 54 removes carbon dioxide from the liquid to be measured, for example, by using a hollow fiber (vacuum degassing) module. Specifically, phosphoric acid is added to the liquid to be measured, and then the liquid is passed through a gas-permeable membrane with one side kept in a vacuum. Note that if the liquid to be measured sent to the TOC meter 54 has a low concentration of carbon dioxide and has little effect on the detection of CO2, the removal of carbon dioxide by the decarbonation device 56 may be omitted.

[0030] The TOC meter 54 may be configured not to include the decarbonation device 56. In this case, if it is necessary to remove carbon dioxide from the liquid to be measured, the decarbonation device 56 may be provided, for example, before (upstream of) the TOC meter 54. Examples of such a decarbonation device 56 include a degassing device, and possible examples include a vacuum degassing membrane, a degassing tower, and a vacuum degassing tower, with the vacuum degassing membrane being preferred.

[0031] Before supplying the liquid to be measured to the decarbonator 56, the pH may be adjusted as necessary. When a degasser is used for the decarbonator 56, it is preferable to make the liquid to be measured acidic (for example, pH 5 or less) since this increases the carbon dioxide removal rate. The pH can be adjusted, for example, by adding a known acid. In addition, when a reverse osmosis membrane (RO) or an ion exchange device is used for the above-mentioned filtration device 50, hydroxide ions, if any, can be removed from the liquid to be measured, and therefore at least a part of the pH adjustment can be performed.

[0032] Inside the TOC meter 54, the flow path of the liquid to be measured branches downstream of the decarbonation device 56, with an oxidation device 58 and a CO2 detection device 60 being provided in one flow path, and a CO2 detection device 62 being provided in the other flow path.

[0033] The oxidation device 58 of the TOC meter 54 oxidizes the organic matter contained in the liquid to be measured, including urea, by, for example, irradiating the liquid to be measured with ultraviolet light. In practice, most of the components other than urea are removed from the organic matter contained in the liquid to be measured, so the organic matter oxidized by the oxidation device 58 is urea. That is, in the oxidation device 58, the urea in the liquid to be measured is oxidized and decomposed, and carbon dioxide is generated again at this stage.

[0034] The CO2 detectors 60, 62 of the TOC meter 54 measure the amount of carbon dioxide in the liquid being treated. The amount of carbon dioxide is proportional to the amount of carbon contained in the organic matter in the liquid being measured that has been oxidized and decomposed.

[0035] Here, organic matter in the liquid to be measured is oxidized by the oxidation device 58 upstream of the CO2 detector 60, and the CO2 detector 60 detects the total carbon concentration of the liquid to be measured. In contrast, organic matter in the liquid to be measured is not oxidized by the oxidation device 58 upstream of the CO2 detector 62, and the CO2 detector 62 detects the inorganic carbon concentration of the liquid to be measured. The TOC meter 54 obtains the total organic carbon concentration of the liquid to be measured by subtracting the inorganic carbon concentration detected by the CO2 detector 62 from the total carbon concentration detected by the CO2 detector 60, as shown in the following equation (1). Total organic carbon concentration = total carbon concentration - inorganic carbon concentration (1)

[0036] In addition, when the carbon dioxide removal rate of the decarbonation device 56 is high, some of the urea may be removed before it reaches the oxidation device 58 of the TOC meter 54. In such a case, if these urea removal rates are checked in advance and the urea concentration measurement results by the TOC meter 54 are corrected accordingly, the urea concentration can be calculated with even greater accuracy.

[0037] Furthermore, the specific configuration of the TOC meter 54 is not limited to that described above, and various types of TOC meters can be used in this embodiment.

[0038] The liquid to be treated after the total organic carbon concentration has been measured by the TOC meter 54 may be discarded as waste liquid or may be returned to, for example, the second raw water line.

[0039] The urea concentration measurement process in the TOC meter 54 may be a continuous type in which the measurement target liquid is continuously flowed, or a batch type in which the measurement target liquid is temporarily stored and then measured.

[0040] Even when the urea concentration measurement process in the TOC meter 54 is performed in a batch manner, the measurement target liquid may be supplied more frequently or continuously than in the measurement in the TOC meter 54. Also, the measurement target liquid may be supplied at a flow rate greater than that required for the urea concentration measurement process in the TOC meter 54. In this case, the measurement target liquid that is not supplied to the TOC meter 54 may be discharged from a drain pipe provided, for example, immediately before the TOC meter 54.

[0041] Supplying the measurement target liquid to the pipe at a high flow rate and / or frequently or continuously can suppress the generation of bacteria and adhesion of organic matter to the side walls of the pipe. The generated bacteria and attached organic matter may detach from the side walls at an unexpected time and flow into the measurement target liquid, which may reduce the accuracy of the urea concentration measurement. The urea meter 30 is not limited to the above, and a commercially available device may be used.

[0042] The urea decomposition section 13 includes a urea decomposition device 32 that decomposes urea in the second raw water. When the urea concentration in the second raw water exceeds an allowable value determined by the urea concentration required for ultrapure water, the second raw water is passed through the urea decomposition device 32 to reduce the urea concentration. The urea decomposition section 13 may include a urea meter 31 similar to the above-described urea meter 30 downstream of the urea decomposition device 32 in order to measure the urea concentration of the second raw water that has passed through the urea decomposition device 32.

[0043] As a means for decomposing urea in the urea decomposition unit 32, for example, the following methods can be used, and an appropriate method can be selected depending on the scale of the pure water system and the quality of the second raw water.

[0044] 1) Biological treatment 2) Biological activated carbon treatment 3) Oxidative decomposition treatment using oxidizing agents (bromic acid, hypobromous acid, etc.) 4) Urea decomposition treatment using a reducing agent (sulfurous acid) 5) High-pressure reverse osmosis (RO) treatment 6) Ultraviolet irradiation treatment and treatment using ultraviolet irradiation and oxidizing agents in combination

[0045] Methods 1 and 2 have the problem of stable treatment because they use living organisms, but when combined with this method, ultrapure water production can be continued even if the performance of the biological treatment deteriorates. Also, stable treatment can be expected by installing a pit in front of the biological treatment tank and decomposing the urea in the second raw water little by little in the biological treatment tank.

[0046] In the method 3, a large amount of oxidizing agent is generally added, and a large amount of oxidizing agent remains after the reaction, which must be removed, resulting in a large-scale device, but in this embodiment, the urea decomposition device 32 is provided in the branch line of the second raw water, making it possible to reduce the size of the device.Furthermore, the device can be reduced in size by providing a pit in the stage preceding the oxidative decomposition device and decomposing the second raw water little by little.

[0047] Methods 4, 5, and 6 require large-scale equipment, and method 5 has an issue with the removal rate. However, in this embodiment, the urea decomposition device 32 is provided in the branch line of the second raw water, so that the equipment can be made compact.

[0048] Method 4 is carried out, for example, as follows using an ultraviolet irradiation device. The water to be treated (second raw water) to which a reducing agent has been added is irradiated with ultraviolet light to promote oxidative decomposition. The wavelength of the ultraviolet light may be any wavelength that is capable of oxidizing the water to be treated. For example, ultraviolet light with a wavelength of about 185 nm, which is generally used for ultraviolet oxidation, may be used, or ultraviolet light with a wavelength of about 254 nm, which is used for sterilization.

[0049] It is believed that the reducing agent added to the water to be treated is converted into persulfate radicals or active species having a similar form to the persulfate radicals by the action of ultraviolet light. The generated active species then decomposes urea.

[0050] As a method other than the above 1) to 6), it is also possible to use a urease or a catalyst carrying a urease.

[0051] The amount of the second raw water to be mixed with the raw water or pretreated water, that is, the amount of the second raw water to be accepted for ultrapure water production, is set so that the weighted average of the urea concentration in the raw water or pretreated water and the urea concentration in the second raw water (i.e., the urea concentration after mixing) is equal to or less than the allowable value determined by the urea concentration required for ultrapure water (urea spec). The amount of the second raw water to be accepted in the raw water tank 20 may be determined by back-calculating, taking into account the urea removal rate from the junction to the secondary treatment unit 12. In other words, the weighted average of the urea concentrations may be back-calculated from the urea concentration required for ultrapure water to the urea concentration at the junction of the raw water and the second raw water, and the amount of the second raw water to be accepted in the raw water tank 20 may be set. Note that, when the urea concentration of the second raw water is equal to or less than the allowable value, it can be accepted for ultrapure water production without being mixed with the raw water. In other words, even if the second raw water is 100%, ultrapure water production can be performed.

[0052] It is also possible to store second raw water having a urea concentration exceeding an allowable value in the second raw water pit 38, and return and circulate the treated water from the urea decomposition device 32 to the second raw water pit 38 via a return line (not shown) to the second raw water pit 38, so that the urea concentration of the second raw water in the second raw water pit 38 decreases, and when the value of the urea meter 30 has decreased sufficiently, the second raw water can be supplied to the raw water tank 20 or the primary treatment unit 11. If the urea concentration in the second raw water decreases during this circulation operation, the second raw water can be supplied to the raw water tank 20 or the primary treatment unit 11 via a bypass line (not shown) of the second raw water pit 38.

[0053] In the case where the urea concentration in the second raw water is extremely high and the urea cannot be decomposed even by using the urea decomposition device 32, the water may be supplied to the cooling tower or the like 34 via the cooling tower supply line 40 and used as water for the cooling tower or the like. The cooling tower supply line 40 may be installed so as to branch off from the upstream stage of the second raw water pit 38.

[0054] Furthermore, the quality of raw water, including drinking water, can change significantly temporarily, for example, immediately after a typhoon. It is also possible to respond to such cases. In this case, for example, it is possible to deal with the problem by increasing the amount of the second raw water used, or alternatively, a supply line 42 for raw water including clean water to the urea decomposition device 32 is used to decompose urea in the raw water including clean water and use the decomposed water as raw water. In this case, it is possible to deal with the problem without providing any special equipment for dealing with temporary deterioration in the quality of raw water including clean water.

[0055] FIG. 4 shows an example of the change in the urea concentration of sewage (second raw water) over time and the conditions for accepting the second raw water. If the urea removal rate in the ultrapure water production system 100 is 90%, the urea concentration of the raw water is 0.1 ppb, and the urea concentration required for ultrapure water (urea spec) is 0.5 ppb, then if the urea concentration of the second raw water is 5 ppb or less, the second raw water can be accepted in its entirety for ultrapure water production. "Total Acceptable" in FIG. 4 shows this range. Also, if the mixing ratio of raw water and second raw water is 9:1 and second raw water exceeding this ratio is not accepted, the urea concentration of the second raw water is allowed up to 49 ppb. "Mixed Acceptable" in FIG. 4 shows this range. In this case, 43% of the raw water required for ultrapure water production can be the second raw water.

[0056] [Ultra pure water production method] The ultrapure water production method according to this embodiment includes a pretreatment step in which suspended solids are removed from raw water, including drinking water, to obtain pretreated water; a primary treatment step in which total organic carbon (TOC) components and ionic components are removed from the pretreated water to produce primary pure water; and a secondary treatment step in which impurities are removed from the primary pure water to produce ultrapure water. Second raw water, which includes treated sewage water and has a urea concentration below an allowable value determined by the urea concentration required for ultrapure water, is merged with the raw water or pretreated water upstream of the primary treatment unit.

[0057] Here, when the urea concentration of the second raw water exceeds an allowable value determined by the urea concentration required for ultrapure water, the second raw water may be passed through a urea decomposition device to reduce the urea concentration to the allowable value or lower.

[0058] In addition, the amount of the second raw water to be merged with the raw water or pretreated water may be set so that the weighted average of the urea concentration in the raw water or pretreated water and the urea concentration in the second raw water is equal to or lower than the urea concentration required for ultrapure water.

[0059] (action) The present embodiment is configured as described above, and its operation will be described below. In the ultrapure water production system 100 according to the present embodiment, ultrapure water is produced using second raw water containing treated sewage water in addition to raw water using clean water, so that the proportion of clean water in the raw water used for producing ultrapure water can be reduced.

[0060] Furthermore, by using the urea decomposition unit 13, when the urea concentration of the second raw water exceeds an allowable value required by the urea concentration required for ultrapure water, the second raw water is passed through the urea decomposition device 32 to reduce the urea concentration to below the allowable value, and then the second raw water is merged with the raw water using clean water. Therefore, sewage can be used more effectively.

[0061] Furthermore, since the amount of the second raw water to be mixed with the raw water is set according to the urea concentration required in the ultrapure water, the urea concentration in the ultrapure water can be suppressed to a level equal to or lower than the standard.

[0062] In addition, when the urea decomposition device 32 is installed before mixing the raw water and the second raw water, it can be made smaller than when the urea decomposition device 32 is installed after mixing the raw water and the second raw water. In particular, when the urea decomposition device 32 is installed on the primary treatment device 11 or pretreatment device 10 side from the confluence of the raw water and the second raw water, it is necessary to design so that the urea concentration of the ultrapure water is within the specification even when the urea concentration reaches the maximum value, and the urea decomposition device 32 becomes very large, which increases the installation area and the running cost. On the other hand, in the case of the embodiment shown in FIG. 1, it is possible to deal with the problem by making the device as small as possible while taking into consideration the utilization rate of the second raw water. This ratio depends on the water quality and water quality fluctuation of the sewage, and the target utilization rate of the sewage, but can be about 1 / 2 to 1 / 10.

[0063] Furthermore, even if the urea concentration of the second raw water becomes higher than designed, the second raw water can be used in the cooling tower, etc. 34, and the ultrapure water production system 100 can operate using only the first raw water, so there is an advantage that the production of ultrapure water does not have to be stopped.

[0064] In addition, since the second raw water is used by mixing the raw water with the second raw water, it is possible to minimize the amount of new equipment that needs to be installed.

[0065] In this manner, according to the present embodiment, the proportion of clean water in the raw water used to produce ultrapure water can be reduced, thereby reducing the amount of clean water used in semiconductor manufacturing.

[0066] In addition to urea, other difficult-to-decompose substances include urea derivatives and organic fluorine compounds such as perfluorooctasulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), and the present invention can also be suitably applied to cases where these are included.

[0067] [Other embodiments] An example of an embodiment of the present invention has been described above, but the embodiment of the present invention is not limited to the above, and it goes without saying that various modifications can be made without departing from the spirit and scope of the present invention.

[0068] [Note] Possible aspects of the present invention will be described below.

[0069] [Appendix 1] A pretreatment step of removing suspended solids from raw water, including drinking water, to obtain pretreated water; a primary treatment for producing primary pure water by removing total organic carbon components and ionic components from the pretreated water; A secondary treatment for removing impurities from the primary pure water to produce ultrapure water, A method for producing ultrapure water, comprising: causing second raw water, which contains treated sewage water, to merge with the raw water or the pretreated water upstream of the primary treatment section.

[0070] [Appendix 2] The method for producing ultrapure water described in Appendix 1, wherein the amount of the second raw water to be mixed with the raw water or the pretreated water is set so that a weighted average of the urea concentration in the raw water or the pretreated water and the urea concentration in the second raw water is equal to or less than an allowable value determined by a urea concentration required for the ultrapure water.

[0071] [Appendix 3] 3. The method for producing ultrapure water according to claim 1, wherein, when a urea concentration in the second raw water exceeds an allowable value determined based on a urea concentration required for the ultrapure water, the second raw water is passed through a urea decomposition device to reduce the urea concentration to below the allowable value.

[0072] [Appendix 4] a pretreatment section for removing suspended solids from raw water, including clean water, to obtain pretreated water; a primary treatment section for producing primary pure water by removing total organic carbon components and ionic components from the pretreated water; a secondary treatment unit for removing impurities from the primary pure water to produce ultrapure water, An ultrapure water production apparatus that merges second raw water, which contains sewage treatment plant water and has a urea concentration below an allowable value, with the raw water or the pretreated water upstream of the primary treatment unit.

[0073] [Appendix 5] 5. The ultrapure water producing apparatus according to claim 4, further comprising a urea decomposition unit that includes a urea meter for measuring a urea concentration in the second raw water, and a urea decomposition device for decomposing urea in the second raw water, and that, when the urea concentration exceeds an allowable value determined by a urea concentration required for the ultrapure water, passes the second raw water through the urea decomposition device to reduce the urea concentration.

[0074] [Appendix 6] An ultrapure water producing apparatus as described in Appendix 4 or 5, wherein the amount of the second raw water to be merged with the raw water or the pretreated water is set so that a weighted average of the urea concentration in the raw water or the pretreated water and the urea concentration in the second raw water is equal to or less than an allowable value determined by a urea concentration required for the ultrapure water. [Explanation of symbols]

[0075] 10 Pretreatment section 11 Primary Processing Unit 12 Secondary Processing Section 13 Urea decomposition part 19 POU (Place of use) 20 Raw Water Tank 30 Urea meter 32 Urea decomposition device 100 Ultrapure water production device

Claims

1. A pretreatment step of removing suspended solids from raw water, including drinking water, to obtain pretreated water; a primary treatment for producing primary pure water by removing total organic carbon components and ionic components from the pretreated water; A secondary treatment for removing impurities from the primary pure water to produce ultrapure water, A method for producing ultrapure water, comprising: causing second raw water containing treated sewage water to merge with the raw water or the pretreated water upstream of the primary treatment.

2. 2. The method for producing ultrapure water according to claim 1, wherein the amount of the second raw water to be merged with the raw water or the pretreated water is set so that a weighted average of the urea concentration in the raw water or the pretreated water and the urea concentration in the second raw water is equal to or less than an allowable value determined by a urea concentration required for the ultrapure water.

3. 2. The method according to claim 1, wherein the second raw water is passed through a urea decomposition device when the urea concentration of the second raw water exceeds an allowable value determined based on a urea concentration required for the ultrapure water.

3. The method for producing ultrapure water according to claim 2.

4. a pretreatment section for removing suspended solids from raw water, including clean water, to obtain pretreated water; a primary treatment section for producing primary pure water by removing total organic carbon components and ionic components from the pretreated water; a secondary treatment section for removing impurities from the primary pure water to produce ultrapure water; and a urea meter for measuring a urea concentration in the second raw water including sewage treatment plant water, The ultrapure water producing apparatus merges the second raw water with the raw water or the pretreated water upstream of the primary treatment section.

5. 5. The ultrapure water producing system according to claim 4, further comprising a urea decomposition unit which decomposes urea in the second raw water, and which passes the second raw water through the urea decomposition unit to reduce the urea concentration when the urea concentration exceeds an allowable value determined by a urea concentration required for the ultrapure water.

6. 5. The ultrapure water producing apparatus according to claim 4, wherein the amount of the second raw water to be merged with the raw water or the pretreated water is set so that a weighted average of the urea concentration in the raw water or the pretreated water and the urea concentration in the second raw water is equal to or less than an allowable value determined by a urea concentration required for the ultrapure water.

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