Water treatment device

Abstract

A water treatment device (1) removes metal ions from water to be treated to generate treated water, wherein the water treatment device is provided with an electrolytic cell (10) that has an anode chamber (15) having an anode (12), a cathode chamber (16) having a cathode (13), and a membrane (14) that separates the anode chamber and the cathode chamber and is permeable to ions, and generates acidic water and basic water from the water to be treated by electrolysis in the electrolytic cell (10). The water treatment device is further provided with a control unit (100) that controls the voltage or current between the anode and the cathode. Acidic water is circulated in the anode chamber, and basic water is circulated in the cathode chamber, and the control unit adjusts at least one of the flow rate of the acidic water in the anode chamber and the flow rate of the basic water in the cathode chamber.

Description

Technical Field

[0001] This disclosure relates to a water treatment apparatus. Background Technology

[0002] Previously, an ion exchange resin water softener for removing metal ions from hard water was known (see, for example, Patent Document 1).

[0003] Patent Document 1 describes an ion exchange resin water softener that removes metal ions (calcium and magnesium ions) from hard water using ion exchange resin. Specifically, by circulating hard water through a water softener container equipped with ion exchange resin whose surface is coated with sodium ions, the metal ions in the hard water are replaced with sodium ions, thus removing the metal ions from the hard water. Furthermore, metal ions present in the hard water are captured on the surface of the ion exchange resin. This process reduces the hardness of the hard water, thereby producing soft water.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2000-140840 Summary of the Invention

[0007] However, in the ion exchange resin water softener of Patent Document 1, a large amount of brine is required to regenerate the ion exchange resin that has captured metal ions, resulting in time-consuming and labor-intensive maintenance. Furthermore, regeneration treatment generates regeneration wastewater containing large amounts of brine, leading to soil pollution and an increased burden on wastewater treatment. Moreover, the softened water from the ion exchange resin water softener has a high concentration of sodium ions, which, depending on the region, is sometimes not recommended for drinking water. Therefore, there is room for improvement in water treatment devices using ion exchange resins from the perspectives of maintainability and environmental friendliness.

[0008] This disclosure was made in view of the problems inherent in the prior art. Moreover, the object of this disclosure is to provide a water treatment apparatus that can efficiently remove metal ions from hard water even without the use of ion exchange resins.

[0009] To address the aforementioned problems, the water treatment apparatus disclosed herein removes metal ions from treated water to generate treated water. The water treatment apparatus comprises: an electrolytic cell having an anode chamber with an anode, a cathode chamber with a cathode, and a membrane separating the anode chamber and the cathode chamber and allowing ions to permeate; wherein acidic water and alkaline water are generated from the treated water by electrolysis in the electrolytic cell; and a control unit that controls the voltage or current between the anode and the cathode, wherein the acidic water flows in the anode chamber, and the alkaline water flows in the cathode chamber, and the control unit adjusts at least one of the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating an example of the structure of the water treatment apparatus according to this embodiment.

[0011] Figure 2 This is a schematic diagram showing the migration and insolubility of metal ions in the electrolytic cell of the water treatment apparatus according to this embodiment.

[0012] Figure 3 This is a schematic diagram showing the migration and neutralization of hydrogen ions in the electrolyzer of the water treatment apparatus according to this embodiment.

[0013] Figure 4 This shows the carbonic acid (H₂CO₃) and bicarbonate (HCO₃) ions when carbonate ions are dissolved in water. - ) and carbonate ions (CO3) 2- A graph showing the relationship between the presence of ( ) and pH.

[0014] Figure 5 This is a table used to explain the electrolysis control in the water treatment apparatus involved in this embodiment.

[0015] Figure 6 It is a graph that summarizes the relationship between the conductivity of the treated water and the ion mobility, insolubility and softening rate of metal ions under the following conditions: constant current control only, constant voltage control only, and electrolysis control.

[0016] Figure 7 This is a graph showing an example of the relationship between the conductivity and power consumption of the treated water when only constant voltage control, only constant current control, and electrolysis control were performed.

[0017] Figure 8 This is a schematic diagram illustrating the migration of hydrogen ions in the electrolyzer of the water treatment apparatus according to this embodiment.

[0018] Figure 9 This shows the pH change (vertical axis) and the electrical charge between electrodes (horizontal axis) of the alkaline water in the cathode chamber calculated using a theoretical model, versus H+. + A graph showing the relationship between the proportions passing through the membrane.

[0019] Figure 10 It is a graph showing the relationship between the pH change of the water in the cathode chamber (vertical axis) and the charge between the electrodes (horizontal axis) derived from equation (19).

[0020] Figure 11 This is a graph showing an example of the results obtained by measuring the pH of alkaline water in the cathode chamber when the flow rate of acidic water in the anode chamber is set to 4.6 L / min or 14 L / min in a water treatment device.

[0021] Figure 12A It is a summary graph showing the relationship between the conductivity and pH of alkaline water and the conductivity and pH of acidic water under constant voltage control, with the flow rates of acidic and alkaline water being the same.

[0022] Figure 12B This is a summary graph showing the relationship between the conductivity of alkaline water and pH, and the relationship between the conductivity of acidic water and pH, under constant voltage control where the flow rate of acidic water is faster than that of alkaline water.

[0023] Figure 13A It is a summary graph showing the relationship between the conductivity and pH of alkaline water and the conductivity and pH of acidic water under constant current control, with the flow rates of acidic and alkaline water being the same.

[0024] Figure 13B This is a summary graph showing the relationship between the conductivity of alkaline water and pH, and the relationship between the conductivity of acidic water and pH, under the condition that the flow rate of acidic water is faster than that of alkaline water in constant current control.

[0025] Figure 14 This is a graph showing an example of the relationship between the pH (alkaline water pH) of the treated water in the cathode chamber and time. Detailed Implementation

[0026] The water treatment apparatus according to this embodiment will now be described in detail using the accompanying drawings. Furthermore, the scale of the drawings has been exaggerated for ease of explanation and may sometimes differ from the actual scale.

[0027] This embodiment of the water treatment apparatus produces treated water by removing and separating metal ions from the water to reduce the concentration (hardness) of metal ions in the water to below a specified concentration. Metal ions include calcium ions (Ca). 2+ ) and magnesium ions (Mg 2+ Furthermore, the WHO definition can be used as a standard for defining hard and soft water. That is, water with a hardness less than 120 mg / L can be defined as soft water, and water with a hardness greater than 120 mg / L can be defined as hard water.

[0028] like Figure 1 As shown, the water treatment apparatus 1 of this embodiment includes: an electrolytic cell 10 in which acidic water and alkaline water are generated from treated water by electrolysis; a first flow path 20 in which acidic water circulates; and a second flow path 30 in which alkaline water circulates. The water treatment apparatus 1 also includes a treated water flow path 40 for supplying treated water, a first outflow flow path 50 for allowing treated acidic water to flow out from the first flow path 20, and a second outflow flow path 60 for allowing treated alkaline water to flow out from the second flow path 30.

[0029] like Figure 1 and Figure 2 As shown, the electrolytic cell 10 includes a solution tank 11, an anode 12, a cathode 13, and a membrane (ion-permeable membrane) 14 that allows ions to pass through. The solution tank 11 is a container for holding water to be treated containing metal ions, and as described later, the water to be treated held in the solution tank 11 is electrolyzed.

[0030] The anode 12 and cathode 13 are an electrode pair used for electrolyzing the water to be treated in the solution tank 11. The anode 12 is disposed in the anode chamber 15, and the cathode 13 is disposed in the cathode chamber 16. The anode 12 and cathode 13 are arranged facing each other inside the solution tank 11 with an ion-permeable membrane 14 in between. Furthermore, the anode 12 is electrically connected to the positive terminal of the electrolysis power supply 90, and the cathode 13 is electrically connected to the negative terminal of the electrolysis power supply 90.

[0031] An ion-permeable membrane 14 is disposed within a solution tank 11, dividing the solution tank 11 into an anode chamber 15 and a cathode chamber 16. That is, the anode chamber 15 is defined by a portion of the solution tank 11 and the ion-permeable membrane 14, and the cathode chamber 16 is defined by the remaining portion of the solution tank 11 and the ion-permeable membrane 14. Furthermore, the ion-permeable membrane 14 is a component that allows metal ions in the treated water to pass through. Therefore, the ion-permeable membrane 14 is not particularly limited as long as it allows metal ions to pass through; for example, a porous membrane or a cation exchange membrane can be used. Regarding the material of the porous membrane, for example, ceramic materials, resin materials, or metal materials can be used, but there are no particular limitations.

[0032] 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 outlet 15b of the anode chamber 15, respectively. Furthermore, an acidic water tank 21 for temporarily storing acidic water and a first circulation pump 22 for pressurizing and pumping acidic water are disposed in the first flow path 20, downstream of the anode chamber 15. Therefore, acidic water flowing out of 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 interior of the anode chamber 15 from the inlet 15a.

[0033] 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. Moreover, an alkaline water tank 31 for temporarily storing alkaline water and a second circulation pump 32 for pressurizing alkaline water are arranged in the second flow path 30 downstream of the cathode chamber 16. Therefore, alkaline water flowing out of the outlet 16b of the cathode chamber 16 can flow into the interior of the cathode chamber 16 through the alkaline water tank 31 and the second circulation pump 32 and from the inlet 16a of the cathode chamber 16.

[0034] The treated water flow path 40 is used to supply treated water to the electrolytic cell 10. Specifically, the treated water flow path 40 branches into two flow paths and connects to the first flow path 20 and the second flow path 30. Therefore, the treated water is supplied to both the first flow path 20 and the second flow path 30 through the treated water flow path 40. In addition, a solenoid valve 41 for switching the flow and stop of the treated water is provided in the treated water flow path 40.

[0035] The first outflow path 50 is connected downstream of the first circulating pump 22 via a first solenoid valve 51. As described later, the first outflow path 50 is for allowing the softened acidic water in the electrolytic cell 10 to flow out. Furthermore, a tap 52 is provided at the end of the first outflow path 50 to switch between allowing and stopping the flow of the softened acidic water. The treated water flowing out of the first outflow path 50 is treated water with removed or reduced metal ions, and can be appropriately utilized.

[0036] The second outflow path 60 is connected downstream of the second circulation pump 32 via a second solenoid valve 61. As described later, the second outflow path 60 is for allowing alkaline water that has undergone insoluble treatment in the electrolytic cell 10 to flow out. Furthermore, the end of the second outflow path 60 is connected to a faucet 52. The faucet 52 allows switching between the flow and shut-off of the alkaline water that has been softened by the filter 62 after insoluble matter removal. The treated water flowing out of the second outflow path 60 is water with removed or reduced metal ions, and can be appropriately utilized.

[0037] A filter 62 is provided in the second outflow path 60. The filter 62 is used to separate and remove the insoluble matter composed of metal ions after the insoluble treatment in the electrolytic cell 10. The filter 62 is not particularly limited as long as it can remove the insoluble matter. It can be a cartridge filter, a filter layer using granular filter material, a cyclone solid-liquid separator, a hollow fiber membrane, etc.

[0038] In addition, such as Figure 1 As shown, a bypass flow path 53 for conveying softened acidic water to the filter 62 can also be connected to the first solenoid valve 51. The acidic water that has been softened in the electrolytic cell 10 and circulated in the first flow path 20 has had its insoluble matter sufficiently reduced, but if necessary, this acidic water can also be filtered using the filter 62 and then conveyed to the faucet 52. Alternatively, a bypass flow path 63 can be connected to the second solenoid valve 61 for conveying alkaline water that has undergone insoluble treatment in the electrolytic cell 10 directly to the faucet 52 without conveying it to the filter 62.

[0039] like Figure 1 As shown, the water treatment apparatus 1 of this embodiment includes a first conductivity measuring unit 70 for measuring the conductivity of water flowing in the anode chamber and a second conductivity measuring unit 80 for measuring the conductivity of water flowing in the cathode chamber. Furthermore, in this specification, the water flowing in the anode chamber is also referred to as anolyte water, and the water flowing in the cathode chamber is also referred to as catholyte water. The first conductivity measuring unit 70 is located in the first flow path 20 near the inlet 15a of the anode chamber 15, and the second conductivity measuring unit 80 is located in the second flow path 30 near the inlet 16a of the cathode chamber 16. However, the location of the first conductivity measuring unit 70 is not particularly limited as long as it can measure the conductivity of the anolyte water; for example, it can be located inside the anode chamber 15 or inside the acidic water tank 21. Similarly, the location of the second conductivity measuring unit 80 is not particularly limited as long as it can measure the conductivity of the catholyte water; for example, it can be located inside the cathode chamber 16 or inside the alkaline water tank 31.

[0040] Conductivity sensors can be used as the first conductivity measuring unit 70 and the second conductivity measuring unit 80. Furthermore, as long as the first conductivity measuring unit 70 and the second conductivity measuring unit 80 can calculate conductivity, a TDS (Total Dissolved Solids) sensor or a pH sensor can be used.

[0041] The first conductivity measuring unit 70 and the second conductivity measuring unit 80 are electrically connected to the control unit 100 (described later), and send the values ​​of the conductivity of the anolyte 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.

[0042] The water treatment apparatus 1 also 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. Furthermore, the electrolysis power supply 90 flows current and applies voltage between the anode 12 and the cathode 13.

[0043] The control unit 100 is electrically connected to the electrolysis power supply 90, and adjusts the voltage between the anode and cathode by controlling the electrolysis power supply 90. Additionally, the control unit 100 is electrically connected to the solenoid valve 41, the first solenoid valve 51, the second solenoid valve 61, and the faucet 52 of the water flow path 40, and controls their opening and closing. Furthermore, the control unit 100 is electrically connected to the first circulation pump 22 and the second circulation pump 32, and controls their operation.

[0044] Furthermore, the control unit 100 may include storage devices such as ROM (Read Only Memory) and RAM (Random Access Memory) for storing control programs when executing control program-based actions, and a CPU (Central Processing Unit) for executing control programs. Additionally, the control unit 100 may include dedicated electronic circuitry for implementing the control program in hardware when executing predetermined actions. Moreover, the control unit 100 may also include a timing unit such as an RTC (Real Time Clock) for measuring time.

[0045] When the water treatment device 1 configured in this way operates, the following phenomena are assumed. First, the conductivity of acidic water is proportional to the concentration of ions in the acidic water. Therefore, the conductivity of acidic water is proportional to the concentration (hardness) of metal ions contained in the acidic water. Similarly, the conductivity of alkaline water is proportional to the concentration of ions in the alkaline water. Therefore, the conductivity of alkaline water is proportional to the concentration (hardness) of metal ions contained in the alkaline water.

[0046] Next, when the water to be treated is added to the anode chamber 15 and the cathode chamber 16 of the electrolytic cell 10, and a voltage is applied to the anode 12 and the cathode 13, as follows: Figure 2 As shown, metal ions in the anode chamber 15 migrate through the ion-permeable membrane 14 to the cathode chamber 16. That is, as shown in Equation 1, the electrophoretic velocity ν (m / s) of the ions is determined by the ion mobility μ (m / s). 2 The voltage (V / m) is expressed as the product of the electric field (E) and the voltage (V / m). Therefore, the migration of metal ions depends on the magnitude of the voltage (electric field). Furthermore, as... Figure 3 As shown, when a voltage is applied to the anode 12 and the cathode 13, hydrogen ions (H+) present in the anode chamber 15... +It also migrates into cathode chamber 16 and reacts with hydroxide ions (OH-). - It reacts and neutralizes.

[0047] [Number 1]

[0048]

[0049] Next, if the water to be treated is added to the anode chamber 15 and cathode chamber 16 of the electrolytic cell 10 and electrolysis is performed, then... Figure 3 As shown in chemical formula 1, hydrogen ions (H+) are generated in anode 12 through an oxidation reaction. + In cathode 13, hydroxide ions (OH-) are generated through a reduction reaction. - Furthermore, the electrolysis of such water depends on the magnitude of the current.

[0050] [Chemistry 1]

[0051] Anode 12: 2H2O → 4H + +4e - +O2↑

[0052] Cathode 13: 4H2O + 4e - →4OH - +2H2↑

[0053] Moreover, the treated water contains magnesium ions (Mg). 2+ The hydroxide ions react with the generated hydroxide ions to form magnesium hydroxide (Mg(OH)₂), which is insoluble. Here, the solubility product of magnesium hydroxide in water at 25°C is K. sp 1.80×10 -11 (mol / L) 3 Moreover, as shown in Equation 2, in Mg 2+ With OH - The ion product ratio solubility product K sp Under normal conditions, the dissolution equilibrium shifts towards the formation of Mg(OH)₂, thus creating an insoluble product composed of Mg(OH)₂. Therefore, to efficiently insoluble magnesium ions, the pH needs to be increased, which means increasing the number of hydroxide ions.

[0054] [Number 2]

[0055]

[0056] In addition, in the treated water, carbonates in the minerals dissolve or carbon dioxide in the air dissolves, thus the treated water contains carbonate ions (CO3-). 2- Furthermore, the treated water contains calcium ions (Ca). 2+It reacts with carbonate ions to form calcium carbonate (CaCO3), which is insoluble. Here, the solubility product K of calcium carbonate in water at 25°C is... sp It is 4.96×10 -9 (mol / L) 2 Moreover, as shown in Equation 3, in Ca 2+ With CO3 - The ion product ratio solubility product K sp In large cases, the dissolution equilibrium shifts towards the formation of CaCO3, thus generating an insoluble substance composed of CaCO3.

[0057] [Number 3]

[0058]

[0059] Here, in Figure 4 The diagram shows the carbonic acid (H₂CO₃) and bicarbonate (HCO₃) ions dissolved in water. - ) and carbonate ions (CO3) 2- The relationship between the presence of ) and pH. Figure 4 It is known that the more alkaline the pH of water, the fewer carbonate and bicarbonate ions there are, and the more carbonate ions there are. Therefore, in order to efficiently insoluble calcium ions, it is necessary to increase the pH to increase the carbonate ion concentration.

[0060] Thus, the higher the concentration of hydroxide ions, the greater the insolubility of magnesium and calcium ions. Furthermore, the electrolysis of water depends on the magnitude of the current. Therefore, the degree of insolubility of magnesium and calcium ions depends on the magnitude of the current.

[0061] Next, the operation of the water treatment apparatus 1 of this embodiment will be described based on the above phenomena. First, the control unit 100 opens the solenoid valve 41 to inject the raw water to be treated into the treated water flow path 40, the first flow path 20, and the second flow path 30. Furthermore, the treated water is injected into the anode chamber 15, the cathode chamber 16, the acidic water tank 21, and the alkaline water tank 31 of the electrolytic cell 10.

[0062] Next, the control unit 100 measures the conductivity of the anolyte 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 flow current between the anode 12 and the cathode 13 to electrolyze the water to be treated. Additionally, the control unit 100 operates the first circulation pump 22 and the second circulation pump 32 to circulate the water to be treated in the first flow path 20 and the second flow path 30. After a predetermined time of electrolysis and circulation of the water to be treated, the water in the anode chamber 15, the first flow path 20, and the acidic water tank 21 becomes acidic water, and the water in the cathode chamber 16, the second flow path 30, and the alkaline water tank 31 becomes alkaline water.

[0063] Furthermore, the control unit 100 measures the conductivity of the anolyte (acidic water) and catholyte (alkaline water) at predetermined intervals. Here, in cases where metal ions in the acidic and alkaline water are hardly removed, such as... Figure 5 As shown in "(1) Formation of insoluble substances", both acidic and alkaline water exhibit high electrical conductivity. Therefore, the control unit 100 controls the electrolysis power supply 90 to flow a constant current between the anode 12 and the cathode 13. Furthermore, this constant current control can be achieved by adjusting the current or voltage applied between the anode 12 and the cathode 13.

[0064] As mentioned above, the degree of insolubility of metal ions depends on the current; therefore, under constant current control, the insolubility of metal ions can be promoted in alkaline water. As a result, the concentration of metal ions decreases, and thus the conductivity of alkaline water decreases. However, it is difficult to insoluble metal ions in acidic water, thus maintaining a high conductivity.

[0065] Next, in cases where the conductivity of alkaline water decreased while that of acidic water remained high, such as... Figure 5 As shown in “(2) Ion Migration”, the control unit 100 controls the electrolysis power supply 90 to apply a constant voltage between the anode 12 and the cathode 13. Furthermore, such constant voltage control can be achieved by adjusting the voltage applied between the anode 12 and the cathode 13.

[0066] As described above, the electrophoretic migration of metal ions from the anode chamber 15 to the cathode chamber 16 depends on the voltage. Therefore, under constant voltage control, metal ions in the acidic water of the anode chamber 15 migrate through the ion-permeable membrane 14 to the cathode chamber 16. As a result, the concentration of metal ions in the alkaline water of the cathode chamber 16 increases, thus increasing the conductivity of the alkaline water. Conversely, the concentration of metal ions in the acidic water decreases, thus decreasing the conductivity of the acidic water.

[0067] Here, as described above, when a constant voltage is applied to the anode 12 and the cathode 13, hydrogen ions (H+) present in the anode chamber 15... + The alkaline water in the cathode chamber 16 also migrates to the cathode chamber 16, thus causing a neutralization reaction and a decrease in pH. When the pH of the alkaline water in the cathode chamber 16 decreases, the insolubility of metal ions is suppressed. Therefore, when the control unit 100 measures the conductivity after constant current control and finds that the conductivity of the alkaline water has decreased but the conductivity of the acidic water is high, it calculates a voltage value that can maintain the alkaline water at a high pH. For example, the control unit 100 calculates a voltage value that can maintain the pH of the alkaline water at 11 or higher and applies that voltage.

[0068] Next, in cases where the conductivity measurement results show that the conductivity of alkaline water increased while the conductivity of acidic water decreased, such as... Figure 5 As shown in “(3) Formation of insoluble matter”, the control unit 100 controls the electrolysis power supply 90 to flow a constant current between the anode 12 and the cathode 13. Furthermore, such constant current control can be achieved by adjusting the current or voltage applied between the anode 12 and the cathode 13.

[0069] As mentioned above, the degree of insolubility of metal ions depends on the current; therefore, under constant current control, the insolubility of metal ions can be promoted in alkaline water. As a result, the concentration of metal ions decreases, and thus the conductivity of alkaline water decreases.

[0070] Next, when the conductivity measurements showed that the conductivity of both acidic and alkaline water decreased, such as Figure 5 As indicated in “(4) Softening”, the control unit 100 determined that the softening of both acidic and alkaline water had progressed.

[0071] In this manner, the control unit 100 performs electrolysis control by adjusting the voltage applied between the anode 12 and the cathode 13 after measuring the conductivity of the anolyte and cathode water, thereby repeatedly performing constant current control and constant voltage control. As a result, metal ions migrate from the acidic water side to the alkaline water side, where they are insoluble, thus reducing the amount of metal ions in the treated water. Furthermore, in this embodiment, the time for electrolysis control is measured by the timing unit of the control unit 100, allowing this electrolysis control to continue until a predetermined time has elapsed.

[0072] Subsequently, the control unit 100 adjusts the first solenoid valve 51 to direct the acidic water in the first flow path 20 to the first outflow path 50. Additionally, the control unit 100 adjusts the second solenoid valve 61 to direct the alkaline water in the second flow path 30 to the second outflow path 60. Furthermore, this alkaline water passes through a filter 62 installed in the second outflow path 60. Since the alkaline water flowing into the second outflow path 60 contains insoluble metal ions, passing it through the filter 62 removes these insoluble substances. Moreover, by keeping the faucet 52 open, the user can use softened acidic and alkaline water. At this time, by arbitrarily mixing the acidic and alkaline water, neutral treated water can be used.

[0073] Here, in Figure 6 The diagram shows the relationship between the conductivity of the treated water and the ion mobility, insolubility, and softening rate of metal ions under constant voltage control (applying a constant voltage to the anode 12 and cathode 13 of the electrolytic cell 10 regardless of conductivity). Additionally, in... Figure 6The diagram also shows the relationship between the conductivity of the treated water and the ion mobility, insolubility, and softening rate of metal ions, under the condition that the control unit 100 controls the anode 12 and cathode 13 of the electrolytic cell 10 to flow a constant current regardless of conductivity. Furthermore, "metal ion mobility" indicates the efficiency of metal ions migrating from the anode chamber 15 to the cathode chamber 16. "Metal ion insolubility" indicates the efficiency with which metal ions bind to hydroxide and carbonate ions and become insoluble. "Softening rate" indicates the efficiency of removing metal ions from the treated water.

[0074] As described above, the migration of metal ions depends on voltage (electric field). Therefore, when the control unit 100 performs constant voltage control, metal ions migrate from the anode chamber 15 to the cathode chamber 16 regardless of the conductivity of the water being treated, thus maintaining a high ion mobility. However, since the insolubility of metal ions depends on the current, under constant voltage control, the insolubility increases when the conductivity of the water being treated is high, but decreases when the conductivity is low. Therefore, assuming that the control unit 100 only performs constant voltage control and not constant current control, softening can be performed efficiently and the softening rate can be improved when the conductivity of the water being treated is high, i.e., when the concentration of metal ions is high. However, when the conductivity of the water being treated is low, i.e., when the concentration of metal ions is low, the insolubility decreases, and therefore the softening rate also decreases. Thus, when the control unit 100 only performs constant voltage control, the softening rate is good when the concentration of metal ions is high, but deteriorates when the concentration of metal ions is low.

[0075] In contrast, the insolubility of metal ions depends on the current. Therefore, when the control unit 100 performs constant current control, metal ions can remain insoluble regardless of the conductivity of the water being treated, thus maintaining a high insolubility rate. However, as mentioned above, the migration of metal ions depends on the voltage. Therefore, when constant current control is performed, the ion migration rate increases when the conductivity of the water being treated is low, but decreases when the conductivity is high. Therefore, assuming that the control unit 100 only performs constant current control and not constant voltage control, softening can be performed efficiently when the conductivity of the water being treated is low, i.e., when the concentration of metal ions is low, thus increasing the softening rate. However, when the conductivity of the water being treated is high, i.e., when the concentration of metal ions is high, the ion migration rate decreases, and therefore the softening rate also decreases. Thus, when the control unit 100 only performs constant current control, the softening rate is good when the concentration of metal ions is low, but deteriorates when the concentration of metal ions is high.

[0076] In the water treatment apparatus 1 of this embodiment, electrolysis control is performed as follows: constant current control and constant voltage control are repeatedly performed by adjusting the voltage applied between the anode 12 and the cathode 13 according to the conductivity (hardness) of the anode water and the cathode water. Therefore, the state of high ion mobility and insolubility is always set, and as a result, the desired softening rate can be obtained regardless of the conductivity.

[0077] Here, in Figure 7 An example is shown illustrating the relationship between the conductivity of the treated water and power consumption under constant voltage control, constant current control, and electrolysis control. Furthermore, Figure 7 The designation C indicates the relationship between conductivity and power consumption when only constant voltage control is applied, and the designation D indicates the relationship between conductivity and power consumption when only constant current control is applied. Furthermore, the designation E indicates the relationship between conductivity and power consumption when electrolysis control as described in this embodiment is applied. According to... Figure 7 It is known that when only constant voltage control is performed, power consumption increases as the conductivity of the treated water increases. Furthermore, it is known that when only constant current control is performed, power consumption increases as the conductivity of the treated water decreases. However, in this embodiment, the electrolysis control switches between constant current control and constant voltage control based on the conductivity of the treated water, thus, as indicated by label E, power consumption can be kept low.

[0078] Furthermore, in this embodiment, the conductivity range of the water being treated during electrolysis control is preferably set to a range that results in lower power consumption compared to the cases of constant current control only and constant voltage control only. In other words, the conductivity range of the water being treated (acidic and alkaline water) during electrolysis control is preferably set to a range that results in lower power consumption compared to the cases of constant current control only and constant voltage control only. Figure 7 Within the range of the indicated mark F, specifically preferably 30 μS / cm to 8000 μS / cm. Therefore, compared to the cases of constant current control only and constant voltage control only, power consumption can be suppressed.

[0079] Here, as described above, the conductivity of acidic water is proportional to the concentration (hardness) of metal ions contained in the acidic water, and the conductivity of alkaline water is proportional to the concentration (hardness) of metal ions contained in the alkaline water. However, regardless of the conductivity values ​​of the acidic and alkaline water, it is sometimes difficult to achieve stable purification performance when the flow rates of acidic water in the anode chamber 15 and alkaline water in the cathode chamber 16 are constant. Therefore, the water treatment apparatus of this embodiment is characterized in that the control unit 100 adjusts at least one of the flow rates of acidic water in the anode chamber 15 and alkaline water in the cathode chamber 16.

[0080] As described above, when the water to be treated is added to the anode chamber 15 and the cathode chamber 16 of the electrolytic cell 10 and electrolysis is performed, hydrogen ions (H+) are generated at the anode 12 through an oxidation reaction. + At cathode 13, hydroxide ions (OH-) are generated through a reduction reaction. - Moreover, such as Figure 3 As shown, when a voltage is applied to the anode 12 and cathode 13, hydrogen ions (H+) present in the anode chamber 15... + ) migrates into cathode chamber 16 and reacts with hydroxide ions (OH-) - The reaction neutralizes the alkaline water in cathode chamber 16, thus lowering the pH. This decrease in pH can potentially inhibit the insolubility of metal ions.

[0081] To suppress the decrease in pH of the alkaline water in the cathode chamber 16, in the water treatment apparatus 1 of this embodiment, the flow rate of the acidic water in the anode chamber 15 can be made faster than the flow rate of the alkaline water in the cathode chamber 16. Thus, as... Figure 8 As shown, even if hydrogen ions generated near the anode 12 migrate towards the cathode chamber 16, they are more likely to migrate towards the outlet 15b of the anode chamber 15 with the flow of acidic water. In other words, hydrogen ions generated near the anode 12 migrate towards the outlet 15b of the anode chamber 15 more easily than those that migrate through the ion-permeable membrane 14 towards the cathode chamber 16. Furthermore, the hydrogen ions that migrate to the outlet 15b of the anode chamber 15 circulate in the first flow path 20 and flow into the anode chamber 15 from the inlet 15a.

[0082] In this way, by increasing the flow rate of acidic water in anode chamber 15, hydrogen ions generated at anode 12 easily circulate in anode chamber 15 and the first flow path 20, making it difficult for them to migrate through ion permeation membrane 14 to cathode chamber 16. Therefore, it is possible to suppress the pH drop of alkaline water in cathode chamber 16 and promote the insolubility of metal ions.

[0083] Furthermore, even with increased flow rate of acidic water in anode chamber 15, metal ions in the acidic water of anode chamber 15 can migrate through ion-permeable membrane 14 to cathode chamber 16 by applying constant voltage control. In other words, by applying constant voltage control, metal ions in the acidic water of anode chamber 15 located near ion-permeable membrane 14 can migrate through ion-permeable membrane 14 to cathode chamber 16. Additionally, since acidic water circulates in anode chamber 15 and the first flow path 20, by applying constant voltage control, metal ions in the acidic water can gradually migrate through ion-permeable membrane 14 to cathode chamber 16. Therefore, even with increased flow rate of acidic water in anode chamber 15, metal ions can migrate efficiently from anode chamber 15 to cathode chamber 16.

[0084] In this way, by making the flow rate of acidic water faster than that of alkaline water, the transfer of hydrogen ions to the cathode chamber 16 can be suppressed, promoting an increase in the pH of the alkaline water. Furthermore, since the transfer of hydrogen ions is suppressed, the neutralization point where the hydrogen ions generated at the anode 12 neutralize the hydroxide ions generated at the cathode 13 is near the ion-permeable membrane 14. Therefore, the transfer of hydrogen ions to the cathode chamber 16 can be suppressed, promoting an increase in the pH of the alkaline water. Additionally, since the transfer of hydrogen ions to the cathode chamber 16 is suppressed, acidic water with a low pH can be generated in a short time.

[0085] Furthermore, in the water treatment apparatus 1 of this embodiment, the flow rate of alkaline water in the cathode chamber 16 can be made faster than the flow rate of acidic water in the anode chamber 15. By making the flow rate of alkaline water faster than that of acidic water, the number of times the alkaline water circulates in the second flow path 30 increases, resulting in an increase in the number of times the treated water is electrolyzed into alkaline water. Therefore, even if hydroxide ions are consumed due to the insolubility of metal ions, the alkaline water can still be kept at a high pH. As a result, neutral treated water can be easily obtained by mixing this alkaline water with acidic water. In addition, by making the flow rate of alkaline water faster than that of acidic water, the transfer of hydroxide ions to the anode chamber 15 can be suppressed, thus enabling the generation of alkaline water with a high pH in a short time.

[0086] There is no particular limitation on the method for adjusting the flow rate of acidic water in the anode chamber 15 and the flow rate of alkaline water in the cathode chamber 16; for example, it can be performed as follows. As described above, the water treatment apparatus 1 includes: a first flow path 20 connected to the anode chamber 15 for flowing acidic water; and a second flow path 30 connected to the cathode chamber 16 for flowing alkaline water. A first circulation pump 22 for pressurizing acidic water and a first solenoid valve 51 are arranged in the first flow path 20. Similarly, a second circulation pump 32 for pressurizing alkaline water and a second solenoid valve 61 are arranged in the second flow path 30. The first circulation pump 22, the first solenoid valve 51, the second circulation pump 32, and the second solenoid valve 61 are electrically connected to a control unit 100, which controls their operation. Moreover, 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.

[0087] Furthermore, the flow rate of acidic water can be controlled by adjusting the first circulation pump 22 and / or the first solenoid valve 51 of the first flow rate adjustment unit via the control unit 100. In other words, increasing the rotational speed of the first circulation pump 22 can accelerate the flow rate of acidic water, and increasing the opening of the first solenoid valve 51 can also accelerate the flow rate of acidic water. Similarly, the flow rate of alkaline water can be controlled by adjusting the second circulation pump 32 and / or the second solenoid valve 61 of the second flow rate adjustment unit via the control unit 100.

[0088] In the water treatment apparatus 1, the percentage (%) of hydrogen ions generated in the anode chamber 15 through the electrode reaction that do not migrate through the ion-permeable membrane 14 to the cathode chamber 16 can be determined by the following formula 4. In other words, the percentage (%) of hydrogen ions that do not migrate from the anode chamber 15 to the cathode chamber 16 can be determined by the following formula 4.

[0089] [Number 4]

[0090]

[0091] In Equation 4, the electrode distance W (m) is the shortest distance between the anode 12 and the cathode 13, the flow velocity (m / s) in the electrolytic cell is the flow velocity 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 acidic water flow. Regarding the hydrogen ion mobility μ (m... 2 / Vs), the ion mobility μ of hydrogen ions is 36.2×10 -8 (m 2 / Vs). In addition, the solution potential V(V) of the acid is the voltage applied to the acidic water as a control voltage from the electrolysis power supply 90 via the anode 12.

[0092] In contrast, the percentage (%) of hydrogen ions generated by the electrode reaction that migrate through the ion-permeable membrane 14 to the cathode chamber 16 can be calculated using the following equation 5. That is, the percentage (transfer ratio) of hydrogen ions that migrate from the anode chamber 15 to the cathode chamber 16 can be calculated using the following equation 5.

[0093] [Number 5]

[0094]

[0095] Here, in Figure 9 The figure shows the pH change (vertical axis) and the charge between electrodes (horizontal axis) of the alkaline water in cathode chamber 16 calculated using a theoretical model, along with H2O. + The results obtained from the relationship between the proportions passing through the membrane. For example... Figure 9 As shown, it can be seen that as the charge between anode 12 and cathode 13 increases, the pH of alkaline water increases. Furthermore, it can be seen that in H... + When the percentage of ion-permeable membrane passing through the ion-permeable membrane 14 is less than 99.6%, the pH of the alkaline water in the cathode chamber 16 is above 8.2.

[0096] Furthermore, according to Figure 9 It can be seen that, with H + As the proportion of ions passing through membrane 14 decreases, the pH of alkaline water increases. In other words, it can be concluded that in H... + When the percentage of water passing through the ion-permeable membrane 14 is less than 99%, the pH of the alkaline water in the cathode chamber 16 tends to be above 8.2. Furthermore, it is known that as H...+ As the proportion of ions passing through membrane 14 decreases, the pH of the alkaline water becomes higher.

[0097] Furthermore, when the pH of the alkaline water in cathode chamber 16 is above 8.2, such as Figure 4 As shown, carbonate ions (CO3) 2- The increased proportion of H+ ions promotes calcium ion insolubility. Therefore, by increasing the flow rate of acidic water in the anode chamber 15, the H+ ions can be insoluble. + The proportion of ion-permeable membrane 14 that passes through is less than 99.6%, which can promote the insolubility of metal ions.

[0098] In this manner, the proportion of hydrogen ions generated in the anode chamber 15 through the electrode reaction that migrate to the cathode chamber 16 without passing through the ion-permeable membrane 14 is preferably 0.4% to 100%. Furthermore, the proportion of hydrogen ions generated in the anode chamber 15 through the electrode reaction that migrate to the cathode chamber 16 without passing through the ion-permeable membrane 14 is more preferably 1% to 20%. With such a structure, the insolubility of metal ions can be promoted, thereby reducing the amount of metal ions in the treated water.

[0099] Furthermore, the aforementioned theoretical model, which represents the relationship between the pH change of the alkaline water in the cathode chamber 16 and the electrical charge between the electrodes, can be derived as follows.

[0100] In an electrolytic structure having an ion-permeable membrane 14 for suppressing the flow of water between the cathode chamber 16 and the anode chamber 15, if the ratio α of the amount of protons migrating from the anode chamber to the cathode chamber via the ion-permeable membrane to the amount of protons generated by the electrode reaction based on water electrolysis is taken into account, Equation 6 can be obtained.

[0101] [Number 6]

[0102]

[0103] Here, each symbol represents the following.

[0104] i: current [A]

[0105] t: Time (seconds)

[0106] F: Faraday constant [C / mol]

[0107] V0: Water volume [L]

[0108] K w : Ion product of water [mol] 2 / L 2 ]

[0109] K1: Equilibrium constant of carbonic acid and bicarbonate ions [mol] 2 / L 2 ]

[0110] K2: Equilibrium constant between bicarbonate ions and carbonate ions [mol] 2 / L 2 ]

[0111] [H + Molar concentration of protons [mol / L]

[0112] C a Total molar concentration of carbonic acid [mol / L]

[0113] α: The proportion of protons generated by the electrolysis reaction that migrate towards the cathode side [-]

[0114] The derivation process of equation 6 is shown below. First, the chemical formula for the electrolysis reaction of water is given by the following chemical formula 2.

[0115] [Chemistry 2]

[0116]

[0117] In addition, the chemical equilibrium of carbonic acid in water is represented by the following chemical formula 3, and the ratio of carbonic acid present varies with pH.

[0118] [Chemistry 3]

[0119]

[0120] If the total amount of carbonic acid is denoted as a, then the molar concentration C a It is represented by the following formula (1).

[0121] [Number 7]

[0122]

[0123] If the hydroxide ion OH- based on electrolysis - and proton H + Let the amount of substance be b mol, then the molar concentration C b It is represented by the following formula (2).

[0124] [Number 8]

[0125]

[0126] Here, if the equilibrium constants of carbonates are set as K1 and K2, they are represented by the following equations (3) and (4).

[0127] [Number 9]

[0128]

[0129] If we rearrange equations (3) and (4), we get the following equations (5) to (7).

[0130] [Number 10]

[0131]

[0132] In addition, if the ion product of water is set as Kw, then the following equations (8) and (9) are derived.

[0133] [Number 11]

[0134]

[0135] In addition, the total carbonic acid concentration C a It is represented by the following equation (10).

[0136] [Number 12]

[0137]

[0138] If we substitute equations (6) and (7) into equation (10) and rearrange them, we get equations (11) to (13).

[0139] [Number 13]

[0140]

[0141] Substituting equation (13) into equation (7) yields equation (14).

[0142] [Number 14]

[0143]

[0144] Furthermore, substituting equation (13) into equation (6) yields the following equation.

[0145] [Number 15]

[0146]

[0147] Furthermore, according to the principle of electrical neutrality, the following equation holds true.

[0148] [Number 16]

[0149]

[0150] If we substitute equations (8), (13), (14), and (15) into equation (16), we get equation (17).

[0151] [Number 17]

[0152]

[0153] Here, by adding hydroxide ions generated through the electrolysis of water, equations (18) and (19) can be obtained.

[0154] [Number 18]

[0155]

[0156] According to equation (19), the pH value corresponding to the charge can be plotted. Figure 10 Furthermore, in Figure 10 In the example, with Ca = 2.66 × 10⁻⁶ -3 Calculations were performed using [mol / L] and V0 = 6.0 [L].

[0157] Furthermore, if we consider the proportion α of protons generated by the electrolysis reaction in the anode chamber 15 migrating to the cathode chamber 16 via the ion-permeable membrane 14, we obtain equation (20).

[0158] [Number 19]

[0159]

[0160] The pH curve when the value of α is changed is as follows Figure 9 .exist Figure 9 The results show that as protons migrate into cathode chamber 16, the rise in pH of cathode chamber 16 is suppressed, i.e., neutralization occurs.

[0161] In the water treatment apparatus 1, the control unit 100 preferably controls the flow rates of acidic water and alkaline water based on the proportion of hydrogen ions generated in the anode chamber 15 through the electrode reaction that migrate to the cathode chamber 16 without passing through the ion-permeable membrane 14. That is, it is preferable to control the flow rates of acidic water and alkaline water such that the proportion of hydrogen ions generated in the anode chamber 15 through the electrode reaction that migrate to the cathode chamber 16 without passing through the ion-permeable membrane 14 is 0.4% to 100%. By controlling it in this way, the insolubility of metal ions can be promoted in the cathode chamber 16.

[0162] Furthermore, in the water treatment apparatus 1, the control unit 100 preferably controls the flow rate of acidic water in the anode chamber 15 and the flow rate of alkaline water in the cathode chamber 16 to bring the pH of the alkaline water in the cathode chamber 16 to a predetermined value. As described above, by making the pH of the alkaline water in the cathode chamber 16 8.2 or higher, carbonate ions (CO3) are reduced. 2- The increased proportion of [acidic water] promotes the insolubility of calcium ions. Therefore, it is preferable to control the flow rate of acidic water in the anode chamber 15 and the flow rate of 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. Furthermore, this specified value for the pH of the alkaline water is not limited to 8.2; for example, it could be 10 or 12.

[0163] exist Figure 11 An example is shown of the pH measurement results obtained by measuring the alkaline water in the cathode chamber 16 when the flow rate of acidic water in the anode chamber 15 is set to 4.6 L / min or 14 L / min in the water treatment apparatus 1. Furthermore, Figure 9 The measurement results were obtained under conditions where the initial conductivity of the treated water was 550 μS / cm and no electrolysis control was performed. Additionally, Figure 9 The results were obtained under the conditions that the flow rate of acidic water was 4.6 L / min and 14 L / min, while the flow rate of alkaline water was the same and the flow rate of alkaline water was slower than that of acidic water.

[0164] like Figure 11 As shown, when the flow rate of acidic water in anode chamber 15 is 14 L / min, the pH of alkaline water increases rapidly compared to when the flow rate is 4.6 L / min. In other words, when the flow rate of acidic water in anode chamber 15 is high, the migration of hydrogen ions from anode chamber 15 to cathode chamber 16 is inhibited, and the pH of alkaline water increases rapidly.

[0165] As described above, in the water treatment apparatus 1, in order to ensure stable purification performance for treated water with a wide range of conductivity, the control unit 100 is characterized by adjusting at least one of the flow rate of acidic water in the anode chamber 15 and the flow rate of alkaline water in the cathode chamber 16. At this time, the control unit 100 can adjust at least one of the flow rates of acidic water in the anode chamber 15 and alkaline water in the cathode chamber 16 based on at least one of the conductivity of the acidic water and the conductivity of the alkaline water.

[0166] Specifically, as described above, the water treatment apparatus 1 of this embodiment performs electrolysis control as follows: after measuring the conductivity of acidic water and alkaline water, the voltage or current applied between the anode 12 and the cathode 13 is adjusted to repeatedly perform constant current control and constant voltage control.

[0167] exist Figure 12A The diagram provides a summary of the relationships between the conductivity and pH of alkaline water and acidic water under constant voltage control, where the flow rates of acidic and alkaline water are the same. Furthermore, Figure 12A The conductivity of acidic and alkaline water was measured at the upstream side of the electrolyzer 10, and the pH status of acidic and alkaline water at the downstream side of the electrolyzer 10 was shown.

[0168] In constant voltage control, according to Figure 6Regardless of conductivity, ion migration occurs at a constant rate. On the other hand, the current is smaller at low conductivity and larger at high conductivity. In alkaline water, under low conductivity conditions, the pH change is small due to constant voltage control, but the amount of hydrogen ions migrating towards the alkaline side is large, thus neutralizing the pH and causing it to decrease. However, under high conductivity conditions, the pH change is small due to constant voltage control, but the amount of hydrogen ions migrating towards the alkaline side is small, resulting in a higher pH compared to conditions with low conductivity.

[0169] Conversely, in acidic water, under conditions of low conductivity, the pH change is small due to constant voltage control. However, the amount of hydrogen ions migrating towards the alkaline water side is large under constant voltage control, thus the pH of the acidic water becomes higher. Conversely, under conditions of high conductivity, the pH change is small due to constant voltage control, but the amount of hydrogen ions migrating towards the alkaline water side is less, thus the pH becomes lower compared to conditions of low conductivity.

[0170] exist Figure 12B The diagram briefly illustrates the relationship between the conductivity and pH of alkaline water and the relationship between the conductivity and pH of acidic water under constant voltage control, where the flow rate of acidic water is faster than that of alkaline water.

[0171] As described above, in alkaline water, under conditions of low conductivity, the pH change is small due to constant voltage control. However, when flow rate control is implemented, the migration of hydrogen ions into alkaline water is suppressed, thus increasing the pH of the alkaline water. Conversely, under conditions of high conductivity, the pH change is small due to constant voltage control, but the migration of hydrogen ions into alkaline water is suppressed due to flow rate control, thus increasing the pH of the alkaline water. In this way, by implementing flow rate control, compared to the case where the flow rates of acidic and alkaline water are the same, the overall pH of the alkaline water can be increased regardless of its conductivity.

[0172] Conversely, in acidic water, under conditions of low conductivity, the pH change is small due to constant voltage control. However, with flow rate control, the migration of hydrogen ions towards alkaline water is suppressed, thus lowering the pH of the acidic water. Conversely, under conditions of high conductivity, the pH change is small due to constant voltage control, but the amount of hydrogen ions migrating towards alkaline water is less due to flow rate control, thus lowering the pH compared to conditions of low conductivity. In this way, by controlling the flow rate, the overall pH of the acidic water can be lowered compared to the case where the flow rates of acidic and alkaline water are the same, regardless of the conductivity of the acidic water.

[0173] exist Figure 13AThe diagram briefly illustrates the relationship between the conductivity and pH of alkaline water and the conductivity and pH of acidic water under constant current control, where the flow rates of acidic and alkaline water are the same. Furthermore, Figure 13A The conductivity of acidic and alkaline water was also measured on the upstream side of electrolyzer 10, showing the pH state of acidic and alkaline water on the downstream side of electrolyzer 10.

[0174] In constant current control, according to Figure 6 Regardless of conductivity, the rate of hydrogen and hydroxide ion formation based on the electrolysis reaction is constant. On the other hand, the voltage is high when conductivity is low, and low when conductivity is high. In alkaline water, under conditions of low conductivity, the pH change is constant, but the amount of hydrogen ions migrating to the alkaline side is large, thus the pH of the alkaline water decreases through neutralization. However, under conditions of high conductivity, the pH change is constant, but the amount of hydrogen ions migrating to the alkaline side is small, thus the pH becomes higher compared to conditions of low conductivity.

[0175] In contrast, in acidic water, under conditions of low conductivity, the pH change is constant, but the amount of hydrogen ions migrating towards alkaline water is large, thus the pH of acidic water becomes higher. Conversely, under conditions of high conductivity, the pH change is constant, but the amount of hydrogen ions migrating towards alkaline water is small, thus the pH becomes lower compared to conditions of low conductivity.

[0176] exist Figure 13B The diagram briefly illustrates the relationship between the conductivity and pH of alkaline water and the conductivity and pH of acidic water under constant current control, where the flow rate of acidic water is faster than that of alkaline water.

[0177] As mentioned above, in alkaline water, the pH change is constant under conditions of low conductivity. However, with flow rate control, the migration of hydrogen ions into alkaline water is suppressed, thus increasing the pH of the alkaline water. Conversely, under conditions of high conductivity, the pH change is constant, but due to flow rate control, the migration of hydrogen ions into alkaline water is suppressed, thus increasing the pH of the alkaline water. In this way, by controlling the flow rate, the overall pH of the alkaline water can be increased, regardless of its conductivity, compared to the case where the flow rates of acidic and alkaline water are the same.

[0178] In contrast, in acidic water, under conditions of low conductivity, the pH change is constant. However, with flow rate control, the migration of hydrogen ions towards alkaline water is suppressed, thus lowering the pH of the acidic water. Conversely, under conditions of high conductivity, the pH change is constant, but due to flow rate control, the amount of hydrogen ions migrating towards alkaline water is reduced, resulting in a lower pH compared to conditions with low conductivity. Thus, by controlling the flow rate, the overall pH of the acidic water can be lowered regardless of its conductivity, compared to the case where the flow rates of acidic and alkaline water are the same.

[0179] In this way, by controlling the flow rate of acidic water to be faster than that of alkaline water, the pH of alkaline water can be increased, and the pH of acidic water can be decreased, regardless of whether constant current control or constant voltage control is used. Therefore, flow rate control can be performed under both constant current control and constant voltage control, or under either one. In particular, constant current control promotes the insolubility of metal ions, so flow rate control is preferred under constant current control.

[0180] As described above, in the water treatment apparatus 1, it is preferable to repeatedly perform constant current control and constant voltage control based on the conductivity of acidic water or alkaline water, and to perform flow rate control during at least one of the constant current control and constant voltage control. With such a structure, stable purification performance can be achieved for water of any conductivity.

[0181] Figure 14 This is a graph showing the pH of alkaline water versus time with and without flow rate control. (Example) Figure 14 As shown, by controlling the flow rate of acidic water to be faster than that of alkaline water, the pH of the alkaline water rises rapidly, reaching the target pH earlier. Furthermore, Figure 14 The period from the time when the target pH is reached (the arrival time) to the end time is considered the time during which the reaction progresses and the metal ion becomes insoluble.

[0182] Like this, according to Figure 14 By controlling the flow rate, the arrival and end times can be reached earlier compared to the case without flow rate control, thus shortening the electrolysis time and achieving energy savings. Furthermore, flow rate control also facilitates an increase in hydroxide and carbonate ion concentrations, thereby shortening the insoluble reaction time.

[0183] When the water to be treated is softened using the water treatment apparatus 1 of this embodiment, inorganic crystals sometimes gradually precipitate on the surface of the electrodes. When crystals precipitate on the electrode surface, the electrolysis efficiency of the water to be treated decreases, and the generation efficiency of acidic and alkaline water may deteriorate. Therefore, it is preferable that the water treatment apparatus 1 performs electrode purification control after softening a predetermined amount of water to be treated or after using it for a predetermined time.

[0184] Specifically, when purifying the crystals precipitated on the surface of at least one of the anode 12 and cathode 13, firstly, the residual water in the water treatment device 1 is drained and new water is injected. Furthermore, the newly injected water can be the water being treated or softened treated water.

[0185] Next, the polarities of the switching anode 12 and cathode 13 are reversed. That is, the anode 12 is electrically connected to the negative terminal of the electrolysis power supply 90, and the cathode 13 is electrically connected to the positive terminal of the electrolysis power supply 90. By flowing current and applying voltage in this state, the crystals precipitated on the surface of the electrodes dissolve in water.

[0186] Preferably, after the polarities of the anode 12 and cathode 13 are interchanged, the water in the anode chamber 15 is circulated through the first flow path 20 at least once, and the water in the cathode chamber 16 is circulated through the second flow path 30 at least once. In this way, by circulating the water in the anode chamber 15 and the cathode chamber 16 at least once, the crystals on the surface of the electrodes can be dissolved, thereby purifying the electrodes.

[0187] Next, the polarities of the anode 12 and cathode 13 are interchanged. That is, the anode 12 is electrically connected to the positive terminal of the electrolysis power supply 90, and the cathode 13 is electrically connected to the negative terminal of the electrolysis power supply 90. Through this control, the electrode surface can be purified.

[0188] Furthermore, in the water treatment apparatus 1 of this embodiment, a flow rate measuring unit (flow rate sensor) for measuring the flow rate of acidic water can be provided in the first flow path 20, and a flow rate measuring unit (flow rate sensor) for measuring the flow rate of alkaline water can be provided in the second flow path 30. By providing such flow rate measuring units, the accuracy of flow rate control for acidic and alkaline water can be improved. However, even without a flow rate measuring unit, the flow rates of acidic and alkaline water can be estimated by calculation; therefore, in the water treatment apparatus 1 of this embodiment, a flow rate measuring unit is not an essential structure.

[0189] As described above, in the water treatment apparatus 1, the first flow path 20 and the second flow path 30 are configured as circulating flow paths. However, the water treatment apparatus is not limited to this configuration; single-flow flow paths that do not circulate water can also be used as the first and second flow paths. Furthermore, circulating flow paths and single-flow flow paths can be combined as the first and second flow paths. Therefore, in this specification, circulating flow paths and single-flow flow paths are collectively referred to as the "first flow path." Similarly, circulating flow paths and single-flow flow paths are collectively referred to as the "second flow path."

[0190] (Postscript)

[0191] Based on the above description of the embodiments, the following technology is disclosed.

[0192] (Technology 1) A water treatment apparatus for removing metal ions from water to be treated to generate treated water, the water treatment apparatus comprising:

[0193] An electrolytic cell comprising an anode chamber having an anode, a cathode chamber having a cathode, and a membrane separating the anode chamber and the cathode chamber and allowing ions to permeate, wherein acidic water and alkaline water are generated from the water being treated by electrolysis in the electrolytic cell; and

[0194] The control unit controls the voltage or current between the anode and the cathode.

[0195] The acidic water flows through the anode chamber, and the alkaline water flows through the cathode chamber.

[0196] The control unit adjusts at least one of the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber.

[0197] In the water treatment apparatus of this embodiment, at least one of the flow rate of acidic water in the anode chamber 15 and the flow rate of alkaline water in the cathode chamber 16 is adjusted. As a result, hydrogen ions generated at the anode 12 have difficulty migrating through the ion-permeable membrane 14 to the cathode chamber 16. Therefore, the pH decrease of the alkaline water in the cathode chamber 16 can be suppressed, promoting the insolubility of metal ions.

[0198] (Technology 2) The water treatment apparatus according to Technology 1, wherein the control unit controls the flow rate of the acidic water in the anode chamber to be faster than the flow rate of the alkaline water in the cathode chamber, or controls the flow rate of the alkaline water in the cathode chamber to be faster than the flow rate of the acidic water in the anode chamber.

[0199] With this structure, hydrogen ions generated at the anode 12 have difficulty migrating through the ion permeation membrane 14 to the cathode chamber 16, thus inhibiting the pH drop of the alkaline water in the cathode chamber 16 and promoting the insolubility of metal ions.

[0200] (Technology 3) The water treatment apparatus according to Technology 1 or 2, wherein,

[0201] The water treatment apparatus further comprises: a first conductivity measuring unit, which measures the conductivity of the acidic water flowing in the anode chamber; and

[0202] The second conductivity measuring unit measures the conductivity of the alkaline water flowing in the cathode chamber.

[0203] The control unit adjusts at least one of the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber based on at least one of the conductivity of the acidic water and the conductivity of the alkaline water.

[0204] With this structure, stable purification performance can be achieved for water of any conductivity.

[0205] (Technology 4) The water treatment apparatus according to any one of technologies 1 to 3, wherein,

[0206] The water treatment device further includes a first flow path and a second flow path. The first flow path is connected to the anode chamber and is used for the flow of acidic water, and the second flow path is connected to the cathode chamber and is used for the flow of alkaline water.

[0207] A first flow rate adjustment unit for adjusting the flow rate of the acidic water is provided in the first flow path, and a second flow rate adjustment unit for adjusting the flow rate of the alkaline water is provided in the second flow path.

[0208] The control unit adjusts at least one of the first flow rate adjustment unit and the second flow rate adjustment unit.

[0209] This structure allows for easy adjustment of the flow rate of acidic and alkaline water, making it difficult for hydrogen ions to migrate from the anode chamber 15 to the cathode chamber 16.

[0210] (Technology 5) The water treatment apparatus according to any one of technologies 1 to 4, wherein,

[0211] The water treatment device further includes a first flow path and a second flow path. The first flow path is connected to the anode chamber and is used for circulating the water inside the anode chamber. The second flow path is connected to the cathode chamber and is used for circulating the water inside the cathode chamber.

[0212] In order to purify the surface of at least one of the anode and the cathode, after the polarity of the anode and the cathode is interchanged, the water in the anode chamber is circulated through the first flow path at least once, and the water in the cathode chamber is circulated through the second flow path at least once.

[0213] This structure allows the crystals precipitated on the electrode surface to dissolve, thus purifying the electrode.

[0214] (Technology 6) A water treatment apparatus according to any one of technologies 1 to 5, wherein,

[0215] The control unit causes a change in at least one of the voltage and current between the anode and the cathode.

[0216] This structure enables efficient removal of metal ions by controlling their insolubility and migration from the anode chamber to the cathode chamber.

[0217] (Technology 7) The water treatment apparatus according to Technology 6, wherein,

[0218] When the conductivity of the water flowing in the anode chamber and the conductivity of the water flowing in the cathode chamber are 30 μS / cm to 8000 μS / cm, the control unit causes a change in the voltage applied between the anode and the cathode.

[0219] In this embodiment, the conductivity of the water being treated during electrolysis control is preferably set to a range that results in lower power consumption compared to the cases of constant current control only and constant voltage control only. With this structure, power consumption can be reduced compared to the cases of constant current control only and constant voltage control only.

[0220] (Technology 8) The water treatment apparatus according to any one of technologies 1 to 7, wherein,

[0221] The control unit switches between constant current control and constant voltage control by changing the voltage or current applied between the anode and the cathode.

[0222] This structure promotes the insolubility of metal ions in the treated water and suppresses power consumption compared to constant current control and constant voltage control alone.

[0223] The above describes this embodiment, but the embodiment is not limited thereto, and various modifications can be made within the scope of the spirit of this embodiment.

[0224] The entire contents of Japanese Special Application No. 2024-052106 (application date: March 27, 2024) are incorporated herein by reference.

[0225] Industrial availability

[0226] According to this disclosure, a water treatment apparatus can be provided that can efficiently remove metal ions from hard water even without using ion exchange resins.

[0227] Explanation of reference numerals in the attached figures

[0228] 1: Water treatment device; 10: Electrolytic cell; 12: Anode; 13: Cathode; 14: Membrane (ion-permeable membrane); 15: Anode chamber; 16: Cathode chamber; 20: First flow path; 30: Second flow path; 70: First conductivity measuring unit; 80: Second conductivity measuring unit; 100: Control unit.

Claims

1. A water treatment apparatus for removing metal ions from water to be treated to generate treated water, the water treatment apparatus comprising: An electrolytic cell comprising an anode chamber having an anode, a cathode chamber having a cathode, and a membrane separating the anode chamber and the cathode chamber and allowing ions to permeate, wherein acidic water and alkaline water are generated from the water being treated by electrolysis in the electrolytic cell; and The control unit controls the voltage or current between the anode and the cathode. in, The acidic water flows through the anode chamber, and the alkaline water flows through the cathode chamber. The control unit adjusts at least one of the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber.

2. The water treatment apparatus according to claim 1, wherein, The control unit controls the flow rate of the acidic water in the anode chamber to be faster than the flow rate of the alkaline water in the cathode chamber, or controls the flow rate of the alkaline water in the cathode chamber to be faster than the flow rate of the acidic water in the anode chamber.

3. The water treatment apparatus according to claim 1 or 2, wherein, The water treatment device also includes: A first conductivity measuring unit measures the conductivity of the acidic water flowing in the anode chamber; and The second conductivity measuring unit measures the conductivity of the alkaline water flowing in the cathode chamber. The control unit adjusts at least one of the flow rate of the acidic water in the anode chamber and the flow rate of the alkaline water in the cathode chamber based on at least one of the conductivity of the acidic water and the conductivity of the alkaline water.

4. The water treatment apparatus according to any one of claims 1 to 3, wherein, The water treatment device further includes a first flow path and a second flow path. The first flow path is connected to the anode chamber and is used for the flow of acidic water, and the second flow path is connected to the cathode chamber and is used for the flow of alkaline water. A first flow rate adjustment unit for adjusting the flow rate of the acidic water is provided in the first flow path, and a second flow rate adjustment unit for adjusting the flow rate of the alkaline water is provided in the second flow path. The control unit adjusts at least one of the first flow rate adjustment unit and the second flow rate adjustment unit.

5. The water treatment apparatus according to any one of claims 1 to 4, wherein, The water treatment device further includes a first flow path and a second flow path. The first flow path is connected to the anode chamber and is used for circulating the water inside the anode chamber. The second flow path is connected to the cathode chamber and is used for circulating the water inside the cathode chamber. In order to purify the surface of at least one of the anode and the cathode, after the polarity of the anode and the cathode is interchanged, the water in the anode chamber is circulated through the first flow path at least once, and the water in the cathode chamber is circulated through the second flow path at least once.

6. The water treatment apparatus according to any one of claims 1 to 5, wherein, The control unit causes a change in at least one of the voltage and current between the anode and the cathode.

7. The water treatment apparatus according to claim 6, wherein, When the conductivity of the water flowing in the anode chamber and the conductivity of the water flowing in the cathode chamber are 30 μS / cm to 8000 μS / cm, the control unit causes a change in the voltage applied between the anode and the cathode.

8. The water treatment apparatus according to any one of claims 1 to 7, wherein, The control unit switches between constant current control and constant voltage control by changing the voltage or current applied between the anode and the cathode.

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