JP7728382B2 - Electrodeionized water production device and its operating method - Google Patents

Description

The present invention relates to an electrodeionization (EDI) water production system and its operating method.

An EDI device is one type of device that demineralizes feed water (also referred to as water to be treated) to produce deionized water as treated water. An EDI device operates by combining electrophoresis and electrodialysis and includes at least a deionization compartment separated by a diaphragm, such as an ion exchange membrane, between an anode and a cathode. The deionization compartment is filled with an ion exchanger, such as an ion exchange resin. By supplying feed water to the deionization compartment while applying a direct current between the anode and the cathode, deionization proceeds within the deionization compartment, and deionized water flows out of the deionization compartment. In EDI devices, the anode and cathode are typically located in the anode chamber and cathode chamber, respectively. Concentration compartments may be located between the anode chamber and the deionization compartment, and between the deionization compartment and the cathode chamber. In this case, the concentration compartment and the deionization compartment are separated by a diaphragm, such as an ion exchange membrane, and the anode chamber and the concentration compartment, and the concentration compartment and the cathode chamber are also separated by ion exchange membranes. In EDI systems, water must be supplied to the anode chamber, cathode chamber, and concentration chamber, and wastewater from these chambers is often simply discharged to the outside. EDI systems have the advantage of not requiring the use of chemicals to regenerate the ion exchange resin, allowing for continuous desalination over long periods of time.

When using an EDI system to produce pure or ultrapure water, it may be necessary to remove dissolved oxygen from the feed water. Because dissolved oxygen itself is not an ionic substance, it cannot be removed by desalination in the desalination compartment. Patent Document 1 discloses a method for removing dissolved oxygen from feed water by incorporating a catalyst capable of decomposing oxidants, such as a palladium (Pd) catalyst, into the desalination compartment and adding hydrogen to the feed water. The technology disclosed in Patent Document 1 reduces the dissolved oxygen concentration in the feed water by promoting a reaction that produces water from dissolved oxygen and hydrogen in the presence of the catalyst. Because hydrogen is generated by an electrode reaction in the cathode chamber of the EDI system, Patent Document 1 also discloses using the cathode chamber as a hydrogen source and adding outlet water from the cathode chamber to the feed water. Conventionally, outlet water from the cathode chamber has often been discarded as wastewater. Adding outlet water from the cathode chamber to the feed water improves the water recovery rate in the EDI system and reduces the amount of discarded water. The water discharged from the EDI unit is divided into water that is effectively used (called effectively used water), either by being used in an external device as deionized water or by being supplied to a device installed upstream of the EDI unit, and water that is to be discarded as wastewater. The water recovery rate in an EDI unit refers to the ratio of the amount of effectively used water to the total amount of water supplied from outside the EDI unit to the deionization compartment, anode compartment, cathode compartment, and concentration compartment.

In EDI devices, the pressure at the inlet of the deionization compartment is generally higher than the pressure at the outlet of the cathode compartment. Therefore, when adding outlet water from the cathode compartment to feed water supplied to the deionization compartment, a pump must be used to pressurize the outlet water from the cathode compartment and add the pressurized outlet water to the feed water. Therefore, the EDI device shown in Patent Document 1 requires a pump to pressurize the outlet water from the cathode compartment in addition to the pump used to supply feed water to the deionization compartment, which results in increased costs.

Patent Document 2 discloses a water treatment device with a similar structure to an EDI device, designed to remove dissolved oxygen from feed water. In this water treatment device, the section equivalent to the deionization chamber in an EDI device serves as a dissolved oxygen removal chamber, which is filled with ion exchange resin carrying a catalyst capable of decomposing oxidants. Feed water is first supplied to the cathode chamber, and the outlet water from the cathode chamber is supplied directly to the dissolved oxygen removal chamber. In this water treatment device, feed water is not supplied directly to the dissolved oxygen removal chamber, but is supplied to the dissolved oxygen removal chamber via the cathode chamber. Therefore, if a pump for supplying feed water is located on the inlet side of the cathode chamber, there is no need to provide a separate pump for pressurizing the outlet water from the cathode chamber.

Japanese Patent Application Publication No. 10-272474 International Publication No. 2022/190727

The EDI device described in Patent Document 1 can simultaneously desalinate feed water and remove dissolved oxygen, while improving water recovery rates, but requires a pump for pressurizing the cathode water outlet in addition to the pump used to supply feed water to the desalination chamber. Meanwhile, the water treatment device described in Patent Document 2 has the same structure as an EDI device and is therefore equipped with desalination functions, but its primary focus is on removing dissolved oxygen, and there is room for improvement in order to increase desalination capacity and treat large volumes of feed water with a high water recovery rate.

The object of the present invention is to provide an electrodeionized water production system (EDI system) and an operating method thereof that can demineralize large amounts of supplied water with an increased water recovery rate while reducing the number of pumps required.

The electrodeionized water production apparatus (EDI apparatus) of the present invention comprises an anode chamber in which an anode is disposed and which is separated by a first diaphragm, a cathode chamber in which a cathode is disposed and which is separated by a second diaphragm, a deionization chamber disposed between the anode chamber and the cathode chamber and filled with an ion exchanger, a first pipe connected to the inlet of the deionization chamber and which supplies pressurized feed water to the deionization chamber, a first adjusting valve provided in the first pipe, and a second adjusting valve provided in the first pipe at a position between the first adjusting valve and the inlet of the deionization chamber. a junction section in which the first and second piping are joined, a second piping branching off from the first piping at a position upstream of the first adjustment valve and through which the feed water flows, and a third piping connecting the outlet of the target electrode chamber to the junction section, with at least one of the anode chamber and cathode chamber serving as the target electrode chamber; the feed water is supplied to the anode chamber and cathode chamber via the second piping, and the outlet water of the target electrode chamber is mixed with the feed water at the junction section and supplied to the deionization chamber; and a direct current is applied between the anode and cathode.

The method for operating the EDI device of the present invention is a method for operating an electrodeionization water production device having an anode chamber containing an anode and separated by a first diaphragm, a cathode chamber containing a cathode and separated by a second diaphragm, and a deionization chamber filled with an ion exchanger and placed between the anode and cathode chambers. At least one of the anode and cathode chambers is used as the target electrode chamber, and while a direct current is applied between the anode and cathode, feed water pressurized by a pump is supplied to the deionization chamber via a control valve. Also, feed water branched off upstream of the control valve is passed through the anode and cathode chambers. The outlet water from the target electrode chamber is mixed with the feed water downstream of the control valve without being pressurized, and then supplied to the deionization chamber.

According to the present invention, an EDI device can be used to reduce the number of pumps required while enabling desalination of large amounts of supplied water with a high water recovery rate.

FIG. 1 illustrates an example of a configuration of an EDI device according to a first embodiment. FIG. 2 is a diagram illustrating another example of the configuration of the EDI device according to the first embodiment. FIG. 1 is a diagram illustrating a configuration of an EDI system. FIG. 1 is a diagram illustrating a configuration of an EDI system. FIG. 1 is a diagram illustrating a configuration of an EDI system. FIG. 1 is a diagram illustrating a configuration of an EDI system. FIG. 10 illustrates an example of a configuration of an EDI device according to a second embodiment. FIG. 10 is a diagram illustrating another example of the configuration of the EDI device according to the third embodiment. FIG. 10 illustrates an example of a configuration of an EDI device according to a third embodiment. FIG. 10 is a diagram illustrating another example of the configuration of the EDI device according to the third embodiment.

[First embodiment]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an EDI device (electrodeionized water production device) according to a first embodiment of the present invention. The EDI device shown in FIG. 1 includes a main body 10 including an anode chamber (E+) 21, concentration chambers (C) 22 and 24, a deionization chamber (D) 23, and a cathode chamber (E-) 25, a group of pipes connected to each chamber (anode chamber 21, concentration chambers 22 and 24, deionization chamber 23, and cathode chamber 25) of the main body 10, and adjustment valves 51 to 56 attached to the pipes. An anode 11 is provided in the anode chamber 21, and a cathode 12 is provided in the cathode chamber 25. In the main body 10, a concentration chamber 22, a deionization chamber 23, and a concentration chamber 24 are arranged between the anode chamber 21 and the cathode chamber 25, in this order from the anode chamber 21 side. The anode chamber 21 and the concentration chamber 22 are adjacent to each other and separated by a cation exchange membrane 31, the concentration chamber 22 and the deionization chamber 23 are adjacent to each other and separated by an anion exchange membrane 32, the deionization chamber 23 and the concentration chamber 24 are adjacent to each other and separated by a cation exchange membrane 33, and the concentration chamber 24 and the cathode chamber 25 are adjacent to each other and separated by an anion exchange membrane 34. The cation exchange membranes 31, 33 and the anion exchange membranes 32, 34 all function as diaphragms for separating the chambers that make up the main body 10.

Since both the anode 11 and the cathode 12 are electrodes, in this specification, the anode chamber 21 and the cathode chamber 25 may be referred to as "electrode chambers" when there is no need to distinguish between them or when referring to both together. As will be described later, in this embodiment, in order to improve the water recovery rate of the EDI device, at least one of the outlet water from the anode chamber 21 (i.e., anode water) and the outlet water from the cathode chamber 25 (i.e., cathode water) is combined with the feed water to be supplied to the deionization chamber 23. Therefore, the electrode chamber whose outlet water is combined with the feed water is defined as the "target electrode chamber."

The EDI device shown in Figure 1 performs desalination and dissolved oxygen removal on feed water supplied to the desalination chamber 23, producing and discharging treated water. To perform the desalination process, the desalination chamber 23 is filled with an ion exchange resin as an ion exchanger. For example, an anion exchange resin and a cation exchange resin are filled in the desalination chamber 23 in a double-bed or mixed-bed configuration. Furthermore, at least a portion of the ion exchange resin filled in the desalination chamber 23 is supported with a catalyst capable of decomposing oxidants, in order to remove dissolved oxygen from the feed water by reacting the dissolved oxygen with hydrogen in the presence of a catalyst to produce water. The reaction that produces water from dissolved oxygen and hydrogen in the presence of a catalyst is expressed by the following equation (1):

A catalyst with oxidant decomposition ability is a catalyst that promotes the reaction shown in formula (1). Examples include metal oxide catalysts such as manganese dioxide, cobalt oxide, titanium oxide, and zinc oxide, as well as various metal catalysts. Alternatively, enzymes that can decompose oxidants such as dissolved oxygen and hydrogen peroxide (e.g., catalase and peroxidase) can also be used as catalysts with oxidant decomposition ability. When using a metal catalyst as a catalyst with oxidant decomposition ability, chromium, gold, silver, copper, platinum, palladium, iridium, ruthenium, rhodium, etc. are preferably used. From the perspective of being able to rapidly proceed with the reaction shown in formula (1), it is particularly preferable to use a platinum group metal catalyst such as platinum or palladium as a catalyst with oxidant decomposition ability.

To reduce the operating voltage of the EDI device, it is preferable to fill each electrode chamber and the concentration chambers 22 and 24 with ion exchange material. For example, the anode chamber 21 is filled with a cation exchange resin, the cathode chamber 25 is filled with an anion exchange resin, and the concentration chambers 22 and 24 are also filled with anion exchange resin.

To supply feed water to the deionization chamber 23, a pump 15 is provided to pressurize the feed water supplied from outside the EDI device. A feed water pipe 61 connects the secondary side, i.e., outlet, of the pump 15 to the inlet of the deionization chamber 23. A treated water pipe 63 is connected to the outlet of the deionization chamber 23, and the outlet water of the deionization chamber 23, i.e., treated water, is discharged from the deionization chamber 23 via the treated water pipe 63. Adjusting valves 51 and 55 are provided on the feed water pipe 61 and the treated water pipe 63, respectively, to maintain the pressure in the deionization chamber 23 at a predetermined value and to maintain the water flow rate through the deionization chamber at a predetermined value. A junction 81 is also provided on the feed water pipe 61 between the adjusting valve 51 and the inlet of the deionization chamber 23 for mixing cathode water with the feed water, as described below. The junction 81 is configured, for example, by a three-way joint.

To operate the EDI device, water must also be passed through each electrode chamber and concentration chamber 22, 24. To pass water through the electrode chambers and concentration chambers 22, 24, a branch pipe 62 is provided, branching off from the supply water pipe 61 upstream of the adjustment valve 51. Furthermore, since ionic impurities removed from the supply water by the desalination process in the desalination chamber 23 during operation are discharged from the concentration chambers 22, 24, a concentrated water pipe 64 is also provided for discharging the outlet water (i.e., concentrated water) from the concentration chambers 22, 24 to the outside as wastewater. While the concentrated water discharged through the concentrated water pipe 64 is often discarded as is, it may be used separately or circulated upstream of the EDI device. For example, if raw water is treated through a reverse osmosis (RO) membrane and the permeate from the RO membrane is supplied to the EDI device as feed water, the concentrated water discharged from the EDI device may be merged with the raw water supplied to the RO membrane.

A pipe 66 is provided connecting the inlet of the anode chamber 21 to the branch pipe 62. Feed water is supplied to the anode chamber 21 via the pipe 66, and the outlet water from the anode chamber 21 (i.e., anode water) flows directly into the concentrated water pipe 64 and is discharged outside the EDI device. The pipe 66 is equipped with an adjustment valve 52 to maintain a constant flow rate of water to the anode chamber 21. Similarly, a pipe 67 is provided, one end of which connects to the branch pipe 62, to supply feed water to the concentration chambers 22 and 24. The pipe 67 is equipped with an adjustment valve 53. Downstream of the adjustment valve 53, i.e., at the other end of the pipe 67, the pipe 67 branches into two, each connected to the inlet of the concentration chambers 22 and 24. The outlet water from the concentration chambers 22 and 24 join together and then flow into the concentrated water pipe 64 via the adjustment valve 56, before being discharged outside the EDI device. Adjustment valves 53 and 56 are provided to maintain the pressure and water flow rate in the concentration chambers 22 and 24 at predetermined values.

A pipe 68 is provided connecting the inlet of the cathode chamber 25 to the branch pipe 62, and feed water is supplied to the cathode chamber 25 via the pipe 68. A pipe 69 is provided connecting the outlet of the cathode chamber 25 to the junction 81. The outlet water of the cathode chamber 25, i.e., cathode water, is sent to the junction 81 via the pipe 69, mixed with feed water supplied from outside the EDI device, and supplied to the deionization chamber 23. In the EDI device shown in Figure 1, the cathode chamber 25 is the target electrode chamber. In this EDI device, a branch pipe 62 branches off from the feed water pipe 61 upstream of the adjustment valve 51, and feed water is supplied from the branch pipe 62 to the cathode chamber 25 via the pipe 68. By appropriately setting the adjustment valves 51, 54, and 55, the pressure at the outlet of the cathode chamber 25 can be made higher than the pressure at the inlet of the deionization chamber 23, allowing the cathode water to be combined with the feed water and supplied to the deionization chamber 23. In other words, cathode water can be mixed with the feed water supplied to the desalination chamber 23 without the need for a pump to pressurize the cathode water.

Next, we will explain the operation of the EDI device shown in Figure 1. When the pump 15 is driven to pass feed water through the electrode chambers, concentration chambers 22 and 24, and deionization chamber 23, and a direct current is applied between the anode 11 and the cathode 12, a reduction reaction (cathode reaction) shown in formula (2) proceeds in the cathode chamber 25, generating hydrogen (H ₂ ) and hydroxide ions (OH ^- ) as electrolysis products.

2H ₂ O+ 2e ^- → H ₂ ↑ + 2OH ^- (2)

The generated hydroxide ions are contained in the cathode water discharged from the cathode chamber 25 and migrate through the anion exchange membrane 34 to the concentration chamber 24 due to the electric field between the anode 11 and cathode 12. The generated hydrogen is contained in the cathode water and discharged from the cathode chamber 25, passes through piping 69, and is mixed with the cathode water and the feed water at the junction 81. The feed water supplied to the EDI device from outside contains almost no hydrogen, although it may contain dissolved oxygen. However, by mixing with the cathode water, hydrogen is added and the water is supplied to the desalination chamber 23. In the desalination chamber 23, the electric field between the anode 11 and cathode 12 causes a desalination process similar to that of a typical EDI device, and ionic components are removed from the feed water. Of the ionic components removed from the feed water, anionic components migrate to the concentration chamber 22 via the anion exchange membrane 32, and cation components migrate to the concentration chamber 24 via the cation exchange membrane 33. Both ionic components are discharged outside the EDI device as concentrated water. At the same time, in the desalination chamber 23, because a catalyst with oxidant-decomposing properties is present and the supply water contains hydrogen, the reaction shown in equation (1) above proceeds, and the dissolved oxygen in the supply water reacts with the hydrogen and is removed. As a result, treated water is discharged from the desalination chamber 23, from which both ionic components and dissolved oxygen have been removed by the desalination process.

As described above, cathode water contains hydrogen and hydroxide ions and can be used as alkaline functional water with reducing properties. Adding cathode water can shift the pH of the water to which it is added toward the alkaline side. Adding cathode water to feed water not only allows the feed water to contain hydrogen, but also neutralizes oxidizing agents such as chlorine that flow into the EDI device. The EDI device shown in FIG. 1 can efficiently remove dissolved oxygen from the feed water even when the flow rate of the feed water supplied from the outside to the deionization chamber 23 via the adjustment valve 51 is, for example, approximately 11 times the flow rate of the cathode water. Furthermore, in the EDI device shown in FIG. 1, the entire amount of cathode water generated in the cathode chamber 25 is supplied to the deionization chamber 23. However, in order to use the cathode water outside the EDI device as alkaline functional water with reducing properties, a branch pipe from the pipe 69 can be provided to supply a portion of the cathode water to the outside of the EDI device.

In the anode chamber 21, the oxidation reaction (anode reaction) shown in formula (3) proceeds, generating oxygen (O ₂ ) and hydrogen ions (H ⁺ ) as electrolysis products. Depending on the components contained in the water in the anode chamber 21, oxidizing substances such as chlorine (Cl ₂ ), ozone (O ₃ ), hydrogen peroxide (H ₂ O ₂ ), and hypochlorous acid (HClO) may be generated in addition to oxygen.

2H ₂ O→O ₂ ↑ + 4H ⁺ + 4e ^- (3)

The hydrogen ions generated in the anode chamber 21 are contained in the anode water discharged from the anode chamber 21 and are transported to the concentration chamber 22 via the cation exchange membrane 31 due to the electric field between the anode 11 and the cathode 12. Because the anode water also contains oxygen and other oxidizing substances, it can also be used as acidic functional water with oxidizing power. By adding anode water, the pH of the water to which the anode water has been added can be shifted toward the acidic side, which can suppress the formation of hardness scale, for example. Oxidizing gases such as oxygen, chlorine, and ozone generated in the anode chamber 21 can also be introduced into the deionization chamber 23 to sterilize microorganisms in the supply water.

In general, in EDI devices, the deionization compartment itself is divided into two small deionization compartments by an intermediate ion exchange membrane, and these two small deionization compartments can be connected in series to allow water to pass through. The EDI device of this embodiment can also be configured to divide the deionization compartment into two small deionization compartments by an intermediate ion exchange membrane, supplying feed water to one small deionization compartment and supplying the outlet water of one small deionization compartment to the other small deionization compartment. Treated water is obtained from the other small deionization compartment. Hereinafter, the small deionization compartment to which feed water is first supplied will be referred to as the first small deionization compartment, and the small deionization compartment to which treated water is discharged will be referred to as the second small deionization compartment. In this case, it is preferable to perform a process to remove dissolved oxygen in the first small deionization compartment to which feed water is first supplied. The EDI device shown in Figure 2 is the EDI device shown in Figure 1, where the deionization compartment 23 is divided into two small deionization compartments 26 and 27 by an intermediate ion exchange membrane 35. An anion exchange membrane is used as the intermediate ion exchange membrane 35, for example, but a cation exchange membrane or a bipolar membrane can also be used. In the example shown, the small deionization compartment arranged 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 closer to the cathode 12 is the second small deionization compartment (D2) 27. The second small deionization compartment 27 may be arranged closer to the anode 11 across the intermediate ion exchange membrane 35, and the first small deionization compartment may be arranged closer to the cathode 12. Both the first small deionization compartment 26 and the second small deionization compartment 27 are filled with ion exchangers, and at least a portion of the ion exchange resin filled in the first small deionization compartment 26 supports a catalyst having oxidant-decomposing ability. The feed water pressurized by the pump 15 is supplied from the feed water piping 61 through the regulating valve 51 and the confluence 81 to the first small deionization chamber 26, and the outlet water from the first small deionization chamber 26 is supplied to the second small deionization chamber 27. The outlet water from the second small deionization chamber 27 is treated water that has undergone deionization and dissolved oxygen removal processes, and is discharged outside the EDI device through the regulating valve 55 and treated water piping 63.

1 and 2, one pump 15 is provided for each EDI device to supply feed water to the EDI device. However, if a large-capacity pump 15 is used, it is possible to supply feed water to multiple EDI devices using one pump. A system with multiple EDI devices is referred to as an EDI system. Figure 3 shows an EDI system in which two EDI devices, like the one shown in Figure 1, are provided and feed water can be supplied to the two EDI devices using one pump 15. The feed water pipe 61 connected to the secondary side of the pump 15 branches into two at its end, with an adjustment valve 51 and a junction 81 at each branch. Feed water is supplied to the desalination chamber 23 of each EDI device via the adjustment valve 51 and junction 81 provided for that EDI device. The outlet water from the desalination chamber 23 of each EDI device, i.e., treated water, passes through the adjustment valve 55 provided for each EDI device and is discharged outside the EDI device via the treated water pipe 63.

The branch pipe 62, treated water pipe 63, and concentrated water pipe 64 are provided in common to the two EDI units. Each EDI unit is connected to the branch pipe 62 via its own pipes 66-68, and receives feed water for its electrode chambers and concentration chambers 22, 24, similar to the EDI unit shown in Figure 1. The concentrated water discharged from the concentration chambers 22, 24 of each EDI unit is combined for each EDI unit and then passed through the control valve 56 and discharged to the outside as wastewater via the concentrated water pipe 64. The anode water discharged from the anode chamber 21 of each EDI unit flows directly into the concentrated water pipe 64, and the cathode water discharged from the cathode chamber 25 of each EDI unit is sent via pipe 69 to the confluence 81 located on the inlet side of the desalination chamber 23 of that EDI unit.

The EDI system shown in Figure 3 is configured by arranging two EDI systems similar to those shown in Figure 1 in parallel, with the supply water piping 61, branch piping 62, treated water piping 63, and concentrated water piping 64 shared between the two EDI systems. Therefore, the number of regulating valves 51-56 is twice that of the EDI system shown in Figure 1. The number of EDI systems connected in parallel in an EDI system is not limited to two and can be increased as far as the capacity of the pump 15 allows, up to three or more systems. As the number of EDI systems connected in parallel increases, the number of regulating valves also increases. To limit the increase in the number of regulating valves, regulating valves can be shared by multiple EDI systems connected in parallel. The EDI system shown in Figure 4 is configured by providing regulating valves 51-56 in the EDI system shown in Figure 3 in a way that they are shared between the two EDI systems.

In the EDI system shown in Figure 4, a control valve 51 is provided on the supply water pipe 61 connected to the secondary side of the pump 15. The supply water pipe 61 branches into two downstream of the control valve 51, with a junction 81 provided at each branch. The supply water flowing out of the junction 81 is supplied to the desalination chambers 23 of each EDI device. The outlet water, i.e., treated water, from the desalination chambers 23 of both EDI devices merges and, after merging, passes through a control valve 55 and is discharged outside the EDI device via the treated water pipe 63. A pipe 66 is connected to the branch pipe 62, and a control valve 52 is provided on the pipe 66. The pipe 66 branches into two downstream of the control valve 52, and the two branches are connected to the inlets of the anode chambers 21 of the two EDI devices, respectively, to supply the supply water to these anode chambers 21. The outlets of each anode chamber 21 are connected to a concentrated water pipe 64. Similarly, a pipe 67 is connected to the branch pipe 62, and the pipe 67 is provided with an adjustment valve 53. Downstream of the adjustment valve 53, the pipe 67 branches into four, and the four branches are connected to the inlets of the concentration chambers 22 and 24 of one EDI device and the other EDI device, respectively, to supply feed water to these concentration chambers 22 and 24. The concentrated water from the outlets of the concentration chambers 22 and 24 of both EDI devices joins together and is then discharged to the outside via a concentrated water pipe 64 via an adjustment valve 56. A pipe 68 is connected to the branch pipe 62, and the pipe 68 is provided with an adjustment valve 54. Downstream of the adjustment valve 54, the pipe 68 branches into two, and the two branches are connected to the inlets of the cathode chambers 25 of the two EDI devices, respectively, to supply feed water to these cathode chambers 25. In each EDI device, the outlet water from the cathode chamber 25, i.e., cathode water, is sent via piping 69 to the confluence 81 of that EDI device. The EDI system shown in Figure 4 is configured so that the regulating valves 51-56 are shared by two EDI devices, but it is also possible to configure an EDI system consisting of three or more EDI devices using one set of regulating valves 51-56.

As in the cases shown in Figures 3 and 4, multiple EDI devices as shown in Figure 2, in which the deionization compartment is divided into a first small deionization compartment 26 and a second small deionization compartment 27 by an intermediate ion exchange membrane 35, can be provided, and feed water can be supplied to these multiple EDI devices by a single pump 15. Figure 5 shows the EDI system shown in Figure 3, in which the EDI device shown in Figure 2 is used as the EDI device instead of the EDI device shown in Figure 1. Figure 6 shows the EDI system shown in Figure 4, in which the EDI device shown in Figure 2 is used as the EDI device instead of the EDI device shown in Figure 1.

According to the first embodiment, cathode water, which contains hydrogen and has previously been discarded outside the EDI device, is reused within the EDI device, thereby improving the water recovery rate in the EDI device without the need for a separate pump. Furthermore, if the concentrated water is also supplied to the inlet of a reverse osmosis membrane device installed upstream of the EDI device, the concentrated water can also be effectively utilized, further improving the water recovery rate in the EDI device. The configuration shown in the first embodiment, in which cathode water is merged with the feed water to be supplied to the deionization compartment, is also useful for improving water recovery rate in EDI devices that do not have a catalyst with oxidant-decomposing properties installed in the deionization compartment, i.e., EDI devices that do not have the function of removing dissolved oxygen. Therefore, the category of EDI devices based on this invention also includes EDI devices that do not have the function of removing dissolved oxygen.

Second Embodiment
In the EDI device of the first embodiment, outlet water from the anode chamber 21 (i.e., anode water) is discharged as wastewater to the outside of the EDI device via a concentrated water pipe 64. To reduce the amount of wastewater discharged from the EDI device and lower wastewater treatment costs, it is preferable to effectively utilize the anode water as well. The flow rate of the water passing through the anode chamber 21 is set to, for example, 5 to 10% of the flow rate of the water passing through the deionization chamber 23, and the flow rate of the anode water is also, for example, 5 to 10% of the flow rate of the treated water. By not discharging anode water at such a flow rate to the outside as wastewater, the amount of wastewater discharged can be reduced and the water recovery rate can be improved. The EDI device of the second embodiment of the present invention shown in FIG. 7 is similar to the EDI device shown in FIG. 1 , but differs from the EDI device shown in FIG. 1 in that cathode water from the cathode chamber 25 is supplied to the anode chamber 21 via a pipe 70, and anode water from the anode chamber 21 is supplied to a junction 81. The EDI device shown in Figure 7 does not have a pipe 66 connected to a branch pipe 62 to supply feed water to the anode chamber 21, nor does it have an adjustment valve 52 attached to the pipe 66, and the outlet of the anode chamber 21 is not connected to a concentrated water pipe 64. In the EDI device shown in Figure 7, the anode chamber 21 is the electrode chamber to be used.

In the EDI device shown in Figure 7, similar to the EDI device shown in Figure 1, cathode water containing hydrogen and hydroxide ions is discharged from the cathode chamber 25 and passed directly through the anode chamber 21. An oxidation reaction in the anode chamber 21 generates oxidizing substances such as oxygen and hydrogen ions. However, because the anode chamber 21 does not contain a catalyst capable of decomposing oxidants, the hydrogen contained in the water flowing into the anode chamber 21 does not react, and hydrogen remains in the anode water from the anode chamber 21. If oxidizing substances derived from the anode water flow into the deionization chamber 23, the ion exchange resin in the deionization chamber 23 may be decomposed and deteriorated. However, if a catalyst capable of decomposing oxidizing agents is present in the deionization chamber 23, the catalyst will decompose the oxidizing substances, thereby suppressing deterioration of the ion exchange resin in the deionization chamber 23 and simultaneously removing dissolved oxygen from the supply water. The EDI device of this embodiment may be an EDI device in which a catalyst capable of decomposing oxidants is not present in the desalting compartment 23, but is preferably an EDI device in which a catalyst capable of decomposing oxidants is present in the desalting compartment 23.

Even when the deionization compartment is divided into a first small deionization compartment 26 and a second small deionization compartment 27 by an intermediate ion exchange membrane 35, it is possible to prevent the anode water from being discharged to the outside as wastewater. The EDI device shown in Figure 8 is similar to the EDI device shown in Figure 2, but differs from the EDI device shown in Figure 2 in that cathode water from the cathode compartment 25 is supplied to the anode compartment 21 via piping 70, and anode water from the anode compartment 21 is supplied to the confluence 81.

In the EDI device of the second embodiment, cathode water is supplied to the anode chamber and the outlet water of the anode chamber is circulated to the deionization chamber, thereby further improving the water recovery rate of the EDI device compared to the EDI device of the first embodiment. In particular, if the concentrated water is also supplied to the inlet of a reverse osmosis membrane device located upstream of the EDI device, the only water discharged from the EDI device will be treated water (deionized water), which is the outlet water of the deionization chamber, and the water recovery rate of the EDI device can be made 100%.

[Third embodiment]
The configuration for preventing the anode water from being discharged to the outside as wastewater in the EDI device is not limited to that shown in the second embodiment. The EDI device of a third embodiment of the present invention shown in FIG. 9 is similar to the EDI device shown in FIG. 1 , but differs from the EDI device shown in FIG. 1 in that a junction 82 is further provided between the control valve 51 and the junction 81 in the piping supplying the feed water to the deionization chamber 23, and the anode water from the anode chamber 21 flows to the junction 82 via the piping 71 and is added to the feed water at the junction 82. The outlet of the anode chamber 21 is not connected to the concentrated water piping 64. In the EDI device shown in FIG. 9 , both the anode chamber 21 and the cathode chamber 25 are target electrode chambers. In the EDI device shown in FIG. 9 , the anode water and the cathode water circulate within the EDI device, thereby improving the water recovery rate of the EDI device. Furthermore, if a catalyst capable of decomposing oxidizing agents is present in the deionization compartment 23, cathode water containing hydrogen is added at the confluence 81, so that dissolved oxygen can be removed in the deionization compartment 23.

Even when the deionization compartment is divided into the first small deionization compartment 26 and the second small deionization compartment 27 by the intermediate ion exchange membrane 35, anode water and cathode water can be added separately to the feed water supplied to the deionization compartment 23. The EDI device shown in Figure 10 is similar to the EDI device shown in Figure 2, but differs from the device shown in Figure 2 in that a junction 82 is further provided between the control valve 51 and the junction 81 in the piping supplying the feed water to the deionization compartment 23, and anode water from the anode compartment 21 flows to the junction 82 via the piping 71 and is added to the feed water at the junction 82.

The present invention will be explained in more detail below using examples.

[Example 1]
The EDI device shown in Figure 2 was assembled. The first and second small deionization compartments 26 and 27 were filled with ion exchange resins. In particular, the first small deionization compartment 26 was filled with ion exchange resin supporting palladium, a catalyst with oxidant decomposition ability. Pump 15 was then driven to supply feed water with a dissolved oxygen concentration of 2200 μg/L to the electrode compartments, concentration compartments 22 and 24, and first small deionization compartment 26. Since the first small deionization compartment 26 and the second small deionization compartment 27 are connected in series to form the deionization compartment 23, the flow rate in the first small deionization compartment 26 and the flow rate in the second small deionization compartment 27 are equal. In the following description, this flow rate will be referred to as the flow rate in the deionization compartment 23. The DC current applied between the anode 11 and the cathode 12 was set to 4.0 A. The flow rate at the inlet of the first small deionization chamber 26 was constant at 300 L/h, the flow rate at the inlet of the anode chamber 21 was constant at 5 L/h, and the total flow rate at the inlets of the concentrating chambers 22 and 24 was always constant at 30 L/h. Under these conditions, the flow rate a of the feed water supplied from the feed water pipe 61 to the deionization chambers 23 (small deionization chambers 26 and 27) via the regulating valve 51 and the flow rate b of the cathode water discharged from the cathode chamber 25 and added to the feed water at the junction 81 were varied to produce Examples 1-1 to 1-4. In each of Examples 1-1 to 1-4, the dissolved oxygen removal rate of the treated water from the deionization chamber 23, i.e., the treated water discharged from the second small deionization chamber 27, was determined. The dissolved oxygen removal rate is a value indicating the amount of dissolved oxygen removed from the feed water supplied to the deionization chamber 23 via the regulating valve 51. The results are shown in Table 1. In Table 1, the flow rate ratio a:b indicates the ratio between the flow rate a of feed water supplied to deionization chamber 23 (small deionization chambers 26, 27) via adjustment valve 51 and the flow rate b of cathode water added to the feed water at junction 81. If the concentrated water is circulated to the upstream side of the EDI device and only the anode water is discharged to the outside of the EDI device, the water recovery rate of the EDI device at this time was 98.5% in all of Examples 1-1 to 1-4.

The results shown in Table 1 demonstrate that the EDI device shown in Figure 2 can be operated stably with a high water recovery rate of 98.5%. Furthermore, even when the dissolved oxygen concentration in the feed water was relatively high at 2,200 μg/L, a dissolved oxygen removal rate of 90% or more was achieved, even when the flow rate ratio a:b was approximately 11:1 or greater, and the proportion of cathode water was higher. Example 1 demonstrates that dissolved oxygen in the feed water can be removed with high efficiency and high water recovery without the need for a separate pump to pressurize the cathode water. Because the reaction rate between oxygen and hydrogen is high in the presence of a catalyst capable of decomposing oxidants, dissolved oxygen in the feed water can be removed with high efficiency by setting the flow rate of the cathode water so that hydrogen equivalent to the amount of dissolved oxygen contained in the feed water is supplied to the deionization chamber 23 (particularly the first small deionization chamber 26 filled with palladium-loaded ion exchange resin).

[Example 2]
An EDI system as shown in Figure 5 was assembled, with two EDI devices as shown in Figure 2 arranged in parallel. The first and second small deionization compartments 26 and 27 of each EDI device were filled with ion exchange resin. In particular, the first small deionization compartment 26 was filled with ion exchange resin supporting palladium, a catalyst with oxidant decomposition ability. Pump 15 was then driven to supply feed water with a dissolved oxygen concentration of 160 μg/L to the electrode compartments, concentration compartments 22 and 24, and first small deionization compartment 26, in the same manner as in Example 1. The DC current applied between the anode 11 and cathode 12 was set to 4.0 A. The dissolved oxygen removal rate of the treated water was determined in the same manner as in Example 1, assuming that the flow rate a of the feed water supplied from the feed water pipe 61 to the deionization chamber 23 (small deionization chambers 26, 27) via the adjustment valve 51 was 2600 L/h, the flow rate b of the cathode water discharged from the cathode chamber 25 and added to the feed water at the junction 81 was 20 L/h, the flow rate at the inlet of the anode chamber 21 was 19 L/h, and the total flow rate at the inlets of the concentration chambers 22, 24 was 300 L/h. The results are shown in Table 1. Assuming that the concentrated water was circulated to the upstream side of the EDI device and only the anode water was discharged outside the EDI device, the water recovery rate of the EDI device was 99.3%. These results demonstrate that the EDI apparatus shown in Figure 2 can be operated stably with a high water recovery rate of 99.3%, and that when the dissolved oxygen concentration in the feed water is relatively low at 160 μg/L, a dissolved oxygen removal rate of 99% or more can be achieved even when the flow rate ratio a:b is set to 130:1. In other words, when the dissolved oxygen content of the feed water is small, the dissolved oxygen in the feed water can be removed with high efficiency even when the amount of cathode water added is small.

10 Main body 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 chamber (D1)
27 Second Small Desalination Room (D2)
31, 33 Cation exchange membranes 32, 34 Anion exchange membranes 35 Intermediate ion exchange membranes 51 to 56 Adjustment valves 61 Supply water piping 62 Branch piping 63 Treated water piping 64 Concentrated water piping 66 to 70, 75 Pipes 81, 82 Confluence

Claims (10)

an anode chamber in which an anode is disposed and which is partitioned by a first diaphragm;
a cathode chamber in which a cathode is disposed and which is partitioned by a second diaphragm;
a deionization compartment disposed between the anode compartment and the cathode compartment and filled with an ion exchanger;
a first pipe connected to an inlet of the deionization compartment to supply pressurized feed water to the deionization compartment;
a first adjusting valve provided in the first pipe;
a confluence portion provided in the first pipe at a position between the first adjustment valve and the inlet of the desalination compartment;
a second pipe branching from the first pipe at a position upstream of the first regulating valve and through which the supply water flows;
a third pipe that connects an outlet of the target electrode chamber to the junction, with at least one of the anode chamber and the cathode chamber being a target electrode chamber;
and
the supply water is supplied to the anode chamber and the cathode chamber via the second pipe;
the outlet water of the target electrode chamber is mixed with the supply water at the confluence and supplied to the deionization chamber;
An electrodeionization water production apparatus in which a direct current is applied between the anode and the cathode. The electrodeionized water production apparatus according to claim 1, wherein at least a portion of the ion exchanger packed in the deionization chamber is supported with a catalyst capable of decomposing oxidants. The electrodeionization water production apparatus according to claim 2, wherein the catalyst having the ability to decompose oxidants is a platinum group metal catalyst. An electrodeionization water production apparatus according to any one of claims 1 to 3, wherein the target electrode chamber is the cathode chamber. The electrodeionized water production apparatus according to any one of claims 1 to 3, further comprising a second adjustment valve in the path supplying the supply water from the second pipe to the inlet of the target electrode chamber. 4. The electrodeionized water production apparatus according to claim 1, wherein the deionization compartment is partitioned by a first ion exchange membrane disposed closer to the anode and a second ion exchange membrane disposed closer to the cathode, and further comprises an intermediate ion exchange membrane located between the first and second ion exchange membranes, and the deionization compartment is partitioned into a first small deionization compartment and a second small deionization compartment by the intermediate ion exchange membrane, and the first small deionization compartment and the second small deionization compartment are connected to each other so that the feed water is supplied to one of the first and second small deionization compartments and water flowing out of the one small deionization compartment flows into the other small deionization compartment. 1. A method for operating an electrodeionization water production apparatus having an anode chamber in which an anode is disposed and which is separated by a first diaphragm, a cathode chamber in which a cathode is disposed and which is separated by a second diaphragm, and a deionization compartment disposed between the anode chamber and the cathode chamber and which is filled with an ion exchanger, comprising:
At least one of the anode chamber and the cathode chamber is used as a target electrode chamber,
an operating method in which, while applying a direct current between the anode and the cathode, feed water pressurized by a pump is supplied to the deionization compartment via an adjustment valve, and the feed water branched off upstream of the adjustment valve is passed through the anode chamber and the cathode chamber, and outlet water of the target electrode chamber is mixed with the feed water downstream of the adjustment valve without being pressurized, and supplied to the deionization compartment. The operating method described in claim 7, wherein at least a portion of the ion exchanger packed in the desalting compartment is supported with a catalyst having oxidant decomposition ability. The operating method described in claim 7 or 8, wherein the flow rate of the feed water supplied to the deionization compartment via the adjustment valve is set to at least 11 times the flow rate of the outlet water from the target electrode compartment that is mixed with the feed water. The operating method described in claim 9, wherein the target electrode chamber is the cathode chamber.