JP2025025904A - Pure water production method and production equipment, pure water production method and pure water production system - Google Patents

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; and a reverse osmosis membrane step of applying a reverse osmosis membrane treatment to the first treatment water.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and apparatus for producing pure water, a method for producing pure water, and a system for producing pure water.

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

As a method of using PAC in the production of industrial water and wastewater treatment, a method is known in which PAC with a relatively low basicity (75% or less) is mixed with wastewater to form coarse aggregates of suspended solids, and the coarse aggregates are removed 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 100 m ³ /h of raw water is to be treated with this method, a circular slow sand filtration device with a radius of 12 m must be installed. In addition, no facility for further treating the treated water is assumed. Therefore, it is difficult to apply this method except for very limited facilities such as water purification plants, and it is difficult to apply this method to the production of pure water or ultrapure water used in the manufacturing process of semiconductors, liquid crystals, etc.

In the production of pure water or ultrapure water, the raw water is passed through a membrane treatment device such as a reverse osmosis membrane device (RO) or an ultrafiltration device (UF), and then treated with a combination of an ion exchange resin device, an ultraviolet irradiation device, etc., before being supplied to the facility. In order to remove suspended solids from the raw water, the raw water is treated with PAC before being supplied. However, as 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).

The microfloc method using PAC is also used. In this method, PAC is directly injected into tap water or industrial tap water, or the water is rapidly stirred after injection to form microflocs, which are then removed by filtration without a 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 mentioned above.

JP 2012-086149 A JP 2008-86966 A JP 2022-165279 A

As mentioned above, the use of PAC in the production of pure water or ultrapure water has the problem of reduced permeation flux in the reverse osmosis membrane device due to adhesion of residual aluminum in the water to the membrane. However, the method of removing residual aluminum using an iron-based inorganic polymer flocculant has the problems of increased costs and environmental load due to the increased amount of chemical used.

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 suppress a decrease in the permeation flux of a reverse osmosis membrane device caused by residual aluminum over a long period of time.
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.

The manufacturing method, manufacturing apparatus, and pure water manufacturing system according to the embodiments of the present invention are as follows.
[1] A method for producing water for pure water, comprising the steps of:
A step of obtaining a first treated water by adding high basicity polyaluminum chloride to the raw 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 polyaluminum chloride with high basicity to the raw water.
[3] The manufacturing method described in [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 contains aluminum chloride pentahydroxide,
The manufacturing method according to any one of [1] to [4], wherein the amount of _the aluminum chloride _{pentahydroxide} added is an amount equivalent to a concentration of 0.25 mg/L or more and 5 mg/L or less in terms of aluminum oxide (Al 2 O 3 ) relative to the raw water.

[6] The first treated water,
The method includes a filtration step of performing a filtration treatment using one or more filters selected from sand filtration, multimedia filter (MMF) filtration, microfiltration (MF) equipment, ultrafiltration, and activated carbon filtration;
The method according to any one of [1] to [5], further comprising subjecting the third treated water obtained in the filtration step to a reverse osmosis membrane treatment.
[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 to filter it.

[9] A method for producing pure water, comprising the steps of:
A step of obtaining a first treated water by supplying high basicity polyaluminum chloride to raw water;
a reverse osmosis membrane process for 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.

[10] An apparatus for producing pure water, comprising:
A raw water supply device for supplying raw water;
a polyaluminum chloride supplying device for adding high basicity polyaluminum chloride to raw water;
and a reverse osmosis membrane device that performs reverse osmosis membrane treatment on a first treated water produced by adding high basicity polyaluminum chloride to raw water.
[11] The manufacturing apparatus described in [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 the raw water in an amount of 0.25 mg/L or more and 5 mg/L or less, calculated as an aluminum oxide (Al2O3) concentration.
[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 at least one 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 pure water production apparatus 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.

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 caused by residual aluminum.
Furthermore, the present invention can provide a pure water production method and system that can efficiently remove suspended solids from raw water and suppress a decrease in 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.

FIG. 1 is a diagram showing a schematic diagram of a production apparatus used in a method for producing pure water according to an embodiment. FIG. 2 is a schematic diagram showing a production apparatus further including a mixing tank in addition to the production apparatus shown in FIG. 1 . FIG. 13 is a diagram showing a schematic diagram of a production apparatus used in a method for producing pure water according to another embodiment. FIG. 4 is a schematic diagram showing a production apparatus further including a mixing tank in addition to the production apparatus shown in FIG. 3 . 1 is a diagram showing a schematic diagram of a pure water production system using an apparatus for producing pure water according to an embodiment; FIG. 2 is a schematic diagram showing a pure water production apparatus used in the examples. 1 is a graph showing the change over time in permeation flux of a reverse osmosis membrane device. 1 is a graph showing the relationship between the cumulative filtration volume and the permeation flux of an ultrafiltration device in an experimental example. FIG. 2 is a schematic diagram showing a batch-type test apparatus used in the examples.

The following describes an embodiment of the present invention. Figure 1 shows a schematic diagram of a manufacturing apparatus 1 used in the method for manufacturing pure water of this embodiment. The manufacturing 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.

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

Next, the polyaluminum chloride supplying device 12 adds high basicity PAC to the raw water transfer pipe 13. The polyaluminum chloride supplying device 12 is equipped with, for example, a chemical tank that stores high basicity PAC and a chemical injection pump that adds the high basicity PAC from the chemical tank to the raw water transfer pipe 13, and the chemical injection pump measures the high basicity PAC from the chemical tank to a predetermined concentration and adds it to the raw water transfer pipe 13.

Here, when a PAC with a lower basicity than the high basicity PAC (hereinafter referred to as "low basicity PAC") is added to the raw water, the low basicity PAC interacts with suspended matter in the raw water, coagulating and producing fine and coarse flocs. These flocs can be precipitated and separated 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 low basicity PAC has been added, the aluminum in the treated water adheres to the surface of the reverse membrane, making it very likely that the reverse osmosis membrane will become clogged, and causing an early drop in the permeation flux of the reverse osmosis membrane device.

In contrast, in the manufacturing method of this embodiment, high basicity PAC is supplied to the raw water, and the high basicity PAC interacts with suspended matter 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.

Microflocs are aggregates of suspended solids and high basicity PAC with sizes of about 1 to 10 μm. High basicity PAC easily forms microflocs, but does not easily form coarse flocs or flocs that are finer than microflocs (nano flocs). Aluminum ions do not easily leak out of microflocs, so by passing through them, reverse osmosis membrane blockage can be prevented for a long period of time.

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 the basicity is usually less than about 84%. The basicity is a value calculated by n/6×100(%).
[Al ₂ (OH) _n Cl _6-n ] _m (1≦n≦5, m≦10) ... (1)

High basicity PAC can be produced, for example, by the method described in Japanese Patent No. 4104773. Only one type of high basicity PAC may be used, or two or more types may be used in combination. When two or more types are used in combination, the basicity of the two or more high basicity PACs may be the same or different, but it is preferable that the basicity of each of the high basicity PACs used is greater than 75%, and more preferably greater than 83%.

It is preferable to use aluminum chloride pentahydroxide (Al ₂ Cl(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 homogeneous microflocs. This is thought to be because aluminum chloride pentahydroxide has a high basicity and a small molecular weight.

The amount of the high basicity PAC is preferably 0.125 mg/L as Al ₂ O ₃ or more per turbidity 1 NTU in the raw water. Specifically, the amount of the high basicity PAC is preferably 0.25 mg/L as Al ₂ O ₃ or more and 5 mg/L as Al ₂ O ₃ or less per amount of the raw water, and more preferably 0.3 mg/L as Al ₂ O ₃ or more and 3 mg/L as Al ₂ O ₃ or less per amount of the raw water. In particular, when aluminum chloride pentahydroxide (Al ₂ Cl(OH) ₅ ) is used as the high basicity PAC, the amount of aluminum chloride pentahydroxide is preferably 0.25 mg/L as Al ₂ O ₃ or more and 2 mg/L as Al ₂ O ₃ or less per total amount of the raw water. Even if the amount of the high basicity PAC is small as described above, the suspension in the raw water can be microflocculated. In addition, since the high basicity PAC functions even in a small amount as described above, it becomes easier to prevent clogging of the downstream reverse osmosis membrane device 14. The notation "as Al ₂ O ₃ " indicates a value converted into aluminum oxide (Al ₂ O ₃ ) concentration.

2 shows a schematic diagram of 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-mentioned production apparatus 1 in that the production apparatus 2 has a mixing tank 23 in the route of the raw water transfer pipe 13, but the other configurations are the same. In this embodiment, detailed explanations of the configurations and functions 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 an auxiliary for promoting flocculation immediately before or after the addition of the high basicity PAC.

In the manufacturing apparatus 2, raw water is supplied from the raw water supply device 11, and the high basicity PAC is supplied from the polyaluminum chloride supply device 12 into the mixing tank 23. In the mixing tank 23, the suspension in the raw water interacts with the high basicity PAC to form 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 is added to the mixing tank 23 to which the raw water has been supplied.

In the production apparatus 2 shown in Fig. 2, the raw water and high basicity PAC are rapidly stirred in the mixing tank 23, which makes it easier to form more homogeneous microflocs without generating nanoflocs. The stirring speed, for example, in terms of G value, is preferably 150 ^s-1 or more, more preferably 150 to 250 ^s-1 , and even more preferably 250 ^s-1 or more. The stirring time by the 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.

Then, the first treated water containing microflocs is supplied to the reverse osmosis membrane device 14 of FIG. 1 or 2 and treated with the reverse osmosis membrane. As a result, the second treated water is obtained as the permeate of the reverse osmosis membrane device 14. From the viewpoint of suppressing a decrease in the 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%. Just 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 water may be supplied to the reverse osmosis membrane device 14.

As the reverse osmosis membrane device 14, any of ultra-low pressure type, ultra-low pressure type, low pressure type, medium pressure type, and high pressure type reverse osmosis membrane devices may be used. As the reverse osmosis membrane provided in the reverse osmosis membrane device 14, a spiral type reverse osmosis membrane made of aromatic polyamide is preferable as a constituent material. In addition, as the reverse osmosis membrane device 14, there are a positive charge membrane with a positive charge on the reverse osmosis membrane surface, a negative charge membrane with a negative charge on the surface, and an uncharged membrane with an uncharged surface. Among them, a negative charge membrane is preferable because it is less likely to cause clogging due to flocs of the reverse osmosis membrane. As the reverse osmosis membrane device 14, an ultra-low pressure or low pressure type negative charge membrane is preferable. As a reverse osmosis membrane device having an ultra-low pressure or low pressure type negative charge membrane, a commercially available product can be used, for example, "ES20" manufactured by Nitto Denko Corporation, "SU series", "TM series", "TBW series" manufactured by Toray Industries, Inc., and "BW series" manufactured by Dow can be used.

A transfer pipe 15 for the 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 the subsequent stage via the transfer pipe 15. A discharge pipe 16 for the concentrated water is connected to the concentration side of the reverse osmosis membrane device 14. The concentrated water can be discharged to the outside of the system of the manufacturing apparatus 1 via the discharge pipe 16, or returned to the previous 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.

Next, another embodiment of the present invention will be described. FIG. 3 shows a schematic diagram of a manufacturing apparatus 3 used in the method for manufacturing pure water of this embodiment. The manufacturing apparatus 3 differs from the manufacturing apparatus 1 shown in FIG. 1 in that it is provided with a filtration section 31 between the position of the polyaluminum chloride supply device 12 and the reverse osmosis membrane device 14 in the raw water transfer pipe 13, but the other configurations are the same. In this embodiment, detailed descriptions of the configurations and functions that are common to the manufacturing method using the manufacturing apparatus 1 will be omitted.

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

By supplying raw water and high-basicity PAC into the raw water transfer pipe 13, the suspension in the raw water and the high-basicity PAC interact to form microflocs. By passing through these microflocs, the 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. The first treated water containing microflocs in the raw water transfer pipe 13 is then supplied to the filtration section 31. At this time, by providing a water supply pump for the raw water transfer pipe 13, the first treated water can be supplied to the filtration section 31 by the water supply pump. In this embodiment, since a mixing tank is not used, the device is compact, and it is easy to install in a semiconductor manufacturing factory, etc. In addition, if an in-line mixer or the like is installed in the transfer pipe 13 after the high-basicity PAC is supplied to promote mixing, the formation of microflocs can be more reliably performed, and clogging of the equipment in the subsequent stages is more suppressed.

The filtration section 31 includes one or more filtration devices selected from a sand filtration device, a multimedia filter (MMF) filtration device, an ultrafiltration device, a microfiltration (MF) device, and an activated carbon filtration device, and filters the first treated water. This removes microflocs, mainly containing suspended matter, from the water, and produces the third treated water. The third treated water is then supplied to the reverse osmosis membrane device 14.

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 in which anthracite, sand, and garnet are layered from the bottom in order of particle size.
The ultrafiltration (UF) device is provided with an ultrafiltration membrane having a nominal pore size of 0.001 to 0.1 μm as a filter material, and may be of either dead-end filtration type or 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 performing dead-end filtration.

The activated carbon filter has activated carbon as a filter material. Activated carbon used in the activated carbon filter includes granular activated carbon, granulated activated carbon, powdered activated carbon, spherical activated carbon, etc., and it is preferable to use spherical activated carbon. Granular activated carbon is, for example, coconut shell activated carbon crushed into granules, and powdered activated carbon is, for example, coconut shell activated carbon crushed into a powder of 3 μm to 30 μm. Granulated activated carbon is made by granulating the above granular activated carbon or powdered activated carbon into pellets.

Spherical activated carbon is spherical activated carbon with a highly uniform size, with an average particle diameter of about 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. and BAC manufactured by Kureha Corporation.

The filtration section 31 may have one type of filtration device selected from the sand filtration device, multimedia filter (MMF) filtration device, microfiltration (MF) device, ultrafiltration (UF) device, and activated carbon filtration device, or a combination of two or more types, depending on the raw water quality. When combining two or more types, it is preferable to arrange the sand filtration device or multimedia filter (MMF) filtration device on the upstream side, the ultrafiltration device on the downstream side, and the activated carbon filtration device on the most downstream side of the filtration section 31. It is more preferable that the filtration section 31 has an ultrafiltration device and an activated carbon filtration device in this order, and it is even more preferable that it has only an ultrafiltration device. By providing the filtration section 31, microflocs in the first treated water can be removed with high accuracy, which reduces the load on the reverse osmosis membrane device 14 in the subsequent stage, making it possible to obtain high-quality permeated water for a long period of time.

In the manufacturing apparatus 3 shown in FIG. 3, the filtration section 31 is an independent filtration section having an independent filtration device. Examples of independent filtration devices include cartridge-type filtration devices and module-type filtration devices. The cartridge-type filtration device is configured, for example, to house a cartridge of filtration material in a housing, connect piping to a water inlet and a drainage outlet opened in the housing, and pass water through the cartridge through the opening. The cartridge-type filtration device has the advantage that only the cartridge can be replaced when the filtration material deteriorates. The module-type filtration device is configured such that the filtration material is provided inside the housing, and water is passed through the filtration material by connecting the module to piping. The module-type filtration device has the advantage that when the filtration material deteriorates, the entire module can be replaced, and the deteriorated filtration material can be washed for each module. The independent filtration section 31 is effective in preventing blockage of the reverse osmosis membrane device 14 because there is little outflow of nanoflocs downstream. In particular, when using the method of this embodiment to produce ultrapure water for manufacturing semiconductors, etc., by using an independent filtration unit 31, multiple independent filtration units 31 can be installed in parallel, and each of the multiple units can be regenerated by backwashing or module replacement, while the other units continue operation (a so-called merry-go-round operation), making it possible to continue producing ultrapure water without stopping the equipment.

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, it is preferable that the treated water from the ultrafiltration device is in the water quality range of the third treated water. In the method of this embodiment, by using high basicity PAC, stable and homogeneous microflocs can be formed regardless of the pH value of the raw water to which the high basicity PAC is added, so that it is not necessary to add a pH adjuster to the mixed layer 23, and the amount of chemicals used can be reduced. 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.

Figure 4 shows 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 Figure 3 in that it has a mixing tank 23 in the route 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.

In the manufacturing apparatus 4, raw water is supplied from the raw water supply device 11, and high basicity PAC is supplied from the polyaluminum chloride supply device 12 into the mixing tank 23. In the mixing tank 23, the suspension in the raw water interacts with the high basicity PAC to form microflocs. In particular, by using the mixing tank 23, the formation of microflocs by the high basicity PAC is sufficiently carried out, so clogging of the downstream equipment is further suppressed. 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 is added to the mixing tank 23 to which the raw water is 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.

The manufacturing apparatus 4 shown in FIG. 4 has an independent filtration section 31 that is separate and independent from the mixing tank 23, downstream of the mixing tank 23. The configuration of the independent filtration section 31 is the same as that of the manufacturing apparatus 3 described above.

As the filtration section 31, an immersion type filtration device configured for immersion in a tank can be used. The immersion type filtration device configured for immersion in a tank has the advantage that it is immersed in the bottom of the mixing tank 23 and can directly filter the first treated water to which high basicity PAC has been added without using piping. As the immersion type filtration device, an ultrafiltration device or an MMF type filtration device is preferable. In the manufacturing device 4 of this embodiment, by forming microflocs in water using high basicity PAC, it is possible to directly perform filtration processing without going through precipitation removal in a coagulation sedimentation tank as used for coarse flocs. Therefore, the filtration section 31 can be immersed and integrated in the mixing tank 23, and the configuration of the entire device can be simplified.

When a plurality of filtration devices are used in the filtration section 31, only the immersion type or only the stand-alone type may be used, or the immersion type and the stand-alone type may be used in combination. In this embodiment, it is preferable to use only the stand-alone type filtration device, and it is more preferable to use the stand-alone type ultrafiltration device.
The ultrafiltration membranes that can be provided in the stand-alone ultrafiltration device 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 preferable.
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).

By filtering the first treated water using the filtration section 31 in FIG. 3 or FIG. 4, suspended microflocs are removed from the water, and the third treated water is obtained. The third treated water is then supplied to the reverse osmosis membrane device 14 and treated.

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 an ultrapure water production system 5 using the production apparatus 1. In FIG. 5, the production apparatus 1 can be changed to any one of the production apparatuses 2 to 4.

As shown in FIG. 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 by piping to a point of use (POU) 53, so that the ultrapure water produced by the ultrapure water production system 5 is supplied to the POU 53.

The pretreatment system 50 includes the manufacturing apparatus 1 of the embodiment described above, and, if necessary, a prefilter and a heat exchanger for temperature control.

The ultrapure water production 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 there, and then supplied to the primary pure water system 51.

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

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 water quality of the water to be treated.

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

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 μg C/L or less.

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 the 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 (Polisher) 522, a membrane degassing device (MDG) 523, and an ultrafiltration device (UF) 524.

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 base anion exchange resin are mixed and filled in a container such as a cylinder. The non-regenerative polisher 522 adsorbs and removes ion components generated by the ultraviolet oxidation device 521 decomposing organic matter.

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, removing trace amounts of eluted material and fine particle components from the upstream ion exchange resin, and reducing the number of fine particles of 0.05 μm or more to, for example, about 250 Pcs./L or less.

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 μg C/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 the point of use 53.

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

Next, examples will be described. The present invention is not limited to the following examples.

Figure 6 shows a schematic diagram of the pure water production apparatus 6 used in the present embodiment and the comparative example. The production apparatus 6 shown in Figure 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 an ultrafiltration device 65, an activated carbon filtration device 66, and a reverse osmosis membrane device 64, in this order, downstream of the mixing tank 63. In the embodiment and the comparative example, as described below, a predetermined amount of PAC of a predetermined basicity is added to the raw water, and the treatment is continued in the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 in that order, and the change over time in the permeation flux (flow rate) in the reverse osmosis membrane device 64 is measured.

The specifications of the devices used in the examples are as follows.
Mixing tank 63: Capacity ^1m3
Ultrafiltration device 65: Puria GL (PVDF membrane, nominal pore size 0.02 μm) manufactured by Kuraray Co., Ltd.
Reverse osmosis membrane device 64: TM710 manufactured by Toray Industries, Inc. (low pressure type, negatively charged membrane)
Water recovery rate: 85%
Measurement of aluminum concentration: high-frequency inductively coupled plasma (ICP) emission spectrometry Measurement of turbidity: turbidity meter (Hach 2100P, manufactured by Toa Dekk Corporation)
Measurement of pH: 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

Example 1
The raw water was supplied to the mixing tank 63. Then, an aqueous solution of aluminum chloride pentahydroxide (Al ₂ Cl(OH) ₅ ) (prototype by Nomura Micro Science Co., Ltd., basicity 83.33%) was supplied to the mixing tank 63 as a high basicity PAC so that the aluminum concentration in the raw water was 1.2 mg/L in terms of Al ₂ O ₃ , and stirred. After stirring, the raw water was sampled, and 80 ml of the raw water was passed through a membrane (size 47 mmφ) with a nominal pore size of 0.2 μm, and the fine particles captured by the membrane were observed, and fine particles of about 1 to 10 μm were observed. The elemental components of these fine particles were confirmed by energy dispersive X-ray fluorescence spectroscopy (EDX), and Al was contained. Furthermore, when the same amount of water was passed through a membrane (size 47 mmφ) with a nominal pore size of 0.45 μm, almost no differential pressure was observed. From the above results, it was confirmed that microflocs were formed in this embodiment.

The treated water in the mixing tank 63 was filtered by passing it through the ultrafiltration device 65 and the activated carbon filtration device 66 in that order. The treated water from the activated carbon filtration device 66 was then supplied to the reverse osmosis membrane device 64 for 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).

Example 2
In Example 1, high basicity PAC (basicity 76%) produced by the method described in Japanese Patent No. 4104773 was used as the high basicity PAC, and the same procedure as in Example 1 was repeated, with the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 being continuously treated in that order. In Example 2, it was also confirmed that microflocs were formed.

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 filtration device 66, and the SV of the activated carbon filtration device 66 was set to 10 (1/h), but other than this, treatment was performed continuously in the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 in that order in the same manner as in Example 1. It was also confirmed in Example 3 that microflocs were formed.

(Comparative Example 1)
In Example 1, low-basicity PAC (trade name PAC250A, manufactured by Taki Chemical Co., Ltd., basicity 50%) was used as PAC so that the aluminum concentration in the raw water was 0.3 to 0.4 mg/L in terms of Al ₂ O ₃ , the same granular activated carbon as in Example 3 was used for the activated carbon filtration device 66, and the SV of the activated carbon filtration device 66 was 10 (1/h), but otherwise the same treatment was performed as in Example 1, with the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 being continuously treated in that order. In Comparative Example 1, the raw water after adding low-basicity PAC and stirring was sampled, and 80 ml of the sample was passed through a membrane (size 47 mmφ) with a nominal pore size of 0.2 μm, and the fine particles captured by the membrane were observed, and fine particles of about 1 to 10 μm were observed. The elemental components of these fine particles were confirmed by EDX, and Al was found to be included. 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 was observed. From the above results, it was confirmed that microflocs were formed, but also that coarse aggregates with a size of 0.45 μm or more were formed.

(Comparative Example 2)
In Comparative Example 1, the same spherical activated carbon as in Example 1 was used for 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 this, treatment was carried out in the same order as in Comparative Example 1, continuously through 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.

(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, and other than this, treatment was continuously carried out in the ultrafiltration device 65, the activated carbon filtration device 66, and the reverse osmosis membrane device 64 in that order 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.

Table 1 shows the type and basicity of the PAC used, and the aluminum concentration and turbidity (NTU) of the treated water from the ultrafiltration device 65 in the above-mentioned Example 1 to Comparative Example 3. Figure 7 also shows the change over time in the permeation flux (flow rate) in the reverse osmosis membrane device 64.

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 the same. However, there is a difference in the use of high basicity PAC and low basicity PAC, and the source of aluminum (Al) is different. It can be seen that the rate of flux reduction in the reverse osmosis membrane device 64 is significantly different just because of this difference between the use of high basicity PAC and low basicity PAC. In other words, it was revealed that Al derived from high basicity PAC is less likely to clog the reverse osmosis membrane, but Al derived from low basicity PAC is more likely to clog the reverse osmosis membrane.

(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.

(Example 1)
After adjusting the turbidity of raw water to pH=7, the water was passed through the ultrafiltration membrane without adding high basicity PAC until the cumulative water flow rate (water flow rate per membrane area) reached 0.6 m ³ /m ^2. During that time, the water flow rate was stopped every 0.1 m ³ /m ² , the ultrafiltration membrane was backwashed, and water flow was started after the backwash. The backwash was performed by combining air backwashing and air bubbling in the module. As the ultrafiltration membrane device, an ultrafiltration device having an ultrafiltration (UF) membrane made of PDVF (polyvinylidene fluoride) was used, which was a test prototype module containing one hollow fiber, external pressure type, membrane area 10 cm ² , pore size 0.02 μm, and raw water was supplied to the ultrafiltration device at a pressure of 0.1 MPa.

(Examples 2 to 7)
High basicity PAC (basicity 83.3%) was used and the amount added to the raw water was 0.2, 0.5, 0.7, _1.2 , 2.4, and 5.0 mg/ ^L as _Al2O3 , respectively. In the same manner as in Example 1, the water flow was stopped every 0.1 ^m3 /m2 of water flow and the ultrafiltration membrane was backwashed until the accumulated filtration volume (water flow per membrane area) reached 0.6 ^m3 / ^m2 .

(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. However, similarly to Example 1, the water flow was stopped every 0.1 ^m3 / ^m2 of water flow to backwash the ultrafiltration membrane, and water was passed until the cumulative water flow rate (water flow rate per membrane area) reached 0.6 ^m3 / ^m2 .

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

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 in Figure 8.

From Table 2 and FIG. 8, it can be seen that when a high basicity PAC is used, the cleaning recovery is good at an addition amount of 0.5 mg/L as Al ₂ O ₃ , and even if the addition amount is more than that, the Al in the permeate does not increase. On the other hand, when a low basicity PAC is used, the cleaning recovery is good at an addition amount of 1 mg/L as Al ₂ O ₃ , but the amount of Al in the permeate increases approximately proportionally when the addition amount is increased. When a high basicity PAC is used, the addition amount is preferably 0.125 mg/L as Al ₂ O ₃ per turbidity 1, but it is also possible to add an excessive amount in preparation for fluctuations in the raw water quality, since the amount of Al in the permeate of the ultrafiltration device hardly changes. On the other hand, when a low basicity PAC is used, in order to prevent an increase in Al in the permeate of the ultrafiltration device, it is necessary to add an optimal amount according to the fluctuations in the raw water quality.

Next, in Examples 1 to 10, experiments were carried out 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 in which high basicity PAC was used, results almost equivalent 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 in which low basicity PAC was used, results different from those in Table 2 were obtained, showing a tendency for the cleaning recovery to deteriorate in both cases in which the pH of the raw water was adjusted to 8 and 6. In other words, while there is no difference in the coagulation performance of high basicity PAC even if the pH is changed, the coagulation performance of low basicity PAC changes greatly depending on the pH. For this reason, high basicity PAC can be operated without pH adjustment, but pH adjustment is essential in the case of low basicity PAC.

(Examples 4 to 6)
In this example, the types of reverse osmosis membrane devices and the susceptibility of reverse osmosis membranes to clogging were examined.
The reverse osmosis membrane module shown below was disassembled, and each reverse osmosis membrane was taken out, and a flat membrane with an effective membrane area of 23.7 ^cm2 was cut out.
Negatively charged film: TM710 manufactured by Toray Industries, Inc.
Positively charged membrane: Nitto Denko ES10C
Neutral charged membrane: Nitto Denko LFC3-LD-4040

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 holding test water 92, a test membrane 93 provided at the opening at the bottom of the container 91, a measuring cylinder 94 for holding the permeate 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 placed as the test membrane 93 in the batch test apparatus 9, and a water flow test was performed on each of them.

The water flow conditions were as follows:
Test water (raw water): Permeate from ultrafiltration device 65 of Example 1 Test water volume (amount of raw water): 300 ml
Filtration concentration ratio: 10 times Water flow pressure (pressure after pressure reduction by the pressure reducing valve of the cylinder 96): 15 kgf/ ^cm2
Water passing method: The inside of the container 91 was pressurized by the pressure of the cylinder 96, and the permeated water permeating 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 from the test water discharge valve (not shown). Then, 300 ml of test water was newly added and water was passed through again. This operation was repeated 20 times to check the degree of clogging.

The degree of clogging was evaluated 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 water flow rate is 95% of the initial water flow rate.
B: The 20th water flow rate is more than 90% and less than 95% of the initial water flow rate. C: The 20th water flow rate is 80% or more and less than 90% of the initial water flow rate.

These results demonstrate that reverse osmosis membrane devices with negatively charged membranes are less likely to become clogged with microflocs. Note that the test water (raw water) used in Examples 4 to 6 was permeated water from an ultrafiltration membrane, and thus the fine particle components in the raw water were removed. Therefore, the decrease in flow rate of the reverse osmosis membrane is not due to the fine particle 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 coagulant used to form the flocs is usually positively charged, it was expected that negatively charged membranes would be more likely to become clogged, but the unexpected result was that negatively charged membranes were less likely to become clogged.

The experimental examples, examples, and comparative examples described above show that the pure water production apparatus and method of the embodiment adds high basicity PAC to the raw water and then processes it through a reverse osmosis membrane, so that suspended solids are sufficiently removed while the decrease in the permeation flux of the reverse osmosis membrane device is significantly suppressed. This allows high purity pure water or ultrapure water to be produced efficiently over a long period of time, so the pure water production apparatus and method of the embodiment are suitable for mass production of pure water or ultrapure water.

1 to 4, 6...Pure water production equipment, 5...Ultrapure water production system, 11, 61...Raw water supply device, 12, 62...Polyaluminum chloride supply device, 13...Raw water transfer pipe, 14, 64...Reverse osmosis membrane device, 23, 63...Mixing tank, 31...Filtration section, 65...Ultrafiltration device, 66...Activated carbon filtration device, 50...Pretreatment system, 51...Primary pure water system (pure water production system), 52...Secondary pure water system (subsystem), 53...Point of use (POU), 513...Ultraviolet oxidation device (TOC-UV), 514...Ion exchange device, TK1, TK2...Tank, 521...Ultraviolet oxidation device (TOC-UV), 522...Non-regenerative polisher, 523...Membrane degassing device (MDG) 524...Ultrafiltration device (UF)

Claims (15)

A method for producing pure water, comprising the steps of:
A step of obtaining a first treated water by adding high basicity polyaluminum chloride to the raw water;
and a reverse osmosis membrane step of treating the first treated water with a reverse osmosis membrane. The manufacturing method according to claim 1, in which the first treated water containing microflocs is obtained by adding high-basicity polyaluminum chloride to the raw water. The manufacturing method according to claim 1 or 2, wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less. The method according to claim 1 or 2, wherein the basicity of the polyaluminum chloride is greater than 75%. the polyaluminum chloride comprises aluminum chloride pentahydroxide;
The method according to claim 1 or 2, wherein the amount of the aluminum chloride pentahydroxide added is an amount equivalent to an aluminum oxide (Al ₂ O ₃ ) concentration of 0.25 mg/L or more and 5 mg/L or less based on the raw water. The first treated water,
The method includes a filtration step including one or more filtration 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. The manufacturing method according to claim 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. The filtering step includes activated carbon filtering,
The method according to claim 6, wherein the activated carbon filtration is a step of passing water through spherical activated carbon to filter the water. A method for producing pure water, comprising the steps of:
A step of obtaining a first treated water by supplying high basicity polyaluminum chloride to raw water;
a reverse osmosis membrane process for 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. An apparatus for producing pure water, comprising:
A raw water supply device that supplies raw water;
a polyaluminum chloride supplying device for adding high basicity polyaluminum chloride to raw water;
a reverse osmosis membrane device that performs reverse osmosis membrane treatment on a first treated water produced by adding high basicity polyaluminum chloride to raw water;
A manufacturing apparatus having the above structure. The manufacturing apparatus according to claim 10, wherein the turbidity of the raw water is 1 NTU or more and 100 NTU or less. The manufacturing apparatus according to claim 10 or 11, wherein the basicity of the high basicity polyaluminum chloride is greater than 75%. the polyaluminum chloride comprises aluminum chloride pentahydroxide;
The manufacturing apparatus according to claim 10 or 11, wherein the polyaluminum chloride supplying device supplies aluminum chloride pentahydroxide to the raw water in an amount of 0.25 mg/L or more and 5 mg/L or less in terms of aluminum oxide ( _{Al 2} O 3 ). Between the polyaluminum chloride supply device and the reverse osmosis membrane device,
The apparatus has at least one 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. 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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