Pure water production method and production equipment, pure water production method and pure water production system

Abstract

To provide a production method and a production device of water for pure water capable of efficiently removing suspended substances in raw water, while capable of preventing a transmission flow rate of a reverse osmosis membrane device from lowering by residual aluminum for a long period of time, and also to provide a pure water production method and a production system.SOLUTION: A production method of water for pure water includes: a step of adding a poly aluminum chloride of high alkalinity to raw water to obtain first treatment water; a step of passing the first treatment water to spherical active carbon and applying an active carbon treatment to obtain second treatment water; and a reverse osmosis membrane step of applying a reverse osmosis membrane treatment to the second treatment water.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] [1] A method for producing pure water, comprising: adding high-basicity polyaluminum chloride to raw water to obtain first treated water; a step of passing the first treated water through spherical activated carbon to perform activated carbon treatment to obtain second treated water; and a reverse osmosis membrane process for treating the second 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.

[0010] [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. [6] The method according to any one of [1] to [5], wherein the spherical activated carbon has an average particle size of 0.5 mm or more and 4.0 mm or less.

[0011] [7] A filtration step of filtering the first treated water using one or more filters selected from sand filtration, multimedia filter (MMF) filtration, microfiltration (MF) equipment, and ultrafiltration, The method according to any one of [1] to [6], wherein the treated water obtained in the filtration step is treated with activated carbon. [8] The method according to [7], wherein the turbidity of the treated water obtained in the filtration step is 0.01 to 0.17 NTU. [9] A method for producing pure water, comprising the steps of: supplying high-basicity polyaluminum chloride to raw water to obtain first treated water; a step of passing the first treated water through spherical activated carbon to perform activated carbon treatment to obtain second treated water; a reverse osmosis membrane process of treating the second 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, comprising: a raw water supply device that supplies raw water; a polyaluminum chloride supplying device that adds high-basicity polyaluminum chloride to raw water; an activated carbon filtration device that brings first treated water, which is produced by adding high-basicity polyaluminum chloride to raw water, into contact with spherical activated carbon; A manufacturing apparatus having a reverse osmosis membrane device that performs reverse osmosis membrane treatment on the second treated water produced in the activated carbon filtration device.

[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 production apparatus according to

[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

[13] , 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 activated carbon filtration device, there is provided one or more devices selected from a sand filtration device, a multimedia filter (MMF) filtration device, a microfiltration (MF) device, and an ultrafiltration device; The manufacturing apparatus according to any one of

[10] to

[14] .

[15] The apparatus for producing pure water according to

[14] , A pure water production system comprising 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] 7 is a graph showing the relationship between the space velocity (SV) in the activated carbon filtration device and the turbidity of the permeated water after water has been passed through the device shown in FIG. 6 for five years. [Figure 9] 7 is a graph showing the relationship between the space velocity (SV) and the free chlorine concentration in the activated carbon filtration device after water has been passed through the device shown in FIG. 6 for five years. [Figure 10] 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 the method for producing pure water of 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 an activated carbon filtration device 17 that passes the raw water (first treated water) to which the high basicity PAC has been added through spherical activated carbon. The production apparatus 1 further includes a reverse osmosis membrane device 14 that performs reverse osmosis membrane treatment on the second treated water obtained in the activated carbon filtration device 17.

[0016] The method for producing pure water using the production apparatus 1 according to this embodiment 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 city water, 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, a residual chlorine concentration of 0.1 mg / L to 2 mg / L as Cl2, and a pH of 4 to 9. Residual chlorine may be added to the raw water during transport 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 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 addition of the high basicity PAC. Furthermore, an acid or alkali injection facility may be installed to adjust the pH of the raw water as needed.

[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. 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.

[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.

[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 manufacturing 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 activated carbon filtration device 17 shown in Figure 1 or 2 and filtered by activated carbon. As a result, second treated water is obtained as permeate from the activated carbon filtration device 17.

[0029] The activated carbon filtration device 17 uses spherical activated carbon as a filter material. The spherical activated carbon is, for example, spherical activated carbon with a highly uniform size, such as an average particle diameter of 0.5 mm to 4.0 mm. The inventors discovered that treating the first treated water containing microflocs through spherical activated carbon significantly reduces the decrease in permeation flux of the downstream reverse osmosis membrane device 14 compared to using granular or powdered activated carbon. Furthermore, they discovered that using spherical activated carbon can maintain residual chlorine removal performance for a longer period than using granular or powdered activated carbon, thereby suppressing membrane deterioration of the downstream reverse osmosis membrane device 14. Furthermore, using spherical activated carbon improves the recovery of the water flow differential pressure of the spherical activated carbon filtration device after backwashing, thereby reducing the frequency of backwashing and ultimately the amount of wash water required. The average particle diameter of spherical activated carbon can be evaluated in accordance with JIS K 1474. That is, a particle size cumulative diagram of spherical activated carbon is created from the results obtained from the procedure of JIS K 1474. From the intersection of the vertical line at the 50% point on the horizontal axis and the particle size cumulative diagram, a horizontal line is drawn on the vertical axis to determine the sieve opening (mm) indicated by the intersection. This opening value is taken as the average particle size of the spherical activated carbon. Note that granular activated carbon is, for example, activated carbon crushed into granules, and powdered activated carbon is, for example, activated carbon crushed into a powder of 0.5 μm to 30 μm.

[0030] The hardness of the spherical activated carbon is preferably 90 or more, more preferably 93 or more, and even more preferably 94 or more. The hardness of the spherical activated carbon is, for example, 99 or less. The greater the hardness of the spherical activated carbon, the longer it can maintain the residual chlorine removal performance, which can contribute to maintaining the permeation flux of the downstream reverse osmosis membrane device. The uniformity coefficient of the spherical activated carbon is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.4 or less. The uniformity coefficient of the spherical activated carbon is usually greater than 1.0. The smaller the uniformity coefficient, the easier it is to recover the water flow differential pressure after backwashing, making it more suitable for long-term water treatment. The hardness and uniformity coefficient of the spherical activated carbon can be evaluated in accordance with JIS K 1474.

[0031] As the spherical activated carbon, commercially available products can be used, such as the Spherical Shirasagi series manufactured by Osaka Gas Chemicals Co., Ltd. and BAC manufactured by Kureha Corporation.

[0032] In the production method of this embodiment, by using the above-described spherical activated carbon, water can be passed through the activated carbon filtration device 17 preferably at a space velocity (SV) of 5 to 100 (1 / h), more preferably at an SV of 30 to 100 (1 / h). In particular, since the space velocity can be increased to SV of 30 to 100 (1 / h), sufficient water quality can be obtained with a small amount of activated carbon used, and treated water with low turbidity and low residual chlorine concentration can be stably produced while making the activated carbon filtration device 17 compact.

[0033] A stand-alone type filtration device can be used as the activated carbon filtration device 17. Similar to the filtration section described below, a cartridge-type activated carbon filtration device or a module-type activated carbon filtration device can be used as the stand-alone type filtration device. The stand-alone type activated carbon filtration device 17 reduces the amount of nanoflocs that flow downstream, which is effective in preventing blockage of the reverse osmosis membrane device 14. In particular, when the method of this embodiment is used to produce ultrapure water for semiconductor manufacturing, the use of stand-alone type activated carbon filtration devices 17 allows for the continuous production of ultrapure water without shutting down the device by installing multiple stand-alone type activated carbon filtration devices 17 in parallel, performing regeneration such as backwashing or module replacement on each of the multiple devices one by one, and continuing operation using the other devices (so-called merry-go-round operation).

[0034] The quality of the second treated water thus obtained is, for example, a turbidity of 0.01 NTU to 1 NTU and a free chlorine concentration of 0.01 mg / L to 0.1 mg / L as Cl2.

[0035] Subsequently, the second treated water that has been filtered through the spherical activated carbon is supplied to the reverse osmosis membrane device 14 and subjected to reverse osmosis membrane treatment. 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%. Note that a scale inhibitor or bacteriostatic agent may be added to the second treated water as appropriate immediately before it is supplied to the reverse osmosis membrane device 14.

[0036] The reverse osmosis membrane device 14 may be any of ultra-low pressure, ultra-low pressure, low pressure, medium pressure, and high pressure types. 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.

[0037] A permeate transfer pipe 15 is connected to the permeation side of the reverse osmosis membrane device 14, and the permeate is sent to a subsequent stage via the transfer pipe 15. A concentrated water discharge pipe 16 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 permeate 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.

[0038] Next, another embodiment of the present invention will be described. Fig. 3 schematically shows a manufacturing apparatus 3 used in the method for manufacturing pure water of this embodiment. The manufacturing apparatus 3 differs from the manufacturing apparatus 1 shown in Fig. 1 in that it includes a filtration section 31 between the location of the polyaluminum chloride supply device 12 and the activated carbon filtration device 17 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 manufacturing method using the manufacturing apparatus 1 will be omitted.

[0039] 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.

[0040] When raw water and 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, in order, to the filtration section 31 and the activated carbon filtration device 17. By providing a feed pump in 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 reducing clogging of downstream equipment.

[0041] The filtration unit 31 includes one or more filtration devices selected from a sand filter, a multimedia filter (MMF) filter, an ultrafilter, and a microfilter (MF) device, and filters the first treated water. This removes mainly suspended microflocs from the water, yielding the third treated water. The resulting treated water is then supplied to the activated carbon filter 17.

[0042] 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.

[0043] The filtration unit 31 can include one type of filtration device selected from the sand filtration device, multimedia filter (MMF) filtration device, microfiltration (MF) device, and ultrafiltration (UF) device, either singly or in combination, depending on the quality of the raw water. When combining two or more types, it is preferable to arrange the sand filtration device or multimedia filter (MMF) filtration device upstream and the microfiltration (MF) device or ultrafiltration device downstream. It is more preferable that the filtration unit 31 include only an ultrafiltration device. The provision of the filtration unit 31 enables the removal of microflocs from the first treated water with high precision, thereby reducing the load on the downstream reverse osmosis membrane device 14 and enabling high-quality permeate to be obtained over a long period of time.

[0044] 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 by performing regeneration such as backwashing or module replacement on each of the multiple units one by one (so-called merry-go-round operation), it is possible to continue producing ultrapure water without stopping the equipment.

[0045] The water quality of the treated water (treated water from the filtration unit 31) thus obtained is, for example, as follows: turbidity of 0.01 NTU to 0.4 NTU, preferably 0.01 NTU to 0.17 NTU; free chlorine concentration of 0.01 mg / L to 0.1 mg / L as Cl2; 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. In the method of this embodiment, the use of 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 for adding a pH adjuster, 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.

[0046] 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.

[0047] 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.

[0048] 4 has an independent filtration unit 31 separate and independent from the mixing tank 23, located downstream of the mixing tank 23. The aspect of the independent filtration unit 31 is the same as that of the above-described manufacturing apparatus 3.

[0049] 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.

[0050] 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).

[0051] 3 or 4, the first treated water is filtered to remove suspended microflocs from the water, and third treated water is obtained. The third treated water is then treated in an activated carbon filter 17 to produce second treated water, which is then supplied to a reverse osmosis membrane device 14 for treatment.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 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.

[0063] 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.

[0064] 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: VEOLIA Sievers M9e) [Example]

[0065] Next, examples will be described, but the present invention is not limited to the following examples.

[0066] 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 further 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, as described below, 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 over time in the reverse osmosis membrane device 64 was measured.

[0067] 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 (Sievers M9e, manufactured by VEOLIA) Raw water (lake water) quality: Turbidity 4 NTU, pH = 7.2, conductivity 250 μS / cm, TOC 4 mg / L

[0068] Example 1 Hypochlorous acid was added to the raw water to achieve a free chlorine concentration of 2 mg / L as Cl2, and the resulting mixture was fed into the mixing tank 63. Subsequently, an aqueous solution of aluminum chloride pentahydroxide (Al2Cl(OH)5) (prototype, Nomura Micro Science Co., Ltd., basicity 83.33%) was added as a high-basicity PAC to the mixing tank 63 so that the aluminum concentration in the raw water was 1.2 mg / L in terms of Al2O3, and the mixture was stirred. 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 particles trapped by the membrane revealed particles of approximately 1–10 μm in size. The elemental composition of these particles was confirmed by energy dispersive X-ray fluorescence spectroscopy (EDX), which revealed that they contained aluminum. 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. From the above results, it was confirmed that microflocs were formed in this example.

[0069] The treated water in the mixing tank 63 was passed through an ultrafiltration unit 65 and an activated carbon filtration unit 66 in that order and filtered. Subsequently, the treated water from the activated carbon filtration unit 66 was supplied to a reverse osmosis membrane unit 64 and subjected to reverse osmosis membrane treatment. The activated carbon used in the activated carbon filtration unit 66 was spherical activated carbon (Nomulite Beads-AC (prototype), particle size 1.2 mm, hardness 98%, uniformity coefficient 1.4), and the SV of the activated carbon filtration unit 66 was 30 (1 / h).

[0070] 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.

[0071] (Comparative Example 1) In Example 1, granular activated carbon (DIAHOPE M006LFA, manufactured by Mitsubishi Chemical Calgon Corporation, average particle size 1.1 to 1.4 mm, hardness 94%, uniformity coefficient 1.8) was used in the activated carbon filter 66, and the SV of the activated carbon filter 66 was set to 10 (1 / h). Except for this, 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 in that order. It was confirmed that microflocs were formed in Comparative Example 1 as well.

[0072] (Comparative Example 2) In Comparative Example 1, a low-basicity PAC (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 spherical activated carbon as in Example 1 was used for the activated carbon filter 66, and the SV of the activated carbon filter 66 was set to 30 (1 / h). Except for this, treatment was carried out continuously in the same order as in Comparative Example 1 using the ultrafiltration device 65, the activated carbon filter 66, and the reverse osmosis membrane device 64. The state of floc formation was equivalent to that in Comparative Example 1.

[0073] (Comparative Example 3) In Example 1, low-basicity PAC (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 Comparative Example 1 was used for activated carbon filtration device 66, and the SV of activated carbon filtration device 66 was set to 10 (1 / h). Treatment was carried out in the same manner as in Example 1, with ultrafiltration device 65, activated carbon filtration device 66, and reverse osmosis membrane device 64 being used in that order. In this comparative example, raw water was sampled after adding 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.

[0074] Table 1 shows the types and basicities of the PACs used in Examples 1 and 2 and Comparative Examples 1 to 3. Figure 7 shows the change over time in permeation flux (flow rate) in the reverse osmosis membrane device 64.

[0075] [Table 1]

[0076] Furthermore, in Examples 1 and 2 and Comparative Examples 1 to 3, the free chlorine concentration and turbidity of the permeate (treated water) through the activated carbon filtration device 66 after five years of water flow were investigated. The results are shown in Table 1. Furthermore, for Example 1 and Comparative Example 1, the relationship between the space velocity (SV) in the activated carbon filtration device 66 and the turbidity and free chlorine concentration of the permeate through the activated carbon filtration device 66 after five years of water flow was investigated. The results are shown in Figures 8 and 9.

[0077] The above examples and comparative examples demonstrate that by microflocculating suspended solids with high basicity PAC and then filtering with spherical activated carbon, the decrease in permeation flux of the downstream reverse osmosis membrane device 64 can be significantly suppressed. Furthermore, it can be seen that when spherical activated carbon is used, sufficient free chlorine removal performance can be achieved, even though the space velocity of the activated carbon filter is higher than that of granular activated carbon. Furthermore, it can be seen that, compared to the use of granular activated carbon, the use of spherical activated carbon not only enables free chlorine to be removed with high accuracy over a long period of time, but also keeps turbidity low.

[0078] Examples 3 to 5 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

[0079] Figure 10 shows a schematic diagram of the batch test apparatus 9 used in this example. The batch test apparatus shown in Figure 10 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.

[0080] 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.

[0081] 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: 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

[0082] [Table 2]

[0083] These results demonstrate that reverse osmosis membrane devices with negatively charged membranes are less likely to be clogged by microflocs. The test water (raw water) used in Examples 3 to 5 was permeated water from an ultrafiltration membrane, meaning that the fine particle components in the raw water were removed. Therefore, the decrease in flow rate through the reverse osmosis membrane is not due to the fine particle components in the water, but is likely due to the influence of microflocs remaining in the permeated water from the ultrafiltration membrane. 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.

[0084] 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]

[0085] 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, 17...Spherical activated carbon filter, 23, 63...Mixing tank, 31...Filtration section, 65...Ultrafiltration equipment, 66...Activated carbon filter, 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-UV) oxidation equipment, 514...Ion exchange equipment, TK1, TK2...Tank, 521...Total organic charcoal (TOC-UV) oxidation equipment, 522...Non-regenerative polisher, 523...Membrane degassing equipment (MDG), 524...Ultrafiltration equipment (UF)

Claims

1. A method for producing pure water, comprising: A step of adding polyaluminum chloride having a basicity of more than 75% and less than 84% to raw water to obtain first treated water; a step of passing the first treated water through spherical activated carbon to perform activated carbon treatment to obtain second treated water; and a reverse osmosis membrane step of treating the second treated water with a reverse osmosis membrane.

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

5. 3. The method according to claim 1, wherein the spherical activated carbon has an average particle size of 0.5 mm or more and 4.0 mm or less, and a uniformity coefficient of 1.0 or more and 1.4 or less.

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

7. The method according to claim 6, wherein the turbidity of the treated water obtained in the filtration step is 0.01 NTU or more and 0.17 NTU or less.

8. A method for producing pure water, comprising: A step of obtaining first treated water by supplying polyaluminum chloride having a basicity of more than 75% and less than 84% to raw water; a step of passing the first treated water through spherical activated carbon to perform activated carbon treatment to obtain second treated water; a reverse osmosis membrane process of treating the second treated water with a reverse osmosis membrane; The method includes an ultraviolet oxidation step and an ion exchange step in this order. Manufacturing method.

9. A pure water manufacturing apparatus comprising: a raw water supply device that supplies raw water; a polyaluminum chloride supplying device that adds polyaluminum chloride having a basicity of more than 75% and less than 84% to raw water; an activated carbon filtration device that brings first treated water, which is produced by adding the polyaluminum chloride to raw water, into contact with spherical activated carbon; a reverse osmosis membrane device that performs reverse osmosis membrane treatment on the second treated water produced by the activated carbon filtration device; A manufacturing device having the above structure.

10. The manufacturing apparatus according to claim 9, wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less.

11. the polyaluminum chloride comprises aluminum chloride pentahydroxide; The polyaluminum chloride supply device supplies aluminum oxide (Al ２ O ３ 11. The manufacturing apparatus according to claim 9, 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.

12. Between the polyaluminum chloride supply device and the activated carbon filter device, The apparatus has one or more devices selected from a sand filter, a multimedia filter (MMF) filter, a microfiltration (MF) device, and an ultrafiltration device; The manufacturing apparatus according to claim 9 or 10.

13. The apparatus for producing pure water according to claim 12; A pure water production system comprising an ultraviolet oxidation device and an ion exchange device in this order.

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