Water treatment device

Abstract

Provided is a water treatment device (1) for producing treated water by removing metal ions from water to be treated, the water treatment device comprising an electrolytic cell (10) that includes an anode chamber (15) provided with an anode (12), a cathode chamber (16) provided with a cathode (13), and a membrane (14) for partitioning the anode chamber and the cathode chamber and capable of transmitting ions, and that produces acidic water and alkaline water from the water to be treated through electrolysis. The water treatment device further comprises a control unit (100) that controls the voltage or current between the anode and the cathode. The acidic water flows in the anode chamber, the alkaline water flows in the cathode chamber, and the control unit controls the flow velocity of the acidic water in the anode chamber and the flow velocity of the alkaline water in the cathode chamber so as to satisfy mathematical formula 1.

Description

Water treatment equipment

[0001] The present disclosure relates to a water treatment device.

[0002] BACKGROUND ART Ion exchange resin water softeners for removing metal ions from hard water have been known (see, for example, Patent Document 1).

[0003] The ion exchange resin water softener of Patent Document 1 removes metal ions (calcium ions and magnesium ions) from hard water using ion exchange resin. Specifically, by passing hard water through a water softener vessel equipped with ion exchange resin having sodium ions attached to its surface, the metal ions in the hard water are replaced with sodium ions, thereby removing the metal ions from the hard water. The metal ions present in the hard water are captured on the surface of the ion exchange resin. In this way, the hardness of the hard water is reduced to produce soft water.

[0004] Japanese Patent Application Laid-Open No. 2000-140840

[0005] However, the ion exchange resin water softener of Patent Document 1 requires a large amount of saltwater to regenerate the ion exchange resin that has captured metal ions, resulting in problems such as time-consuming maintenance. Furthermore, the regeneration process generates wastewater containing a large amount of saltwater, which can lead to soil contamination and increased burdens on sewage treatment. Furthermore, the treated water softened by the ion exchange resin water softener has a high concentration of sodium ions, and in some areas may not be recommended as drinking water. Thus, water treatment devices using ion exchange resins have room for improvement in terms of ease of maintenance and environmental friendliness.

[0006] The present disclosure has been made in view of the problems inherent in the conventional techniques, and an object of the present disclosure is to provide a water treatment device that can efficiently remove metal ions from hard water without using an ion exchange resin.

[0007] In order to solve the above problems, a water treatment device according to an aspect of the present disclosure is a water treatment device that removes metal ions from water to be treated to produce treated water, and includes an anode chamber having an anode, a cathode chamber having a cathode, and a membrane that separates the anode chamber and the cathode chamber and is permeable to ions, an electrolytic cell that produces acidic water and alkaline water from the water to be treated by electrolysis, and a control unit that controls the voltage or current between the anode and the cathode, wherein the acidic water flows through the anode chamber and the alkaline water flows through the cathode chamber, and the control unit controls the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber so as to satisfy Equation 1.

[0008] FIG. 1 is a schematic diagram showing an example of the configuration of a water treatment device according to this embodiment. FIG. 2 is a schematic diagram showing the state of metal ion migration and insolubilization in the electrolytic cell of the water treatment device according to this embodiment. FIG. 3 is a schematic diagram showing the state of hydrogen ion migration and neutralization in the electrolytic cell of the water treatment device according to this embodiment. FIG. 4 is a schematic diagram showing the state of carbonate (H ２ CO ３ ), bicarbonate ion (HCO ３ － ) and carbonate ions (CO ３ ２－ ) and pH. FIG. 5 is a table for explaining electrolysis control in the water treatment device according to this embodiment. FIG. 6 is a graph schematically showing the relationship between the conductivity of the water to be treated and the ion migration rate, insolubilization rate, and water softening rate of metal ions when only constant current control is performed, when only constant voltage control is performed, and when electrolysis control is performed. FIG. 7 is a graph showing an example of the relationship between the conductivity of the water to be treated and power consumption when only constant voltage control is performed, when only constant current control is performed, and when electrolysis control is performed. FIG. 8 is a schematic diagram showing the migration of hydrogen ions in the electrolytic cell of the water treatment device according to this embodiment. FIG. 9 is a table for explaining electrolysis control in the water treatment device according to this embodiment. FIG. 6 is a graph schematically showing the relationship between the conductivity of the water to be treated and the ion migration rate, insolubilization rate, and water softening rate of metal ions when only constant voltage control is performed, when only constant current control is performed, and when electrolysis control is performed. ＋FIG. 10 is a graph showing the relationship between the pH change (vertical axis) of water in the cathode chamber and the amount of electricity (horizontal axis) between the electrodes, derived from equation (19). FIG. 11 is a graph showing an example of the results of measuring the pH of alkaline water in the cathode chamber in a water treatment device when the flow rate of acidic water in the anode chamber is 4.6 L / min or 14 L / min. FIG. 12 is a flowchart showing an example of a method for controlling the flow rate of acidic water in the anode chamber based on the pH of alkaline water measured by the pH measurement unit. FIG. 13 is a graph showing an example of the relationship between the pH (alkaline side pH) of the water to be treated in the cathode chamber and time.

[0009] The water treatment device according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of convenience and may differ from the actual proportions.

[0010] The water treatment device of this embodiment is a device that removes and separates metal ions from the water to be treated, thereby reducing the concentration (hardness) of metal ions in the water to a predetermined concentration or less, and producing treated water. ２＋ ) and magnesium ions (Mg ２＋ The definitions of hard water and soft water may be, for example, those of the WHO. That is, soft water may be defined as water with a hardness of less than 120 mg / L, and hard water may be defined as water with a hardness of 120 mg / L or more.

[0011] 1, the water treatment device 1 of this embodiment includes an electrolytic cell 10 that produces acidic water and alkaline water from water to be treated by electrolysis, a first flow path 20 through which the acidic water circulates, and a second flow path 30 through which alkaline water circulates. The water treatment device 1 further includes a water to be treated flow path 40 through which the water to be treated is supplied, a first outlet flow path 50 through which the treated acidic water flows from the first flow path 20, and a second outlet flow path 60 through which the treated alkaline water flows from the second flow path 30.

[0012] 1 and 2, the electrolytic cell 10 includes a solution tank 11, an anode 12, a cathode 13, and an ion-permeable membrane (ion-permeable membrane) 14. The solution tank 11 is a container that holds water to be treated that contains metal ions, and electrolyzes the water to be treated held therein, as described below.

[0013] The anode 12 and the cathode 13 are an electrode pair for electrolyzing the water to be treated in the solution tank 11. The anode 12 is provided in an anode chamber 15, and the cathode 13 is provided in a cathode chamber 16. The anode 12 and the cathode 13 are arranged inside the solution tank 11 so as to face each other with an ion permeable membrane 14 therebetween. The anode 12 is electrically connected to the positive electrode of a power source 90 for electrolysis, and the cathode 13 is electrically connected to the negative electrode of the power source 90 for electrolysis.

[0014] The ion-permeable membrane 14 is disposed in the solution tank 11 and divides the solution tank 11 into an anode chamber 15 and a cathode chamber 16. That is, the anode chamber 15 is partitioned by a portion of the solution tank 11 and the ion-permeable membrane 14, and the cathode chamber 16 is partitioned by another portion of the solution tank 11 and the ion-permeable membrane 14. The ion-permeable membrane 14 is a member through which metal ions in the water to be treated permeate. Therefore, the ion-permeable membrane 14 is not particularly limited as long as it allows metal ions to permeate, and for example, a porous membrane or a cation exchange membrane can be used. The material of the porous membrane is not particularly limited, and may be, for example, a ceramic material, a resin material, or a metal material.

[0015] A first flow path 20 is connected to the anode chamber 15 of the electrolytic cell 10. That is, the first flow path 20 is connected to the inlet 15a and the outlet 15b of the anode chamber 15, respectively. In the first flow path 20, an acidic water tank 21 for temporarily storing acidic water and a first circulation pump 22 for pumping the acidic water are disposed downstream of the anode chamber 15. Therefore, the acidic water flowing out from the outlet 15b of the anode chamber 15 can pass through the acidic water tank 21 and the first circulation pump 22 and flow into the anode chamber 15 from the inlet 15a of the anode chamber 15.

[0016] Similarly, a second flow path 30 is connected to the cathode chamber 16 of the electrolytic cell 10. That is, the second flow path 30 is connected to the inlet 16a and the outlet 16b of the cathode chamber 16, respectively. In the second flow path 30, an alkaline water tank 31 for temporarily storing alkaline water and a second circulation pump 32 for pressure-feeding the alkaline water are disposed downstream of the cathode chamber 16. Therefore, the alkaline water flowing out from the outlet 16b of the cathode chamber 16 can pass through the alkaline water tank 31 and the second circulation pump 32 and flow into the cathode chamber 16 from the inlet 16a of the cathode chamber 16.

[0017] The water to be treated flow path 40 is a flow path that supplies the water to be treated to the electrolytic cell 10. Specifically, the water to be treated flow path 40 branches into two flow paths, which are connected to the first flow path 20 and the second flow path 30. Therefore, the water to be treated is supplied to both the first flow path 20 and the second flow path 30 through the water to be treated flow path 40. The water to be treated flow path 40 is provided with an electromagnetic valve 41 that switches between allowing the water to be passed and stopping the flow of water to be treated.

[0018] The first outlet flow path 50 is connected to the downstream side of the first circulation pump 22 via a first electromagnetic valve 51. As will be described later, the first outlet flow path 50 is a flow path for discharging acidic water softened in the electrolytic cell 10. A water valve 52 is provided at the end of the first outlet flow path 50 to switch between allowing and stopping the flow of acidic water softened. The treated water discharged from the first outlet flow path 50 is treated water in which metal ions have been removed or reduced, and can be suitably used.

[0019] The second outlet flow path 60 is connected to the downstream side of the second circulation pump 32 via a second electromagnetic valve 61. As will be described later, the second outlet flow path 60 is a flow path for discharging alkaline water that has been insolubilized in the electrolytic cell 10. The end of the second outlet flow path 60 is connected to a water tap 52. The water tap 52 can be used to switch between passing and stopping the alkaline water that has been softened by removing insolubilized matter using a filter 62. The treated water that has been discharged from the second outlet flow path 60 is water in which metal ions have been removed or reduced, and can be used suitably.

[0020] The second outlet flow path 60 is provided with a filter 62 for separating and removing insolubilized matter consisting of metal ions insolubilized in the electrolytic cell 10. The filter 62 is not particularly limited as long as it is capable of removing insolubilized matter, and a cartridge-type filter, a filtration layer using a granular filter medium, a cyclone-type solid-liquid separator, a hollow fiber membrane, etc. can be used.

[0021] 1 , a bypass flow path 53 may be connected to the first solenoid valve 51 for sending the softened acidic water to a filter 62. The acidic water that has been softened in the electrolytic cell 10 and circulating through the first flow path 20 has had insolubilized matter sufficiently reduced, but if necessary, the acidic water may be filtered through the filter 62 before being sent to the faucet 52. Furthermore, a bypass flow path 63 may be connected to the second solenoid valve 61 for sending the alkaline water that has been insolubilized in the electrolytic cell 10 directly to the faucet 52 without sending it to the filter 62.

[0022] As shown in FIG. 1 , the water treatment device 1 of this embodiment includes a first conductivity measuring unit 70 that measures the conductivity of water flowing through the anode chamber and a second conductivity measuring unit 80 that measures the conductivity of water flowing through the cathode chamber. In this specification, the water flowing through the anode chamber is also referred to as anode water, and the water flowing through the cathode chamber is also referred to as cathode water. The first conductivity measuring unit 70 is provided on the inlet 15 a side of the anode chamber 15 in the first flow path 20, and the second conductivity measuring unit 80 is provided on the inlet 16 a side of the cathode chamber 16 in the second flow path 30. However, the location where the first conductivity measuring unit 70 is installed is not particularly limited as long as it can measure the conductivity of the anode water. For example, the first conductivity measuring unit 70 may be installed inside the anode chamber 15 or inside the acidic water tank 21. Similarly, the location where the second conductivity measuring unit 80 is installed is not particularly limited as long as it can measure the conductivity of the cathode water, and it may be installed, for example, inside the cathode chamber 16 or inside the alkaline water tank 31.

[0023] Conductivity sensors can be used as the first conductivity measuring unit 70 and the second conductivity measuring unit 80. Furthermore, a TDS (total dissolved solids) sensor or a pH sensor can be used as the first conductivity measuring unit 70 and the second conductivity measuring unit 80, as long as the sensors are capable of calculating conductivity.

[0024] The first conductivity measuring unit 70 and the second conductivity measuring unit 80 are connected to the control unit 100 described later, and transmit the numerical values ​​of the conductivity of the anode water and the conductivity of the cathode water measured by the first conductivity measuring unit 70 and the second conductivity measuring unit 80 to the control unit 100.

[0025] As shown in FIG. 1 , the water treatment device 1 includes a first pH measurement unit 15c that measures the pH of water flowing through the anode chamber 15 and a second pH measurement unit 16c that measures the pH of water flowing through the cathode chamber 16. In this embodiment, the first pH measurement unit 15c is provided inside the anode chamber 15, and the second pH measurement unit 16c is provided inside the cathode chamber 16. The location of the first pH measurement unit 15c is not particularly limited as long as it can measure the pH of the anode water. For example, it may be provided in the first flow path 20 or inside the acidic water tank 21. Similarly, the location of the second pH measurement unit 16c is not particularly limited as long as it can measure the pH of the cathode water. For example, it may be provided in the second flow path 30 or inside the alkaline water tank 31.

[0026] The first pH measuring unit 15c and the second pH measuring unit 16c are electrically connected to the control unit 100, and transmit the numerical values ​​of the pH of the anode water and the pH of the cathode water measured by the first pH measuring unit 15c and the second pH measuring unit 16c to the control unit 100.

[0027] The water treatment device 1 further includes an electrolysis power supply 90 and a control unit 100. The electrolysis power supply 90 is electrically connected to the anode 12 and the cathode 13. The electrolysis power supply 90 passes a current between the anode 12 and the cathode 13 and applies a voltage therebetween.

[0028] The control unit 100 is electrically connected to the electrolysis power supply 90 and adjusts the voltage between the anode and the cathode by controlling the electrolysis power supply 90. The control unit 100 is also electrically connected to the solenoid valve 41, the first solenoid valve 51, the second solenoid valve 61, and the water faucet 52 in the treated water flow path 40 and controls their opening and closing. The control unit 100 is also electrically connected to the first circulation pump 22 and the second circulation pump 32 and controls their operation.

[0029] When the control unit 100 executes operations based on a control program, the control unit 100 may include a storage device such as a ROM (Read Only Memory) or a RAM (Random Access Memory) that stores the control program, and a CPU (Central Processing Unit) that executes the control program. When the control unit 100 executes predetermined operations, the control unit 100 may include a dedicated electronic circuit or the like that realizes the control program in hardware. Furthermore, the control unit 100 may include a timing unit such as an RTC (Real Time Clock) to measure time.

[0030] The operation of the water treatment device 1 configured as described above is premised on the following facts. First, the conductivity of acidic water is proportional to the ion concentration in the acidic water. Therefore, the conductivity of acidic water is proportional to the concentration of metal ions (hardness) contained in the acidic water. Similarly, the conductivity of alkaline water is proportional to the ion concentration in the alkaline water. Therefore, the conductivity of alkaline water is proportional to the concentration of metal ions (hardness) contained in the alkaline water.

[0031] Next, when a voltage is applied to the anode 12 and the cathode 13 with the water to be treated placed in the anode chamber 15 and the cathode chamber 16 of the electrolytic cell 10, the metal ions in the anode chamber 15 permeate the ion permeable membrane 14 and move to the cathode chamber 16, as shown in Figure 2. That is, as shown in the electrophoretic velocity equation of Equation 2, the electrophoretic velocity of ions ν (m / s) is proportional to the ion mobility μ (m ２The voltage is expressed as the product of the voltage (V / Vs) and the electric field E (V / m). Therefore, the movement of metal ions depends on the magnitude of the voltage (electric field). As shown in FIG. 3, when a voltage is applied to the anode 12 and the cathode 13, hydrogen ions (H ＋ ) also moves to the cathode chamber 16, and hydroxide ions (OH － ) and neutralizes it.

[0032] Next, when the water to be treated is placed in the anode chamber 15 and the cathode chamber 16 of the electrolytic cell 10 and electrolyzed, hydrogen ions (H ＋ ) is generated at the cathode 13 by a reduction reaction, and hydroxide ions (OH － ) is produced. Note that this type of water electrolysis depends on the magnitude of the current.

[0033] The magnesium ions (Mg ２＋ ) reacts with the generated hydroxide ions to form magnesium hydroxide (Mg(OH) ２ ) and becomes insoluble. Here, the solubility product K of magnesium hydroxide in water at 25°C is ｓｐ is 1.80 x 10 －１１ (mol / L) ３ Then, as shown in Equation 3, Mg ２＋ and OH － The ionic product with is the solubility product K ｓｐ When it becomes larger than Mg(OH) ２ The dissolution equilibrium shifts in the direction of the formation of Mg(OH) ２ Therefore, in order to efficiently insolubilize magnesium ions, it is necessary to increase the pH, that is, to increase the hydroxide ions.

[0034] In addition, carbonate ions (CO ３ ２－ ) contained in the water to be treated. ２＋) reacts with carbonate ions to form calcium carbonate (CaCO ３ ) and becomes insoluble. Here, the solubility product K of calcium carbonate in water at 25°C is ｓｐ is 4.96 x 10 －９ (mol / L) ２ Then, as shown in Equation 4, Ca ２＋ and CO ３ － The ionic product with is the solubility product K ｓｐ If it is larger than ３ The dissolution equilibrium shifts in the direction of CaCO ３ An insoluble matter consisting of the following is produced.

[0035] Here, in FIG. 4, the carbonic acid (H ２ CO ３ ), bicarbonate ion (HCO ３ － ) and carbonate ions (CO ３ ２－ ) and pH. Figure 4 shows the relationship between the abundance ratio of these ions and pH. As the pH of water becomes more alkaline, the amount of carbonate and bicarbonate ions decreases and the amount of carbonate ions increases. Therefore, in order to efficiently insolubilize calcium ions, it is necessary to increase the pH and increase the amount of carbonate ions.

[0036] Thus, the insolubilization of magnesium ions and calcium ions increases with increasing hydroxide ion concentration. Furthermore, the electrolysis of water depends on the magnitude of the current. Therefore, the insolubilization of magnesium ions and calcium ions depends on the magnitude of the current.

[0037] Next, based on the above-mentioned events, the operation of the water treatment device 1 of this embodiment will be described. First, the control unit 100 opens the solenoid valve 41 and injects raw water (water to be treated) into the water-to-be-treated flow path 40, the first flow path 20, and the second flow path 30. Next, the control unit 100 injects the water to be treated into the anode chamber 15 and the cathode chamber 16 of the electrolytic cell 10, the acidic water tank 21, and the alkaline water tank 31.

[0038] Next, the control unit 100 measures the conductivity of the anode water and the cathode water using the first conductivity measuring unit 70 and the second conductivity measuring unit 80. Furthermore, the control unit 100 controls the electrolysis power supply 90 to pass a current between the anode 12 and the cathode 13, thereby electrolyzing the water to be treated. The control unit 100 also operates the first circulation pump 22 and the second circulation pump 32 to circulate the water to be treated through the first flow path 20 and the second flow path 30. By performing the electrolysis and circulation of the water to be treated for a predetermined period of time, the water to be treated in the anode chamber 15, the first flow path 20, and the acidic water tank 21 becomes acidic water, and the water to be treated in the cathode chamber 16, the second flow path 30, and the alkaline water tank 31 becomes alkaline water.

[0039] The control unit 100 then measures the conductivity of the anode water (acidic water) and the cathode water (alkaline water) at predetermined time intervals. When metal ions are hardly removed from the acidic water and alkaline water, both the acidic water and the alkaline water have high conductivity, as shown in "(1) Formation of insolubilized matter" in FIG. 5 . Therefore, the control unit 100 controls the electrolysis power supply 90 to pass a constant current between the anode 12 and the cathode 13. Such constant current control can be achieved by adjusting the current or voltage applied between the anode 12 and the cathode 13.

[0040] As mentioned above, the insolubilization of metal ions is current-dependent, so constant current control promotes the insolubilization of metal ions in alkaline water. As a result, the concentration of metal ions decreases, and the conductivity of alkaline water decreases. However, in acidic water, the insolubilization of metal ions is less likely to occur, so the conductivity remains high.

[0041] Next, when the conductivity measurement shows that the conductivity of the alkaline water has decreased but the conductivity of the acidic water remains high, the control unit 100 controls the electrolysis power supply 90 to apply a constant voltage between the anode 12 and the cathode 13, as shown in "(2) Ion migration" in Figure 5. Note that such constant voltage control can be performed by adjusting the voltage applied between the anode 12 and the cathode 13.

[0042] As described above, electrophoresis, in which metal ions move from the anode chamber 15 to the cathode chamber 16, is voltage-dependent, so when constant voltage control is performed, metal ions in the acidic water in the anode chamber 15 permeate the ion-permeable membrane 14 and move to the cathode chamber 16. As a result, the metal ion concentration in the alkaline water in the cathode chamber 16 increases, and the conductivity of the alkaline water increases. In contrast, the metal ion concentration in the acidic water decreases, and the conductivity of the acidic water decreases.

[0043] Here, as described above, when a constant voltage is applied to the anode 12 and the cathode 13, hydrogen ions (H ＋ ) also moves to the cathode chamber 16, causing a neutralization reaction and lowering the pH. If the pH of the alkaline water in the cathode chamber 16 drops, the insolubilization of metal ions is suppressed. Therefore, when the control unit 100 measures the conductivity after performing constant current control and finds that the conductivity of the alkaline water has dropped but the conductivity of the acidic water is high, it calculates a voltage value that can maintain the pH of the alkaline water at a high level. For example, the control unit 100 calculates and applies a voltage value that can maintain the pH of the alkaline water at 11 or higher.

[0044] Next, if the conductivity measurement shows that the conductivity of the alkaline water has increased but that of the acidic water has decreased, the control unit 100 controls the electrolysis power supply 90 to pass a constant current between the anode 12 and the cathode 13, as shown in "(3) Formation of insolubilized matter" in Figure 5. Note that such constant current control can be performed by adjusting the current or voltage applied between the anode 12 and the cathode 13.

[0045] As mentioned above, since the insolubilization of metal ions is current-dependent, constant current control promotes the insolubilization of metal ions in alkaline water, resulting in a decrease in the concentration of metal ions and a decrease in the conductivity of the alkaline water.

[0046] Next, if the conductivity measurement shows that the conductivity of both the acidic water and the alkaline water has decreased, the control unit 100 determines that softening of both the acidic water and the alkaline water has progressed, as shown in "(4) Softening" in Figure 5.

[0047] In this way, the control unit 100 measures the conductivity of the anode water and the cathode water, and then adjusts the voltage applied between the anode 12 and the cathode 13 to perform electrolysis control that alternates between constant current control and constant voltage control. As a result, metal ions on the acidic water side electrophorese to the alkaline water side, and the metal ions are insolubilized on the alkaline water side, thereby reducing the metal ions in the water to be treated. In this embodiment, the timer of the control unit 100 measures the time during which electrolysis control is performed, and therefore the electrolysis control is performed until a predetermined time has elapsed.

[0048] The control unit 100 then adjusts the first solenoid valve 51 to allow the acidic water in the first flow path 20 to flow into the first outlet flow path 50. The control unit 100 also adjusts the second solenoid valve 61 to allow the alkaline water in the second flow path 30 to flow into the second outlet flow path 60. The alkaline water then passes through a filter 62 provided in the second outlet flow path 60. Because the alkaline water flowing into the second outlet flow path 60 contains insolubilized metal ions, the insolubilized material is removed by passing the alkaline water through the filter 62. By opening the water tap 52, the user can use the softened acidic water and alkaline water. At this time, the acidic water and alkaline water can be mixed as desired to produce neutral treated water.

[0049] FIG. 6 shows the relationship between the conductivity of the water to be treated and the ion migration rate, insolubilization rate, and water softening rate of metal ions when the control unit 100 only performs constant voltage control, in which a constant voltage is applied to the anode 12 and cathode 13 of the electrolytic cell 10 regardless of the conductivity. FIG. 6 also shows the relationship between the conductivity of the water to be treated and the ion migration rate, insolubilization rate, and water softening rate of metal ions when the control unit 100 only performs constant current control, in which a constant current is applied to the anode 12 and cathode 13 of the electrolytic cell 10 regardless of the conductivity. The "ion migration rate of metal ions" indicates the efficiency with which metal ions migrate from the anode chamber 15 to the cathode chamber 16. The "insolubilization rate of metal ions" indicates the efficiency with which metal ions bind with hydroxide ions and carbonate ions to become insolubilized. The "water softening rate" indicates the efficiency with which metal ions are removed from the water to be treated.

[0050] As described above, because the movement of metal ions depends on the voltage (electric field), when the control unit 100 performs constant voltage control, metal ions move from the anode chamber 15 to the cathode chamber 16 regardless of the conductivity of the water to be treated. This means that a high ion migration rate can be maintained. However, because the insolubilization of metal ions depends on the current, constant voltage control improves the insolubilization rate when the conductivity of the water to be treated is high, but decreases the insolubilization rate when the conductivity is low. Therefore, if the control unit 100 only performs constant voltage control and does not perform constant current control, the water to be treated can be efficiently softened and the water softening rate increased when the conductivity of the water to be treated is high, i.e., when the metal ion concentration is high. However, when the conductivity of the water to be treated is low, i.e., when the metal ion concentration is low, the insolubilization rate decreases, and therefore the water softening rate also decreases. Thus, when the control unit 100 only performs constant voltage control, the water softening rate is good when the metal ion concentration is high, but the water softening rate deteriorates when the metal ion concentration is low.

[0051] In contrast, because the insolubilization of metal ions depends on the current, when the control unit 100 performs constant current control, metal ions are insolubilized regardless of the conductivity of the water being treated, i.e., a high insolubilization rate can be maintained. However, as described above, because the movement of metal ions depends on the voltage, when constant current control is performed, the ion migration rate improves when the conductivity of the water being treated is low, but decreases when the conductivity is high. Therefore, if the control unit 100 only performs constant current control and does not perform constant voltage control, the water can be efficiently softened and the water softening rate increased when the conductivity of the water being treated is low, i.e., when the metal ion concentration is low. However, when the conductivity of the water being treated is high, i.e., when the metal ion concentration is high, the ion migration rate decreases, and the water softening rate also decreases. Thus, when the control unit 100 only performs constant current control, the water softening rate is good when the metal ion concentration is low, but the water softening rate deteriorates when the metal ion concentration is high.

[0052] In the water treatment device 1 of this embodiment, the voltage applied between the anode 12 and the cathode 13 is adjusted according to the electrical conductivity (hardness) of the anode water and the cathode water, and electrolysis control is performed by repeating constant current control and constant voltage control. This keeps the ion migration rate and insolubilization rate high at all times, and as a result, it becomes possible to obtain a desired water softening rate regardless of the electrical conductivity.

[0053] FIG. 7 shows an example of the relationship between the conductivity of the water to be treated and power consumption when constant voltage control, constant current control, and electrolysis control are performed. Note that symbol C in FIG. 7 shows the relationship between the conductivity and power consumption when only constant voltage control is performed, symbol D shows the relationship between the conductivity and power consumption when only constant current control is performed, and symbol E shows the relationship between the conductivity and power consumption when electrolysis control of this embodiment is performed. From FIG. 7 , it can be seen that when only constant voltage control is performed, power consumption increases as the conductivity of the water to be treated increases. It can also be seen that when only constant current control is performed, power consumption increases as the conductivity of the water to be treated decreases. However, the electrolysis control of this embodiment switches between constant current control and constant voltage control depending on the conductivity of the water to be treated, so power consumption can be kept low, as shown by symbol E.

[0054] In this embodiment, the range of conductivity of the water to be treated when electrolysis control is performed is preferably a range in which power consumption is lower than when only constant current control or only constant voltage control is performed. In other words, the range of conductivity of the water to be treated (acidic water and alkaline water) to be electrolysis control is preferably within the range indicated by symbol F in Figure 7, specifically, 30 to 8000 μS / cm. This makes it possible to reduce power consumption compared to when only constant current control or only constant voltage control is performed.

[0055] As described above, when water to be treated is placed in the anode chamber 15 and the cathode chamber 16 of the electrolytic cell 10 and electrolyzed, hydrogen ions (H ＋ ) is generated at the cathode 13 by a reduction reaction, and hydroxide ions (OH － ) is generated. When a voltage is applied to the anode 12 and the cathode 13, hydrogen ions (H＋ ) moves to the cathode chamber 16, and hydroxide ions (OH － ) and neutralizes it, lowering the pH of the alkaline water in the cathode chamber 16. If the pH of the alkaline water in the cathode chamber 16 decreases, there is a possibility that the insolubilization of the metal ions may be inhibited.

[0056] To prevent such a decrease in the pH of the alkaline water in the cathode chamber 16, the water treatment device 1 of this embodiment is configured so that the flow rate of the acidic water in the anode chamber 15 is faster than the flow rate of the alkaline water in the cathode chamber 16. As a result, even if hydrogen ions generated near the anode 12 attempt to move toward the cathode chamber 16, as shown in FIG. 8 , the hydrogen ions are more likely to move along the flow of the acidic water to the outlet 15b of the anode chamber 15. In other words, the hydrogen ions generated near the anode 12 are more likely to move to the outlet 15b of the anode chamber 15 than to permeate the ion-permeable membrane 14 and move to the cathode chamber 16. The hydrogen ions that have moved to the outlet 15b of the anode chamber 15 then circulate through the first flow path 20 and flow into the anode chamber 15 from the inlet 15a of the anode chamber 15.

[0057] In this way, by increasing the flow rate of the acidic water in the anode chamber 15, the hydrogen ions generated in the anode 12 are more likely to circulate through the anode chamber 15 and the first flow path 20, and are less likely to permeate the ion-permeable membrane 14 and move to the cathode chamber 16. Therefore, a decrease in the pH of the alkaline water in the cathode chamber 16 is suppressed, and the insolubilization of metal ions can be promoted.

[0058] Even when the flow rate of the acidic water in the anode chamber 15 is increased, constant voltage control allows metal ions in the acidic water in the anode chamber 15 to permeate the ion permeable membrane 14 and migrate to the cathode chamber 16. That is, constant voltage control allows metal ions in the acidic water in the anode chamber 15 that are located near the ion permeable membrane 14 to permeate the ion permeable membrane 14 and migrate to the cathode chamber 16. Furthermore, because the acidic water circulates through the anode chamber 15 and the first flow path 20, constant voltage control allows the metal ions in the acidic water to gradually permeate the ion permeable membrane 14 and migrate to the cathode chamber 16. Therefore, even when the flow rate of the acidic water in the anode chamber 15 is increased, metal ions can efficiently migrate from the anode chamber 15 to the cathode chamber 16.

[0059] The method for adjusting the flow rates of the acidic water in the anode chamber 15 and the alkaline water in the cathode chamber 16 is not particularly limited, and can be performed, for example, as follows. As described above, the water treatment device 1 includes the first flow path 20 connected to the anode chamber 15 and through which the acidic water flows, and the second flow path 30 connected to the cathode chamber 16 and through which the alkaline water flows. A first circulation pump 22 and a first solenoid valve 51 are disposed in the first flow path 20 for pumping the acidic water. Similarly, a second circulation pump 32 and a second solenoid valve 61 are disposed in the second flow path 30 for pumping the alkaline water. The first circulation pump 22 and the first solenoid valve 51, as well as the second circulation pump 32 and the second solenoid valve 61, are electrically connected to the control unit 100, and the control unit 100 controls their operation. In this embodiment, the first circulation pump 22 and the first solenoid valve 51 constitute a first flow rate adjustment unit, and the second circulation pump 32 and the second solenoid valve 61 constitute a second flow rate adjustment unit.

[0060] The flow rate of the acidic water can be controlled by the control unit 100 adjusting the first circulation pump 22 and / or the first solenoid valve 51 of the first flow rate adjustment unit. That is, the flow rate of the acidic water can be increased by increasing the rotation speed of the first circulation pump 22, and the flow rate of the acidic water can be increased by increasing the opening of the first solenoid valve 51. Similarly, the flow rate of the alkaline water can be controlled by the control unit 100 adjusting the second circulation pump 32 and / or the second solenoid valve 61 of the second flow rate adjustment unit.

[0061] In the water treatment device 1, the percentage of hydrogen ions generated in the anode chamber 15 by the electrode reaction that do not migrate across the ion permeable membrane 14 to the cathode chamber 16 can be calculated using the following formula 5. In other words, the percentage of hydrogen ions that do not migrate from the anode chamber 15 to the cathode chamber 16 can be calculated using the following formula 5. In Equation 5, the inter-electrode distance W (m) is the shortest distance between the anode 12 and the cathode 13, the flow rate in the electrolytic cell (m / s) is the flow rate of the acidic water in the anode chamber 15, and the electrode length L (m) is the length of the anode 12 in the direction of the flow of the acidic water. ２ / Vs) is the ion mobility μ of hydrogen ions, and is 36.2 × 10 －８ (m ２ The acid solution potential V (V) is a voltage applied as a control voltage to the acidic water from the electrolysis power supply 90 via the anode 12.

[0062] Similarly, in the water treatment device 1, the percentage of hydroxide ions generated in the cathode chamber 16 by the electrode reaction that do not migrate across the ion permeable membrane 14 to the anode chamber 15 can be calculated using the following formula 6. In other words, the percentage of hydroxide ions that do not migrate from the cathode chamber 16 to the anode chamber 15 can be calculated using the following formula 6. In Equation 6, the inter-electrode distance W (m) is the shortest distance between the anode 12 and the cathode 13, the flow rate in the electrolytic cell (m / s) is the flow rate of the alkaline water in the cathode chamber 16, and the electrode length L (m) is the length of the cathode 13 in the direction of the alkaline water flow. ２ / Vs) is the ion mobility μ of hydroxide ions, which is 20.55 × 10 －８ (m ２ The alkaline solution potential V (V) is a voltage applied as a control voltage to the alkaline water from the electrolysis power supply 90 via the cathode 13.

[0063] In the water treatment device 1, the condition where the neutralization point where the hydrogen ions generated at the anode 12 and the hydroxide ions generated at the cathode 13 are neutralized is the ion permeable membrane 14, is [H ＋ does not cross the membrane] = [OH － Therefore, based on Equation 5, Equation 6, and the above conditions, when the control unit 100 controls the flow rates of the acidic water and the alkaline water so as to satisfy Equation 7, it becomes difficult for the hydrogen ions generated at the anode 12 to permeate the ion permeable membrane 14 and move to the cathode chamber 16. As a result, a decrease in the pH of the alkaline water in the cathode chamber 16 can be suppressed, and the insolubilization of the metal ions can be promoted.

[0064] In the water treatment device 1, it is more preferable that the control unit 100 controls the flow rate of the acidic water in the anode chamber 15 and the flow rate of the alkaline water in the cathode chamber 16 so as to satisfy Equation 8. Such control makes it even more difficult for hydrogen ions to move to the cathode chamber 16. Therefore, it is possible to further suppress a decrease in the pH of the alkaline water in the cathode chamber 16 and promote the insolubilization of metal ions.

[0065] Here, the percentage of hydrogen ions generated in the electrode reaction that migrate across the ion-permeable membrane 14 to the cathode chamber 16 can be calculated using the following formula 9. In other words, the percentage of hydrogen ions that migrate from the anode chamber 15 to the cathode chamber 16 (transfer percentage) can be calculated using the following formula 9.

[0066] In FIG. 9, the pH change of the alkaline water in the cathode chamber 16 (vertical axis) and the amount of electricity between the electrodes (horizontal axis) are plotted against the H ＋ The relationship between the ratio of H to the film thickness is shown in Fig. 9. ＋The flow rate of the acidic water in the anode chamber when the ratio of H exceeding the membrane is a predetermined value is also shown. ＋ When the proportion of the acid water passing through the membrane is 99.60%, the flow rate of the acid water in the anode chamber is 0.185 L / min, and H ＋ When the proportion of the acidic water that crosses the membrane is 67%, the flow rate of the acidic water in the anode chamber is 15 L / min.

[0067] As shown in FIG. 9, it can be seen that the pH increases as the amount of electricity between the anode 12 and the cathode 13 increases. ＋ It can be seen that when the proportion of H exceeding the ion permeable membrane 14 is 99.6% or less, the pH of the alkaline water in the cathode chamber 16 is 8.2. ＋ It can be seen that as the proportion of ions that exceed the ion permeable membrane 14 decreases, the pH of the alkaline water increases.

[0068] When the pH of the alkaline water in the cathode chamber 16 is 8.2 or higher, as shown in FIG. ３ ２－ ) increases, which can promote the insolubilization of calcium ions. ＋ By increasing the flow rate of the acidic water in the anode chamber 15 so that the proportion of the metal ions that exceed the ion-permeable membrane 14 is 99.6% or less, it is possible to promote the insolubilization of the metal ions.

[0069] Thus, the proportion of hydrogen ions generated in the anode chamber 15 by the electrode reaction that do not migrate across the ion-permeable membrane 14 to the cathode chamber 16 is preferably 0.4 to 100%. Furthermore, the proportion of hydrogen ions generated in the anode chamber 15 by the electrode reaction that do not migrate across the ion-permeable membrane 14 to the cathode chamber 16 is more preferably 1 to 20%. This configuration promotes the insolubilization of metal ions, thereby reducing the amount of metal ions in the water to be treated.

[0070] The above theoretical model showing the relationship between the pH change of the alkaline water in the cathode chamber 16 and the amount of electricity between the electrodes can be obtained as follows.

[0071] In an electrolysis structure having an ion-permeable membrane 14 that suppresses the movement of water between the cathode chamber 16 and the anode chamber 15, when the ratio α of the amount of protons that migrates from the anode chamber to the cathode chamber through the ion-permeable membrane to the amount of protons generated by the electrode reaction due to water electrolysis is taken into consideration, Equation 10 can be obtained. Here, each symbol represents the following: i: current [A] t: time [sec] F: Faraday's constant [C / mol] V0: volume of water [L] K w : Ionic product of water [mol 2 / L 2 ] K1: Equilibrium constant of carbonic acid and bicarbonate ion [mol 2 / L 2 ] K2: Equilibrium constant of bicarbonate ion and carbonate ion [mol 2 / L 2 ] [H + ]: Molar concentration of protons [mol / L] C a : Molar concentration of total carbon dioxide [mol / L] α: Proportion of protons generated in the electrolysis reaction that migrate to the cathode [-]

[0072] The process of deriving Equation 10 is shown below. First, the chemical formula of the water electrolysis reaction is given by Equation 2 below.

[0073] The chemical equilibrium of carbon dioxide in water is expressed by the following chemical formula 3, and the ratio of carbon dioxide present in water changes depending on the pH.

[0074] If the total amount of carbonic acid is a, the molar concentration is C ａ is expressed by the following equation (1).

[0075] Hydroxide ions (OH) produced by electrolysis － and proton H ＋ If the amount of substance is b mol, the molar concentration C ｂ is expressed by the following equation (2).

[0076] Here, if the equilibrium constants of carbonate species are K1 and K2, they are expressed by the following equations (3) and (4).

[0077] By rearranging the equations (3) and (4), the following equations (5) to (7) are obtained.

[0078] Furthermore, if the ionic product of water is Kw, the following equations (8) and (9) are derived.

[0079] In addition, the total carbon dioxide concentration C ａ is expressed by the following equation (10).

[0080] Substituting equations (6) and (7) into equation (10) and rearranging the equations, equations (11) to (13) are obtained.

[0081] Equation (13) is substituted into equation (7) to obtain equation (14). Furthermore, by substituting equation (13) into equation (6), the following equation is obtained.

[0082] Furthermore, the following equation holds true based on the principle of electrical neutrality:

[0083] By substituting the formulas (8), (13), (14), and (15) into the formula (16), the formula (17) is obtained.

[0084] Here, by adding hydroxide ions generated by the electrolysis reaction of water, formulas (18) and (19) are obtained.

[0085] From equation (19), Fig. 10 can be drawn from the pH corresponding to the quantity of electricity. Note that Fig. 10 shows an example of Ca=2.66×10 -3 [mol / L], V0=6.0[L].

[0086] Furthermore, when the rate α of the protons generated in the electrolytic reaction in the anode chamber 15 that migrate to the cathode chamber 16 through the ion-permeable membrane 14 is taken into consideration, the following equation (20) is obtained. The pH curves obtained when the value of α is changed are shown in Figure 9. Figure 9 shows that the increase in pH in the cathode chamber 16 is suppressed, i.e., neutralized, as protons move to the cathode chamber 16.

[0087] In the water treatment device 1, the control unit 100 preferably controls the flow rates of the acidic water and the alkaline water based on the proportion of hydrogen ions generated in the anode chamber 15 by the electrode reaction that do not migrate across the ion-permeable membrane 14 to the cathode chamber 16. In other words, it is preferable to control the flow rates of the acidic water and the alkaline water so that the proportion of hydrogen ions generated in the anode chamber 15 by the electrode reaction that do not migrate across the ion-permeable membrane 14 to the cathode chamber 16 is 0.4 to 100%. By controlling in this manner, it is possible to promote the insolubilization of metal ions in the cathode chamber 16.

[0088] Furthermore, in the water treatment device 1, the control unit 100 preferably controls the flow rate of the acidic water in the anode chamber 15 and the flow rate of the alkaline water in the cathode chamber 16 so that the pH of the alkaline water in the cathode chamber 16 reaches a predetermined value. As described above, when the pH of the alkaline water in the cathode chamber 16 reaches 8.2 or more, the amount of carbonate ions (CO ３ ２－ ) increases, which can promote the insolubilization of calcium ions. Therefore, it is preferable to control the flow rates of the acidic water in the anode chamber 15 and the alkaline water in the cathode chamber 16 so that the pH of the alkaline water in the cathode chamber 16 reaches, for example, 8.2 or higher. The predetermined value of the pH of the alkaline water is not limited to 8.2, and may be, for example, 10 or 12.

[0089] 11 shows an example of the results of measuring the pH of alkaline water in the cathode chamber 16 when the flow rate of acidic water in the anode chamber 15 in the water treatment device 1 was 4.6 L / min or 14 L / min. The measurement results in FIG. 11 were obtained when the initial conductivity of the water to be treated was 550 μS / cm and electrolysis control was not performed. The measurement results in FIG. 11 were also obtained when the flow rate of alkaline water was the same for both the 4.6 L / min and 14 L / min flow rates of acidic water, and the flow rate of alkaline water was slower than the flow rate of acidic water.

[0090] 11, it can be seen that when the flow rate of the acidic water in the anode chamber 15 is 14 L / min, the pH of the alkaline water increases in a shorter time than when the flow rate is 4.6 L / min. In other words, when the flow rate of the acidic water in the anode chamber 15 is high, the migration of hydrogen ions from the anode chamber 15 to the cathode chamber 16 is suppressed, and the pH of the alkaline water increases in a shorter time.

[0091] Table 1 shows an example of the ion migration rate, insolubilization rate, and water softening rate of metal ions when the flow rate of acidic water in the anode chamber 15 in the water treatment device 1 is set to 4.6 L / min and 14 L / min. As shown in Table 1, by increasing the flow rate of acidic water from 4.6 L / min to 14 L / min, the insolubilization rate (the efficiency with which metal ions are insolubilized by bonding with hydroxide ions and carbonate ions) and the water softening rate (the efficiency with which metal ions are removed from the water to be treated) are improved. In other words, when the flow rate of acidic water in the anode chamber 15 is high, the migration of hydrogen ions from the anode chamber 15 to the cathode chamber 16 is suppressed, and the pH of the alkaline water increases in a short period of time, thereby increasing the insolubilization rate and water softening rate. However, since the ion migration rate (the efficiency with which metal ions move from the anode chamber 15 to the cathode chamber 16) remains unchanged, it can be seen that metal ions can efficiently move from the anode chamber 15 to the cathode chamber 16 even when the flow rate of acidic water is increased.

[0092]

[0093] As described above, the water treatment device 1 of this embodiment includes the first pH measurement unit 15c that measures the pH of the water flowing through the anode chamber 15, and the second pH measurement unit 16c that measures the pH of the water flowing through the cathode chamber 16. The control unit 100 preferably controls the flow rate of the acidic water in the anode chamber 15 based on the pH of the alkaline water measured by the pH measurement unit.

[0094] Fig. 12 is a flowchart showing an example of a method for controlling the flow rate of acidic water in the anode chamber 15 based on the pH of alkaline water measured by the second pH measuring unit 16c. Fig. 13 is a graph showing an example of the relationship between the pH (alkaline side pH) of the water to be treated in the anode chamber 15 and time.

[0095] In the water treatment device 1, the control unit 100 first injects the water to be treated into the water flow path 40, the first flow path 20, the second flow path 30, the anode chamber 15 and cathode chamber 16 of the electrolytic cell 10, the acidic water tank 21, and the alkaline water tank 31. Next, the control unit 100 controls the electrolysis power supply 90 to pass a current between the anode 12 and the cathode 13, thereby electrolyzing the water to be treated. The control unit 100 also operates the first circulation pump 22 and the second circulation pump 32 to circulate the water to be treated through the first flow path 20 and the second flow path 30. By performing the electrolysis and circulation of the water to be treated for a predetermined time, the water to be treated in the anode chamber 15, the first flow path 20, and the acidic water tank 21 becomes acidic water, and the water to be treated in the cathode chamber 16, the second flow path 30, and the alkaline water tank 31 becomes alkaline water.

[0096] Here, the control unit 100 starts control in accordance with the flowchart of Fig. 12. In step S1, the control unit 100 measures the pH of the water to be treated (alkaline water) in the cathode chamber 16. Next, in step S2, the control unit 100 measures the pH of the alkaline water in the cathode chamber 16, and if the pH of the alkaline water is lower than the target, that is, if the pH of the alkaline water is lower than the target pH curve as shown by symbol (1) in Fig. 13, proceeds to step S3.

[0097] In step S3, the control unit 100 increases the flow rate of the acidic water by adjusting the first circulation pump 22 and / or the first electromagnetic valve 51 of the first flow rate adjusting unit. Specifically, the flow rate of the acidic water is increased by increasing the rotation speed of the first circulation pump 22 and increasing the opening of the first electromagnetic valve 51.

[0098] After the process of step S3, in step S1, the control unit 100 again measures the pH of the alkaline water in the cathode chamber 16. Next, in step S2, the control unit 100 measures the pH of the alkaline water in the cathode chamber 16, and if the pH of the alkaline water is equal to or higher than the target value, as indicated by symbol (2) in Figure 13, proceeds to step S4.

[0099] In step S4, if the pH of the alkaline water in the cathode chamber 16 is equal to or higher than the target pH curve and has reached the target pH, it is determined whether the water treatment end time has been reached. Note that the period from the time when the target pH is reached (the arrival time) to the end time in Figure 13 is the time during which the reaction of insolubilizing metal ions progresses. If the pH of the alkaline water is equal to or higher than the target pH curve and has reached the water treatment end time, the flow rate control of the acidic water and alkaline water is terminated.

[0100] In step S4, if the water treatment end time has not been reached, the pH of the alkaline water in the cathode chamber 16 is measured again to determine whether the pH of the alkaline water is equal to or higher than the target pH curve. If the pH of the alkaline water has not reached the target pH curve, the difference between the pH of the alkaline water and the target pH curve is calculated, and the flow rate of the acidic water is increased so that the pH of the alkaline water reaches the target pH curve.

[0101] In this way, the control unit 100 controls the flow rate of the acidic water in the anode chamber 15 based on the pH of the alkaline water measured by the pH measuring unit, which makes it easier for the alkaline water to reach the target pH, thereby further promoting the insolubilization of metal ions.

[0102] In the water treatment device 1 of this embodiment, a flow rate measurement unit (flow rate sensor) for measuring the flow rate of acidic water may be provided in the first flow path 20, and a flow rate measurement unit (flow rate sensor) for measuring the flow rate of alkaline water may be provided in the second flow path 30. By providing such flow rate measurement units, the accuracy of flow rate control of acidic water and alkaline water can be improved. However, since the flow rates of acidic water and alkaline water can be estimated by calculation even without the flow rate measurement unit, the flow rate measurement unit is not an essential component in the water treatment device 1 of this embodiment.

[0103] As described above, in the water treatment device 1, the first flow path 20 and the second flow path 30 are circulation flow paths. However, the water treatment device is not limited to this configuration, and the first flow path and the second flow path may be single-pass flow paths that do not circulate water. Furthermore, the first flow path and the second flow path may be a combination of a circulation flow path and a single-pass flow path. Therefore, in this specification, the circulation flow path and the single-pass flow path are collectively referred to as the "first flow path." Similarly, the circulation flow path and the single-pass flow path are collectively referred to as the "second flow path."

[0104] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0105] (Technology 1) A water treatment device that removes metal ions from water to be treated to produce treated water, comprising: an anode chamber having an anode, a cathode chamber having a cathode, and an ion-permeable membrane separating the anode chamber and the cathode chamber, the electrolytic cell producing acidic water and alkaline water from the water to be treated by electrolysis; and a control unit that controls the voltage or current between the anode and the cathode, wherein the acidic water flows through the anode chamber and the alkaline water flows through the cathode chamber, and the control unit controls the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber so as to satisfy the following mathematical formula 24.

[0106] In the water treatment device of this embodiment, by increasing the flow rate of the acidic water in the anode chamber 15 so as to satisfy the relationship of Equation 24, it becomes difficult for the hydrogen ions generated in the anode 12 to permeate through the ion permeable membrane 14 and move to the cathode chamber 16. Therefore, a decrease in the pH of the alkaline water in the cathode chamber 16 can be suppressed, and the insolubilization of metal ions can be promoted.

[0107] (Technology 2) The water treatment device according to Technology 1, further comprising a pH measuring unit that measures at least one of the pH of the acidic water flowing through the anode chamber and the pH of the alkaline water flowing through the cathode chamber.

[0108] With this configuration, the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber can be controlled based on the pH measured by the pH measuring unit, thereby preventing the pH of the alkaline water in the cathode chamber 16 from decreasing and promoting the insolubilization of metal ions.

[0109] (Technology 3) The water treatment device according to Technology 2, wherein the control unit controls the flow rate of the acidic water in the anode chamber based on the pH of the alkaline water measured by the pH measuring unit.

[0110] This configuration can prevent the pH of the alkaline water in the cathode chamber 16 from decreasing, and promote the insolubilization of metal ions.

[0111] (Technology 4) The water treatment device according to any one of technologies 1 to 3, wherein the pH of the alkaline water in the cathode chamber is 8.2 or higher.

[0112] This configuration promotes the insolubilization of metal ions, thereby reducing the amount of metal ions in the water to be treated.

[0113] (Technology 5) The water treatment device according to any one of Technologies 1 to 4, wherein the control unit changes at least one of the voltage and the current between the anode and the cathode.

[0114] This configuration controls the insolubilization of metal ions and the migration of metal ions from the anode chamber to the cathode chamber, thereby enabling efficient removal of metal ions.

[0115] (Technology 6) The water treatment device according to Technology 5, wherein the control unit changes the voltage applied between the anode and the cathode when the conductivity of the water flowing through the anode chamber and the conductivity of the water flowing through the cathode chamber are 30 to 8000 μS / cm.

[0116] In this embodiment, the range of the conductivity of the water to be treated when electrolysis control is performed is preferably set to a range that results in lower power consumption than when only constant current control or only constant voltage control is performed. With this configuration, it is possible to reduce power consumption compared to when only constant current control or only constant voltage control is performed.

[0117] (Technology 7) A water treatment device described in any one of Technologies 1 to 6, wherein the control unit switches from one of constant current control and constant voltage control to the other by changing the voltage or current applied between the anode and the cathode.

[0118] This configuration makes it possible to promote the insolubilization of metal ions in the water to be treated, while reducing power consumption compared to the case of constant current control alone or constant voltage control alone.

[0119] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

[0120] The entire contents of Japanese Patent Application No. 2024-052088 (filing date: March 27, 2024) are incorporated herein by reference.

[0121] According to the present disclosure, it is possible to provide a water treatment device that can efficiently remove metal ions from hard water without using an ion exchange resin.

[0122] REFERENCE SIGNS LIST 1 Water treatment device 10 Electrolytic cell 12 Anode 13 Cathode 14 Membrane (ion-permeable membrane) 15 Anode chamber 15c First pH measurement unit 16 Cathode chamber 16c Second pH measurement unit 100 Control unit

Claims

1. A water treatment device that removes metal ions from water to be treated to produce treated water, comprising: an anode chamber having an anode, a cathode chamber having a cathode, and an ion-permeable membrane separating the anode chamber and the cathode chamber, and an electrolytic cell that produces acidic water and alkaline water from the water to be treated by electrolysis; and a control unit that controls the voltage or current between the anode and the cathode, wherein the acidic water flows through the anode chamber and the alkaline water flows through the cathode chamber, and the control unit controls the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber so as to satisfy Equation 1.

2. The water treatment device according to claim 1, further comprising a pH measuring unit that measures at least one of the pH of the acidic water flowing through the anode chamber and the pH of the alkaline water flowing through the cathode chamber.

3. The water treatment device according to claim 2, wherein the control unit controls the flow rate of the acidic water in the anode chamber based on the pH of the alkaline water measured by the pH measuring unit.

4. The water treatment device according to any one of claims 1 to 3, wherein the pH of the alkaline water in the cathode chamber is 8.2 or higher.

5. The water treatment device according to any one of claims 1 to 4, wherein the control unit changes at least one of the voltage and the current between the anode and the cathode.

6. The water treatment device according to claim 5, wherein the control unit changes the voltage applied between the anode and the cathode when the conductivity of the water flowing through the anode chamber and the conductivity of the water flowing through the cathode chamber are 30 to 8000 μS / cm.

7. A water treatment device as described in any one of claims 1 to 6, wherein the control unit switches from one of constant current control and constant voltage control to the other by changing the voltage or current applied between the anode and the cathode.

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