Production method and production device of water for pure water, 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 adding a chemical agent to feed water of a reverse osmosis membrane when applying a reverse osmosis treatment to raw water including chlorine.SOLUTION: A production method of water for pure water includes: a step of adding a poly aluminum chloride to raw water containing free chlorine to obtain first treatment water; a step of adding a reducer having sodium disulfite as an active ingredient to the first treatment water 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 an apparatus for producing water for pure water, and a method and system for producing pure water. [Background technology]

[0002] 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.

[0003] A known method of using PAC in the production of industrial water and wastewater treatment is to mix PAC, which has a relatively low basicity (75% or less), with 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 on a 100m 3 To treat raw water of 10 ...

[0004] Therefore, the microfloc method using PAC has also been used. This is a method in which 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 2).

[0005] In the production of pure water and ultrapure water used in the manufacturing processes of semiconductors, liquid crystals, etc., tap water or industrial tap water is used as raw water. The raw water is pretreated and passed through membrane treatment devices such as reverse osmosis (RO) and ultrafiltration (UF), and then treated using a combination of ion exchange resin devices and ultraviolet irradiation devices.

[0006] Here, in the above pretreatment, in order to prevent problems such as the proliferation of live bacteria present in the raw water and the generation of slime, a chlorine-based bactericide such as hypochlorous acid is generally added before treatment. However, when raw water containing free chlorine (also called residual chlorine) derived from this bactericide is treated with a reverse osmosis membrane, it leads to rapid deterioration of the reverse osmosis membrane, so the free chlorine is decomposed with a reducing agent before being supplied to the reverse osmosis membrane device. Then, in order to prevent problems caused by live bacteria in the latter stage, an oxidizing bactericide other than a free chlorine-based bactericide is added after the addition of the reducing agent. However, in this method, an excess of the reducing agent is added to completely decompose the free chlorine, so an excess of the reducing agent is generated, which causes the oxidizing bactericide to decompose and disappear. The decomposition and disappearance of the oxidizing bactericide is likely to cause a biofilm by live bacteria, so an excess of the oxidizing bactericide is sometimes added by the amount of the excess reducing agent. However, these methods have the problem that the control of the amount of the reducing agent and the oxidizing agent added is complicated and the amount of the reducing agent and the oxidizing agent added is large. To address this issue, a device is known which is provided with a means for measuring the residual chlorine concentration in the raw water, and controls the injection of a reducing agent by an injection means so that a predetermined concentration of chlorine remains (see, for example, Patent Document 3). Also, instead of chlorine-based disinfectants, a mixture of chlorine-based disinfectants and sulfamic acid compounds has been used to disinfect live bacteria in raw water. However, in raw water containing a large amount of live bacteria, the amount of chlorine-based disinfectants and sulfamic acid compounds added is large, and as a result, there is a problem that a small amount of free chlorine contained in the mixture of chlorine-based disinfectants and sulfamic acid compounds remains in the raw water (for example, see Patent Document 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2012-086149 A [Patent Document 2] JP 2022-165279 A [Patent Document 3] JP 2021-137710 A [Patent Document 4] JP 2010-202524 A Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, in the case of producing pure water or ultrapure water, when raw water containing residual chlorine is treated with a reverse osmosis membrane, there are problems such as the complicated control of the amount of oxidizing agent or reducing agent added and the problem of increased chemical usage, which leads to problems of increased costs and environmental load. In addition, it is difficult to determine the amount of excess reducing agent added, which makes it difficult to determine the optimal amount of the agent to be used.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a method and apparatus for producing pure water that can efficiently add chemicals to the water supplied to a reverse osmosis membrane. Another object of the present invention is to provide a method and system for producing pure water that can efficiently add chemicals to the water supplied to the reverse osmosis membrane. [Means for solving the problem]

[0010] 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 pure water, comprising the steps of: adding polyaluminum chloride to raw water containing free chlorine to obtain a first treated water; and adding a reducing agent containing sodium disulfite as an active ingredient to the first treated water to obtain a second treated water. and a reverse osmosis membrane process for treating the second treated water using 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 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 comprises 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 (Al2O3) relative to the raw water.

[0011] [6] The first treated water, The method has a filtration process using one or more filtration methods selected from sand filtration, multimedia filter (MMF) filtration, microfiltration (MF) equipment, and ultrafiltration, The manufacturing method according to any one of [1] to [5], further comprising adding the reducing agent to the treated water obtained in the filtration step. [7] The manufacturing method according to any one of [1] to [6], wherein the concentration of free chlorine in the raw water is 0.1 mg / L or more and 2 mg / L or less as Cl2, and the amount of the reducing agent added is, in terms of sodium disulfite, 0.1 mg / L or more and 5 mg / L or less. [8] The manufacturing method described in [1] to [6], wherein the turbidity of the permeate from the reverse osmosis membrane device is 0.01 or more and 0.4 or less, and the aluminum concentration is 0.01 mg / L or more and 0.04 mg / L or less.

[0012] [9] A method for producing pure water, comprising, in this order, a process for producing water for use in pure water, the process comprising a step of adding polyaluminum chloride to raw water containing free chlorine to obtain first treated water, a step of adding a reducing agent having sodium disulfite as an active ingredient to the first treated water to obtain second treated water, and a step of treating the second treated water using a reverse osmosis membrane, an ultraviolet oxidation step, and an ion exchange step.

[0013]

[10] An apparatus for producing pure water, comprising: A raw water supply device for supplying raw water containing free chlorine; A polyaluminum chloride supplying device for adding polyaluminum chloride to raw water; A reducing agent supplying device that adds a reducing agent having sodium disulfite as an active ingredient to a first treated water generated by adding polyaluminum chloride to raw water; a reverse osmosis membrane device that performs reverse osmosis membrane treatment on the second treated water produced by adding the reducing agent; A manufacturing device having a.

[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 of claim

[10] or

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

[13] The manufacturing apparatus according to any one of

[10] to

[12] , wherein the polyaluminum chloride contains aluminum chloride pentahydroxide, and the polyaluminum chloride supplying device supplies aluminum chloride pentahydroxide to raw water in an amount 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 reducing agent supply device, The manufacturing apparatus according to any one of

[10] to

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

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

[10] to

[14] , an ultraviolet oxidation device, and an ion exchange device, in that order. The symbol "~" indicates a range of values ​​including the values ​​before and after it. The amounts added are all based on the amount of active ingredient. Effect of the Invention

[0014] According to the present invention, it is possible to provide a method and apparatus for producing pure water, which is capable of efficiently adding chemicals to water supplied to a reverse osmosis membrane. Furthermore, the present invention can provide a method and system for producing pure water that can produce high-quality pure water over a long period of time by efficiently adding chemicals to the water supplied to the reverse osmosis membrane. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of a production apparatus used in a method for producing pure water according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing a production apparatus further including a mixing tank in addition to the production apparatus shown in FIG. [Diagram 3] FIG. 13 is a schematic diagram showing a production apparatus used in a method for producing pure water according to another embodiment. [Figure 4] 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. [Diagram 5] 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; [Figure 6] FIG. 2 is a schematic diagram showing a pure water production apparatus used in the examples. [Figure 7] 1 is a graph showing the relationship between raw water pH and the amount of residual reducing agent in an experimental example in which sodium disulfite, sodium sulfite, and sodium hydrogen sulfite were used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described. FIG. 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 supplying device 11 for supplying raw water, a polyaluminum chloride supplying device 12 for supplying polyaluminum chloride (hereinafter also referred to as "PAC"), a raw water transfer pipe 13 for transferring raw water, and a reverse osmosis membrane device 14 for performing reverse osmosis membrane treatment on the raw water (first treated water) to which PAC has been added. The manufacturing apparatus 1 further includes a reducing agent supplying device 17 for adding a reducing agent to the water supplied to the reverse osmosis membrane device 14, and a disinfectant supplying device 18 for adding an oxidizing disinfectant to the water to which the reducing agent has been added. A permeate transfer pipe 15 is connected to the permeation side of the reverse osmosis membrane device 14. A concentrated water discharge pipe 16 is connected to the concentration side of the reverse osmosis membrane device 14. The disinfectant supplying device 18 is not essential and may be provided as necessary.

[0017] The method for producing pure water in the embodiment using the production apparatus 1 is as follows. First, raw water is supplied from the raw water supply device 11 into the raw water transfer pipe 13. The raw water is urban water such as city water or industrial water, or natural water such as river water, lake water, groundwater, or well water. The raw water contains free chlorine. Alternatively, free chlorine may be added to the raw water during transportation through the raw water transfer pipe 13. 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, free chlorine concentration of 0.1 mg / L to 2 mg / L as Cl2, and pH of 4 to 9. The raw water supply device 11 includes, for example, a raw water tank for storing raw water and a feed water pump for transferring the raw water in the raw water tank, and the feed water pump supplies the raw water in the raw water tank into the raw water transfer pipe 13. Depending on the quality of the raw water, a prefilter (not shown) may be installed as a pretreatment device to pretreat the raw water before the subsequent addition of high basicity PAC. Also, an acid or alkali injection facility may be installed to adjust the pH of the raw water as necessary.

[0018] Next, the polyaluminum chloride supplying device 12 adds PAC to the raw water transfer pipe 13. The polyaluminum chloride supplying device 12 includes, for example, a chemical tank for storing PAC and a chemical injection pump for adding the PAC in the chemical tank to the raw water transfer pipe 13, and the chemical injection pump measures the PAC in the chemical tank to a predetermined concentration and adds it to the raw water transfer pipe 13. This produces the first treated water.

[0019] At this time, a pH adjusting device (not shown) adds an acid and an alkali, which are pH adjusting agents, to the raw water according to the basicity of the PAC to adjust the pH of the raw water. Either one or both of the acid and the alkali may be added. When a low-basic PAC described later is used, the pH adjusting device adds a pH adjusting agent to the raw water transfer pipe 13 to adjust the pH of the raw water before the PAC is added. The pH adjusting device includes, for example, an acid storage tank for storing an acid and an acid injection pump for adding the acid in the acid storage tank to the raw water transfer pipe 13. The pH adjusting device also includes an alkali storage tank for storing an alkali and an alkali injection pump for adding the alkali in the alkali storage tank to the raw water transfer pipe 13. The acid injection pump and the alkali injection pump measure the acid in the acid storage tank and the alkali in the alkali storage tank and add them to the raw water transfer pipe 13 so that the raw water has a predetermined pH. The acid used here is typically sulfuric acid, and the alkali is typically sodium hydroxide (aqueous solution).

[0020] The PAC in this embodiment contains polyaluminum chloride represented by the following chemical formula (1). As the PAC in this embodiment, either a low basicity PAC or a high basicity PAC can be used. As the PAC in this embodiment, it is preferable to use either a low basicity PAC or a high basicity PAC. When using a low basicity PAC (hereinafter referred to as "low basicity PAC"), it is preferable to provide the above-mentioned pH adjustment device to adjust the pH of the raw water. The basicity is a value calculated by n / 6×100(%). [Al2(OH) n Cl 6-n ] m(1≦n≦5, m≦10) (1)

[0021] The low basicity PAC preferably has a basicity of 75% or less, more preferably 60% or more and 70% or less. The low basicity PAC can be produced, for example, by the method described in JP-A-2009-203125. Only one low basicity PAC may be used, or two or more low basicity PACs may be used in combination. When two or more low basicity PACs are used in combination, the basicity of the two or more low basicity PACs may be the same or different, but the basicity of each of the low basicity PACs used is preferably 75% or less, more preferably 60% or more and 70% or less.

[0022] The amount of low basicity PAC is preferably 0.03 mg / L as Al2O3 or more per 1 NTU of turbidity in the raw water. Specifically, the amount of low basicity PAC is preferably 0.05 mg / L as Al2O3 or more and 5 mg / L as Al2O3 or less, and more preferably 0.1 mg / L as Al2O3 or more and 2 mg / L as Al2O3 or less, per amount of raw water.

[0023] In this embodiment, it is preferable to use a high basicity PAC (hereinafter referred to as "high basicity PAC") as the PAC. The basicity of the high basicity PAC is preferably greater than 75%, more preferably greater than 83%. The upper limit of the basicity is usually less than about 84%. The high basicity PAC can be produced, for example, by the method described in Japanese Patent No. 4104773. As the high basicity PAC, only one type may be used, or two or more types may be used in combination. When two or more types are used in combination, the 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%, more preferably greater than 83%.

[0024] When high-basicity PAC is used, the high-basicity PAC interacts with suspended matter in the raw water 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, and the performance of the reverse osmosis membrane device can be maintained for a long period of time. Microflocs are aggregates of suspended matter and high-basicity PAC with a size of about 1 to 10 μm. High-basicity PAC is likely to form microflocs, but is unlikely to form coarse flocs larger than microflocs or fine flocs (nanoflocs) smaller than microflocs. Aluminum ions are unlikely to leak from microflocs, so by passing through these, clogging of the reverse osmosis membrane can be prevented for a long period of time.

[0025] As the high basicity PAC, it is preferable to use aluminum chloride pentahydroxide (Al2Cl(OH)5). Aluminum chloride pentahydroxide is a polyaluminum chloride with n=5 and m=1 in the above chemical formula (1), and has a basicity of 83.3%. Aluminum chloride pentahydroxide is more likely to form more homogeneous microflocs. This is thought to be due to the high basicity and small molecular weight of aluminum chloride pentahydroxide.

[0026] The amount of high basicity PAC is preferably 0.125 mg / L as Al2O3 or more per turbidity of 1 NTU in the raw water. 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 per amount of raw water, and more preferably 0.3 mg / L as Al2O3 or more and 3 mg / L as Al2O3 or less per amount of raw water. 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 per total amount of raw water. Even if the amount of high basicity PAC is small as described above, it is possible to micro-flocculate the suspended solids in the raw water. In addition, since the high basicity PAC functions even in a small amount as described above, it is easy to prevent clogging of the reverse osmosis membrane device 14 in the downstream stage. The notation "as Al2O3" indicates that the value is converted into aluminum oxide (Al2O3) concentration.

[0027] 2 shows a schematic diagram of a pure water manufacturing apparatus 2 having a mixing tank 23 for adding PAC to raw water. The manufacturing apparatus 2 differs from the above-mentioned manufacturing apparatus 1 in that the raw water transfer pipe 13 has a mixing tank 23 and a transfer pipe 131 for supplying treated water in the mixing tank 23 to a subsequent stage, and the reducing agent supply device 17 and the disinfectant supply device 18 are connected to the transfer pipe 131, but the other configurations are the same. In this embodiment, detailed explanations of configurations and functions common to the manufacturing method using the manufacturing apparatus 1 will be omitted.

[0028] In the production apparatus 2, raw water is supplied from a raw water supply device 11, and PAC is supplied from a polyaluminum chloride supply device 12 into a mixing tank 23. When a low basicity PAC is used, a pH adjuster supplies an acid and an alkali into the mixing tank 23. As a result, a first treated water is produced.

[0029] When a high-basicity PAC is used, the coagulation property of the high-basicity PAC is less dependent on pH, and therefore it is not necessary to add an acid or alkali using a pH adjusting device. When a high-basicity PAC is used, the suspension in the raw water interacts with the high-basicity PAC in the mixing tank 23 to form microflocs. The order of supplying the raw water and the PAC into the mixing tank 23 may be either first or simultaneously, but it is preferable to add the PAC, and if necessary, an acid and an alkali, to the mixing tank 23 to which the raw water has been supplied.

[0030] In the mixing tank 23 of the production apparatus 2 shown in FIG. 2, when a high-basicity PAC is used, the raw water and the high-basicity PAC are rapidly stirred to form more homogeneous microflocs without generating nanoflocs. The stirring speed is, for example, 150 s in terms of G value. ー1 More than 150 to 250 s is preferable. ー1 More preferably, 250s ー1 It is more preferable that the stirring time is 2 minutes or more, preferably 3 minutes or more, and more preferably 6 minutes or more. The larger the G value of the rapid stirring, the shorter the stirring time can be.

[0031] Next, the first treated water is supplied to the raw water transfer pipe 13 in Fig. 1 or the transfer pipe 131 in Fig. 2. While the first treated water flows through the raw water transfer pipe 13 (or the transfer pipe 131, the same applies hereinafter in this embodiment), the reducing agent supplying device 17 adds a reducing agent to the first treated water. This produces the second treated water.

[0032] The reducing agent supply device 17 includes, for example, a chemical tank for storing a reducing agent and a chemical injection pump that adds the reducing agent in the chemical tank to the raw water transfer pipe 13, and the chemical injection pump measures a predetermined amount of reducing agent in the chemical tank and adds it to the raw water transfer pipe 13.

[0033] The reducing agent used in the manufacturing apparatus 1 (or manufacturing apparatus 2, hereinafter the same in this embodiment) of this embodiment has sodium disulfite (Na2S2O5) as an active ingredient. The present inventors have found that when sodium disulfite is used as a reducing agent, the amount of reducing agent remaining after reaction with free chlorine is extremely small, regardless of the pH value of the raw water. For this reason, the amount of oxidizing bactericide to be added subsequently can be reduced. In particular, by using it in combination with high basicity PAC, the pH adjustment of the raw water can be omitted. Therefore, the amount of chemicals such as pH adjusters, reducing agents, and bactericides to be added and the associated workload can be significantly reduced. In particular, when high basicity PAC is not used to adjust the pH in the previous treatment, if sodium disulfite is used, which does not change the amount of reducing agent remaining even if a pH fluctuation occurs, in other words, the amount of residual chlorine does not change, it is possible to avoid, for example, clogging of the reverse osmosis membrane by bacteria due to a lack of bactericide, or deterioration of the reverse osmosis membrane due to a lack of reducing agent, which is caused by the influence of pH fluctuation. In addition, since the amount of residual reducing agent can be ignored, it is easy to set the optimal amount to be added even in a method of monitoring the amount of residual chlorine and adding the optimal amount to it. In addition to the active ingredient, the reducing agent may contain, for example, water as a solvent, and may also contain other substances such as a stabilizer.

[0034] In contrast, when sodium sulfite (Na2SO3) or sodium hydrogen sulfite (NaHSO3) is used as a reducing agent, the residual amount of reducing agent is large over the entire pH range, and the residual amount varies depending on the pH value. Although the reason is not entirely clear, sodium sulfite (Na2SO3) and sodium hydrogen sulfite (NaHSO3) are in equilibrium with each other, and when sodium sulfite (Na2SO3) or sodium hydrogen sulfite (NaHSO3) is added to raw water, an equilibrium shift reaction progresses due to pH fluctuation. At the same time, an oxidation-reduction reaction occurs between sodium sulfite (Na2SO3) and sodium hydrogen sulfite (NaHSO3) and free chlorine. Therefore, depending on the pH of the raw water, the rate of the oxidation-reduction reaction is slower than the equilibrium shift reaction, which is thought to be why more sodium sulfite (Na2SO3) or sodium hydrogen sulfite (NaHSO3) is added. Furthermore, this increase in the amount of addition can be affected by factors such as the amount of oxidizing agent, the size of the equipment, and differences in the stirring speed after the addition of the reducing agent, so even if the pH of the raw water is the same, the amount is not necessarily constant, making it difficult to set an appropriate amount to be added.

[0035] In the manufacturing apparatus 1 of this embodiment, the amount of reducing agent to be added depends on the free chlorine concentration of the raw water, but is preferably 0.1 mg / L to 5 mg / L as the amount of the active ingredient (sodium disulfite). In particular, when the free chlorine concentration is about 0.2 mg / L as Cl2, the amount of the active ingredient (sodium disulfite) can be 0.2 mg / L to 0.4 mg / L, and the amount of the residual reducing agent can be suppressed to, for example, 0.06 mg / L or less. The amount of reducing agent to be added may be determined as follows. For example, the free chlorine concentration can be monitored using an ORP meter (oxidation-reduction potential meter), a residual chlorine meter, an SO2 meter, or the like, and the amount of reducing agent to be added can be adjusted according to the monitored amount. The amount of reducing agent remaining after the addition of the reducing agent may be monitored, and the amount of reducing agent to be added may be feedback-controlled according to the monitored value. The amount of reducing agent can be monitored, for example, by taking a portion of the raw water to which the reducing agent has been added as sample water, irradiating the raw water and the sample water with ultraviolet light to obtain dissolved oxygen concentrations that are compared to determine the amount of reducing agent in the sample water.

[0036] Next, if necessary, the disinfectant supplying device 18 adds an oxidizing disinfectant to the second treated water. The disinfectant supplying device 18 is equipped with, for example, a chemical tank for storing the oxidizing disinfectant and a chemical injection pump for adding the oxidizing disinfectant in the chemical tank to the raw water transfer pipe 13. The chemical injection pump measures a predetermined amount of the oxidizing disinfectant in the chemical tank and adds it to the raw water transfer pipe 13.

[0037] The oxidizing bactericide may be an oxidizing bactericide other than a free chlorine-based one, and may be, for example, an oxidizing bactericide such as an amine-based compound or a sulfamic acid-based compound. It may contain a halogen bonded to a sulfamic acid-based compound, such as sulfamoyl chloride or chlorosulfamic acid. It may also be a bactericide containing an isothiazolin-based compound such as 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT), a bromate compound such as sodium hypobromite, or 2,2-dibromo-3-nitrilopropionamide (DBNPA). The oxidizing bactericide may contain a stabilized halogen-based component and an excess of a sulfamic acid-based compound. This allows the stabilized halogen acid salt to be used as a bactericide in addition to the stabilized hypochlorous acid and stabilized hypobromous acid. As the oxidizing bactericide, commercially available products may be used, and examples of commercially available products include Kuriverter IK110 manufactured by Kurita Water Industries, Orpersion E266 series manufactured by Organo Corporation, Caisson WT manufactured by Dow Chemical Company, and Stabrex manufactured by Nalco Corporation.

[0038] The amount of bactericide to be added is generally the amount used to inhibit the growth of bacteria, and it is preferable to confirm in advance the MIC (minimum inhibitory concentration) of the bacteria contained in the raw water, and add an amount that reaches the MIC to about 5 times the MIC. In particular, in this embodiment, the residual amount of the reducing agent is small, and therefore the amount of the oxidizing bactericide lost by the reducing agent is small, so it is sufficient to use an amount that reaches the MIC.

[0039] The second treated water to which the bactericide has been added is then supplied to the reverse osmosis membrane device 14 via the transfer pipe 13 and treated with a reverse osmosis membrane. This results in permeated water from the reverse osmosis membrane device 14. In order to suppress 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%. Just before being supplied to the reverse osmosis membrane device 14, a scale inhibitor may be added as appropriate to the second treated water, and the water may be supplied to the reverse osmosis membrane device 14.

[0040] The reverse osmosis membrane device 14 may be any of ultra-low pressure type, ultra-low pressure type, low pressure type, medium pressure type, and high pressure type reverse osmosis membrane devices. The reverse osmosis membrane provided in the reverse osmosis membrane device 14 is preferably a spiral type reverse osmosis membrane made of aromatic polyamide as a constituent material. 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 which a negatively charged membrane is preferable because it is less likely to cause clogging due to flocs of the reverse osmosis membrane. The reverse osmosis membrane device 14 is preferably a negatively charged membrane of ultra-low or low pressure type. As a reverse osmosis membrane device having a negatively charged membrane of ultra-low or low pressure type, commercially available products may 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.

[0041] The permeated water from the reverse osmosis membrane device 14 is sent to a subsequent stage via a transfer pipe 15 on the permeation side of the reverse osmosis membrane device 14. The concentrated water from the reverse osmosis membrane device 14 can be discharged to the outside of the system of the production apparatus 1 via a discharge pipe 16 or returned to the upstream stage of the reverse osmosis membrane device 14 for reprocessing. The quality of the permeated water from the reverse osmosis membrane device 14 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 30 μS / cm to 100 μS / cm.

[0042] 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 a filtration section 31 is provided between the polyaluminum chloride supply device 12 and the reducing agent supply device 17 in the raw water transfer pipe 13, but the other configurations are the same. In this embodiment, detailed descriptions of the configurations and functions common to the manufacturing method using the manufacturing apparatus 1 will be omitted.

[0043] The method for producing pure water according to the embodiment using the production apparatus 3 shown in Fig. 3 is as follows. First, raw water is supplied from a raw water supply device 11 into a raw water transfer pipe 13. Next, PAC is added by a polyaluminum chloride supply device 12 into the raw water transfer pipe 13 to which the raw water has been supplied. A preferred embodiment of the PAC used here is the same as the production method using the production apparatus 1 shown in Fig. 1.

[0044] When a high basicity PAC is used, raw water and the high basicity PAC are supplied into the raw water transfer pipe 13, whereby the suspension in the raw water interacts with the high basicity PAC 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.

[0045] The first treated water in the raw water transfer pipe 13 is supplied to the filtration section 31. At this time, by providing a feed water pump in the raw water transfer pipe 13, the first treated water can be supplied to the filtration section 31 by the feed water pump. In this embodiment, since a mixing tank is not used, the manufacturing equipment is compact, which has the advantage of making it easy to install in a semiconductor manufacturing factory or the like. Note that, if an in-line mixer or the like is installed in the raw water transfer pipe 13 after the PAC is supplied to promote mixing, clogging of downstream equipment can be further suppressed.

[0046] The filtration unit 31 includes one or more types of filtration devices selected from a sand filtration device, a multimedia filter (MMF) filtration device, an ultrafiltration device, and a microfiltration (MF) device, and filters the first treated water. This removes microflocs and other substances that mainly contain suspended solids from the water. The treated water from the filtration unit 31 is sent to the subsequent stage through piping.

[0047] The sand filter has, for example, supporting gravel or sand (filter sand) as a filter material. A multimedia filter (MMF) filtration device is equipped with a three-layer filter material in which, for example, 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.

[0048] The filtration unit 31 may have one type of filtration device selected from the sand filtration device, multimedia filter (MMF) filtration device, microfiltration (MF) device, and ultrafiltration (UF) device, or a combination of two or more types, depending on the raw water quality. When two or more types are combined, it is preferable to arrange the sand filtration device or multimedia filter (MMF) filtration device on the upstream side and the ultrafiltration device on the downstream side. It is more preferable that the filtration unit 31 has an ultrafiltration device, and it is even more preferable that it has only an ultrafiltration device. By providing the filtration unit 31, suspended solids and the like in the first treated water can be removed with high accuracy, and therefore the load on the reverse osmosis membrane device 14 in the subsequent stage is reduced, making it possible to obtain high-quality permeate water for a long period of time.

[0049] 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 the independent filtration device include a cartridge type filtration device and a module type filtration device. The cartridge type filtration device is configured, for example, to accommodate a cartridge of filtration material in a housing, connect piping to a water inlet and a drainage port 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 and regenerated for each module. The independent filtration section 31 is effective in preventing clogging of the reverse osmosis membrane device 14 because there is little outflow of nanoflocs to the downstream side. Note that nanoflocs are finer flocs than microflocs, and tend to cause clogging of the reverse osmosis membrane to progress. In particular, when the method of this embodiment is used to produce ultrapure water for manufacturing semiconductors and the like, by using an independent filtration unit 31, multiple independent filtration units 31 can be installed in parallel, and regeneration such as backwashing or module replacement can be performed on each of the multiple units one by one, while operation can be continued using other equipment (so-called merry-go-round operation), making it possible to continue producing ultrapure water without stopping the equipment.

[0050] The quality of the 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 electrical conductivity of 140 μS / cm to 270 μS / cm. When high basicity PAC is used, 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 treated water from the filtration unit 31 may fluctuate, the aluminum concentration remains low and stable.

[0051] 4 shows a schematic diagram of a pure water manufacturing apparatus 4 having a mixing tank 23 for adding PAC to raw water, and a filtration section 31. The manufacturing apparatus 4 has a mixing tank 23 and a transfer pipe 131 for supplying the water in the mixing tank 23 to a subsequent stage in the path of a raw water transfer pipe 13, and differs from the manufacturing apparatus 3 shown in FIG. 3 in that a filtration section 31, a reducing agent supplying device 17, and a disinfectant supplying device 18 are installed in that order in the path of the transfer pipe 131, but the other configurations are the same. In this embodiment, detailed explanations of configurations and functions common to the manufacturing method using the manufacturing apparatus 3 will be omitted.

[0052] In the production apparatus 4, raw water is supplied from a raw water supply device 11, and PAC is supplied from a polyaluminum chloride supply device 12 into a mixing tank 23. When a low basicity PAC is used, a pH adjuster supplies acid and alkali into the mixing tank 23. As a result, a first treated water is produced.

[0053] When a high basicity PAC is used, it is not necessary to add acid and alkali using a pH adjusting device. When a high basicity PAC is used, the high basicity PAC interacts with the suspension in the raw water in the mixing tank 23 to form microflocs. In particular, by using the mixing tank 23, the high basicity PAC sufficiently forms microflocs, which further suppresses 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 to add the high basicity PAC to the mixing tank 23 to which the raw water has been supplied.

[0054] 4 has an independent filtration section 31 that is separate and independent from the mixing tank 23, downstream of the mixing tank 23. The aspect of the independent filtration section 31 is the same as that of the manufacturing apparatus 3 described above.

[0055] In addition, as the filtration section 31, a submerged type filtration device configured for tank immersion can be used. The submerged type filtration device configured for tank immersion has the advantage that it is submerged in the bottom of the mixing tank 23 and can directly filter the first treated water to which PAC has been added without using piping. As the submerged type filtration device, an ultrafiltration device or an MMF type filtration device is preferable. In the manufacturing apparatus 4 of this embodiment, particularly when high basicity PAC is used, by forming microflocs mainly in water, it is possible to directly perform filtration treatment without going through precipitation removal in a coagulation sedimentation tank. Therefore, the filtration section 31 can be integrated by immersing it in the mixing tank 23, and the configuration of the entire apparatus can be simplified.

[0056] When a plurality of filtration devices are used in the filtration section 31, only immersion type or only stand-alone type may be used, or immersion type and stand-alone type may be used in combination. 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. 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).

[0057] The first treated water is filtered by the filtration unit 31 in Fig. 3 or Fig. 4 to remove microflocs and coarse flocs containing suspended solids and the like from the water. Next, the reducing agent supplying device 17 adds a reducing agent to the treated water from the filtration unit 31. This produces second treated water. Furthermore, if necessary, the disinfectant supplying device 18 adds an oxidizing disinfectant to the second treated water, and the second treated water to which the oxidizing disinfectant has been added is supplied to the reverse osmosis membrane device 14. Preferred modes for adding the reducing agent and the oxidizing disinfectant are the same as those for the above-mentioned manufacturing apparatus 1 (Fig. 1) and manufacturing apparatus 2 (Fig. 2).

[0058] Next, a pure water producing system 5 according to an embodiment using the above-mentioned 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 producing system 5 using the production apparatus 1. In Fig. 5, the production apparatus 1 can be changed to any one of production apparatuses 2 to 4.

[0059] 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.

[0060] The pretreatment system 50 includes the production apparatus 1 of the embodiment described above, and, if necessary, a prefilter, a heat exchanger for temperature adjustment, and the like.

[0061] 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.

[0062] The primary pure water system 51 produces primary pure water by removing organic matter, ion components, and dissolved gases from the pretreated water. The primary pure water system 51 includes an ultraviolet oxidation device (TOC-UV) 513 and an ion exchange device 514 in this order.

[0063] The ultraviolet oxidation device 513 has an ultraviolet lamp that emits ultraviolet rays with a wavelength of, for example, about 185 nm and ultraviolet rays with a wavelength of about 254 nm, and oxidizes and decomposes the total organic carbon (TOC) in the water to be treated by irradiating the water with ultraviolet rays from the ultraviolet lamp. The ultraviolet rays emitted by the ultraviolet oxidation device 513 decompose the water to generate OH radicals, and the organic matter in the water to be treated is oxidized and decomposed into organic acids by the OH radicals. The amount of ultraviolet irradiation in the ultraviolet oxidation device 513 of the primary pure water system can be appropriately changed depending on the water quality of the water to be treated.

[0064] The ion exchange device 514 is one or more of an ion exchange resin device and an electric deionization device. As the ion exchange resin device, one or more selected from a cation exchange resin device, an anion exchange resin device, a mixed bed ion exchange resin device, and a double bed ion exchange resin device can be appropriately combined and used according to the required water quality. The cation exchange resin used in the cation exchange resin device may be a strong acid cation exchange resin or a weak acid cation exchange resin. The anion exchange resin used in the anion exchange resin device may be a strong basic anion exchange resin or a weak basic anion exchange resin. As the ion exchange resin, a boron adsorbent ion exchange resin may be used.

[0065] 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.

[0066] The ultrapure water production system 5 is provided with a primary pure water tank TK2 for storing primary pure water, and a secondary pure water system 52, in this order, downstream of a primary pure water system 51. The primary pure water produced in the primary pure water system is temporarily stored in the primary pure water tank TK2, and then sent to the secondary pure water system 52. The secondary pure water system 52 is provided with an ultraviolet oxidation device (TOC-UV) 521, a non-regenerative polisher (Polisher) 522, a membrane degasser (MDG) 523, and an ultrafiltration device (UF) 524.

[0067] The ultraviolet oxidation device 521 in the secondary pure water system 52 has the same configuration as the ultraviolet oxidation device 513 in the primary pure water system 51. The non-regenerative polisher 522 is a mixed-bed ion exchange resin device in which a strong acid cation exchange resin and a strong basic anion exchange resin are mixed and filled in a container such as a cylinder. The non-regenerative polisher 522 adsorbs and removes ion components generated by the ultraviolet oxidation device 521 decomposing organic matter.

[0068] The membrane degassing device 523 removes dissolved gases through a degassing membrane. The membrane degassing device 523 removes trace amounts of dissolved oxygen in the primary pure water to reduce the dissolved oxygen concentration, for example, to about 1 μg / L or less. The ultrafiltration membrane device 524 performs filtration using an ultrafiltration membrane to remove trace amounts of eluted matter and fine particle components from the upstream ion exchange resin, for example, to reduce the number of fine particles of 0.05 μm or more to about 250 Pcs. / L or less.

[0069] 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.

[0070] In each of the above-mentioned embodiments, the water quality of the raw water and the treated water can be measured by the following methods or devices. Turbidity: Light scattering method Aluminum concentration: ICP emission spectrometry pH:electrode method Conductivity: Conductivity meter (HORIBA HE-960CW) Total organic carbon (TOC) concentration: TOC meter (except ultrapure water: SUEZ Sievers M9e) EXAMPLES

[0071] Next, examples will be described, but the present invention is not limited to the following examples.

[0072] Fig. 6 shows a schematic diagram of a pure water production apparatus 6 used in the present embodiment and the comparative example. The production apparatus 6 shown in Fig. 6 includes a raw water supplying device 61 for supplying raw water, a polyaluminum chloride supplying device 62 for supplying PAC, and a mixing tank 63 into which the raw water and PAC are supplied. The production apparatus 6 further includes, in the downstream path of the mixing tank 63, an ultrafiltration device 65, a reducing agent supplying device 67, a disinfectant supplying device 68, and a reverse osmosis membrane device 64, in this order.

[0073] The specifications of the devices used in the examples and experimental 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%, operating pressure 12kgf / cm 2 Measurement of aluminum concentration: Inductively coupled plasma (ICP) optical emission spectrometry Turbidity measurement: Turbidimeter (Hach2100P, manufactured by Toa Dekk Corporation) pH measurement: Water quality meter (Horiba 9630-10D, manufactured by Horiba) Residual chlorine concentration or total chlorine concentration: AQ-201 (manufactured by SIBATA) Sulfite ion (SO3 2- ) Concentration (amount of reducing agent): MD600 (manufactured by LOVIBOND) Free chlorine concentration: AQ-201 (SIBATA) Water quality of raw water (lake water): turbidity 4 NTU, pH=7.2, conductivity 250 μS / cm, TOC 4 mg / L. The pH fluctuated from 6.7 to 7.8 during the water flow period.

[0074] Example 1 Hypochlorous acid was added to the raw water so that the free chlorine concentration was 0.2 mg / L as Cl2, and the mixture was fed to the mixing tank 63. Then, an aqueous solution of aluminum chloride pentahydroxide (Al2Cl(OH)5) (Nomura Micro Science Co., Ltd. prototype, basicity 83.33%) was fed 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 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 (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 they contained Al. 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 example.

[0075] The treated water in the mixing tank 63 was passed through an ultrafiltration device 65 for filtration, and then sent to the subsequent stage via piping. During this process, 0.2 mg / L of sodium disulfite was added as a reducing agent, and then 0.3 mg / L of chlorosulfamic acid (Nomulite (prototype), manufactured by Nomura Micro Science Co., Ltd.) was added as an oxidizing bactericide. The treated water was then supplied to a reverse osmosis membrane device 64 for reverse osmosis treatment. The amount of sodium disulfite added was the minimum amount (chemical equivalent) required when the following reaction occurs completely. Na2S2O5+H2O+2NaOCl → 2HCl+2Na2SO4

[0076] 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 treatment being continuously carried out in the ultrafiltration device 65 and the reverse osmosis membrane device 64 in that order. In Example 2 as well, it was confirmed that microflocs were formed.

[0077] Example 3 In Example 1, except that 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) were added as oxidizing germicides in a total amount of 0.05 mg / L, treatment was continuously carried out in the ultrafiltration device 65 and the reverse osmosis membrane device 64 in the same manner as in Example 1. In Example 3, it was confirmed that microflocs were formed.

[0078] Example 4 Acid or alkali was added to the raw water to maintain the pH at 7.2 and eliminate pH fluctuations. In addition, 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 Al2O3. Except for this, the ultrafiltration device 65 and the reverse osmosis membrane device 64 were treated in sequence in the same manner as in Example 1. In Example 4, 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 to observe the fine particles captured by the membrane, and fine particles of about 1 to 10 μm were observed. The elemental components of these fine particles were confirmed by EDX and found to contain 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 pressure difference was suddenly generated. From the above results, it was confirmed that microflocs were formed, but also coarse aggregates with sizes of 0.45 μm or more were formed.

[0079] Comparative Example 1 In Example 1, low basicity PAC (product name PAC250A, manufacturer 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, but treatment was performed continuously in the same manner as in Example 1, successively using the ultrafiltration device 65 and the reverse osmosis membrane device 64. In Comparative Example 1, the state of floc formation was the same as in Example 4.

[0080] Comparative Example 2 In Comparative Example 1, 0.05 mg / L of the same 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) as in Example 3 were added as oxidizing bactericides, and treatment was carried out in the same manner as in Comparative Example 1, successively using the ultrafiltration device 65 and the reverse osmosis membrane device 64. The state of floc formation was equivalent to that in Comparative Example 1.

[0081] Comparative Example 3 In Example 1, except that sodium sulfite was used as the reducing agent, treatment was performed in the same manner as in Example 1, successively using the ultrafiltration device 65 and the reverse osmosis membrane device 64. In Comparative Example 3, the state of formation of microflocs was the same as in Example 1. The amount of sodium sulfite added was the minimum amount (chemical equivalent) required when the following reaction occurs completely. NaOCl+Na2SO3 → NaCl+Na2SO4

[0082] Comparative Example 4 In Example 1, except that sodium hydrogen sulfite was used as the reducing agent, treatment was performed in the same manner as in Example 1, successively in the ultrafiltration device 65 and the reverse osmosis membrane device 64. In Comparative Example 3, the state of formation of microflocs was the same as in Example 1. The amount of sodium hydrogen sulfite added was the minimum amount (chemical equivalent) required when the following reaction occurs completely. 2NaHSO3+3NaClO → 3NaCl+H2O +2Na2SO4

[0083] Table 1 shows the type and basicity of the PAC used, the type and amount of the reducing agent, the type of oxidizing bactericide, the aluminum concentration in the treated water from the ultrafiltration device 65, the turbidity (NTU), and the residual reducing agent concentration in the above-mentioned Example 1 to Comparative Example 4. In Table 1, the amount of the reducing agent is shown as the amount of the active ingredient, and the residual reducing agent amount is shown as the amount of sulfite ion (SO3 2- In Table 1, the mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) is referred to as "fungicide b."

[0084] [Table 1]

[0085] Comparing Example 1 with Comparative Examples 3 and 4, it is found that the permeation flux (flow rate) is increased in Comparative Examples 3 and 4. This is because Comparative Example 3 uses sodium sulfite (Na2SO3), and Comparative Example 4 uses sodium hydrogen sulfite (NaHSO3), and therefore the amount of the reducing agent is insufficient in the reaction equivalent with the oxidizing agent (free chlorine), so that the reverse osmosis membrane provided in the reverse osmosis membrane device 64 deteriorates in a short period of time after three months, which is thought to be the reason for the increase in the permeation flux.

[0086] (Experimental Examples 1 to 3) The relationship between the type of reducing agent and the residual amount was investigated when the pH of the raw water was changed. A specified amount of raw water with a turbidity of 4 was collected in a beaker, and a pH adjuster (NaOH or H2SO4) was added to adjust the pH to a specified value between 6 and 9. Sodium hypochlorite (NaClO) was added to each of the pH-adjusted samples so that the free chlorine concentration was 2 mg / L as Cl2. Next, add the reducing agent shown below in a predetermined amount (0 to 20 mg / L) until the free chlorine concentration disappears. 2- The concentration was measured. The amount of reducing agent remaining when the free chlorine disappeared was calculated from the difference between the amount of reducing agent added and the amount of reducing agent consumed calculated from the reaction formula. The results are shown in Figure 7.

[0087] Experimental Example 1: Sodium disulfite (Na2S2O5) Experimental Example 2: Sodium Sulfite (Na2SO3) Experimental Example 3: Sodium Bisulfite (NaHSO3)

[0088] From Experimental Examples 1 to 3, when sodium sulfite (Na2SO3) or sodium hydrogen sulfite (NaHSO3) is used as a reducing agent, if added until free chlorine disappears, the reducing agent remains, and furthermore, the residual amount changes depending on the pH. In contrast, when sodium disulfite (Na2S2O5) is used, the residual amount of the reducing agent is smaller than sodium sulfite or sodium hydrogen sulfite, and the pH dependency of the residual amount is also low.

[0089] From the experimental examples, examples, and comparative examples described above, the pure water production apparatus and method of the embodiment uses sodium disulfite (Na2S2O5) as a reducing agent, so the residual amount of the reducing agent is smaller than that of sodium sulfite or sodium hydrogen sulfite, and the residual amount also has low pH dependency. Therefore, when raw water containing chlorine is treated with a reverse osmosis membrane, chemicals can be added efficiently and the amount of chemicals added can be reduced. As a result, high purity pure water or ultrapure water can be efficiently produced 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. [Explanation of symbols]

[0090] 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, 67...Reducing agent supply equipment, 18, 68...Bactericide supply equipment, ...23, 63...Mixing tank, 31...Filtration section, 65...Ultrafiltration equipment, 50...Pretreatment system, 51...Primary pure water system (pure water production system), 52...Secondary pure water system (subsystem), 53...Point of use (POU), 513...Ultraviolet oxidation equipment (TOC-UV), 514...Ion exchange equipment, TK1, TK2...Tank, 521...Ultraviolet oxidation equipment (TOC-UV), 522...Non-regenerative polisher (Polisher), 523...Membrane degassing equipment (MDG) 524...Ultrafiltration equipment (UF)

Claims

1. A method for producing pure water, comprising the steps of: A step of obtaining a first treated water by adding polyaluminum chloride to raw water containing free chlorine; A step of adding a reducing agent containing sodium disulfite as an active ingredient to the first treated water to obtain a second treated water; and a reverse osmosis membrane step of treating the second treated water with a reverse osmosis membrane.

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

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

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

5. the polyaluminum chloride comprises aluminum chloride pentahydroxide; The amount of aluminum chloride pentahydroxide added is aluminum oxide (Al ２ O ３ 3. The method according to claim 1, wherein the concentration of the nitrile 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 converted nitrile in the raw water.

6. The first treated water, The method includes a filtration step of filtering the wastewater by 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 reducing agent is added to the treated water obtained in the filtration step.

7. The free chlorine concentration in the raw water is 0.1 mg / L or more and 2 mg / L or less as Cl ２ The method according to claim 1 or 2, wherein the amount of the reducing agent added is, in terms of sodium disulfite, 0.1 mg / L or more and 5.0 mg / L or less.

8. 3. The method according to claim 1, wherein the turbidity of the permeate from the reverse osmosis membrane device is from 0.01 to 0.4, and the aluminum concentration is from 0.01 to 0.04 mg / L.

9. A method for producing pure water, comprising the steps of: A step of obtaining a first treated water by adding polyaluminum chloride to raw water containing free chlorine; A step of adding a reducing agent containing sodium disulfite as an active ingredient to the first treated water to obtain a second treated water; a reverse osmosis membrane process for subjecting the second treated water to a reverse osmosis membrane process; The method includes an ultraviolet oxidation step and an ion exchange step in this order. Manufacturing method.

10. An apparatus for producing pure water, comprising: A raw water supply device for supplying raw water containing free chlorine; A polyaluminum chloride supplying device for adding polyaluminum chloride to raw water; a reducing agent supplying device that adds a reducing agent having sodium disulfite as an active ingredient to a first treated water produced by adding polyaluminum chloride to raw water; a reverse osmosis membrane device that performs reverse osmosis membrane treatment on the second treated water produced by adding the reducing agent; A manufacturing apparatus having the above structure.

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

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

13. the polyaluminum chloride comprises aluminum chloride pentahydroxide; The polyaluminum chloride supplying device supplies aluminum oxide (Al ２ O ３ 12. The manufacturing apparatus according to claim 10, wherein the aluminum chloride pentahydroxide is supplied in an amount of 0.25 mg / L or more and 5 mg / L or less in terms of a concentration calculated based on the converted aluminum chloride.

14. Between the polyaluminum chloride supply device and the reducing agent supply device, The apparatus has at least one selected from a sand filter, a multimedia filter (MMF) filter, a microfiltration (MF) device, and an ultrafiltration device; The manufacturing apparatus according to claim 10 or 11.

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

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