Water treatment system equipped with an electro-deionized water production device and its operating method

Abstract

In a water treatment system including an EDI (Electronized Deionization Intake) device, the goal is to increase the water recovery rate in the EDI device and to obtain treated water with stable quality even when water quality fluctuates significantly. [Solution] The water treatment system includes a circulation pipe 36 that circulates treated water (deionized water) from the EDI device 10 to the upstream of the EDI device 10, a water supply pipe 35 that delivers the treated water to the use point, a flow rate adjustment unit 34 that distributes the treated water to the circulation pipe 36 and the water supply pipe 35, a circulation pipe 44 that circulates concentrated water from the EDI device 10 to the upstream of the EDI device 10, a discharge pipe 43 that discharges the concentrated water outside the system, a flow rate adjustment unit 42 that distributes the concentrated water to the circulation pipe 44 and the discharge pipe 43, and water quality monitoring devices 51 to 54 that monitor the water quality within the water treatment system from the EDI device 10. Based on the monitoring results from at least one of the water quality monitoring devices 51 to 54, at least one of the flow rate adjustment units 34 and 42 is controlled.

Description

Technical Field

[0001] The present invention relates to a water treatment system including an electric deionized water production apparatus and an operation method thereof.

Background Art

[0002] As a deionized water production apparatus capable of performing regeneration treatment of an ion exchanger while performing desalination treatment on treated water, there is an electric deionized water production apparatus that generates deionized water from treated water by combining electrophoresis and electrodialysis. The electric deionized water production apparatus is called an EDI (Electrodeionization) apparatus, and includes a desalination chamber and concentration chambers disposed on both sides of the desalination chamber via ion exchange membranes between an anode and a cathode. The ion exchange membrane partitioning the concentration chamber disposed on the anode side as viewed from the desalination chamber and the desalination chamber is an anion exchange membrane, and the ion exchange membrane partitioning the concentration chamber disposed on the cathode side as viewed from the desalination chamber and the desalination chamber is a cation exchange membrane.A desalination chamber is filled with an ion exchanger such as an ion exchange resin. It is preferable to fill the inside of the concentration chamber with an ion exchanger as well. In practice, in the EDI apparatus, the desalination chambers and the concentration chambers are often alternately arranged in the direction from the anode to the cathode between the anode and the cathode. The anode and the cathode may be respectively disposed inside the concentration chambers located at both ends when the desalination chambers and the concentration chambers are alternately arranged, or may be respectively disposed inside the anode chamber and the cathode chamber partitioned from the concentration chambers at both ends via ion exchange membranes. The anode chamber and the cathode chamber are collectively referred to as an electrode chamber. When providing an electrode chamber, it is preferable to fill the inside of the electrode chamber with an ion exchanger as well.

[0003] In the EDI apparatus, when the treated water is passed through the desalination chamber with a direct current applied between the anode and the cathode, the ion components in the treated water are adsorbed by the ion exchanger, and at the same time, hydrogen ions (H + ) and hydroxide ions (OH -The ion exchanger is regenerated by the following process. Water is also supplied to the concentration chamber. As a result, deionized water is discharged from the desalination chamber as treated water. Anions released from the ion exchanger during the regeneration of the ion exchanger in the desalination chamber move to the concentration chamber located on the anode side as viewed from the desalination chamber via the anion exchange membrane and are discharged from that concentration chamber. Similarly, cations released from the ion exchanger move to the concentration chamber located on the cathode side as viewed from the desalination chamber via the cation exchange membrane and are discharged from that concentration chamber. Therefore, water with concentrated ionic impurities, i.e., concentrated water, is discharged from the concentration chamber. The EDI system has the advantage of being able to continuously perform desalination on the water to be treated without the need for a chemical regeneration process of the ion exchange resin. The EDI system is used, for example, in semiconductor equipment manufacturing plants that require large amounts of pure water or ultrapure water.

[0004] When operating an EDI (Electronic Data Interchange) system, concentrated water with a high concentration of ionic impurities was traditionally discharged outside the EDI system. However, in recent years, from the perspective of water resource conservation, there has been a demand to reduce the amount of concentrated water discharged and improve the water recovery rate in the EDI system. The water recovery rate of an EDI system is the sum of the amount of deionized water obtained from the EDI system and supplied to use points, etc., and the amount of water recovered from the EDI system for reuse, divided by the amount of water supplied to the EDI system. In an EDI system, frequent operation and shutdown are undesirable, and large fluctuations in the amount of deionized water discharged are also undesirable. Therefore, some concentrated water is returned to the upstream stage of the EDI system, or surplus deionized water is returned to the upstream stage of the EDI system when the demand for deionized water is low. For example, Patent Document 1 discloses a water treatment system configured such that permeate water from a first reverse osmosis membrane device is supplied to an EDI device, in which concentrated water from the EDI device is mixed with concentrated water from the first reverse osmosis membrane device and supplied to a second reverse osmosis membrane device, and the permeate water from the second reverse osmosis membrane device is returned to the inlet of the first reverse osmosis membrane device to improve the water recovery rate in the EDI device. Furthermore, Patent Document 1 also discloses that in a water treatment system, the concentrated water from the EDI device may be returned to the inlet of the first reverse osmosis membrane without providing a second reverse osmosis membrane device.

[0005] In water treatment systems equipped with EDI devices, it has also been proposed to monitor flow rate and water quality to adjust the flow rate of concentrated water and control the applied current value. For example, Patent Document 2 discloses that in a primary pure water system that incorporates an EDI device to produce primary pure water, the flow rate of concentrated water in the EDI device and the applied current value to the EDI device are adjusted based on the water quality of the water supplied to the primary pure water system, the water quality of the treated water (deionized water) discharged from the EDI device, and the flow rates measured at various points within the primary pure water system. Patent Document 3 discloses that in an EDI device, a pressure fluctuation-responsive constant flow valve is provided in the path through which concentrated water is discharged from the concentration chamber in order to control the flow rate balance between the treated water flow rate and the concentrated water flow rate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-102200 [Patent Document 2] Japanese Patent Publication No. 2021-126624 [Patent Document 3] Japanese Patent Publication No. 2007-222724 [Overview of the project] [Problems that the invention aims to solve]

[0007] In a water treatment system including an EDI device, returning concentrated water to the upstream stage of the EDI device is an effective means of improving the water recovery rate of the EDI device. For example, if 100% of the concentrated water is returned to the upstream stage of the EDI device, the water recovery rate can be 100% by ignoring the electrode water discharged from the electrode chamber or by combining the electrode water with the concentrated water. However, in this case, the ion load in the water treatment system will increase. If there are large fluctuations in the water quality of the water supplied to the water treatment system from an external source, returning some or all of the concentrated water to the upstream stage of the EDI device may cause large fluctuations in the ion load in the water treatment system, making it difficult to operate the EDI device stably. Furthermore, if the water treatment system is configured so that treated water is also circulated to the inlet side of the EDI device in addition to concentrated water, for example, if the circulation rate of treated water fluctuates, the water quality of the water supplied to the EDI device will fluctuate greatly, making it difficult to properly control the operation of the EDI device and obtain treated water (deionized water) with stable water quality.

[0008] The object of the present invention is to provide a water treatment system including an EDI device that can increase the water recovery rate of the EDI device and produce treated water with stable water quality even when there are large fluctuations in water quality throughout the water treatment system, as well as a method for operating such a water treatment system. [Means for solving the problem]

[0009] A water treatment system according to one aspect of the present invention is a water treatment system comprising an electric deionized water production apparatus (EDI apparatus), the system comprising: a first circulation line for circulating treated water, which is deionized water discharged from the EDI apparatus, to the upstream of the EDI apparatus; a water supply line for supplying treated water to a point of use; a first adjustment means connected to the outlet of the treated water of the EDI apparatus for distributing the treated water to the first circulation line and the water supply line; a second circulation line for circulating concentrated water discharged from the EDI apparatus to the upstream of the EDI apparatus; a discharge line for discharging concentrated water to the outside of the water treatment system; a second adjustment means connected to the outlet of the concentrated water of the EDI apparatus for distributing concentrated water to the second circulation line and the discharge line; and a water quality monitoring device for monitoring the water quality within the water treatment system, wherein at least one of the first adjustment means and the second adjustment means is controlled based on the monitoring results from the water quality monitoring device.

[0010] A method for operating a water treatment system according to one aspect of the present invention includes an EDI device, a first circulation line for circulating treated water, which is deionized water discharged from the EDI device, to the upstream of the EDI device, a water supply line for supplying treated water to a point of use, a second circulation line for circulating concentrated water discharged from the EDI device to the upstream of the EDI device, and a discharge line for discharging concentrated water to the outside, wherein the water quality within the water treatment system is monitored, and at least one of the distribution ratio of treated water between the first circulation line and the water supply line and the distribution ratio of concentrated water between the second circulation line and the discharge line is controlled according to the monitoring results. [Effects of the Invention]

[0011] According to the present invention, in a water treatment system including an EDI device, the water recovery rate in the EDI device can be increased, and treated water with stable quality can be produced even when there are large fluctuations in water quality throughout the entire water treatment system. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of the configuration of a water treatment system. [Figure 2]It is a graph explaining the principle of the operation method of an embodiment. [Figure 3] It is a flowchart explaining the operation method of an embodiment. [Figure 4] It is a diagram showing another example of the configuration of the water treatment system. [Figure 5] It is a diagram showing the water treatment system used in operation examples 1-1 and 1-2. [Figure 6] It is a graph showing the result of operation example 1-1. [Figure 7] It is a graph showing the result of operation example 1-2. [Figure 8] It is a diagram showing the water treatment system used in operation examples 2-1 and 2-2. [Figure 9] It is a graph showing the result of operation example 2-1. [Figure 10] It is a graph showing the result of operation example 2-2. [Figure 11] It is a diagram showing the water treatment system used in operation examples 3-1 and 3-2. [Figure 12] It is a graph showing the result of operation example 3-1. [Figure 13] It is a graph showing the result of operation example 3-2.

Embodiments for Carrying Out the Invention

[0013] Next, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows an example of the configuration of a water treatment system. In the water treatment system shown in FIG. 1, raw water such as tap water, well water, river water, and recycled water is supplied through a pipe 20, and this raw water is treated to supply treated water, which is deionized water, to its use point (place of use). The use point may be a subsystem that further purifies the treated water to produce ultrapure water. This water treatment system includes at least an EDI device (electrical deionized water production device) 10, and an operation method based on the present invention is applied.

[0014] The water to be treated supplied to the water treatment system through the pipe 20 is first supplied to a reverse osmosis membrane device (RO) 21 equipped with a reverse osmosis membrane 22. The water that did not permeate through the reverse osmosis membrane 22 in the reverse osmosis membrane device 21, that is, the RO concentrate, is discharged to the outside of the system through the pipe 23. On the other hand, the water that permeated through the reverse osmosis membrane 22 in the reverse osmosis membrane device 21, that is, the RO permeate, is sent to a supply water tank 15 provided in the front stage of the EDI device 10 through the permeate pipe 24. The supply water tank 15 temporarily stores the water supplied to the EDI device 10, that is, the EDI supply water. The capacity of the supply water tank 15 and the like will be described later. A supply water pipe 31 is connected to the outlet of the supply water tank 15 to supply the EDI supply water to the concentration chamber (C) and the desalination chamber (D) of the EDI device 10. A pump 32 for feeding the EDI supply water is provided in the supply water pipe 31. By providing the pump 32, the EDI supply water is supplied to the desalination chamber (D) at a constant flow rate in the EDI device 10, and the EDI supply water is also supplied to the concentration chamber (C) at a constant flow rate. The EDI device 10 may be provided with an electrode chamber separately from the concentration chamber (C). In that case, a part of the EDI supply water supplied to the concentration chamber (C) branches off and is supplied to the electrode chamber.

[0015] Deionized treated water is discharged from the desalination chamber (D) of the EDI device 10 at a constant flow rate. This treated water is supplied to the use point, but there is not always a demand for treated water at the use point. In addition, use points are generally equipped with a receiving tank that receives and temporarily stores treated water from the water treatment system, but once the receiving tank is full, it is not possible to supply any more treated water to the use point. Therefore, the supply of treated water from the EDI device 10 to the use point may have to be intermittent. On the other hand, the EDI device 10 is a device that is preferably able to operate continuously without interruption. In the water treatment system shown in Figure 1, one end of the treated water piping 33 is connected to the outlet of the desalination chamber (D) of the EDI device 10, and a flow rate adjustment unit 34, for example, consisting of a three-way valve, is attached to the other end of the treated water piping 33. The flow rate adjustment unit 34 is connected to a water supply piping 35 that supplies treated water to the use point and a circulation piping 36 that returns treated water to the supply water tank 15. The flow rate adjustment unit 34 corresponds to the first adjustment means, the water supply piping 35 constitutes the water supply line, and the circulation piping 36 constitutes the first circulation line. By operating the flow rate adjustment unit 34, it is possible to switch between a state in which treated water from the desalination chamber (D) is supplied to the use point via the water supply piping 35 and a state in which the treated water is circulated to the supply water tank 15 via the circulation piping 36.

[0016] The flow rate adjustment unit 34 can be configured using components other than a three-way valve, as long as it can switch the supply of treated water from the treated water piping 33 to the water supply piping 35 and the circulation piping 36. For example, the flow rate adjustment unit 34 can be configured using automatic valves, flow control valves, constant flow valves, pressure reducing valves, adjustment valves, manual valves, solenoid valves, on / off valves, etc., individually or in combination. Even when the EDI device 10 is provided with multiple desalination chambers (D), one common flow rate adjustment unit 34 is provided for all of these multiple desalination chambers (D). In that case, the outlet water (deionized water) from the multiple desalination chambers (D) merges and flows into the treated water piping 33 and is supplied to the flow rate adjustment unit 34.

[0017] Concentrated water is discharged from the concentration chamber (C) of the EDI device 10 at a constant flow rate. Since the concentration of ionic impurities is high in the concentrated water, it is preferable to discharge the concentrated water outside the system from the viewpoint of removing impurities from the system. However, if the concentrated water is discharged outside the system, the water recovery rate in the EDI device 10 decreases, which is undesirable from the viewpoint of effective use of water resources. Therefore, the water treatment system shown in Figure 1 is configured to discharge the concentrated water discharged from the concentration chamber (C) to the outside, and also to circulate the concentrated water to the upstream stage of the EDI device 10, specifically to the supply water tank 15. For this purpose, a concentrated water pipe 41 is provided in the EDI device 10, into which concentrated water flowing out from each outlet of the multiple concentration chambers (C) is combined and supplied, and the concentrated water pipe 41 extends to the flow rate adjustment unit 42. The flow rate adjustment unit 42 has three ports a to c, and the concentrated water pipe 41 is connected to port a. A discharge pipe 43 for discharging concentrated water outside the system is connected to port b, and a circulation pipe 44 for circulating concentrated water to the supply water tank 15 is connected to port c. The flow rate adjustment unit 42 corresponds to the second adjustment means, the discharge piping 43 constitutes the discharge line, and the circulation piping 44 constitutes the second circulation line. In the EDI device 10, the flow rate of concentrated water is preferably 1 / 20 to 1 / 5 of the flow rate of treated water.

[0018] The flow rate adjustment unit 42 is configured to change the ratio of the flow rate of concentrated water sent to the discharge pipe 43 to the flow rate of concentrated water sent to the circulation pipe 44 in steps or continuously within the range of 0:100 to 100:0 with respect to the concentrated water sent via the concentrated water piping 41. If the proportion of the concentrated water discharged from the EDI device 10 that is circulated to the upstream stage of the EDI device 10 is called the concentrated water recovery rate r, then the flow rate adjustment unit 42 is configured to change the recovery rate r between 0 and 100%. The flow rate adjustment unit 42 that functions in this way is composed of, for example, a three-way valve that can continuously change the distribution ratio. In addition to a three-way valve, the flow rate adjustment unit 42 can also be configured by using, for example, a flow control valve, constant flow valve, pressure reducing valve, adjustment valve, manual valve, solenoid valve, on / off valve, etc., individually or in combination. If an electrode chamber is provided independently of the concentration chamber (C) in the EDI device 10, the electrode water discharged from the electrode chamber is sent to the concentrated water piping 41 so as to merge with the concentrated water. In this case, it is preferable to remove the gaseous components contained in the electrode water before combining it with the concentrated water. If the amount of electrode water is negligible compared to the amount of concentrated water, the electrode water may be discharged directly from the system.

[0019] The water treatment system is equipped with one or more water quality monitoring devices to measure water quality at various points within the system. In the illustrated example, a water quality monitoring device 51 is attached to the permeate piping 24 to monitor the quality of RO permeate from the reverse osmosis membrane device 21, and a water quality monitoring device 52 is attached to the supply water piping 31 to monitor the quality of EDI supply water stored in the supply water tank 15 and supplied to the EDI device 10. A water quality monitoring device 53 is attached to the treated water piping 33 to monitor the quality of treated water (deionized water) discharged from the desalination chamber (D) of the EDI device 10, and a water quality monitoring device 54 is attached to the concentrated water piping 41 to monitor the quality of concentrated water. The water quality monitoring devices 51-54 are configured using one type of instrument from among those that are to be monitored, such as a conductivity meter, resistivity meter, pH meter, TOC meter for measuring the total organic carbon (TOC) concentration in water, silica meter for measuring the silica concentration in water, or boron meter for measuring the boron concentration in water, or a combination of two types of such instruments. Some of the water quality monitoring devices 51-54 shown in Figure 1 do not need to be installed, or the water quality monitoring devices may be placed in locations other than the water quality monitoring locations shown in Figure 1.

[0020] Furthermore, the water treatment system is equipped with a control unit 50 that controls the operation of the water treatment system. In particular, the control unit 50 controls the flow rate adjustment unit 34 according to the usage status of treated water at the point of use, and controls the flow rate adjustment unit 42 according to the water quality measurement results measured by at least one of the water quality monitoring devices 51 to 54. If a receiving tank is provided at the point of use to receive and temporarily store treated water, for example, the control unit 50 controls the flow rate adjustment unit 42 based on signals from a level sensor or the like provided in the receiving tank, so that if the amount of water in the receiving tank is above a threshold, treated water is circulated to the supply water tank 15 via the circulation pipe 36, and if the amount of water in the receiving tank is below the threshold, treated water is supplied to the receiving tank via the water supply pipe 35. In addition to control based on the amount of water in the receiving tank, the control unit 50 may also control the treated water flow rate adjustment unit 34 based on water quality measured by the water quality monitoring devices 51 to 54.

[0021] Assume that the entire volume of treated water discharged from the desalination chamber (D) of the EDI device 10 is supplied to the point of use. If the entire volume of concentrated water discharged from the concentration chamber (C) is circulated to the supply water tank 15, the water recovery rate in the EDI device 10 will be 100%, but the impurity concentration in the system will increase, and in the worst case, scale may form in the EDI device 10, or the production of deionized water, which is treated water, may become impossible. Therefore, the control unit 50 controls the flow rate adjustment unit 42 so that a large portion of the concentrated water is circulated to the supply water tank 15, that is, so that the recovery rate r for concentrated water is a large value, while monitoring the water quality values ​​in the water treatment system with water quality monitoring devices 51 to 54. At this time, the recovery rate r of concentrated water is assumed to be 100%. Since the water quality value gradually deteriorates due to the large recovery rate r of concentrated water, the control unit 50 controls the flow rate adjustment unit 42 so that the recovery rate r is reduced and the proportion of concentrated water discharged outside the system via the discharge pipe 43 increases when the water quality value deteriorates beyond an acceptable value. This control is called the first control. The recovery rate r of concentrated water at this time is set to a range in which the water recovery rate at the EDI device 10 at that time is, for example, 90% or more, preferably 95% or more, in order to improve the water recovery rate of the entire water treatment system. In the standard case where the flow rate of concentrated water is 1 / 10 of the flow rate of treated water, if the recovery rate r of concentrated water is set to 35%, the water recovery rate at the EDI device 10 will be 95% or more. By increasing the proportion of concentrated water discharged outside the system, the water quality value gradually improves. Once the water quality value has improved to a certain extent, the control unit 50 controls the flow rate adjustment unit 42 again so that a large portion of the concentrated water is circulated back into the supply water tank 15. This control is called the second control.

[0022] When such control is implemented, and assuming that the concentration of a specific impurity component is used as the water quality value, the water quality value changes as shown in Figure 2 depending on the elapsed time from the time the water treatment system is started and the EDI device 10 starts operating. Figure 2 is a diagram illustrating the principle of the operating method based on the present invention. The impurity concentration is maximum at P1, P2,... and minimum at Q1, Q2,... During the period from the start of operation to P1, the period from Q1 to P2, the period from Q2 to P3, etc., almost all of the concentrated water is circulated to the supply water tank 15, while during the period from P1 to Q1, the period from P2 to Q2, the period from P3 to Q3, etc., the proportion of concentrated water discharged outside the system is increased. The time length from one maximum value of impurity concentration to the next maximum value is called the period. By appropriately setting the timing of switching the concentrated water recovery rate r according to the impurity concentration and the concentrated water recovery rate r before and after the switch, it is possible to increase the water recovery rate in the EDI device 10 while gradually reducing the range of fluctuation in impurity concentration. In reality, frequently switching the valves in the flow rate adjustment unit 42 can cause malfunctions. Also, switching the valves in the flow rate adjustment unit 42 can cause pressure fluctuations within the water treatment system, which can result in an increase in the applied voltage at the EDI device 10. Therefore, it is preferable to keep the cycle within 10 cycles per hour. To keep the cycle within 10 cycles per hour, the sum of the number of executions of the first control and the number of executions of the second control should be 20 or less per hour. To set the cycle in this way, the recovery rate r of concentrated water should be appropriately set during periods in which the proportion of concentrated water discharged outside the system is large, for example, the period from P1 to Q1, the period from P2 to Q2, and the period from P3 to Q3.

[0023] The above explanation assumes that water quality values ​​are measured continuously, and that the flow rate adjustment unit 42 is controlled continuously based on the measurement results of the water quality values. However, in an actual water treatment system, it is not necessary to continuously measure water quality values ​​and control the flow rate adjustment unit 42. Instead, water quality values ​​can be measured and the recovery rate r of concentrated water in the flow rate adjustment unit 42 can be changed at control cycles ranging from a few minutes to several hours. If it is not necessary to gradually reduce the fluctuation range of water quality values, the water treatment system can be operated according to the flowchart shown in Figure 3. Here, a first threshold T1 and a second threshold T2 are predetermined with respect to water quality values. The water quality value indicated by the first threshold T1 is assumed to be a water quality value that is worse than the water quality value indicated by the second threshold T2. That is, if the water quality value is impurity concentration or conductivity, T1 > T2, and if the water quality value is resistivity, T1 <T2である。

[0024] In the processing procedure shown in Figure 3, first, in step 101, the flow rate adjustment unit 42 is set so that the recovery rate r of concentrated water is R1, and the water treatment system is operated. Then, in step 102, it is determined whether the water quality value obtained from the water quality monitoring device has deteriorated and reached the first threshold T1. If the water quality is better than the water quality indicated by the first threshold T1, step 102 is repeated. If the water quality has reached or deteriorated from the water quality indicated by the first threshold T1, in step 103, the flow rate adjustment unit 42 is set so that the recovery rate r of concentrated water is R2 (R1 > R2), and the operation of the water treatment system is continued. After that, in step 104, it is determined whether the water quality value obtained from the water quality monitoring device has improved and reached the second threshold T2. If the water quality is worse than the water quality indicated by the second threshold T2, step 104 is repeated. If the water quality has reached or improved from the water quality indicated by the second threshold T2, the process returns to step 101 and the processing from step 101 onwards is repeated.

[0025] To increase the recovery rate in the EDI device 10, at least a portion of the concentrated water should be returned to any position upstream of the EDI device 10. In the water treatment system shown in Figure 1, the circulation pipe 44 is connected to the supply water tank 15, and the concentrated water is returned to the supply water tank 15 via the circulation pipe 44. However, in the water treatment system shown in Figure 4, the circulation pipe 44 is connected to the pipe 20 of the water to be treated, and the concentrated water merges with the water to be treated and circulates to the inlet of the reverse osmosis membrane device 21. Since the reverse osmosis membrane device 21 is located upstream of the supply water tank 15, at least a portion of the concentrated water from the EDI device 10 is also returned upstream of the EDI device 10 in the water treatment system shown in Figure 4. The water treatment system shown in Figure 4 has the same configuration as the water treatment system shown in Figure 1, except for the connection point of the circulation pipe 44 for the concentrated water, and operates in the same way as the water treatment system shown in Figure 1.

[0026] The operating method based on the present invention will be explained in more detail below by describing an example of a simulation of the operation of a water treatment system.

[0027] [Example of operation 1-1] In the water treatment system shown in Figure 1, the simulation was performed assuming that all treated water from the desalination chamber (D) of the EDI device 10 is supplied directly to the point of use via the treated water piping 33, that is, that the flow rate adjustment unit 34, water supply piping 35, and circulation piping 36 are not provided. Figure 5 shows the configuration of the main parts of the water treatment system in operation example 1-1. The supply water tank 15 is fitted with an overflow pipe 16 for discharging the tank's overflow. RO permeate water with a boron concentration of 20 μg / L was supplied to the supply water tank 15, which has a capacity of 1000 L, at a flow rate of 1000 L / h. EDI supply water was supplied from the supply water tank 15 to the EDI device 10 at a flow rate of 550 L / h, and treated water with a boron concentration of 20 ng / L was discharged from the EDI device 10 at a flow rate of 500 L / h, and concentrated water with a boron concentration of 400 μg / L was discharged at a flow rate of 50 L / h. Regarding the boron concentration of the EDI supply water measured by the water quality monitoring device 52, an upper limit (first threshold T1) of 100 μg / L was set, and a lower limit (second threshold T2) of 80 μg / L was set, and the water treatment system was operated according to the flowchart shown in Figure 3.

[0028] The flow rate adjustment unit 42 installed in the concentrated water piping 41 is designed to switch the concentrated water recovery rate r in six stages: 100%, 75%, 50%, 35%, 25%, and 0%. Based on the flow rates of the EDI supply water, treated water, and concentrated water described above, the water recovery rate in the EDI device 10 is 95% or higher when the concentrated water recovery rate r is 100%, 75%, and 50%. The relationship between the elapsed time since the start of operation and the boron concentration of the EDI supply water measured by the water quality monitoring device 52 was investigated. The results are shown in Figure 6. In Figure 6, P1, P2, ... indicate the maximum boron concentration, and Q1, Q2, ... indicate the minimum boron concentration. The boron concentration of the EDI supply water at the start of operation is 20 μg / L, the same as the boron concentration of the RO permeate water. At the start of operation, the concentrated water recovery rate r is set to 100% (step 101 in Figure 3). When the water treatment system is operated in this state, the boron concentration of the EDI supply water gradually increases and reaches 100 μg / L, i.e., the upper limit (first threshold T1), after 7 hours (step 102 in Figure 3). Once the upper limit is reached, the flow rate adjustment unit 4 is controlled to reduce the concentrated water recovery rate r (step 103 in Figure 3). To maintain the water recovery rate of the EDI device 10 at 95% or higher, either 75% or 50% can be selected as the concentrated water recovery rate r. Therefore, the change in the boron concentration of the EDI supply water over time was calculated for each case where the concentrated water recovery rate r is 75% and 50%. As shown in Figure 6, when the concentrated water recovery rate r is 50%, the rate of decrease in boron concentration is large. Since a longer period between the boron concentration maxima and the next maxima is preferable, 75% is selected as the concentrated water recovery rate r. As a result, 13 hours after the start of operation, the boron concentration reaches 79 μg / L, falling below the lower limit (second threshold T2) (step 104 in Figure 3). Therefore, the water treatment system continues operating with the concentrated water recovery rate r set to 100%, as in the initial state. As a result, 15 hours after the start of operation, the boron concentration reaches 100 μg / L again, so the concentrated water recovery rate r is switched to 75%. The same control is then repeated.

[0029] [Example of operation 1-2] The water treatment system shown in Figure 5 was operated in the same manner as in Operation Example 1-1, except that the capacity of the supply water tank 15 was 500 L, EDI supply water was supplied from the supply water tank 15 at a flow rate of 945 L / h, treated water with a boron concentration of 200 ng / L was discharged from the EDI device 10 at a flow rate of 900 L / h, and concentrated water with a boron concentration of 420 μg / L was discharged at a flow rate of 45 L / h. The change in boron concentration in the water treatment system shown in Figure 5 was investigated. The results are shown in Figure 7. In this case, the water recovery rate of the EDI device 10 exceeds 95% in all cases of the concentrated water recovery rate r being 100%, 75%, 50%, 35%, 25%, and 0%. In this case as well, in order to lengthen the time between the boron concentration maxima and the next maxima, i.e., the period, 75% is selected as the concentrated water recovery rate r after the boron concentration reaches the upper limit.

[0030] [Example of operation 2-1] In the water treatment system shown in Figure 1, the change in boron concentration in the EDI supply water was investigated by simulation when the process of alternately sending 100% of the treated water from the desalination chamber (D) of the EDI device 10 to the point of use and circulating 100% of the treated water back into the supply water tank 15 for recovery was repeated. Figure 8 shows the configuration of the main parts of the water treatment system in operation example 2-1, and Figure 9 shows the change in boron concentration in the EDI supply water. The supply water tank 15 is fitted with an overflow pipe 16 for discharging the tank's overflow. Here, as in operation example 1-1, RO permeate with a boron concentration of 20 μg / L was supplied to the supply water tank 15, which has a capacity of 1000 L, at a flow rate of 1000 L / h. EDI supply water was supplied from the supply water tank 15 to the EDI device 10 at a flow rate of 550 L / h. From the EDI device 10, treated water with a boron concentration of 20 ng / L was discharged at a flow rate of 500 L / h, and concentrated water with a boron concentration of 400 μg / L was discharged at a flow rate of 50 L / h. Regarding the boron concentration measured by the water quality monitoring device 52, an upper limit (first threshold T1) of 100 μg / L was set, and a lower limit (second threshold T2) of 80 μg / L was set, and the water treatment system was operated according to the flowchart shown in Figure 3.

[0031] The flow rate adjustment unit 42 installed in the concentrated water piping 41 is designed to switch the concentrated water recovery rate r in six stages: 100%, 75%, 50%, 35%, 25%, and 0%. Based on the flow rates of the EDI supply water, treated water, and concentrated water described above, the overall water recovery rate of the EDI device 10 is 95% or more when the concentrated water recovery rate r is 100%, 75%, and 50%. At the start of operation, the entire amount of treated water is sent to the use point, and the concentrated water recovery rate r is set to 100%. By operating the water treatment system in this state, the boron concentration of the EDI supply water gradually increases. After 7 hours from the start of operation, the boron concentration reached the upper limit of 102 μg / L, so the system was switched to circulate the entire amount of treated water to the supply water tank 15. The concentrated water recovery rate r remains at 100%. The boron concentration then rapidly decreases and asymptotically approaches 40 μg / L. Subsequently, 13 hours after the start of operation, when the system was switched to supplying the entire amount of treated water to the use point, the boron concentration rose again. When the treated water is recovered into the supply water tank 15, the boron concentration in the EDI supply water decreases significantly, so in the case of operation example 2-1, it is considered unnecessary to switch the recovery rate r of the concentrated water to a value less than 100%.

[0032] [Example of operation 2-2] Except for setting the EDI supply water flow rate to 945 L / h, and discharging treated water with a boron concentration of 200 ng / L from the EDI device 10 at a flow rate of 900 L / h, and discharging concentrated water with a boron concentration of 420 μg / L at a flow rate of 45 L / h, the change in boron concentration in the EDI supply water was investigated in the same manner as in operation example 2-1, as shown in Figure 8. The results are shown in Figure 10. In this case, the overall water recovery rate of the EDI device 10 exceeds 95% in all cases of the concentrated water recovery rate r being 100%, 75%, 50%, 35%, 25%, and 0%. However, when the treated water is recovered into the supply water tank 15, the boron concentration in the EDI supply water decreases significantly. Therefore, in operation example 2-2 as well, it is considered unnecessary to switch the concentrated water recovery rate r to a value smaller than 100%.

[0033] [Example of operation 3-1] In the water treatment system shown in Figure 1, the simulation was performed assuming that all treated water from the desalination chamber (D) of the EDI device 10 is supplied directly to the point of use via the treated water piping 33, and that the supply of RO permeate to the supply water tank 15 is intermittent. Figure 11 shows the configuration of the main parts of the water treatment system in operation example 3-1. The water treatment system shown in Figure 11 is the same as the water treatment system in operation example 1-1 shown in Figure 5, but with an on / off valve 25 installed in the permeate piping 24 that supplies RO permeate to the supply water tank 15. Here, RO permeate with a boron concentration of 20 μg / L was supplied to the supply water tank 15, which has a capacity of 1000 L, at a flow rate of 1000 L / h. EDI supply water was supplied from the supply water tank 15 to the EDI device 10 at a flow rate of 945 L / h. From the EDI device 10, treated water with a boron concentration of 200 ng / L was discharged at a flow rate of 900 L / h, and concentrated water with a boron concentration of 420 μg / L was discharged at a flow rate of 45 L / h. The boron concentration measured by the water quality monitoring device 52 was set to an upper limit (first threshold T1) of 100 μg / L and a lower limit (first threshold T1) of 80 μg / L, and the water treatment system was operated according to the flowchart shown in Figure 3.

[0034] The flow rate adjustment unit 42 installed in the concentrated water piping 41 is designed to switch the concentrated water recovery rate r in six stages: 100%, 75%, 50%, 35%, 25%, and 0%. Based on the flow rates of the EDI supply water, treated water, and concentrated water described above, the water recovery rate of the EDI device 10 is 95% or higher in all cases of the concentrated water recovery rate r being 100%, 75%, 50%, 35%, 25%, and 0%. At the start of operation, the on-off valve 25 was opened to allow RO permeate water to be supplied to the supply water tank 15, and the concentrated water recovery rate r was set to 100%. By operating the water treatment system in this state, the boron concentration of the EDI supply water gradually increased, and after 6 hours, the boron concentration reached 102 μg / L, exceeding the upper limit (first threshold T1). At this point, the on-off valve 25f was closed to stop the supply of RO permeate water to the supply water tank 15, and the flow rate adjustment unit 42 was controlled to change the concentrated water recovery rate r. Figure 12 shows the change in boron concentration in the EDI feedwater, and in particular, how the boron concentration changes for each changed recovery rate r after the boron concentration has reached its upper limit. As shown in Figure 12, when at least a portion of the concentrated water is circulated to the feedwater tank 15 without a new supply of RO permeate, the boron concentration in the EDI feedwater exceeds the upper limit and increases further. Therefore, it is preferable to send the entire amount of treated water to the point of use and to discharge the entire amount of concentrated water outside the system when the supply of RO permeate is interrupted.

[0035] [Example of operation 3-2] The change in the boron concentration of the EDI feedwater was investigated in the same manner as in operation example 3-1, except that the capacity of the supply water tank 15 was set to 500 L. The results are shown in Figure 13. When at least a portion of the concentrated water was circulated to the supply water tank 15 without any new RO permeate being supplied, the boron concentration of the EDI feedwater exceeded the upper limit and increased further, and the rate of increase was greater than in operation example 3-1, where the capacity of the supply water tank 15 was larger. In this case as well, it is preferable to send the entire amount of treated water to the point of use and, when the supply of RO permeate is interrupted, to discharge the entire amount of concentrated water outside the system.

[0036] Comparing operation example 1-1 and operation example 1-2, the supply flow rate of RO permeate to the supply water tank 15 is the same at 1000 L / h, but the capacity of the supply water tank 15 is 1000 L in operation example 1-1, while it is 500 L in operation example 1-2. Similarly, comparing operation example 3-1 and operation example 3-2, the capacity of the supply water tank 15 is 1000 L in operation example 3-1, while it is 500 L in operation example 3-2. In order to minimize the impact of water quality fluctuations in the water supplied to the water treatment system, it is generally considered preferable to use a large-capacity supply water tank 15. However, as shown in operation example 1-2 or operation example 3-2, according to the operating method based on the present invention, it is possible to suppress water quality fluctuations in the treated water even when a small-capacity supply water tank 15 is used. In conventional water treatment systems, the capacity of the tank that stores EDI supply water, located upstream of the EDI device, is typically 1 to 2 times the amount of EDI supply water per hour. In contrast, according to the operating method of the present invention, the capacity of the tank that stores EDI supply water, located upstream of the EDI device, can be less than the amount of EDI supply water per hour. This reduces the tank footprint and contributes to the miniaturization of the water treatment system. [Explanation of symbols]

[0037] 10 EDI equipment 15. Water supply tank 21 Reverse osmosis membrane equipment 22 Reverse osmosis membrane 24 Permeated water piping 31 Water supply piping 32 pumps 33. Treated water piping 34,42 Flow rate adjustment part 35 Water supply piping 36,44 Circulation piping 41 Concentrated water piping 43 Discharge piping 50 Control Unit 51~54 Water quality monitoring device

Claims

1. A water treatment system equipped with an electro-deionized water production device, A first circulation line that circulates treated water, which is deionized water discharged from the aforementioned electric deionized water production apparatus, to the upstream stage of the aforementioned electric deionized water production apparatus, A water supply line for sending the treated water toward the point of use, A first adjustment means connected to the outlet of the treated water of the electric deionized water production apparatus, which distributes the treated water to the first circulation line and the water supply line, A second circulation line that circulates the concentrated water discharged from the aforementioned electro-deionized water production apparatus to the upstream stage of the electro-deionized water production apparatus, A discharge line for discharging the concentrated water to the outside of the water treatment system, A second adjustment means connected to the outlet of the concentrated water of the electric deionized water production apparatus, which distributes the concentrated water to the second circulation line and the discharge line, A water quality monitoring device for monitoring water quality within the aforementioned water treatment system, Equipped with, A water treatment system in which at least one of the first adjustment means and the second adjustment means is controlled based on the monitoring results from the water quality monitoring device.

2. When the water quality value obtained by the water quality monitoring device deteriorates and reaches a first threshold for water quality, the second adjustment means controls to increase the amount of concentrated water sent to the discharge line, and when the water quality value improves and reaches a second threshold for water quality, the second adjustment means controls to increase the amount of concentrated water sent to the second circulation line. The water treatment system according to claim 1, wherein the water quality corresponding to the second threshold is of better quality than the water quality corresponding to the first threshold.

3. The water treatment system according to claim 1 or 2, wherein the water quality monitoring device is provided in the water treatment system to monitor the quality of at least one of the waters supplied to the electrodeionized water production device, the concentrated water, and the treated water.

4. The water treatment system according to claim 3, wherein the water quality monitoring device is composed of one type of device selected from a conductivity meter, a resistivity meter, a pH meter, a TOC meter for measuring total organic carbon concentration, a silica meter for measuring silica concentration, and a boron meter for measuring boron concentration, or a combination of two or more types of devices.

5. The water treatment system according to claim 1 or 2, wherein the first adjustment means is controlled so that, in response to the demand for the treated water at the use point, the treated water flows through the water supply line when there is demand, and the treated water flows through the second circulation line when there is no demand.

6. The water treatment system according to claim 5, wherein a receiving tank for receiving the treated water is provided at the use point, and it is determined that there is no demand when the amount of treated water in the receiving tank is above a predetermined threshold.

7. The water treatment system according to claim 1 or 2, wherein the first adjustment means and the second adjustment means are each independently configured with one type of valve selected from an automatic valve, a flow control valve, a constant flow valve, a pressure reducing valve, a control valve, a manual valve, or a three-way valve, or a combination of two or more types of valves.

8. A method for operating a water treatment system comprising: an electric deionized water production apparatus; a first circulation line for circulating treated water, which is deionized water discharged from the electric deionized water production apparatus, to the upstream stage of the electric deionized water production apparatus; a water supply line for supplying the treated water to a point of use; a second circulation line for circulating concentrated water discharged from the electric deionized water production apparatus to the upstream stage of the electric deionized water production apparatus; and a discharge line for discharging the concentrated water to the outside, wherein An operating method comprising monitoring the water quality within the water treatment system and controlling at least one of the distribution ratio of the treated water between the first circulation line and the water supply line, and the distribution ratio of the concentrated water between the second circulation line and the discharge line, according to the monitoring results.

9. When the water quality value obtained for water quality deteriorates and reaches a first threshold for water quality, a first control is performed to increase the amount of concentrated water sent to the discharge line, and when the water quality value improves and reaches a second threshold for water quality, a second control is performed to increase the amount of concentrated water sent to the second circulation line. The operating method according to claim 8, wherein the sum of the number of executions of the first control and the number of executions of the second control is 20 times or less per hour.

10. The operating method according to claim 8 or 9, wherein the ratio of the amount of concentrated water sent to the second circulation line and the amount of concentrated water sent to the discharge line is controlled within a range that satisfies the condition that the water recovery rate in the electric deionized water production apparatus is 95% or more.

11. The operating method according to claim 8 or 9, wherein the flow rate of the concentrated water discharged from the electric deionized water production apparatus is set to be 1 / 20 or more and 1 / 5 or less of the flow rate of the treated water discharged from the electric deionized water production apparatus.

12. The operating method according to claim 8 or 9, wherein the capacity of a tank provided upstream of the electric deionized water production apparatus for temporarily storing water supplied to the electric deionized water production apparatus, including the concentrated water circulated via the second circulation line, is less than the amount of water supplied to the electric deionized water production apparatus per hour.

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