JP7672248B2 - Water treatment method and water treatment device - Google Patents

Description

The present invention relates to a water treatment device and a water treatment method that can remove dissolved oxygen from water.

A membrane degassing method using a degassing membrane is well known as a method for removing dissolved oxygen from water to be treated when the water is treated to produce pure water or the like. However, in the membrane degassing method, it is necessary to maintain a vacuum on the gas phase side, which is the opposite side of the water to be treated, across the degassing membrane, and therefore a vacuum pump or the like is required. Therefore, a method has been put into practical use in which a reducing agent such as hydrogen or hydrazine is added to the water to be treated, and the water is brought into contact with a deoxygenation catalyst carrying palladium or the like, and a reaction is caused to proceed to produce water from the dissolved oxygen and hydrogen (or hydrazine) to remove the dissolved oxygen. Patent Document 1 discloses an example of removing dissolved oxygen by contacting the water with a deoxygenation catalyst in the presence of hydrogen. Patent Document 2 discloses a method using an electrolytic cell in which a cathode chamber and an anode chamber are partitioned by a solid polymer electrode membrane, in which the water to be treated is supplied to the cathode chamber while electrolysis is carried out, and the dissolved oxygen is reduced and removed by a cathode reaction in the cathode chamber, and the dissolved oxygen that could not be removed is brought into contact with a deoxygenation catalyst together with the hydrogen produced by electrolysis to remove the dissolved oxygen.

One of the devices that produces desalted water from water to be treated is the electrodeionization water production device (EDI (Electrodeionization) device). The EDI device is a device that combines electrophoresis and electrodialysis, and at least the desalting chamber is filled with ion exchange resin. The EDI device has the advantage of eliminating the need for a process to regenerate the ion exchange resin with chemicals. Patent Document 3 discloses that the desalting chamber of the EDI device is filled with a mixture of anion exchange resin and cation exchange resin, and part of the anion exchange resin is made of catalytic resin carrying copper or palladium, and hydrogen is added to the water to be treated that is supplied to the desalting chamber, thereby desalting the water to be treated in the desalting chamber and removing dissolved oxygen from the water to be treated. Since the cathode water discharged from the cathode chamber of the EDI device contains hydrogen, Patent Document 3 also discloses that the cathode water is used as a hydrogen source and added to the water to be treated. However, even if cathode water is added to the water being treated, the pressure at the outlet of the cathode chamber is generally lower than the pressure of the water being treated at the inlet of the desalting chamber, so a pump is required to pressurize the water being treated in order to add the cathode water to the water being treated. Patent Document 4 discloses that hydrogen peroxide in the water being treated can be decomposed and removed by contacting the water with an anion exchange resin carrying platinum, palladium, or the like.

Japanese Patent Application Publication No. 5-96283 Japanese Patent Application Publication No. 7-241569 Japanese Patent Application Publication No. 10-272474 JP 2007-185587 A

The EDI device disclosed in Patent Document 3 is a device that can remove dissolved oxygen from the water being treated while also desalination without the need for a vacuum pump or the like, but the inventors' studies have revealed that there is room for improvement in the rate at which dissolved oxygen is removed from the water being treated.

The object of the present invention is to provide a water treatment method and water treatment device that can efficiently remove dissolved oxygen from the water to be treated.

In the EDI device disclosed in Patent Document 3, part of the anion exchange resin filled in the desalting chamber is a catalytic resin carrying copper or palladium, and the catalytic resin is mixed with a cation exchange resin that is not a catalytic resin, i.e., filled in the desalting chamber in a mixed bed form. However, as will be clear from the examples and comparative examples described later, the dissolved oxygen removal rate was improved and power consumption was reduced when the catalytic resin was filled in a single bed form in at least a part of the desalting chamber compared to when the catalytic resin was filled in a mixed bed form in the desalting chamber. Therefore, the water treatment method of the present invention is a water treatment method for removing at least dissolved oxygen contained in the water to be treated, which includes a step of applying a direct current between an anode and a cathode, and a step of passing the water to be treated through a dissolved oxygen removal chamber disposed between the anode and the cathode and filled with an ion exchanger, at least a part of the ion exchanger filled in the dissolved oxygen removal chamber is an ion exchanger carrying a metal catalyst, and the ion exchanger carrying the metal catalyst is filled in a single bed form in at least a part of the dissolved oxygen removal chamber. In this water treatment method, the step of applying a direct current between the anode and the cathode and the step of passing the water to be treated through the dissolved oxygen removal chamber may be performed simultaneously or separately.

The water treatment device of the present invention is a water treatment device that removes at least dissolved oxygen contained in the water to be treated, and has an anode and a cathode, and a dissolved oxygen removal chamber that is arranged between the anode and the cathode and is filled with an ion exchanger, and through which the water to be treated passes, at least a portion of the ion exchanger filled in the dissolved oxygen removal chamber is an ion exchanger carrying a metal catalyst, and the ion exchanger carrying the metal catalyst is filled in a single bed form in at least a portion of the dissolved oxygen removal chamber, and a direct current is applied between the anode and the cathode.

In the present invention, dissolved oxygen can be removed in the dissolved oxygen removal chamber because dissolved oxygen reacts with hydrogen in the presence of a metal catalyst to form water. Therefore, except when hydrogen is originally contained in the water to be treated, hydrogen must be generated in the dissolved oxygen removal chamber or hydrogen must be added to the water to be treated upstream of the dissolved oxygen removal chamber. The water treatment device of the present invention is basically configured in the same way as a general EDI device, except that it is configured to remove dissolved oxygen. In the cathode chamber of the EDI device, hydrogen is generated by a cathode reaction on the cathode surface, so in the present invention, the water to be treated is first supplied to the cathode chamber, and the outlet water of the cathode chamber, i.e., the water to be treated that has passed through the cathode chamber, is passed through the dissolved oxygen removal chamber, so that the water to be treated containing hydrogen can be supplied to the dissolved oxygen removal chamber. Alternatively, the cathode chamber itself can be used as the dissolved oxygen removal chamber.

In the EDI device disclosed in Patent Document 3, the outlet water of the cathode chamber is added to the water to be treated that is supplied to the desalination chamber that functions as the dissolved oxygen removal chamber. However, since the pressure of the outlet water of the cathode chamber is generally significantly smaller than the pressure of the water to be treated at the inlet of the desalination chamber, a pump is required to boost the outlet water of the cathode chamber. When boosting the pressure with a pump, the hydrogen bubbles contained in the outlet water of the cathode chamber may cause so-called air entrapment in the pump. In order to prevent air entrapment, it is possible to receive the outlet water of the cathode chamber in a tank and then pump it, but when the outlet water is received in the tank, hydrogen present in excess of the solubility will diffuse into the atmosphere, reducing the efficiency of hydrogen utilization. In contrast, in the present invention, the outlet water of the cathode chamber is used as it is as the inlet water to the dissolved oxygen removal chamber. In other words, the dissolved oxygen removal chamber is connected in series to the cathode chamber with respect to the flow of the water to be treated. By configuring in this way, in the present invention, a pump for boosting the pressure is not required, and the hydrogen generated in the cathode chamber is not dissipated, thereby increasing the efficiency of hydrogen utilization. If the amount of hydrogen contained in the water at the outlet of the cathode chamber is insufficient to remove the dissolved oxygen, for example, hydrogen can be injected into the line connecting the outlet of the cathode chamber and the inlet of the dissolved oxygen removal chamber. Even if the hydrogen generated in the cathode chamber is not used to remove dissolved oxygen, if a means for supplying hydrogen to the water being treated is provided upstream of the dissolved oxygen removal chamber, the water being treated containing hydrogen can be supplied to the dissolved oxygen removal chamber.

The mass of hydrogen that stoichiometrically reacts with oxygen is 1/8, or 0.125 times, the mass of oxygen. In light of this, in the present invention, regardless of the means used to add hydrogen to the water to be treated, it is preferable to adjust the amount of hydrogen contained in the water to be treated that is supplied to the dissolved oxygen removal chamber so that the mass ratio of the amount of hydrogen supplied to the dissolved oxygen removal chamber per unit time to the dissolved oxygen load to be treated in the water to be treated is 0.1 or more and 0.4 or less.

In the present invention, any metal catalyst can be used as long as it promotes the reaction of generating water from hydrogen and oxygen as the metal catalyst supported on the ion exchanger filled in the dissolved oxygen removal chamber. Examples of such metal catalysts include iron, copper, manganese, palladium, platinum, etc. Among them, platinum group metal catalysts not only promote the reduction reaction of oxygen, but also have high catalytic activity for decomposing hydrogen peroxide, so they can be used preferably when hydrogen peroxide is contained in the water to be treated. A platinum group metal catalyst is a catalyst containing one or more metals selected from ruthenium, rhodium, palladium, osmium, iridium, and platinum. The platinum group metal catalyst may contain any of these metal elements alone, or may be a combination of two or more of these. Among these, platinum, palladium, and platinum/palladium alloys have high catalytic activity and are preferably used as platinum group metal catalysts.

The water treatment device of the present invention is typically designed to remove dissolved oxygen in the desalination chamber of the EDI device. Therefore, the dissolved oxygen removal chamber is preferably partitioned by an ion exchange membrane, and by partitioning by an ion exchange membrane, the desalination treatment of the water to be treated can also be efficiently performed in the dissolved oxygen removal chamber. Alternatively, the anode chamber or cathode chamber in the EDI device can be used as the dissolved oxygen removal chamber, in which case the dissolved oxygen removal chamber is partitioned by an electrode plate that is an anode or an electrode plate that is a cathode.

The present invention makes it possible to efficiently remove dissolved oxygen from the water being treated.

1 is a diagram showing a water treatment device according to an embodiment of the present invention; FIG. 13 is a diagram showing another example of a water treatment device. FIG. 13 is a diagram showing another example of a water treatment device. FIG. 13 is a diagram showing another example of a water treatment device. FIG. 13 is a diagram showing another example of a water treatment device. FIG. 13 is a diagram showing another example of a water treatment device. FIG. 13 is a diagram showing another example of a water treatment device. 1 is a flow chart showing an example of a water treatment system including a water treatment device. 1 is a flow chart showing another example of a water treatment system including a water treatment device. 1 is a flow chart showing another example of a water treatment system including a water treatment device. FIG. 2 is a diagram showing a water treatment device according to a first comparative example. 1 is a graph showing the relationship between current density and dissolved oxygen removal rate. 1 is a graph showing the relationship between power consumption and dissolved oxygen removal rate. 1 is a graph showing the relationship between current per dissolved oxygen load and dissolved oxygen removal rate. 1 is a graph showing the relationship between space velocity and dissolved oxygen removal rate in a Pd-supported anion exchange resin.

Next, a preferred embodiment of the present invention will be described with reference to the drawings. Figure 1 shows the basic configuration of a water treatment device based on the present invention.

This water treatment device removes dissolved oxygen from the water to be treated and also performs desalination. Like a general EDI device, it is equipped with an anode chamber 21 in which an anode 11 is provided, and a cathode chamber 25 in which a cathode 12 is provided. Between the anode chamber 21 and the cathode chamber 25, a concentration chamber 22, a dissolved oxygen removal chamber 23, and a concentration chamber 24 are provided in this order from the anode chamber 21 side. The anode chamber 21 and the concentration chamber 22 are partitioned by a cation exchange membrane 31, the concentration chamber 22 and the dissolved oxygen removal chamber 23 are partitioned by an anion exchange membrane 32, the dissolved oxygen removal 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. The anode chamber 21 is filled with a cation exchange resin (CER) which is a cation exchanger, and the concentration chambers 22, 24, and the cathode chamber 25 are filled with an anion exchange resin (AER) which is an anion exchanger. The dissolved oxygen removal chamber 23 is filled in a single bed with an ion exchanger having a metal catalyst supported on its surface. In this embodiment, the dissolved oxygen removal chamber 23 is filled in a single bed with an anion exchange resin having palladium (Pd) supported on its surface. In the following description, the anion exchange resin having palladium (Pd) supported on its surface is referred to as Pd-supported anion exchange resin (Pd AER).

The water to be treated is supplied to the cathode chamber 25, and the outlet water of the cathode chamber 25 is supplied directly to the inlet of the dissolved oxygen removal chamber 23. Treated water from which dissolved oxygen has been removed and desalted is discharged from the dissolved oxygen removal chamber 23. Supply water is supplied to the concentration chambers 22 and 24, the outlet water of the concentration chambers 22 and 24 is supplied to the anode chamber 21, and the outlet water of the anode chamber 21 is discharged to the outside of the water treatment device. The supply water that has passed through the anode chamber 21 is discharged from the anode chamber 21 as wastewater. The supply water is not particularly limited, and may be, for example, water obtained by removing turbidity and oxidizing substances from city water, industrial water, groundwater, etc., and then treating it with a reverse osmosis membrane device.

Next, the removal of dissolved oxygen using the water treatment device shown in FIG. 1 will be described. A direct current is applied between the anode 11 and the cathode 12, and the water to be treated is supplied to the cathode chamber 25 while the feed water is supplied to the concentration chambers 22 and 24. In the cathode chamber 25, the direct current causes a cathode reaction to proceed on the surface of the cathode 12, generating hydrogen, so that the water to be treated discharged as outlet water from the cathode chamber 25 contains hydrogen. This hydrogen may not only dissolve in the water to be treated, but may also be dispersed in the water to be treated as tiny bubbles. The water to be treated containing hydrogen thus flows directly into the dissolved oxygen removal chamber 23. On the surface of the Pd-supported anion exchange resin (Pd AER) filled in the dissolved oxygen removal chamber 23, the dissolved oxygen in the water to be treated reacts with hydrogen to generate water. The amount of dissolved oxygen in the water to be treated decreases by the amount of reaction with hydrogen. Since the reaction rate between hydrogen and oxygen is high in the presence of palladium, a metal catalyst, if a sufficient amount of hydrogen is contained in the water to be treated, treated water from which dissolved oxygen has been sufficiently removed will be discharged from the cathode chamber 25. If hydrogen is present in the dissolved oxygen removal chamber 23, dissolved oxygen will be removed. Therefore, dissolved oxygen can also be removed by intermittently applying a direct current between the anode 11 and the cathode 12, taking into account the residence time of the water to be treated in the dissolved oxygen removal chamber 23 and the cathode chamber 25. Furthermore, the water to be treated may be passed intermittently through the dissolved oxygen removal chamber 23 while applying a direct current continuously or intermittently.

Since the Pd-loaded anion exchange resin is an anion exchanger, the dissolved oxygen removal chamber 23 filled with the Pd-loaded anion exchange resin functions in the same way as a desalination chamber in a general EDI device, and the desalination process of the water to be treated also proceeds in the dissolved oxygen removal chamber 23. For example, anions such as carbonate ions (CO ₃ ²⁻ ) and bicarbonate ions (HCO ₃ ⁻ ) in the water to be treated are captured by the Pd-loaded anion exchange resin. Hydroxide ions (OH ⁻ ) are also generated by dissociation of water on the surface of the cation exchange membrane 33 facing the dissolved oxygen removal chamber 23, so the anions captured by the Pd-loaded anion exchange resin (Pd AER) are ion-exchanged by the hydroxide ions and liberated, and move due to the electric field between the anode 11 and the cathode 12, and move through the anion exchange membrane 32 to the concentration chamber 22. The anions that have moved to the concentration chamber 22 are carried by the flow of the supply water in the concentration chamber 22 and discharged to the outside of the device via the anode chamber 21.

Since Pd-loaded anion exchange resin can also decompose hydrogen peroxide, the water treatment device of this embodiment can also remove hydrogen peroxide from the water being treated. When Pd-loaded anion exchange resin decomposes hydrogen peroxide, the decomposition products are hydrogen and oxygen. The oxygen generated reacts with hydrogen in the presence of Pd-loaded anion exchange resin to become water, so the decomposition and removal of hydrogen peroxide does not result in an increase in the dissolved oxygen concentration.

Figure 2 shows a water treatment device of another embodiment. The water treatment device shown in Figure 2 is similar to the water treatment device shown in Figure 1, but differs from that shown in Figure 1 in that the dissolved oxygen removal chamber 23 has a double-bed structure and the Pd-loaded anion exchange resin is provided only on the upstream side of the dissolved oxygen removal chamber 23. The downstream side of the dissolved oxygen removal chamber 23 is filled with anion exchange resin (AER) that does not support a metal catalyst. Since the reaction rate between hydrogen and oxygen in the presence of Pd-loaded anion exchange resin is sufficiently high, even if the Pd-loaded anion exchange resin is filled in a double-bed form so as to be placed in a part of the dissolved oxygen removal chamber 23, the dissolved oxygen in the water to be treated can be sufficiently removed. When the Pd-loaded anion exchange resin is arranged in the dissolved oxygen removal chamber 23 in a double-bed configuration, if there is nothing other than the Pd-loaded anion exchange resin in the region where the Pd-loaded anion exchange resin is arranged (i.e., a single-bed configuration), the layer of the Pd-loaded anion exchange resin may be packed at any location in the dissolved oxygen removal chamber 23. In that case, it is of course necessary to prevent the generation of water to be treated that flows through the dissolved oxygen removal chamber 23 without passing through the layer of the Pd-loaded anion exchange resin. In the configuration shown in FIG. 2, the amount of expensive palladium catalyst used can be reduced, thereby reducing costs.

Figure 3 shows a water treatment device of another embodiment. The water treatment device shown in Figure 3 is similar to the water treatment device shown in Figure 2, but differs from that shown in Figure 2 in that the ion exchanger filled in the downstream region of the dissolved oxygen removal chamber 23, which has a double-bed configuration, is a cation exchange resin (CER) that does not support a metal catalyst, rather than an anion exchange resin that does not support a metal catalyst.

Figure 4 shows a water treatment device of another embodiment. The water treatment device shown in Figure 4 is similar to the water treatment device shown in Figure 2, but differs from that shown in Figure 2 in that the downstream region of the dissolved oxygen removal chamber 23, which has a double-bed configuration, is filled with an anion exchange resin that does not support a metal catalyst and a cation exchange resin that does not support a metal catalyst in a mixed bed configuration (MB).

In the water treatment device shown in Figures 1 to 4, a desalination chamber is provided adjacent to the dissolved oxygen removal chamber 23 via an intermediate ion exchange membrane between the anode 11 and the cathode 12 on the cathode side or anode side of the dissolved oxygen removal chamber 23, and outlet water from the dissolved oxygen removal chamber 23 can be passed through the desalination chamber, or outlet water from the cathode chamber 25 can be passed through the desalination chamber and then supplied to the dissolved oxygen removal chamber 23. The desalination chamber is filled with an ion exchanger. The intermediate ion exchange membrane may be an anion exchange membrane or a cation exchange membrane, or may be a composite membrane such as a bipolar membrane. By configuring in this way, the desalination performance of the water treatment device as a whole can be further improved.

Figure 5 shows an example of a water treatment device in which a desalination chamber is provided adjacent to the dissolved oxygen removal chamber 23. The water treatment device shown in Figure 5 is the water treatment device shown in Figure 1, in which a desalination chamber 26 is arranged between the dissolved oxygen removal chamber 23 and the concentration chamber 24. The dissolved oxygen removal chamber 23 and the desalination chamber 26 are separated by a cation exchange membrane 35, which is an intermediate ion exchange membrane, and the desalination chamber 26 and the concentration chamber 24 are separated by a cation exchange membrane 33. The desalination chamber 26 is filled with a cation exchange resin. The outlet water of the cathode chamber 25 is first supplied to the dissolved oxygen removal chamber 23, the outlet water of the dissolved oxygen removal chamber 23 is supplied to the desalination chamber 26, and the treated water from which the dissolved oxygen has been removed and desalination treatment has been performed flows out from the desalination chamber 26.

The water treatment device shown in Figures 1 to 5 has the same configuration as a general EDI device, except that the desalination chamber is used as a dissolved oxygen removal chamber so that not only desalination processing but also removal of dissolved oxygen can be performed in the dissolved oxygen removal chamber. In a general EDI device, multiple desalination chambers can be arranged between the anode and the cathode. In the water treatment device shown in Figures 1 to 5, a repeating unit is formed of a configuration consisting of an anion exchange membrane 32, a dissolved oxygen removal chamber 23, a cation exchange membrane 33, and a concentration chamber 24, and multiple repeating units are arranged between the anion exchange membrane 34 that divides the concentration chamber 22 adjacent to the anode chamber 21 and the cathode chamber 25, so that multiple dissolved oxygen removal chambers 23 can be arranged between the anode 11 and the cathode 12. The water treatment device shown in Figure 6 is the water treatment device shown in Figure 1, in which multiple dissolved oxygen removal chambers 23 are arranged, and the outlet water of the cathode chamber 25 is distributed in parallel to the multiple dissolved oxygen removal chambers 23 and passed through them. Each dissolved oxygen removal chamber 23 discharges desalinated water from which dissolved oxygen has been removed and which has been desalted.

In the water treatment device based on the present invention, the cathode chamber itself can function as the dissolved oxygen removal chamber. In that case, there is no need to provide a dissolved oxygen removal chamber separate from the cathode chamber. Figure 7 shows a water treatment device in which the cathode chamber itself serves as the dissolved oxygen removal chamber.

The water treatment device shown in FIG. 7 includes an anode chamber 21 in which an anode 11 is provided, a concentration chamber 24 separated from the anode chamber 21 by a cation exchange membrane 31, and a cathode chamber 25 in which a cathode 12 is provided and separated from the concentration chamber 24 by an anion exchange membrane 34. The anode chamber 21 is filled with a cation exchange resin, and the concentration chamber 24 is filled with an anion exchange resin. The cathode chamber 25 is filled with a single bed of Pd-loaded anion exchange resin. Water to be treated containing dissolved oxygen is supplied to the cathode chamber 25, and the water to be treated passes through the cathode chamber 25. Supply water is supplied to the concentration chamber 24, and the outlet water of the concentration chamber 24 is supplied directly to the anode chamber 21. The supply water that has passed through the anode chamber 21 is discharged from the anode chamber 21 as wastewater. The supply water is not particularly limited, and may be water obtained by removing turbidity and oxidizing substances from city water, industrial water, groundwater, etc., and then treating it with a reverse osmosis membrane device.

In the water treatment device shown in FIG. 7, a direct current is applied between the anode 11 and the cathode 12, and the water to be treated is supplied to the cathode chamber 25 while the feed water is supplied to the concentration chamber 24. In the cathode chamber 25, the direct current causes a cathode reaction on the surface of the cathode 12 to generate hydrogen. This hydrogen reacts with the dissolved oxygen in the water to be treated on the surface of the Pd-supported anion exchange resin, thereby generating water. The amount of dissolved oxygen in the water to be treated is reduced by the amount of hydrogen that reacts with the hydrogen. As a result, treated water from which dissolved oxygen has been sufficiently removed is discharged from the cathode chamber 25. If hydrogen is present in the cathode chamber 25, dissolved oxygen is removed, so the application of a direct current between the anode 11 and the cathode 12 can be intermittent, taking into account the residence time of the water to be treated in the cathode chamber 25. Furthermore, the water to be treated may be passed through the dissolved oxygen removal chamber 23 intermittently while the direct current is applied continuously or intermittently.

Since the Pd-loaded anion exchange resin is an anion exchanger, anions in the water to be treated are captured by the Pd-loaded anion exchange resin. Since hydroxide ions (OH ⁻ ) are also generated by the cathode reaction at the cathode 12, the anions captured by the Pd-loaded anion exchange resin are ion-exchanged by the hydroxide ions and liberated, and move by the electric field between the anode 11 and the cathode 12, and move through the anion exchange membrane 34 to the concentration chamber 24. The anions that have moved to the concentration chamber 24 are carried by the flow of the feed water in the concentration chamber 24 and are discharged to the outside of the device through the anode chamber 21. That is, in the water treatment device shown in FIG. 7, the cathode chamber 25 also performs desalination treatment for anions. In addition, since the Pd-loaded anion exchange resin can also decompose hydrogen peroxide, this water treatment device can also remove hydrogen peroxide from the water to be treated, as in the water treatment devices shown in FIGS. 1 to 6.

The water treatment device according to the present invention has been described above, but this water treatment device can be incorporated into a water treatment system that produces pure water or ultrapure water. The water treatment system that produces pure water or ultrapure water is composed of, for example, an activated carbon device (AC), a reverse osmosis membrane device (RO), an ultraviolet irradiation device (UV), an ion exchange resin device (IER), a membrane degassing device (MD), an EDI device, a non-regenerative ion exchange device (CP), various filters, etc. The water treatment device according to the present invention can remove dissolved oxygen, remove hydrogen peroxide, and perform desalination treatment, so it can be used to replace one or more of the membrane degassing device, ion exchange resin device, EDI device, and non-regenerative ion exchange device, or can be installed in the front or rear of the membrane degassing device, ion exchange resin device, EDI device, and non-regenerative ion exchange device to improve the removal performance of impurity components. Figure 8 shows an example of a water treatment system incorporating a water treatment device according to the present invention.

The water treatment system shown in FIG. 8 is a system for producing ultrapure water from raw water such as city water, and is composed of a primary pure water system for producing primary pure water from raw water, and a subsystem for producing ultrapure water from primary pure water. In the figure, the reference numeral 100 denotes any of the water treatment devices described with reference to FIG. 1 to FIG. 7. In the primary pure water system, the raw water tank 41, the first reverse osmosis membrane device 51, the second reverse osmosis membrane device 52, the reverse osmosis membrane treated water tank 42, the ultraviolet irradiation device (UV) 55, and the water treatment device 100 are arranged in this order, and the raw water is treated in this order, and as a result, primary pure water is produced. If the water treatment device 100 based on the present invention is not used, an ion exchange resin device, an EDI device, and a membrane degassing device will be provided instead of the water treatment device 100. In the primary pure water system, when the downstream equipment to which the pure water is supplied becomes full, the produced primary pure water is circulated to the reverse osmosis membrane treated water tank 42.

In the subsystem, a pure water tank 45 is provided to store the primary pure water from the primary pure water system, and an ultraviolet ray irradiation device (UV) 61, a non-regenerative ion exchange device (CP) 63, a membrane degassing device (MD) 65, and an ultrafiltration membrane (UF) 67 are arranged in this order at the outlet of the pure water tank 45, and the primary pure water is treated in this order to produce ultrapure water. A part of the produced ultrapure water is circulated to the pure water tank 45. A microfiltration membrane may be used instead of the ultrafiltration membrane (UF) 67. In addition, in the subsystem, instead of the non-regenerative ion exchange device 63 and the membrane degassing device 65, a water treatment device based on the present invention may be provided, or may be provided before or after the non-regenerative ion exchange device 63 and the membrane degassing device 65. When a membrane degasser is installed in both the primary pure water system and the subsystem, the overall dissolved oxygen removal rate may be increased by installing multiple membrane degassers in series. When installing multiple membrane degassers in series in this way, some of the membrane degassers can be replaced with water treatment equipment based on the present invention.

9 shows another example of a water treatment system incorporating a water treatment device according to the present invention. In the water treatment system shown in FIG. 9, the water treatment device 100 is positioned in front of the ultraviolet irradiation device 55 of the primary pure water system in the water treatment system shown in FIG. 8, and a treatment device (IER/EDI) 56, which is an ion exchange resin device or an EDI device, is arranged behind the ultraviolet irradiation device 55. The water in the reverse osmosis membrane treated water tank 42 passes through the water treatment device 100 based on the present invention, the ultraviolet irradiation device 55, and the treatment device 56 in that order, and primary pure water is discharged from the treatment device 56, which is an ion exchange resin device or an EDI device. When the ultraviolet irradiation device 55 irradiates ultraviolet rays to the water to be treated to decompose and remove total organic carbon (TOC) components, it is known that the removal rate of TOC decreases when the dissolved oxygen concentration in the water to be treated is high. Therefore, in the water treatment system shown in FIG. 9, the dissolved oxygen concentration in the inlet water of the ultraviolet irradiation device 55 can be lowered, and the TOC removal rate in the ultraviolet irradiation device can be increased when the dissolved oxygen concentration in the raw water is high.

Figure 10 shows yet another example of a water treatment system incorporating a water treatment device according to the present invention. The water treatment system shown in Figure 10 is the water treatment system shown in Figure 8, in which a water treatment device 100 based on the present invention is also placed between the outlet of the ultraviolet irradiation device 61 and the inlet of the non-regenerative ion exchange device 63 of the subsystem. When organic matter in water is decomposed and removed by ultraviolet irradiation, carbonate ions and bicarbonate ions are generated, but the water treatment device 100 can also remove carbonate ions and bicarbonate ions. Therefore, by placing the water treatment device 100 in the subsystem as shown in Figure 8, the processing load on the subsequent non-regenerative ion exchange device 63 can be reduced and the impurity removal performance can be improved.

Next, the present invention will be explained in more detail with reference to examples and comparative examples.

[Example 1]
As Example 1, the water treatment device shown in Fig. 1 was assembled. The dimensions of the anode chamber 21, the concentration chambers 22, 24, and the cathode chamber 25 were all 105 mm x 105 mm x 9.5 mm, and the dimensions of the dissolved oxygen removal chamber 23 were 105 mm x 105 mm x 19.5 mm. In Example 1, the dissolved oxygen removal chamber 23 was filled with a single bed of Pd-supported anion exchange resin (Pd AER). The size of the anode 11 and the cathode 12 was 105 mm x 105 mm, and the current density can be calculated by dividing the applied current by the area of these electrodes.

[Example 2]
As Example 2, the water treatment device shown in Fig. 3 was assembled. This water treatment device has the same configuration and dimensions as those of Example 1, but differs from Example 1 in that the dissolved oxygen removal chamber 23 is filled with Pd-supported anion exchange resin (Pd AER) in a multiple bed. Specifically, in the dissolved oxygen removal chamber 23 of Example 2, a layer of Pd-supported anion exchange resin (Pd AER) is arranged on the inlet side of the water to be treated, and a layer of cation exchange resin (CER) not supporting a metal catalyst is arranged on the outlet side of the water to be treated. The ratio of the flow path length in the layer of Pd-supported anion exchange resin to the flow path length in the layer of cation exchange resin not supporting a metal catalyst was 1:1.

[Comparative Example 1]
As Comparative Example 1, the water treatment device shown in Fig. 11 was assembled. This water treatment device was the same as that of Example 1 in terms of configuration and dimensions, but differed from that of Example 1 in that the dissolved oxygen removal chamber 23 was filled with a Pd-supported anion exchange resin and a cation exchange resin not supporting a metal catalyst in a mixed bed form. Specifically, in Comparative Example 1, the Pd-supported anion exchange resin and the cation exchange resin not supporting a metal catalyst were mixed in a bulk volume ratio of 1:1, and the mixed state (Pd AER MB) was filled in the dissolved oxygen removal chamber 23.

For each of the water treatment devices of Examples 1 and 2 and Comparative Example 1, the water to be treated was passed through at a flow rate of 50 L/h and the feed water was passed through at a flow rate of 5 L/h while changing the applied current in the range of 0.5 A to 2.5 A. The change in the dissolved oxygen concentration according to the current density was examined from the dissolved oxygen concentration of the water to be treated at the inlet of the cathode chamber 25 and the dissolved oxygen concentration of the treated water discharged from the dissolved oxygen removal chamber 23. The results are shown in FIG. 12. As shown in FIG. 12, in Comparative Example 1 in which the filling form of the Pd-supported anion exchange resin is a mixed bed form, the dissolved oxygen removal rate plateaued at about 70% even when the current density increased, but in Example 1 in which the filling form of the Pd-supported anion exchange resin is a single bed form and Example 2 in which the filling form of the Pd-supported anion exchange resin is a multiple bed form, the dissolved oxygen removal rate could be increased to 80% or more by increasing the current density. Also, as shown in FIG. 12, in order to achieve a dissolved oxygen removal rate of at least 20%, it is preferable to set the current density to 0.45 A/dm ² or more and 2.3 A/dm ² or less. In order to obtain a better dissolved oxygen removal rate, it is more preferable to set the current density to 1.0 A/dm ² or more and 2.0 A/dm ² or less.

In the water treatment device, when the applied current between the anode 11 and the cathode 12 is changed, the applied voltage at that time also changes, and the power consumption, which is the product of the current and the voltage, changes more than the change in the applied current. The power consumption for each result shown in FIG. 12 was calculated and converted into the power consumption per unit flow rate of the water to be treated, and the results are shown in FIG. 13. In FIG. 13, the horizontal axis is the power consumption per unit flow rate of the water to be treated, and the power consumption in Comparative Example 1 is larger than that in Examples 1 and 2. Since the applied current is the same in Examples 1 and 2 and Comparative Example 1, the applied voltage in Comparative Example 1, which is a mixed bed form, is higher than that in Examples 1 and 2, and the power consumption required to obtain the same dissolved oxygen removal rate is larger. In other words, in the case of the single bed form shown in Example 1 and the case of the multiple bed form shown in Example 2, dissolved oxygen can be removed with less energy. Considering the same as the preferred range of current density, the power consumption per unit flow rate of the water being treated is preferably 0.06 W·h/L or more and 0.70 W·h/L or less, and more preferably 0.17 W·h/L or more and 0.50 W·h/L or less.

Based on the dissolved oxygen concentration of the water to be treated at the inlet of the cathode chamber 25 when the results shown in FIG. 12 were obtained and the current value at that time, the relationship between the current value per dissolved oxygen load (the mass of dissolved oxygen contained in the water to be treated flowing in per unit time) and the dissolved oxygen removal rate was investigated. The results are shown in FIG. 14. From FIG. 14, the current value per dissolved oxygen load needs to be 2 mA·h/mg to achieve a dissolved oxygen removal rate of 50% or more, and needs to be 4 mA·h/mg to achieve a dissolved oxygen removal rate of 80% or more. Therefore, the current value per dissolved oxygen load is preferably 2 mA·h/mg or more and 8 mA·h/mg or less, and more preferably 4 mA·h/mg or more and 8 mA·h/mg or less.

The water treatment devices of Examples 1 and 2 and Comparative Example 1 were operated with the applied current fixed at 2A, and the change in the dissolved oxygen removal rate when the flow rate of the water to be treated was changed was examined. The results are shown in FIG. 15 as the change in the dissolved oxygen removal rate with respect to the space velocity based on the volume of the Pd-supported anion exchange resin in the dissolved oxygen removal chamber 23. As shown in FIG. 15, the dissolved oxygen removal rate decreases as the flow rate of the water to be treated increases, and in the case of a single bed form, the space velocity of the water to be treated based on the volume of the Pd-supported anion exchange resin, that is, the quotient obtained by dividing the flow rate of the water to be treated by the volume of the Pd-supported anion exchange resin, was 500 h ^-1 , and the dissolved oxygen removal rate decreased to 50%. It is considered that the dissolved oxygen removal rate decreases when the flow rate of the water to be treated is further increased, and it was found that in practice, the space velocity of the water to be treated based on the volume of the Pd-supported anion exchange resin filled in the dissolved oxygen removal chamber 23 is preferably 1000 h ^-1 or less, and more preferably 500 h ^-1 or less.

[Example 3]
The water to be treated had a dissolved oxygen concentration of 7.9 mg/L and a carbon dioxide concentration of 3.2 mg/L, and this water was supplied to the water treatment device of Example 1 having a single bed configuration at a flow rate of 50 L/h, and the water treatment device was operated with an applied current of 1.0 A. The dissolved oxygen concentration and carbon dioxide concentration in the treated water discharged from the dissolved oxygen removal chamber 23 were then measured to determine the respective removal rates. The results are shown in Table 1. From Table 1, it was found that the water treatment device based on the present invention can remove not only dissolved oxygen but also carbon dioxide from the water to be treated.

[Example 4]
The water to be treated had a dissolved oxygen concentration of 7.8 mg/L to 8.2 mg/L, and was supplied to the water treatment devices of Examples 1 and 2 and Comparative Example 1 at a flow rate of 50 L/h, and each water treatment device was operated with an applied current of 1.5 A. The hydrogen concentration in the outlet water of the cathode chamber 25 and the dissolved oxygen concentration in the treated water discharged from the dissolved oxygen removal chamber 23 were measured. From the dissolved oxygen concentration of the treated water, the amount of oxygen removed in the dissolved oxygen removal chamber 23 was calculated, and from this and the hydrogen concentration in the outlet water of the cathode chamber, the utilization efficiency of the hydrogen generated in the cathode chamber 25 was calculated. In the calculation, it was assumed that 1 mole of hydrogen (H ₂ ) reacts with 0.5 moles of oxygen (O ₂ ). The results are shown in Table 2.

When comparing Example 2 with the double-bed configuration and Comparative Example 1 with the mixed-bed configuration, the hydrogen utilization efficiency was lower in Comparative Example 1 with the mixed-bed configuration, even though the amount of Pd-loaded anion exchange resin packed in the dissolved oxygen removal chamber 23 was the same. On the other hand, when comparing Example 2 with the single-bed configuration, no significant difference was observed in the hydrogen utilization efficiency, even though the amount of Pd-loaded anion exchange resin packed in the dissolved oxygen removal chamber 23 was twice that of Example 2. In Examples 1 and 2, almost the entire amount of hydrogen generated in the cathode chamber 25 was used to remove dissolved oxygen.

REFERENCE SIGNS LIST 11 anode 12 cathode 21 anode chamber 22, 24 concentration chamber 23 dissolved oxygen removal chamber 25 cathode chamber 26 deionization chamber 31, 33, 35 cation exchange membrane 32, 34 anion exchange membrane 100 water treatment device

Claims (11)

A water treatment method for removing at least dissolved oxygen contained in water to be treated, comprising the steps of:
applying a direct current between an anode provided in the anode chamber and a cathode provided in the cathode chamber ;
A step of passing the water to be treated through a dissolved oxygen removal chamber disposed between the anode chamber and the cathode chamber and filled with an ion exchanger , the dissolved oxygen removal chamber being provided separately from the cathode chamber ;
having
At least a part of the ion exchanger packed in the dissolved oxygen removal chamber is an ion exchanger carrying a metal catalyst,
The water treatment method, wherein the ion exchanger carrying the metal catalyst is packed in a single bed form in at least a part of the dissolved oxygen removing chamber. 2. The water treatment method according to claim 1, further comprising the steps of supplying the water to be treated to the cathode chamber, and causing the water to be treated after passing through the cathode chamber to pass through a dissolved oxygen removing chamber. A water treatment device that removes at least dissolved oxygen contained in water to be treated,
an anode and a cathode;
a dissolved oxygen removal chamber, which is disposed between an anode chamber in which the anode is provided and a cathode chamber in which the cathode is provided, and which is filled with an ion exchanger and through which the water to be treated passes;
having
At least a part of the ion exchanger packed in the dissolved oxygen removal chamber is an ion exchanger carrying a metal catalyst,
The ion exchanger carrying the metal catalyst is filled in at least a portion of the dissolved oxygen removing chamber in a single bed form,
A water treatment device in which a direct current is applied between the anode and the cathode. The water treatment device according to claim 3 , wherein the dissolved oxygen removal chamber is defined by at least one of an electrode plate serving as the anode and an ion exchange membrane. The water treatment device according to claim 3 or 4, wherein the dissolved oxygen removal chamber is connected in series with the cathode chamber with respect to the flow of the water to be treated. The water treatment device according to any one of claims 3 to 5, further comprising a means for supplying hydrogen to the water to be treated, provided upstream of the dissolved oxygen removal chamber. The water treatment device according to claim 3 , wherein a current value of the direct current with respect to a dissolved oxygen load to be treated in the water to be treated is set to 2 mA·h/mg or more and 8 mA·h/mg or less. The water treatment device according to any one of claims 3 to 7, wherein the space velocity of the water to be treated based on the volume of the ion exchanger carrying the metal catalyst filled in the dissolved oxygen removal chamber is set to 1000 h ^-1 or less. 9. The water treatment device according to claim 3, wherein the amount of hydrogen contained in the water to be treated and supplied to the dissolved oxygen removal chamber is adjusted so that the mass ratio of the amount of hydrogen supplied to the dissolved oxygen removal chamber per unit time to the dissolved oxygen load to be treated in the water to be treated is 0.1 or more and 0.4 or less. The water treatment device according to claim 3 , wherein a current density in the dissolved oxygen removal chamber is 0.45 A/dm ² or more and 2.3 A/dm ² or less. The water treatment device according to any one of claims 3 to 10, wherein the power consumption per flow rate of the water to be treated in the dissolved oxygen removal chamber is 0.06 W·h/L or more and 0.70 W·h/L or less.

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