Method and apparatus for manufacturing pure water, method for manufacturing pure water, and system for manufacturing pure water

Abstract

To provide a method and apparatus for manufacturing pure water capable of efficiently removing suspended matter and the like from water, significantly improving the water recovery rate, and suppressing blockage of the membrane filtration apparatus for a long period of time.SOLUTION: A method for manufacturing pure water includes: a process of obtaining first treated water by adding poly aluminum chloride to raw water; and two or more filtration processes in which the first treated water is filtered through a first-stage filtration membrane device to obtain first concentrated water, and the first concentrated water is filtered through a second-stage filtration membrane device, so as to obtain pure water as permeate water from the two or more filtration processes.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for producing water for pure water, and a method and system for producing pure water. [Background technology]

[0002] Sand filtration, coagulation and sedimentation have been used as turbidity removal techniques in the production of industrial water from river water, well water, lake water, and the like, and in water treatment such as wastewater treatment. However, sand filtration and coagulation and sedimentation using slow filtration have problems such as requiring a large facility area for the equipment and requiring strict operation management depending on the water to be treated. As a technique that can eliminate these drawbacks, membrane separation using filtration membranes such as microfiltration membranes (MF) and ultrafiltration membranes (UF) has been widely adopted. In this membrane separation method, in order to increase the turbidity removal efficiency, an inorganic coagulant such as polyaluminum chloride (PAC) is added to the water to be treated prior to membrane separation to perform a coagulation reaction to generate coagulated flocs, and the coagulated treated water containing the coagulated flocs is filtered through a filtration membrane (see, for example, Patent Documents 1 and 2).

[0003] In the method of filtering and separating the coagulated treated water using a filtration membrane, there is an issue of fouling of the filtration membrane caused by the addition of inorganic coagulants. To suppress this, a method of adding organic anionic substances to the water to be treated has been proposed (see, for example, Patent Document 3).

[0004] In the production of pure water or ultrapure water for the semiconductor and electronics industries or pharmaceuticals, tap water or industrial tap water is used as raw water, and the raw water is generally passed through a membrane treatment device such as a reverse osmosis membrane device (RO) or an ultrafiltration membrane device (UF), and then treated by a combination of an ion exchange resin device, an ultraviolet irradiation device, etc. When tap water or industrial water is used as raw water, the raw water is treated with PAC before being supplied to a downstream treatment device in order to remove suspended solids in the raw water. However, since the raw water contains residual aluminum derived from PAC, a method of removing this using an iron-based inorganic polymer flocculant is also known. This is because residual aluminum in the raw water adheres to the membrane of a reverse osmosis membrane device or the like, significantly reducing the permeation flux of the membrane treatment device (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-168729 A [Patent Document 2] JP 2005-246157 A [Patent Document 3] JP 2022-165279 A [Patent Document 4] JP 2008-86966 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned method of filtering the coagulated water has a problem of low water recovery rate compared to the scale of the equipment. Therefore, the conventional method of filtering the coagulated water is not suitable for the production of large amounts of pure water or ultrapure water for the semiconductor electronics industry or pharmaceuticals. In addition, the use of PAC in the production of pure water or ultrapure water for the semiconductor electronics industry or pharmaceuticals has the problem of fouling and membrane blockage due to adhesion of residual aluminum in the water to the membrane. However, the method using organic anionic substances or iron-based inorganic polymer coagulants has the problem of increased costs and environmental load due to the increased amount of chemicals used. In addition, there is also the problem of membrane blockage caused by the residual polymer coagulant being adsorbed to the membrane surface of the downstream membrane treatment device.

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a method and apparatus for producing pure water that can efficiently remove suspended matter and the like from raw water, significantly improve the water recovery rate, and suppress clogging of the membrane filtration device over the long term. Another object of the present invention is to provide a pure water production method and production system that can efficiently remove suspended solids from raw water, significantly improve the water recovery rate, and suppress clogging of the membrane filtration device over the long term, thereby producing high-quality pure water over the long term. [Means for solving the problem]

[0008] The manufacturing method, manufacturing apparatus, and pure water manufacturing system according to the embodiments of the present invention are as follows. [1] A method for producing water for pure water, comprising the steps of: A step of obtaining a first treated water by adding polyaluminum chloride to the raw water; A manufacturing method comprising two or more filtration stages in which a first treated water is filtered by a membrane filtration device in a first stage to obtain a first concentrated water, and the first concentrated water is filtered by a membrane filtration device in a second stage, and water for pure water is obtained as the permeate of the two or more filtration stages. [2] The method according to [1], wherein a first treated water containing microflocs is obtained by adding high basicity polyaluminum chloride to the raw water. [3] The method according to [1] or [2], wherein the basicity of the polyaluminum chloride is greater than 75%. [4] The polyaluminum chloride comprises aluminum chloride pentahydroxide; The manufacturing method according to any one of [1] to [3], wherein the amount of the aluminum chloride pentahydroxide added is an amount equivalent to an aluminum oxide (Al2O3) concentration of 0.25 mg / L or more and 25 mg / L or less relative to the raw water. [5] The basicity of the polyaluminum chloride is 75% or less; The method according to [1], further comprising a pH adjustment step of adjusting the pH of raw water to which the polyaluminum chloride is added. [6] The manufacturing method according to any one of [1] to [5], further comprising at least one step of adding polyaluminum chloride to the concentrated water of at least one of the two or more stages of filtration membrane devices, and then supplying the concentrated water to a subsequent stage of the filtration membrane device. [7] Further, a step of obtaining a second treated water by adding polyaluminum chloride to the concentrated water of at least the final stage of the filtration membrane device among the two or more stages of the filtration membrane device; A total filtration step of filtering the second treated water by a filtration membrane device, The method according to any one of [1] to [6], wherein the permeate obtained in the dead-end filtration step is used as the raw water. [8] Further, a cleaning process for cleaning the filtration membrane device after the total filtration process; A sedimentation and concentration step is provided for separating a supernatant from the washing wastewater generated in the washing step, The manufacturing method according to [7], wherein the supernatant is used as the raw water.

[0009] [9] A method for producing pure water, comprising the steps of: A step of obtaining a first treated water by adding polyaluminum chloride to the raw water; A process for producing pure water, the process including a two or more stages of filtration steps in which the first treated water is filtered by a membrane filtration device in a first stage to obtain a first concentrated water, and the first concentrated water is filtered by a membrane filtration device in a second stage, and the process for producing pure water is obtained as a permeate of the two or more stages of the membrane filtration steps; The method includes an ultraviolet oxidation step and an ion exchange step in this order. Manufacturing method.

[0010]

[10] An apparatus for producing pure water, comprising: A raw water supply device for supplying raw water; A polyaluminum chloride supplying device for adding polyaluminum chloride to raw water; A two or more stage filtration membrane device for filtering first treated water generated by adding polyaluminum chloride to raw water; Among the two or more stages of filtration membrane devices, a concentrated water pipe that supplies concentrated water from a previous stage filtration membrane device to a subsequent stage filtration membrane device, and a plurality of transfer pipes that transfer permeated water from the two or more stages of filtration membrane devices to obtain pure water; A manufacturing apparatus having the above structure.

[11] The manufacturing apparatus according to

[10] , wherein the basicity of the polyaluminum chloride is greater than 75%.

[12] The polyaluminum chloride comprises aluminum chloride pentahydroxide; The manufacturing apparatus according to

[10] or

[11] , wherein the polyaluminum chloride supplying device supplies aluminum chloride pentahydroxide to raw water in an amount of 0.25 mg / L or more and 25 mg / L or less, calculated as an aluminum oxide (Al2O3) concentration.

[13] The basicity of the polyaluminum chloride is 75% or less; The manufacturing apparatus according to

[10] , further comprising a pH adjusting device for adjusting the pH of raw water to which the polyaluminum chloride is added.

[14] The manufacturing apparatus according to any one of

[10] to

[13] , further comprising one or more polyaluminum chloride supply devices that add polyaluminum chloride to the concentrated water of at least one of the two or more stages of filtration membrane devices, and the concentrated water to which polyaluminum chloride has been added is filtered by a subsequent filtration membrane device.

[15] Further, a polyaluminum chloride supplying device for adding polyaluminum chloride to the concentrated water of at least the final stage of the filtration membrane device among the two or more stages of the filtration membrane device; The system is equipped with a filtration membrane device that filters the entire amount of the second treated water produced by adding polyaluminum chloride to the concentrated water from the final stage filtration membrane device, The manufacturing apparatus according to any one of

[10] to

[14] , further comprising a pipe for sending the permeate of the filtration membrane device that performs total filtration to the raw water supply device for use as the raw water.

[16] Further, a cleaning device for cleaning the filtration membrane device for total filtration; a sedimentation and concentration device for separating a supernatant liquid from the washing wastewater generated in the washing device; The manufacturing apparatus according to

[15] , further comprising a pipe for sending the supernatant liquid to the raw water supply device.

[17] An apparatus for producing pure water according to

[10] or

[15] , A pure water production system comprising an ultraviolet oxidation device and an ion exchange device in this order. The symbol "~" indicates a numerical range including the numerical values ​​before and after it. Effect of the Invention

[0011] According to the method and apparatus for producing pure water of the present invention, suspended matter in raw water can be efficiently removed, the water recovery rate can be significantly improved, and clogging of the membrane filtration device can be suppressed for a long period of time. Furthermore, according to the pure water production method and production system of the present invention, suspended solids in the raw water can be efficiently removed, the water recovery rate can be significantly improved, and clogging of the membrane filtration device can be suppressed for a long period of time, thereby making it possible to produce high-quality pure water over a long period of time. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of a production apparatus used in a method for producing pure water according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing a production apparatus in which the production apparatus shown in FIG. 1 further includes an ultrafiltration membrane device for performing dead-end filtration. [Diagram 3] FIG. 3 is a schematic diagram showing a production apparatus in which the production apparatus shown in FIG. 2 further includes a cleaning device for an ultrafiltration membrane device that performs dead-end filtration. [Figure 4] 1 is a diagram showing a schematic diagram of a pure water production system using an apparatus for producing pure water according to an embodiment; [Diagram 5] FIG. 2 is a schematic diagram showing a pure water production apparatus used in the examples. [Figure 6] FIG. 2 is a schematic diagram illustrating an apparatus used in a comparative example. [Figure 7] FIG. 1 is a schematic diagram showing a production apparatus that uses a method of transferring water to be treated to a downstream stage using a blower and a bubbling tank. [Figure 8] FIG. 2 is a diagram showing a schematic diagram of a test device used in the experimental examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described. Fig. 1 shows a schematic diagram of a manufacturing apparatus 1 used in a method for manufacturing pure water according to a first embodiment. The manufacturing apparatus 1 includes a raw water supplying device 11 for supplying raw water, a polyaluminum chloride supplying device 12 for supplying polyaluminum chloride (hereinafter also referred to as "PAC"), and a raw water transfer pipe 13 for transferring the raw water. The manufacturing apparatus 1 further includes a first ultrafiltration membrane device 14 as a front-stage filtration membrane device for filtering the raw water (first treated water) to which PAC has been added. The first ultrafiltration membrane device 14 includes a transfer pipe 15 for transferring the permeated water to a rear stage, and a concentrated water pipe 16 for discharging the concentrated water.

[0014] The production apparatus 1 further includes a second ultrafiltration membrane device 24, which is connected to the concentrated water pipe 16 of the first ultrafiltration membrane device 14 and serves as a downstream filtration membrane device for filtering the concentrated water of the first ultrafiltration membrane device 14. The second ultrafiltration membrane device 24 includes a transfer pipe 25 for transferring the permeated water to the downstream stage and a concentrated water pipe 26 for discharging the concentrated water.

[0015] The production apparatus 1 further includes a reaction tank 17 that contains raw water supplied from the raw water supply device 11, and a pH adjustment device 18 that adds a pH adjuster to the raw water. The reaction tank 17 may be a mixing tank in which PAC is mixed with the raw water to form microflocs (microfloc method), or a settling tank for rapid filtration, but is preferably a mixing tank. The polyaluminum chloride supply device 12 is connected to the reaction tank 17. The reaction tank 17 is provided on the upstream side of the first ultrafiltration membrane device 14 in the raw water transfer pipe 13. The pH adjustment device 18 is provided on the upstream side of the reaction tank 17 in the raw water transfer pipe 13. That is, the pH adjustment device 18, the reaction tank 17, and the first ultrafiltration membrane device 14 are arranged in this order in the raw water transfer pipe 13. The reaction tank 17 and the pH adjustment device 18 are not essential, and may be installed as necessary.

[0016] In the manufacturing apparatus 1, two ultrafiltration membrane devices, a first ultrafiltration membrane device 14 and a second ultrafiltration membrane device 24, are connected in series (two stages), and each performs filtration by a cross-flow system. Then, concentrated water from the ultrafiltration membrane device in the front stage is filtered by the ultrafiltration membrane device in the rear stage, and the permeated water from the ultrafiltration membrane device in the front stage and the permeated water from the ultrafiltration membrane device in the rear stage are collected as pure water. This connection mode in which the treated liquid obtained from the secondary side (discharge side) of the device in the front stage is treated in the device in the rear stage is called "series" and is distinguished from a "parallel" connection in which the water to be treated is branched and supplied to multiple devices for treatment respectively. That is, in this embodiment, the concentrated water (first concentrated water) of the first ultrafiltration membrane device 14 is filtered by the second ultrafiltration membrane device 24, and the permeated water (first permeated water) of the first ultrafiltration membrane device 14 and the permeated water (second permeated water) of the second ultrafiltration membrane device 24 are collected as pure water. The concentrated water (second concentrated water) of the second ultrafiltration membrane device 24 may be discharged outside the system, or may be subjected to additional treatment and returned to the previous stage. In this embodiment, an embodiment having two stages of ultrafiltration membrane devices will be described, but the same configuration may be used with three or more stages of ultrafiltration membrane devices.

[0017] Here, in this embodiment, "two or more stages" means that the filtration membrane devices are arranged in multiple stages. Specifically, "two or more stages" refers to a mode in which two or more filtration membrane devices are connected in series, and each filtration membrane device filters the concentrated water of the previous stage, and is referred to as the first stage, the second stage, etc. (hereinafter the same) from the beginning of the series connection. In addition, the filtration membrane devices provided in multiple stages are not limited to a method in which each filtration membrane device filters the concentrated water of the filtration membrane device of the previous stage, but also include a case in which the filtration membrane device filters the concentrated water of any filtration membrane device on the previous stage side. In addition, in this embodiment, an example having a polyaluminum chloride supply device 12 that adds PAC to raw water will be described, but one or more polyaluminum chloride supply devices that add PAC to each of the supply water to the filtration membrane devices of the second stage and thereafter may be provided. In this case, one or more polyaluminum chloride supply devices may add PAC to all of the supply water to the filtration membrane devices of the second stage and thereafter, or may add PAC to the supply water to some of the filtration membrane devices. It is preferable to add PAC upstream of the filtration membrane device of the frontmost stage.

[0018] The method for producing pure water in the embodiment using the production apparatus 1 is as follows. First, raw water is supplied from the raw water supply device 11 into the raw water transfer pipe 13. The raw water is urban water such as city water and industrial water, or natural water such as river water, lake water, groundwater, and well water. The quality of the raw water is, for example, turbidity of 1 NTU to 100 NTU, suspended solids (SS) of 5 mg / L to 500 mg / L, total organic carbon (TOC) of 0.5 mg / L to 7 mg / L, aluminum concentration of 0.01 mg / L to 5 mg / L, and pH of 4 to 9. Free chlorine may be added to the raw water during transportation through the raw water transfer pipe 13. The raw water supply device 11 includes, for example, a raw water tank for storing raw water and a feed water pump for transporting the raw water in the raw water tank, and the feed water pump supplies the raw water in the raw water tank into the raw water transfer pipe 13. Depending on the quality of the raw water, a pre-filter (not shown) may be installed as a pre-treatment device to pre-treat the raw water before adding PAC. If the raw water contains urea or low-molecular-weight organic matter, chemical oxidation or accelerated oxidation using ultraviolet light may be performed.

[0019] In the production apparatus 1, raw water is supplied from a raw water supply device 11, and PAC is supplied from a polyaluminum chloride supply device 12, into a reaction tank 17. In the reaction tank 17, suspended matter in the raw water interacts with the PAC to form flocs, microflocs, nanoflocs, and the like. In this case, the order of supplying the raw water and the PAC into the reaction tank 17 may be either first or simultaneously, but it is preferable that the PAC is added to the reaction tank 17 to which the raw water has been supplied.

[0020] When the manufacturing apparatus 1 does not include the reaction tank 17, the polyaluminum chloride supplying device 12 is connected to the raw water transfer pipe 13, and PAC is added into the raw water transfer pipe 13. This produces first treated water. When the reaction tank 17 is not used, the manufacturing apparatus 1 can be made smaller, which makes it easier to install in a semiconductor manufacturing factory or the like. Note that by installing an in-line mixer or the like in the raw water transfer pipe 13 after the PAC is supplied to promote mixing of the raw water and the PAC, clogging of downstream equipment can be further suppressed.

[0021] The polyaluminum chloride supplying device 12 is equipped, for example, with a chemical tank for storing PAC and a chemical injection pump for adding the PAC in the chemical tank to the reaction tank 17, and the chemical injection pump measures the PAC in the chemical tank to a predetermined concentration and adds it to the reaction tank 17.

[0022] At this time, the pH adjusting device 18 adds an acid and an alkali, which are pH adjusting agents, to the raw water according to the basicity of the PAC, to adjust the pH of the raw water. Either one or both of the acid and the alkali may be added. Specifically, when a low-basic PAC described later is used, the pH adjusting device 18 adds a pH adjusting agent to the reaction tank 17 to adjust the pH of the raw water before the PAC is added. The pH adjusting device 18 includes, for example, an acid storage tank for storing an acid and an acid injection pump for adding the acid in the acid storage tank to the reaction tank 17. The pH adjusting device 18 also includes an alkali storage tank for storing an alkali and an alkali injection pump for adding the alkali in the alkali storage tank to the reaction tank 17. The acid injection pump and the alkali injection pump then measure the acid in the acid storage tank and the alkali in the alkali storage tank and add them to the reaction tank 17 so that the raw water has a predetermined pH. The acid used here is typically sulfuric acid, and the alkali is typically sodium hydroxide (aqueous solution). When the production apparatus 1 does not include the reaction tank 17, the pH adjuster 18 is connected to the raw water transfer pipe 13, and a pH adjuster is added to the raw water transfer pipe 13.

[0023] The PAC in this embodiment contains polyaluminum chloride represented by the following chemical formula (1). [Al2(OH) n Cl 6-n ] m (1≦n≦5, m≦10) (1) As the PAC of this embodiment, either a low basicity PAC or a high basicity PAC can be used. As the PAC of this embodiment, it is preferable to use either a low basicity PAC or a high basicity PAC. When using a low basicity PAC (hereinafter referred to as "low basicity PAC"), it is preferable to provide the above-mentioned pH adjustment device to adjust the pH of the raw water. The basicity is a value calculated by n / 6×100(%) in the above chemical formula (1).

[0024] The low basicity PAC preferably has a basicity of 75% or less, more preferably 60% or more and 70% or less. The low basicity PAC can be produced, for example, by the method described in JP-A-2009-203125. Only one low basicity PAC may be used, or two or more low basicity PACs may be used in combination. When two or more low basicity PACs are used in combination, the basicity of the two or more low basicity PACs may be the same or different, but the basicity of each of the low basicity PACs used is preferably 75% or less, more preferably 60% or more and 70% or less.

[0025] The amount of low basicity PAC is preferably 0.03 mg / L as Al2O3 or more per 1 NTU of turbidity in the raw water. In general, the amount of PAC to be added is determined by the quality of the water to be treated, and the optimal amount can be determined by performing a jar test. Specifically, the amount of low basicity PAC is preferably 0.05 mg / L as Al2O3 or more and 25 mg / L as Al2O3 or less relative to the amount of raw water, and more preferably 0.1 mg / L as Al2O3 or more and 20 mg / L as Al2O3 or less.

[0026] When PAC is used, the optimum pH for forming coagulated flocs (microflocs and larger flocs) is in the range of 6 to 8, preferably 6.5 to 7.5. When PAC is dissolved in water, it separates into positively charged alkaline components and hydrogen ions, and since the positively charged alkaline components are consumed during coagulation, the more coagulated flocs are produced, the lower the pH becomes. If the pH of the raw water to which PAC is added is less than 6 or more than 8, there is a risk that aluminum derived from the PAC or turbid components derived from suspended solids will leak into the treated water of the downstream device.

[0027] Therefore, particularly when a low-basicity PAC is used, it is preferable to provide a pH measuring device that measures the pH of the liquid to be treated in the reaction tank 17, and to feedback-control the amount of pH adjuster supplied by the pH adjuster using the pH value measured by the pH measuring device to control the pH of the liquid to be treated in the reaction tank 17. When the reaction tank 17 is not used, the pH measuring device can be provided in the raw water transfer pipe 13. When a pH measuring device is used, it is preferable that a plurality of pH measuring devices are provided at two or more locations, and that the pH of the supply water of each stage of the filtration membrane device is adjusted. That is, when a pH measuring device is used in the manufacturing apparatus 1 of the embodiment, it is preferable that the pH measuring device is provided in the stage before the first ultrafiltration membrane device 14 and the stage before the second ultrafiltration membrane device 24. The installation mode of the pH measuring device is not limited to these, and may be provided in any of the paths until the liquid to be treated to which PAC is added is supplied to the filtration device.

[0028] In this embodiment, it is preferable to use a high-basicity PAC (hereinafter referred to as "high-basicity PAC") as the PAC. Even when a high-basicity PAC is used, the pH decreases with the formation of microflocs, but the amount of decrease is small enough to not be a problem. The basicity of the high-basicity PAC is preferably greater than 75%, more preferably greater than 83%. The upper limit of the basicity is usually less than about 84%. The high-basicity PAC can be produced, for example, by the method described in Japanese Patent No. 4104773. As the high-basicity PAC, only one type may be used, or two or more types may be used in combination. When two or more types are used in combination, the basicities of the two or more high-basicity PACs may be the same or different, but the basicity of each of the high-basicity PACs used is preferably greater than 75%, more preferably greater than 83%.

[0029] When high-basicity PAC is used, the high-basicity PAC interacts with suspended solids in the raw water and selectively forms microflocs. By passing through these microflocs, adhesion of residual aluminum to the membranes in the first ultrafiltration membrane device 14 and the second ultrafiltration membrane device 24 is significantly reduced, and the performance of the ultrafiltration membrane can be maintained for a long period of time. In addition, since the microflocs are not easily broken even during the process of transportation by piping or pumps, etc., the turbidity removal rate is not likely to decrease in multi-stage filtration membrane treatment. The microflocs are aggregates of suspended solids and high-basicity PAC with a size of about 1 to 10 μm. High-basicity PAC is likely to form microflocs, but is unlikely to form coarse flocs larger than microflocs or fine flocs (nanoflocs) smaller than microflocs. Since aluminum ions are unlikely to leak out of the microflocs, by passing through them, clogging of the ultrafiltration membrane can be prevented for a long period of time.

[0030] As the high basicity PAC, it is preferable to use aluminum chloride pentahydroxide (Al2Cl(OH)5). Aluminum chloride pentahydroxide is a polyaluminum chloride with n=5 and m=1 in the above chemical formula (1), and has a basicity of 83.3%. Aluminum chloride pentahydroxide is more likely to form more homogeneous microflocs. This is thought to be due to the high basicity and small molecular weight of aluminum chloride pentahydroxide.

[0031] The amount of high basicity PAC is preferably 0.125 mg / L as Al2O3 or more per turbidity of 1 NTU in the raw water. In general, the amount of PAC to be added is determined by the quality of the water to be treated, and the optimal amount can be determined by performing a jar test. Specifically, the amount of high basicity PAC is preferably 0.25 mg / L as Al2O3 or more and 25 mg / L as Al2O3 or less relative to the amount of raw water, and more preferably 0.3 mg / L as Al2O3 or more and 22 mg / L as Al2O3 or less. In particular, when aluminum chloride pentahydroxide (Al2Cl(OH)5) is used as the high basicity PAC, the amount of aluminum chloride pentahydroxide is preferably 0.25 mg / L as Al2O3 or more and 20 mg / L as Al2O3 or less relative to the total amount of raw water. Even if the amount of high basicity PAC is small as described above, suspended solids in the raw water can be microflocculated. In addition, because high-basicity PAC functions even in small amounts as described above, it becomes easier to prevent clogging of the ultrafiltration membrane device in the downstream stage. Note that the notation "as Al2O3" indicates that the value is calculated based on aluminum oxide (Al2O3) concentration.

[0032] When using a high-basicity PAC, by rapidly stirring the raw water and the high-basicity PAC in the reaction tank 17, more uniform microflocs can be formed without generating nanoflocs. The stirring speed is, for example, 150 s ー1 More than 150 to 250 s is preferable. ー1 More preferably, 250s ー1 It is more preferable that the stirring time is 2 minutes or more, preferably 3 minutes or more, and more preferably 6 minutes or more. The larger the G value of the rapid stirring, the shorter the stirring time can be.

[0033] When PAC is added, an inorganic flocculant other than PAC or an organic polymer flocculant may be used in combination as a flocculation aid. In this case, the amount of flocculation aid to be added can be determined by conducting a jar test.

[0034] The first treated water is then supplied to the first ultrafiltration membrane device 14 and filtered. By providing a water supply pump in the raw water transfer pipe 13 downstream of the reaction tank 17, the first treated water can be supplied to the first ultrafiltration membrane device 14 by the water supply pump. In order to suppress a decrease in the permeation flux in the first ultrafiltration membrane device 14, the differential pressure between the inlet pressure and the outlet pressure of the first ultrafiltration membrane device 14 at this time is preferably 0.004 MPa to 0.04 MPa. In order to increase the water recovery rate of the entire production apparatus 1, the water recovery rate in the first ultrafiltration membrane device 14 is preferably 75% to 95%, more preferably 80% to 95%, and even more preferably 90% to 95%. As a result, permeated water (first permeated water) and concentrated water (first concentrated water) of the first ultrafiltration membrane device 14 are obtained. Immediately before being supplied to the first ultrafiltration membrane device 14, a scale inhibitor or a bacteriostatic agent may be added to the first treated water, as appropriate.

[0035] The first concentrated water is then supplied to the second ultrafiltration membrane device 24 and filtered. From the viewpoint of suppressing a decrease in the permeation flux in the second ultrafiltration membrane device 24, the differential pressure between the inlet pressure and the outlet pressure of the second ultrafiltration membrane device 24 at this time is preferably 0.004 MPa to 0.04 MPa. In order to increase the water recovery rate of the entire production apparatus 1, the water recovery rate in the second ultrafiltration membrane device 24 is preferably 75% to 95%, more preferably 80% to 95%, and even more preferably 90% to 95%. As a result, permeated water (second permeated water) and concentrated water (second concentrated water) of the second ultrafiltration membrane device 24 are obtained. The first permeated water and the second permeated water obtained by these processes are appropriately collected and supplied to pure water production as water for pure water.

[0036] The filtration membrane device in the first stage is provided with a filtration membrane capable of capturing microflocs as a filtration material. For example, a filtration membrane having a nominal pore size of 0.1 μm to 5 μm can be used as such a filtration membrane. Examples of such filtration membranes include ultrafiltration membranes and microfiltration membranes, and in this embodiment, an ultrafiltration membrane device is used. In this embodiment, the filtration material is preferably an ultrafiltration membrane having a nominal pore size of 0.001 to 0.1 μm. The ultrafiltration membrane provided in the first ultrafiltration membrane device 14 includes a hollow fiber membrane, a spiral membrane, and a flat membrane made of a material such as cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, and polyvinylidene fluoride, and among them, a hollow fiber membrane made of a fluorine-based material such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) is preferable. The first ultrafiltration membrane device 14 is preferably an external pressure type ultrafiltration membrane device using the hollow fiber membrane.

[0037] Either an independent or submerged type filtration membrane device may be used as the front and rear stage filtration membrane devices. The independent type filtration membrane device is also called a pressurized type, and is a device that fills a pressure-resistant container with a filtration membrane and performs high-pressure filtration, and is suitable for treating water with low turbidity. The independent type filtration membrane device has a large membrane area and can achieve high flow rate operation, so it has the advantage of being able to treat a large amount of water with a small installation area. The membrane provided in the independent type filtration membrane is preferably a ceramic membrane or a membrane made of a fluorine-based material such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). The supply pressure of the independent type filtration membrane device can be set to any value so that the differential pressure between the inlet pressure and the outlet pressure of the filtration membrane device is 0.004 MPa to 0.04 MPa. The supply pressure to the independent type filtration membrane device is preferably greater than 0.03 MPa and less than 0.1 MPa.

[0038] The independent filtration membrane device is effective in preventing clogging of the filtration membrane device at the subsequent stage because there is little outflow of nanoflocs downstream. In particular, when the method of this embodiment is used to produce ultrapure water for manufacturing semiconductors, etc., the use of the independent filtration membrane device makes it possible to continue producing ultrapure water without stopping the device by installing two or more independent filtration membrane devices in parallel at each stage, performing regeneration such as backwashing or module replacement on one of the multiple devices, and continuing operation with the other devices (so-called merry-go-round operation).

[0039] It is preferable to use an independent ultrafiltration membrane device as the first ultrafiltration membrane device 14. The ultrafiltration membrane provided in the independent ultrafiltration device includes a hollow fiber membrane, a spiral membrane, and a flat membrane made of a material such as cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, or polyvinylidene fluoride, and among these, a hollow fiber membrane made of a fluorine-based material such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is preferable.

[0040] Examples of independent ultrafiltration membrane devices include cartridge-type devices and module-type devices. For example, a cartridge-type device is configured to house an ultrafiltration membrane cartridge in a housing, connect piping to a water inlet and a drain opening in the housing, and pass water through the cartridge through the opening. A cartridge-type device has the advantage that only the cartridge can be replaced when the ultrafiltration membrane deteriorates. When an independent ultrafiltration membrane device is used, a water supply pump is provided on the primary side (water supply side) of the first-stage ultrafiltration membrane device, so that filtration processing can be performed in the second-stage ultrafiltration membrane device. Therefore, compared to a case where a water supply pump is provided on the primary side of each ultrafiltration membrane device, the destruction of flocs by the pump can be minimized. In this way, when two independent ultrafiltration membrane devices are operated with one water supply pump on the primary side, it is preferable to set the supply pressure of the pump higher than the desired pressure to be realized by each ultrafiltration membrane device, taking into account the pressure loss in the process of passing through the piping and filtration membrane. In order to prevent the pressure applied to the filtration membrane of each ultrafiltration membrane device from becoming too high, it is preferable to install a pressure adjustment valve, such as a pressure reducing valve, on the secondary side (e.g., the transfer pipe for the permeate) of the ultrafiltration membrane device of each stage. As a pump to be installed on the primary side of a stand-alone ultrafiltration device, it is preferable to use a floc decomposition suppressing pump, such as a hydrostal pump, a hydrostal chemical pump, a hose pump, or a mono pump, which can suppress the destruction of flocs.

[0041] In a modular device, an ultrafiltration membrane is provided inside a housing, and water is passed through the ultrafiltration membrane by connecting the module to piping. The modular device has the advantage that when the filter material deteriorates, the entire module can be replaced, and the deteriorated ultrafiltration membrane can be washed for each module.

[0042] The submerged type filtration membrane device is a device configured for immersion in a tank, and is suitable for filtering raw water with high turbidity. The submerged type filtration membrane device is submerged in the bottom of the reaction tank 17, and has the advantage that the first treated water to which PAC has been added can be directly filtered without using piping. In this embodiment, when a high basicity PAC is used, microflocs are formed in the water, and the filtration can be directly performed without the need for precipitation removal in a coagulation sedimentation tank as used for coarse flocs. Therefore, the filtration membrane device can be integrated by immersing it in the reaction tank 17, and the overall configuration of the device can be simplified. When a submerged type filtration membrane device is used, a low-pressure suction pump is provided downstream of the multiple stages of filtration membrane devices, and the liquid to be treated can be supplied to the multiple stages of ultrafiltration membrane devices by this low-pressure suction pump for filtration. In this case, since the pump is located downstream of the membrane treatment device, there is an advantage that the collapse of flocs due to the impact of the pump during operation is unlikely to occur. Therefore, the submerged type membrane filtration device can be used in both cases of using low basicity PAC and using high basicity PAC. In addition, a water level difference can be set on the secondary side (discharge side) of a multi-stage filtration membrane device, and permeate water can be obtained by filtration using gravity. This can reduce operating costs by eliminating the need for large amounts of energy to operate pumps.

[0043] When an ultrafiltration device is used as the immersion type filtration membrane device, the filtration membrane provided in the ultrafiltration membrane device is preferably made of ceramic or fluorine-based materials such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc. Also, the suction pressure is preferably 0.004 MPa or more and 0.03 MPa or less.

[0044] The second ultrafiltration membrane device 24 may be an ultrafiltration membrane device similar to the first ultrafiltration membrane device 14 described above, and the preferred embodiments are also similar. The characteristics of the first ultrafiltration membrane device 14 and the second ultrafiltration membrane device 24 may be the same or different. Commercially available products may be used for the first ultrafiltration membrane device 14 and the second ultrafiltration membrane device 24. Examples of commercially available products that may be used include HSU-1515 manufactured by Toray Industries, hollow fiber membrane Microza UNA620A manufactured by Asahi Kasei Corporation, and hollow fiber membrane Microza UHS-620A manufactured by Asahi Kasei Corporation.

[0045] The water quality of the first permeated water and the second permeated water thus obtained is, for example, a turbidity of 0.01 NTU to 0.4 NTU, an aluminum concentration of 0 mg / L to 0.02 mg / L, a pH of 5.9 to 7.5, and a conductivity of 140 μS / cm to 270 μS / cm.

[0046] According to the manufacturing apparatus 1 described above, by filtering the concentrated water from the first ultrafiltration membrane device 14 with the second ultrafiltration membrane device 24, it is possible to obtain permeated water of good purity and to dramatically improve the water recovery rate in the manufacturing apparatus 1. The water recovery rate in the manufacturing apparatus 1 thus obtained is, for example, 98% or more, preferably 99% or more, and more preferably 99.5% or more.

[0047] Next, a method for producing pure water according to the second embodiment will be described. FIG. 2 is a schematic diagram of a production apparatus 2 used in the method for producing pure water according to the second embodiment. The production apparatus 2 shown in FIG. 2 includes a third ultrafiltration membrane device 34 as a third-stage filtration membrane device at the rear of the concentrated water pipe 26, and the second concentrated water is filtered by the third ultrafiltration membrane device 34. The production apparatus 2 also includes a polyaluminum chloride supply device 22 that supplies polyaluminum chloride to the second concentrated water flowing through the concentrated water pipe 26. A permeate transfer pipe 35 is connected to the third ultrafiltration membrane device 34. The end of the permeate transfer pipe 35 opposite to the third ultrafiltration membrane device 34 is connected to the raw water transfer pipe 13 upstream of the pH adjustment device 18. Other configurations are the same as those of the production apparatus 1, so detailed descriptions of the configurations common to the production apparatus 1 will be omitted.

[0048] The production of raw water using the production apparatus 2 is carried out as follows. As in the production apparatus 1, raw water is received in the reaction tank 17 via the raw water transfer pipe 13, and after PAC is added to the raw water, it is supplied in turn to the first ultrafiltration membrane device 14 and the second ultrafiltration membrane device 24. As described above, in the production apparatus 2, the polyaluminum chloride supply device 22 adds PAC to the second concentrated water while the second concentrated water flows through the concentrated water pipe 26. If an in-line mixer or the like is provided in the concentrated water pipe 26 after the PAC is supplied to promote mixing of the second concentrated water and the PAC, clogging of downstream equipment can be further suppressed.

[0049] The second ultrafiltration membrane device 24 filters the concentrated water from the first ultrafiltration membrane device 14, so that the second concentrated water contains highly concentrated flocs and microflocs composed of suspended solids and PAC derived from the raw water. These flocs and microflocs may disintegrate during the process of passing through piping and pumps (not shown). Therefore, if the second concentrated water is directly filtered by the third ultrafiltration membrane device 34, the aluminum derived from PAC and the suspended solids derived from the raw water contained in the flocs may cause rapid clogging of the ultrafiltration membrane.

[0050] Therefore, in the production apparatus 2 of this embodiment, the second treated water obtained by adding polyaluminum chloride to the second concentrated water is supplied to the third ultrafiltration membrane device 34. The type and preferred mode of PAC at this time are the same as those of the production apparatus 2. Also, as in the production apparatus 1, a reaction tank may be provided upstream of the third ultrafiltration membrane device 34, the polyaluminum chloride supply device 22 may be connected to the reaction tank, the second concentrated water may be stored in the reaction tank, and the PAC may be added to the second concentrated water in the reaction tank.

[0051] When a low basicity PAC is used, it is preferable to provide a pH adjuster upstream of the polyaluminum chloride supply device 22 and add a pH adjuster to the second concentrated water, as in the manufacturing apparatus 1. This allows the pH adjuster to adjust the pH of the second concentrated water (provide a pH adjustment step) by appropriately adding acid and alkali to the second concentrated water according to the basicity of the low basicity PAC. The amount of pH adjuster to be added in this case can be feedback-controlled based on the measured value by providing a pH measuring device, as in the manufacturing apparatus 1, which measures the pH of the second concentrated water before the PAC is added.

[0052] When a high-basicity PAC is used, the pH of the second concentrate does not need to be adjusted. By adding a high-basicity PAC to the second treated water, the suspended matter in the second treated water and the high-basicity PAC interact with each other to form microflocs. By passing through these microflocs, clogging of the membrane of the third ultrafiltration membrane device 34 is significantly suppressed, so that the performance of the ultrafiltration membrane can be maintained for a long period of time. Furthermore, the inventor's experiments have found that the use of a high-basicity PAC reduces the TOC (total organic carbon) in the third permeate compared to the use of a low-basicity PAC.

[0053] Next, the second treated water is filtered by the third ultrafiltration membrane device 34. The filtration in the third ultrafiltration membrane device 34 is dead-end filtration (full-end filtration), which can improve the water recovery rate in the production apparatus 2. In this embodiment, the full-end filtration includes a range that is substantially equivalent to full-end filtration, that is, where almost no concentrated water is produced, and represents, for example, a case where the water recovery rate exceeds 98%. The differential pressure between the inlet pressure and the outlet pressure to the third ultrafiltration membrane device 34 is preferably 0.004 MPa to 0.04 MPa. In addition, the water supply pressure to the third ultrafiltration membrane device 34 is preferably 0.03 MPa to 0.1 MPa. In this manner, the third permeate is obtained as the permeate of the third ultrafiltration membrane device 34.

[0054] The third-stage filtration membrane device is provided with a filtration membrane having a nominal pore size of, for example, 0.001 to 0.1 μm as a filtration material. Examples of such filtration membranes include ultrafiltration membranes and microfiltration membranes, and in this embodiment, an ultrafiltration membrane device is used. In this embodiment, the filtration material is preferably an ultrafiltration membrane having a nominal pore size of 0.001 to 0.1 μm. The ultrafiltration membrane provided in the third ultrafiltration membrane device 34 includes a hollow fiber membrane, a spiral membrane, and a flat membrane made of a material such as cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, or polyvinylidene fluoride, and among these, a hollow fiber membrane made of a fluorine-based material such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is preferable. The third ultrafiltration membrane device 34 is preferably an external pressure type ultrafiltration membrane device using the hollow fiber membrane.

[0055] It is preferable to use an independent ultrafiltration membrane device as the third ultrafiltration membrane device 34. By using an independent ultrafiltration membrane device, two or more independent ultrafiltration membrane devices are installed in parallel in the third ultrafiltration membrane device 34 at the third stage, and the production of ultrapure water can be continued without stopping the device by performing regeneration such as backwashing or module replacement one by one out of the multiple devices and continuing operation with other devices (so-called merry-go-round operation). In addition, it is preferable to use a floc decomposition suppression pump that can suppress the destruction of flocs, such as a hydrostal pump, a hydrostal chemical pump, a hose pump, or a mono pump, as a pump to be installed on the primary side of the independent ultrafiltration device.

[0056] The third permeate is then returned to the upstream side of the reaction tank 17 via the transfer pipe 35 and treated again as the raw water 11.

[0057] According to the manufacturing apparatus 2 described above, the second concentrated water to which PAC has been added is filtered by the third ultrafiltration membrane device 34 to obtain a third permeate of good purity and to dramatically improve the water recovery rate in the manufacturing apparatus 2. The water recovery rate in the manufacturing apparatus 2 thus obtained is, for example, 99% or more, and preferably 99.5% or more. In addition, since flocs are formed from the suspended matter remaining in the second concentrated water using PAC, the residual aluminum and residual suspended matter in the third permeate can be significantly reduced. Furthermore, the use of high basicity PAC can reduce the TOC (total organic carbon) in the third permeate. This improves the quality of the raw water treated in the manufacturing apparatus 2, making it possible to reduce the amount of chemicals used and efficiently produce pure water of good quality.

[0058] The reason why TOC is efficiently reduced in the second and subsequent stages of filtration membrane equipment is presumed to be as follows. In the first stage ultrafiltration membrane equipment, turbid components react preferentially with PAC to form flocs. This is because the reaction rate between turbid components and PAC is faster than the reaction rate between TOC and PAC. When PAC is added upstream of the second or subsequent stage ultrafiltration membrane equipment, most of the turbid components in the concentrated water from the first stage filtration membrane equipment are in the form of flocs, so it is thought that the TOC and PAC in the concentrated water will combine and be removed by the filtration membrane.

[0059] Next, another embodiment of the present invention will be described. FIG. 3 shows a schematic diagram of a manufacturing apparatus 3 used in the method for manufacturing pure water of this embodiment. The manufacturing apparatus 3 is an apparatus for reusing the washing wastewater when washing the third ultrafiltration membrane device 34. The manufacturing apparatus 3 includes a sedimentation concentrator 191 for separating the washing wastewater into a high-concentration waste liquid and a supernatant liquid, and a transfer device 192 for storing the supernatant liquid and supplying it to the raw water transfer pipe 13. The manufacturing apparatus 3 also includes a tank TK for storing washing (backwash) water, a backwash pipe 193 for supplying the washing water in the tank TK to the third ultrafiltration membrane device 34, a backwash pipe 194 for sending the washing wastewater discharged from the third ultrafiltration membrane device 34 to the sedimentation concentrator 191, and a valve V installed in the backwash pipe 194. The other configurations are the same as those of the manufacturing apparatus 2 shown in FIG. 2, so that repeated explanations will be omitted. The transfer device 192 is composed of, for example, a tank for storing the supernatant liquid, and a pump and piping for transferring the supernatant liquid.

[0060] In the manufacturing equipment 3, a part of the second concentrated water is collected from the concentrated water pipe 26 as water for cleaning (backwashing) and stored in the tank TK. The remaining part of the second concentrated water is sent to the rear stage as water to be treated, and the polyaluminum chloride supplying device 22 adds PAC to the water to be treated. With the valve V closed, the third ultrafiltration membrane device 34 continues full filtration of the second concentrated water (water to be treated) to which PAC has been added. After full filtration of the second concentrated water (water to be treated) is continued, when clogging progresses, chemical cleaning is performed on the third ultrafiltration membrane device 34. The chemical cleaning is performed, for example, as follows. First, sodium hydroxide (NaOH) is added to the cleaning water in the tank TK to generate alkaline cleaning water mainly composed of sodium hydroxide, and then the valve V is opened to pass the alkaline cleaning water through the ultrafiltration membrane device from the secondary side during the filtration process. After that, phosphoric acid (H3PO4) is added to the cleaning water in the tank TK to generate acid cleaning water mainly composed of phosphoric acid, and the acid cleaning water is passed through the ultrafiltration membrane device from the secondary side during filtration treatment. As for chemicals, in addition to the above, potassium hydroxide and ammonia can be used as alkaline cleaning water, sulfuric acid, hydrochloric acid, oxalic acid, and citric acid can be used as substitutes for acid cleaning water, and sodium hypochlorite can be used as an oxidizing agent depending on the membrane deposits to be cleaned. Chemical cleaning is performed by mixing chemicals with the cleaning water collected above, and using the resulting alkaline cleaning water, acid cleaning water, etc. The frequency of chemical cleaning is usually about once every 14 to 21 days. The cleaning wastewater generated by this is stored in the sedimentation concentrator 191 through the backwash pipe 194, and is separated into a supernatant and a concentrated liquid in the sedimentation concentrator 191. The separated supernatant is temporarily stored in the transfer device 192, and then supplied to the raw water transfer pipe 13 for retreatment.

[0061] According to the manufacturing apparatus 3 of this embodiment, clogging that occurs when the third ultrafiltration membrane device 34 performs dead-end filtration can be quickly eliminated by chemical cleaning, and the cleaning wastewater can be used as raw water, thereby reducing the amount of wastewater. Similarly, the first ultrafiltration membrane device 14 and the second ultrafiltration membrane device 24 may also be provided with devices for cleaning each device and reusing the cleaning wastewater.

[0062] Next, a manufacturing apparatus 8 using a blower and a bubbling tank will be described. FIG. 7 is a schematic diagram of a manufacturing apparatus 8 using a method of transferring the water to be treated, to which PAC has been added, to a subsequent stage using a blower and a bubbling tank. The manufacturing apparatus 8 includes a reaction tank 471 that contains raw water, a polyaluminum chloride supplying device 42 that supplies PAC into the reaction tank 471, and a raw water transfer pipe 13 that transfers the raw water. The manufacturing apparatus 8 includes a bubbling tank 472 downstream of the reaction tank 471. An aeration pipe 47a is provided at the bottom of the bubbling tank 472. The manufacturing apparatus 8 includes a blower B that sends air to the aeration pipe, and the blower B and the aeration pipe 47a are connected by piping.

[0063] The production apparatus 8 further includes a first-stage ultrafiltration membrane device 44 that filters the raw water (first treated water) to which PAC has been added. A transfer pipe 15 that transfers the permeated water to the subsequent stage and a concentrated water pipe 16 that discharges the concentrated water are connected to the first-stage ultrafiltration membrane device 44. A suction pump P is installed in the transfer pipe 15.

[0064] The production apparatus 8 further has a bubbling tank 441 that stores concentrated water (first concentrated water) from the first-stage ultrafiltration membrane device 44. An air diffuser 44a is provided at the bottom of the bubbling tank 441. The production apparatus 8 has a blower B that sends air to the air diffuser 44a, and the blower B and the air diffuser 44a are connected by piping.

[0065] The production apparatus 8 further includes a second-stage ultrafiltration membrane device 54 that filters the first concentrated water. A transfer pipe 25 that transfers the permeated water to the subsequent stage and a concentrated water pipe 26 that discharges the concentrated water are connected to the second-stage ultrafiltration membrane device 54. A suction pump P is installed in the transfer pipe 25.

[0066] The first-stage ultrafiltration membrane device 44 and the second-stage ultrafiltration membrane device 54 each include an immersion tank and an ultrafiltration membrane immersed in the immersion tank. The bubbling tank 472 and the immersion tank in which the first-stage ultrafiltration membrane device 44 is immersed are connected by a transfer pipe 13b, and the bubbling tank 441 and the second-stage ultrafiltration membrane device 54 are connected by a concentrated water pipe 16b. Both the transfer pipe 13b and the concentrated water pipe 16b are inclined so that the front stage side is higher than the rear stage side so that water flows from the front stage to the rear stage by its own weight.

[0067] Air supplied from a blower B is bubbled through an air diffuser 47a into the bubbling tank 472. In the bubbling tank 472, air bubbles rise in the water, causing the flocs to rise to the vicinity of the water surface of the bubbling tank 472. By connecting the transfer pipe 13b to the vicinity of the water surface of the bubbling tank, the treated water containing the flocs is sent by its own weight to the first-stage ultrafiltration membrane device 44 through the transfer pipe 13b, the latter of which is inclined downward. In the first-stage ultrafiltration membrane device 44, the permeated water is sucked by the suction pump P, and the concentrated water is sent to the bubbling 441 through the concentrated water pipe 16.

[0068] Air supplied from a blower B is bubbled through an air diffuser 44a into the bubbling tank 441. In the bubbling tank 441, air bubbles rise in the water, causing the flocs to rise to the vicinity of the water surface of the bubbling tank 441. By connecting the transfer pipe 16b to the vicinity of the water surface of the bubbling tank 441, the treated water containing the flocs is sent by its own weight to the second-stage ultrafiltration membrane device 54 through the transfer pipe 16b, the latter of which is inclined downward. In the second-stage ultrafiltration membrane device 54, the permeated water is sucked in by the suction pump P, and the concentrated water is sent to the latter stage through the concentrated water pipe 26.

[0069] There is a method of transferring treated water containing flocs generated by adding PAC to raw water to a downstream stage by sucking or pumping with a pump. In the production apparatus 8 shown in FIG. 7, which uses a blower to transfer to a downstream stage, the treated water containing flocs is bubbled to float the flocs to the top of the reaction tank, and the treated water containing flocs can be made to flow to the downstream stage by its own weight through a pipe connected to the top of the reaction tank and inclined so as to become lower toward the downstream stage. This method is particularly suitable when a low basicity PAC is used, but can also be suitably applied when a high basicity PAC that generates microflocs that are not easily broken is used. In the production apparatus 8, the same reference numerals are used to designate components common to the production apparatuses 1 to 3 and the production apparatus 4 described later, and detailed explanations thereof are omitted.

[0070] Next, a pure water producing system 5 according to an embodiment using the above-mentioned producing apparatus 1 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing a schematic configuration of the ultrapure water producing system 5 using the producing apparatus 1. In Fig. 4, the producing apparatus 1 can be changed to any one of producing apparatuses 2 to 3.

[0071] 4, the ultrapure water production system 5 produces pure water or ultrapure water using the pure water obtained in the production apparatus 1. The ultrapure water production system 5 comprises, in this order, a pretreatment system 50, a primary pure water system (pure water production system) 51, and a secondary pure water system (subsystem) 52. The secondary pure water system 52 is connected to a point of use (POU) 53 by piping, so that the ultrapure water produced by the ultrapure water production system 5 is supplied to the POU 53.

[0072] The pretreatment system 50 includes the production apparatus 1 of the embodiment described above, and, if necessary, a prefilter, a heat exchanger for temperature adjustment, and the like.

[0073] The ultrapure water manufacturing system 5 is equipped with a tank TK1 downstream of the pretreatment system 50, and the water to be treated that has been pretreated by the pretreatment system 50 is introduced into the tank TK1, temporarily stored therein, and then supplied to the primary pure water system 51.

[0074] The primary pure water system 51 produces primary pure water by removing organic matter, ion components, and dissolved gases from the pretreated water. The primary pure water system 51 includes an ultraviolet oxidation device (TOC-UV) 513 and an ion exchange device 514 in this order.

[0075] The ultraviolet oxidation device 513 has an ultraviolet lamp that emits ultraviolet rays with a wavelength of, for example, about 185 nm and ultraviolet rays with a wavelength of about 254 nm, and oxidizes and decomposes the total organic carbon (TOC) in the water to be treated by irradiating the water with ultraviolet rays from the ultraviolet lamp. The ultraviolet rays emitted by the ultraviolet oxidation device 513 decompose the water to generate OH radicals, and the organic matter in the water to be treated is oxidized and decomposed into organic acids by the OH radicals. The amount of ultraviolet irradiation in the ultraviolet oxidation device 513 of the primary pure water system can be appropriately changed depending on the water quality of the water to be treated.

[0076] The ion exchange device 514 is one or more of an ion exchange resin device and an electric deionization device. As the ion exchange resin device, one or more selected from a cation exchange resin device, an anion exchange resin device, a mixed bed ion exchange resin device, and a double bed ion exchange resin device can be appropriately combined and used according to the required water quality. The cation exchange resin used in the cation exchange resin device may be a strong acid cation exchange resin or a weak acid cation exchange resin. The anion exchange resin used in the anion exchange resin device may be a strong basic anion exchange resin or a weak basic anion exchange resin. As the ion exchange resin, a boron adsorbent ion exchange resin may be used.

[0077] The primary pure water obtained by the primary pure water system 51 has, for example, a resistivity of 17 MΩ·cm or more and a TOC concentration of 10 μgC / L or less.

[0078] The ultrapure water production system 5 includes a primary pure water tank TK2 for storing primary pure water, and a secondary pure water system 52, in this order, downstream of a primary pure water system 51. The primary pure water produced in the primary pure water system is temporarily stored in the primary pure water tank TK2, and then sent to the secondary pure water system 52. The secondary pure water system 52 includes an ultraviolet oxidation device (TOC-UV) 521, a non-regenerative polisher (Polisher) 522, a membrane degassing device (MDG) 523, and an ultrafiltration membrane device (UF) 524.

[0079] The ultraviolet oxidation device 521 in the secondary pure water system 52 has the same configuration as the ultraviolet oxidation device 513 in the primary pure water system 51. The non-regenerative polisher 522 is a mixed-bed ion exchange resin device in which a strong acid cation exchange resin and a strong basic anion exchange resin are mixed and filled in a container such as a cylinder. The non-regenerative polisher 522 adsorbs and removes ion components generated by the ultraviolet oxidation device 521 decomposing organic matter.

[0080] The membrane degassing device 523 removes dissolved gases through a degassing membrane. The membrane degassing device 523 removes trace amounts of dissolved oxygen in the primary pure water to reduce the dissolved oxygen concentration, for example, to about 1 μg / L or less. The ultrafiltration membrane device 524 performs filtration using an ultrafiltration membrane to remove trace amounts of eluted matter and fine particle components from the upstream ion exchange resin, for example, to reduce the number of fine particles of 0.05 μm or more to about 250 Pcs. / L or less.

[0081] In this way, the secondary pure water system 52 processes the primary pure water to produce ultrapure water of even higher purity. The quality of the ultrapure water is, for example, a total organic carbon (TOC) concentration of 1 μgC / L or less, a resistivity of 18 MΩ·cm or more, and a boron concentration of 0.1 ppb (μg / L) or less. The ultrapure water produced by the secondary pure water system is supplied to a point of use 53.

[0082] In each of the above-mentioned embodiments, the water quality of the raw water and the treated water can be measured by the following methods or devices. Turbidity: Light scattering method Aluminum concentration: ICP emission spectrometry pH: Electrode method Conductivity: Conductivity meter (HORIBA HE-960CW) Total organic carbon (TOC) concentration: TOC meter (except ultrapure water: SUEZ Sievers M9e) EXAMPLES

[0083] Next, examples will be described, but the present invention is not limited to the following examples.

[0084] FIG. 5 is a schematic diagram of the pure water production apparatus 4 used in the present embodiment and the comparative example. The production apparatus 4 shown in FIG. 5 includes a raw water supply device 41 for supplying raw water, polyaluminum chloride supply devices 42 and 52 for supplying PAC, and a reaction tank 47 into which raw water and high basicity PAC are supplied. The production apparatus 4 further includes an ultrafiltration membrane device 44, an ultrafiltration membrane device 54 for treating concentrated water from the ultrafiltration membrane device 44, and an ultrafiltration membrane device 64 for treating concentrated water from the ultrafiltration membrane device 54, downstream of the reaction tank 47. A reaction tank 63 for storing concentrated water from the ultrafiltration membrane device 44, which is the second stage of the filtration membrane device, is provided in front of the ultrafiltration membrane device 54. In the production apparatus 4, the polyaluminum chloride supply device 42 supplies PAC into the reaction tank 47, and the polyaluminum chloride supply device 52 supplies PAC into the reaction tank 63.

[0085] The specifications of the devices used in the examples and experimental examples are as follows. Reactor 47: Capacity 1m 3 Ultrafiltration membrane device 44, 54: Veolia ZeeWeed 500 Membrane (immersed type membrane PVDF membrane, nominal pore size 0.04 μm) Ultrafiltration membrane device 64: Puria GL manufactured by Kuraray Co., Ltd. (pressure type membrane PVDF membrane, nominal pore size 0.02 μm) Measurement of aluminum concentration: Inductively coupled plasma (ICP) optical emission spectrometry Turbidity measurement: Turbidimeter (Hach2100P, manufactured by Toa Dekk Corporation) pH measurement: Water quality meter (Horiba D200, manufactured by Horiba) TOC measurement: TOC meter (Suez M9e) Water quality of raw water (lake water): Turbidity 2.2 NTU, pH = 8.0, aluminum concentration 0.019 mg / L, conductivity 250 μS / cm, TOC 2 mg / L

[0086] Example 1 The raw water was supplied to the reaction tank 47. Then, an aqueous solution of aluminum chloride pentahydroxide (Al2Cl(OH)5) as a high basicity PAC (prototype product of Nomura Micro Science Co., Ltd., basicity 83.33%) was supplied to the reaction tank 47 by the polyaluminum chloride supply device 42 so that the aluminum concentration in the raw water was 2 mg / L in terms of Al2O3 concentration, and stirred. After stirring, the raw water was sampled, and 80 ml of the raw water was passed through a membrane (size 47 mmφ) with a nominal pore size of 0.2 μm, and the fine particles captured by the membrane were observed, and fine particles of about 1 to 10 μm were observed. The elemental components of these fine particles were confirmed by energy dispersive X-ray fluorescence spectroscopy (EDX), and Al was contained. Furthermore, when the same amount of water was passed through a membrane (size 47 mmφ) with a nominal pore size of 0.45 μm, almost no differential pressure was observed. From the above results, it was confirmed that microflocs were formed in this embodiment.

[0087] The treated water in the reaction tank 47 was passed through the ultrafiltration membrane device 44 and filtered to obtain the first permeate and the first concentrated water. The second concentrated water was passed through the ultrafiltration membrane device 54 and filtered to obtain the second permeate and the second concentrated water. The first permeate and the second permeate were recovered through piping. Next, the second concentrated water was stored in the reaction tank 63, and the same high basicity PAC as above was added by the polyaluminum chloride supply device 52 so that the aluminum concentration in the water was 20 mg / L in terms of Al2O3 concentration, and the water was passed through the ultrafiltration membrane device 64 and filtered in its entirety to obtain the third permeate. The third permeate was mixed with the raw water and reprocessed, and these processes were repeated. The water recovery rates of the ultrafiltration membrane device 44 (first stage) and the ultrafiltration membrane device 54 (second stage) were both set to 90%, and the suction pressure was set to 10 kPa for the first stage and 5 kPa for the second stage.

[0088] Example 2 In Example 1, instead of the high basicity PAC, a low basicity PAC (trade name PAC250A, manufactured by Taki Chemical Co., Ltd., basicity 51%) was used, and added so that the aluminum concentration in the raw water was 2 mg / L in terms of Al2O3, and the aluminum concentration in the second concentrated water (supply water to the ultrafiltration membrane device 64 (third stage)) after the addition of PAC was 20 mg / L in terms of Al2O3. In addition, a pH adjuster (sulfuric acid and aluminum hydroxide aqueous solution) was added to the raw water and the second concentrated water when the PAC was added to adjust the pH to 6.5 to 7.5, and the treatment was repeated in the same manner as in Example 1.

[0089] Comparative Example 1 The treatment was repeated in the same manner as in Example 2, except that the pH was not adjusted. The pH of the feed water to the ultrafiltration membrane device 64 (third stage) was 5.8. In Comparative Example 1, the aluminum concentration of the third permeate was about 25 times that of the raw water, the turbidity components were about 17 times that of the raw water, and the TOC concentration was 1.5 times that of the raw water, and the water quality was worse than that of the raw water. Therefore, the third permeate could not be returned to the upstream side of the reaction tank 47. If the third permeate, whose water quality is worse than that of the raw water, is returned to the upstream side of the reaction tank 47, the raw water quality is likely to gradually deteriorate, and membrane clogging due to turbid components derived from the raw water is likely to occur. In addition, in a preliminary experiment conducted prior to this comparative example, when the water recovery rate of the entire two-stage ultrafiltration membrane device was set to 99% and treatment was performed, membrane clogging frequently occurred in the ultrafiltration membrane device 44, especially the ultrafiltration membrane device 54. Therefore, based on the results of the preliminary experiment, in this comparative example, operation was performed so that the water recovery rate of the entire two-stage ultrafiltration membrane device was 90%.

[0090] Comparative Example 2 6 shows a conventional pure water production apparatus 6 used in this comparative example. The production apparatus 6 differs from the production apparatus 4 in that it does not include the ultrafiltration membrane device 54 and the ultrafiltration membrane device 64. Using the production apparatus 6, sulfuric acid was added to the raw water as a pH adjuster to adjust the pH of the feed water of the ultrafiltration membrane device 44 to 7.2, and then the water was passed through the ultrafiltration membrane device 44 and filtered in the same manner as in Comparative Example 1 to obtain a first permeate and a first concentrated water. Except for this, the treatment was repeated in the same manner as in Comparative Example 1.

[0091] In Examples 1 and 2 and Comparative Example, the turbidity (NTU) and aluminum concentration in the mixed water of the first permeate and the second permeate, the TOC concentration, turbidity and aluminum concentration in the third permeate, and the water recovery rate of the entire apparatus were measured. The results are shown in Table 1. In Table 1, the mixed water of the first permeate and the second permeate is shown as "first permeate and second permeate." Note that the value of "water quality of the first permeate and second permeate" in Comparative Example 2 represents the water quality of only the "first permeate" since Comparative Example 2 was treated with a single-stage ultrafiltration membrane device.

[0092] [Table 1]

[0093] (Experimental Example) The TOC concentrations of the permeated water were compared when high-basicity PAC was added to the raw water, the first concentrate, and the second concentrate of Example 1 and filtered through an ultrafiltration device.

[0094] FIG. 8 shows a schematic diagram of the test apparatus 7 used in this experimental example. The test apparatus shown in FIG. 8 includes a supply device 71 for supplying water to be treated, a reaction tank 77 for accommodating the water to be treated and PAC, a polyaluminum chloride supply device 72 for adding a predetermined amount of high-basicity PAC to the reaction tank 77, and an agitator S for agitating the water to be treated in the reaction tank 77. The test apparatus 7 further includes a pump P for sending the water to be treated in the reaction tank 77 to a subsequent stage, and an ultrafiltration membrane device 74 for filtering the water to which the high-basicity PAC has been added by an ultrafiltration membrane. The ultrafiltration membrane device 74 is connected to a transfer pipe 75 for transferring the permeated water and a concentrated water pipe 76 for discharging the concentrated water. The test apparatus 7 also includes an air compressor (not shown) for feeding air into the ultrafiltration membrane device during air washing.

[0095] (Experimental Example 1) The raw water from Example 1 was stored in a reaction tank 77 as the water to be treated, and 20 mg / L of high basicity PAC in terms of Al2O3 concentration was added to the water to be treated. The water to be treated in the reaction tank 77 was then passed through the ultrafiltration membrane 74 and filtered with a water recovery rate of 90%. The water passage was then stopped and the ultrafiltration membrane was backwashed, and treatment was resumed after the backwash. This process was repeated several times and the permeated water was collected. The backwashing was performed by combining air backwashing and air bubbling inside the module. The ultrafiltration membrane device was a test prototype module containing one hollow fiber, external pressure type, with a membrane area of ​​10 cm. 2 An ultrafiltration device having an ultrafiltration (UF) membrane made of PDVF (polyvinylidene fluoride) with a nominal pore size of 0.02 μm was used, and the supply pressure of the raw water to the ultrafiltration membrane device was set to 0.06 MPa.

[0096] (Experimental Example 2, Experimental Example 3) The test was carried out in the same manner as in Experimental Example 1, except that the high basicity PAC was added to the water to be treated as the first concentrate in Example 1 in Example 2, and as the second concentrate in Example 3. That is, after the PAC was added, the water was passed through the ultrafiltration membrane and filtered. Thereafter, as in Experimental Example 1, the water passing was stopped and the ultrafiltration membrane was backwashed, and the treatment was resumed after the backwashing. This process was repeated several times, and the permeated water was collected.

[0097] (Experimental Example 4, Experimental Example 5) In Experimental Example 2 and Experimental Example 3, the first concentrated water and the second concentrated water of Example 1, which are the water to be treated, were passed through an ultrafiltration membrane in the same manner as in Experimental Example 2 and Experimental Example 3, except that high-basicity PAC was not added. After filtering, the water passing was stopped and the ultrafiltration membrane was backwashed. After the backwashing, the treatment was resumed. This process was repeated several times.

[0098] The results of measuring the TOC concentration in the collected permeate are shown in Table 2. In Example 1, Experimental Examples 4 and 5, almost no TOC was removed, but in Experimental Examples 1 and 2, the TOC removal rates were approximately 68% and 73%, respectively.

[0099] [Table 2]

[0100] From the examples and comparative examples, it can be seen that by adding PAC to the raw water and the second concentrate, and then filtering the entire amount of the second concentrate with added PAC using an ultrafiltration membrane device, it is possible to suppress clogging of the three-stage ultrafiltration membrane device while achieving a water recovery rate of 99.0% or more using the three-stage ultrafiltration membrane device. In addition, the turbidity is slightly higher in Example 2 than in Example 1. This is thought to be because, in the case of low basicity PAC, the flocs are slightly broken during transfer from the first stage ultrafiltration membrane device to the second stage ultrafiltration membrane device, which reduces the turbidity removal rate and causes aluminum to leak into the subsequent stages. Also, according to the experimental example, it is found that the total organic carbon (TOC) in the water can be reduced by adding high basicity PAC to the first concentrated water and the second concentrated water and filtering them with an ultrafiltration membrane device. Therefore, when applied to a pure water or ultrapure water production system, it is possible to reduce the TOC removal load on the downstream equipment (such as an ultraviolet oxidation device and an ion exchange device downstream). [Explanation of symbols]

[0101] 1-4: Pure water production equipment, 5: Ultrapure water production system, 11, 41: Raw water supply equipment, 12, 22, 42, 52: Polyaluminum chloride supply equipment, 13: Raw water transfer pipe, 14, 24, 34, 44, 54, 64: Ultrafiltration membrane equipment, 17, 63: Reaction tank, 18: pH adjustment equipment, 50: Pretreatment system, 51: Primary pure water system (pure water production system), 52: Secondary pure water system (subsystem), 53: Point of use (POU), 513: Ultraviolet oxidation equipment (TOC-UV), 514: Ion exchange equipment, TK1, TK2: Tank, 521: Ultraviolet oxidation equipment (TOC-UV), 522: Non-regenerative polisher (Polisher), 523: Membrane degassing equipment (MDG) 524: Ultrafiltration membrane equipment (UF)

Claims

1. A method for producing pure water, comprising the steps of: A step of obtaining a first treated water by adding polyaluminum chloride to the raw water; The method includes two or more filtration stages in which a first treated water is filtered by a membrane filtration device in a first stage to obtain a first concentrated water, and the first concentrated water is filtered by a membrane filtration device in a second stage, and water for pure water is obtained as a permeate of the two or more filtration stages.

2. 2. The method according to claim 1, wherein the first treated water containing microflocs is obtained by adding polyaluminum chloride with high basicity to the raw water.

3. 3. The process according to claim 1 or 2, wherein the basicity of the polyaluminum chloride is greater than 75%.

4. the polyaluminum chloride comprises aluminum chloride pentahydroxide; The amount of aluminum chloride pentahydroxide added is aluminum oxide (Al ２ O ３ 3. The method according to claim 1, wherein the concentration of the fluoride-containing compound in the raw water is 0.25 mg / L or more and 25 mg / L or less in terms of the concentration calculated based on the converted value.

5. The basicity of the polyaluminum chloride is 75% or less, The method according to claim 1, further comprising a pH adjustment step of adjusting the pH of raw water to which the polyaluminum chloride is added.

6. The manufacturing method according to claim 1 or 2, further comprising at least one step of adding polyaluminum chloride to concentrated water from at least one of the two or more stages of filtration membrane devices and then supplying the concentrated water to a subsequent stage of the filtration membrane device.

7. Furthermore, a step of obtaining a second treated water by adding polyaluminum chloride to the concentrated water of at least the final stage of the filtration membrane device among the two or more stages of the filtration membrane device; A total filtration step of filtering the second treated water by a filtration membrane device, The method according to claim 1 or 2, wherein the permeate obtained in the dead-end filtration step is used as the raw water.

8. Furthermore, a cleaning process for cleaning the filtration membrane device that has been subjected to the total filtration process; A sedimentation and concentration step is provided for separating a supernatant from the washing wastewater generated in the washing step, The method according to claim 7 , wherein the supernatant is used as the raw water.

9. A method for producing pure water, comprising the steps of: A step of obtaining a first treated water by adding polyaluminum chloride to the raw water; A process for producing pure water, the process including a two or more stages of filtration steps in which the first treated water is filtered by a membrane filtration device in a first stage to obtain a first concentrated water, and the first concentrated water is filtered by a membrane filtration device in a second stage, and the process for producing pure water is obtained as a permeate of the two or more stages of the membrane filtration steps; The method includes an ultraviolet oxidation step and an ion exchange step in this order. Manufacturing method.

10. An apparatus for producing pure water, comprising: A raw water supply device that supplies raw water; A polyaluminum chloride supplying device for adding polyaluminum chloride to raw water; A two or more stage filtration membrane device for filtering a first treated water produced by adding polyaluminum chloride to raw water; Among the two or more stages of filtration membrane devices, a concentrated water pipe that supplies concentrated water from a previous stage filtration membrane device to a subsequent stage filtration membrane device, and a plurality of transfer pipes that transfer permeated water from the two or more stages of filtration membrane devices to obtain pure water; A manufacturing apparatus having the above structure.

11. 11. The apparatus of claim 10, wherein the basicity of the polyaluminum chloride is greater than 75%.

12. the polyaluminum chloride comprises aluminum chloride pentahydroxide; The polyaluminum chloride supplying device supplies aluminum oxide (Al ２ O ３ 12. The manufacturing apparatus according to claim 10, wherein the aluminum chloride pentahydroxide is supplied in an amount of 0.25 mg / L or more and 25 mg / L or less in terms of a concentration calculated based on the converted aluminum chloride.

13. The basicity of the polyaluminum chloride is 75% or less, The manufacturing apparatus according to claim 10, further comprising a pH adjusting device for adjusting the pH of raw water to which the polyaluminum chloride is added.

14. The manufacturing apparatus according to claim 10 or 11, further comprising one or more polyaluminum chloride supply devices that add polyaluminum chloride to concentrated water of at least one of the two or more stages of filtration membrane devices, and the concentrated water to which polyaluminum chloride has been added is filtered by a subsequent stage of filtration membrane device.

15. Furthermore, a polyaluminum chloride supplying device that adds polyaluminum chloride to the concentrated water of at least the final stage of the filtration membrane device among the two or more stages of the filtration membrane device; The system includes a filtration membrane device that filters the entire amount of second treated water produced by adding polyaluminum chloride to the concentrated water from the final stage filtration membrane device, The manufacturing apparatus according to claim 10 or 11, further comprising a pipe for sending permeate from the filtration membrane device that performs total filtration to the raw water supply device to be used as the raw water.

16. Further, a cleaning device for cleaning the filtration membrane device for total filtration; a sedimentation and concentration device for separating a supernatant liquid from the washing wastewater generated in the washing device; The manufacturing apparatus according to claim 15 , further comprising a pipe for sending the supernatant liquid to the raw water supply device.

17. The apparatus for producing pure water according to claim 10 or 15, A pure water production system comprising an ultraviolet oxidation device and an ion exchange device in this order.

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