JP6040856B2 - Water treatment system - Google Patents

Description

  The present invention relates to a water treatment system including a reverse osmosis membrane module that separates supplied water into permeated water and concentrated water.

  In the semiconductor manufacturing process, the cleaning of electronic parts and medical instruments, etc., high-purity pure water containing no impurities is used. In this type of application, it is generally manufactured by subjecting supply water (raw water) such as groundwater or tap water to membrane separation treatment with a reverse osmosis membrane module (hereinafter also referred to as “RO membrane module”) as a membrane separation device. The permeated water is used as pure water.

  In conventional pure water production, in order to increase the removal rate of dissolved salts, a so-called multi-stage RO membrane system is proposed in which the permeated water produced by the former RO membrane module is supplied to the latter RO membrane module and desalted. (See Patent Document 1). Moreover, in order to keep the flow rate of the permeated water produced by the RO membrane module constant, a water treatment system that performs flow rate feedback water volume control has been proposed. In this flow rate feedback water amount control, the operating pressure of the pump that sends the supply water to the RO membrane module is controlled so that the flow rate of the permeated water produced by the RO membrane module becomes a preset target value (Patent Literature). 2).

Japanese Patent Laid-Open No. 11-128923 JP 2005-296945 A

  In general, it is known that the RO membrane module has higher permeated water quality as the operating pressure is higher (the flow rate of permeated water is higher). On the other hand, the higher the operating pressure of the RO membrane module, the higher the operating pressure of the pump that feeds the supply water to the RO membrane module, thus increasing the power consumption of the pump.

  In the multi-stage RO membrane system described above, if the quality of the permeated water produced by the subsequent RO membrane module is excessively good, high-quality permeated water is produced even if the operating pressure of the latter RO membrane module is lowered. be able to. Therefore, when the quality of the permeated water produced by the downstream RO membrane module is excessively good, the operating pressure of the pump that sends the feed water to the upstream RO membrane module (hereinafter also referred to as “first pump”) is set. The power consumption of the first pump can be suppressed by lowering.

  However, if the operating pressure of the first pump is lowered, it becomes impossible to maintain the flow rate and quality of the permeated water sent to the subsequent RO membrane module. Therefore, in the conventional multi-stage RO membrane system, even when the quality of the permeated water produced by the subsequent RO membrane module is excessively good, the operating pressure of the first pump is controlled to be a preset target value, It has been difficult to suppress power consumption.

  Therefore, the present invention provides water that can suppress the power consumption of the first pump while maintaining the amount and quality of the permeated water when the quality of the permeated water produced by the subsequent RO membrane module is excessively good. An object is to provide a processing system.

  The present invention provides a supply water tank that stores supply water, a first reverse osmosis membrane module that separates supply water into first permeated water and first concentrated water, and supply water stored in the supply water tank. A supply water line that can be delivered to the first reverse osmosis membrane module, and a first pump that is driven at a rotational speed corresponding to the input first drive frequency and discharges the supply water toward the first reverse osmosis membrane module A first inverter that outputs a first drive frequency corresponding to the input command signal to the first pump, and a second reverse osmosis membrane module that separates the first permeate into second permeate and second concentrated water A first permeate line capable of sending the first permeate separated by the first reverse osmosis membrane module to the second reverse osmosis membrane module, and a part of the feed water stored in the feed water tank. Supply water auxiliary that can be sent to the first permeate line And a second pump that is driven at a rotational speed corresponding to the input second driving frequency and discharges the first permeated water toward the second reverse osmosis membrane module, and a second pump corresponding to the input command signal. A second inverter that outputs two drive frequencies to the second pump, a water quality detecting means for detecting the quality of the first permeated water or the second permeated water, and a first flow rate detecting means for detecting the flow rate of the first permeated water; The second flow rate detecting means for detecting the flow rate of the second permeated water, and the first detected flow rate value of the first flow rate detecting means by the feedback control algorithm so that the first detected flow rate value becomes a preset first target flow rate value. A first driving frequency of one pump is calculated, a command signal corresponding to the calculated value of the first driving frequency is output to the first inverter, a preset reference water quality value and a detected water quality value of the water quality detecting means The difference with A first control unit for decreasing the first target flow rate value and a second target flow rate value in which a second detected flow rate value of the second flow rate detection means is preset. A second control unit that calculates a second drive frequency of the second pump by a feedback control algorithm and outputs a command signal corresponding to the calculated value of the second drive frequency to the second inverter; And when the first control unit decreases the first target flow rate value, the supply water is defined as a shortage of the first permeate supplied to the second pump via the first permeate line. The present invention relates to a water treatment system in which supply water is supplied from a tank to the first permeate water line through the supply water auxiliary line.

  Further, in the first control unit, when the first target flow rate value is not decreased, the first permeate is sent to the first permeate line mainly by the discharge force of the first pump, and the first When the target flow rate value is decreased, the first permeate is sent to the first permeate line mainly by the discharge force of the first pump, and the supply water assist is made by the suction force of the second pump. It is preferable that the supply water is sent to the first permeate water line through the line.

  Further, the first control unit sets the first target flow rate value in advance when the difference between the detected water quality value of the water quality detecting means and the preset reference water quality value exceeds a preset specified value. It is preferable to decrease at a set rate.

  A purification unit that purifies the second permeate to produce purified water; and a second permeate line that is capable of delivering the second permeate produced by the second reverse osmosis membrane module to the purification unit. It is preferable to provide a configuration.

  The purification unit preferably includes an electrodeionization stack or an ion exchange resin bed.

  Moreover, the 1st concentrated water line which sends out the 1st concentrated water from the said 1st reverse osmosis membrane module, and the 1st concentrated water which discharges a part of 1st concentrated water which distribute | circulates the said 1st concentrated water line out of a system. A discharge line, a first concentrated water reflux line for refluxing a remaining portion of the first concentrated water flowing through the first concentrated water line upstream of the first pump in the supply water line, and the first concentrated water reflux A first concentrated water recirculation valve capable of adjusting a flow rate of the first concentrated water flowing through the line, a second concentrated water line for sending the second concentrated water from the second reverse osmosis membrane module, and the second concentrated water line. A second concentrated water discharge line for discharging a part of the second concentrated water flowing through the system and a remaining portion of the second concentrated water flowing through the second concentrated water line from the first pump in the supply water line. The second concentrated water to be refluxed upstream The flow line, it is preferable to have a structure in which and a second concentrated water recirculation valve adjustable flow rate of the second concentrated water flowing through the second concentrated water return line.

  According to the present invention, when the quality of the permeated water produced by the subsequent RO membrane module is excessively good, the water that can suppress the power consumption of the first pump while maintaining the amount and quality of the permeated water. A processing system can be provided.

1 is an overall configuration diagram of a water treatment system 1 according to an embodiment. 4 is a flowchart showing a processing procedure when a first target flow rate value is set in the first control unit 11. 4 is a flowchart showing a processing procedure when the flow rate feedback water amount control of the first RO membrane module 5 is executed in the first control unit 11. 7 is a flowchart showing a processing procedure when the flow rate feedback water amount control of the second RO membrane module 8 is executed in the second controller 12.

  Hereinafter, the water treatment system 1 which concerns on embodiment of this invention is demonstrated, referring drawings. The water treatment system 1 according to the present embodiment is applied to, for example, a pure water production system that produces pure water from fresh water.

  FIG. 1 is an overall configuration diagram of a water treatment system 1 according to the present embodiment. FIG. 2 is a flowchart showing a processing procedure when the first control unit 11 sets the first target flow rate value. FIG. 3 is a flowchart showing a processing procedure when the first control unit 11 executes the flow rate feedback water amount control of the first RO membrane module 5. FIG. 4 is a flowchart showing a processing procedure when the flow rate feedback water amount control of the second RO membrane module 8 is executed in the second control unit 12.

  As shown in FIG. 1, the water treatment system 1 according to this embodiment includes a supply water tank 2, a first pump 3, a first inverter 4, and a first RO membrane module 5 as a first reverse osmosis membrane module. The second pump 6, the second inverter 7, the second RO membrane module 8 as the second reverse osmosis membrane module, the decarboxylation device 9, the electrodeionization stack 10 as the purification unit, and the first controller 11 And a second control unit 12.

  The water treatment system 1 includes a first flow rate sensor 13 as a first flow rate detection unit, a second flow rate sensor 14 as a second flow rate detection unit, an electrical conductivity sensor 15 as a water quality detection unit, and a first A drain valve 21 to a third drain valve 23, a first concentrated water reflux valve 24, a check valve 25, a fourth drain valve 26 to a sixth drain valve 28, and a second concentrated water reflux valve 29 are provided. .

  Further, the water treatment system 1 includes a supply water supply line L1, a supply water line L2, a first permeate water line L3, a feed water auxiliary line L4, a second permeate water line L5, and a desalted water line L6. Is provided. Further, the water treatment system 1 includes a first concentrated water line L7, a first concentrated water discharge line L8, a first concentrated water recirculation line L9, a first drainage line L10 to a third drainage line L12, and a second concentration. A water line L13, a second concentrated water discharge line L14, a second concentrated water reflux line L15, a fourth drainage line L16 to a sixth drainage line L18, and a third concentrated water line L19 are provided.

  The “line” in the present specification is a general term for lines capable of flowing a fluid such as a flow path, a path, and a pipeline. In the following description, the first RO membrane module 5 and the second RO membrane module 8 are abbreviated as “RO membrane module” as appropriate.

  The supply water tank 2 is a tank that stores the supply water W1. The supply water supply line L1 is a line for supplying supply water W1 to the supply water tank 2. The upstream end of the supply water supply line L1 is connected to a supply source (not shown) of the supply water W1. Further, the downstream end of the supply water supply line L <b> 1 is opened toward the supply water W <b> 1 stored in the supply water tank 2. As the supply water W1, ground water, tap water, or the like is used.

  The supply water line L <b> 2 is a line capable of sending the supply water W <b> 1 stored in the supply water tank 2 to the first RO membrane module 5. The upstream end of the feed water line L2 is connected to a feed water outlet (not shown) in the feed water tank 2. The downstream end of the supply water line L <b> 2 is connected to the primary inlet port of the first RO membrane module 5.

  The first pump 3 is a device that sucks in the supply water W1 (including the first concentrated water W3 that has been refluxed) and discharges it toward the first RO membrane module 5. The first pump 3 is provided between the supply water tank 2 (connection portion J1) and the first RO membrane module 5 in the supply water line L2. The first pump 3 is electrically connected to a first inverter 4 (described later). The first pump 3 is supplied with driving power whose frequency is converted from the first inverter 4. The first pump 3 is driven at a rotational speed corresponding to the frequency of drive power supplied from the first inverter 4 (hereinafter also referred to as “first drive frequency”).

  The first inverter 4 is an electric circuit that supplies driving power whose frequency is converted to the first pump 3. The first inverter 4 is electrically connected to a first control unit 11 (described later). A current value signal is input to the first inverter 4 from the first control unit 11. The first inverter 4 outputs drive power having a first drive frequency corresponding to the input current value signal to the first pump 3.

  The first RO membrane module 5 performs a membrane separation process on the supply water W1 sent from the first pump 3 into a first permeate W2 from which dissolved salts have been removed and a first concentrated water W3 from which dissolved salts have been concentrated. Equipment. The first RO membrane module 5 includes a single or a plurality of RO membrane elements (not shown). The first RO membrane module 5 performs membrane separation treatment on the supply water W1 with these RO membrane elements to produce the first permeated water W2 and the first concentrated water W3.

  The upstream end of the first concentrated water line L7 is connected to the primary outlet port of the first RO membrane module 5. The first concentrated water line L7 is a line for sending the first concentrated water W3 out of the first RO membrane module 5. The downstream side of the first concentrated water line L7 branches into a first concentrated water discharge line L8 and a first concentrated water reflux line L9 at a branch portion J7.

  The first concentrated water discharge line L8 is a line for discharging a part of the first concentrated water W3 flowing through the first concentrated water line L7 to the outside of the system. The downstream side of the first concentrated water discharge line L8 branches to the first drainage line L10, the second drainage line L11, and the third drainage line L12 at the connection portions J8 and J9.

  A first drain valve 21 is provided in the first drain line L10. A second drain valve 22 is provided in the second drain line L11. A third drain valve 23 is provided in the third drain line L12.

  The first drain valve 21 to the third drain valve 23 are valves that adjust the drain flow rate of the first concentrated water W3 sent from the first concentrated water line L7. The first drain valve 21 can open and close the first drain line L10. The second drain valve 22 can open and close the second drain line L11. The third drain valve 23 can open and close the third drain line L12.

  Each of the first drain valve 21 to the third drain valve 23 includes a constant flow valve mechanism (not shown). The constant flow valve mechanisms are set to different flow values in the first drain valve 21 to the third drain valve 23, respectively. For example, the drainage flow rate of the first drain valve 21 is set so that the recovery rate of the first RO membrane module 5 is 80% in the open state. The drainage flow rate of the second drain valve 22 is set so that the recovery rate of the first RO membrane module 5 is 75% in the open state. The drainage flow rate of the third drain valve 23 is set so that the recovery rate of the first RO membrane module 5 is 70% in the open state.

  The drainage flow rate of the first concentrated water W3 discharged from the first concentrated water discharge line L8 can be adjusted stepwise by selectively opening and closing the first drain valve 21 to the third drain valve 23. For example, only the second drain valve 22 is opened, and the first drain valve 21 and the third drain valve 23 are closed. In this case, the recovery rate of the first RO membrane module 5 can be 75%. Further, only the third drain valve 23 is opened, and the first drain valve 21 and the second drain valve 22 are closed. In this case, the recovery rate of the first RO membrane module 5 can be set to 70%. Therefore, in this embodiment, the drainage flow rate of the first concentrated water W3 is set such that the recovery rate of the first RO membrane module 5 is 50% to 80% by selectively opening and closing the first drainage valve 21 to the third drainage valve 23. Can be adjusted in steps of every 5%.

  The first drain valve 21 to the third drain valve 23 are electrically connected to the first control unit 11, respectively. The opening / closing of the first drain valve 21 to the third drain valve 23 is controlled by a drive signal from the first control unit 11.

  The first concentrated water reflux line L9 is a line that recirculates a part of the first concentrated water W3 flowing through the first concentrated water line L7 to the upstream side of the first pump 3 in the supply water line L2. The upstream end of the first concentrated water reflux line L9 is connected to the first concentrated water line L7 at the branch portion J7. The branch part J7 is disposed between the primary side outlet port of the first RO membrane module 5 and the connection part J8. The downstream end of the first concentrated water recirculation line L9 is connected to the supply water line L2 at the connection J1. The connection portion J1 is disposed between the supply water tank 2 and the first pump 3.

  A first concentrated water reflux valve 24 is provided in the first concentrated water reflux line L9. The first concentrated water reflux valve 24 is a device that adjusts the flow rate of the first concentrated water reflux line L9. The first concentrated water recirculation valve 24 is electrically connected to the first control unit 11. The opening degree of the first concentrated water recirculation valve 24 is controlled by a drive signal from the first control unit 11.

  The supply water auxiliary line L4 is a line capable of sending a part of the supply water W1 stored in the supply water tank 2 to the first permeate water line L3. When the first target flow rate value (described later) of the first permeate water W2 is decreased in the first control unit 11 described later, the first control unit 11 stores the first permeate water W2 in the supply water tank 2 to compensate for the shortage. A part of the supplied water W1 is sent to the first permeated water line L3. The upstream end of the supply water auxiliary line L4 is connected to the supply water tank 2. The downstream end of the feed water auxiliary line L4 is connected to the first permeated water line L3 at the connection portion J3. The connection part J3 is arrange | positioned between the connection part J2 and the connection part J4. A check valve 25 is provided in the supply water auxiliary line L4. The check valve 25 is a valve for preventing the supply water W1 from flowing backward from the connection portion J3 side to the supply water tank 2 in the supply water auxiliary line L4.

  The first permeated water line L3 is a line that can send the first permeated water W2 manufactured by the first RO membrane module 5 to the second RO membrane module 8. The upstream end of the first permeate line L <b> 3 is connected to the secondary port of the first RO membrane module 5. The downstream end of the first permeate line L <b> 3 is connected to the primary inlet port of the second RO membrane module 8.

  The first flow rate sensor 13 is a device that detects the flow rate of the first permeate water W2 flowing through the first permeate line L3. The first flow rate sensor 13 is connected to the first permeate line L3 at the connection portion J2. The connection portion J2 is disposed between the first RO membrane module 5 and the second pump 6 (connection portion J3). The first flow sensor 13 is electrically connected to the first control unit 11. The flow rate of the first permeated water W2 detected by the first flow rate sensor 13 (hereinafter also referred to as “first detected flow rate value”) is transmitted to the first control unit 11 as a detection signal.

  The second pump 6 is a device that sucks the first permeated water W <b> 2 and discharges it toward the second RO membrane module 8. The second pump 6 is provided between the first RO membrane module 5 (connection portion J4) and the second RO membrane module 8 in the first permeate line L3. The second pump 6 is electrically connected to a second inverter 7 (described later). The second pump 6 is supplied with driving power having a frequency converted from the second inverter 7. The second pump 6 is driven at a rotational speed corresponding to the frequency of drive power supplied from the second inverter 7 (hereinafter also referred to as “second drive frequency”).

  The second inverter 7 is an electric circuit that supplies driving power whose frequency is converted to the second pump 6. The second inverter 7 is electrically connected to a second control unit 12 (described later). A current value signal is input to the second inverter 7 from the second control unit 12. The second inverter 7 outputs drive power having a second drive frequency corresponding to the input current value signal to the second pump 6.

  The second RO membrane module 8 separates the first permeate W2 sent from the second pump 6 into a second permeate W4 from which dissolved salts have been removed and a second concentrated water W5 from which dissolved salts have been concentrated. It is equipment to process. The second RO membrane module 8 includes a single or a plurality of RO membrane elements (not shown). The second RO membrane module 8 membrane-separates the first permeated water W2 with these RO membrane elements to produce the second permeated water W4 and the second concentrated water W5.

  The upstream end of the second concentrated water line L13 is connected to the primary outlet port of the second RO membrane module 8. The second concentrated water line L13 is a line for sending the second concentrated water W5 out of the second RO membrane module 8. The downstream side of the second concentrated water line L13 branches into a second concentrated water discharge line L14 and a second concentrated water reflux line L15 at a branching portion J10.

  The second concentrated water discharge line L14 is a line for discharging a part of the second concentrated water W5 flowing through the second concentrated water line L13 to the outside of the system. The downstream side of the second concentrated water discharge line L14 branches to a fourth drain line L16, a fifth drain line L17, and a sixth drain line L18 at the connecting portions J11 and J12.

  A fourth drain valve 26 is provided in the fourth drain line L16. A fifth drain valve 27 is provided in the fifth drain line L17. A sixth drain valve 28 is provided in the sixth drain line L18.

  The fourth drain valve 26 to the sixth drain valve 28 are valves that adjust the drainage flow rate of the second concentrated water W5 discharged from the second concentrated water discharge line L14. The fourth drain valve 26 can open and close the fourth drain line L16. The fifth drain valve 27 can open and close the fifth drain line L17. The sixth drain valve 28 can open and close the sixth drain line L18.

  The fourth drain valve 26 to the sixth drain valve 28 are each electrically connected to the second control unit 12. The opening / closing of the valves in the fourth drain valve 26 to the sixth drain valve 28 is controlled by a drive signal from the second control unit 12. In addition, since the structure and function of the 4th drain valve 26-the 6th drain valve 28 are substantially the same as the 1st drain valve 21-the 3rd drain valve 23 demonstrated previously, description regarding adjustment of a waste_water | drain flow rate is demonstrated. Omitted.

  The second concentrated water recirculation line L15 is a line that recirculates a part of the second concentrated water W5 flowing through the second concentrated water line L13 to the upstream side of the second pump 6 in the first permeated water line L3. . The upstream end of the second concentrated water recirculation line L15 is connected to the second concentrated water line L13 at the branch portion J10. The branch part J10 is disposed between the primary side outlet port of the second RO membrane module 8 and the connection part J11. The downstream end of the second concentrated water recirculation line L15 is connected to the first permeate line L3 at the connection J4. The connection part J4 is disposed between the connection part J3 and the second pump 6.

  A second concentrated water reflux valve 29 is provided in the second concentrated water reflux line L15. The second concentrated water reflux valve 29 is a device that adjusts the flow rate of the second concentrated water reflux line L15. The second concentrated water recirculation valve 29 is electrically connected to the second control unit 12. The opening degree of the second concentrated water recirculation valve 29 is controlled by a drive signal from the second control unit 12.

  The second permeated water line L <b> 5 is a line capable of sending the second permeated water W <b> 4 manufactured by the second RO membrane module 8 to the electrodeionization stack 10. The upstream end of the second permeate line L5 is connected to the secondary port of the second RO membrane module 8. The downstream end of the second permeate line L5 is connected to the primary port of the electrodeionization stack 10.

  The second flow rate sensor 14 is a device that detects the flow rate of the second permeated water W4 that flows through the second permeated water line L5. The second flow rate sensor 14 is connected to the second permeated water line L5 at the connection portion J5. The connection part J5 is arrange | positioned between the 2nd RO membrane module 8 and the decarboxylation apparatus 9 (connection part J6). The second flow rate sensor 14 is electrically connected to the second control unit 12. The flow rate of the second permeated water W4 detected by the second flow rate sensor 14 (hereinafter also referred to as “second detected flow rate value”) is transmitted to the second control unit 12 as a detection signal.

  The electrical conductivity sensor 15 is a device that measures the electrical conductivity of the second permeated water W4 flowing through the second permeated water line L5. The electrical conductivity sensor 15 is connected to the second permeated water line L5 at the connection portion J6. The connection part J6 is arrange | positioned between the 2nd RO membrane module 8 (connection part J5) and the decarboxylation apparatus 9 in the 2nd permeated water line L5. The electrical conductivity sensor 15 is electrically connected to the first control unit 11. The electrical conductivity of the second permeated water W4 measured by the electrical conductivity sensor 15 (hereinafter also referred to as “detected EC value”) is transmitted to the first control unit 11 as a detection signal.

  The decarboxylation device 9 degasses free carbonic acid (dissolved carbon dioxide gas) contained in the second permeated water W4 by the gas separation membrane module, and the second permeated water W4 as degassed water (degassed permeated water) is obtained. Is a facility to get. The decarboxylation device 9 is provided between the second RO membrane module 8 (connection portion J6) and the electrodeionization stack 10 (described later) in the second permeated water line L5. In the present embodiment, the decarboxylation device 9 is provided as an optional device.

  The electrodeionization stack 10 demineralizes (deionizes) the second permeated water W4 (degassed water) separated by the decarboxylation device 9, and demineralized water W6 (deionized water) and the third concentrated water. It is a water treatment apparatus which manufactures W7. The electrodeionization stack 10 is electrically connected to a DC power supply device (not shown). A direct current voltage is applied to the electrodeionization stack 10 from a direct current power supply device as electric power for the desalination treatment. The electrodeionization stack 10 is energized by a DC voltage applied from a DC power supply device and operates.

  A demineralized water line L <b> 6 is connected to the demineralized water outlet side port of the electric deionized stack 10. The demineralized water line L6 is a line for sending demineralized water W6 obtained by the electrodeionization stack 10 as pure water toward a demand point. In addition, a third concentrated water line L19 is connected to the concentrated water outlet side port of the electrodeionization stack 10. The third concentrated water line L19 is a line for delivering the third concentrated water W7 obtained in the electrodeionization stack 10 to the outside of the electrodeionization stack 10. The third concentrated water W7 may be discharged out of the system or returned to the supply water tank 2.

  The first control unit 11 controls the flow rate, the recovery rate, and the like of the first permeated water W <b> 2 manufactured in the first RO membrane module 5. The first control unit 11 is configured by a microprocessor (not shown) including a CPU and a memory.

  The microprocessor constituting the first control unit 11 incorporates an integrated timer unit (hereinafter also referred to as “ITU”) for managing time keeping and the like. Further, in addition to various programs necessary for controlling the first RO membrane module 5, a first target flow rate value, a reference EC value, a specified value (described later), and the like are stored in the memory of the microprocessor.

The first control unit 11, as a flow feedback water volume control for the first 1RO membrane module 5, the first target flow rate value first detected flow value detected by the first flow rate sensor 13 (Q _p1) is set in advance (Q _p1 ′), The first drive frequency for driving the first pump 3 is calculated by the speed type digital PID algorithm, and a current value signal (command signal) corresponding to the calculated value of the first drive frequency is calculated. Output to the first inverter 4. The flow rate feedback water amount control by the first control unit 11 will be described later.

  Moreover, the 1st control part 11 sets a 1st target flow value as follows based on the detection EC value (detection water quality value) of the electrical conductivity sensor 15, and the preset reference EC value.

  The first control unit 11 sets the first target flow rate value to 100% (100% flow rate) when the detected EC value ≧ reference EC value. When the detected EC value ≧ reference EC value, the water quality of the second permeated water W4 is not good. Therefore, the first control unit 11 sets the first target flow rate value to 100% flow rate in order to improve water quality.

  The first target flow rate value (100% flow rate) is, for example, the total flow rate value of the second permeated water W4 and the second concentrated water W5 manufactured by the second RO membrane module 8. The reference EC value is desirably set lower than the allowable EC value required at the decarboxylation device 9, the electrodeionization stack 10, or the demand point provided on the downstream side of the second RO membrane module 8. Thereby, the water quality of the 2nd permeated water W4 can always be maintained above an allowable EC value.

  Further, the first control unit 11 calculates a difference between the reference EC value and the detected EC value when the detected EC value <the reference EC value. Then, the first control unit 11 decreases the first target flow rate value when the calculated difference value exceeds a preset specified value (for example, 1 μS / cm). That is, when the detected EC value <the reference EC value, if the difference value between the reference EC value and the detected EC value exceeds the specified value, the water quality of the second permeated water W4 is excessively good. The first control unit 11 sets the first target flow rate value lower than the 100% flow rate. In the present embodiment, the first control unit 11 decreases the first target flow rate value at a preset rate (for example, by 5% for 100% flow rate).

  Note that when the first target flow rate value (100% flow rate) is decreased, an insufficient amount of water of the first permeate W2 supplied to the second pump 6 via the first permeate line L3 is generated. The shortage of the first permeated water W2 is replenished by supplying a part of the feed water W1 stored in the feed water tank 2 to the first permeate water line L3 through the feed water auxiliary line L4.

  Specifically, in the first control unit 11, when the first target flow rate value is not decreased (100% flow rate), the first permeate water is mainly fed to the first permeate line L3 by the discharge force of the first pump 3. W2 is sent out. On the other hand, in the first control unit 11, when the first target flow rate value is decreased, the first permeate W2 is sent to the first permeate line L3 mainly by the discharge force of the first pump 3, The supply water W1 as a shortage of the first permeate water W2 is sent to the first permeate water line L3 via the supply water auxiliary line L4 by the suction force of the second pump 6.

  When the water quality of the second permeated water W4 is excessively good, the operating pressure of the first pump 3 can be reduced (the operating pressure of the first RO membrane module 5 can be reduced) by reducing the first target flow rate value. . Thus, the power consumption of the first pump 3 can be suppressed by lowering the hand pressure of the first pump 3. Further, when the first target flow rate value is decreased, the shortage of the first permeate water W2 is obtained by mixing the supply water W1 with the first permeate water W2 within a range in which the water quality of the second permeate water W4 can be maintained. Can be replenished. In addition, when the water quality of the 2nd permeated water W4 is excessively good, the ratio which decreases the 1st target flow rate value can maintain the water quality of the 2nd permeated water W4 even if the feed water W1 is mixed with the 1st permeated water W2. Is set as follows.

  Further, when the detected EC value <the reference EC value, the first control unit 11 maintains the first target flow rate value at the current value when the difference value is less than the specified value. When the detected EC value is smaller than the reference EC value, if the difference value is less than the specified value, the second permeated water W4 is in a state of maintaining the acceptable water quality. Therefore, the first control unit 11 maintains the current value without changing the first target flow rate value. In addition, the control which reduces the 1st target flow value value in the 1st control part 11 is mentioned later.

  The second control unit 12 controls the flow rate, the recovery rate, and the like of the second permeated water W4 manufactured in the second RO membrane module 8. The second control unit 12 is configured by a microprocessor (not shown) including a CPU and a memory. The microprocessor constituting the second control unit 12 incorporates an ITU for managing time keeping and the like. In the second control unit 12, in addition to various programs necessary for controlling the second RO membrane module 8, data related to a second target flow rate value (described later) is stored in the memory of the microprocessor.

The second control unit 12, as a flow feedback water volume control for the first 2RO membrane module 8, the second target flow rate value by the second detected flow value detected by the second flow rate sensor 14 (Q _p2) is set in advance (Q _p2 ′), The second drive frequency for driving the second pump 6 is calculated by the speed type digital PID algorithm, and a current value signal (command signal) corresponding to the calculated value of the second drive frequency is calculated. Output to the second inverter 7. The flow rate feedback water amount control by the second control unit 12 will be described later.

Next, operation | movement of the water treatment system 1 which concerns on this embodiment is demonstrated.
First, a processing procedure when the first control unit 11 sets the first target flow value will be described with reference to FIG. The process of the flowchart shown in FIG. 2 is repeatedly performed every predetermined time (10 minutes) during the operation of the water treatment system 1.

  In step ST101 shown in FIG. 2, the first control unit 11 determines whether or not the time t measured by the ITU has reached 10 min (minutes). In step ST101, when the first control unit 11 determines that the time t measured by the ITU has reached 10 min (YES), the process proceeds to step ST102. In Step ST101, when the first control unit 11 determines that the time measured by the ITU has not reached 10 min (NO), the process returns to Step ST101.

  Note that the time t (10 min) in step ST101 is counted as the time (standby time) necessary for the water quality of the second permeated water W4 to become stable after changing the first target flow rate value.

  In step ST102 (step ST101: YES), the first control unit 11 acquires the detected EC value of the second permeated water W4 detected by the electrical conductivity sensor 15 and the reference EC value stored in the memory of the microprocessor. To do.

  In step ST103, the first control unit 11 determines whether or not the detected EC value ≧ the reference EC value is satisfied. In step ST103, when the first control unit 11 determines that the detected EC value ≧ the reference EC value (YES), the process proceeds to step ST104. If the first control unit 11 determines in step ST103 that the detected EC value is smaller than the reference EC value (NO), the process proceeds to step ST105.

  In step ST104 (step ST103: YES), the first control unit 11 sets the first target flow rate value to 100% flow rate. The first target flow rate value set by the first control unit 11 is stored in the memory of the microprocessor. When the detected EC value ≧ the reference EC value, since the water quality of the second permeated water W4 is not good, the first target flow value is set to 100% flow rate in order to improve the water quality. When the first target flow rate value is set to 100% flow rate in step ST104, the process of this flowchart ends (returns to step ST101).

  On the other hand, in step ST105 (step ST103: NO), the first control unit 11 determines whether or not the reference EC value−the detected EC value (difference value)> 1 μS / cm (specified value). In step ST105, when the first control unit 11 determines that the reference EC value−detected EC value> 1 μS / cm (YES), the process proceeds to step ST106.

  Also, in step ST105, when the first control unit 11 determines that the reference EC value−the detected EC value ≦ 1 μS / cm (NO), the processing of this flowchart ends (returns to step ST101). . If the first control unit 11 determines that reference EC value−detected EC value ≦ 1 μS / cm (NO), the first target flow rate value is not changed and the current value is maintained.

  In step ST106 (step ST105: YES), the first control unit 11 decreases the first target flow rate value by 5% (5 points) from the current value, and sets the value as the first target flow rate value. For example, if the current value of the first target flow rate value is 100% flow rate, the 95% flow rate is set as the first target flow rate value. Further, if the current value of the first target flow rate value is 95% flow rate, 90% flow rate is set as the first target flow rate value. When the first target flow value is set in step ST106, the process of this flowchart ends (returns to step ST101).

  Next, the flow rate feedback water amount control of the first RO membrane module 5 executed in the first control unit 11 will be described with reference to FIG. The process of the flowchart shown in FIG. 3 is repeatedly executed during operation of the water treatment system 1.

In step ST201 shown in FIG. 3, the first control unit 11 acquires a first target flow rate value Q _p1 ′ of the first permeated water W2. The first target flow rate value Q _p1 ′ is a current value set (or maintained without change) in step ST104 or step ST106 in the flowchart shown in FIG.

In step ST 202, the first control unit 11 determines whether the time count _{t 1} by ITU reaches 100ms which is a control period (Delta] t). In this step ST 202, the first control unit 11, when the timing _{t 1} by ITU is determined to have reached 100 ms (YES), the process proceeds to step ST 203. Further, in step ST 202, the first control unit 11, when the timing _{t 1} by ITU is determined not to reach the 100 ms (NO), the process returns to the step ST 202.

Step ST 203: In (step ST 202 YES determination), the first control unit 11, a first detected flow value _{Q p1} of the first permeate W2 detected by the first flow rate sensor 13, and acquires as a feedback value.

In step ST 204, the first control unit 11 includes a first detected flow value _{Q p1} acquired in step ST 203, so that the deviation between the first target flow rate value _{Q p1} 'acquired in step ST201 becomes zero, velocity type calculating a manipulated variable _{U n} by digital PID algorithm. In the velocity type digital PID algorithm, the control period Delta] t (100 ms) calculates a variation .DELTA.U _n of the manipulated variables for each, which operate at the present time by adding the operation amount U _n-1 of the previous control cycle time The quantity _Un is determined.

An arithmetic expression used for the velocity type digital PID algorithm is expressed by the following expressions (1a) and (1b).
_{ΔU n = K p {(e} n -e n-1) + (Δt / T i) × e n + (T d / Δt) × (e n -2e n-1 + e n-2)} (1a)
U _n = U _n-1 + ΔU _n (1b)

In Expression (1a) and Expression (1b), Δt: control period, U _n : current operation amount, U _n-1 : operation amount at the previous control period, ΔU _n : change in operation amount from the previous time to this time. Minute, e _n : magnitude of current deviation, e _n-1 : magnitude of deviation at the previous control cycle, e _n-2 : magnitude of deviation at the previous control cycle, K _p : proportional gain, T _i : integration time, T _d : differentiation time. The size e _n of the current deviation is obtained by the following formula (2).
e _n = Q _p1 ′ −Q _p1 (2)

In step ST205, the first control unit 11 uses the amount of operation of the current _{U n,} the maximum driving frequency F'the first target flow rate value _{Q p1} 'and the first pump 3 (the set value of 50Hz or 60 Hz), The first drive frequency F ₁ for driving the first pump 3 is calculated by a predetermined calculation formula.

In step ST 206, the first control unit 11, a first calculation value of the drive frequency _{F 1,} it is converted into a corresponding current value signal (4 to 20 mA), and outputs the current value signal to the first inverter 4. Thereby, the process of this flowchart is complete | finished (it returns to step ST201).

  In step ST206, when the first control unit 11 outputs the current value signal to the first inverter 4, the first inverter 4 uses the drive power converted to the frequency specified by the input current value signal as the first. Supply to pump 3. As a result, the first pump 3 is driven at a rotational speed corresponding to the drive frequency input from the first inverter 4.

  Next, the flow rate feedback water amount control of the second RO membrane module 8 executed in the second control unit 12 will be described with reference to FIG. The process of the flowchart shown in FIG. 4 is repeatedly executed during operation of the water treatment system 1.

In step ST301 shown in FIG. 4, the second control unit 12 acquires a second target flow rate value Q _p2 ′ of the second permeated water W4. The second target flow rate value Q _p2 ′ is, for example, a set value that is stored in the memory of the microprocessor by the system administrator via a user interface (not shown).

In step ST 302, the second control unit 12 determines whether the time count _{t 2} by ITU reaches 100ms which is a control period (Delta] t). In this step ST 302, the second control unit 12, when the timing _{t 2} by ITU is determined to have reached 100 ms (YES), the process proceeds to step ST 303. Further, in step ST 302, the second control unit 12, when the timing _{t 2} by ITU is determined not to reach the 100 ms (NO), the process returns to the step ST 302.

Step ST 303: In (step ST 302 YES determination), the second control unit 12, the second detected flow value _{Q p2} of the second permeate W4 detected by the second flow sensor 14 is acquired as a feedback value.

In step ST 304, the second control unit 12, a second detected flow value _{Q p2} obtained in step ST 303, so that the deviation between the second target flow rate value _{Q p2} 'acquired in step ST301 becomes zero, velocity type calculating a manipulated variable _{U n} by digital PID algorithm. In the velocity type digital PID algorithm, the control period Delta] t (100 ms) calculates a variation .DELTA.U _n of the manipulated variables for each, which operate at the present time by adding the operation amount U _n-1 of the previous control cycle time The quantity _Un is determined. The arithmetic expression used for the velocity type digital PID algorithm is as described above.

In step ST305, the second control unit 12 uses the current operation amount U _n , the second target flow rate value Q _p2 ′, and the maximum drive frequency F ′ (set value of 50 Hz or 60 Hz) of the second pump 6, the predetermined arithmetic expression, calculates a second driving frequency F ₂ for driving the second pump 6.

In step ST 306, the second control unit 12, a second calculation value of the drive frequency _{F 2,} and converted into a corresponding current value signal (4 to 20 mA), and outputs the current value signal to the second inverter 7. Thereby, the process of this flowchart is complete | finished (it returns to step ST301).

  In step ST306, when the second control unit 12 outputs a current value signal to the second inverter 7, the second inverter 7 converts the drive power converted to the frequency specified by the input current value signal to the second value. Supply to pump 6. As a result, the second pump 6 is driven at a rotational speed corresponding to the drive frequency input from the second inverter 7.

  According to the water treatment system 1 which concerns on embodiment mentioned above, the following effects are show | played, for example.

  In the water treatment system 1 according to the present embodiment, the first control unit 11 sets in advance a difference between a preset reference EC value and a detected EC value of the second permeated water W4 detected by the electrical conductivity sensor 15. When exceeding the specified value, the first target flow rate value of the first RO membrane module 5 is decreased. Further, the shortage of the first permeated water W2 due to the decrease in the first target flow rate value is that a part of the feed water W1 stored in the feed water tank 2 is supplied to the first permeate water line L3 through the feed water auxiliary line L4. To replenish.

  Therefore, when the difference between the reference EC value and the detected EC value exceeds the specified value, the discharge flow rate of the first pump 3 can be reduced by reducing the first target flow rate value. Can be suppressed. When the difference between the reference EC value and the detected EC value exceeds the specified value, the water quality of the second permeated water W4 is in an excessively good state, so the supply water W1 is insufficient as the first permeated water W2. Even if it supplements, the water quality of the 2nd permeated water W4 can be maintained. Furthermore, by replenishing the supply water W1 as a shortage of the first permeate water W2, the amount of the first permeate water W2 to be sent to the second RO membrane module 8 at the subsequent stage can be maintained.

  Therefore, according to the water treatment system 1 according to the present embodiment, when the water quality of the second permeated water W4 manufactured by the second RO membrane module 8 is excessively good, the flow rate and water quality of the first permeated water W2 are maintained. However, the power consumption of the first pump can be suppressed.

  Further, in the water treatment system 1 according to the present embodiment, when the first target flow rate value is not decreased, the first permeate water W2 is sent to the first permeate line L3 mainly by the discharge force of the first pump 3. When the first target flow rate value is decreased, the first permeate water W2 is sent to the first permeate line L3 mainly by the discharge force of the first pump 3, and the suction force of the second pump 6 is used. Via the supply water auxiliary line L4, the supply water W1 as a shortage of the first permeate water W2 is sent to the first permeate water line. This eliminates the need for a dedicated pump or the like for supplying the supply water W1 from the supply water auxiliary line L4 to the first permeate water line L3, so that the configuration of the water treatment system 1 can be simplified.

  Moreover, in the water treatment system 1 which concerns on this embodiment, when the 1st control part 11 reduces the 1st target flow value of the 1st RO membrane module 5, it reduces a 1st target flow value by the preset ratio. Let According to this, since the first target flow rate value does not extremely decrease at one control timing, even if the second permeated water W4 is temporarily in a state where the water quality of the second permeated water W4 is excessively good, Variations in water quality can be suppressed.

  In addition, the water treatment system 1 according to the present embodiment is a purification unit that produces the desalted water W6 and the third concentrated water W7 by desalting the second permeated water W4 after the second RO membrane module 8. The electrodeionization stack 10 is provided. Therefore, demineralized water W6 as pure water with high purity can be sent out to the demand point.

  Moreover, the water treatment system 1 which concerns on this embodiment deaerates the free carbonic acid contained in the 2nd permeated water W4 by the gas separation membrane module between the 2nd RO membrane module 8 and the electrodeionization stack 10. A decarboxylation device 9 for obtaining second permeated water W4 as deaerated water is provided. According to this, since the free carbonic acid that easily permeates the RO membrane can be removed from the second permeated water W4 in the decarboxylation device 9, the second permeated water W4 with higher purity can be obtained.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and can be implemented in various forms.

  For example, in the present embodiment, the water treatment system 1 in which the electrodeionization stack 10 as a purification unit is provided in the subsequent stage of the second RO membrane module 8 has been described. Not limited to this, instead of the electrodeionization stack 10, a non-regenerative mixed bed ion exchange tower may be provided as a purification unit. In this case, the deionized water can be obtained by deionizing the second permeated water W4 produced by the second RO membrane module 8 using the ion exchange resin bed. Further, immediately after the operation of the water treatment system 1 is started, deionized water whose water quality has been recovered can be supplied to the demand point. Further, by using the mixed bed type ion exchange tower, the power required for the treatment for obtaining deionized water from the second permeated water W4 can be made substantially zero.

  Further, in the present embodiment, when the detected EC value <the reference EC value, the first target flow rate value is set when the difference value between the reference EC value and the detected EC value exceeds a preset specified value. An example in which the rate is decreased at a rate of 5% (a constant value) has been described. Not limited to this, the ratio at which the first target flow rate value is decreased may be changed according to the magnitude of the difference between the reference EC value and the detected EC value exceeding a preset specified value.

  Moreover, in this embodiment, the water treatment system 1 which provided the decarboxylation apparatus 9 and the electrodeionization stack 10 in the back | latter stage of the 1st RO membrane module 5 and the 2nd RO membrane module 8 was demonstrated. Not only this but the water treatment system 1 may be comprised only with the 1st RO membrane module 5 and the 2nd RO membrane module 8. FIG. Moreover, the water treatment system which provided the electrodeionization stack 10 or the said mixed bed type ion exchange tower, without providing the decarboxylation apparatus 9 as an optional apparatus in the back | latter stage of the 1st RO membrane module 5 and the 2nd RO membrane module 8. It may be 1.

  Moreover, in this embodiment, the structure which provided the electrical conductivity sensor 15 as a water quality detection means of the 2nd permeated water W4 was demonstrated. It is good also as a structure which provided not only this but the silica concentration meter, the hardness meter, the total organic carbon meter etc. as a water quality detection means of the 2nd permeated water W4. Further, the target for detecting the water quality is not limited to the second permeated water W4, but may be the first permeated water W2 flowing through the first permeated water line L3.

  In the present embodiment, an example of calculating the drive frequency of the pump (the first pump 3 and the second pump 6) by the speed type digital PID algorithm in the control units (the first control unit 11 and the second control unit 12) will be described. did. The feedback control algorithm in the control unit is not limited to this, and may be, for example, a position type digital PID algorithm.

  Moreover, in this embodiment, the example which adjusts the waste_water | drain flow volume of the 1st concentrated water W3 in steps by selecting the open | release number of the 1st drain valve 21-the 3rd drain valve 23, for example was demonstrated. For example, the first concentrated water discharge line L8 may be provided with a proportional control valve without branching the first concentrated water discharge line L8. In this case, the drain flow rate of the first concentrated water W3 can be adjusted by transmitting a current value signal from the first control unit 11 to the proportional control valve to control the valve opening. The same applies to the second concentrated water discharge line L14 connected to the fourth drain valve 26 to the sixth drain valve 28.

  Moreover, in the structure which provided the proportional control valve in the 1st concentrated water discharge line L8, it is good also as a structure which provided the flow sensor in the 1st concentrated water discharge line L8. In this case, the actual drainage flow rate of the first concentrated water W3 can be more accurately controlled by inputting the flow rate value measured by the flow rate sensor to the first control unit 11 as a feedback value.

  The change of the said structure is applicable also to the 2nd concentrated water discharge line L14 connected to the 4th drain valve 26-the 6th drain valve 28. FIG.

Further, in the present embodiment, the timing _{(t, t 1, t 2} ) The time by ITU, without being limited to the examples of FIGS. 2 to 4 can be set appropriately. Further, the specified value (1 μS / cm) in step ST105 in FIG. 2 and the amount of decrease (5%) in the first target flow rate value in step ST106 are not limited to the example of the present embodiment, and are set appropriately. Is possible.

  Further, in the present embodiment, the supply water W1 is not limited to groundwater or tap water, but is water pretreated by, for example, a iron removal manganese removal device, a sand filtration device, a microfiltration membrane device, an ultrafiltration membrane device, or the like. There may be.

DESCRIPTION OF SYMBOLS 1 Water treatment system 2 Supply water tank 3 1st pump 4 1st inverter 5 1st RO membrane module (1st reverse osmosis membrane module)
6 Second pump 7 Second inverter 8 Second RO membrane module (second reverse osmosis membrane module)
DESCRIPTION OF SYMBOLS 9 Decarbonation apparatus 10 Electrodeionization stack 11 1st control part 12 2nd control part 13 1st flow sensor (1st flow detection means)
14 Second flow rate sensor (second flow rate detection means)
15 Electrical conductivity sensor (water quality detection means)
24 1st concentrated water recirculation valve 29 2nd concentrated water recirculation valve L3 1st permeated water line L4 Supply water auxiliary line L5 2nd permeated water line L7 1st concentrated water line L8 1st concentrated water discharge line L9 1st concentrated water reflux Line L13 Second concentrated water line L14 Second concentrated water discharge line L15 Second concentrated water reflux line

Claims (6)

A supply water tank for storing supply water;
A first reverse osmosis membrane module that separates supply water into first permeate and first concentrated water;
A supply water line capable of sending the supply water stored in the supply water tank to the first reverse osmosis membrane module;
A first pump that is driven at a rotational speed corresponding to the input first driving frequency and discharges the supplied water toward the first reverse osmosis membrane module;
A first inverter that outputs a first drive frequency corresponding to an input command signal to the first pump;
A second reverse osmosis membrane module for separating the first permeate into the second permeate and the second concentrated water;
A first permeate line capable of delivering the first permeate separated by the first reverse osmosis membrane module to the second reverse osmosis membrane module;
A feed water auxiliary line capable of sending a part of the feed water stored in the feed water tank to the first permeate water line;
A second pump that is driven at a rotational speed according to the input second driving frequency and discharges the first permeated water toward the second reverse osmosis membrane module;
A second inverter that outputs a second drive frequency corresponding to the input command signal to the second pump;
Water quality detecting means for detecting the quality of the first permeated water or the second permeated water;
First flow rate detection means for detecting the flow rate of the first permeate,
Second flow rate detection means for detecting the flow rate of the second permeated water;
The first drive frequency of the first pump is calculated by a feedback control algorithm so that the first detected flow rate value of the first flow rate detection means becomes a preset first target flow rate value, and the first drive frequency When the command signal corresponding to the calculated value is output to the first inverter, and the difference between the preset reference water quality value and the detected water quality value of the water quality detection means exceeds the preset specified value, A first control unit for decreasing the first target flow rate value;
The second drive frequency of the second pump is calculated by a feedback control algorithm so that the second detected flow rate value of the second flow rate detection means becomes a preset second target flow rate value, and the second drive frequency of the second drive frequency is calculated. A second control unit that outputs a command signal corresponding to the calculated value to the second inverter;
With
When the first control unit decreases the first target flow rate value, the shortage of the first permeate supplied to the second pump via the first permeate line is determined from the supply water tank. Supply water is supplied to the first permeate water line through the supply water auxiliary line.
Water treatment system. In the first control unit, when the first target flow rate value is not decreased, the first permeate is sent to the first permeate line mainly by the discharge force of the first pump, and the first target flow rate When the value is decreased, the first permeate is sent to the first permeate line mainly by the discharge force of the first pump, and the supply water auxiliary line is turned by the suction force of the second pump. Supply water is sent to the first permeate line through
The water treatment system according to claim 1. The first control unit is configured to preset the first target flow rate value when a difference between a detected water quality value of the water quality detection means and a preset reference water quality value exceeds a preset specified value. Decrease at a certain rate,
The water treatment system according to claim 1 or 2. A purification unit for purifying the second permeate to produce purified water;
A second permeate line capable of delivering the second permeate produced by the second reverse osmosis membrane module to the purification unit;
Comprising
The water treatment system as described in any one of Claims 1-3. The purification unit comprises an electrodeionization stack or an ion exchange resin bed,
The water treatment system according to claim 4. A first concentrated water line for delivering first concentrated water from the first reverse osmosis membrane module;
A first concentrated water discharge line for discharging a part of the first concentrated water flowing through the first concentrated water line to the outside of the system;
A first concentrated water recirculation line that recirculates the remainder of the first concentrated water flowing through the first concentrated water line upstream of the first pump in the supply water line;
A first concentrated water reflux valve capable of adjusting a flow rate of the first concentrated water flowing through the first concentrated water reflux line;
A second concentrated water line for delivering second concentrated water from the second reverse osmosis membrane module;
A second concentrated water discharge line for discharging a part of the second concentrated water flowing through the second concentrated water line to the outside of the system;
A second concentrated water reflux line for refluxing the remaining portion of the second concentrated water flowing through the second concentrated water line to the upstream side of the first pump in the supply water line;
A second concentrated water reflux valve capable of adjusting a flow rate of the second concentrated water flowing through the second concentrated water reflux line,
The water treatment system according to any one of claims 1 to 5.

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