Pure water production apparatus and pure water production method

Abstract

To provide a pure water production device capable of increasing a production of high quality pure water.SOLUTION: There is provided a pure water production device 1 including: a first raw water tank 2; a reverse osmosis membrane device 3 that produces permeated water and concentrated water; a circulation flow path L1 that returns the concentrated water to the first raw water tank 2; a first drainage flow path L2 that discharges remaining concentrated water to outside; drainage flow rate adjusting means 6 that adjusts a flow rate of the concentrated water in the first drainage flow path L2; circulating water flow rate adjusting means 7 that adjusts a flow rate of the concentrated water in the circulation flow path L1; a first flow meter 8 that measures a total flow rate of the concentrated water; a first measurement point P1; a water quality measuring device 10 that can measure a water quality of the concentrated water at the first measurement point P1; and a control unit 11 that has a function of controlling either or both of the drainage flow rate adjusting means 6 and the circulating water flow rate adjusting means 7 based on the water quality at the first measurement point P1 and the flow rate at the first flow meter 8 so that the water quality of the concentrated water is maintained within a water quality control range and the total flow rate of the concentrated water is equal to or greater than a flow rate control value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pure water production apparatus and a method for producing pure water.

Background Art

[0002] In semiconductor manufacturing equipment and the like, it has become common to use high-purity water called pure water or ultrapure water as washing water. The standard for the water quality required as high-purity water is usually that the content of impurities is at the ppb level or lower. In particular, when an improvement in product yield is required, water with an impurity content of several tens of ppt to several ppt or lower is desired. Also, in semiconductor manufacturing equipment, water is used for various purposes in auxiliary equipment attached to the main equipment.

[0003] High-purity water such as pure water or ultrapure water used in the main production line of semiconductor manufacturing equipment is used, for example, for washing purposes. The washing wastewater after being used for purposes such as washing can be classified, in terms of concentration, into first washing water wastewater (high-concentration wastewater) containing impurities at a high concentration and second washing water wastewater (low-concentration wastewater) with a low impurity concentration like the wastewater after the second washing and subsequent washings. And the wastewater after the second washing and subsequent washings (low-concentration wastewater) that can be classified into the low-concentration part is often of better water quality than general industrial water or municipal water. Therefore, it is generally practiced to use the above low-concentration wastewater as recycled water as the raw water for producing pure water or ultrapure water, or as the water (equipment water) used in the equipment classified as auxiliary equipment. Also, when recycling the above high-concentration wastewater, the countermeasures often vary depending on conditions such as treatment costs and the presence or absence of intake and discharge restrictions.

[0004] However, the low-concentration wastewater used for cleaning or the like naturally has a lower water quality compared to the high-purity water before use. As such, if it is to be reused as recycled water as it is, its applications are greatly restricted. Therefore, in order to reuse the recovered (low-concentration wastewater), certain treatment is carried out. As an example, Patent Document 1 describes a method for treating recovered water in which the used wastewater of high-purity water used for semiconductor cleaning or the like is recovered, a non-ionic silica component that does not react with molybdic acid reagent contained in this recovered water is ionized, and then the ionic silica component is removed by membrane rejection using a reverse osmosis membrane device. In addition to Patent Document 1, there is also known a technique for reusing recovered water by producing pure water by treating the recovered water with a reverse osmosis membrane.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, the water quality of the recovered water used for cleaning or the like may vary at any time. Therefore, generally, when reusing the recovered water as raw water for pure water production, the water quality of the recovered water is measured, and for the recovered water whose measured value is below the reference value, treatment such as by a reverse osmosis membrane is carried out. However, even for the recovered water whose water quality is below the reference value, the water quality may vary within the range below the reference value. On the other hand, a pure water production apparatus equipped with a reverse osmosis membrane is usually operated under operating conditions where, for example, the recovery rate is fixed at a certain value, and it has not usually been done to adjust the recovery rate according to the variation in the water quality of the raw water.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a pure water production apparatus and a method for producing pure water that enable production of pure water under appropriate conditions according to variations in the water quality of raw water and can increase the production of high-quality pure water.

Means for Solving the Problem

[0008] To solve the above problems, the inventors of the present invention conducted intensive studies. Generally, when treating treated water with a lower solute concentration than expected using a reverse osmosis membrane, it is possible to increase the amount of permeated water produced by increasing the recovery rate of the reverse osmosis membrane. Conversely, when treating treated water with a higher solute concentration than expected, it is possible to suppress the clogging of the reverse osmosis membrane by solutes by decreasing the recovery rate. However, conventional pure water production devices have always kept the recovery rate of the reverse osmosis membrane device constant.

[0009] Therefore, in order to increase the amount of permeated water produced, the inventors considered making it possible to change the recovery rate of the reverse osmosis membrane device according to the quality of the treated water. Focusing on the fact that the quality of the concentrated water also changes when the quality of the treated water changes, the quality of the concentrated water is monitored. When the quality of the concentrated water deviates from the appropriate water quality range, the recovery rate of the reverse osmosis membrane device is changed by adjusting the flow rate of the concentrated water. As a result, it became possible to maximize the capacity of the reverse osmosis membrane and successfully increase the amount of permeated water produced.

[0010] The present invention adopts the following configuration.

[0011] [1] A raw water tank for storing treated water, A reverse osmosis membrane device disposed downstream of the raw water tank, which generates permeated water and concentrated water by treating the treated water with a reverse osmosis membrane, A circulation flow path that enables a part of the concentrated water to be returned to the raw water tank, A first drainage flow path for discharging the remaining part of the concentrated water to the outside, Drainage flow rate adjustment means for adjusting the flow rate of the concentrated water in the first drainage flow path, Circulating water flow rate adjustment means for adjusting the flow rate of the concentrated water in the circulation flow path, A flow meter for measuring the total flow rate of the concentrated water generated in the reverse osmosis membrane device, A first measurement point provided in the first drainage flow path and serving as a measurement position for the quality of the concentrated water, A water quality measuring device capable of measuring the water quality of the concentrated water at the first measurement point; A control unit having a function of controlling either or both of the drainage flow rate adjusting means and the circulating water flow rate adjusting means so that the water quality of the concentrated water is maintained within the water quality management range and the total flow rate of the concentrated water is equal to or greater than the flow rate management value, based on the water quality of the concentrated water at the first measurement point measured by the water quality measuring device and the total flow rate of the concentrated water measured by the flow meter; A pure water manufacturing apparatus comprising the same. [2] The function of the control unit is as follows: When the water quality of the concentrated water falls below the lower limit of the water quality management range, either or both of the drainage flow rate adjusting means and the circulating water flow rate adjusting means are controlled so as to increase the return flow rate of the concentrated water through the circulation flow path; When the water quality of the concentrated water exceeds the upper limit of the water quality management range, either or both of the drainage flow rate adjusting means and the circulating water flow rate adjusting means are controlled so as to decrease the return flow rate of the concentrated water through the circulation flow path; The pure water manufacturing apparatus according to [1], which has a function of controlling either or both of the drainage flow rate adjusting means and the circulating water flow rate adjusting means so as to increase the total flow rate of the concentrated water when the total flow rate of the concentrated water generated in the reverse osmosis membrane device is less than the flow rate management value. [3] A supply flow path for sending the water to be treated to the raw water tank; A second measurement point provided in the supply flow path and serving as a measurement position for the water quality of the water to be treated; A second drainage flow path branched from the supply flow path between the second measurement point and the raw water tank and enabling the water to be treated to be discharged to the outside; A switching means for enabling the supply destination of the water to be treated to be switched between the raw water tank and the second drainage flow path; and The water quality measuring device is capable of switching the measurement position between the first measurement point and the second measurement point. The control unit further has a function of controlling the switching means so as to send the total amount of the water to be treated to the second drainage channel when at least one of the following cases occurs: when the water quality of the water to be treated at the first measurement point measured by the water quality measuring device exceeds the water quality management value, and when the total flow rate of the concentrated water generated in the reverse osmosis membrane device is less than the flow rate management value. The pure water production device according to [1]. [4] The control unit further has a function of controlling the switching means so as to send the total amount of the water to be treated to the raw water tank when the water quality of the water to be treated at the second measurement point measured by the water quality measuring device is equal to or less than the water quality management value. The pure water production device according to [3]. [5] The pure water production device according to [3] or [4] further comprises a function that when the control unit sends the total amount of the water to be treated to the raw water tank, it sets the measurement position of the water quality measuring device to the first measurement point, and when it sends the total amount of the water to be treated to the second drainage channel, it sets the measurement position of the water quality measuring device to the second measurement point. [6] The control unit estimates the solute concentration on the membrane surface on the primary side of the reverse osmosis membrane, and when the solute concentration on the membrane surface exceeds the management concentration value, it further has a function of controlling either one or both of the drainage flow rate adjusting means and the circulating water flow rate adjusting means so as to reduce the return flow rate of the concentrated water through the circulation channel. The pure water production device according to any one of [1] to [4]. [7] The control unit estimates the solute concentration on the membrane surface on the primary side of the reverse osmosis membrane, and when the solute concentration on the membrane surface exceeds the management concentration value, it further has a function of controlling either one or both of the drainage flow rate adjusting means and the circulating water flow rate adjusting means so as to reduce the return flow rate of the concentrated water through the circulation channel. The pure water production device according to [5].

[0012] [8] By treating the water to be treated with a reverse osmosis membrane, permeate water and concentrated water are generated. The permeate water is taken out as pure water, and a part of the concentrated water can be supplied to the primary side of the reverse osmosis membrane through a circulation channel. The remaining part of the concentrated water is discharged to the outside through a first drainage channel. A method for producing pure water, measuring the water quality of the concentrated water and measuring the total flow rate of the concentrated water generated by the reverse osmosis membrane, and adjusting the flow rate of the concentrated water in the circulation channel or the flow rate of the concentrated water in the first drainage channel so that the water quality of the concentrated water is maintained within the water quality management range and the total flow rate of the concentrated water is equal to or greater than the flow rate management value. A method for producing pure water. [9] When the water quality of the concentrated water is below the lower limit of the water quality management range, increase the return flow rate of the concentrated water through the circulation channel, When the water quality of the concentrated water exceeds the upper limit of the water quality management range, decrease the return flow rate of the concentrated water through the circulation channel, The method for producing pure water according to [8], wherein when the total flow rate of the concentrated water generated in the reverse osmosis membrane is less than the flow rate management value, the total flow rate of the concentrated water is increased.

[10] When at least one of the following cases occurs: the water quality of the water to be treated measured upstream of the reverse osmosis membrane exceeds the water quality management value, or the total flow rate of the concentrated water generated in the reverse osmosis membrane is less than the flow rate management value, the total amount of the water to be treated is discharged to the outside through a second drainage channel without being sent to the reverse osmosis membrane. The method for producing pure water according to [8].

[11] The method for producing pure water according to

[10] , wherein when the water quality of the water to be treated measured upstream of the reverse osmosis membrane is equal to or less than the water quality management value, the total amount of the water to be treated is sent to the primary side of the reverse osmosis membrane.

[12] Estimating the membrane surface solute concentration on the primary side of the reverse osmosis membrane, and when the membrane surface solute concentration exceeds the management concentration value, decreasing the return flow rate of the concentrated water through the circulation channel. The method for producing pure water according to any one of [8] to

[11] .

Advantages of the Invention

[0013] According to the pure water production device of the present invention, the control unit controls either one or both of the drainage flow rate adjustment means or the circulating water flow rate adjustment means so that the water quality of the concentrated water is maintained within the water quality management range, thereby controlling the flow rate of the concentrated water and changing the recovery rate of the reverse osmosis membrane device. Therefore, the recovery rate can be appropriately changed according to the water quality of the water to be treated. In addition, since the control unit controls either one or both of the drainage flow rate adjustment means or the circulating water flow rate adjustment means so that the total flow rate of the concentrated water is equal to or greater than the flow rate management value, it is possible to ensure that the flow rate of the concentrated water is a certain value or more and prevent the occurrence of concentration polarization on the membrane surface of the reverse osmosis membrane.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] Hereinafter, a pure water production device and a method for producing pure water according to an embodiment of the present invention will be described with reference to the drawings.

[0016] FIG. 1 shows a schematic diagram of the pure water production apparatus 1 of the present embodiment. The pure water production apparatus 1 includes a first raw water tank 2 (raw water tank) for storing the water to be treated, a reverse osmosis membrane device 3, a circulation flow path L1 that enables a part of the concentrated water generated in the reverse osmosis membrane device 3 to be returned to the first raw water tank 2, a first drainage flow path L2 for discharging the remaining part of the concentrated water to the outside, a drainage flow rate adjusting means 6 provided in the first drainage flow path L2, a circulating water flow rate adjusting means 7 provided in the circulation flow path L1, a first flow meter 8 (flow meter) for measuring the total flow rate of the generated concentrated water, a first measurement point P1 provided in the first drainage flow path L2, a water quality measurement device 10, and a control unit 11. Further, a concentrated water flow path L5 for discharging the concentrated water from the reverse osmosis membrane device 3 is connected to the reverse osmosis membrane device 3, and the concentrated water flow path L5 branches in the middle to form the circulation flow path L1 and the first drainage flow path L2.

[0017] In addition, the pure water production apparatus 1 shown in FIG. 1 further includes a supply flow path L3 for sending the water to be treated to the first raw water tank 2, a second measurement point P2 provided in the supply flow path L3, a second drainage flow path L4 branched from the supply flow path L3 for enabling the water to be treated to be discharged to the outside, and a switching means 12 for switching the supply destination of the water to be treated.

[0018] Furthermore, the pure water production apparatus 1 shown in FIG. 1 includes a second raw water tank 13 disposed between the switching means 12 and the first raw water tank 2, a pretreatment device 14, a third drainage flow path L6 for sending the drainage generated in the pretreatment device 14 to the first drainage flow path L2, a permeate water tank 17 disposed downstream of the reverse osmosis membrane device 3 for storing the permeate water generated in the reverse osmosis membrane device 3, a second flow meter 16 for measuring the flow rate of the permeate water, and a third flow meter 15 for measuring the flow rate of the concentrated water in the first drainage flow path L2.

[0019] Hereinafter, the details of the components of the pure water production apparatus 1 will be described in the order of the general flow of the water to be treated.

[0020] The supply flow path L3 is a flow path for sending the water to be treated to the first raw water tank 2 (raw water tank). A second measurement point P2 is provided in the supply flow path L3.

[0021] The second measurement point P2 is a measurement position for measuring the water quality of the water to be treated flowing through the supply channel L3. The water quality of the water to be treated at the second measurement point P2 can be measured by the water quality measurement device 10.

[0022] The switching means 12 is a device for switching the supply destination of the water to be treated to the first raw water tank 2 or the second drainage channel L4 based on a command from the control unit 11.

[0023] The second drainage channel L4 is a channel for discharging the water to be treated as drainage outside the pure water production device 1 when the water quality of the water to be treated exceeds the water quality management value. A drainage treatment facility for treating the drainage may be connected to the end of the second drainage channel L4.

[0024] The second raw water tank 13 stores the water to be treated supplied by the supply channel L3.

[0025] The pretreatment device 14 is a device for performing coagulation sedimentation treatment etc. on the water to be treated, and is installed, for example, for the purpose of removing turbidity contained in the water to be treated by coagulation sedimentation treatment. The drainage containing the sludge generated by the coagulation sedimentation treatment is configured to be sent to the first drainage channel L2 via the third drainage channel L6.

[0026] The first raw water tank 2 stores the water to be treated after pretreatment. Also, the first raw water tank 2 is configured to receive the concentrated water returned by the circulation channel L1.

[0027] The reverse osmosis membrane device 3 has a reverse osmosis membrane. The reverse osmosis membrane device 3 treats the water to be treated with the reverse osmosis membrane. Permeate water and concentrated water are generated by the treatment with the reverse osmosis membrane.

[0028] The second flowmeter 16 is arranged downstream of the reverse osmosis membrane device 3 and measures the total flow rate of the permeate water generated in the reverse osmosis membrane device 3. Also, the permeate water tank 17 is installed downstream of the second flowmeter 16 and stores the generated permeate water.

[0029] The reverse osmosis membrane device 3 is connected to a concentrated water flow path L5 for flowing the generated concentrated water. The flow paths into which the concentrated water flow path L5 branches midway are the circulation flow path L1 and the first drainage flow path L2. The concentrated water generated in the reverse osmosis membrane device 3 flows through the concentrated water flow path L5 and into the circulation flow path L1 and the first drainage flow path L2.

[0030] A first flow meter 8 (flow meter) is provided in the concentrated water flow path L5. The first flow meter 8 continuously or intermittently measures the total flow rate of the concentrated water generated in the reverse osmosis membrane device 3. The measurement result is sent to the control unit 11.

[0031] The circulation flow path L1 is connected to the first raw water tank 2, and the concentrated water can be returned to the first raw water tank 2. The circulation flow path L1 is provided with a circulation water flow rate adjustment means 7 for adjusting the flow rate of the concentrated water. The circulation water flow rate adjustment means 7 may be, for example, an on-off valve for stopping or continuing the return of the concentrated water, or a flow rate adjustment valve capable of adjusting the return flow rate of the concentrated water. The circulation water flow rate adjustment means 7 is connected to the control unit 11 and operates based on the command of the control unit 11. Also, the circulation flow path L1 may be provided with a manual flow rate adjustment valve (not shown).

[0032] The first drainage flow path L2 is connected to the second drainage flow path L4, and the concentrated water can be discharged outside the pure water production device 1. The first drainage flow path L2 is provided with a drainage flow rate adjustment means 6 for adjusting the flow rate of the concentrated water. The drainage flow rate adjustment means 6 is, for example, a flow rate adjustment valve capable of adjusting the flow rate of the concentrated water stepwise or continuously. The drainage flow rate adjustment means 6 is connected to the control unit 11 and operates based on the command of the control unit 11.

[0033] Also, the first drainage flow path L2 is provided with a third flow meter 15 for measuring the flow rate of the concentrated water flowing through the first drainage flow path L2. Further, a first measurement point P1 is provided in the first drainage flow path L2.

[0034] The first measurement point P1 is a measurement position for measuring the water quality of the concentrated water flowing through the first drainage channel L2. The water quality of the water to be treated at the first measurement point P1 can be measured by the water quality measuring device 10. Since the first measurement point P1 is a position (point) for measuring the water quality of the concentrated water, it may be provided in the concentrated water channel L5.

[0035] The water quality measuring device 10 can switch the measurement position to the first measurement point P1 or the second measurement point P2, and measures the water quality of the water to be treated or the concentrated water. The switching of the measurement position is made based on a command from the control unit 11.

[0036] Based on the water quality of the concentrated water at the first measurement point P1 measured by the water quality measuring device 10 and the total flow rate of the concentrated water measured by the first flow meter 8, the control unit 11 is configured to maintain the water quality of the concentrated water within the water quality management range and ensure that the total flow rate of the concentrated water is equal to or greater than the flow rate management value. It has the function of controlling either or both of the drainage flow rate adjustment means 6 or the circulating water flow rate adjustment means 7.

[0037] More specifically, when the water quality of the concentrated water falls below the lower limit of the water quality management range, the control unit 11 controls either or both of the drainage flow rate adjustment means 6 or the circulating water flow rate adjustment means 7 to increase the return flow rate of the concentrated water through the circulation channel L1. When the water quality of the concentrated water exceeds the upper limit of the water quality management range, the control unit 11 controls either or both of the drainage flow rate adjustment means 6 or the circulating water flow rate adjustment means 7 to decrease the return flow rate of the concentrated water through the circulation channel L1. Furthermore, when the total flow rate of the concentrated water generated in the reverse osmosis membrane device 3 is less than the flow rate management value, the control unit 11 controls either or both of the drainage flow rate adjustment means 6 or the circulating water flow rate adjustment means 7 to increase the total flow rate of the concentrated water.

[0038] Furthermore, when at least one of the following cases occurs: the water quality of the water to be treated at the first measurement point P1 measured by the water quality measuring device 10 exceeds the water quality management value, or the total flow rate of the concentrated water generated in the reverse osmosis membrane device 3 becomes less than the flow rate management value, the control unit 11 also controls the switching means 12 so as to send the total amount of the water to be treated to the second drainage channel L4 by controlling either one or both of the drainage flow rate adjusting means 6 or the circulating water flow rate adjusting means 7. Furthermore, when the water quality of the water to be treated at the second measurement point P2 measured by the water quality measuring device 10 is equal to or less than the water quality management value, the control unit 11 also has a function of controlling the switching means 12 so as to send the total amount of the water to be treated to the first raw water tank 2.

[0039] Also, when sending the total amount of the water to be treated to the first raw water tank 2, the control unit 11 has a function of setting the measurement position of the water quality measuring device 10 to the first measurement point P1, and when sending the total amount of the water to be treated to the second drainage channel L4, the control unit 11 has a function of setting the measurement position of the water quality measuring device 10 to the second measurement point P2.

[0040] Furthermore, the control unit 11 estimates the solute concentration on the membrane surface on the primary side of the reverse osmosis membrane, and when the solute concentration on the membrane surface exceeds the management concentration value, the control unit 11 has a function of controlling either one or both of the drainage flow rate adjusting means 6 or the circulating water flow rate adjusting means 7 so as to reduce the return flow rate of the concentrated water through the circulation channel L1.

[0041] The specific operation of the control unit 11 will be described in the explanation of the pure water production method.

[0042] Next, a pure water production method using the pure water production device 1 shown in FIG. 1 will be described.

[0043] The water to be treated is, for example, the drained water after washing used in a washing process or the like in a manufacturing facility for electronic components such as semiconductor devices or liquid crystal display devices. Since such drained water was originally pure water or ultrapure water, even the washing drained water has better water quality compared to general industrial water or municipal water. Therefore, in this embodiment, such drained water is used as raw water or equipment water for pure water production.

[0044] However, the drained water after cleaning used in the cleaning process of semiconductor manufacturing equipment contains organic substances, calcium, fluorine, etc. derived from the semiconductor manufacturing process. There are concerns about the generation of slime due to organic substances and the generation of scale due to calcium and fluorine, and these may pose a risk of blocking the reverse osmosis membrane. Therefore, along with the increase in the production volume of permeated water, it is necessary to consider measures against SS and scale.

[0045] In the following description, the outline of the method for producing pure water in the pure water production apparatus 1 will be described, and then the operation of the control unit 11 will be described in detail.

[0046] When the passage of the water to be treated is started, the water to be treated is supplied to the pure water production apparatus 1 through the supply channel L3, and the water quality is measured at the second measurement point P2. The measurement of the water quality is performed by the water quality measurement apparatus 10. Examples of the water quality to be measured include TOC (total organic carbon). The measurement result is sent to the control unit 11.

[0047] The control unit 11 determines whether the water quality of the water to be treated (for example, the TOC value) at the second measurement point P2 exceeds the water quality management value. When the water quality of the water to be treated exceeds the water quality management value, the control unit 11 issues a command to the switching means 12 to switch the flow path of the water to be treated from the supply channel L3 to the second drainage channel L4. In this case, the water to be treated is not supplied toward the first raw water tank 2 but is discharged outside the pure water production apparatus 1 via the second drainage channel L4.

[0048] On the other hand, when the water quality of the water to be treated is below the water quality management value, the control unit 11 issues a command to the switching means 12 to keep the flow path of the water to be treated as the supply channel L3, and the water to be treated is sent toward the first raw water tank 2.

[0049] When the water quality of the water to be treated exceeds the water quality control value, since the water to be treated contains relatively high concentrations of organic substances and the like, if such water to be treated is sent to the reverse osmosis membrane device 3, fouling of the reverse osmosis membrane will progress, and it becomes necessary to frequently perform backwashing operations. For this reason, when the water quality of the water to be treated exceeds the water quality control value, the water to be treated is discharged to the outside.

[0050] The water quality control value serving as the criterion is a threshold value at which SS adhesion and scale formation can become significant when water to be treated having a water quality exceeding this value flows into the reverse osmosis membrane device 3, and it may be appropriately set according to the properties of the water to be treated and the performance of the reverse osmosis membrane device 3.

[0051] Water to be treated with a water quality below the water quality control value is sent to the second raw water tank 13, and then sent to the pretreatment device 14. In the pretreatment device 14, pretreatment is performed on the water to be treated. Examples of the pretreatment include a treatment in which coagulation treatment, sedimentation treatment, pressure flotation treatment, filtration treatment, etc. are appropriately combined. The pretreated water to be treated is sent to the first raw water tank 2. On the other hand, the drainage containing turbidity generated along with sedimentation treatment, pressure flotation treatment, or filtration treatment is discharged to the outside through the third drainage channel L6, the first drainage channel L2, and the second drainage channel L4.

[0052] The water to be treated after pretreatment is sent to the reverse osmosis membrane device 3 via the first raw water tank 2. In the reverse osmosis membrane device 3, treatment by the reverse osmosis membrane is performed at a predetermined recovery rate, and as a result, permeate water and concentrated water are generated.

[0053] The flow rate of the permeate water is measured by the second flow meter 16 and then sent to the permeate water tank 17. Further, the permeate water is sent to a predetermined use point or used as raw water for another pure water production device.

[0054] The concentrated water is sent to the circulation channel L1 and the first drainage channel L2 via the concentrated water channel L5. In the concentrated water channel L5, the total flow rate of the generated concentrated water is measured by the first flow meter 8, and the result is sent to the control unit 11.

[0055] Part of the concentrated water may be returned to the first raw water tank 2 through the circulation channel L1 and processed again by the reverse osmosis membrane device 3. Returning the concentrated water is preferable in terms of increasing the water utilization rate. However, on the other hand, there is a risk that the quality of the water to be treated supplied to the reverse osmosis membrane deteriorates due to the return of the concentrated water. Therefore, it is desirable for the control unit 11 to determine whether to return the concentrated water.

[0056] On the other hand, the remainder of the concentrated water is discharged outside the pure water production device 1 through the first drainage channel L2. In the first drainage channel L2, the quality of the concentrated water is measured at the second measurement point P2. The water quality measurement is performed by the water quality measurement device 10. Examples of the water quality to be measured include TOC (total organic carbon). The measurement results are sent to the control unit 11.

[0057] Based on the measurement results of the total flow rate of the concentrated water and the quality of the concentrated water, the control unit 11 adjusts the flow rate of the concentrated water in the circulation channel L1 or the flow rate of the concentrated water in the first drainage channel L2 so that the quality of the concentrated water is maintained within the water quality management range and the total flow rate of the concentrated water is equal to or greater than the flow rate management value.

[0058] Hereinafter, for convenience of explanation, the concentrated water in the circulation channel L1 may be referred to as circulating water, and the concentrated water in the circulation channel L1 may be referred to as concentrated drainage.

[0059] In this embodiment, based on the measurement results of the total flow rate of the concentrated water and the quality of the concentrated water (concentrated drainage), the total flow rate of the circulating water and the concentrated drainage is controlled to adjust the recovery rate of the permeated water in the reverse osmosis membrane and ensure the minimum required flow rate of the concentrated water.

[0060] Regarding the recovery rate of permeated water, generally, when treating water to be treated with a lower solute concentration than expected using a reverse osmosis membrane, it is possible to increase the amount of permeated water produced by increasing the recovery rate. Conversely, when treating water to be treated with a higher solute concentration than expected, it is possible to suppress the clogging of the reverse osmosis membrane by solutes by decreasing the recovery rate. Therefore, in this embodiment, paying attention to the fact that the quality of the concentrated water also changes when the quality of the water to be treated changes, the quality of the concentrated water is monitored, and the flow rates of the circulating water and the concentrated drainage are controlled so that the quality of the concentrated drainage is maintained within an appropriate water quality range (water quality management range).

[0061] The water quality management range is the allowable range of the quality of the concentrated water. When the quality of the concentrated water is within the water quality management range, there is no need to change the recovery rate of the permeated water in the reverse osmosis membrane. On the other hand, when the quality of the concentrated water falls below the lower limit of the water quality management range, since there is room to increase the production of permeated water by increasing the recovery rate of the permeated water, it is desirable to perform control to increase the recovery rate. On the other hand, when the quality of the concentrated water exceeds the upper limit of the water quality management range, there is concern about the adhesion of fouling substances such as organic substances and SS and the generation of scale to the reverse osmosis membrane. Therefore, it is desirable to perform control to lower the recovery rate of the permeated water. Specific upper and lower limit values for specifying the water quality management range may be determined based on the properties of the water to be treated and the performance of the reverse osmosis membrane device 3.

[0062] Also, when the quality of the water to be treated significantly deteriorates (for example, when the TOC concentration increases), the recovery rate is decreased to suppress the adhesion of organic substances and SS and the generation of scale. However, even at a concentration that can suppress the adhesion of organic substances and SS and the generation of scale in the concentrated water, the quality of the permeated water may deteriorate. Therefore, the solute concentration on the membrane surface in the reverse osmosis membrane is estimated. When the solute concentration on the membrane surface exceeds the management concentration value, the flow rate of the concentrated drainage is increased and the flow rate of the circulating water is decreased to prevent the deterioration of the quality of the permeated water.

[0063] The management concentration value is a threshold value at which the quality of the permeated water may exceed the guaranteed range when the solute concentration on the membrane surface exceeds this value, and may be appropriately set according to the performance of the reverse osmosis membrane device 3.

[0064] Furthermore, regarding the minimum required flow rate of the concentrated water, when the flow rate of the concentrated water decreases, SS adheres to the primary side of the reverse osmosis membrane or scale deposition due to concentration polarization occurs. Therefore, in order to prevent these, the total flow rate of the concentrated water is controlled to be equal to or higher than the flow rate management value. The total flow rate of the concentrated water is the total flow rate of the concentrated water measured by the first flow meter 8, which is the sum of the flow rates of the circulating water and the concentrated drainage.

[0065] The flow rate management value is a threshold value at which the flow rate of the concentrated water becomes insufficient and the adhesion of SS to the reverse osmosis membrane and the generation of scale increase significantly when the total flow rate of the concentrated water is below this value, and it may be set appropriately according to the performance of the reverse osmosis membrane device 3.

[0066] Hereinafter, a specific example of the control method by the control unit 11 will be described with reference to the flowcharts shown in FIGS. 2 to 5.

[0067] In FIG. 2, the initial state is as follows. The supply destination of the water to be treated is the second drainage channel L4. That is, the water to be treated is in a state of being discharged outside the pure water production device 1. Also, the drainage flow rate adjustment means 6 is fully open, and the circulating water flow rate adjustment means 7 is fully closed.

[0068] In step ST1-1, the TOC concentration TOCb, which is the water quality of the water to be treated, is measured by the TOC meter, which is the water quality measuring device 10, at the second measurement point P2. If TOCb is equal to or less than the water quality management value B, the process proceeds to step ST1-2. If TOCb exceeds the water quality management value B, with the supply destination of the water to be treated remaining the second drainage channel L4, step ST1-1 is repeated at a predetermined frequency.

[0069] In step ST1-2, a command is issued from the control unit 11 to the switching means 12 to switch the supply destination of the water to be treated to the first raw water tank 2 side. As a result, the pretreatment of the water to be treated by the pretreatment device 14 is started, and the treatment by the reverse osmosis membrane device 3 is started. Also, the measurement position of the water quality measuring device 10 is switched from the second measurement point P2 to the first measurement point P1. That is, the water quality of the concentrated drainage can be measured. Next, the process proceeds to step ST1-3.

[0070] In step ST1-3, at the first measurement point P1, the TOC concentration TOCa of the concentrated drainage water quality is measured by the TOC meter which is the water quality measurement device 10. When TOCa is within the water quality management range (lower limit value A1 to upper limit value A2), proceed to step ST1-4. When TOCa is outside the water quality management range, proceed to step ST2-1 in FIG. 3.

[0071] In step ST1-4, it is determined whether the flow rate FIA2 of the concentrated water measured by the first flow meter 8 is equal to or greater than the flow rate management value FIA2min. If the flow rate FIA2 of the concentrated water is equal to or greater than the flow rate management value FIA2min, assuming that the risk of reverse osmosis membrane blockage is low, return to step ST1-3. When the flow rate FIA2 of the concentrated water is less than the flow rate management value FIA2min, assuming that there is a risk of reverse osmosis membrane blockage, proceed to step ST1-5.

[0072] (Control when the flow rate of the concentrated water is less than the flow rate management value) ST1-5 to ST1-8)) In steps ST1-5 to ST1-8, control is performed to make the flow rate of the concentrated water equal to or greater than the flow rate management value.

[0073] In step ST1-5, it is confirmed whether the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%. When the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%, proceed to step ST1-6. When the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is 100% (fully open), proceed to step ST1-7.

[0074] Before reaching step ST1-6, since the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%, there is room to further increase the opening degree to increase the flow rate of the concentrated water. Therefore, in step ST1-6, the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is increased to increase the flow rate of the concentrated drainage water, and thus control is performed so that the total flow rate of the concentrated water becomes equal to or greater than the flow rate management value. After performing this control, return to step ST1-3.

[0075] On the other hand, before reaching step ST1-7, since the opening degree of the drainage flow rate adjustment means 6 (flow control valve) is 100%, it is impossible to increase the opening degree further. Therefore, in step ST1-7, the state of the circulating water flow rate adjustment means 7 (on-off valve) is checked. If the circulating water flow rate adjustment means 7 (on-off valve or flow control valve) is already fully open, after returning to the same operating conditions as at startup, the control is restarted from step ST1-1. If the circulating water flow rate adjustment means 7 (on-off valve or flow control valve) is not fully open, the process proceeds to step ST1-8.

[0076] In step ST1-8, the circulating water flow rate adjustment means 7 (on-off valve) is fully opened, and the concentrated water is returned to the first raw water tank 2 via the circulation flow path L1. Thereby, the flow rate FIA2 of the concentrated water is increased and controlled so as to be equal to or higher than the flow rate management value FIA2min. After performing this control, the process returns to step ST1-3. When the circulating water flow rate adjustment means 7 is a flow control valve, the flow rate of the concentrated water when returning the concentrated water to the first raw water tank 2 via the circulation flow path L1 may be increased. Thereby, the flow rate FIA2 of the concentrated water may be increased and controlled so as to be equal to or higher than the flow rate management value FIA2min.

[0077] Next, with reference to FIG. 3, the control when the quality of the concentrated drainage (TOC concentration TOCa) is out of the water quality management range will be described.

[0078] In step ST2-1 of FIG. 3, it is determined whether the quality of the concentrated drainage (TOC concentration TOCa) exceeds the upper limit value A2 of the water quality management range. If the TOC concentration TOCa exceeds the upper limit value A2 of the water quality management range (when A2 < TOCa), the process proceeds to step ST2-2. On the other hand, when the TOC concentration TOCa is out of the water quality management range (when TOCa < A1 or A2 < TOCa), and the TOC concentration TOCa is less than or equal to the upper limit value A2 of the water quality management range (TOCa ≤ A2), this means that the TOC concentration TOCa is less than the lower limit value A1 of the water quality management range (TOCa < A1). Therefore, in this case, the process proceeds to step ST3-1 of FIG. 4.

[0079] (Control when the quality of the concentrated drain exceeds the upper limit of the water quality management range (when A2 < TOCa) (ST2-2 to 2-5)) In steps ST2-2 to ST2-5, control is performed to return the quality of the concentrated water from a state where it exceeds the upper limit value A2 of the water quality management range (A2 < TOCa) to within the water quality management range (A1 ≤ TOCa ≤ A2). That is, control is performed to reduce the recovery rate of the permeate water to prevent clogging of the reverse osmosis membrane.

[0080] In step ST2-2, it is confirmed whether the opening degree of the drain flow rate adjustment means 6 (flow rate adjustment valve) is less than 100% (fully open). If the opening degree of the drain flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%, the process proceeds to step ST2-3. If the opening degree of the drain flow rate adjustment means 6 (flow rate adjustment valve) is 100% (fully open), the process proceeds to step ST2-4.

[0081] Before reaching step ST2-3, since the opening degree of the drain flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%, there is room to further increase the opening degree to increase the flow rate of the concentrated water. Therefore, in step ST2-3, the opening degree of the drain flow rate adjustment means 6 (flow rate adjustment valve) is increased to increase the flow rate of the concentrated drain, and thereby control is performed to lower the recovery rate of the permeate water. As a result, the quality of the concentrated water is improved (the TOC concentration TOCa decreases) and returns within the water quality management range. After performing this control, the process returns to step ST1-3.

[0082] On the other hand, before reaching step ST2-4, since the opening degree of the drain flow rate adjustment means 6 (flow rate adjustment valve) is 100%, it is impossible to further increase the opening degree. Therefore, in step ST2-4, it is confirmed whether the circulating water flow rate adjustment means 7 (on-off valve or flow rate adjustment valve) is closed. If the circulating water flow rate adjustment means 7 (on-off valve or flow rate adjustment valve) is fully open, the process proceeds to step ST2-5. If the circulating water flow rate adjustment means 7 (on-off valve or flow rate adjustment valve) is closed, after returning to the same operating conditions as at the start, the control is restarted from step ST1-1.

[0083] In step ST2-5, the return flow rate of the circulating water is decreased by the circulating water flow rate adjusting means 7 (on-off valve or flow rate adjusting valve). The return of the circulating water may be stopped. As a result, the inflow amount of the concentrated water into the water to be treated is decreased, and the deterioration of the quality of the water to be treated is suppressed. Consequently, the quality of the water to be treated is improved, and thus the quality of the concentrated water generated by the reverse osmosis membrane is improved, and the quality of the concentrated drainage returns within the water quality management range. After performing this control, the process returns to step ST1-3.

[0084] Next, with reference to FIG. 4, the control when the quality of the concentrated drainage (TOC concentration TOCa) deviates from the water quality management range will be described continuously.

[0085] As described in FIG. 2, when the TOC concentration TOCa is less than the lower limit of the water quality management range (TOC a < A1), the process proceeds to step ST3-1 in FIG. 4. After step ST3-1, control is performed to return the quality of the concentrated water from the state where it is below the lower limit of the water quality management range (TOC a < A1) to within the water quality management range (A1 ≤ TOC a ≤ A2). That is, control is performed to increase the recovery rate of the permeated water and increase the production efficiency of the permeated water.

[0086] In step ST3-1, it is confirmed whether the circulating water flow rate adjusting means 7 (on-off valve or flow rate adjusting valve) is closed. If the circulating water flow rate adjusting means 7 (on-off valve or flow rate adjusting valve) is closed, the process proceeds to step ST3-2, and if the circulating water flow rate adjusting means 7 (on-off valve or flow rate adjusting valve) is already fully open, the process proceeds to step ST3-3.

[0087] In step ST3-2, the circulating water flow rate adjusting means 7 (on-off valve) is fully opened, and the concentrated water is returned to the first raw water tank 2 via the circulation flow path L1. When the circulating water flow rate adjusting means 7 is a flow rate adjusting valve, the return flow rate of the concentrated water passing through the circulation flow path L1 may be increased. This aims to reuse the concentrated water and improve the production efficiency of the permeated water. Also, by returning the concentrated water to the first raw water tank 2, the quality of the water to be treated is deteriorated (the TOC concentration is increased), and consequently, the quality of the concentrated water generated by the reverse osmosis membrane is deteriorated (the TOC concentration TOCa is increased), so that the quality of the concentrated water is brought back within the water quality management range. After performing this control, the process returns to step ST1-3.

[0088] In step ST3-3, it is confirmed whether the opening degree of the drainage flow rate adjusting means 6 (flow rate adjusting valve) has reached the minimum (min). If the opening degree of the drainage flow rate adjusting means 6 (flow rate adjusting valve) is not the minimum (min), the process proceeds to step ST3-4. If the opening degree of the drainage flow rate adjusting means 6 (flow rate adjusting valve) is the minimum (min), after returning to the same operating conditions as at the start, the control is restarted from step ST1-1.

[0089] In step ST3-4, the opening degree of the drainage flow rate adjusting means 6 (flow rate adjusting valve) is decreased. This increases the flow rate of the concentrated water flowing through the circulation flow path L1. This aims to reuse the concentrated water and improve the production efficiency of the permeated water. Also, by returning the concentrated water to the first raw water tank 2, the quality of the water to be treated is deteriorated (the TOC concentration is increased), and consequently, the quality of the concentrated water is deteriorated (the TOC concentration TOCa is increased), so that the quality of the concentrated water is brought back within the water quality management range. After performing this control, the process returns to step ST1-3.

[0090] Furthermore, when the quality of the water to be treated at the first measurement point P1 measured by the water quality measuring device 10 exceeds the water quality management value, and / or when the total flow rate of the concentrated water generated in the reverse osmosis membrane device 3 becomes less than the flow rate management value, at least in either case, the control unit 11 controls the switching means 12 to send the total amount of the water to be treated to the second drainage flow path L4 by controlling either one or both of the drainage flow rate adjusting means 6 and the circulating water flow rate adjusting means 7.

[0091] Next, with reference to FIGS. 5 and 6, when ensuring the quality of the permeate water of the reverse osmosis membrane, that is, for the control to prevent the quality of the permeate water of the reverse osmosis membrane from deteriorating beyond a preset predetermined value, an explanation will be given. In this control, the solute concentration on the membrane surface in the reverse osmosis membrane is estimated. When the solute concentration on the membrane surface exceeds the management concentration value, the flow rate of the concentrated drain water is increased and the flow rate of the circulating water is decreased to reduce the recovery rate, thereby performing control to prevent the quality of the permeate water from deteriorating.

[0092] The flowchart shown in FIG. 5 has a step ST4-1 for determining whether the solute concentration on the membrane surface exceeds the management concentration value between step ST1-2 and step ST1-3. Since the flowchart shown in FIG. 5 is the same as the flowchart shown in FIG. 2 except for including step ST4-1, the description of steps other than step ST4-1 will be omitted.

[0093] In step ST4-1 of FIG. 5, in the control unit 11, the solute concentration TOCx on the membrane surface is estimated, and it is determined whether TOCx exceeds the management concentration value X. When the solute concentration TOCx on the membrane surface is less than or equal to the management concentration value X, the process proceeds to step ST1-3. Thereafter, the same control as the control described above is performed. On the other hand, when the solute concentration TOCx on the membrane surface exceeds the management concentration value X, the process proceeds to step ST5-1 of FIG. 6.

[0094] Note that the solute concentration TOCx on the membrane surface is obtained by the following equations (1) and (2).

[0095] TOCx (ppm) = TOCc × (ln(1 / (1 - R / 100))) / (R / 100) …(1) R (%) = (1 - TOCc / TOCa) × 100 …(2)

[0096] In the above formula (1), TOCx is the solute concentration on the membrane surface, TOCc is the solute concentration (TOC concentration) of the water to be treated immediately before the reverse osmosis membrane, and R is the rejection rate (%) obtained by formula (2). Also, in the above formula (2), R(%) is the rejection rate, TOCc is the solute concentration (TOC concentration) of the water to be treated immediately before the reverse osmosis membrane, and TOCa is the solute concentration (TOC concentration) in the concentrated water.

[0097] When the solute concentration TOCx on the membrane surface exceeds the control concentration value X, there is a risk that the quality of the permeate water deteriorates in the reverse osmosis membrane, so proceed to ST5-1 in Fig. 6. In steps ST5-1 to ST5-4 in Fig. 6, the recovery rate is further decreased by reducing the flow rate of the circulating water.

[0098] That is, in step ST5-1 of Fig. 6, it is confirmed whether the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is less than 100% (fully open). If the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%, proceed to step ST5-2. If the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is 100% (fully open), proceed to step ST5-3.

[0099] Before reaching step ST5-2, since the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is less than 100%, there is room to further increase the opening degree to increase the flow rate of the concentrated water. Therefore, in step ST5-3, the opening degree of the drainage flow rate adjustment means 6 (flow rate adjustment valve) is increased to increase the flow rate of the concentrated drainage, and thereby control is performed to lower the recovery rate of the permeate water. As a result, the quality of the permeate water is improved. After performing this control, proceed to step ST1-3.

[0100] On the other hand, before reaching step ST5-3, since the opening degree of the drainage flow rate adjusting means 6 (flow control valve) is 100%, it is impossible to increase the opening degree further. Therefore, in step ST5-3, it is confirmed whether the circulating water flow rate adjusting means 7 (on-off valve) is closed. If the circulating water flow rate adjusting means 7 (on-off valve or flow control valve) is fully open, the process proceeds to step ST5-4. If the circulating water flow rate adjusting means 7 (on-off valve or flow control valve) is closed, after returning to the same operating conditions as at the start, the control is restarted from step ST1-1.

[0101] In step ST5-4, the circulating water flow rate adjusting means 7 (on-off valve or flow control valve) is fully closed to stop the return of the circulating water, or the flow rate of the circulating water is decreased. As a result, the return amount of the concentrated water to the water to be treated is decreased, the deterioration of the water quality of the water to be treated is suppressed, and ultimately the water quality of the permeated water is improved. After performing this control, the process proceeds to step ST1-3.

[0102] As described above, the case where the water quality of the measurement target is total organic carbon has been described as an example. However, the present invention is not limited to this, and it may be implemented with other water quality items as the measurement target. In the above embodiment, the water quality at the first measurement point P1 and the second measurement point P2 is measured using one water quality measurement device 10. However, water quality measurement devices may be provided at the first measurement point P1 and the second measurement point P2, respectively.

[0103] As described above, according to the pure water production apparatus 1 of the present embodiment, the control unit 11 controls either one or both of the drainage flow rate adjusting means 6 or the circulating water flow rate adjusting means 7 so that the water quality of the concentrated water is maintained within the water quality management range, thereby controlling the flow rate of the concentrated water and changing the recovery rate of the reverse osmosis membrane device 3. Therefore, the recovery rate can be appropriately changed according to the water quality of the water to be treated.

[0104] Further, since the control unit 11 controls either or both of the drainage flow rate adjustment means 6 and the circulating water flow rate adjustment means 7 so that the total flow rate FIA2 of the concentrated water becomes equal to or higher than the flow rate management value FIA2min, it is possible to secure a flow rate of the concentrated water of a certain level or higher and prevent the occurrence of concentration polarization on the membrane surface of the reverse osmosis membrane.

[0105] Also, according to the pure water production apparatus 1 of the present embodiment, when the water quality of the concentrated water deviates from the water quality management range, the recovery rate of the reverse osmosis membrane is controlled by adjusting the discharge flow rate of the concentrated water or controlling the circulation of the concentrated water. Further, when the total flow rate of the concentrated water is less than the flow rate management value, the occurrence of polarization on the surface of the reverse osmosis membrane is suppressed by increasing the flow rate of the concentrated water. Therefore, it is possible to increase the amount of produced permeated water while suppressing a decrease in the water quality of the permeated water.

[0106] Also, according to the pure water production apparatus 1 of the present embodiment, a second drainage channel L4 branched from the supply channel L3 and a switching means 12 are provided. When the water quality of the water to be treated exceeds the water quality management value B, the entire amount of the water to be treated is not sent to the reverse osmosis membrane device 3 but discharged to the outside from the second drainage channel L4. Thus, it is possible to prevent the water to be treated with deteriorated water quality from flowing into the reverse osmosis membrane, suppress clogging of the reverse osmosis membrane, and reduce the frequency of cleaning of the reverse osmosis membrane device 3. Further, since the water quality measuring device 10 can switch the measurement position to the first measurement point P1 or the second measurement point P2, the recovery rate can be efficiently managed and controlled.

[0107] Also, when the water quality of the water to be treated at the first measurement point measured by the water quality measuring device 10 exceeds the water quality management value, or when at least one of the cases where the total flow rate of the concentrated water generated in the reverse osmosis membrane device 3 becomes less than the flow rate management value occurs, by controlling either or both of the drainage flow rate adjustment means 6 and the circulating water flow rate adjustment means 7, the switching means 12 is controlled so that the entire amount of the water to be treated is sent to the second drainage channel L4. Therefore, clogging of the reverse osmosis membrane in the reverse osmosis membrane device 3 can be suppressed, and the frequency of the reverse washing operation can be reduced.

[0108] Further, according to the pure water production apparatus 1 of the present embodiment, when the water quality of the water to be treated is below the water quality management value, the entire amount of the water to be treated can be sent to the reverse osmosis membrane apparatus 3, and the production amount of the permeated water can be increased.

[0109] Further, according to the pure water production apparatus 1 of the present embodiment, when sending the entire amount of the water to be treated to the first raw water tank 2, the measurement position of the water quality measurement apparatus 10 is set to the first measurement point P1, and when sending it to the second drainage channel L4, the measurement position of the water quality measurement apparatus 10 is set to the second measurement point P2. Therefore, the water quality measurement apparatus 10 can be used efficiently.

[0110] Further, according to the pure water production apparatus 1 of the present embodiment, the membrane surface solute concentration on the primary side of the reverse osmosis membrane is estimated. When the membrane surface solute concentration exceeds the management concentration value, in order to further reduce the recovery rate of the reverse osmosis membrane apparatus 3, the return flow rate of the concentrated water through the circulation channel L1 is decreased. Therefore, even when the water quality of the water to be treated deteriorates, a decrease in the water quality of the permeated water can be suppressed, and high-purity pure water can be produced.

[0111] According to the method for producing pure water of the present embodiment, the recovery rate of the reverse osmosis membrane apparatus 3 is changed by adjusting the flow rate of the concentrated water in the circulation channel L1 or the flow rate of the concentrated water in the first drainage channel L2 so that the water quality of the concentrated water is maintained within the water quality management range. Therefore, the recovery rate can be changed according to the water quality of the water to be treated. Further, by adjusting the flow rate of the concentrated water in the circulation channel L1 or the flow rate of the concentrated water in the first drainage channel L2 so that the total flow rate FIA2 of the concentrated water is equal to or greater than the flow rate management value FIA2min, it becomes possible to ensure that the flow rate of the concentrated water is equal to or greater than a certain value and prevent the occurrence of concentration polarization on the membrane surface of the reverse osmosis membrane.

[0112] Further, according to the method for producing pure water of the present embodiment, when the water quality of the concentrated water deviates from the water quality management range, the flow rate of the concentrated water in the first drainage channel L2 is increased or decreased, or the return flow rate of the concentrated water through the circulation channel L1 is controlled to control the recovery rate of the reverse osmosis membrane. Also, when the total flow rate of the concentrated water is less than the flow rate management value, the total flow rate of the concentrated water is increased to suppress the occurrence of concentration polarization on the surface of the reverse osmosis membrane. Therefore, it is possible to increase the amount of produced permeate water while suppressing a decrease in the water quality of the permeate water.

[0113] Further, according to the method for producing pure water of the present embodiment, when the water quality of the water to be treated exceeds the water quality management value, the total amount of the water to be treated is not sent to the reverse osmosis membrane but discharged to the outside through the second drainage channel L4. Therefore, it is possible to prevent the water to be treated with deteriorated water quality from flowing into the reverse osmosis membrane, suppress the clogging of the reverse osmosis membrane, and reduce the frequency of cleaning of the reverse osmosis membrane.

[0114] Also, when at least one of the cases where the water quality of the water to be treated at the first measurement point P1 exceeds the water quality management value or the total flow rate of the concentrated water generated in the reverse osmosis membrane is less than the flow rate management value occurs, the total amount of the water to be treated is controlled to be sent to the second drainage channel L4. Therefore, the clogging of the reverse osmosis membrane can be suppressed, and the frequency of the reverse washing operation can be reduced.

[0115] Further, according to the method for producing pure water of the present embodiment, when the water quality of the water to be treated is equal to or less than the water quality management value, the total amount of the water to be treated can be sent to the reverse osmosis membrane, and the amount of produced permeate water can be increased.

[0116] Further, according to the method for producing pure water of the present embodiment, the solute concentration on the membrane surface on the primary side of the reverse osmosis membrane is estimated. When the solute concentration on the membrane surface exceeds the management concentration value, the return flow rate of the concentrated water through the circulation channel L1 is decreased to further lower the recovery rate of the reverse osmosis membrane. Therefore, even when the water quality of the water to be treated deteriorates, a decrease in the water quality of the permeate water can be suppressed, and high-purity pure water can be produced.

Explanation of Reference Numerals

[0117] 1... Pure water manufacturing device, 2... First raw water tank (raw water tank), 3... Reverse osmosis membrane device, 6... Flow rate adjustment valve (drainage flow rate adjustment means), 7... On-off valve (circulating water flow rate adjustment means), 8... First flow meter (flow meter), 10... Water quality measurement device, 11... Control unit, 12... Switching means, L3... Supply flow path, L1... Circulation flow path, L2... First drainage flow path, L4... Second drainage flow path, P1... First measurement point, P2... Second measurement point.

Claims

1. A raw water tank for storing the water to be treated, A reverse osmosis membrane device arranged on the downstream side of the raw water tank, for generating permeate water and concentrated water by treating the water to be treated with a reverse osmosis membrane, A circulation flow path that enables a part of the concentrated water to be returned to the raw water tank, A first drainage flow path for discharging the remaining part of the concentrated water to the outside, Drainage flow rate adjustment means for adjusting the flow rate of the concentrated water in the first drainage flow path, Circulating water flow rate adjustment means for adjusting the flow rate of the concentrated water in the circulation flow path, A flow meter for measuring the total flow rate of the concentrated water generated in the reverse osmosis membrane device, A first measurement point provided in the first drainage flow path and serving as the measurement position of the water quality of the concentrated water, A water quality measurement device capable of measuring the water quality of the concentrated water at the first measurement point, Based on the water quality of the concentrated water at the first measurement point measured by the water quality measurement device and the total flow rate of the concentrated water measured by the flow meter, so that the water quality of the concentrated water is maintained within the water quality management range, and the total flow rate of the concentrated water is equal to or greater than the flow rate management value, a control unit having a function of controlling either or both of the drainage flow rate adjustment means or the circulating water flow rate adjustment means, A pure water production device comprising the above.

2. The function of the control unit is, When the water quality of the concentrated water falls below the lower limit of the water quality management range, to control either or both of the drainage flow rate adjustment means or the circulating water flow rate adjustment means so as to increase the return flow rate of the concentrated water through the circulation flow path, When the water quality of the concentrated water exceeds the upper limit of the water quality management range, to control either or both of the drainage flow rate adjustment means or the circulating water flow rate adjustment means so as to decrease the return flow rate of the concentrated water through the circulation flow path, When the total flow rate of the concentrated water generated in the reverse osmosis membrane device is less than the flow rate management value, it is a function of controlling either or both of the drainage flow rate adjustment means or the circulating water flow rate adjustment means so as to increase the total flow rate of the concentrated water. The pure water production device according to Claim 1.

3. A supply flow path for sending the water to be treated to the raw water tank, A second measurement point provided in the supply flow path and serving as the measurement position of the water quality of the water to be treated, A second drainage flow path branched from the supply flow path between the second measurement point and the raw water tank, enabling the water to be treated to be discharged to the outside. switching means for making it possible to switch the supply destination of the water to be treated to the raw water tank or the second drainage channel; the water quality measuring device is configured to be able to switch the measurement position to the first measurement point or the second measurement point; The control unit controls either one or both of the drainage flow rate adjusting means or the circulating water flow rate adjusting means, and when the water quality of the water to be treated at the first measurement point measured by the water quality measuring device exceeds the water quality control value, and when the total flow rate of the concentrated water generated in the reverse osmosis membrane device is less than the flow rate control value, the control unit further has a function of controlling the switching means so as to send the total amount of the water to be treated to the second drainage channel. The pure water production device according to claim 1.

4. The control unit further has a function of controlling the switching means so as to send the total amount of the water to be treated to the raw water tank when the water quality of the water to be treated at the second measurement point measured by the water quality measuring device is equal to or less than the water quality control value. The pure water production device according to claim 3.

5. When the control unit sends the total amount of the water to be treated to the raw water tank, the control unit further has a function of setting the measurement position of the water quality measuring device to the first measurement point, and when sending the total amount of the water to be treated to the second drainage channel, setting the measurement position of the water quality measuring device to the second measurement point. The pure water production device according to claim 3 or claim 4.

6. The control unit estimates the solute concentration on the primary side of the reverse osmosis membrane, and when the solute concentration on the primary side of the reverse osmosis membrane exceeds the control concentration value, the control unit further has a function of controlling either one or both of the drainage flow rate adjusting means or the circulating water flow rate adjusting means so as to reduce the return flow rate of the concentrated water through the circulation channel. The pure water production device according to any one of claims 1 to 4.

7. The control unit estimates the solute concentration on the primary side of the reverse osmosis membrane, and when the solute concentration on the primary side of the reverse osmosis membrane exceeds the control concentration value, the control unit further has a function of controlling either one or both of the drainage flow rate adjusting means or the circulating water flow rate adjusting means so as to reduce the return flow rate of the concentrated water through the circulation channel. The pure water production device according to claim 5.

8. A method for producing pure water, which generates permeated water and concentrated water by treating water to be treated with a reverse osmosis membrane, takes out the permeated water as pure water, makes part of the concentrated water supplyable to the primary side of the reverse osmosis membrane through a circulation channel, and discharges the remainder of the concentrated water to the outside through a first drainage channel, comprising: measuring the water quality of the concentrated water and measuring the total flow rate of the concentrated water generated by the reverse osmosis membrane, and adjusting the flow rate of the concentrated water in the circulation channel or the flow rate of the concentrated water in the first drainage channel so that the water quality of the concentrated water is maintained within a water quality management range and the total flow rate of the concentrated water is equal to or greater than a flow rate management value.

9. When the water quality of the concentrated water is below the lower limit of the water quality management range, increasing the return flow rate of the concentrated water through the circulation channel; When the water quality of the concentrated water exceeds the upper limit of the water quality management range, decreasing the return flow rate of the concentrated water through the circulation channel; The method for producing pure water according to claim 8, wherein when the total flow rate of the concentrated water generated by the reverse osmosis membrane is less than the flow rate management value, increasing the total flow rate of the concentrated water.

10. The method for producing pure water according to claim 8, wherein when at least one of the case where the water quality of the water to be treated measured upstream of the reverse osmosis membrane exceeds a water quality management value and the case where the total flow rate of the concentrated water generated by the reverse osmosis membrane is less than the flow rate management value occurs, discharging the total amount of the water to be treated to the outside through a second drainage channel without sending it to the reverse osmosis membrane.

11. The method for producing pure water according to claim 10, wherein when the water quality of the water to be treated measured upstream of the reverse osmosis membrane is equal to or less than a water quality management value, sending the total amount of the water to be treated to the primary side of the reverse osmosis membrane.

12. The method for producing pure water according to any one of claims 8 to 11, wherein estimating the membrane surface solute concentration on the primary side of the reverse osmosis membrane, and when the membrane surface solute concentration exceeds a management concentration value, decreasing the return flow rate of the concentrated water through the circulation channel.

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