Electrical deionized water production device and operation method thereof

Abstract

To greatly shorten a time from an operation start to when water quality of treated water reaches a predetermined level, in an EDI device (electrical deionized water production device), while attaining effective utilization of a water resource.SOLUTION: An EDI device includes: a positive electrode 11 and a negative electrode 12; and a demineralization chamber 23 which is disposed between the positive electrode 11 and the negative electrode 12 and is packed with an ion exchanger and through which water to be treated is passed and from which treated water is discharged. In an operation of the EDI device, at first, circulation operation is performed which circulates the treated water toward an inlet of the demineralization chamber 23 to supply it to the demineralization chamber 23 in a state of a direct current being applied between the positive electrode 11 and the negative electrode 12. The value of the applied direct current is changed (is risen, for example) during a time period when the circulation operation is performed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electrodeionization water production apparatus that performs a desalination process on water to be treated to produce deionized water, and to an operating method thereof. [Background technology]

[0002] In order to remove ion components contained in the water to be treated and produce pure water or deionized water, a deionized water production system is known in which the water to be treated is passed through an ion exchanger such as an ion exchange resin to cause an ion exchange reaction, thereby removing ion components from the water to be treated. However, in such a system, as the water to be treated continues to pass through the ion exchanger, the ion exchange groups of the ion exchanger are saturated and the deionization performance is reduced. Therefore, it is necessary to perform a process to restore the deionization performance of the ion exchanger. As a method for restoring the deionization performance of the ion exchanger, in addition to a method of replacing the ion exchanger itself, a method of regenerating the ion exchanger using a chemical such as an acid or alkali is known. The method of regenerating the ion exchanger using a chemical has the problems that the cost is high because of the use of the chemical, and the desalination treatment of the water to be treated cannot be performed during regeneration.

[0003] As a deionized water production system capable of desalination of water to be treated and regenerating ion exchangers at the same time, there is an electrodeionization water production apparatus that produces deionized water from water to be treated by combining electrophoresis and electrodialysis. The electrodeionization water production apparatus is called an EDI (Electrodeionization) apparatus, and is provided with a desalting compartment between an anode and a cathode, which is partitioned by a pair of ion exchange membranes and filled with an ion exchanger, a first concentrating compartment arranged on the side of the desalting compartment facing the anode, and a second concentrating compartment arranged on the side facing the cathode. The ion exchange membrane that partitions the first concentrating compartment from the desalting compartment is an anion exchange membrane, and the ion exchange membrane that partitions the second concentrating compartment from the desalting compartment is a cation exchange membrane. In the EDI apparatus, when the water to be treated is passed through the desalting compartment with a direct current applied between the anode and the cathode, the ion components in the water to be treated are adsorbed to the ion exchanger, and at the same time, hydrogen ions (H + ) and hydroxide ion (OH - ) to regenerate the ion exchanger. As a result, deionized water is discharged from the desalting compartment as treated water. Anions desorbed from the ion exchanger by regeneration of the ion exchanger move through the anion exchange membrane to the first concentrating compartment and are discharged from the first concentrating compartment, and similarly, desorbed cations move through the cation exchange membrane to the second concentrating compartment and are discharged from the second concentrating compartment. The EDI device has the advantage of being able to perform a continuous desalting process on the water to be treated without the need for a process to regenerate the ion exchange resin with a chemical.

[0004] In the EDI device, deionized water can be generated instantly by passing the water to be treated through the desalting chamber and applying a direct current. However, when the EDI device starts operating, the impurity concentration in the treated water generated as deionized water tends to be high due to contamination during the manufacturing of the device and the influence of elution from the internal parts during the period when the device is not in operation. Specifically, in the early stage of the EDI device operation, treated water containing a lot of ionic impurities, having a low resistivity, and a high total organic carbon (TOC (Total Organic Carbon)) concentration tends to be generated. When the treated water is supplied as deionized water to a device installed in the subsequent stage of the EDI device, it is necessary to perform a trial run for, for example, about 1 to 2 days in the early stage of the operation of the EDI device, depending on the size of the EDI device, so that the treated water generated during the trial run is not supplied to the subsequent device. The treated water generated during the trial run is usually discarded as wastewater as it is, so it is not preferable to perform a trial run for a long time from the viewpoint of effective use of water resources.

[0005] In an EDI device in operation, the ion exchanger is regenerated in the desalting compartment, but if the operation of the EDI device is continued for a long period of time, the regeneration of the ion exchanger cannot keep up and the amount of impurity ions adsorbed to the ion exchanger increases, which can result in a decrease in the resistivity of the generated treated water and an increase in the applied voltage value required to pass a specified direct current in the EDI device. Patent Document 1 discloses that when the EDI device is operated by applying a direct current between the anode and cathode, carbon dioxide is added to the treated water discharged from the desalting compartment, and the treated water with added carbon dioxide is passed through the desalting compartment again to remove the impurity ions adsorbed to the ion exchanger in the desalting compartment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-129861 A Summary of the Invention [Problem to be solved by the invention]

[0007] The method described in Patent Document 1 can be performed in place of a trial run at the beginning of operation of the EDI device, but high-purity carbon dioxide is required to reduce the impurity concentration in the treated water generated as deionized water, and the method cannot be performed in places where such carbon dioxide is not available. Furthermore, even if the method described in Patent Document 1 is performed, the time required for the quality of the treated water to stabilize is not significantly reduced compared to a typical trial run in which the generated treated water is not returned to the desalting chamber.

[0008] An object of the present invention is to provide an EDI device and an operating method thereof that can significantly shorten the time from the start of operation until the quality of treated water reaches a predetermined level while achieving effective utilization of water resources. [Means for solving the problem]

[0009] The inventors have discovered that, when starting the operation of an EDI device (electrodeionized water production device), a circulation operation is performed in which the treated water discharged from the desalting compartment is returned to the inlet of the desalting compartment before being supplied to the place of use, and that by changing, for example increasing, the value of the direct current applied between the anode and cathode during the circulation operation, the quality of the treated water improves within a short period of time after the start of operation, and have completed the present invention. Therefore, the EDI device of the present invention comprises an anode and a cathode, a desalting compartment arranged between the anode and the cathode, partitioned by a first ion exchange membrane provided on the side facing the anode and a second ion exchange membrane provided on the side facing the cathode, filled with an ion exchanger, supplied with water to be treated and discharging the treated water, a power supply device for applying a direct current between the anode and the cathode, switching means connected to the outlet of the desalting compartment into which the treated water flows and for switching the destination to discharge the treated water, a first pipe for returning the treated water discharged from the switching means to the inlet of the desalting compartment, a second pipe for discharging the treated water discharged from the switching means to the outside of the EDI device, and control means capable of controlling the power supply device and the switching means so that the EDI device operates by circulation operation in which the treated water is returned to the inlet of the desalting compartment via the first pipe and supplied to the desalting compartment. The control means controls the power supply device to execute current value change control for changing the value of the direct current during the period in which the EDI device is operating by circulation operation.

[0010] The method for operating an EDI device of the present invention includes an anode and a cathode, and a desalting compartment arranged between the anode and the cathode, partitioned by a first ion exchange membrane provided on the side facing the anode and a second ion exchange membrane provided on the side facing the cathode, filled with an ion exchanger, through which water to be treated is passed and through which treated water is discharged, and performs a circulation operation in which a direct current is applied between the anode and the cathode and the treated water is returned to the inlet of the desalting compartment to be supplied to the desalting compartment, and performs current value change control to change the value of the direct current during the period in which the circulation operation is performed. Effect of the Invention

[0011] According to the present invention, in an EDI device, it is possible to effectively utilize water resources and to significantly shorten the time from the start of operation until the quality of treated water reaches a predetermined level. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a configuration of an EDI device according to an embodiment of the present invention. [Diagram 2] 1 is a flowchart illustrating a method of operating the EDI device. [Diagram 3] 10 is a flowchart illustrating another method of operating the EDI device. [Figure 4] FIG. 13 is a diagram illustrating another example of the configuration of an EDI device. [Diagram 5] 13A is a graph showing the results of Example 1, and FIG. 13B is a graph showing the results of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows an EDI device according to an embodiment of the present invention. In Fig. 1 and Fig. 4, the pipes through which the liquid flows are shown by solid lines, and the wiring used for power supply and signal transmission is shown by dashed lines.

[0014] The EDI device shown in Fig. 1 uses water supplied from outside the EDI device as the water to be treated and performs a desalination process on the water to be treated to generate treated water, which is deionized water. The EDI device includes an anode chamber 21 in which an anode 11 is disposed, a cathode chamber 25 in which a cathode 12 is disposed, and a desalination chamber 23 disposed between the anode 11 and the cathode 12. A concentration chamber 22 is provided between the anode chamber 21 and the desalination chamber 23, and the anode chamber 21 and the concentration chamber 22 are partitioned by a cation exchange membrane 31, and the concentration chamber 22 and the desalination chamber 23 are partitioned by an anion exchange membrane 32. Similarly, a concentration chamber 24 is provided between the desalination chamber 23 and the cathode chamber 25, and the desalination chamber 23 and the concentration chamber 24 are partitioned by a cation exchange membrane 33, and the concentration chamber 24 and the cathode chamber 25 are partitioned by an anion exchange membrane 34. In the end, the desalting chamber 23 is disposed between the anode 11 and the cathode 12 and is partitioned by an anion exchange membrane 32, which is an ion exchange membrane, provided on the side facing the anode 11, and a cation exchange membrane 32, which is an ion exchange membrane, provided on the side facing the cathode 12.

[0015] The deionization compartment 23 is filled with an ion exchanger such as an ion exchange resin. As an example, the deionization compartment 23 is filled with a mixture of anion exchange resin and cation exchange resin, i.e., a mixed bed. In order to lower the operating voltage of the EDI device, it is preferable to also fill the anode compartment 21, the concentration compartments 22 and 24, and the cathode compartment 25 with ion exchangers. For example, the anode compartment 21 is filled with a cation exchange resin, the cathode compartment 25 is filled with an anion exchange resin, and the concentration compartments 22 and 24 are also filled with anion exchange resin.

[0016] In the EDI device, it is also possible to arrange a plurality of deionization compartments 23 between the anode 11 and the cathode 12. In this case, a repeating unit consisting of an anion exchange membrane 32, a deionization compartment 23, a cation exchange membrane 33, and a concentration compartment 24 may be arranged between the anion exchange membrane 34 that divides the concentration compartment 22 adjacent to the anode compartment 21 and the cathode compartment 25. In addition, the cation exchange membrane 31 that divides the anode compartment 21 and the concentration compartment 22 adjacent to the anode compartment 21 may be removed, and the anode compartment 21 and the concentration compartment 22 may be configured as one chamber. In that case, this chamber is a concentration chamber having the function of an anode chamber. Similarly, the anion exchange membrane 34 that divides the cathode compartment 25 and the concentration compartment 24 adjacent to the cathode chamber 25 may be removed, and the cathode compartment 25 and the concentration compartment 24 may be configured as one chamber. In that case, this chamber is a concentration chamber having the function of a cathode chamber.

[0017] Feed water is supplied to the EDI device from the outside, and this feed water is temporarily stored in the tank 10 via a feed water pipe 40. An inlet pipe 41 is provided connecting the outlet of the tank 10 and the inlet of the desalting chamber 23, and a pump 15 is provided on the inlet pipe 41. The feed water in the tank 10 is supplied to the desalting chamber 23 as water to be treated by the pump 15. One end of an outlet pipe 42 is connected to the outlet of the desalting chamber 23, and the other end of the outlet pipe 42 is connected to the inlet of a three-way valve 43 serving as a switching means. One end of a circulation pipe 44 is connected to one outlet of the three-way valve 43, i.e., the first outlet, and the other end of the circulation pipe 44 is connected to the tank 10. The circulation pipe 44 is a pipe for returning the outlet water of the desalting chamber 23, i.e., the treated water discharged from the desalting chamber 23, toward the inlet of the desalting chamber 23, and the treated water that has passed through the circulation pipe 44 merges with the feed water in the tank 10. The other outlet of the three-way valve 43, i.e., the second outlet, is connected to a treated water pipe 45 for discharging the treated water outside the EDI device. Outside the EDI device, the treated water pipe 45 may be branched and connected to a pipe for supplying the treated water to a place where the treated water is used and a drain line. In this case, when the impurity concentration in the treated water is high, such as during initial operation described below, the treated water is allowed to flow into the drain line, and during normal operation when the impurity concentration in the treated water is sufficiently reduced, the treated water is supplied to the place where the treated water is used as deionized water or pure water.

[0018] To operate the EDI device, water must also be passed through the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25. Thus, feed water is supplied to the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25 through pipes branching from the inlet pipe 41. The outlet waters of the concentration chambers 22 and 24 join together and are discharged as concentrated water to the outside of the EDI device through concentrated water pipe 46. Similarly, the outlet waters of the anode chamber 21 and the cathode chamber 25 join together and are discharged as electrode water to the outside of the EDI device through electrode water pipe 47.

[0019] The EDI device further includes a control device 50, a power supply device 51 that applies a direct current between the anode 11 and the cathode 12, and water quality sensors that are provided at various locations in the EDI device to measure the water quality. As an example, the water quality sensors include a conductivity meter (CI) 52 that is provided on the outlet side of the pump 15 in the inlet pipe 41 to measure the conductivity of the water to be treated and supplied to the desalting chamber 23, a resistivity meter (RI) 53 that is provided in the outlet pipe 42 to measure the resistivity of the treated water discharged from the desalting chamber 23, and a conductivity meter (CI) 54 that is provided in the concentrated water pipe 46 to measure the conductivity of the concentrated water. The control device 50 is a control means that controls the entire EDI device, and in particular, controls the power supply device 51 and the three-way valve 43. Measurement values ​​from each water quality sensor (conductivity meters 52, 54 and resistivity meter 53) are input to the control unit 50. Control by the control device 50 will be described below.

[0020] When the EDI device is operated for the first time after assembly, when the EDI device is installed at its installation location, or when the EDI device is started after being stopped for a certain period of time, the impurity concentration in the treated water generated as deionized water tends to be high due to the influence of contamination during the manufacture of the device and elution from internal components during the period when the device was stopped. In this embodiment, the treated water with a high impurity concentration discharged from the outlet of the desalting chamber 23 immediately after the start of operation of the EDI device is not discharged to the outside of the EDI device, but is returned to the inlet side of the desalting chamber 23 through the circulation pipe 44. In the EDI device, an operating mode in which the treated water from the desalting chamber 23 is returned to the inlet of the desalting chamber 23 while applying a direct current between the anode 11 and the cathode 12 is called a circulation operation. Even during the circulation operation, water continues to be passed through the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25. The amount of concentrated water passed through during the circulation operation is set, for example, so that the flow rate of the concentrated water is 15% or less of the flow rate of the treated water.

[0021] In this embodiment, when the circulation operation is performed, a current value change control is performed to change the value of the direct current applied between the anode 11 and the cathode 12 by the power supply device 51. For example, when a predetermined condition is satisfied while the circulation operation is performed, the current value is increased. The current value change control may include a control to decrease the current value, but preferably includes a control to increase the current value. In addition, the current value change control may change the current value multiple times, and in that case, the current value increases as a whole in a series of controls, but may include a control to decrease the current value once. Since the impurity concentration in the treated water discharged from the desalting chamber 23 is sufficiently decreased by continuing the circulation operation, a normal operation is performed following the circulation operation, in which the treated water discharged from the desalting chamber 23 is supplied to the outside of the EDI device through the treated water pipe 45 while continuing to flow a direct current between the anode 11 and the cathode 12. The normal operation is an operation mode for supplying the treated water, which is deionized water in which the impurity concentration has been sufficiently reduced, to equipment and the like provided outside the EDI device.

[0022] In order to execute the circulation operation and the normal operation following the circulation operation as described above, when the control device 50 starts the operation of the EDI device, it first controls the power supply device 51 and the three-way valve 43 so that the EDI device operates by the circulation operation. Specifically, the control device 50 controls the three-way valve 43 so that the treated water discharged from the desalting compartment 23 flows into the circulation pipe 44, and further controls the power supply device 51 so that a direct current flows between the anode 11 and the cathode 12. As a result, the treated water from the desalting compartment 23 is supplied to the tank 10 through the circulation pipe 44 from the three-way valve 43, and is returned to the inlet of the desalting compartment 23 via the pump 15. Then, when the first condition is satisfied during the period during which the circulation operation is being performed, the control device 50 controls the power supply device 51 at that time to change the current value of the direct current flowing between the anode 11 and the cathode 12, for example, to increase the current value, and continues the circulation operation as it is. The first condition for determining the timing for changing the current value may be, for example, any one of the following conditions: a predetermined time has elapsed since the start of circulation operation or the start of EDI operation; the conductivity of the water to be treated supplied to the desalting chamber 23 has become equal to or lower than a predetermined value; the conductivity of the concentrated water discharged from the concentration chambers 22 and 24 has become equal to or lower than a predetermined value; the pH of the concentrated water is within a predetermined range; the resistivity of the treated water is equal to or higher than a predetermined value; the TOC concentration of the treated water is equal to or lower than a predetermined value; or the pH of the water to be treated supplied to the desalting chamber 23 is within a predetermined range; or a combination of these conditions. In order to change the current value when a predetermined time has elapsed since the start of circulation operation or the start of EDI operation, timer control may be performed in the control device 50. The conductivity of the water to be treated supplied to the desalting chamber 23 can be measured by a conductivity meter 52 provided in the inlet pipe 41, the conductivity of the concentrated water can be measured by a conductivity meter 54 provided in the concentrated water pipe 46, and the resistivity of the treated water can be measured by a resistivity meter 53 provided in the outlet pipe 42. As an example, the current value of the direct current can be increased when 20 hours have passed since the start of the circulation operation.

[0023] When the second condition is satisfied while the circulation operation is continued, the control device 50 switches the three-way valve 43 at that time so that the treated water from the desalting chamber 23 is discharged to the outside of the EDI device through the treated water pipe 45. Since the application of the direct current continues, the operation of the EDI device is shifted from the circulation operation to the normal operation. As the second condition, for example, any one of the following conditions can be used: a predetermined time has elapsed since the start of the circulation operation; the conductivity of the water to be treated supplied to the desalting chamber 23 is equal to or lower than a predetermined value; the pH of the water to be treated supplied to the desalting chamber 23 is within a predetermined range; the conductivity of the concentrated water discharged from the concentration chambers 22 and 24 is equal to or lower than a predetermined value; the pH of the concentrated water is within a predetermined range; the resistivity of the treated water is equal to or higher than a predetermined value; the TOC concentration of the treated water is equal to or lower than a predetermined value; or a combination of these conditions. As in the case described for the first condition, when the operation is shifted to the normal operation when a predetermined time has elapsed since the start of the circulation operation, the control device 50 may execute timer control. Furthermore, the conductivity of the water to be treated supplied to the desalting chamber 23 can be measured by a conductivity meter 52, the conductivity of the concentrated water can be measured by a conductivity meter 54, and the resistivity of the treated water can be measured by a resistivity meter 53. The value of the direct current applied between the anode 11 and the cathode 12 during normal operation may be the same as or different from the value during circulation operation, but it is preferable to set the current value to be suitable for normal operation.

[0024] FIG. 2 is a flow chart for explaining the above-described operation method. When starting the operation of the EDI device, the control device 50 first switches the three-way valve 43 so that the treated water is circulated to the tank 10 in step 101, starts the pump 15 in step 102, and supplies the feed water from the tank 10 to the desalting chamber 23, the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25 as the water to be treated, and starts the power supply device 51 in step 103 so that a direct current is applied between the anode 11 and the cathode 12. This causes the EDI device to start operating in a circulation operation. Next, the control device 50 waits until the first condition is satisfied in step 104, and when the first condition is satisfied, controls the power supply device 51 in step 105 to increase the current value of the direct current applied between the anode 11 and the cathode 12. Thereafter, in step 106, the control device 50 waits until the second condition is met, and when the second condition is met, in step 107, the control device 50 switches the three-way valve 43 so that the treated water is discharged outside the EDI device through the treated water piping, and in step 108, the operation state of the EDI device is shifted to normal operation, for example by controlling the power supply device 51 so that the current conditions for normal operation are met. This enables the EDI device to operate in normal operation and supply the treated water, which is deionized water, to the place where it is used, and the process of starting up the EDI device is completed.

[0025] Here, we will explain how the value of the direct current applied between the anode 11 and the cathode 12 is changed during circulation operation. As is well known, ion exchangers such as ion exchange resins can take two states: a salt form in which impurity ions are adsorbed to the ion exchange groups, and a regenerated form in which impurity ions are not adsorbed. Specifically, when the ion exchanger is an anion exchanger such as an anion exchange resin, the counter ion for the ion exchange group is a hydroxide ion (OH) when in the salt form. - ), such as chloride ion (Cl - ) when in the regenerated form, and hydroxide ions when in the regenerated form. Similarly, if the ion exchanger is a cation exchanger, such as a cation exchange resin, the counter ion to the ion exchange group is a hydrogen ion (H+ ), such as sodium ion (Na + ) and hydrogen ions when in regenerated form. It is known that the radius of granular ion exchange resin, which is an ion exchanger, is generally smaller when in the salt form than when in the regenerated form. When an electric field is applied to an ion exchanger, ions move within the ion exchanger and an electric current flows, but ions move more easily within the regenerated ion exchanger than within the salt form, and the electrical resistance is smaller accordingly. The salt form ion exchanger does not contribute to the production of deionized water in the deionization chamber 23, and instead causes an increase in the impurity concentration in the deionized water. The purpose of the circulation operation is to convert the ion exchanger in the deionization chamber from the salt form to the regenerated form.

[0026] Immediately after the EDI device is assembled or after the EDI device has been suspended for a long period of time, the proportion of the salt form in the ion exchanger in the desalting compartment 23 is large. The salt form ion exchanger is smaller in size than the regenerated ion exchanger, and the area of ​​the part where they come into close contact with each other in the desalting compartment 23 is small, and the electric resistance of the salt form ion exchanger itself is large. Therefore, at the start of the circulation operation, the direct current applied between the anode 11 and the cathode 12 cannot be increased without increasing the applied voltage. As the circulation operation continues, the conversion of the ion exchanger from the salt form to the regenerated form progresses, the electric resistance of the desalting compartment 23 decreases, and the direct current can be increased without increasing the applied voltage. If the current value of the direct current is increased here, the conversion of the ion exchanger from the salt form to the regenerated form in the desalting compartment 23 is further accelerated. As a result, the time until the quality of the ionized water discharged from the desalting compartment 23, i.e., the treated water, reaches a predetermined level can be shortened compared to the case where the direct current is not increased. In the above description, the current value of the direct current is increased once during the period in which the circulation operation is performed, but the current value may be increased multiple times. Also, the current value may be decreased once, and then increased to a current value greater than that before the decrease.

[0027] The treated water discharged from the desalting chamber 23 at the very beginning of the circulation operation contains a large amount of impurities, and the impurity concentration may exceed the impurity concentration in the feed water supplied to the EDI device from the outside. If the treated water with a high impurity concentration is returned to the inlet of the desalting chamber 23, the conversion rate from the salt form of the ion exchanger to the regenerated form decreases, and it takes longer to obtain treated water of good quality. Therefore, it is preferable to perform an initial operation in which the treated water is discharged to the outside of the EDI device at the very beginning of the operation of the EDI device, and switch to circulation operation when the impurity concentration in the treated water has decreased to a certain extent. The destination of the treated water during the initial operation is assumed to be a drainage line, for example, where impurities may flow. When performing the initial operation, the control device 50 first controls the three-way valve 43 so that the treated water is discharged through the treated water pipe 45, and controls the power supply device 51 so that a direct current flows between the anode 11 and the cathode 12, and starts the EDI device to operate in the initial operation. If the third condition is satisfied while the initial operation is continuing, the control device 50 controls the three-way valve 43 so that the EDI device operates in the above-mentioned circulation operation while continuing the application of the direct current. As the third condition, for example, any one of the conditions, such as a predetermined time has passed since the start of the initial operation, or the resistivity of the treated water has reached a predetermined value or more, or a combination of these conditions can be used. As an example, the initial operation may be switched to the circulation operation when either one or both of the two conditions, that the initial operation continues for 0.5 hours or more, and that the resistivity of the treated water has reached 1 MΩ·cm or more, is satisfied. After the circulation operation is started in this way, the control device 50 executes the control of the three-way valve 43 and the power supply device 51 in the same manner as described above.

[0028] FIG. 3 is a flow chart for explaining the operation method of the EDI device when performing the initial operation prior to the circulation operation. When starting the operation of the EDI device, the control device 50 first switches the three-way valve 43 in step 111 so that the treated water is discharged outside the EDI device, starts the pump 15 in step 112 to start the water flow to the deionization chamber 23, the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25, and starts the power supply device 51 in step 113 so that a direct current is applied between the anode 11 and the cathode 12. As a result, the EDI device starts operating in the initial operation. Next, the control device 50 waits until the third condition is satisfied in step 114, and when the third condition is satisfied, switches the three-way valve 43 in step 115 so that the treated water is circulated to the tank 10 while continuing the application of the direct current. As a result, the EDI device shifts from the initial operation to the circulation operation, and thereafter, the control device 50 executes the process from step 104 described with reference to FIG. 2.

[0029] As described above, according to the EDI device of this embodiment, during the circulation operation that is performed after the EDI device starts up and prior to normal operation, the current value of the direct current applied between the anode 11 and the cathode 12 is changed, thereby making it possible to obtain treated water of a specified quality more quickly and shortening the time required to start up the EDI device. In addition, since the treated water is returned to the inlet of the desalting chamber 23 during the circulation operation, it is also possible to reduce the amount of water that is not supplied to the destination of the treated water, which is deionized water, and is discharged as wastewater.

[0030] In general, in an EDI device, the desalting compartment itself is divided into two small desalting compartments by an intermediate ion exchange membrane, and these two small desalting compartments can be connected in series to pass water through them. In the EDI device to which the present invention is applied, the desalting compartment can also be divided into two small desalting compartments by an intermediate ion exchange membrane, and feed water can be supplied to one small desalting compartment, and outlet water from one small desalting compartment can be supplied to the other small desalting compartment. Treated water is obtained from the other small desalting compartment. The EDI device shown in FIG. 4 is the EDI device shown in FIG. 1, in which the desalting compartment 23 is divided into two small desalting compartments 26 and 27 by an intermediate ion exchange membrane 35. For example, an anion exchange membrane is used as the intermediate ion exchange membrane 35, but a cation exchange membrane or a bipolar membrane can also be used in addition to the anion exchange membrane. The small deionization compartment arranged on the side closer to the anode 11 across the intermediate ion exchange membrane 35 is the first small deionization compartment (D1) 26, and the small deionization compartment arranged on the side closer to the cathode 12 is the second small deionization compartment (D2) 27. Both the first small deionization compartment 26 and the second small deionization compartment 27 are filled with ion exchangers. By applying the above-mentioned operating method to the EDI device shown in Figure 4, the time required to start up the EDI device can be shortened and the amount of wastewater can be reduced. EXAMPLES

[0031] Next, the present invention will be described in more detail with reference to examples and comparative examples.

[0032] [Example 1] The anode chamber 21, the concentration chambers 22 and 24, the deionization chamber 23, and the cathode chamber 25 were all filled with ion exchange resins, and the EDI device shown in FIG. 1 was assembled. Of the ion exchange resins filled in each chamber, only salt-type anion exchange resins were used, and only regenerated cation exchange resins were used. An electrical current test was performed on this EDI device in which a direct current was applied between the anode 11 and the cathode 12 while the treated water was supplied to each chamber. In the electrical current test, the change in the resistivity of the treated water discharged from the deionization chamber 23 was measured, and the regeneration ratio of the anion exchange resin inside the EDI device was calculated from the salt component concentration discharged into the concentrated water, and the change was examined. The regeneration ratio is the ratio of the regenerated anion exchange resin to the total amount of the anion exchange resin. In the electrical current test, the current value of the direct current was initially set to 1A. At the start of operation, the treated water discharged from the desalting chamber 23 was discharged to the outside as an initial operation, and when the resistivity of the treated water exceeded 1 MΩ·cm, the initial operation was switched to circulation operation by returning the treated water to the inlet side of the desalting chamber 23. Furthermore, four hours after the start of operation, the current value was increased from 1 A to 2.5 A. The results are shown in Figure 5(a).

[0033] As can be seen from Figure 5(a), in Example 1, in which the current value was increased during the circulation operation, the regeneration ratio of the anion exchange resin reached 60% after 20 hours of operation, and the quality of the treated water, expressed in terms of resistivity, reached 16 MΩ·cm.

[0034] [Comparative Example 1] An EDI device was assembled in the same manner as in Example 1, and a current test was performed. In the current test, the current value of the direct current was fixed at 1 A, and initial operation was performed until the resistivity of the treated water reached 5 MΩ·cm, and when the resistivity reached 5 MΩ·cm, the operation was switched to circulation operation. In Comparative Example 1, in which the current value of the direct current was not changed during circulation operation, the regeneration ratio of the anion exchange resin was 43% after 20 hours of operation, and the treated water quality only reached 14 MΩ·cm.

[0035] [Example 2] Using the EDI device of Example 1, initial operation and subsequent circulation operation were performed under different operating conditions, and the time elapsed from the start of operation until treated water with a resistivity of 15 MΩ·cm was obtained, the total amount of wastewater up to that point, and the regeneration ratio of the anion exchange resin at that time were determined. The total amount of wastewater is the sum of the amount of water discharged as concentrated water and electrode water, and the amount of treated water discharged outside the EDI device without being circulated to the desalting chamber. The operating conditions and the results obtained are shown in Table 1. In Table 1, "initial current value" indicates the current value of the direct current during initial operation and until the current value was changed in circulation operation. In addition, when the resistivity of the treated water reached a predetermined value, the initial operation was switched to circulation operation, and the resistivity of the treated water at that time is shown in the column "resistivity of treated water when switching from initial operation to circulation operation" in Table 1. During circulation operation, the current value of the direct current was increased when a predetermined time had elapsed from the start of operation, including the initial operation. The elapsed time from the start of operation when the current value was increased and the current value after it was increased are entered in the columns "Elapsed time from the start of operation when the current value was increased" and "Current value after it was increased," respectively.

[0036] [Table 1]

[0037] In all of the operating conditions of Examples 2-1 to 2-3, the regeneration ratio of the anion exchange resin exceeded 70% when the resistivity of the treated water reached 15 MΩ·cm. Comparing Example 2-1 with Example 2-2, by halving the flow rate of the concentrated water while keeping the treated water flow rate constant, and instead setting a high current value after the current was raised, the time until the resistivity of the treated water reached 15 MΩ·cm could be shortened by 10 hours, and the total amount of wastewater could be reduced by about 21,200 L. Comparing Example 2-2 with Example 2-3, by changing the resistivity of the treated water to 1 MΩ·cm when shifting from the initial operation to the circulation operation, and further changing the timing of raising the current to 5 hours after the start of operation, it was possible to further shorten the time until the resistivity of the treated water reached 15 MΩ·cm by 17 hours, and the total amount of wastewater could be further reduced by 8,440 L.

[0038] In Example 2-3, the TOC concentration of the treated water was also measured. The TOC concentration of the treated water was 8.5 ppb when the operation was switched from the initial operation to the circulation operation, but the TOC concentration of the treated water decreased to 0.7 ppb when the resistivity of the treated water reached 15 MΩ cm.

[0039] From the above examples and comparative examples, it has been found that by performing a circulation operation when the EDI device starts up and increasing the DC current value during the circulation operation, a high regeneration ratio in the ion exchanger in the deionization chamber 23 and a high resistivity in the treated water can be achieved in a short time and with a small amount of wastewater discharged outside the EDI device, and a reduction in the amount of TOC elution can be achieved. Therefore, by manufacturing the EDI device in a factory and then applying the operating method based on the present invention to the EDI device before it is shipped, the trial run time required at the site where the EDI device is installed can be shortened. [Explanation of symbols]

[0040] 10. Tank 11 Anode 12 Cathode 15 Pump 21 Anode chamber (E+) 22,24 Concentration chamber (C) 23 Desalination room (D) 25 Cathode chamber (E-) 26 First Small Desalination Room (D1) 27 Second Small Desalination Room (D2) 31,33 Cation exchange membrane 32,34 Anion exchange membrane 35 Intermediate ion exchange membrane 40 Water supply piping 41 Inlet pipe 42 Outlet piping 43 Three-way valve 44 Circulation piping 45 Treated water piping 50 Control device 51 Power supply 52,54 Conductivity meter (CI) 53 Specific resistance meter (RI)

Claims

1. An electrodeionized water production apparatus, comprising: an anode and a cathode; a desalting chamber disposed between the anode and the cathode, partitioned by a first ion exchange membrane provided on a side facing the anode and a second ion exchange membrane provided on a side facing the cathode, filled with an ion exchanger, supplied with water to be treated and discharging the treated water; a power supply device that applies a direct current between the anode and the cathode; a switching means connected to an outlet of the deionization chamber, into which the treated water flows, and which switches the destination of the treated water between a first outlet and a second outlet to discharge the treated water; a first pipe connected to the first outlet and for returning the treated water toward the inlet of the desalting chamber; a second pipe connected to the second outlet for discharging the treated water to the outside of the electrodeionization water production apparatus; a control means capable of controlling the power supply device and the switching means so that the electrical deionized water production apparatus operates by a circulation operation in which the treated water is returned to an inlet of the deionization compartment through the first pipe and supplied to the deionization compartment; and having The control means of the electrical deionized water production apparatus performs current value change control to change the value of the DC current by controlling the power supply device during the period in which the electrical deionized water production apparatus is operating through the circulation operation.

2. The electrodeionized water producing apparatus according to claim 1 , wherein the current value change control includes at least a control for increasing a value of the direct current.

3. 3. The electrodeionized water production apparatus according to claim 1, wherein the control device performs the current value change control when a predetermined time has elapsed since the start of operation of the electrodeionized water production apparatus or the start of the circulation operation.

4. a water quality sensor for detecting water quality at a predetermined position in the electrodeionization water production apparatus; 3. The electrodeionization water producing apparatus according to claim 1, wherein the control means executes the current value change control when the value measured by the water quality sensor satisfies a predetermined condition.

5. The electrical deionized water production apparatus of claim 1 or 2, wherein the control means controls the power supply device and the switching means so that the electrical deionized water production apparatus operates by an initial operation in which the treated water is discharged through the second piping prior to the circulation operation.

6. 1. An operating method for an electrodeionization water production apparatus comprising: an anode; a cathode; and a desalination chamber disposed between the anode and the cathode, partitioned by a first ion exchange membrane provided on a side facing the anode and a second ion exchange membrane provided on a side facing the cathode, filled with an ion exchanger, through which water to be treated is passed and through which the treated water is discharged, the method comprising the steps of: A circulation operation is performed in which the treated water is returned to the inlet of the deionization compartment while a direct current is applied between the anode and the cathode, and the treated water is supplied to the deionization compartment; A current value change control is performed to change the value of the DC current during the period in which the circulation operation is performed.

7. The operating method according to claim 6 , wherein the current value change control at least includes increasing a value of the direct current.

8. 8. The method according to claim 6, wherein the current value change control is performed when a predetermined time has elapsed since the start of operation of the electrodeionized water production apparatus or the start of the circulation operation.

9. 8. The operating method according to claim 6 or 7, further comprising detecting water quality at a predetermined position in the electrical deionization water production apparatus during the period in which the circulation operation is performed, and executing the current value change control when the detected water quality value satisfies a predetermined condition.

10. The operating method according to claim 6 or 7, further comprising the step of: prior to the circulation operation, performing an initial operation in which the treated water is discharged through the second pipe while the direct current is being applied.

11. 11. The operating method according to claim 10, wherein the initial operation is switched to the circulation operation when at least one of the following conditions is satisfied: the initial operation is performed for 0.5 hours or more; and the resistivity of the treated water is 1 MΩ·cm or more.

12. 8. The method according to claim 6 or 7, wherein the circulation operation is carried out continuously for 20 hours or more.

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