Patent Publication Number: US-2018037477-A1

Title: Water treatment apparatus and operation method for water treatment apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a water treatment apparatus and a method for operating the water treatment apparatus. 
     BACKGROUND ART 
     A water treatment apparatus is an apparatus that includes an ion-exchange resin disposed between electrodes and absorbs cations or anions into the ion-exchange resin to remove impurities from an aqueous solution. It is known that a water treatment apparatus having this configuration is provided with a variable voltage supply capable of maintaining electrodes at a plurality of voltage levels during an ion exchange stage (e.g., refer to PTL 1). 
     The apparatus disclosed in PTL 1 can control the concentration of ions in an effluent solution flowing out of the apparatus by maintaining the electrodes at a plurality of voltage levels. 
     Unfortunately, the apparatus disclosed in PTL 1 still has room for improvement in terms of restraint on scale formation when the ion exchange membrane is regenerated. 
     CITATION LIST 
     Patent Literature 
     PTL1: Unexamined Japanese Patent Publication No. 2007-501702 
     SUMMARY OF THE INVENTION 
     The present disclosure has been accomplished to solve the conventional problem described above. It is an object of the present disclosure to provide a water treatment apparatus that can restrain scale formation at the time of regeneration of an ion exchange membrane. It is another object of the present disclosure to provide a method for operating such a water treatment apparatus. 
     In order to solve the conventional problem, a water treatment apparatus of the present disclosure includes an electrochemical cell including: a casing provided with an inlet and an outlet; a pair of electrodes that is disposed in the casing and forms an anode and a cathode opposing each other; and an ion exchange membrane that is disposed between the anode and the cathode and has a cation exchange substrate and an anion exchange substrate. The water treatment apparatus further includes a power supply that supplies electric power to the electrodes, a first water flow path connected with the inlet, a second water flow path connected with the outlet, a soft water supply unit that feeds soft water to the inlet, and a flow adjustor that is provided on the second water flow path and regulates a flow rate of water passing through the second water flow path. The water treatment apparatus further includes a controller that controls electric power supplied from the power supply to the electrodes, the flow rate of water passing through the second water flow path by use of the flow adjustor, and the soft water fed to the inlet through the soft water supply unit when a process for regenerating the anion and the cation exchange substrates is executed. 
     This configuration can reduce the hardness and electric conductivity of water fed into the electrochemical cell during regeneration of the ion exchange membrane. As a result, the apparatus can restrain scale formation. 
     In a method for operating a water treatment apparatus of the present disclosure, the water treatment apparatus includes an electrochemical cell including; a casing provided with an inlet and an outlet; a pair of electrodes that is disposed in the casing and forms an anode and a cathode opposite to each other; and an ion exchange membrane that is disposed between the anode and the cathode and has a cation exchange substrate and an anion exchange substrate. The water treatment apparatus further includes a power supply that supplies electric power to the electrodes, a first water flow path connected with the inlet, a second water flow path connected with the outlet, a soft water supply unit that feeds soft water to the inlet, and a flow adjustor that is provided on the second water flow path and regulates a flow rate of water passing through the second water flow path. The method includes a step A of adjusting electric power supplied from the power supply to the electrodes, a step B of regulating the flow rate of water passing through the second water flow path by use of the flow adjustor, and a step C of feeding the soft water to the inlet by use of the soft water supply unit. 
     This configuration can reduce the hardness and electric conductivity of water fed into the electrochemical cell during regeneration of the ion exchange membrane. As a result, the apparatus can restrain scale formation. 
     These and other objects, features and advantages of the present disclosure will become apparent with reference to the accompanying drawings, and the following detailed description of the preferred exemplary embodiments. 
     A water treatment apparatus of the present disclosure can restrain scale formation at the time of regeneration of an ion exchange membrane. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view illustrating a configuration of a water treatment apparatus according to a first exemplary embodiment. 
         FIG. 2  is a schematic view illustrating a configuration of a water treatment apparatus according to a first modification example of the first exemplary embodiment. 
         FIG. 3  is a schematic view illustrating a configuration of a water treatment apparatus according to a second exemplary embodiment. 
         FIG. 4  is a schematic view illustrating a configuration of a water treatment apparatus according to a third exemplary embodiment. 
         FIG. 5  is a flowchart illustrating a procedure conducted by the water treatment apparatus according to the third exemplary embodiment. 
         FIG. 6  is a schematic view illustrating a configuration of a water treatment apparatus according to a fourth exemplary embodiment. 
         FIG. 7  is a flowchart illustrating a procedure conducted by the water treatment apparatus according to the fourth exemplary embodiment. 
         FIG. 8  is a flowchart illustrating a procedure conducted by a water treatment apparatus according to a fifth exemplary embodiment. 
         FIG. 9  is a graph illustrating a relationship between an elapsed time of a regeneration process and a concentration of calcium ions contained in water discharged from a second water flow path when the regeneration process has been executed by the water treatment apparatus according to the fifth exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments of the present disclosure will now be described with reference to the accompanying drawings. In all the drawings, identical or equivalent components are denoted by identical reference signs, and redundant descriptions thereof are omitted as appropriate. All the drawings show excerpted components necessary to describe the present disclosure and may omit other components. The exemplary embodiments described below should not be construed to limit the scope of the present disclosure. 
     First Exemplary Embodiment 
     A water treatment apparatus according to a first exemplary embodiment includes an electrochemical cell including: a casing provided with an inlet and an outlet; a pair of electrodes that is disposed in the casing and forms an anode and a cathode opposing each other; and an ion exchange membrane that is disposed between the anode and the cathode and has a cation exchange substrate and an anion exchange substrate. The water treatment apparatus further includes a power supply that supplies electric power to the electrodes a first water flow path connected with the inlet, a second water flow path connected with the outlet, a soft water supply unit that feeds soft water to the inlet, and a flow adjustor that is provided on the second water flow path and regulates a flow rate of water passing through the second water flow path. The water treatment apparatus further includes a controller that controls electric power supplied from the power supply to the electrodes, the flow rate of water passing through the second water flow path by use of the flow adjustor, and the soft water fed to the inlet through the soft water supply unit when a process for regenerating the anion and the cation exchange substrates is executed. 
     In the water treatment apparatus according to the first exemplary embodiment, the soft water supply unit may include a tank that stores water softened with the electrochemical cell and a pump that sends soft water from the tank to the inlet. 
     With reference to  FIG. 1 , one example of the water treatment apparatus according to the first exemplary embodiment will now be described. 
     [Configuration of Water Treatment Apparatus] 
       FIG. 1  is a schematic view illustrating a configuration of a water treatment apparatus according to the first exemplary embodiment. 
     With reference to  FIG. 1 , water treatment apparatus  100  according to the first exemplary embodiment includes electrochemical cell  10 , power supply  20 , first water flow path  21 , second water flow path  22 , a soft water supply unit equipped with tank  31  and pump  32 , flow adjustor  40 , and controller  50 . When a regeneration process is executed, controller  50  controls electric power supplied from power supply  20  to electrodes of electrochemical cell  10  and the flow rate of water passing through second water flow path  22  by flow adjustor  40 . At the same time, controller  50  controls pump  32  so as to feed soft water to an inlet of electrochemical cell  10 . 
     Electrochemical cell  10  includes casing  13 , and electrode  14 A, electrode  14 B, and ion exchange membrane  15  that are disposed in casing  13 . A first end of casing  13  is provided with inlet  11 , while a second end of casing  13  is provided with outlet  12 . Ion exchange membrane  15  includes anion exchange substrate (anion exchange resin)  15 A and cation exchange substrate (cation exchange resin)  15 B. Electrochemical cell  10  may be a publicly-known electrochemical cell, and thus detailed description thereof is omitted. 
     Inlet  11  of electrochemical cell  10  is connected with a downstream end of first water flow path  21 . Valve  34  is provided on a middle part of first water flow path  21 . Examples of valve  34  include on-off valves and flow regulating valves. Outlet  12  of electrochemical cell  10  is connected with an upstream end of second water flow path  22 . A downstream end of second water flow path  22  forms a drain port. 
     First and second water flow paths  21  and  22  are connected via third water flow path  23 . Specifically, an upstream end of third water flow path  23  is connected with a middle part of second water flow path  22 , while a downstream end of third water flow path  23  is connected with a middle part of first water flow path  21 . 
     On a middle part of third water flow path  23 , first valve  41 , tank  31 , and pump  32  are disposed in this order. Examples of first valve  41  include on-off valves and flow regulating valves. Tank  31  stores water (hereinafter referred to as soft water) softened with electrochemical cell  10 . Pump  32  feeds soft water stored in tank  31  to inlet  11  via first water flow path  21 . Tank  31  is connected with an upstream end of fourth water flow path  24 . A downstream end of fourth water flow path  24  forms a water intake port. This configuration enables a user of water treatment apparatus  100  to be supplied with soft water stored in tank  31 . 
     Second water flow path  22  has flow adjustor  40  that is disposed on a part of second water flow path  22  downstream of a joint between second and third water flow paths  22  and  23  (a pipe section forming part of flow path  22 ). Flow adjustor  40  is any adjustor capable of regulating the flow rate of water passing through second water flow path  22 , and may be made up of a flow regulating valve. 
     Second water flow path  22  also has second valve  42  that is disposed on a section between the connecting end of third water flow path  23  and flow adjustor  40 . Examples of second valve  42  include on-off valves. The scope of the present disclosure should not be limited to the first exemplary embodiment in which flow adjustor  40  and second valve  42  are separately disposed. Flow adjustor  40  may also serve as second valve  42 . 
     Power supply  20  may be any power supply capable of supplying electric power to electrochemical cell  10 . For example, power supply  20  may be made up of a converter that converts an alternating-current (AC) voltage supplied from an AC power supply, i.e., electricity from utility power, to a direct-current (DC) voltage. Power supply  20  may be other DC power supplies such as a secondary cell. 
     Input device  60  is configured to set a voltage and/or an electric current, as well as a quantity of flow of water passing through second water flow path  22 . Input device  60  may be designed to input a concentration of any ions contained in water treated in each of a water softening process and a regeneration process. If flow adjustor  40  is a flow regulating valve, input device  60  may be configured to input an opening degree of the valve so as to regulate the flow rate of water passing through second water flow path  22 . Input device  60  may include a touchpad, a keyboard, and a remote controller. 
     Controller  50  controls power supply  20 , flow adjustor  40  and other components that constitute water treatment apparatus  100 . Controller  50  is made up of an arithmetic processor such as a microprocessor or a central processing unit (CPU), a storage unit including a memory that stores programs for executing various control operations, and a timepiece having a schedule function (all not illustrated). Controller  50  controls the operation of water treatment apparatus  100  by letting the arithmetic processor read any of predetermined control programs stored in the storage unit and execute the read programs. 
     Controller  50  may be made up of a group of controllers so that these controllers collaborate to control water treatment apparatus  100 , other than the single controller. Controller  50  may be a microcontroller, a microprocessor unit (MPU), a programmable logic controller (PLC), or a logic circuit, for example. 
     [Operation of Water Treatment Apparatus and Effects of the Same] 
     With reference to  FIG. 1 , the operation of water treatment apparatus  100  according to the first exemplary embodiment will now be described. A process for regenerating anion and cation exchange substrates  15 A and  15 B in electrochemical cell  10  is described below. 
     When an operator sets up water treatment apparatus  100 , a pH or an electric conductivity of water such as tap water (hereinafter referred to as raw water) that is to be fed to electrochemical cell  10  of water treatment apparatus  100  is measured. The operator gets the measured pH or the electric conductivity to be stored on the storage unit of controller  50  via input device  60 . 
     Controller  50  calculates set points from the input pH or the electric conductivity. The set points include a value of electric power (voltage and/or current) that is applied from power supply  20  to electrodes  14 A and  14 B of electrochemical cell  10  and a value of the flow rate of water that passes through second water flow path  22  when a regeneration process is executed, as well as a length of time for the regeneration process. Controller  50  stores the calculated set points on the storage unit. 
     Controller  50  may calculate set points for electric power so that the electric power is smaller during a predetermined length of time following the start of a regeneration process than after the elapse of the predetermined length of time. Controller  50  may calculate set points for the flow rate of water so that the water flow rate is smaller during a predetermined length of time following the start of a regeneration process than after the elapse of the predetermined length of time. 
     When the measured electric conductivity is low (e.g., 0.2 mS/cm or lower), controller  50  may calculate set points for the flow rate of water so that the water flow rate is higher during a predetermined length of time following the start of a regeneration process than after the elapse of the predetermined length of time. 
     When the process for regenerating anion and cation exchange substrates  15 A and  15 B is executed, controller  50  closes first valve  41  and opens second valve  42  before activating pump  32 . 
     Controller  50  closes valve  34  and lets the soft water supply unit feed soft water stored in tank  31  first water flow path  21  to inlet  11  through third water flow path  23 . This configuration can reduce the hardness and electric conductivity of water fed into electrochemical cell  10  via inlet  11 . 
     Third water flow path  23  may have an additional valve. In the case of a region where the hardness of raw water is low (a low measured electric conductivity), controller  50  closes the valve on third water flow path  23  to stop the supply of soft water stored in tank  31  upon and after the elapse of a predetermined length of time during a regeneration process, and opens valve  34  to feed raw water into electrochemical cell  10  and go on regeneration. This configuration as well prevents an increase in the concentration of calcium ions in waste water. 
     Controller  50  controls power supply  20  so that electric power with a predetermined value stored in the storage unit is applied to electrodes  14 A and  14 B of electrochemical cell  10  and controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches a predetermined flow rate stored in the storage unit. 
     This causes a potential difference across ion exchange membrane  15  and thereby causes dissociation of water at an interface between anion and cation exchange substrates  15 A and  15 B in ion exchange membrane  15 . The dissociation of the water generates hydrogen ions and hydroxide ions. 
     Hardness ions (cations) such as calcium and magnesium absorbed into cation exchange substrate  15 B are exchanged for the generated hydrogen ions and desorbed, and thus cation exchange substrate  15 B is regenerated. Anions such as chloride ions absorbed into anion exchange substrate  15 A are exchanged for the generated hydroxide ions and desorbed, and thus anion exchange substrate  15 A is regenerated. Water that has passed through electrochemical cell  10  is discharged to the drain port via outlet  12  and second water flow path  22 . 
     Water treatment apparatus  100  configured as described above according to the first exemplary embodiment can reduce the electric conductivity of water fed into electrochemical cell  10  via inlet  11  during a regeneration process by feeding soft water into electrochemical cell  10 . This configuration prevents desorption of calcium ions in large quantity and thus restrains scale formation at the time of start of the regeneration process. 
     Water treatment apparatus  100  according to the first exemplary embodiment can reduce the hardness of water fed into electrochemical cell  10  via inlet  11  during a regeneration process by feeding soft water into electrochemical cell  10 . This configuration can reduce the concentration of desorbed calcium ions and restrain scale formation. 
     Water treatment apparatus  100  according to the first exemplary embodiment may further include a water level detector disposed inside tank  31  and a valve provided on fourth water flow path  24 . In this configuration, controller  50  closes the valve provided on fourth water flow path  24  to prevent soft water from being drawn through the water intake port when controller  50  detects the level of water in tank  31  via the water level detector and determines that the water level has reached or fallen below a predetermined water level. This enables tank  31  to maintain the volume of soft water necessary to regenerate electrochemical cell  10 . 
     When a cumulative amount of soften raw water has reached a predetermined level, controller  50  may put the apparatus into a refresh mode so as to store a higher electric power or regeneration period set point for membrane regeneration than that specified for normal regeneration conditions on the storage unit and increase the quantity of calcium ions during a regeneration process. This configuration can enhance the regeneration of ion exchange membrane  15  and maintain the hardness of soft water. 
     First Modification Example 
     A modification example of water treatment apparatus  100  according to the first exemplary embodiment is described below. 
     A water treatment apparatus according to a first modification example of the first exemplary embodiment further includes a scale inhibitor supply unit that supplies a scale inhibitor to an inlet of an electrochemical cell when the regeneration process is executed. 
     With reference to  FIG. 2 , one example of the water treatment apparatus according to the first modification example of the first exemplary embodiment will now be described. 
       FIG. 2  is a schematic view illustrating a configuration of a water treatment apparatus according to the first modification example of the first exemplary embodiment. 
     With reference to  FIG. 2 , water treatment apparatus  100  of the first modification example shares a basic configuration with water treatment apparatus  100  according to the first exemplary embodiment, but differs in that water treatment apparatus  100  of the first modification example includes scale inhibitor supply unit  33  disposed downstream of tank  31  on third water flow path  23 . 
     Scale inhibitor supply unit  33  may be any inhibitor supply unit that can inhibit scale deposition or eliminate deposited scale. For example, a scale inhibitor may be disposed in a housing and be supplied to third water flow path  23 . A scale inhibitor may be disposed inside third water flow path  23 . 
     The scale inhibitor may be sodium polyphosphate or other polyphosphate, for example. Polyphosphate inhibits aggregation and crystal growth of CaCO3, and thus prevents CaCO3 from being deposited on membrane and other surfaces inside electrochemical cell  10 . 
     The scale inhibitor may be a chelating agent, acrylate, or carboxylate other than polyphosphate. Any of these substances produce the similar effects described above. The apparatus may have polyphosphate or a chelating agent as a solid built into the housing and dissolve the inhibitor in water before supplying the dissolved inhibitor to electrochemical cell  10 . A solution of polyphosphate, acrylate, carboxylate, or any other inhibitor stored in a chemical solution tank (not illustrated) may be diluted by a pump (not illustrated) and supplied to electrochemical cell  10 . 
     The scale inhibitor may be an acid. The acid eliminates scale even if scale is deposited inside electrochemical cell  10  and other locations, and thus prevents the sticking of scale. An acid scale inhibitor can not only eliminate deposited CaCO3 by decomposition and dissolution but also reduce the pH of waste water at the time of membrane regeneration. Thus, the acid inhibitor can prevent the deposition of CaCO3 resulting from formation of CaCO3. The acid scale inhibitor may be citric acid, sulfamic acid, or other weak acid. 
     Water treatment apparatus  100  configured as described above according to the first modification example produces effects similar to those produced by water treatment apparatus  100  according to the first exemplary embodiment. Water treatment apparatus  100  of the first modification example is provided with scale inhibitor supply unit  33  and thus prevents CaCO3 formed at the time of the regeneration process from being deposited on ion exchange membrane  15  and other surfaces in electrochemical cell  10 . 
     Water treatment apparatus  100  of the modification example includes scale inhibitor supply unit  33  disposed downstream of tank  31 . As a result, water treatment apparatus  100  can restrict supply of the scale inhibitor into electrochemical cell  10  when water softening process is executed and satisfactorily supply the scale inhibitor into electrochemical cell  10  when a regeneration process is executed. 
     If the scale inhibitor is citric acid or other acid, controller  50  may execute a cleaning mode as described below. Specifically, when a cumulative amount of soften raw water has reached a predetermined level, controller  50  executes the cleaning mode so as to supply a citric acid or other acid with a concentration higher than a concentration specified for normal regeneration conditions from a chemical solution tank to electrochemical cell  10 . 
     This configuration enables the elimination of CaCO3 deposited on ion exchange membrane  15  and prevents scale accumulation. 
     Second Exemplary Embodiment 
     A water treatment apparatus according to a second exemplary embodiment includes a plurality of electrochemical cells. One of the electrochemical cells is subject to a regeneration process, whereas the other electrochemical cell configures a soft water supply unit. 
     With reference to  FIG. 3 , one example of water treatment apparatus according to the second exemplary embodiment will now be described. 
     [Water Treatment Configuration] 
       FIG. 3  is a schematic view illustrating a configuration of a water treatment apparatus according to the second exemplary embodiment. 
     With reference to  FIG. 3 , water treatment apparatus  100  according to the second exemplary embodiment shares a basic configuration with water treatment apparatus  100  according to the first exemplary embodiment, but differs in that water treatment apparatus  100  of the second exemplary embodiment includes a plurality of electrochemical cells (two electrochemical cells  10 A,  10 B in this example), and one of the electrochemical cells (e.g. electrochemical cell  10 A) is subject to a regeneration process whereas the other electrochemical cell (e.g. electrochemical cell  10 B) constitutes a water softening device. 
     Specifically, inlet  11  of electrochemical cell  10 A is connected with a downstream end of first water flow path  21 . Outlet  12  of electrochemical cell  10 A is connected with an upstream end of second water flow path  22 . Flow adjustor  40  is provided on a middle part of second water flow path  22 . 
     Second water flow path  22  has second valve  42  that is disposed upstream of flow adjustor  40 . An upstream end of sixth water flow path  26  is connected with a part of second water flow path  22  upstream of second valve  42 . A downstream end of sixth water flow path  26  forms a water outlet. Third valve  43  is provided on a middle part of sixth water flow path  26 . Examples of third valve  43  include open-close valves and flow regulating valves. The scope of the present disclosure should not be limited to the second exemplary embodiment in which second valve  42  and third valve  43  are disposed. Second and third valves  42  and  43  may be replaced with a three-way valve disposed on a joint between second and sixth water flow paths  22  and  26 . 
     Apart of second water flow path  22  upstream of the joint between second and sixth water flow paths  22  and  26  is connected with an upstream end of seventh water flow path  27 . A downstream end of seventh water flow path  27  is connected with a middle part of fifth water flow path  25 . Fourth valve  44  is provided on a middle part of seventh water flow path  27 . Examples of fourth valve  44  include open-close valves and flow regulating valves. 
     A middle part of first water flow path  21  is connected with an upstream end of fifth water flow path  25 . A downstream end of fifth water flow path  25  is connected with inlet  11  of electrochemical cell  10 B. Valve  35  is provided on a middle part of fifth water flow path  25 . Examples of valve  35  include open-close valves and flow regulating valves. 
     Outlet  12  of electrochemical cell  10 B is connected with an upstream end of eighth water flow path  28 . A downstream end of eighth water flow path  28  is connected with a part of second water flow path  22  between second valve  42  and flow adjustor  40 . 
     Fifth valve  45  is provided on a middle part of eighth water flow path  28 . Examples of fifth valve  45  include open-close valves and flow regulating valves. A part of eighth water flow path  28  upstream of fifth valve  45  is connected with an upstream end of ninth water flow path  29 . A downstream end of ninth water flow path  29  is connected with a part of sixth water flow path  26  downstream of third valve  43 . Sixth valve  46  is provided on a middle part of ninth water flow path  29 . Examples of sixth valve  46  include open-close valves and flow regulating valves. The scope of the present disclosure should not be limited to the second exemplary embodiment in which fifth valve  45  and sixth valve  46  are disposed. Fifth and sixth valves  45  and  46  may be replaced with a three-way valve disposed on a joint between eighth and ninth water flow paths  28  and  29 . 
     A part of eighth water flow path  28  upstream of the joint between eighth and ninth water flow paths  28  and  29  is connected with an upstream end of tenth water flow path  30 . A downstream end of tenth water flow path  30  is connected with a part of first water flow path  21  downstream of a joint between first and fifth water flow paths  21  and  25 . Seventh valve  47  is provided on a middle part of tenth water flow path  30 . Examples of seventh valve  47  include open-close valves and flow regulating valves. 
     [Operation of Water Treatment Apparatus and Effects of the Same] 
     With reference to  FIG. 3 , the operation of water treatment apparatus  100  according to the second exemplary embodiment will now be described. A process for regenerating anion and cation exchange substrates  15 A and  15 B in electrochemical cell  10 A is described below. 
     In like manner with water treatment apparatus  100  according to the first exemplary embodiment, when an operator sets up water treatment apparatus  100  of the second exemplary embodiment, a pH or an electric conductivity of raw water that is to be fed to electrochemical cell  10  of water treatment apparatus  100  is measured. The operator gets the measured pH or the electric conductivity to be stored on a storage unit of controller  50  via input device  60 . 
     Controller  50  calculates set points from the input pH or the electric conductivity. The set points include a value of electric power (voltage and/or current) that is applied (supplied) from power supply  20  to electrodes  14 A and  14 B of electrochemical cells  10 A,  10 B and a value of the flow rate of water that passes through second water flow path  22  when a regeneration process is executed, as well as a length of time for the regeneration process. Controller  50  stores the calculated set points on the storage unit. 
     When the process for regenerating anion and cation exchange substrates  15 A and  15 B in electrochemical cell  10 A is executed, controller  50  opens second valve  42  and closes third and fourth valves  43  and  44 . This configuration allows water that has passed through electrochemical cell  10 A to flow through second water flow path  22  and be discharged out of a drain port. 
     Controller  50  closes fifth and sixth valves  45  and  46 , and opens seventh valve  47 . Then, controller  50  gets a voltage to be applied to electrochemical cells  10 A and  10 B, and raw water to be fed to electrochemical cells  10 A and  10 B. The voltage is applied so that electrode  14 A and electrode  14 B of electrochemical cell  10 A form an anode and a cathode, respectively, and electrode  14 A and electrode  14 B of electrochemical cell  10 B form a cathode and an anode, respectively. 
     Controller  50  controls power supply  20  so that electric power with a predetermined value stored in the storage unit is applied to the electrodes of electrochemical cell  10  and controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches a predetermined flow rate stored in the storage unit. 
     Consequently, hardness ions (cations) contained in the raw water that is fed into electrochemical cell  10 B are removed and absorbed into cation exchange substrate  15 B, while anions such as chloride ions contained in the raw water are removed and absorbed into anion exchange substrate  15 A. This processing softens the water (generation of soft water). 
     Soft water generated in electrochemical cell  10 B is fed to first water flow path  21  through outlet  12 , and eighth and tenth water flow paths  28  and  30 . Both the soft water fed to first water flow path  21  and raw water flowing through first water flow path  21  are fed to inlet  11  of electrochemical cell  10 A. This configuration can reduce the hardness and electric conductivity of water fed into electrochemical cell  10 A via inlet  11 . 
     The quantity of soft water passing through tenth water flow path  30  and the quantity of raw water passing through first water flow path  21  may be adjusted as appropriate by opening or closing at least one of seventh valve  47  and valve  35 . As a result, the hardness and electric conductivity of water fed into electrochemical cell  10  via inlet  11  may be adjusted. 
     In electrochemical cell  10 A, anion and cation exchange substrates  15 A and  15 B are regenerated. Water that has passed through electrochemical cell  10 A is discharged to the drain port via outlet  12  of electrochemical cell  10 A and second water flow path  22 . 
     Water treatment apparatus  100  configured as described above according to the second exemplary embodiment produces effects similar to those produced by water treatment apparatus  100  according to the first exemplary embodiment. 
     Water treatment apparatus  100  according to the second exemplary embodiment closes sixth valve  46  when the regeneration process is executed. However, the scope of the present disclosure should not be limited to this configuration. Sixth valve  46  may be opened to allow the intake of soft water, with proviso that the flow of the water is small. In this case, soft water can be taken from the apparatus even during a regeneration process. 
     Third Exemplary Embodiment 
     A water treatment apparatus according to a third exemplary embodiment includes a conductivity detector that detects an electric conductivity of water passing through a second water flow path. A controller controls electric power supplied from a power supply to electrodes and the flow rate of water passing through the second water flow path by use of a flow adjustor so that the electric conductivity detected by the conductivity detector is lower than a first threshold. 
     With reference to  FIGS. 4 and 5 , one example of a water treatment apparatus according to the third exemplary embodiment will now be described. 
     [Configuration of Water Treatment Apparatus] 
       FIG. 4  is a schematic view illustrating a configuration of the water treatment apparatus according to the third exemplary embodiment. 
     With reference to  FIG. 4 , the water treatment apparatus according to the third exemplary embodiment shares a basic configuration with water treatment apparatus  100  according to the first exemplary embodiment, but differs in that water treatment apparatus  100  of the third exemplary embodiment further includes conductivity detector  48 . Conductivity detector  48  is provided on a part of second water flow path  22  upstream of flow adjustor  40 . 
     Conductivity detector  48  may be any detector that can detect electric conductivity of water passing through second water flow path  22  and output the detected conductivity to controller  50 . For example, conductivity detector  48  may be a publicly-know conductivity detector, or a detector that detects the temperature of water passing through second water flow path  22  and corrects electric conductivity. 
     [Operation of Water Treatment Apparatus and Effects of the Same] 
     With reference to  FIGS. 4 and 5 , the operation of water treatment apparatus  100  according to the third exemplary embodiment will now be described. A process for regenerating anion and cation exchange substrates  15 A and  15 B in electrochemical cell  10  is described below. 
       FIG. 5  is a flowchart illustrating a procedure conducted by the water treatment apparatus according to the third exemplary embodiment. 
     With reference to  FIG. 5 , controller  50  starts a process for regenerating electrochemical cell  10 , and acquires an electric conductivity that is detected by conductivity detector  48  and sent from conductivity detector  48  (step S 101 ). In like manner with water treatment apparatus  100  according to the first exemplary embodiment, controller  50  in the present exemplary embodiment controls power supply  20  so that electric power with a predetermined value stored in a storage unit is applied to the electrodes of electrochemical cell  10  and controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches a predetermined flow rate stored in the storage unit. Controller  50  ends the regeneration process when the time elapsed from the start of the regeneration process has reached a predetermined regeneration time length stored in the storage unit. 
     Next, controller  50  determines whether the electric conductivity acquired in step S 101  is higher than or equal to a first threshold (step S 102 ). The first threshold is a value determined by experiment or testing in advance. The first threshold may be higher than or equal to an electric conductivity of water used for membrane regeneration plus 0.2 mS/cm from the viewpoint of efficient regeneration, or lower than or equal to 5.0 mS/cm from the viewpoint of restraint on scale formation in electrochemical cell  10  and other locations. 
     If the electric conductivity acquired in step S 101  is lower than the first threshold (No in step S 102 ), controller  50  goes back to step S 101  and repeats steps S 101  and S 102  until the electric conductivity acquired in step S 101  reaches the first threshold or higher. If the electric conductivity acquired in step S 101  is the first threshold or higher (Yes in step S 102 ), controller  50  goes to step S 103 . 
     In step S 103 , controller  50  regulates power supply  20 . Specifically, controller  50  controls power supply  20  so that the electric power (voltage and/or current) applied from power supply  20  to electrodes  14 A and  14 B of electrochemical cell  10  falls below a predetermined value stored in the storage unit and an operation period of power supply  20  is extended. 
     Next, controller  50  controls flow adjustor  40  (step S 104 ) and goes back to step S 101 . Specifically, controller  50  controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches or falls below a predetermined flow rate stored in the storage unit. 
     Water treatment apparatus  100  configured as described above according to the third exemplary embodiment produces effects similar to those produced by water treatment apparatus  100  according to the first exemplary embodiment. 
     In water treatment apparatus  100  according to the third exemplary embodiment, controller  50  controls power supply  20  and flow adjustor  40  during the process for regenerating electrochemical cell  10  so that the electric conductivity is lower than the first threshold. As a result, water treatment apparatus  100  in this exemplary embodiment can restrain scale formation in electrochemical cell  10  and other locations more satisfactorily than water treatment apparatus  100  according to the first exemplary embodiment can. This configuration facilitates reduction in the quantity of water discharged at the time of the regeneration process and enables the efficient regeneration. 
     Fourth Exemplary Embodiment 
     A water treatment apparatus according to a fourth exemplary embodiment further includes a pH detector that detects a pH of water passing through a second water flow path. A controller controls electric power supplied from a power supply to electrodes and the flow rate of water passing through the second water flow path by use of a flow adjustor so that the pH detected by the pH detector is lower than a second threshold. 
     With reference to  FIGS. 6 and 7 , one example of the water treatment apparatus according to the fourth exemplary embodiment will now be described. 
     [Configuration of Water Treatment Apparatus] 
       FIG. 6  is a schematic view illustrating a configuration of the water treatment apparatus according to the fourth exemplary embodiment. 
     With reference to  FIG. 6 , the water treatment apparatus according to the fourth exemplary embodiment shares a basic configuration with water treatment apparatus  100  according to the first exemplary embodiment, but differs in that water treatment apparatus  100  of the fourth exemplary embodiment further includes pH detector  49 . pH detector  49  is provided on a part of second water flow path  22  upstream of flow adjustor  40 . 
     pH detector  49  may be any detector that can detect the pH of water passing through second water flow path  22  and output the detected pH to controller  50 . For example, pH detector  49  may be a publicly-know pH detector. 
     [Operation of Water Treatment Apparatus and Effects of the Same] 
     With reference to  FIGS. 6 and 7 , the operation of water treatment apparatus  100  according to the fourth exemplary embodiment will now be described. The process for Regenerating anion and cation exchange substrates  15 A and  15 B in electrochemical cell  10  is described below. 
       FIG. 7  is a flowchart illustrating a procedure conducted by the water treatment apparatus according to the fourth exemplary embodiment. 
     With reference to  FIG. 7 , controller  50  starts a process for regenerating electrochemical cell  10 , and acquires a pH that is detected by pH detector  49  and sent from pH detector  49  (step S 201 ). In like manner with water treatment apparatus  100  according to the first exemplary embodiment, controller  50  in the present exemplary embodiment controls power supply  20  so that electric power with a predetermined value stored in a storage unit is applied to the electrodes of electrochemical cell  10  and controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches a predetermined flow rate stored in the storage unit. Controller  50  ends the regeneration process when the time elapsed from the start of the regeneration process has reached a predetermined regeneration time length stored in the storage unit. 
     Next, controller  50  determines whether the pH acquired in step S 201  is higher than or equal to a second threshold (step S 202 ). The second threshold is a value determined by experiment or testing in advance. The second threshold may be higher than a pH of water used for membrane regeneration from the viewpoint of an efficient regeneration process, or lower than or equal to 12 from the viewpoint of restraint on scale formation in electrochemical cell  10  and other locations, for example. 
     If the pH acquired in step S 201  is lower than the second threshold (No in step S 202 ), controller  50  goes back to step S 201  and repeats steps S 201  and S 202  until the pH acquired in step S 201  reaches the second threshold or higher. If the pH acquired in step S 201  is the second threshold or higher (Yes in step S 202 ), controller  50  goes to step S 203 . 
     In step S 203 , controller  50  regulates power supply  20 . Specifically, controller  50  controls power supply  20  so that the electric power (voltage and/or current) applied from power supply  20  to electrodes  14 A and  14 B of electrochemical cell  10  falls below a predetermined value stored in the storage unit and an operation period of power supply  20  is extended. 
     Next, controller  50  controls flow adjustor  40  (step S 204 ) and goes back to step S 201 . Specifically, controller  50  controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches or falls below a predetermined flow rate stored in the storage unit. 
     Water treatment apparatus  100  configured as described above according to the fourth exemplary embodiment produces effects similar to those produced by water treatment apparatus  100  according to the first exemplary embodiment. 
     In water treatment apparatus  100  according to the fourth exemplary embodiment, controller  50  controls power supply  20  and flow adjustor  40  during the process for regenerating electrochemical cell  10  so that the pH is lower than the second threshold. As a result, water treatment apparatus  100  in this exemplary embodiment can restrain scale formation in electrochemical cell  10  and other locations more satisfactorily than water treatment apparatus  100  according to the first exemplary embodiment can. This configuration facilitates reduction in the quantity of water discharged at the time of the regeneration process and enables the efficient regeneration. 
     Fifth Exemplary Embodiment 
     In a water treatment apparatus according to a fifth exemplary embodiment, a controller controls a soft water supply unit so that soft water supply unit feeds soft water to an inlet when a regeneration process is executed. The controller also controls a power supply to supply electric power rated below a third threshold to electrodes and controls a flow adjustor so that the flow rate of water passing through a second water flow path is lower than a fourth threshold when a regeneration process is executed. Thereafter, the controller controls the power supply so that supply electric power rated at the third threshold or higher is supplied to the electrodes and controls the flow adjustor so that the flow rate of water passing through the second water flow path is the fourth threshold or higher. 
     With reference to  FIG. 8 , one example of water treatment apparatus according to the fifth exemplary embodiment will now be described. Since the water treatment apparatus according to the fifth exemplary embodiment has a configuration identical to that of the water treatment apparatus according to the first exemplary embodiment, detailed description thereof is omitted. A process for regenerating anion and cation exchange substrates  15 A and  15 B in electrochemical cell  10  is described below. 
     [Operation of Water Treatment Apparatus] 
       FIG. 8  is a flowchart illustrating a procedure executed by the water treatment apparatus according to the fifth exemplary embodiment. The apparatus executes the procedure described below by letting an arithmetic processor of controller  50  execute a program stored in a storage unit. 
     With reference to  FIG. 8 , controller  50  closes first valve  41  and opens second valve  42  (step S 301 ). Then, controller  50  activates pump  32  (step S 302 ). As a result, soft water stored in tank  31  is fed to first water flow path  21  through third water flow path  23 . Both the soft water fed to first water flow path  21  and raw water flowing through first water flow path  21  are fed to inlet  11 . 
     Next, controller  50  controls power supply  20  and flow adjustor  40  (step S 303 ). Specifically, controller  50  controls power supply  20  so that the electric power (voltage and/or current) applied from power supply  20  to electrodes  14 A and  14 B of electrochemical cell  10  falls below a third threshold stored in the storage unit. The third threshold is a value determined by experiment or testing in advance. The third threshold may be a current ranging from 0.1 A to 40 A inclusive specified from the viewpoint of restraint on desorption of calcium ions in large quantity and prevention of the occurrence of an overcurrent. 
     Controller  50  controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  falls below a fourth threshold stored in the storage unit. The fourth threshold is a value determined by experiment or testing in advance, and may range from 0.5 L/min to 30 L/min inclusive specified from the viewpoint of restraint on desorption of calcium ions in large quantity and prevention of the occurrence of an overcurrent. 
     Controller  50  measures a length of time that has elapsed from the start of step S 303  for controlling power supply  20  and flow adjustor  40  (step S 304 ). Controller  50  determines whether the time elapsed from the start of step S 303  is equal to or longer than a first predetermined period (step S 305 ). The first predetermined period is a value determined by experiment or testing in advance. The first predetermined period may range from 1 min to 60 min inclusive from the viewpoint of restraint on scale formation in electrochemical cell  10  and other locations, or range from 2 min to 20 min inclusive from the viewpoint of an efficient regeneration process. 
     If the time elapsed from the start of step S 303  is not equal to or longer than the first predetermined period (No in step S 305 ), controller  50  repeats steps S 304  and S 305  until the time elapsed from the start of step S 303  reaches or exceeds the first predetermined period. If the time elapsed from the start of step S 303  is equal to or longer than the first predetermined period (Yes in step S 305 ), controller  50  goes to step S 306 . 
     In step S 306 , controller  50  controls power supply  20  so that the electric power (voltage and/or current) applied from power supply  20  to electrodes  14 A and  14 B of electrochemical cell  10  reaches or exceeds the third threshold. Controller  50  controls flow adjustor  40  so that the flow rate of water passing through second water flow path  22  reaches or exceeds the fourth threshold. 
     When the apparatus includes a conductivity detector that detects the electric conductivity of water passing through second water flow path  22 , controller  50  may, in response to a low electric conductivity detected by the conductivity detector, control flow adjustor  40  so that the flow rate of water passing through second water flow path  22  is equal to or falls below the fourth threshold. 
     Controller  50  measures a length of time that has elapsed from the start of step S 306  for controlling power supply  20  and flow adjustor  40  (step S 307 ). Controller  50  determines whether the time elapsed from the start of step S 306  is equal to or longer than a second predetermined period (step S 308 ). The second predetermined period is a value determined by experiment or testing in advance. The second predetermined period may range from 1 min to 60 min inclusive from the viewpoint of satisfactory regeneration of the ion exchange membrane in electrochemical cell  10 , or range from 2 min to 20 min inclusive from the viewpoint of an efficient regeneration process. 
     If the time elapsed from the start of step S 306  is not equal to or longer than the second predetermined period (No in step S 308 ), controller  50  repeats steps S 307  and S 308  until the time elapsed from the start of step S 306  reaches or exceeds the second predetermined period. If the time elapsed from the start of step S 306  is equal to or longer than the second predetermined period (Yes in step S 308 ), controller  50  terminates the program (the regeneration process). After that, controller  50  may start water softening or interrupt the supply of electric power to electrodes  14 A and  14 B of electrochemical cell  10  to deactivate the water treatment apparatus. 
     [Effects of Water Treatment Apparatus] 
     With reference to  FIGS. 8 and 9 , effects produced by the water treatment apparatus according to the fifth exemplary embodiment will now be described. 
       FIG. 9  is a graph illustrating a relationship between the elapsed time of a regeneration process and a concentration of calcium ions contained in water discharged from the second water flow path when the regeneration process has been executed by the water treatment apparatus according to the fifth exemplary embodiment. 
     With reference to  FIG. 9 , a dot-and-dash line represents an instance in which raw water alone is fed to electrochemical cell  10 , electric power rated at the third threshold or higher is applied from power supply  20  to electrodes  14 A and  14 B, and the flow rate of water passing through second water flow path  22  is the fourth threshold or higher throughout a regeneration process. In this instance, calcium ions absorbed into anion exchange substrate  15 A are emitted into the raw water after start of the regeneration process. Thus, calcium ions contained in water discharged from the second water flow path had a concentration greater than or equal to a degree that causes scale deposition and might result in the deposition of scale in electrochemical cell  10  and other locations. 
     Meanwhile, a dashed line in  FIG. 9  represents an instance in which raw water alone is fed to electrochemical cell  10  while the electric power supplied from power supply  20  is rated below the third threshold and the water flow rate is lower than the fourth threshold during the first predetermined period following start of a regeneration process, and the electric power supplied from power supply  20  is rated at the third threshold or higher and the water flow rate is the fourth threshold or higher after the first predetermined period. In this instance, calcium ions absorbed into anion exchange substrate  15 A are emitted at a restrained level after start of the regeneration process. Thus, calcium ions contained in water discharged from the second water flow path have a concentration lower than the degree that causes scale deposition. This inhibited scale deposition. 
     A solid line in  FIG. 9  represents an instance shown by water treatment apparatus  100  according to the fifth exemplary embodiment, in which the procedure involves feeding both raw water and soft water to electrochemical cell  10  while supplying electric power rated below the third threshold from power supply  20  and regulating the water flow rate to below the fourth threshold during the first predetermined period following start of a regeneration process and supplying electric power rated at the third threshold or higher from power supply  20  and regulating the water flow rate to the fourth threshold or higher after the first predetermined period. In this instance, hardness and conductivity can be lower for water fed to electrochemical cell  10  than for raw water. Thus, this procedure enables the concentration of calcium ions contained in water discharged from the second water flow path to be lower than the concentration in the instance (the dashed line in  FIG. 9 ) in which raw water alone is fed. 
     Consequently, water treatment apparatus  100  according to the fifth exemplary embodiment can restrain scale formation in electrochemical cell  10  and other locations more satisfactorily than water treatment apparatus  100  according to the first exemplary embodiment. 
     In view of the foregoing description, numerous modifications and alternative exemplary embodiments of the disclosure will be apparent to those skilled in the art. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the disclosure. Details of the structure and/or the function may be varied substantially without departing from the spirit of the disclosure. Moreover, other aspects of the present disclosure can be achieved by appropriately combining constituents that are disclosed in the exemplary embodiments described above. 
     INDUSTRIAL APPLICABILITY 
     A water treatment apparatus of the present disclosure can reduce the hardness and electric conductivity of water fed into an electrochemical cell during regeneration of an ion exchange membrane. As a result, the apparatus can restrain scale formation and thus be useful for water treatment applications. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
         
           
               10 : electrochemical cell 
               10 A: electrochemical cell 
               10 B: electrochemical cell 
               11 : inlet 
               12 : outlet 
               13 : casing 
               14 A: electrode 
               14 B: electrode 
               15 : ion exchange membrane 
               15 A: anion exchange substrate 
               15 B: cation exchange substrate 
               20 : power supply 
               21 : first water flow path 
               22 : second water flow path 
               23 : third water flow path 
               24 : fourth water flow path 
               25 : fifth water flow path 
               26 : sixth water flow path 
               27 : seventh water flow path 
               28 : eighth water flow path 
               29 : ninth water flow path 
               30 : tenth water flow path 
               31 : tank 
               32 : pump 
               33 : scale inhibitor supply unit 
               40 : flow adjustor 
               41 : first valve 
               42 : second valve 
               43 : third valve 
               44 : fourth valve 
               45 : fifth valve 
               46 : sixth valve 
               47 : seventh valve 
               48 : conductivity detector 
               49 : pH detector 
               50 : controller 
               60 : input device 
               100 : water treatment apparatus