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

Abstract

To provide a method and an apparatus for producing water for pure water capable of efficiently removing a suspended substance in raw water and suppressing the lowering of the permeation flux of a reverse osmosis membrane device caused by residual aluminum over a long period of time, and a method and a system for producing pure water using the same.SOLUTION: A method for producing water for purification, comprising: a step of adding polyaluminum chloride having a high basicity to raw water to obtain first treated water; and a reverse osmosis membrane step of subjecting the first treated water to reverse osmosis membrane treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In water treatment, such as the production of industrial water from river water, well water, lake water, etc., and wastewater treatment, coagulation treatment is carried out to remove suspended solids such as suspended solids, dissolved organic matter, and colloidal silica. In this coagulation treatment, polyaluminum chloride (PAC) is used as a coagulant. PAC is widely used because it is inexpensive and has a wide pH range for coagulation.

[0003] A known method of using PAC in industrial water production and wastewater treatment is to mix PAC with relatively low basicity (75% or less) into wastewater to form coarse aggregates of suspended solids, and then remove these coarse aggregates by dead-end filtration (see, for example, Patent Document 1). However, this method requires a slow sand filtration device, and therefore requires a large site area for the installation of the slow sand filtration device. For example, if this method is used to remove 100m 3 To treat raw water of 10000 sq. ft. / h, a circular slow sand filtration device with a radius of 12 m would be required. Furthermore, no facilities for further treatment of the treated water are anticipated. Therefore, it is difficult to apply this method to anything other than very limited facilities such as water purification plants, and it is difficult to apply it to the production of pure water or ultrapure water used in the manufacturing processes of semiconductors, liquid crystal displays, etc.

[0004] In the production of pure water or ultrapure water, raw water such as tap water or industrial tap water is passed through a membrane treatment device such as a reverse osmosis membrane device (RO) or an ultrafiltration device (UF), and then treated using a combination of an ion exchange resin device, an ultraviolet irradiation device, etc. To remove suspended solids from the raw water, tap water, industrial water, etc., is treated with PAC before being supplied. However, since the raw water contains residual aluminum derived from the 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 2).

[0005] A microfloc method using PAC is also used. In this method, PAC is directly injected into tap water, industrial tap water, or the like, or the water is rapidly stirred after injection to form microflocs, which are then removed by filtration without any precipitation treatment (see, for example, Patent Document 3). However, in this method, if a reverse osmosis membrane device is installed in the downstream stage, the permeation flux of the reverse osmosis membrane device will be significantly reduced, as described above. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-086149 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-86966 [Patent Document 3] Japanese Patent Application Publication No. 2022-165279 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, the use of PAC in the production of pure water or ultrapure water poses the problem of reduced permeation flux through reverse osmosis membrane equipment due to adhesion of residual aluminum in the water to the membrane. However, methods that use iron-based inorganic polymer flocculants to remove residual aluminum pose problems of increased costs and environmental impact due to the increased amount of chemical used.

[0008] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method and apparatus for producing pure water that can efficiently remove suspended solids from raw water and can suppress, over a long period of time, a decrease in the permeation flux of a reverse osmosis membrane device caused by residual aluminum. Another object of the present invention is to provide a method and system for producing pure water that can efficiently remove suspended solids from raw water and suppress the permeation flux of a reverse osmosis membrane device caused by residual aluminum, thereby producing high-quality pure water over a long period of time. [Means for solving the problem]

[0009] 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: adding high-basicity polyaluminum chloride to raw water to obtain first treated water; and a reverse osmosis membrane step of treating the first treated water with a reverse osmosis membrane. [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 manufacturing method according to [1] or [2], wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less. [4] The method according to any one of [1] to [3], wherein the basicity of the polyaluminum chloride is greater than 75%. [5] The polyaluminum chloride comprises aluminum chloride pentahydroxide; The manufacturing method according to any one of [1] to [4], wherein the amount of aluminum chloride pentahydroxide added is an amount equivalent to an aluminum oxide (Al2O3) concentration of 0.25 mg / L or more and 5 mg / L or less relative to the raw water.

[0010] [6] The first treated water, The method has a filtration process including one or more filtration methods selected from sand filtration, multimedia filter (MMF) filtration, microfiltration (MF) equipment, ultrafiltration, and activated carbon filtration, The manufacturing method according to any one of [1] to [5], wherein the third treated water obtained in the filtration step is treated with the reverse osmosis membrane. [7] The manufacturing method described in [6], wherein the turbidity of the third treated water is 0.01 NTU or more and 0.4 NTU or less, and the aluminum concentration is 0.01 mg / L or more and 0.04 mg / L or less. [8] The filtration step includes activated carbon filtration; The method according to [6], wherein the activated carbon filtration is a process of passing water through spherical activated carbon and filtering it.

[0011] [9] A method for producing pure water, comprising: A step of obtaining first treated water by supplying high basicity polyaluminum chloride to raw water; a pure water producing process including a reverse osmosis membrane process of treating the first treated water with a reverse osmosis membrane; A manufacturing method comprising an ultraviolet oxidation step and an ion exchange step in this order.

[0012]

[10] A pure water manufacturing apparatus, a raw water supply device that supplies raw water; a polyaluminum chloride supplying device that adds high-basicity polyaluminum chloride to raw water; A manufacturing apparatus having a reverse osmosis membrane device that performs reverse osmosis membrane treatment on first treated water produced by adding high-basicity polyaluminum chloride to raw water.

[11] The manufacturing apparatus according to

[10] , wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less.

[12] The manufacturing apparatus according to claim

[10] or

[11] , wherein the basicity of the high-basicity polyaluminum chloride is greater than 75%.

[13] The manufacturing apparatus according to any one of

[10] to

[12] , wherein the polyaluminum chloride contains aluminum chloride pentahydroxide, and the polyaluminum chloride supplying device supplies aluminum chloride pentahydroxide to raw water in an amount such that the concentration, calculated as aluminum oxide (Al2O3), is 0.25 mg / L or more and 5 mg / L or less.

[14] Between the polyaluminum chloride supply device and the reverse osmosis membrane device, The manufacturing apparatus according to any one of

[10] to

[13] , comprising one or more types selected from a sand filtration apparatus, a multimedia filter (MMF) filtration apparatus, a microfiltration (MF) apparatus, an ultrafiltration apparatus, and an activated carbon filtration apparatus.

[15] A pure water production system comprising the apparatus for producing pure water according to any one of

[10] to

[14] , an ultraviolet oxidation device, and an ion exchange device, in this order. The symbol "~" indicates a range of values ​​including the values ​​before and after it. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method and apparatus for producing pure water that can efficiently remove suspended solids from raw water and suppress a decrease in the permeation flux of a reverse osmosis membrane device due to residual aluminum. Furthermore, the present invention can provide a method and system for producing pure water that can efficiently remove suspended solids from raw water and suppress a decrease in the permeation flux of a reverse osmosis membrane device due to residual aluminum, thereby producing high-quality pure water over a long period of time. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram schematically illustrating a manufacturing apparatus used in a method for manufacturing pure water according to an embodiment. [Figure 2] FIG. 2 is a diagram schematically illustrating a production apparatus in which a mixing tank is further added to the production apparatus shown in FIG. [Figure 3]FIG. 10 is a diagram schematically illustrating a manufacturing apparatus used in a method for manufacturing pure water according to another embodiment. [Figure 4] FIG. 4 is a diagram schematically illustrating a production apparatus in which a mixing tank is further added to the production apparatus shown in FIG. [Figure 5] 1 is a diagram schematically illustrating a pure water production system using an apparatus for producing pure water according to an embodiment. [Figure 6] FIG. 1 is a diagram schematically illustrating a pure water production apparatus used in the examples. [Figure 7] 1 is a graph showing the change over time in permeation flux of a reverse osmosis membrane device. [Figure 8] 1 is a graph showing the relationship between the cumulative filtration volume and the permeation flux of the ultrafiltration device in an experimental example. [Figure 9] FIG. 1 is a diagram schematically illustrating a batch-type testing device used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will now be described. Fig. 1 schematically shows a production apparatus 1 used in a method for producing pure water according to this embodiment. The production apparatus 1 includes a raw water supply device 11 that supplies raw water, a polyaluminum chloride supply device 12 that supplies high-basicity polyaluminum chloride (hereinafter also referred to as "high-basicity PAC"), a raw water transfer pipe 13 that transfers the raw water, and a reverse osmosis membrane device 14 that performs reverse osmosis membrane treatment on the raw water (first treated water) to which the high-basicity PAC has been added.

[0016] The method for producing pure water in this embodiment using the production apparatus 1 is as follows. First, raw water is supplied from a raw water supply device 11 into a raw water transfer pipe 13. The raw water may be municipal water such as city water or industrial water, or natural water such as river water, lake water, groundwater, or well water. The quality of the raw water may be, for example, a turbidity of 1 NTU to 100 NTU, a suspended solids (SS) of 5 mg / L to 500 mg / L, a total organic carbon (TOC) of 0.5 mg / L to 7 mg / L, an aluminum concentration of 0.01 mg / L to 5 mg / L, and a pH of 4 to 9. The raw water supply device 11 includes, for example, a raw water tank for storing raw water and a feed water pump for transferring 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 prefilter (not shown) may be installed as a pretreatment device to pretreat the raw water before the subsequent addition of the high-basicity PAC. Furthermore, if necessary, an acid or alkali injection facility may be installed to adjust the pH of the raw water.

[0017] Next, the polyaluminum chloride supply device 12 adds the high-basicity PAC into the raw water transfer pipe 13. The polyaluminum chloride supply device 12 includes, for example, a chemical tank for storing the high-basicity PAC and a chemical injection pump for adding the high-basicity PAC from the chemical tank into the raw water transfer pipe 13. The chemical injection pump measures the high-basicity PAC from the chemical tank so as to achieve a predetermined concentration, and adds it into the raw water transfer pipe 13.

[0018] When a PAC with a lower basicity than a high-basic PAC (hereinafter referred to as "low-basic PAC") is added to raw water, the low-basic PAC interacts with suspended solids in the raw water, causing coagulation and the formation of fine and coarse flocs. These flocs can be separated by settling using a coagulation and sedimentation tank, but aluminum ions are likely to leak from the flocs, or many nanoflocs, which are smaller than microflocs, are formed. Therefore, when treated water to which a low-basic PAC has been added, is treated with a reverse osmosis membrane, aluminum in the treated water adheres to the reverse membrane surface, making it very likely to clog the reverse osmosis membrane and causing an early decrease in the permeation flux of the reverse osmosis membrane device.

[0019] In contrast, in the production method of this embodiment, a high basicity PAC is supplied to raw water, and the high basicity PAC interacts with suspended solids and the like in the raw water to form microflocs. Through the process of these microflocs, adhesion of residual aluminum to the membrane of the reverse osmosis membrane device 14 is significantly reduced, and the performance of the reverse osmosis membrane device can be maintained for a long period of time.

[0020] Microflocs are aggregates of suspended solids and high-basicity PAC with a size of approximately 1 to 10 μm. High-basicity PAC easily forms microflocs, but does not easily form coarse flocs or nanoflocs, which are finer than microflocs. Aluminum ions do not easily leak from microflocs, so by passing through them, reverse osmosis membrane blockage can be prevented for a long period of time.

[0021] The high basicity PAC of this embodiment contains polyaluminum chloride represented by the following chemical formula (1). The high basicity PAC of this embodiment preferably has a basicity of more than 75%, more preferably more than 83%. The upper limit of basicity is usually less than about 84%. The basicity is a value calculated by n / 6×100(%). [Al2(OH) n Cl 6-n ] m (1≦n≦5, m≦10) (1)

[0022] High basicity PACs can be produced, for example, by the method described in Japanese Patent No. 4104773. Only one high basicity PAC may be used, or two or more may be used in combination. When two or more high basicity PACs are used in combination, the basicity 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%, and more preferably greater than 83%.

[0023] It is preferable to use aluminum chloride pentahydroxide (Al2Cl(OH)5) as the high basicity PAC. 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 makes it easier to form more uniform microflocs. This is thought to be due to the high basicity and small molecular weight of aluminum chloride pentahydroxide.

[0024] The amount of high-basicity PAC is preferably 0.125 mg / L as Al2O3 or more per 1 NTU of turbidity in the raw water. Specifically, the amount of high-basicity PAC is preferably 0.25 mg / L as Al2O3 or more and 5 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 3 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 2 mg / L as Al2O3 or less relative to the total amount of raw water. Even a small amount of high-basicity PAC, as described above, can microflocculate the suspension in the raw water. Furthermore, because the high-basicity PAC functions even in a small amount, as described above, it is easier to prevent clogging of the downstream reverse osmosis membrane device 14. The notation "as Al2O3" indicates that the value is converted into aluminum oxide (Al2O3) concentration.

[0025] 2 schematically shows a pure water production apparatus 2 having a mixing tank 23 for adding high basicity PAC to raw water. The production apparatus 2 differs from the above-described production apparatus 1 in that it has a mixing tank 23 in the path of the raw water transfer pipe 13, but the other configurations are the same. In this embodiment, detailed explanations of the configurations and functions that are common to the production method using the production apparatus 1 will be omitted. If necessary, a polymer flocculant or other inorganic flocculant may be added as a flocculation promoter immediately before or after the addition of the high basicity PAC.

[0026] In the production apparatus 2, raw water is supplied from a raw water supply device 11, and high basicity PAC is supplied from a polyaluminum chloride supply device 12, both of which are supplied into a mixing tank 23. In the mixing tank 23, the high basicity PAC interacts with the suspension in the raw water, forming microflocs. In this case, the order of supplying the raw water and the high basicity PAC into the mixing tank 23 may be either first or simultaneously, but it is preferable that the high basicity PAC be added to the mixing tank 23 to which the raw water has been supplied.

[0027] In the production apparatus 2 shown in FIG. 2, raw water and high-basicity PAC are rapidly stirred in the mixing tank 23, which makes it easier to form more uniform microflocs without generating nanoflocs. The stirring speed is, for example, 150 s ー1 It is preferable that the temperature is 150 to 250 s or more. ー1 It is more preferable that it is 250s ー1 It is more preferable that the stirring time using a rapid stirrer is 2 minutes or more, preferably 3 minutes or more, and more preferably 6 minutes or more. The larger the G value of rapid stirring, the shorter the stirring time can be.

[0028] Next, the first treated water containing microflocs is supplied to the reverse osmosis membrane device 14 of Fig. 1 or 2 and subjected to reverse osmosis membrane treatment. As a result, second treated water is obtained as permeate from the reverse osmosis membrane device 14. In order to prevent a decrease in permeation flux in the reverse osmosis membrane device 14, the water supply pressure to the reverse osmosis membrane device 14 at this time is preferably 0.5 MPa to 3 MPa, and the water recovery rate in the reverse osmosis membrane device 14 is preferably 75% to 95%. Immediately before being supplied to the reverse osmosis membrane device 14, a scale inhibitor or bacteriostatic agent may be added as appropriate to the first treated water, and the resulting water may be supplied to the reverse osmosis membrane device 14.

[0029] The reverse osmosis membrane device 14 may be any of ultra-low pressure, ultra-low pressure, low pressure, medium pressure, and high pressure reverse osmosis membrane devices. The reverse osmosis membrane provided in the reverse osmosis membrane device 14 is preferably a spiral reverse osmosis membrane made of aromatic polyamide. The reverse osmosis membrane device 14 may be a positively charged membrane with a positively charged surface, a negatively charged membrane with a negatively charged surface, or an uncharged membrane with an uncharged surface. Among these, a negatively charged membrane is preferred because it is less likely to clog the reverse osmosis membrane with flocs. The reverse osmosis membrane device 14 is preferably an ultra-low or low pressure negatively charged membrane. Commercially available reverse osmosis membrane devices with ultra-low or low pressure negatively charged membranes can be used, such as the "ES20" manufactured by Nitto Denko Corporation, the "SU Series," "TM Series," and "TBW Series" manufactured by Toray Industries, Inc., and the "BW Series" manufactured by Dow.

[0030] A transfer pipe 15 for permeated water (second treated water) is connected to the permeation side of the reverse osmosis membrane device 14, and the permeated water is sent to a subsequent stage via the transfer pipe 15. A discharge pipe 16 for concentrated water is connected to the concentration side of the reverse osmosis membrane device 14. The concentrated water is discharged to the outside of the production apparatus 1 via the discharge pipe 16, or returned to the upstream stage of the reverse osmosis membrane device 14 for reprocessing. The quality of the second treated water (permeated water) thus obtained is, for example, a turbidity of 0.01 NTU to 0.2 NTU, an aluminum concentration of 0 mg / L to 0.002 mg / L, a pH of 5.9 to 6.5, and a conductivity of 3 μS / cm to 6 μS / cm.

[0031] Next, another embodiment of the present invention will be described. Fig. 3 schematically shows a production apparatus 3 used in the method for producing pure water of this embodiment. The production apparatus 3 differs from the production apparatus 1 shown in Fig. 1 in that it includes a filtration section 31 between the installation position of the polyaluminum chloride supply device 12 and the reverse osmosis membrane device 14 in the route of the raw water transfer pipe 13, but the other configurations are the same. In this embodiment, detailed description of the configurations and functions that are common to the production method using the production apparatus 1 will be omitted.

[0032] The method for producing pure water according to an embodiment using the production apparatus 3 shown in Figure 3 is as follows. First, raw water is supplied from a raw water supply device 11 into a raw water transfer pipe 13. Next, a high basicity PAC is added to the raw water transfer pipe 13 by a polyaluminum chloride supply device 12. A preferred embodiment of the high basicity PAC used here is the same as that of the production method using the production apparatus 1 shown in Figure 1.

[0033] When raw water and the high-basicity PAC are supplied into the raw water transfer pipe 13, the suspension in the raw water interacts with the high-basicity PAC to form microflocs. By passing through these microflocs, adhesion of residual aluminum to the membrane of the reverse osmosis membrane device 14 is significantly reduced, allowing the performance of the reverse osmosis membrane device to be maintained for a long period of time. The first treated water containing microflocs in the raw water transfer pipe 13 is then supplied to the filtration section 31. By providing a feed pump for the raw water transfer pipe 13, the first treated water can be supplied to the filtration section 31 by the feed pump. Since this embodiment does not use a mixing tank, the device is compact and can be easily installed in semiconductor manufacturing plants, etc. To promote mixing, installing an in-line mixer or the like in the transfer pipe 13 after the high-basicity PAC is supplied can more reliably form microflocs, thereby further preventing clogging of downstream equipment.

[0034] The filtration unit 31 includes one or more filtration devices selected from a sand filter, a multimedia filter (MMF) filter, an ultrafilter, a microfilter (MF) device, and an activated carbon filter, and filters the first treated water. This removes mainly suspended microflocs from the water, and the third treated water is obtained. The third treated water is then supplied to the reverse osmosis membrane device 14.

[0035] The sand filter has, for example, supporting gravel or sand (filter sand) as a filter material. A multimedia filter (MMF) filtration device includes a three-layer filter material, for example, made by stacking anthracite, sand, and garnet from the bottom up in order of particle size. The ultrafiltration (UF) device is equipped with an ultrafiltration membrane having a nominal pore size of 0.001 to 0.1 μm as a filtering material, and may be either a dead-end filtration type or a cross-flow filtration type. The ultrafiltration (UF) device is preferably an external pressure type ultrafiltration device using a hollow fiber membrane. The microfiltration (MF) device is equipped with a microfiltration membrane having a nominal pore size of, for example, 0.1 to 5 μm, and is capable of dead-end filtration.

[0036] The activated carbon filter device has activated carbon as a filtering material. Activated carbon used in the activated carbon filter device includes granular activated carbon, granulated activated carbon, powdered activated carbon, spherical activated carbon, etc., with spherical activated carbon being preferred. Granular activated carbon is, for example, coconut shell activated carbon or the like pulverized into granules, and powdered activated carbon is, for example, coconut shell activated carbon pulverized into a powder of 3 μm to 30 μm. Granulated activated carbon is produced by granulating the granular activated carbon or powdered activated carbon into pellets.

[0037] Spherical activated carbon is spherical activated carbon with a highly uniform size, with an average particle diameter of approximately 0.5 mm to 4.0 mm. Commercially available spherical activated carbon can be used, such as the Spherical Shirasagi series manufactured by Osaka Gas Chemicals Co., Ltd. or BAC manufactured by Kureha Corporation.

[0038] Depending on the quality of the raw water, the filtration unit 31 may include one or a combination of two or more of the above-mentioned filtration devices selected from the group consisting of a sand filter, a multimedia filter (MMF), a microfiltration (MF), an ultrafiltration (UF), and an activated carbon filter. When combining two or more devices, it is preferable to arrange the sand filter or multimedia filter (MMF) upstream, the ultrafiltration downstream, and the activated carbon filter most downstream of the filtration unit 31. It is more preferable that the filtration unit 31 includes an ultrafiltration device and an activated carbon filter in this order, and even more preferable that it includes only an ultrafiltration device. The provision of the filtration unit 31 enables the high-precision removal of microflocs from the first treated water, thereby reducing the load on the downstream reverse osmosis membrane device 14 and enabling the production of high-quality permeate water over a long period of time.

[0039] In the production apparatus 3 shown in FIG. 3 , the filtration unit 31 is a stand-alone filtration unit having a stand-alone filtration device. Examples of stand-alone filtration devices include cartridge-type filtration devices and modular filtration devices. A cartridge-type filtration device, for example, houses a filtration cartridge in a housing, and pipes are connected to water inlets and outlets in the housing, allowing water to flow through the cartridge. A cartridge-type filtration device has the advantage that only the cartridge can be replaced when the filtration material deteriorates. A modular filtration device has a filtration material disposed inside the housing, and water is passed through the filtration material by connecting a module to pipes. A modular filtration device has the advantage that when the filtration material deteriorates, the entire module can be replaced and the deteriorated filtration material can be cleaned separately. The stand-alone filtration unit 31 effectively prevents clogging of the reverse osmosis membrane device 14 because it minimizes the outflow of nanoflocs downstream. In particular, when the method of this embodiment is used to produce ultrapure water for manufacturing semiconductors, etc., by using a standalone filtration unit 31, multiple standalone filtration units 31 can be installed in parallel, and each of the multiple units can be regenerated by backwashing or module replacement, while operation continues using other equipment (so-called merry-go-round operation), making it possible to continue producing ultrapure water without stopping the equipment.

[0040] The water quality of the third treated water (treated water from the filtration unit 31) thus obtained is, for example, turbidity of 0.01 NTU to 0.4 NTU, aluminum concentration of 0.01 mg / L to 0.04 mg / L, pH of 7.2 to 8.3, and conductivity of 140 μS / cm to 270 μS / cm. When the filtration unit 31 includes an ultrafiltration device, the treated water from the ultrafiltration device preferably has a water quality within the range of the third treated water. In the method of this embodiment, the use of a high-basicity PAC allows stable and uniform formation of microflocs regardless of the pH value of the raw water to which the high-basicity PAC is added. This eliminates the need to add a pH adjuster to the mixed layer 23, thereby reducing the amount of chemicals used. Therefore, although the pH of the third treated water (treated water from the filtration unit 31) may fluctuate, the aluminum concentration remains low and stable.

[0041] 4 is a schematic diagram of a pure water production apparatus 4 having a mixing tank 23 for adding high basicity PAC to raw water, and a filtration section 31. The production apparatus 4 differs from the production apparatus 3 shown in FIG. 3 in that it has a mixing tank 23 in the path of the raw water transfer pipe 13, but the other configurations are the same. In this embodiment, detailed explanations of the configurations and functions that are common to the production method using the production apparatus 3 will be omitted.

[0042] In the production apparatus 4, raw water is supplied from a raw water supply device 11, and high basicity PAC is supplied from a polyaluminum chloride supply device 12, both of which are supplied into a mixing tank 23. In the mixing tank 23, the high basicity PAC interacts with the suspension in the raw water, resulting in the formation of microflocs. In particular, the use of the mixing tank 23 allows sufficient microfloc formation by the high basicity PAC, thereby further suppressing clogging of downstream equipment. In this case, the order of supplying the raw water and the high basicity PAC into the mixing tank 23 may be either first or simultaneously, but it is preferable that the high basicity PAC be added to the mixing tank 23 after the raw water has been supplied. As described above, in the method of this embodiment, it is not essential to adjust the pH of the raw water in the mixing tank 23.

[0043] 4 has an independent filtration unit 31 separate and independent from the mixing tank 23, downstream of the mixing tank 23. The aspect of the independent filtration unit 31 is the same as that of the above-mentioned manufacturing apparatus 3.

[0044] Furthermore, a submerged filtration device configured for submersion in a tank can be used as the filtration unit 31. A submerged filtration device configured for submersion in a tank is submerged in the bottom of the mixing tank 23, and has the advantage that the first treated water to which the high basicity PAC has been added can be directly filtered by the filtration device without using piping. As the submerged filtration device, an ultrafiltration device or an MMF type filtration device is preferred. In the production apparatus 4 of this embodiment, by forming microflocs in water using the high basicity PAC, the microflocs can be directly filtered without undergoing precipitation removal in a coagulation and sedimentation tank as is used for coarse flocs. Therefore, the filtration unit 31 can be immersed and integrated into the mixing tank 23, simplifying the overall configuration of the apparatus.

[0045] When multiple filtration devices are used in the filtration section 31, only immersion type or only stand-alone type may be used, or both immersion type and stand-alone type may be used. In this embodiment, it is preferable to use only stand-alone type filtration devices, and it is more preferable to use stand-alone type ultrafiltration devices. Ultrafiltration membranes that can be installed in stand-alone ultrafiltration devices include hollow fiber membranes, spiral membranes, and flat membranes made of materials such as cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, and polyvinylidene fluoride. Among these, hollow fiber membranes made of fluorine-based materials such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferred. The filtration membrane provided in the immersion type ultrafiltration device is preferably a flat membrane made of ceramic or a fluorine-based material such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE).

[0046] The first treated water is filtered by the filtration unit 31 shown in Fig. 3 or 4 to remove microflocs containing suspended matter from the water, thereby obtaining third treated water. The third treated water is then supplied to the reverse osmosis membrane device 14 and treated there.

[0047] Next, a pure water production system 5 according to an embodiment using the above-described production apparatus 1 will be described with reference to Fig. 5. Fig. 5 is a block diagram showing a schematic configuration of the ultrapure water production system 5 using the production apparatus 1. In Fig. 5, the production apparatus 1 can be replaced with any of the production apparatuses 2 to 4.

[0048] 5, 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.

[0049] The pre-treatment system 50 includes the manufacturing apparatus 1 of the embodiment described above, and, if necessary, a pre-filter, a heat exchanger for temperature adjustment, and the like.

[0050] 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.

[0051] The primary pure water system 51 produces primary pure water by removing organic matter, ionic components, and dissolved gases from 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.

[0052] The ultraviolet oxidation device 513 has an ultraviolet lamp that emits ultraviolet light with a wavelength of, for example, about 185 nm and ultraviolet light with a wavelength of about 254 nm, and irradiates the water to be treated with ultraviolet light from this ultraviolet lamp to oxidize and decompose the total organic carbon (TOC) in the water to be treated. The ultraviolet light emitted by the ultraviolet oxidation device 513 decomposes the water to generate OH radicals, and these OH radicals oxidize and decompose the organic matter in the water to be treated into organic acids. The amount of ultraviolet light irradiated by the ultraviolet oxidation device 513 in the primary pure water system can be changed as appropriate depending on the quality of the water to be treated.

[0053] The ion exchange device 514 is one or more of an ion exchange resin device and an electrodeionization 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 used in appropriate combination depending on 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. A boron-adsorbing ion exchange resin may be used as the ion exchange resin.

[0054] 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.

[0055] The ultrapure water production system 5 comprises, in this order, a primary pure water tank TK2 for storing primary pure water, and a secondary pure water system 52, 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 comprises an ultraviolet oxidation device (TOC-UV) 521, a non-regenerative polisher 522, a membrane degasser (MDG) 523, and an ultrafiltration device (UF) 524.

[0056] The configuration of the ultraviolet oxidation device 521 in the secondary pure water system 52 is the same as that of 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 ionic components generated by the decomposition of organic matter by the ultraviolet oxidation device 521.

[0057] The membrane degassing device 523 removes dissolved gases through a degassing membrane. The membrane degassing device 523 removes trace amounts of dissolved oxygen from the primary pure water, reducing the dissolved oxygen concentration to, for example, about 1 μg / L or less. The ultrafiltration membrane device 524 performs a filtration process using an ultrafiltration membrane to remove trace amounts of eluates and particulate components from the upstream ion exchange resin, reducing the number of particulates of 0.05 μm or larger to, for example, about 250 Pcs. / L or less.

[0058] 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.

[0059] In each of the above-described 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 optical emission spectrometry pH: Electrode method Conductivity: Conductivity meter (Horiba, Ltd. HE-960CW) Total organic carbon (TOC) concentration: TOC meter (other than ultrapure water: SUEZ Sievers M9e) [Example]

[0060] Next, examples will be described, but the present invention is not limited to the following examples.

[0061] FIG. 6 is a schematic diagram of a pure water production apparatus 6 used in the present examples and comparative examples. The production apparatus 6 shown in FIG. 6 includes a raw water supply device 61 that supplies raw water, a polyaluminum chloride supply device 62 that supplies high-basicity PAC, and a mixing tank 63 into which the raw water and high-basicity PAC are supplied. The production apparatus 6 also includes, downstream of the mixing tank 63, an ultrafiltration device 65, an activated carbon filtration device 66, and a reverse osmosis membrane device 64, in this order. In the examples and comparative examples, a predetermined amount of PAC of a predetermined basicity was added to the raw water, and the water was treated in the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64, in that order, and the change in permeation flux (flow rate) over time in the reverse osmosis membrane device 64 was measured, as described below.

[0062] The specifications of the devices used in the examples are as follows: Mixing tank 63: Capacity 1m 3 Ultrafiltration device 65: Puria GL manufactured by Kuraray Co., Ltd. (PVDF membrane, nominal pore size 0.02 μm) Reverse osmosis membrane device 64: Toray Industries, Inc. TM710 (low-pressure type, negatively charged membrane) Water recovery rate: 85% Measurement of aluminum concentration: Inductively coupled plasma (ICP) optical emission spectrometry Turbidity measurement: Turbidity meter (Hach2100P, manufactured by Toa Dekk Corporation) pH measurement: Water quality meter (Horiba D200, manufactured by Horiba) TOC measurement: TOC meter (Suez M9e) Raw water (lake water) quality: Turbidity 4 NTU, pH = 7.2, conductivity 250 μS / cm, TOC 4 mg / L

[0063] Example 1 Raw water was supplied to the mixing tank 63. Subsequently, an aqueous solution of aluminum chloride pentahydroxide (AlCl(OH)) (prototype, Nomura Micro Science Co., Ltd., basicity 83.33%) as a high-basicity PAC was supplied to the mixing tank 63 and stirred so that the aluminum concentration in the raw water was 1.2 mg / L in terms of AlO. After stirring, the raw water was sampled, and 80 ml of the raw water was passed through a membrane (47 mm diameter) with a nominal pore size of 0.2 μm. Observation of the microparticles captured by the membrane revealed microparticles of approximately 1 to 10 μm in size. The elemental composition of these microparticles was confirmed by energy dispersive X-ray fluorescence spectroscopy (EDX), revealing that they contained Al. Furthermore, when the same amount of water was passed through a membrane (47 mm diameter) with a nominal pore size of 0.45 μm, almost no differential pressure was observed. These results confirmed the formation of microflocs in this example.

[0064] The treated water in the mixing tank 63 was filtered by passing it through an ultrafiltration device 65 and an activated carbon filtration device 66 in that order. Subsequently, the treated water from the activated carbon filtration device 66 was supplied to a reverse osmosis membrane device 64 and subjected to reverse osmosis membrane treatment. The activated carbon used in the activated carbon filtration device 66 was spherical activated carbon (Nomulite Beads-AC (prototype), particle size 1.2 mm), and the SV of the activated carbon filtration device 66 was 30 (1 / h).

[0065] Example 2 In Example 1, except that a high basicity PAC (basicity 76%) produced by the method described in Japanese Patent No. 4104773 was used as the high basicity PAC, treatment was carried out in the same manner as in Example 1, successively using an ultrafiltration device 65, an activated carbon filtration device 66, and a reverse osmosis membrane device 64. In Example 2 as well, it was confirmed that microflocs were formed.

[0066] Example 3 In Example 1, granular activated carbon (brand: Diahope M006LFA (manufactured by Mitsubishi Chemical Calgon Corporation), average particle size 1.1 to 1.4 mm) was used in the activated carbon filter 66, and the SV of the activated carbon filter 66 was set to 10 (1 / h), but treatment was carried out continuously in the same manner as in Example 1, with the ultrafiltration device 65, the activated carbon filter 66, and the reverse osmosis membrane device 64 being carried out in that order. It was also confirmed in Example 3 that microflocs were formed.

[0067] (Comparative Example 1) In Example 1, a low-basicity PAC (trade name PAC250A, manufactured by Taki Chemical Co., Ltd., basicity 50%) was used as the PAC so that the aluminum concentration in the raw water was 0.3 to 0.4 mg / L in terms of Al2O3. The same granular activated carbon as in Example 3 was used in the activated carbon filtration device 66, and the SV of the activated carbon filtration device 66 was set to 10 (1 / h). Treatment was carried out in the same manner as in Example 1, with the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 being used in that order. In Comparative Example 1, the raw water was sampled after adding the low-basicity PAC and stirring, and 80 ml of the sample was passed through a membrane (47 mm diameter) with a nominal pore size of 0.2 μm. The fine particles captured by the membrane were observed to be approximately 1 to 10 μm in size. The elemental composition of these fine particles was confirmed by EDX, and they contained Al. Furthermore, when the same amount of water was passed through a membrane (47 mmφ) with a nominal pore size of 0.45 μm, a sudden pressure difference occurred.These results confirmed that microflocs were formed, but also that coarse aggregates with sizes of 0.45 μm or larger were formed.

[0068] (Comparative Example 2) In Comparative Example 1, the same spherical activated carbon as in Example 1 was used in the activated carbon filtration device 66, and the SV of the activated carbon filtration device 66 was set to 30 (1 / h), but other than that, treatment was carried out continuously in the same order as in Comparative Example 1, using the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64. The state of floc formation was equivalent to that in Comparative Example 1.

[0069] (Comparative Example 3) A predetermined amount of permeated water from the reverse osmosis membrane device 64 was added to the treated water from the ultrafiltration device 65 to adjust the aluminum concentration in the water supplied to the activated carbon filtration device to a value equivalent to that in Example 1. Except for this, treatment was carried out continuously in the same order in the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 in the same manner as in Comparative Example 1. In Comparative Example 3, the state of floc formation was the same as in Comparative Example 1.

[0070] The types and basicities of the PACs used, and the aluminum concentrations and turbidity (NTU) of the treated water from the ultrafiltration device 65 in Example 1 to Comparative Example 3 are shown in Table 1. Also, Fig. 7 shows the change over time in the permeation flux (flow rate) in the reverse osmosis membrane device 64.

[0071] Comparing Example 1 and Comparative Example 3, in Comparative Example 3, the permeate from the ultrafiltration device 65 is diluted, so the Al concentration in the water supplied to the reverse osmosis membrane device 64 is equivalent. However, the difference lies in the use of a high-basicity PAC and a low-basicity PAC, and the source of aluminum (Al) is different. It can be seen that the rate of decrease in the flux of the reverse osmosis membrane device 64 differs significantly just due to this difference between the use of a high-basicity PAC and a low-basicity PAC. In other words, it was revealed that Al derived from a high-basicity PAC is less likely to clog the reverse osmosis membrane, but Al derived from a low-basicity PAC is more likely to clog the reverse osmosis membrane.

[0072] [Table 1]

[0073] (Experimental example) When high-basicity PAC (or low-basicity PAC) was added to the same raw water as in Example 1 and filtered through an ultrafiltration device, the amount of PAC added, the cleaning recovery of the ultrafiltration membrane, and the aluminum concentration in the permeate from the ultrafiltration membrane device were investigated.

[0074] (Example 1) After adjusting the raw water with a turbidity of 4 to pH = 7, without adding high-basicity PAC, the cumulative water flow rate (water flow rate per membrane area) was 0.6 m 3 / m 2During this time, the water flow rate is 0.1 m 3 / m 2 At each stage, the water flow was stopped and the ultrafiltration membrane was backwashed, and after the backwashing, the water flow was restarted. Backwashing was performed by combining air backwashing and air bubbling inside the module. The ultrafiltration membrane device used 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 pore size of 0.02 μm was used, and the supply pressure of raw water to the ultrafiltration device was set to 0.1 MPa.

[0075] (Examples 2 to 7) High basicity PAC (basicity 83.3%) was used, and the amount of Al2O3 added to the raw water was 0.2, 0.5, 0.7, 1.2, 2.4, and 5.0 mg / L, respectively. 3 / m 2 Every time the water flow is stopped, the ultrafiltration membrane is backwashed, and the cumulative filtration volume (amount of water flowing per membrane area) is 0.6 m 3 / m 2 Water was passed through until

[0076] (Examples 8 to 10) In Example 2, low-basicity PAC (basicity 50%) was used instead of high-basicity PAC, and the amount of low-basicity PAC added to the raw water was 0.5, 1, and 2 mg / L as Al2O3, respectively. 3 / m 2 Every time, the water flow is stopped and the ultrafiltration membrane is backwashed. The cumulative water flow rate (water flow rate per membrane area) is 0.6 m 3 / m 2 Water was passed through until

[0077] The aluminum (Al) concentrations in the permeate of the ultrafiltration unit (UF) in Examples 1 to 10 and the results of evaluation of the UF washing recovery are shown in Table 2. The evaluation of the washing recovery in Table 2 is as follows. F: The permeation flux after five backwashes is reduced to less than 20% of the initial permeation flux, and the cleaning recovery is poor. A: The permeation flux after five backwashes exceeds 60% of the initial permeation flux, demonstrating excellent cleaning recovery. B: The permeation flux after five backwashes exceeds 40% of the initial permeation flux, and the cleaning recovery is sufficient.

[0078] The relationship between the cumulative filtration volume and the permeation flux of the ultrafiltration device in Examples 1 and 3 is shown in the graph of FIG.

[0079] [Table 2]

[0080] Table 2 and Figure 8 show that when a high-basicity PAC is used, good cleaning recovery is achieved with an addition of 0.5 mg / L as Al2O3, and even at higher additions, the Al content in the permeate does not increase. In contrast, when a low-basicity PAC is used, good cleaning recovery is achieved with an addition of 1 mg / L as Al2O3, but increasing the addition amount increases the Al content in the permeate roughly proportionally. When using a high-basicity PAC, the preferred addition amount is 0.125 mg / L as Al2O3 per turbidity of 1. However, adding an excess amount is also possible in case of fluctuations in raw water quality, since the amount of Al in the ultrafiltration permeate remains almost constant. In contrast, when using a low-basicity PAC, the optimal amount must be added depending on fluctuations in raw water quality to prevent an increase in Al in the ultrafiltration permeate.

[0081] Next, in Examples 1 to 10, experiments were performed in the same manner as in Examples 1 to 10, except that the pH of the raw water was adjusted to 8 and 6. In the examples using a high basicity PAC, results similar to those in Table 2 were obtained whether the pH of the raw water was adjusted to 8 or 6. In contrast, in the examples using a low basicity PAC, results different from those in Table 2 showed a tendency for the wash recovery to deteriorate whether the pH of the raw water was adjusted to 8 or 6. In other words, while the coagulation performance of a high basicity PAC does not change even when the pH is changed, the coagulation performance of a low basicity PAC changes significantly depending on the pH. For this reason, a high basicity PAC can be operated without pH adjustment, but pH adjustment is essential for a low basicity PAC.

[0082] Examples 4 to 6 In this example, the types of reverse osmosis membrane devices and the susceptibility of reverse osmosis membranes to clogging were investigated. The reverse osmosis membrane module shown below was disassembled, and each reverse osmosis membrane was removed. The effective membrane area was 23.7 cm. 2 The flat membrane was cut out. Negatively charged film: Toray Industries, Inc. TM710 Positively charged membrane: Nitto Denko ES10C Neutral charged membrane: Nitto Denko LFC3-LD-4040

[0083] Figure 9 shows a schematic diagram of the batch test apparatus 9 used in this example. The batch test apparatus shown in Figure 9 includes a container 91 for containing test water 92, a test membrane 93 provided at the opening at the bottom of the container 91, a measuring cylinder 94 for containing permeated water W filtered through the test membrane 93, a nitrogen cylinder 96 for supplying nitrogen into the container 91 to apply pressure, and a pressure gauge 95. In this example, the flat membrane cut out above was installed as the test membrane 93 in the batch test apparatus 9, and a water flow test was performed on each.

[0084] The water flow conditions were as follows: Test water (raw water): Ultrafiltration device 65 permeate water of Example 1 Test water volume (raw water volume): 300ml Filtration concentration ratio: 10 times Water pressure (pressure after pressure reduction by the pressure reducing valve of cylinder 96): 15 kgf / cm 2 Water flow method: The container 91 was pressurized with the pressure of the cylinder 96, and the permeated water that permeated the test membrane 93 was collected while stirring the test water 92 with a stirrer (not shown). When 270 ml of permeated water was obtained, the remaining test water was drained through the test water discharge valve (not shown). After that, 300 ml of test water was replenished and the water was again passed through. This procedure was repeated 20 times to check the degree of clogging.

[0085] The degree of clogging was determined by measuring the amount of permeated water per unit time using a measuring cylinder 94, and the clogging rate was determined as follows. The results are shown in Table 3. A: The 20th time the water flow rate is 95% of the initial water flow rate. B: The 20th time the water flow rate is more than 90% but less than 95% of the initial water flow rate C: The 20th time the water flow rate is 80% to 90% of the initial water flow rate

[0086] [Table 3]

[0087] From the above results, it was found that reverse osmosis membrane devices having negatively charged membranes are less likely to be clogged by microflocs. Note that the test water (raw water) used in Examples 4 to 6 was permeated water from an ultrafiltration membrane, and thus particulate components in the raw water were removed. Therefore, the decrease in flow rate of the reverse osmosis membrane is not due to particulate components in the water, but is thought to be due to the influence of microflocs remaining in the permeated water from the ultrafiltration membrane. Here, since the flocculant used to form the flocs is usually positively charged, it was expected that negatively charged membranes would be more likely to clog, but the unexpected result was that negatively charged membranes were less likely to clog.

[0088] From the experimental examples, examples, and comparative examples described above, it can be seen that the apparatus and method for producing pure water according to the embodiment adds a high basicity PAC to raw water and then performs reverse osmosis membrane treatment, thereby significantly suppressing a decrease in the permeation flux of the reverse osmosis membrane device while sufficiently removing suspended solids. This allows high-purity pure water or ultrapure water to be produced efficiently over a long period of time, and the apparatus and method for producing pure water according to the embodiment are therefore suitable for mass production of pure water or ultrapure water. [Explanation of symbols]

[0089] 1-4, 6...Pure water production equipment, 5...Ultrapure water production system, 11, 61...Raw water supply equipment, 12, 62...Polyaluminum chloride supply equipment, 13...Raw water transfer pipe, 14, 64...Reverse osmosis membrane equipment, 23, 63...Mixing tank, 31...Filtration section, 65...Ultrafiltration equipment, 66...Activated carbon filtration 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...Total organic charcoal (TOC) oxidation equipment, 514...Ion exchange equipment, TK1, TK2...Tank, 521...Total organic charcoal (TOC) oxidation equipment, 522...Non-regenerative polisher, 523...Membrane degassing equipment (MDG), 524...Ultrafiltration equipment (UF)

Claims

1. A method for producing pure water, comprising: adding high-basicity polyaluminum chloride to raw water to obtain first treated water; and a reverse osmosis membrane step of treating the first treated water with a reverse osmosis membrane.

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

3. The method according to claim 1 or 2, wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less.

4. 3. The method according to claim 1, wherein the basicity of the polyaluminum chloride is greater than 75%.

5. the polyaluminum chloride comprises aluminum chloride pentahydroxide; The amount of aluminum chloride pentahydroxide added is such that aluminum oxide (Al ２ O ３ 3. The method according to claim 1, wherein the concentration of the hydroxybenzoates in the raw water is 0.25 mg / L or more and 5 mg / L or less in terms of the concentration calculated based on the hydroxybenzoates in the raw water.

6. The first treated water, The method includes a filtration step of performing a filtration treatment using one or more methods selected from sand filtration, multimedia filter (MMF) filtration, microfiltration (MF) equipment, ultrafiltration, and activated carbon filtration, The method according to claim 1 or 2, wherein the third treated water obtained in the filtration step is treated with the reverse osmosis membrane.

7. The method according to claim 6, wherein the third treated water has a turbidity of 0.01 NTU or more and 0.4 NTU or less, and an aluminum concentration of 0.01 mg / L or more and 0.04 mg / L or less.

8. the filtering step comprises activated carbon filtering; The method according to claim 6, wherein the activated carbon filtration is a step of passing water through spherical activated carbon and filtering it.

9. A method for producing pure water, comprising: A step of obtaining first treated water by supplying high basicity polyaluminum chloride to raw water; a pure water producing process including a reverse osmosis membrane process of treating the first treated water with a reverse osmosis membrane; The method includes an ultraviolet oxidation step and an ion exchange step in this order. Manufacturing method.

10. A pure water manufacturing apparatus comprising: a raw water supply device that supplies raw water; a polyaluminum chloride supplying device that adds high-basicity polyaluminum chloride to raw water; a reverse osmosis membrane device that performs reverse osmosis membrane treatment on first treated water produced by adding high-basicity polyaluminum chloride to raw water; A manufacturing device having the above structure.

11. The manufacturing apparatus according to claim 10, wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less.

12. 12. The manufacturing apparatus according to claim 10 or 11, wherein the basicity of the high basicity polyaluminum chloride is greater than 75%.

13. 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 such that the concentration thereof is 0.25 mg / L or more and 5 mg / L or less in terms of a concentration calculated as a function of the concentration of aluminum chloride pentahydroxide.

14. Between the polyaluminum chloride supply device and the reverse osmosis membrane device, The apparatus has one or more filters selected from a sand filter, a multimedia filter (MMF) filter, a microfiltration (MF) device, an ultrafiltration device, and an activated carbon filter. The manufacturing apparatus according to claim 10 or 11.

15. The apparatus for producing pure water according to claim 14; A pure water production system comprising an ultraviolet oxidation device and an ion exchange device in this order.

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