Method for operating electrodeionization device

Abstract

Water to be treated (supplied water) (W4) having a pH of 8 or more is supplied to an electrodeionization device (8), and the water to be treated (W4) is supplied to a desalination chamber (25) of the electrodeionization device (8). Then, desalted water (W5) that has passed through the desalination chamber (25) is separated and supplied to the concentration chamber (26) in the opposite direction to the desalination chamber (25). As a result, even if the pH of the water to be treated (water supply) (W4) is 8 or more, the ion concentration in the water to be concentrated in the concentration chamber (26) is lower toward the extraction side of the desalination chamber (25). In particular, the movement of inorganic carbonate ions from the concentration chamber (26) near the outlet of the desalination chamber of the electrodeionization device (8) to the desalination chamber (25) can be reduced, and a decrease in the electrical resistivity of the desalted water (W5) can be prevented. According to this method for operating an electrodeionization device, it is possible to efficiently produce high-quality treated water even if water having a high pH is supplied to the electrodeionization device.

Description

Technical Field

[0001] The present invention relates to an operating method of an electrodeionization apparatus, and more particularly to an operating method of an electrodeionization apparatus capable of producing high-quality treated water even when water having a high pH is supplied to the electrodeionization apparatus. Background Art

[0002] Conventionally, ultrapure water used in the semiconductor and other electronics industries is produced by treating raw water using an ultrapure water production system consisting of a pretreatment system, a primary pure water production device, and a subsystem for treating the primary pure water (a secondary pure water production device).

[0003] For example, Figure 1 As shown, the ultrapure water production system 1 is composed of three stages: a pretreatment device 2, a primary pure water production device (pure water production device) 3, and a subsystem 4. In the pretreatment device 2 of the ultrapure water production system 1, pretreatment is performed on the raw water W through filtration, coagulation and sedimentation, and microfiltration membranes, mainly to remove suspended matter.

[0004] The primary pure water production device 3 includes a reverse osmosis membrane device 5 for treating pretreated water W1, an ultraviolet oxidation device 6, an electrodeionization device 8, and a water supply pump 7 for supplying water to the electrodeionization device 8. In the primary pure water production device 3, most electrolytes, particulates, and live bacteria in the pretreated water W1 are removed, and organic matter is decomposed to produce primary pure water (pure water) W2.

[0005] Furthermore, the subsystem 4 includes a sub-tank 10, a supply pump 11, an ultraviolet oxidation device 12, a non-regenerative mixed-bed ion exchange device 13, and an ultrafiltration membrane (UF membrane) 14. The sub-tank 10 is fed back from the ultrafiltration membrane (UF membrane) 14 via a water point 15. In this sub-system 4, trace amounts of organic matter (TOC (total organic carbon)) contained in the primary pure water W2 produced by the primary pure water production device 3 are oxidatively decomposed, and carbonate ions, organic acids, and anionic substances are removed. Furthermore, metal ions and cationic substances are removed. Finally, particulates are removed using the ultrafiltration (UF) membrane 14 to produce ultrapure water W3, which is then supplied to the water point 15. Unused ultrapure water W3 is then fed back to the sub-tank 10.

[0006] In the primary pure water production device 3 of the ultrapure water production system 1 as described above, with the purpose of improving the treatment performance such as reducing the concentration of boron in the reverse osmosis membrane device 5, alkali such as NaOH is injected into the feed water of the reverse osmosis membrane device to make the pH above 8, so as to promote the ionization of various components for treatment.

[0007] The electrodeionization device 8 used in such a primary pure water production device 3 is generally a device in which cation exchange membranes and anion exchange membranes are alternately arranged between the cathode and the anode, and these cation exchange membranes and anion exchange membranes form a region to form a desalting chamber and a concentrating chamber, and the desalting chamber and the concentrating chamber are filled with ion exchange resin. As ion exchange membranes such as cation exchange membranes and anion exchange membranes, in addition to heterogeneous membranes formed by adding a binder such as polystyrene to a powdered ion exchange resin, homogeneous membranes formed by polymerizing styrene-divinylbenzene, etc., membranes formed by graft polymerization of monomers having various anion exchange functions or cation exchange functions are also used.

[0008] The desalination chamber is filled with ion exchangers (anion exchangers and cation exchangers) composed of ion exchange resins, ion exchange fibers, or graft exchangers in a mixed or multi-layered manner. The concentration chamber, anode chamber, and cathode chamber are also filled with ion exchangers.

[0009] The electrodeionization device 8 is equipped with a water flow mechanism for introducing treated water (feed water) into the desalination chamber and removing treated water, and a concentrated water flow mechanism for introducing concentrated water into the concentrating chamber. Typically, the direction of introduction of treated water into the desalination chamber and the direction of introduction of concentrated water into the concentrating chamber are aligned.

[0010] Pure water production equipment (primary pure water production equipment within ultrapure water production equipment) using such electrodeionization devices typically uses water treated by a reverse osmosis membrane system as the electrodeionization device's feed water, or uses water treated by a reverse osmosis membrane system using an ultraviolet oxidation device as the feed water. Furthermore, to reduce boron concentration, alkali is added to the reverse osmosis membrane system's feed water to adjust the pH to 8 or higher. Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, when the pH of the feed water to the electrodeionization apparatus is high, the parallel flow of treated water in the desalination chamber and concentrated water in the concentration chamber may cause the resistivity of the treated water to decrease, that is, the quality of the treated water to deteriorate.

[0013] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for operating an electrodeionization apparatus capable of producing high-quality treated water even when feed water having a high pH is supplied to the electrodeionization apparatus.

[0014] Technical solutions to problems

[0015] To achieve the above-mentioned object, the present invention provides a method for operating an electrodeionization apparatus, wherein feed water having a pH of 8 or higher is passed into a desalination chamber of the electrodeionization apparatus, and treated water from the desalination chamber or feed water from the desalination chamber is passed into a concentrating chamber of the electrodeionization apparatus in a direction opposite to the desalination chamber (Invention 1). In particular, in the above-mentioned invention (Invention 1), the pH of the feed water to the electrodeionization apparatus is preferably between 8 and 11 (Invention 2).

[0016] According to the above inventions (Inventions 1 and 2), if water having a pH of 8 or above, particularly a pH of 8 to 11, is supplied to the electrodeionization apparatus, the quality of the treated water (desalted water) deteriorates. However, by supplying concentrated water to the electrodeionization apparatus or using treated water and setting the water flow direction in the desalination chamber and the concentration chamber to countercurrent (in opposite directions), the deterioration of the water quality (e.g., resistivity) of the treated water can be prevented.

[0017] In the above invention (Invention 2), the inorganic carbonic acid concentration of the feed water of the electrodeionization apparatus is preferably 1 mg / L or less in terms of CO 2 (Invention 3).

[0018] According to the above invention (Invention 3), by treating such supply water using an electrodeionization device, the migration of inorganic carbonate ions from the concentrating chamber near the outlet of the desalination chamber of the electrodeionization device to the desalination chamber can be reduced, thereby preventing a decrease in the resistivity of the treated water. Furthermore, any such supply water can be suitably used as concentrated water.

[0019] In the above invention (Invention 3), the feed water to the electrodeionization device is preferably permeate water of a reverse osmosis membrane (Invention 4).

[0020] According to the above invention (Invention 4), if the treated water with a pH of 8 to 11 is treated using a reverse osmosis membrane, the removal rate of weakly ionic impurities such as inorganic carbonate and boron is improved, so it can be preferably used not only as water supply to the desalination chamber of the electrodeionization device, but also as concentrated water supplied to the concentration chamber.

[0021] In the above inventions (Inventions 1 to 4), it is preferred that the concentrated water flowing into the concentration chamber of the electrodeionization device is switched to the treated water of the desalination chamber and the supply water of the desalination chamber according to the inorganic carbonate concentration of the supply water of the electrodeionization device (Invention 5).

[0022] In the above invention (Invention 5), when the inorganic carbonate concentration of the water supplied to the electrodeionization apparatus is low, the supply water is circulated as concentrated water. On the other hand, when the inorganic carbonate concentration of the water supplied to the electrodeionization apparatus is high, the treated water desalinated in the desalination chamber is circulated as concentrated water, thereby maintaining the water quality of the electrodeionization apparatus and efficiently producing deionized water even in terms of water usage.

[0023] Effects of the Invention

[0024] According to the operating method of the electrodeionization device of the present invention, by supplying water with a pH of 8 or above to the electrodeionization device, passing the supply water into the desalination chamber of the electrodeionization device, and passing the treated water of the desalination chamber or the supply water of the desalination chamber into the desalination chamber of the electrodeionization device in the opposite direction from the desalination chamber, it is possible to prevent the water quality of the electrodeionization device from deteriorating. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart showing an ultrapure water production system to which the operating method of the electrodeionization apparatus of the present invention can be applied.

[0026] Figure 2 This is a schematic diagram showing the flow of water in the desalting compartment and the concentrating compartment in the operating method of the electrodeionization apparatus according to the first embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram showing the flow of water in the desalting compartment and the concentrating compartment in the operating method of the electrodeionization apparatus according to the second embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram showing the flow of water in the desalting compartment and the concentrating compartment in the operating method of the electrodeionization apparatus according to the third embodiment of the present invention.

[0029] Figure 5 This is a graph showing the results of measuring the resistivity of treated water by the electrodeionization apparatus when the treated water in Example 1 was circulated in reverse.

[0030] Figure 6 This is a graph showing the results of measuring the resistivity of water treated by the electrodeionization apparatus when horizontally flowing water is supplied.

[0031] Figure 7 It is a graph showing the relationship between the concentration of inorganic carbonic acid and pH. DETAILED DESCRIPTION

[0032] [First embodiment]

[0033] Hereinafter, an operating method of the electrodeionization apparatus according to the first embodiment of the present invention will be described with reference to the accompanying drawings.

[0034] (Electrodeionization device)

[0035] Figure 2 The flow of water in the desalting chamber and the concentrating chamber of the electrodeionization device to which the operation method of this embodiment can be applied is shown. Figure 2 In the electrodeionization device 8, a plurality of anion exchange membranes 23 and cation exchange membranes 24 are alternately arranged between electrodes (anode 21 and cathode 22) to alternately form desalination chambers 25 and concentrating chambers 26, with anode chambers 27 and cathode chambers 28 formed on both sides. Ion exchangers (not shown) (anion exchangers and cation exchangers) composed of ion exchange resins, ion exchange fibers, or grafted exchangers, etc., are filled in a mixed or multi-layered manner in the desalination chambers 25. Ion exchangers are also filled in the concentrating chambers 26, anode chambers 27, and cathode chambers 28.

[0036] Furthermore, the electrodeionization device 8 is provided with a concentrating chamber water-flow mechanism (not shown) that draws treated water (feed water) W4 into the desalination chamber 25 to extract desalted water (treated water) W5, which is then separated and passed into the concentrating chamber 26. The desalted water W5 is introduced into the concentrating chamber 26 from the side closest to the desalination chamber 25 outlet for the desalted water W5 and discharged from the side closest to the inlet for the treated raw water (treated water W4) in the desalination chamber 25. In other words, the desalted water W5 is introduced into the concentrating chamber 26 in a direction opposite to the flow direction of the treated water W4 in the desalination chamber 25, and concentrated water W6 is discharged. Meanwhile, the treated water W4 flows as electrode water through the anode chamber 27 and the cathode chamber 28, and is discharged as anode discharge water W7 and cathode discharge water W8, respectively.

[0037] (Water supply to the electrodeionization device (treated water))

[0038] In this embodiment, Figure 2The electrodeionization device 8 shown is configured as a reverse osmosis membrane device for treating pre-processed water from a primary pure water system, and as a downstream device for an ultraviolet oxidation device, if required. The treated water (feed water) W4 supplied to the electrodeionization device 8 is then supplied to the reverse osmosis membrane device. In the reverse osmosis membrane device 8, alkali is added to reduce the boron concentration, so treated water with a pH of 8 or above is supplied to the electrodeionization device 8. If the pH of the feed water to the reverse osmosis membrane device is set above 11, the amount of chemicals used increases, not only increasing the cost of the chemicals but also failing to achieve a corresponding improvement in the effect, resulting in a decrease in cost-effectiveness. Therefore, it is preferably set to a pH of approximately 8 to 11. Furthermore, the inorganic carbonic acid concentration (IC) of the feed water W4 to the electrodeionization device is preferably 1 mg / L or less, as CO2. In addition to salts, the reverse osmosis membrane (RO) device also removes ionic and colloidal TOC (total organic carbon), and ionizes and removes carbon dioxide gas. Residual organic matter in the ultraviolet oxidation device 6 is then decomposed as required.

[0039] [Operation method of electrodeionization device]

[0040] Next, a method for operating the electrodeionization apparatus of this embodiment using the electrodeionization apparatus 8 having the above-described structure will be described.

[0041] First, water to be treated (feed water) W4 having a pH of 8 or higher is passed through the desalination chamber 25 of the electrodeionization device 8 to remove ionic impurities and the like.

[0042] Specifically, if Figure 2 As shown, treated water W4 is supplied to the desalination chamber 25 of the electrodeionization device 8. Then, desalted water W5 that has passed through the desalination chamber 25 is separated and supplied to the concentrating chamber 26 in the opposite direction from the concentrating chamber 25. In this manner, by passing a portion of the treated water W5 that has passed through the desalination chamber 25 as concentrated water into the concentrating chamber 26 using a countercurrent method in the opposite direction of the water flow through the desalination chamber 25, and then discharging concentrated water W6 from the concentrating chamber 26 to the outside of the system, the ion concentration in the concentrated water in the concentrating chamber 26 decreases as it approaches the outlet side of the desalination chamber 25. This suppresses diffusion from the concentrating chamber 26 into the desalination chamber 25, and maintains good water quality for the treated water W5. In particular, the migration of inorganic carbonate ions from the concentrating chamber 26 to the desalination chamber 25 near the outlet of the desalination chamber of the electrodeionization device 8 can be reduced, thereby preventing a decrease in the resistivity of the desalted water W5.

[0043] The operating method of the electrodeionization apparatus of the first embodiment as described above is particularly effective when the inorganic carbonate concentration (IC) of the feed water W4 of the electrodeionization apparatus exceeds 1 mg / L in terms of CO2, by separating the desalted water W5 and supplying it to the concentration chamber 26 in the opposite direction to the desalting chamber 25, thereby achieving excellent ion removal performance due to inorganic carbonate.

[0044] [Second embodiment]

[0045] Next, an operating method of an electrodeionization apparatus according to a second embodiment of the present invention will be described with reference to the accompanying drawings.

[0046] (Electrodeionization device)

[0047] Figure 3 FIG. 1 shows the flow of water in the desalting chamber and the concentrating chamber of the electrodeionization device to which the operation method of this embodiment can be applied. Figure 3 In the electrodeionization device 8, a plurality of anion exchange membranes 23 and cation exchange membranes 24 are alternately arranged between electrodes (anode 21 and cathode 22) to alternately form desalination chambers 25 and concentrating chambers 26, with anode chambers 27 and cathode chambers 28 formed on both sides. Ion exchangers (not shown) (anion exchangers and cation exchangers) composed of ion exchange resins, ion exchange fibers, or grafted exchangers, etc., are filled in a mixed or multi-layered manner in the desalination chambers 25. Ion exchangers are also filled in the concentrating chambers 26, anode chambers 27, and cathode chambers 28.

[0048] Furthermore, the electrodeionization device 8 is provided with a concentrating chamber water supply mechanism (not shown) that passes treated water (supply water) W4 into the desalination chamber 25 to extract desalted water (treated water) W5, and then passes treated water (supply water) W4 into the concentrating chamber 26, supplying treated water (supply water) W4 to the concentrating chamber 26 in a direction opposite to the desalination chamber 25, and discharging concentrated water W6 from the side of the desalination chamber 25 proximal to the outlet of the treated raw water (treated water W4). In other words, the treated water (supply water) W4 is passed in a direction opposite to the flow direction of the treated water W4 in the desalination chamber 25 to discharge concentrated water W6. Meanwhile, the treated water W4 is configured to flow as electrode water into the anode chamber 27 and the cathode chamber 28, and is discharged as anode discharge water W7 and cathode discharge water W5, respectively.

[0049] (Water supply to the electrodeionization device (treated water))

[0050] In this embodiment, the same water as that in the first embodiment can be used as the feed water (water to be treated) for the electrodeionization apparatus.

[0051] [Operation method of electrodeionization device]

[0052] Next, a method for operating the electrodeionization apparatus of this embodiment using the electrodeionization apparatus 8 having the above-described configuration will be described.

[0053] First, water to be treated (feed water) W4 having a pH of 8 or higher is passed through the desalination chamber 25 of the electrodeionization device 8 to remove ionic impurities and the like.

[0054] Specifically, if Figure 3 As shown, treated water W4 is supplied to the desalination chamber 25 of the electrodeionization device 8. On the other hand, treated water W4 is also supplied to the concentration chamber 26 in the opposite direction to the desalination chamber 25. In this way, by using the convection-through method to pass the treated water W4 as concentrated water in the direction opposite to the water flow direction of the desalination chamber 25, and discharging the concentrated water W6 from the concentration chamber 26 to the outside of the system, even if the pH of the treated water (feed water) W4 is 8 or above, the ion concentration in the concentrated water in the concentration chamber 26 decreases as it approaches the extraction side of the desalination chamber 25. Therefore, the diffusion from the concentration chamber 26 to the desalination chamber 25 can be suppressed, and the water quality of the treated water W5 can be maintained at a good level. In particular, the movement of inorganic carbonate ions from the concentration chamber 26 near the outlet of the desalination chamber of the electrodeionization device 8 to the desalination chamber 25 can be reduced, and the resistivity of the desalted water W5 can be prevented from decreasing.

[0055] The operating method of the electrodeionization apparatus of the second embodiment as described above is particularly effective when the inorganic carbonate concentration (IC) of the feed water W4 of the electrodeionization apparatus is less than 1 mg / L in terms of CO2, since the treated water W4 is supplied to the concentration chamber 26 in the opposite direction to the desalination chamber 25.

[0056] [Third embodiment]

[0057] Next, an operating method of an electrodeionization apparatus according to a third embodiment of the present invention will be described with reference to the drawings.

[0058] (Electrodeionization device)

[0059] Figure 4 The flow of water in the desalting chamber and the concentrating chamber of the electrodeionization device to which the operation method of this embodiment can be applied is shown. Figure 4In the electrodeionization device 8, a plurality of anion exchange membranes 23 and cation exchange membranes 24 are alternately arranged between electrodes (anode 21 and cathode 22) to alternately form desalination chambers 25 and concentrating chambers 26, with anode chambers 27 and cathode chambers 28 formed on both sides. Ion exchangers (not shown) (anion exchangers and cation exchangers) composed of ion exchange resins, ion exchange fibers, or grafted exchangers, etc., are filled in a mixed or multi-layered manner in the desalination chambers 25. Ion exchangers are also filled in the concentrating chambers 26, anode chambers 27, and cathode chambers 28.

[0060] Furthermore, the electrodeionization apparatus 8 is provided with a concentrating chamber water supply mechanism (not shown). This concentrating chamber water supply mechanism (not shown) allows treated water (feed water) W4 to flow into the desalination chamber 25, extracts desalted water (treated water) W5, and then distributes this desalted water W5 to the concentrating chamber 26. A switching mechanism (not shown) allows switching between introducing the desalted water W5 into the concentrating chamber 26 from the side of the desalination chamber 25 closest to the outlet for the desalted water W5 and introducing the treated water (feed water) W4 into the concentrating chamber 26 from the side closest to the outlet for the desalted water W5. Furthermore, a mechanism (not shown) for measuring the inorganic carbonate concentration (IC) of the treated water (feed water) W4 (including an analogy mechanism) is provided. Based on the measurement result of the inorganic carbonate concentration (IC) measurement mechanism, switching can be made between introducing the desalted water W5 into the concentrating chamber 26 and introducing the treated water (feed water) W4 into the concentrating chamber 26.

[0061] (Water supply to the electrodeionization device (treated water))

[0062] In this embodiment, the same water as that in the first embodiment can be used as the feed water (water to be treated) for the electrodeionization apparatus.

[0063] [Operation method of electrodeionization device]

[0064] Next, a method for operating the electrodeionization apparatus of this embodiment using the electrodeionization apparatus 8 having the above-described structure will be described.

[0065] First, water to be treated (feed water) W4 having a pH of 8 or higher is passed through the desalination chamber 25 of the electrodeionization device 8 to remove ionic impurities and the like.

[0066] Specifically, if Figure 4As shown, treated water W4 is supplied to the desalination chamber 25 of the electrodeionization device 8. Meanwhile, based on the measurement results of the inorganic carbonate concentration (IC) measuring mechanism (not shown), the desalted water W5 or the treated water (feed water) W4 is switched to be introduced into the concentrating chamber 26, and the desalted water W5 or treated water W4 is supplied to the concentrating chamber 26 in the opposite direction to the desalination chamber 25. In this way, by passing the treated water W5 into the concentrating chamber 26 in a countercurrent manner in the direction opposite to the water flow direction of the desalination chamber 25 and discharging the concentrated water W6 from the concentrating chamber 26 to the outside of the system, even if the pH of the treated water (feed water) W4 is 8 or higher, the ion concentration in the concentrated water in the concentrating chamber 26 decreases as it approaches the outlet side of the desalination chamber 25. Therefore, diffusion from the concentrating chamber 26 to the desalination chamber 25 can be suppressed, and the water quality of the treated water W5 can be maintained at a good level. In particular, the migration of inorganic carbonate ions from the concentrating chamber 26 to the desalting chamber 25 near the outlet of the desalting chamber of the electrodeionization device 8 can be reduced, and a decrease in the resistivity of the desalted water W5 can be prevented.

[0067] The operating method of the electrodeionization device of the third embodiment as described above maintains the water quality of the desalted water W5 and improves the utilization rate of the desalted water W5 by switching to introduce the desalted water W5 into the concentration chamber 26 or the treated water (supply water) W4 into the concentration chamber 26 according to the inorganic carbonate concentration (IC) of the supply water W4 of the electrodeionization device.

[0068] While the operating method of the electrodeionization device of the present invention has been described above with reference to the accompanying drawings, the present invention is not limited to the aforementioned embodiment and can be implemented with various modifications. For example, in the aforementioned embodiment, treated water from a reverse osmosis membrane device is used as the feed water to the electrodeionization device. However, this is not limiting as long as the pH of the feed water to the electrodeionization device is at least 8.

[0069] Example

[0070] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples.

[0071] [Example 1]

[0072] by Figure 2 The structure shown in the figure prepared a test electrodeionization device 8 with the number of units shown in Table 1. The feed water (treated water) W4 shown in Table 3 was passed into the desalination chamber 25 under the water flow conditions shown in Table 2. The treated water W5 was separated and supplied to the concentration chamber 26 in the opposite direction to the desalination chamber 25 (treated water countercurrent), and the electrodeionization device 8 was set to constant current operation. Then, NaOH was added to the feed water (treated water) W4, and the resistivity of the treated water W5 after adjusting it to pH 10.5 was measured. The results are shown in Figure 5 .

[0073] [Table 1] Structure of electrodeionization device

[0074] Components Number of units Desalination chamber 1 Concentration Room 2 Electrode chamber (anode) 1 Electrode chamber (cathode) 1

[0075] [Table 2] Water flow conditions

[0076] Desalination chamber flow 200mL / min Concentration chamber flow 30mL / min Electrode chamber flow 50mL / min Current value 0.85A Water supply method Treating water backflow

[0077] [Table 3] Water supply conditions

[0078] Added ingredients concentration <![CDATA[B(OH)3]]> 10 μg / L in terms of B <![CDATA[Na2SiO3·9H2O]]> <![CDATA[100 μg / L in terms of SiO2]]> <![CDATA[CaCl2·2H2O]]> Calculated as Ca: 10 μg / L <![CDATA[MgCl2·6H2O]]> 10 μg / L in terms of Mg <![CDATA[NaHCO3]]> 270 μg / L in terms of C

[0079] like Figure 5 As clearly shown, even after NaOH was added to feed water (treated water) W4 to adjust the pH to 10.5, the resistivity of treated water W5 in electrodeionization device 8 remained almost unchanged. This is presumably because by passing treated water W5 through concentrating chamber 26, ion diffusion from concentrating chamber 26 to desalting chamber 25 was prevented, thereby maintaining water quality and preventing a decrease in the resistivity of the treated water.

[0080] [Comparative Example 1]

[0081] by Figure 2 The structure shown was prepared as shown in Table 1. The water supply (treated water) W4 shown in Table 3 was changed to be supplied to the desalination chamber 25 and the concentration chamber 26 in the same direction (parallel flow water supply) under the water flow conditions shown in Table 4. The electrodeionization device 8 was operated at a constant current. Then, NaOH was added to the water supply (treated water) W4, and the resistivity of the treated water W5 after adjusting the pH to 10.5 was measured. The results are shown in Figure 6 .

[0082] [Table 4] Water flow conditions

[0083] Desalination chamber flow 200mL / min Concentration chamber flow 30mL / min Electrode chamber flow 50mL / min Current value 0.85A Water supply method Parallel flow water supply

[0084] like Figure 6 As clearly shown, after adding NaOH to feed water (treated water) W4 and adjusting the pH to 10.5, the resistivity of treated water W5 in electrodeionization device 8 dropped significantly. This is believed to be due to the increase in the ion concentration in concentrating chamber 26, which led to the diffusion of ions from concentrating chamber 26 to desalting chamber 25.

[0085] [Reference Example 1]

[0086] by Figure 2A test electrodeionization apparatus 8 with the number of units shown in Table 5 was prepared. The feed water (treated water) W4 shown in Table 7 was changed to be supplied to the desalination chamber 25 and the concentrating chamber 26 in the same direction (parallel flow) under the water flow conditions shown in Table 6. The electrodeionization apparatus 8 was then operated at a constant current. NaOH was then added to the feed water (treated water) W4, and the resistivity, boron concentration, sodium concentration, and chloride ion concentration of the treated water W5, adjusted to a pH of 10.5, were measured. The results are shown in Table 8.

[0087] [Reference Example 2]

[0088] In Reference Example 1, NaOH was added instead of NaOH to equalize the Na feed water concentration in Reference Example 1 and adjust the pH to approximately 7. Electrodeionization apparatus 8 was operated at a constant current in the same manner. NaOH was then added to feed water (treated water) W4, and the resistivity, boron concentration, sodium concentration, and chloride ion concentration of treated water W5, adjusted to a pH of 10.5, were measured. The results are shown in Table 8.

[0089] [Table 5] Structure of electrodeionization device

[0090] Components Number of units Desalination chamber 2 Concentration Room 3 Electrode chamber (anode) 1 Electrode chamber (cathode) 1

[0091] [Table 6] Water flow conditions

[0092] Desalination chamber flow 400mL / min Concentration chamber flow 45mL / min Electrode chamber flow 50mL / min Current value 0.85A Water supply method Parallel flow water supply

[0093] [Table 7] Water supply conditions

[0094] Added ingredients concentration <![CDATA[B(OH)3]]> 10 μg / L in terms of B <![CDATA[Na2SiO3·9H2O]]> <![CDATA[100 μg / L in terms of SiO2]]> <![CDATA[NaHCO3]]> 135 μg / L in terms of C

[0095] [Table 8]

[0096] Measurement items Reference Example 1 Reference Example 2 Resistivity [MΩ·cm] 10.5 17.3 Boron concentration [μg / L] Less than 0.5 Less than 0.5 Sodium concentration [μg / L] Less than 0.1 0.2 Chloride ion concentration [μg / L] Less than 0.1 0.3

[0097] As shown in Table 8, if the reference example 1 with high pH and the reference example 2 with the same Na load as the reference example 1 are compared, the side of the treated water W5 of reference example 1 shows low resistivity. On the other hand, if the ion analysis result of treated water W5 is compared between reference example 1 and reference example 2, the boron concentration is the same, and for Na ions and Cl ions, the side of reference example 1 shows a low value. Therefore, for reference example 1, the ion that makes the resistivity of treated water W5 decline can be inferred to be derived from by NaHCO3 caused inorganic carbonic acid. Thus, when the pH of water supply W4 is high, inorganic carbonate ions are considered to be ions that are easily moved from the concentrating chamber to the desalting chamber near the desalting chamber outlet. Therefore, it can be said that when the pH of water supply W4 is high, in order to keep the water quality of the treated water W5 of electrodeionization device 8, it is effective to maintain the low inorganic carbonate ion concentration of water supply W4.

[0098] [Example 2]

[0099] The pH of the feed water to the reverse osmosis membrane device was varied, and the change in the removal rate of inorganic carbonic acid (IC) associated with this change was confirmed. ES-20-D4 (manufactured by Nitto Denko Corporation) was used as the reverse osmosis membrane device. Operation was adjusted to a feed water pressure of 0.75 MPa and a concentrated water flow rate of 1.0 m 3 / h. Under the water supply conditions shown in Table 9, the removal rate of inorganic carbonate ions when the pH was changed was confirmed. The results are shown in Figure 7 , and the removal rate of inorganic carbonate ions in the pH range of 7.5 to 9.5 of the feed water of the reverse osmosis membrane device is shown in Table 10.

[0100] [Table 9] Water supply conditions

[0101] Added ingredients concentration <![CDATA[CaCl2·2H2O]]> Calculated as Ca: 200 μg / L <![CDATA[NH4F]]> 50 μg / L in terms of F <![CDATA[NaNO3]]> <![CDATA[100 μg / L as NO3]]> <![CDATA[Na2SiO3·9H2O]]> <![CDATA[50 μg / L in terms of SiO2]]> <![CDATA[B(OH)3]]> 10 μg / L in terms of B <![CDATA[NaHCO3]]> 2000 μg / L in terms of C

[0102] [Table 10]

[0103] Water supply pH Removal rate 7.5 93.6％ 8.5 98.7％ 9.5 99.6％

[0104] like Figure 7 As shown in Table 10, the removal rate of inorganic carbonic acid using the reverse osmosis membrane device is correlated with the presence ratio of each ion. － or CO2 － The presence rate of HCO3 increases, and the removal rate of inorganic carbonic acid in the reverse osmosis membrane device increases. In addition, by adjusting the pH of the feed water of the reverse osmosis membrane device to above 8.0, the removal rate of inorganic carbonic acid in the reverse osmosis membrane device increases. － or CO3 2－The presence rate of increases, thereby improving the removal rate of inorganic carbonic acid in reverse osmosis membrane treatment. If the pH of the feed water of the reverse osmosis membrane device is adjusted to 11 or above, the amount of chemicals used and the cost of chemicals increase, thereby reducing the cost-effectiveness of contributing to the improvement of the water quality of the treated water. It is preferably adjusted to a pH of about 8 to 11.

[0105] Description of Reference Numerals

[0106] 1: Ultrapure water production system.

[0107] 2: Pre-processing device.

[0108] 3: Primary pure water production device (pure water production device).

[0109] 4: Subsystem.

[0110] 5: Reverse osmosis membrane device.

[0111] 6: Ultraviolet oxidation device.

[0112] 7: Water supply pump.

[0113] 8: Electrodeionization device.

[0114] 10: Auxiliary tank.

[0115] 11: Supply pump.

[0116] 12: Ultraviolet oxidation device.

[0117] 13: Non-regenerative mixed bed ion exchange unit.

[0118] 14: Ultrafiltration membrane (UF membrane).

[0119] 15: Use water.

[0120] 21: Anode (electrode).

[0121] 22: cathode (electrode).

[0122] 23: Anion exchange membrane.

[0123] 24: Cation exchange membrane.

[0124] 25: Desalination chamber.

[0125] 26: Concentration room.

[0126] 27: Anode chamber.

[0127] 28: cathode chamber.

[0128] W: raw water.

[0129] W1: pre-treated water.

[0130] W2: Primary pure water (pure water). W3: Ultrapure water.

[0131] W4: Processed water (supply water). W5: Desalinated water (processed water). W6: Concentrated water.

[0132] W7: Anode discharge water.

[0133] W8: Cathode discharges water.

Claims

1. A method for operating an electrodeionization device, wherein: Feed water with a pH of 8 or higher is passed into the desalination chamber of the electrodeionization device, and treated water or feed water of the desalination chamber is passed into the concentration chamber of the electrodeionization device in the opposite direction to the desalination chamber.

2. The method for operating the electrodeionization device according to claim 1, wherein: The pH of the water supplied to the electrodeionization device is 8-11.

3. The method for operating the electrodeionization device according to claim 2, wherein: The inorganic carbonic acid concentration of the water supplied to the electrodeionization device is 1 mg / L or less in terms of CO2.

4. The method for operating the electrodeionization device according to claim 3, wherein: The water supplied to the electrodeionization device is the permeate water of the reverse osmosis membrane.

5. The method for operating an electrodeionization device according to any one of claims 1 to 4, wherein: The concentrated water flowing into the concentration chamber of the electrodeionization device is switched to the treated water of the desalination chamber and the supply water of the desalination chamber according to the inorganic carbonate concentration of the supply water of the electrodeionization device.

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