Water treatment system and water treatment method

Abstract

A water treatment system for removing at least boron contained in water to be treated, the water treatment system comprising: RO membrane devices (10-1, 10-2) comprising extremely ultra-low pressure RO membranes; and EDI devices (20-1, 20-2) that are disposed in the subsequent stages of the RO membrane devices (10-1, 10-2) and that include a high-purity EDI stack that is filled with at least an anion exchange resin in the most downstream layer of the desalination chamber and is filled with at least a cation exchange resin in the concentration chambers adjacent to each other across a cation exchange membrane that partitions the desalination chamber, the EDI devices (20-1, 20-2) being disposed in the subsequent stages of the RO membrane devices (10-1, 10-2), and the EDI stacks (20-1, 20-2) being disposed in the subsequent stages of the RO membrane devices (10-1, 10-2). The RO membrane device is a two-stage RO membrane device, and an extremely ultra-low pressure RO membrane is disposed in at least one of a first stage and a second stage.

Description

Technical Field

[0001] The invention relates to a water treatment system and a water treatment method. Background Art

[0002] In the manufacturing process of semiconductor devices and liquid crystal devices, pure water (including ultrapure water) with highly removed organic matter, ionic components, particles, bacteria, etc. is used as cleaning water. In particular, the requirements for the water quality of pure water used in the cleaning process of electronic components including semiconductor devices are increasing year by year. In recent years, as one of the requirements, it is required to improve the removal rate of boron contained in pure water. It is known to use a reverse osmosis membrane device (hereinafter referred to as an RO membrane device) and an electrically regenerated deionized water production device (hereinafter referred to as an EDI device) to remove boron as a weak acid component (for example, refer to Patent Document 1). In addition, in order to obtain a high boron removal rate, there is also a case where a high-pressure device is used as an RO membrane device (for example, refer to Patent Document 2). Furthermore, it is also known that the boron removal efficiency is improved by adjusting the pH of the supply water to the RO membrane device to the alkaline side.

[0003] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 4045658 Patent Document 2: Japanese Patent No. 5733351 Summary of the invention

[0004] Technical problem to be solved by the invention The boron removal rate using RO membrane is low. Even if an ultra-low pressure RO membrane is used in the neutral region, the boron removal rate is only about 45% to 60%. On the other hand, if a high-pressure membrane is used as the RO membrane, the boron removal rate also rises to about 80% to 90%, but it will increase the power consumption of the pump. In addition, if the pH of the supply water to the RO membrane is adjusted to the alkaline side of 9 or more, the boron removal rate will increase, but not only the chemical injection equipment is required, but also the replenishment management of the chemical. As a result, the management cost also increases. In addition, the addition of alkali will promote the deterioration of the RO membrane. Therefore, there is also a concern that the frequency of replacement of the RO membrane will increase.

[0005] Thus, in the above-mentioned technology, there is a problem that the boron removal rate cannot be improved without applying a large load.

[0006] An object of the present invention is to provide a water treatment system and a water treatment method, which can improve the removal rate of boron without applying a large load.

[0007] Technical solutions for solving technical problems The water treatment system of the present invention is a water treatment system for removing at least boron contained in the treated water, and comprises: an RO membrane device, which includes an ultra-low pressure RO membrane; and an EDI device, which is arranged at the rear stage of the RO membrane device and includes a high-purity EDI stack, the high-purity EDI stack is filled with at least anion exchange resin in the most downstream layer of the desalination chamber, and is filled with at least cation exchange resin in the concentration chamber adjacent to the cation exchange membrane that divides the desalination chamber. The RO membrane device is a two-stage RO membrane device, and the ultra-low pressure RO membrane is arranged in at least one of the first stage and the second stage.

[0008] Furthermore, the water treatment method of the present invention is a water treatment method for removing at least boron contained in the water to be treated. An RO membrane device that is provided at the front stage of the EDI device and includes an ultra-low pressure RO membrane device is operated so that the boron concentration of the treated water supplied to the EDI device including the high-purity EDI stack becomes 20 [μg / L] to 100 [μg / L], the silica concentration becomes 50 [μg / L] or less, and the hardness becomes 0.05 [mgCaCO3 / L] or less.

[0009] Effects of the Invention In the present invention, the boron removal rate can be improved without applying a large load. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a diagram showing a first embodiment of the water treatment system of the present invention.

[0011] Figure 2 Yes means Figure 1 A diagram showing an example of the structure of an EDI device.

[0012] Figure 3 It is a diagram showing a second embodiment of the water treatment system of the present invention.

[0013] Figure 4 Yes means Figure 3 A diagram showing an example of the structure of a general EDI device.

[0014] Figure 5 It is a diagram showing a third embodiment of the water treatment system of the present invention.

[0015] Figure 6 It is a diagram showing a fourth embodiment of the water treatment system of the present invention.

[0016] Figure 7 It is a diagram showing a first comparative example for comparison with the embodiment.

[0017] Figure 8It is a diagram showing a second comparative example for comparison with the embodiment.

[0018] Fig. 9 It is a diagram showing an example of arrangement of pumps in the water treatment system of the present invention.

[0019] Fig.10 Yes means Figure 3 A diagram of the pressure values ​​at various points in the manner shown.

[0020] Fig.11 This is a diagram showing another example of the structure of the high-purity EDI device used in the present invention. DETAILED DESCRIPTION

[0021] The WHO's Guidelines for drinking-water quality (fourth edition incorporating the first and second addenda, 4th ed+1st add+2nd add. World Health Organization) reports that the boron concentration in drinking water in almost all regions of the world is less than 0.5 [mg / L]. Furthermore, the average value in the water quality distribution table (raw water) of the tap water quality database (2019) of the Japan Waterworks Association (http: / / www.jwwa.or.jp / mizu / ) is: Among the locations where the concentration of boron and its compounds is 0.1 [mg / L] or less, 99% is in surface water and 97% is in groundwater. Therefore, it is assumed that the range of boron concentration in raw water to which the present invention is applied is preferably 0.01 [mg / L] to 0.2 [mg / L], and more preferably 0.02 [mg / L] to 0.1 [mg / L].

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The present invention is a water treatment system that uses an RO membrane (reverse osmosis membrane) device and an EDI device (electrically regenerated deionized water production device) connected in series to remove at least the boron contained in the treated water. The EDI device is arranged at the rear stage of the RO membrane device. The EDI device is a device that combines electrophoresis and electrodialysis. The structure of the EDI device is a structure in which a desalination chamber is arranged between the anode and the cathode, and the desalination chamber is divided by a pair of ion exchange membranes. In the EDI device, at least the desalination chamber is filled with ion exchange resin. The treated water is passed into the desalination chamber under the condition that a DC voltage is applied between the anode and the cathode. Thus, the treated water is desalinated in the desalination chamber, and the treated water with the ion components removed flows out of the desalination chamber. The structure of the RO membrane device is a two-stage structure (two-stage RO membrane device). The two-stage structure of the RO membrane device is, for example, as follows: an ultra-low pressure RO membrane device and an ultra-low pressure RO membrane device, an ultra-low pressure RO membrane device and an ultra-low pressure RO membrane device. In addition, it can also be another RO membrane device such as one of the two-stage structures is an ultra-low pressure RO membrane device and the other is a low pressure RO membrane device. According to the structure of the RO membrane device, it is divided into a plurality of zones, and the water quality of the supply water supplied to the EDI device is set in each zone. The water quality parameters of the supply water (treated water of the RO membrane device) to the EDI device in each zone are shown in Table 1.

[0023] [Table 1]

[0024] As shown in Table 1, when the structure of the RO membrane device is assumed to be a structure in which an ultra-low pressure RO membrane device is arranged at the rear stage of the ultra-low pressure RO membrane device, the supply water supplied to the EDI device is set to the category A. In addition, when the structure of the RO membrane device is assumed to be a structure in which an ultra-low pressure RO membrane device is arranged at the rear stage of the ultra-low pressure RO membrane device, the supply water supplied to the EDI device is set to the category B. In addition, when the structure of the RO membrane device is assumed to be a structure in which an ultra-low pressure RO membrane device is arranged at the rear stage of the low pressure RO membrane device, the supply water supplied to the EDI device is set to the category C. Regarding the supply water of category A, the conductivity is 3 [μS / cm] ~ 4 [μS / cm], the boron concentration is 0.10 [mg / L] ~ 0.12 [mg / L], the sodium concentration is 0.5 [mg / L] ~ 0.6 [mg / L], the silica concentration is 0.04 [mg / L] ~ 0.06 [mg / L], and the hardness is 0.04 [mgCaCO3 / L] ~ 0.05 [mgCaCO3 / L]. In addition, regarding the supply water of the zone B, the conductivity is 2 [μS / cm] to 3 [μS / cm], the boron concentration is 0.02 [mg / L] to 0.03 [mg / L], the sodium concentration is 0.2 [mg / L] to 0.3 [mg / L], the silica concentration is 0.00 [mg / L] to 0.02 [mg / L], and the hardness is 0.02 [mgCaCO3 / L] to 0.03 [mgCaCO3 / L]. In addition, regarding the supply water of the zone C, the conductivity is 1 [μS / cm] to 2 [μS / cm], the boron concentration is 0.005 [mg / L] to 0.01 [mg / L], the sodium concentration is 0.1 [mg / L] to 0.15 [mg / L], the silica concentration is less than 0.005 [mg / L], and the hardness is less than 0.01 [mgCaCO3 / L].

[0025] When the boron concentration contained in the raw water supplied to the RO membrane device arranged in the first stage is set to 0.1 [mg / L], the boron removal rate in the structure of the partition A is 0%, the boron removal rate in the structure of the partition B is 70% to 80%, and the boron removal rate in the structure of the partition C is 90% to 95%. In addition, when the boron concentration contained in the raw water supplied to the RO membrane device arranged in the first stage is set to 0.2 [mg / L], the boron removal rate in the structure of the partition A is 40% to 50%, the boron removal rate in the structure of the partition B is 85% to 90%, and the boron removal rate in the structure of the partition C is 95% to 98%. It should be noted that in the structure of the partition C, a system is envisaged in which alkali is added to the water supply line of the low-pressure RO in the first stage to adjust the pH of the concentrated water outlet to 10 to 11.

[0026] Here, the ultra-low pressure type RO membrane provided in the ultra-low pressure RO membrane device is a membrane that has a salt removal rate of less than 99.4% when a raw liquid containing a NaCl concentration of 500 [mg / L] to 2000 [mg / L], a pH value of 6 to 8, a water temperature of 25°C, and a permeate recovery rate of 10% to 25% is supplied. 2 ] is 1.3[(m 3 / d) / (m 2 For example, under the above test conditions, when the supply pressure is 0.86 [MPa] and the permeate flow rate is 53 [m 3 / d], and the membrane area is 41[m 2 ], for every supply pressure 1 [MPa] and membrane area 1 [m 2 ]The permeation water volume is 53÷(41×0.86)=1.50[(m 3 / d) / (m 2 ·MPa)]. Examples of ultra-low pressure RO membranes include XLE-440 and XLE-440i manufactured by Dupont, ESPA4 (ESPA4-LD-4040, ESPA4-LD, ESPA4-LD HP, ESPA4 MAX) manufactured by Hydranautics, and TMHA (TMH10A, TMH20A-400C, TMH20A-440C) manufactured by Toray Industries, etc. Ultra-low pressure RO membranes refer to membranes such as those having a water permeate flow rate per unit pressure and unit area of ​​less than 1.3 [(m 3 / d) / (m 2 ·MPa)], and the salt removal rate is 99.3% or more. Examples of ultra-low pressure RO membranes include BW30HRLE-440 and SG30LE-440i manufactured by Dupont, ESPA2 MAX manufactured by Hydranautics, and TMG20D-400 manufactured by Toray Industries, etc. In addition, low-pressure RO membranes refer to membranes such as the following: Under the same test conditions as above, the permeate flow rate per unit pressure and unit area is 0.8 [(m 3 / d) / (m 2 ·MPa)] or less, and the salt removal rate is 99.5% or more. Examples of the low-pressure RO membrane include CR100 manufactured by Dupont.

[0027] (Example 1) Figure 1 1 is a diagram showing a first embodiment of the water treatment system of the present invention. Figure 1As shown, the RO membrane device 10-1, RO membrane device 10-2 and the EDI device 20-1, EDI device 20-2 are connected in series. The RO membrane device 10-1, RO membrane device 10-2 are ultra-low pressure RO membrane devices each having an ultra-low pressure type RO membrane. The EDI device 20-1, EDI device 20-2 is a high-purity EDI device. Figure 1 The raw water is supplied to the RO membrane device 10 - 1 shown, and the supplied raw water is processed in the RO membrane device 10 - 1 , the RO membrane device 10 - 2 , and the EDI device 20 - 1 , and the EDI device 20 - 2 , respectively.

[0028] Here, the high-purity EDI device is an EDI device in which the boron removal rate is 99.0% or more when the permeate water (boron concentration of 0.01 [mg / L] to 0.20 [mg / L], water temperature of 20°C to 28°C) treated with two-stage RO membrane is treated as the treated water of the EDI device. When an ultra-low pressure RO membrane device is provided in the front stage of the EDI device, it can be considered that the boron removal rate of the RO membrane device is lower than the removal rate when an ultra-low pressure, low pressure or high pressure RO membrane device is provided in the front stage of the EDI device. Therefore, EDI devices 20-1 and 20-2 including high-purity EDI stacks are provided as the EDI devices in the rear stage of the RO membrane device 10-1 and 10-2. In the most downstream layer of the desalination chamber of the high-purity EDI device, at least anion exchange resin is filled, and more preferably, anion exchange resin is filled in a single bed. Furthermore, the concentrating chambers adjacent to each other across the cation exchange membranes that partition the desalting chambers are filled with at least a cation exchange resin, and more preferably, an anion exchange resin and a cation exchange resin are filled in a mixed bed.

[0029] Figure 2 Yes means Figure 1 The diagram shows an example of the configuration of the EDI device 20-1 and the EDI device 20-2. Figure 1 The EDI devices 20-1 and 20-2 are shown as Figure 2As shown, there are provided: an anode chamber 101 filled with a cation exchange resin (CER); a cathode chamber 102 filled with an anion exchange resin (AER); a concentration chamber 103 and a concentration chamber 104, which are mixed beds (MB) filled with cation exchange resins and anion exchange resins; a first desalination chamber 105 filled with an anion exchange resin; and a second desalination chamber 106, which are filled with cation exchange resins and anion exchange resins in sequence from the upstream side. The anode chamber 101 is adjacent to the concentration chamber 103 via a cation exchange membrane 201. The concentration chamber 103 is adjacent to the first desalination chamber 105 via an anion exchange membrane 202. The first desalination chamber 105 is adjacent to the second desalination chamber 106 via an anion exchange membrane 202. The second desalination chamber 106 is adjacent to the concentration chamber 104 via a cation exchange membrane 201. The concentration chamber 104 is adjacent to the cathode chamber 102 via an anion exchange membrane 202. It should be noted that cation exchange membrane 201 may not be provided between anode chamber 101 and concentrating chamber 103 and anode chamber 101 may also serve as concentrating chamber 103. Also, anion exchange membrane 202 may not be provided between cathode chamber 102 and concentrating chamber 104 and cathode chamber 102 may also serve as concentrating chamber 104.

[0030] Will Figure 1 The results of water flow operation in the manner of division A shown in Table 2 are shown. Here, the ultra-low pressure RO membrane XLE-440 manufactured by Dupont was used in the RO membrane device 10-1 and the RO membrane device 10-2, and three elements were arranged in parallel in the RO membrane device 10-1 and the RO membrane device 10-2, respectively, and water was flowed. The operation was performed so that the permeate flow rate of the RO membrane device 10-1 became 3.5 [m 3 / h], and the permeate flow rate of the RO membrane device 10-2 becomes 3.10 [m 3 / h]. In addition, in the EDI device 20-1 and the EDI device 20-2, use Figure 2 The high-purity EDI stack shown in the figure has a basic structure of anion exchange membrane 202, first desalination chamber 105, anion exchange membrane 202, second desalination chamber 106, cation exchange membrane 201 and concentration chamber 104 stacked in 20 sets, and is operated under the following high flow rate and high current conditions. The EDI device 20-1 as the first EDI is operated under the following conditions: the flow rate (SV) per unit volume of the ion exchange resin in the first desalination chamber 105 or the second desalination chamber 106 becomes 440 [h -1 ], the current density becomes 1.2[A / dm 2], and the pressure difference of the desalination chamber becomes 0.22±0.02 [MPa]. In addition, the EDI device 20-2 as the second EDI is operated under the following conditions: the flow rate (SV) per unit volume of the ion exchange resin in the first desalination chamber 105 or the second desalination chamber 106 becomes 400 [h -1 ], the current density becomes 1.2[A / dm 2 ], and the pressure difference of the desalination chamber becomes 0.20±0.02[MPa]. The high flow rate condition of the EDI stack means that water is passed so that the flow rate (SV) per unit volume of the ion exchange resin in the first desalination chamber 105 or the second desalination chamber 106 of the EDI device 20-1 or the EDI device 20-2 becomes 300[h -1 ]~450[h -1 The high current condition of the EDI stack is that the current density flowing through the EDI device 20-1 and the EDI device 20-2 is 0.8 [A / dm 2 ]~1.2[A / dm 2 ] current. In addition, the high flow rate and high current conditions of the EDI stack are conditions for passing water in a manner such that the water pressure difference of the desalination chamber becomes 0.18 [MPa] to 0.3 [MPa]. Here, water is passed so that the flow rate (SV) per unit volume of the ion exchange resin in the first desalination chamber 105 or the second desalination chamber 106 of the EDI device 20-1 or the EDI device 20-2 becomes 350 [h -1 ]~450[h -1 In addition, the current density flowing through the EDI device 20-1 and the EDI device 20-2 is 0.7 [A / dm 2 ]~1.4[A / dm 2 ] current. In addition, water is passed so that the water pressure difference in the desalination chamber becomes 0.18 [MPa] to 0.3 [MPa].

[0031] [Table 2]

[0032] As shown in Table 2, in the present method, in the EDI supply water zone A of the RO treated water which is assumed to be treated by using an ultra-low pressure RO membrane device in a two-stage structure, the boron concentration can be reduced to the ultrapure water requirement level (less than 1 ng / L) of the most advanced semiconductor manufacturers by using a high-purity EDI device in a two-stage structure for water treatment.

[0033] (Example 2) Figure 3 2 is a diagram showing a second embodiment of the water treatment system of the present invention. Figure 3As shown, the RO membrane devices 10-1 and 10-2 are connected in series with the EDI devices 21-1 and 20-2. The RO membrane devices 10-1 and 10-2 and the EDI devices 20-2 are the same as those in the first embodiment. The EDI device 21-1 is a general-purpose EDI device. Figure 3 The raw water is supplied to the RO membrane device 10 - 1 shown, and the supplied raw water is processed in the RO membrane device 10 - 1 , the RO membrane device 10 - 2 , and the EDI device 21 - 1 , and the EDI device 20 - 2 , respectively.

[0034] Figure 4 Yes means Figure 3 FIG. 2 is a diagram showing an example of the structure of the EDI device 21-1. Figure 4 As shown, Figure 3 The EDI device 21-1 shown is provided with: an anode chamber 101 filled with a cation exchange resin; a cathode chamber 102 filled with an anion exchange resin; a concentrating chamber 107 and a concentrating chamber 108 filled with an anion exchange resin; a first desalting chamber 105 filled with an anion exchange resin; and a second desalting chamber 109 filled with a cation exchange resin. The anode chamber 101 is adjacent to the concentrating chamber 107 via a cation exchange membrane 201. The concentrating chamber 107 is adjacent to the first desalting chamber 105 via an anion exchange membrane 202. The first desalting chamber 105 is adjacent to the second desalting chamber 109 via a cation exchange membrane 201. The second desalting chamber 109 is adjacent to the concentrating chamber 108 via a cation exchange membrane 201. The concentrating chamber 108 is adjacent to the cathode chamber 102 via an anion exchange membrane 202. It should be noted that cation exchange membrane 201 may not be provided between anode chamber 101 and concentration chamber 107, and anode chamber 101 may also serve as concentration chamber 107. Also, anion exchange membrane 202 may not be provided between cathode chamber 102 and concentration chamber 108, and cathode chamber 102 may also serve as concentration chamber 108.

[0035] Will Figure 3 The results of water flow operation in the above-mentioned classification A are shown in Table 3. The operating conditions of each device were the same as those in Example 1.

[0036] [Table 3]

[0037] As shown in Table 3, in the present method, in the EDI supply water area A of the RO treated water which is assumed to be treated by using an ultra-low pressure RO membrane device in a two-stage structure, by combining a general EDI device and a high-purity EDI device to perform water treatment, the boron concentration of ultrapure water can be reduced to the level (less than 50 ng / L) required by the IRDS (International Roadmap for Devices and Systems) which is a given benchmark.

[0038] (Example 3) Figure 5 1 is a diagram showing a third embodiment of the water treatment system of the present invention. Figure 5 As shown, the RO membrane device 10-1, the RO membrane device 10-2, the EDI device 20-1, and the boron selective resin 30 are connected in series. The RO membrane device 10-1, the RO membrane device 10-2, and the EDI device 20-1 are respectively the same as the devices in the first embodiment. The boron selective resin 30 is a device that selectively removes boron from the supplied liquid. The boron selective resin 30 has a functional group that specifically reacts with boron and can selectively remove boron. The boron selective resin 30 is not particularly limited as long as it can selectively adsorb boron. As the boron selective resin 30, an ion exchange resin into which a polyol group is introduced as a functional group is used. It is particularly preferred that the boron selective resin 30 is a resin having a functional group that has high selectivity for boron, namely, an N-methylglucosamine group. For example, as the boron selective resin 30, Amberlite IRA743 (manufactured by Dupont) and DIAION CRB03 (manufactured by Mitsubishi Chemical Corporation) can be listed. To Figure 5 The RO membrane device 10 - 1 shown is supplied with raw water, and the supplied raw water is processed in the RO membrane device 10 - 1 , the RO membrane device 10 - 2 , the EDI device 20 , and the boron selective resin 30 .

[0039] Will Figure 5 The results of water flow operation in the above-mentioned classification A are shown in Table 4. The operating conditions of each device were the same as those in Example 1.

[0040] [Table 4]

[0041] As shown in Table 4, in the present method, in the EDI supply water area A of the RO treated water which is assumed to be treated by using an ultra-low pressure RO membrane device in a two-stage structure, a first-stage high-purity EDI device is provided at its subsequent stage, and a boron selective resin is further provided at its subsequent stage to perform water treatment, thereby being able to reduce the boron concentration to the ultrapure water requirement level (less than 1 ng / L) of the most advanced semiconductor manufacturers.

[0042] (Example 4) Figure 6 1 is a diagram showing a fourth embodiment of the water treatment system of the present invention. Figure 6 As shown, the RO membrane device 11-1, the RO membrane device 10-2 and the EDI device 21-1, the EDI device 20-2 are connected in series. The RO membrane device 10-2 and the EDI device 20-2 are respectively the same as the devices in the first embodiment. The EDI device 21-1 is the same as the device in the second embodiment. The RO membrane device 11-1 is a device having an ultra-low pressure RO membrane. The RO membrane device 11-1 is, for example, an ultra-low pressure RO membrane (SG30LE-440i) manufactured by Dupont. Figure 6 The raw water is supplied to the RO membrane device 11 - 1 shown, and the supplied raw water is processed in the RO membrane device 11 - 1 , the RO membrane device 10 - 2 , and the EDI device 21 - 1 , and the EDI device 20 - 2 , respectively.

[0043] Will Figure 6 The results of water flow operation in the above-mentioned classification B are shown in Table 5. The operating conditions of each device were the same as those in Example 1.

[0044] [Table 5]

[0045] As shown in Table 5, in the present method, in the EDI supply water zone B of the RO treated water which is assumed to be subjected to two-stage treatment by combining an ultra-low pressure RO membrane device and an ultra-ultra-low pressure RO membrane device, by combining a general EDI device and a high-purity EDI device to perform water treatment, the boron concentration can be reduced to the ultrapure water requirement level (less than 1 ng / L) of the most advanced semiconductor manufacturers.

[0046] (Comparative Example 1) Figure 7 1 is a diagram showing a first comparison method for comparison with the above-mentioned embodiment. Figure 7 As shown, the RO membrane devices 10-1 and 10-2 are connected in series with the EDI devices 21-1 and 21-2. The RO membrane devices 10-1 and 10-2 are the same as those in the first embodiment. The EDI devices 21-1 and 21-2 are the same as those in the second embodiment. Figure 7 The raw water is supplied to the RO membrane device 10 - 1 shown, and the supplied raw water is processed in the RO membrane device 10 - 1 , the RO membrane device 10 - 2 , and the EDI device 21 - 1 , and the EDI device 21 - 2 , respectively.

[0047] Will Figure 7The results of water flow operation in the manner of the division A shown in Table 6 are shown. Here, three elements were arranged in parallel in each of the RO membrane device 10-1 and the RO membrane device 10-2, and water was flowed and operated so that the permeate flow rate of the RO membrane device 10-1 became 3.5 [m 3 / h], and the permeate flow rate of the RO membrane device 10-2 becomes 3.10 [m 3 / h]. In addition, the EDI device 21-1 and the EDI device 21-2 use Figure 4 The high-purity EDI stack shown in the figure has a basic structure of a concentrating chamber 107, a concentrating chamber 108, a first desalting chamber 105, and a second desalting chamber 109, and is stacked in 20 sets, and is operated under the following high flow rate and high current conditions. The EDI device 21-1 as the first EDI is operated under the following conditions: the flow rate (SV) per unit volume of the ion exchange resin in the first desalting chamber 105 or the second desalting chamber 109 is 440 [h -1 ], the current density becomes 1.0[A / dm 2 ], and the pressure difference of the desalination chamber becomes 0.22±0.02 [MPa]. In addition, the EDI device 21-2 as the second EDI is operated under the following conditions: the flow rate (SV) per unit volume of the ion exchange resin in the first desalination chamber 105 or the second desalination chamber 109 becomes 400 [h -1 ], the current density becomes 1.0[A / dm 2 ], and the pressure difference in the desalination chamber becomes 0.20±0.02[MPa].

[0048] [Table 6]

[0049] As shown in Table 6, in this comparison method, the boron concentration contained in the treated water in the last-stage EDI device 21-2 is 0.06 μg / L, and the boron cannot be fully removed from the raw water and cannot be reduced to the boron concentration level of ultrapure water required by the given standard (less than 50 ng / L).

[0050] (Comparative Example 2) Figure 8 is a diagram showing a second comparison method for comparison with the above-mentioned embodiment. Figure 8As shown, the RO membrane device 12-1 and the RO membrane device 11-2 are connected in series with the EDI device 21-1 and the EDI device 21-2. The RO membrane device 12-1 is a device having a low-pressure RO membrane. The RO membrane device 12-1 is, for example, CR100 manufactured by Dupont. The RO membrane device 11-2 is the same as the RO membrane device 11-1 in the fourth embodiment. The EDI device 21-1 and the EDI device 21-2 are the same as the EDI device 21-1 in the second embodiment. Figure 8 The RO membrane device 12-1 shown is supplied with raw water, and the supplied raw water is processed in the RO membrane device 12-1, the RO membrane device 11-2, and the EDI device 21-1, the EDI device 21-2. It should be noted that a predetermined amount of sodium hydroxide is added to the raw water supplied to the RO membrane device 12-1.

[0051] Will Figure 8 The results of water flow operation in the manner of the division C shown are shown in Table 7. Here, three elements were arranged in parallel in each of the RO membrane device 12-1 and the RO membrane device 11-2, and water was flowed and operated so that the permeate flow rate of the RO membrane device 12-1 became 3.5 [m 3 / h], and the permeate flow rate of the RO membrane device 11-2 becomes 3.10 [m 3 / h]. In addition, the EDI device 21-1 and the EDI device 21-2 use Figure 4 The high-purity EDI stack shown in the figure has a basic structure of a concentrating chamber 107, a concentrating chamber 108, a first desalting chamber 105, and a second desalting chamber 109, and is stacked in 20 sets, and is operated under the following high flow rate and high current conditions. The EDI device 21-1 as the first EDI is operated under the following conditions: the flow rate (SV) per unit volume of the ion exchange resin in the first desalting chamber 105 or the second desalting chamber 109 is 440 [h -1 ], the current density becomes 1.0[A / dm 2 ], and the pressure difference of the desalination chamber becomes 0.22±0.02 [MPa]. In addition, the EDI device 21-2 as the second EDI is operated under the following conditions: the flow rate (SV) per unit volume of the ion exchange resin in the first desalination chamber 105 or the second desalination chamber 109 becomes 400 [h -1 ], the current density becomes 1.0[A / dm 2 ], and the pressure difference in the desalination chamber becomes 0.20±0.02[MPa].

[0052] [Table 7]

[0053] As shown in Table 7, in this comparative method, even if the boron concentration is sufficiently reduced in the RO membrane device 12-1 and the RO membrane device 11-2, the boron concentration of the treated water in the water treatment in the two-stage structure of the EDI device 21-1 and the EDI device 21-2 in the subsequent stage is 0.04 μg / L, which can reach the level required by the IRDS as a given standard, but is higher than the level required by advanced semiconductor manufacturers, that is, 1 ng / L. In particular, it was confirmed that the boron removal rate was significantly reduced when the general EDI was used in the second-stage EDI device.

[0054] In the above-mentioned method, a supply pump for increasing the pressure of the supply water is used for the supply (liquid flow) of water to the RO membrane device and the EDI device. Based on the required power capacity of the supply pump calculated from the water flow pressure of the ultra-low pressure RO membrane, the ultra-low pressure RO membrane, and the low pressure RO membrane, and the operating current and operating voltage of the general EDI and the high purity EDI, the power consumption per unit processing flow rate is calculated, and the increase and decrease rates of each system are compared. In Table 8, the power consumption value in the second comparison method is set as the reference (set to an increase and decrease rate of 0), and the reduction rate of power consumption in each method is shown.

[0055] [Table 8]

[0056] As shown in Table 8, by using a device with an ultra-low pressure RO membrane as the RO membrane device, the operating power consumption of the RO-EDI can be reduced by about 25% to 35% based on the value in the second comparison method, compared with the device using a RO membrane with a low pressure membrane or an ultra-low pressure membrane. From the purpose of removing boron to a higher degree than general EDI, there is a tendency for high-purity EDI to consume more power than general EDI. On the other hand, by properly managing the operation of the RO membrane device, the concentration and hardness of silicon dioxide, which are the main causes of the voltage increase of the EDI device, are maintained at low values, and the power consumption of the high-purity EDI device can be suppressed to about 1.5 times the power consumption of the general EDI device. In addition, the power consumption reduction effect brought about by the use of an ultra-low pressure RO membrane can reduce the power consumption of the entire system.

[0057] Hereinafter, the arrangement of the supply pump in the water treatment system of the present invention will be described. Fig. 9 It is a diagram showing an example of arrangement of pumps in the water treatment system of the present invention. Fig. 9Three configuration examples of Case 1 to Case 3 are shown. The RO membrane device 10-1, RO membrane device 10-2 and EDI device 20-1, EDI device 20-2 in each case are respectively the same as the devices in the first embodiment. In Case 1, the first pump 40-1 is configured in the front stage of the RO membrane device 10-1. The second pump 40-2 is configured between the RO membrane device 10-2 and the EDI device 20-1. The third pump 40-3 is configured between the EDI device 20-1 and the EDI device 20-2. In Case 2, the first pump 40-1 is configured in the front stage of the RO membrane device 10-1. The second pump 40-2 is configured between the RO membrane device 10-1 and the RO membrane device 10-2. The third pump 40-3 is configured between the EDI device 20-1 and the EDI device 20-2. In Case 3, the first pump 40-1 is configured in the front stage of the RO membrane device 10-1. The second pump 40 - 2 is disposed between the EDI device 20 - 1 and the EDI device 20 - 2 .

[0058] In the above-mentioned embodiment, by using an RO membrane device having an ultra-low pressure RO membrane, the pressure difference of the RO membrane portion becomes small, and water can be passed through two or more components (RO membrane devices or EDI devices) arranged in series with each other using one pump. It should be noted that other components (tanks, ultraviolet irradiation devices, degassing membranes, etc.) may be arranged between the components.

[0059] Fig.10 Yes means Figure 3A diagram showing pressure values ​​at various points in the manner shown. Here, the first pump 40-1 is arranged at the front stage of the RO membrane device 10-1. The second pump 40-2 is arranged between the EDI device 21-1 and the EDI device 20-2. That is, one pump 40-1 is used to pass water from the RO membrane device 10-1 to the EDI device 21-1. The pump 40-2 increases the pressure of the treated water treated by the EDI device 21-1 and passes the water to the EDI device 20-2. In such a structure, the pressure value of the point between the pump 40-1 and the RO membrane device 10-1 is 1.2 [MPa]. In addition, the pressure value of the point between the RO membrane device 10-2 and the EDI device 21-1 is 0.34 [MPa]. In addition, the pressure value of the point between the EDI device 21-1 and the pump 40-2 is 0.14 [MPa]. In addition, the pressure value of the point between the pump 40-2 and the EDI device 20-2 is 0.28 [MPa]. In addition, the pressure value at the point after the EDI device 20-2 is 0.10 [MPa]. Since the EDI device increases the flow rate, the pressure difference of the EDI device 21-1 becomes 0.2 [MPa], and the pressure difference of the EDI device 20-2 becomes 0.18 [MPa]. However, it is possible to operate without providing a pump between the RO membrane device 10-2 and the EDI device 21-1, which is the front stage of the EDI device 21-1. It is also conceivable to arrange the pump 40 arranged between the EDI device 21-1 and the EDI device 20-2 between the RO membrane device 10-2 and the EDI device 21-1. However, if such an arrangement is made, the pressure difference of the EDI device 20-2 is added to the pressure difference of the EDI device 21-1, and the supply water pressure to the EDI device 21-1 needs to be increased. That is, the pump 40-2 will bear the supply water pressure to both the EDI device 21-1 and the EDI device 20-2, which becomes a large burden. The pressure resistance of the EDI device is lower than that of the RO membrane device. Therefore, the EDI device is preferably operated below 0.5 [MPa]. In order to set the supply water pressure to the EDI device 20-2 to Fig.10 The water supply pressure of the EDI device 21-1 needs to be at least 0.48 [MPa], which is 0.28 [MPa] shown in the figure. Therefore, it is not necessarily preferable if a certain degree of margin is taken into consideration.

[0060] Fig.11 FIG. 1 is a diagram showing another example of the structure of the high-purity EDI device used in the present invention. Figure 2 as well as Figure 4 Examples are given in Fig.11 Two other structural examples are shown in FIG. Fig.11In the structure shown on the upper side, there are provided: an anode chamber 101 filled with a cation exchange resin; a cathode chamber 102 filled with an anion exchange resin; concentration chambers 103 and 104, which are mixed beds filled with cation exchange resins and anion exchange resins; and a first desalination chamber 110, which is a mixed bed filled with cation exchange resins and anion exchange resins. The anode chamber 101 is adjacent to the concentration chamber 103 via a cation exchange membrane 201. The concentration chamber 103 is adjacent to the first desalination chamber 110 via an anion exchange membrane 202. The first desalination chamber 110 is adjacent to the concentration chamber 104 via a cation exchange membrane 201. The concentration chamber 104 is adjacent to the cathode chamber 102 via an anion exchange membrane 202. In Fig.11 In the structure shown on the lower side of , there are provided: an anode chamber 101 filled with a cation exchange resin; a cathode chamber 102 filled with an anion exchange resin; a concentrating chamber 111 and a concentrating chamber 112 filled with a cation exchange resin; and a first desalting chamber 110, which is a mixed bed filled with a cation exchange resin and an anion exchange resin. The anode chamber 101 is adjacent to the concentrating chamber 111 via a cation exchange membrane 201. The concentrating chamber 111 is adjacent to the first desalting chamber 110 via an anion exchange membrane 202. The first desalting chamber 110 is adjacent to the concentrating chamber 112 via a cation exchange membrane 201. The concentrating chamber 112 is adjacent to the cathode chamber 102 via an anion exchange membrane 202. In this way, regarding the high-purity EDI device, at least an anion exchange resin is filled in the most downstream layer of the desalting chamber, and at least a cation exchange resin is filled in the concentrating chamber adjacent to the cation exchange membrane that divides the desalting chamber. It should be noted that only anion exchange resin may be filled in the desalting chamber. In addition, as described in Example 1 and Example 2, multiple basic structures may be stacked. This can increase the amount of water that can be treated. Furthermore, the cation exchange membrane 201 located between the anode chamber 101 and the concentration chambers 103 and 111 may not be provided, and the anode chamber 101 may also serve as the concentration chamber 103 and 111. In addition, the anion exchange membrane 202 located between the cathode chamber 102 and the concentration chambers 104 and 112 may not be provided, and the cathode chamber 102 may also serve as the concentration chamber 104 and 112. It should be noted that Fig.11 The high flow rate condition of the EDI stack in the structure shown is that water is passed so that the flow rate (SV) per unit volume of the ion exchange resin in the desalination chamber 110 becomes 300 [h -1 ]~450[h -1 ].

[0061] The EDI device can continuously perform electrical regeneration by supplying direct current. Therefore, compared with other ion exchange resin devices, the EDI device has a faster flow rate (SV) per unit volume of resin, usually around 150 [h -1]~250[h -1 ], and the water pressure difference at this time is about 0.09 [MPa] to 0.15 [MPa]. Research has been conducted to increase the flow rate of such an EDI device, and an attempt has been made to operate at a flow rate 1.5 times higher than that of the existing device. As a result, the water pressure difference also becomes a value exceeding 1.5 times, and the result is that the pressure required to supply water to the EDI device also becomes higher. In addition, in the present invention, by adopting a device with an ultra-low pressure RO membrane, the pressure loss of the RO membrane device is reduced, and it is not necessary to set up a supply (boosting) pump and tank between all the devices constituting the system. In addition, by avoiding the addition of chemicals for adjusting the pH of the target water, it is possible to reduce chemical costs, chemical addition equipment, and management costs. Furthermore, the RO membrane device is operated so that the silica concentration and hardness in the permeated water of the RO membrane, which are the causes of the increase in the resistance of the EDI device, are below a certain concentration. Therefore, the current can be increased while suppressing the voltage increase of the EDI device, and a higher purity treated water can be obtained. In addition, by using an ultra-low pressure RO membrane device, power consumption can be greatly reduced. Thus, in the present invention, a water treatment system with low energy consumption and low management cost can be provided. Moreover, the boron removal rate can be increased without applying a large load.

[0062] As mentioned above, although the present invention has been described with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. The structure and details of the present invention can be modified in various ways that can be understood by those skilled in the art within the scope of the present invention.

[0063] This application claims the benefit of priority based on Japanese patent application No. 2022-138237, filed on August 31, 2022, the disclosure of which is incorporated herein in its entirety by reference.

Claims

1. A water treatment system for removing at least boron contained in treated water, the water treatment system comprising: An RO membrane device comprising an ultra-low pressure RO membrane; and The EDI device is arranged at the rear stage of the RO membrane device and includes a high-purity EDI stack, wherein the most downstream layer of the desalination chamber is filled with at least an anion exchange resin, and the concentration chamber adjacent to the desalination chamber is filled with at least a cation exchange resin via a cation exchange membrane, wherein the cation exchange membrane divides the desalination chamber. The RO membrane device is a two-stage RO membrane device, and the ultra-low pressure RO membrane is arranged in at least one of the first stage and the second stage.

2. The water treatment system according to claim 1, wherein: The EDI device is a two-stage EDI device, and the high-purity EDI stack is arranged in at least one of the first stage and the second stage.

3. The water treatment system according to claim 2, wherein: The water treatment system has a plurality of pumps, and the pumps are used to pass the treated water into the RO membrane device and the EDI device. At least one pump among the plurality of pumps is configured to supply the water to be treated to two or more devices among the RO membrane device and the EDI device that are arranged in series with each other.

4. The water treatment system according to any one of claims 1 to 3, wherein: The ultra-low pressure RO membrane is a membrane that has a salt removal rate of less than 99.4% under the conditions of a NaCl concentration of 500 mg / L to 2000 mg / L in the stock solution, a pH of 6 to 8, a water temperature of 25°C, and a permeate recovery rate of 10% to 25%, and a supply pressure of 1 MPa and a flow rate of 1 m 2 The permeate flow rate per unit pressure and per unit area of ​​the membrane is 1.3 (m 3 / d) / (m 2 ·MPa) or above.

5. A water treatment method for removing at least boron contained in the water to be treated, In the water treatment method, an RO membrane device that is provided at the front stage of the EDI device and includes an ultra-low pressure RO membrane device is operated so that the boron concentration of the treated water supplied to the EDI device including the high-purity EDI stack becomes 20μg / L to 100μg / L, the silica concentration becomes less than 50μg / L, and the hardness becomes less than 0.05mgCaCO3 / L.

6. The water treatment method according to claim 5, wherein: In the water treatment method, water is passed through the desalination chamber of the EDI device including the high-purity EDI stack so that the flow rate per unit volume of the ion exchange resin filled in the desalination chamber becomes 350 h -1 ~450h -1 .

7. The water treatment method according to claim 6, wherein: In the water treatment method, water is passed through the desalination chamber so that the water passing pressure difference becomes 0.18 MPa to 0.3 MPa.

8. The water treatment method according to any one of claims 5 to 7, wherein: In the water treatment method, the current density flowing through the EDI device including the high-purity EDI stack is 0.8 A / dm 2 ~1.2A / dm 2 of current.

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