Water treatment apparatus and its operation method

Abstract

The present invention provides a water treatment device that can appropriately control the operating conditions of a reverse osmosis membrane device in response to changes in the mixing ratio of a mixture of two or more types of water. [Solution] The water treatment device 1 includes a first confluence section (2) where two or more types of water merge and discharge a first mixed water; a second confluence section (41) where two or more types of water, including the first mixed water discharged from the first confluence section, merge and discharge a second mixed water; a reverse osmosis membrane device 52 that separates the water, including the second mixed water discharged from the second confluence section, into permeate and concentrated water; a first concentration detection means (8) located upstream of the second confluence section for detecting the concentration of a specific component contained in the first mixed water; and a control unit 10 that controls the operating conditions of the reverse osmosis membrane device 52 based on the detected value of the first concentration detection means.

Description

Technical Field

[0001] The present invention relates to a water treatment apparatus and an operation method thereof.

Background Art

[0002] In the manufacturing processes of semiconductor devices and liquid crystal display devices, pure water and ultrapure water are used for applications such as washing water. Pure water and ultrapure water are produced by removing impurities (for example, organic substances, ionic components, fine particles, bacteria, etc.) contained in raw water. In recent years, from the perspective of water resource depletion, in the production of pure water and ultrapure water, in addition to tap water and industrial water, reclaimed water obtained by treating domestic sewage (sewage) and reusing it, or recovered water obtained by treating and reusing industrial wastewater, etc. are used as raw water to effectively utilize water resources.

[0003] FIG. 1 shows an example of a water treatment apparatus that treats two types of raw water with different water qualities to produce pure water. The water treatment apparatus 100 includes a raw water tank 2 to which tap water and reclaimed water are supplied as raw water. A pump 3, a pretreatment system 4, and a primary pure water system 5 are provided downstream of the raw water tank 2. The pretreatment system 4 includes, for example, a filtration device 40, a filtration water tank 41, a pump 42, a K tower 44, and a decarbonation device 45. The primary pure water system 5 includes, for example, an RO raw water tank 50, pumps 51a to 51c, an RO membrane device 52, an EDI raw water tank 53, an electrically regenerative deionization device (EDI) 54, and a B-RO (brine reverse osmosis) raw water tank 55. The RO membrane device 52 includes two RO membrane devices 52a, 52b and a B-RO membrane device 52c.

[0004] The mixed water of tap water and recycled water stored in the raw water tank 2 is treated in the filtration device 40 and then stored in the hydrogenated water tank 41. Recovered water is supplied to the filtered water tank 41 from an external source. The water stored in the filtered water tank 41 is treated in the K tower 44 and the decarbonation device 45 and then stored in the RO raw water tank 50 as RO raw water. The water stored in the RO raw water tank 50 is supplied to the RO membrane device 52a. In the RO membrane device 52a, the permeate is supplied to the RO membrane device 52b, and the concentrated water is stored in the B-RO raw water tank 55. In the RO membrane device 52b, the permeate is stored in the EDI raw water tank 53, and the concentrated water is returned to the RO raw water tank 50. The water stored in the B-RO raw water tank 55 is treated in the B-RO membrane device 52c, and the permeate from the B-RO membrane device 52c is returned to the filtered water tank 41. The water stored in EDI raw water tank 53 is treated in EDI 54.

[0005] Conductivity meter 6 measures the conductivity of the water supplied from the B-RO raw water tank 55 to the B-RO membrane unit 52c. Conductivity meter 7 measures the conductivity of the concentrated water in the B-RO raw water tank 55. Based on the measurements from these conductivity meters 6 and 7, the operating conditions of the B-RO membrane unit 52c are controlled. For example, if the conductivity of either the supply water or the concentrated water becomes high, the recovery rate of the B-RO membrane unit 52c is reduced.

[0006] As a related technology, Patent Document 1 describes a pure water production apparatus comprising a first RO membrane apparatus, a second RO membrane apparatus to which permeate water from the first RO membrane apparatus is supplied, an EDI to which permeate water from the second RO membrane apparatus is supplied, and a third RO membrane apparatus to which concentrated water from the first RO membrane apparatus is supplied via a brine tank. The water recovery rate is improved by returning the permeate water from the third RO membrane apparatus to the upstream side of the first RO membrane apparatus.

[0007] Patent Document 2 describes a reverse osmosis membrane system comprising a first RO membrane apparatus, a second RO membrane apparatus supplied with permeate from the first RO membrane apparatus, and an electrodeionizer supplied with permeate from the second RO membrane apparatus, wherein concentrated water from the second RO membrane apparatus is returned to the upstream side of the first RO membrane apparatus. Scale failure in the first RO membrane apparatus is prevented by controlling the flow rate of concentrated water from the first RO membrane apparatus based on the conductivity of the water supplied to the first RO membrane apparatus. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-146618 [Patent Document 2] Japanese Patent Publication No. 2020-131087 [Overview of the project] [Problems that the invention aims to solve]

[0009] Tap water contains certain components (silica, aluminum, TOC (total organic carbon), etc.) that can cause RO membrane clogging, and has a higher ion load (higher conductivity) compared to recycled water, thus posing a higher risk of RO membrane clogging. In the water treatment device 100, mixed water, which is typically a mixture of tap water and recycled water in a predetermined ratio, is used as the raw water, and the operating conditions of the B-RO membrane device 52c are set according to this mixing ratio (the proportion of tap water in the raw water). If the supply amount of tap water or recycled water changes, the mixing ratio changes, which will have a significant impact on RO membrane clogging. Therefore, it is necessary to detect changes in the mixing ratio and appropriately control the operating conditions of the B-RO membrane device 52c.

[0010] However, in the water treatment device 100, the conductivity meter 6 is located at the inlet of the B-RO membrane device 52c and is not configured to directly measure the conductivity of the mixed water of tap water and recycled water. This leads to the following problems.

[0011] The mixture of tap water and recycled water undergoes pretreatment in a filtration device 40, a K tower 44, a decarbonation device 45, and other devices before being supplied to a B-RO membrane device 52c via an RO membrane device 52a. During this pretreatment process, the mixture is mixed with the permeate and recovered water from the B-RO membrane device 52c. Since both the permeate and recovered water from the B-RO membrane device 52c have lower conductivity than tap water, mixing these permeate and recovered waters dilutes the tap water-recycled water mixture, reducing the concentration of certain components in the tap water. This dilution changes the mixing ratio of the tap water-recycled water mixture.

[0012] Furthermore, in tower K 44, H is converted by ion exchange resin. + The calcium components in the water are exchanged with the treated water, and H + Water rich in H + (Water with a high concentration of H) is produced. + Because water with a high concentration of H has high conductivity, the conductivity of treated water changes when ion exchange occurs. + The change in conductivity due to the source of the water makes it difficult to see the change in conductivity due to the ratio of tap water to recycled water in the mixture of tap water and recycled water.

[0013] Therefore, because the conductivity meter 6 is affected by dilution and changes in conductivity in the pretreatment system, it is difficult to determine the change in the mixing ratio of tap water and recycled water based on the measurements of the conductivity meter 6.

[0014] In addition, even at levels of a few ppb to tens of ppb, the concentration of certain components, particularly aluminum, significantly affects the RO membrane clogging rate of the RO membrane system 52, especially the B-RO membrane system 52c. Therefore, if there is a difference in the aluminum concentration of the two types of raw water, for example, if the aluminum concentration of one type of water is 10-50 ppb and the aluminum concentration of the other type of water is 10 ppb or less, changes in the mixing ratio have a significant impact on RO membrane operation.

[0015] The problem that it is difficult to detect changes in the mixing ratio of tap water and recycled water due to the effects of dilution and changes in conductivity in the aforementioned pretreatment system was discovered for the first time by the inventors of this invention after diligent research, and such a problem had not been considered until now. Naturally, no technical concept regarding the above problem is disclosed in either Patent Document 1 or 2. Therefore, it is difficult to resolve the above problem using the technologies described in Patent Documents 1 and 2.

[0016] It should be noted that the above problem is not limited to a mixture of tap water and recycled water. The same problem occurs when using a mixture of two or more types of water as the raw water source.

[0017] The object of the present invention is to solve the above problems and to provide a water treatment apparatus and a method for operating the reverse osmosis membrane apparatus that can appropriately control the operating conditions of a reverse osmosis membrane apparatus in accordance with changes in the mixing ratio of mixed water obtained by mixing two or more types of water. [Means for solving the problem]

[0018] To achieve the above objective, the water treatment apparatus of the present invention comprises: a first confluence section where two or more types of water merge and discharge a first mixed water; a second confluence section where two or more types of water, including the first mixed water discharged from the first confluence section, merge and discharge a second mixed water; a reverse osmosis membrane apparatus that separates the water, including the second mixed water discharged from the second confluence section, into permeate and concentrated water; a first concentration detection means arranged upstream of the second confluence section for detecting the concentration of a specific component contained in the first mixed water; and a control unit that controls the operating conditions of the reverse osmosis membrane apparatus based on the detected value of the first concentration detection means.

[0019] The operation method of the water treatment apparatus of the present invention is such that two or more types of water merge, a first merging section that discharges a first mixed water, and two or more types of water including the first mixed water discharged from the first merging section merge, and a second merging section that discharges a second mixed water, and a reverse osmosis membrane apparatus that separates water including the second mixed water discharged from the second merging section into permeate water and concentrated water, and is an operation method of a water treatment apparatus having: detecting a concentration of a specific component contained in the first mixed water upstream of the second merging section, and controlling an operation condition of the reverse osmosis membrane apparatus based on a detection value of the concentration of the specific component.

Advantages of the Invention

[0020] According to the present invention, it is possible to appropriately control the operation conditions of the reverse osmosis membrane apparatus according to changes in the mixing ratio of the mixed water obtained by mixing two or more types of water.

Brief Description of the Drawings

[0021] [Figure 1] It is a block diagram showing an example of a water treatment apparatus for treating two types of raw water with different water qualities to produce pure water. [Figure 2] It is a block diagram showing the configuration of the water treatment apparatus according to the first embodiment of the present invention. [Figure 3] It is a schematic diagram showing the detailed configuration of the portion surrounded by the broken line A in FIG. 2. [Figure 4] It is a block diagram showing the configuration of the water treatment apparatus according to the second embodiment of the present invention.

Modes for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiments are merely examples, and are not intended to limit the scope of the present invention thereto.

[0023] (First Embodiment) Figure 2 is a block diagram showing the configuration of a water treatment apparatus according to the first embodiment of the present invention. In Figure 2, solid arrows indicate piping (or flow paths), and dashed arrows indicate signal lines (or signals). At the intersection of two pipes, for convenience, the solid line representing one of the pipes is shown as broken.

[0024] Referring to Figure 2, the water treatment apparatus 1 of this embodiment includes a raw water tank 2 to which tap water and recycled water are supplied as raw water. Downstream of the raw water tank 2, a pump 3, a pretreatment system 4, and a primary pure water system 5 are provided. The raw water tank 2 can be called a first storage tank. The pretreatment system 4 and the primary pure water system 5 are the same as those shown in Figure 1. Hereinafter, each component of the pretreatment system 4 and the primary pure water system 5 will be described in detail.

[0025] In the pretreatment system 4, the raw water tank 2 is connected to the filtration device 40 via piping, and a pump 3 is installed in this piping. The filtration device 40 is connected to the filtered water tank 41 via piping. The filtered water tank 41 is connected to the K tower 44 via piping, and a pump 42 is installed in this piping. The K tower 44 is connected to the decarbonation device 45 via piping. The decarbonation device 45 is connected to the RO raw water tank 50 via piping. The filtered water tank 41 can be called a second storage tank.

[0026] By operating pumps 3 and 42, the mixed water stored in the raw water tank 2 can be passed through the filtration device 40, the filtered water tank 41, the K tower 44, and the decarbonation device 45. The filtration device 40 filters the water to be treated using filter media (for example, sand). The K tower 44 is filled with ion exchange resin (in this case, cation exchange resin) and removes cation components by ion exchange. In this ion exchange, for example, H + The calcium components in the water are exchanged with the treated water, and H + Water rich in H + Water with a high concentration of [unclear] is produced. The decarbonation device 45, for example, uses a decarbonation membrane through which gas can pass to degas (remove) carbon dioxide from the treated water from the K tower 44.

[0027] In addition, the unit devices that perform unit operations in the pretreatment system 4 are not limited to the configuration shown in the figure. For example, unit devices such as a turbidity removal membrane device or a softening device (an alkaline softening device that removes hardness components by adding an alkaline agent) may be used as needed to remove turbidity from the raw water. Furthermore, a decarbonation tower that removes carbon dioxide components from water by bringing pH-acidified water into contact with air may be used as the decarbonation device 45. Each unit device in the pretreatment system 4 can be called a water quality adjustment means. The water quality adjustment means may include a pH adjustment means that adjusts the pH by adding an acid or alkaline agent.

[0028] In the primary pure water system 5, the RO raw water tank 50 is connected to the RO membrane device 52a via piping, and a pump 51a is installed in this piping. By operating the pump 51a, the RO raw water (water to be treated) stored in the RO raw water tank 50 is supplied to the RO membrane device 52a.

[0029] RO membrane system 52a can be called a first reverse osmosis membrane system that separates the water to be treated into a first permeate and a first concentrated water. RO membrane system 52a is configured, for example, to have one or more reverse osmosis membrane elements and to remove impurities from the RO raw water using reverse osmosis. RO membrane system 52a discharges the permeate that has passed through the reverse osmosis membrane and the concentrated water containing the impurities separated by the reverse osmosis membrane. The permeate from RO membrane system 52a is supplied to RO membrane system 52b. RO membrane system 52b has the same structure as RO membrane system 52a and discharges the permeate and concentrated water, respectively. A booster pump, a decarbonation device, a degassing device, an ultraviolet irradiation device, a chemical injection device, etc., may be placed between pump 51a and RO membrane system 52b.

[0030] The concentrated water discharge side of the RO membrane unit 52a is connected to the B-RO raw water tank 55 via piping. The B-RO raw water tank 55 stores the concentrated water from the RO membrane unit 52a as B-RO raw water. The B-RO raw water tank 55 is connected to the B-RO membrane unit 52c via piping, and a pump 51c is installed in this piping. The B-RO membrane unit 52c can be called a second reverse osmosis membrane unit that separates the water to be treated into a second permeate and a second concentrated water. By operating the pump 51c, the stored water (B-RO raw water) from the B-RO raw water tank 55 is supplied to the B-RO membrane unit 52c. The B-RO membrane unit 52c has the same structure as the RO membrane unit 52a and discharges permeate and concentrated water, respectively. The permeate discharge side of the B-RO membrane unit 52c is connected to the filtered water layer 41 via piping.

[0031] The permeate discharge side of the RO membrane unit 52b is connected to the EDI raw water tank 53 via piping. The EDI raw water tank 53 stores the permeate from the RO membrane unit 52b as EDI raw water. The EDI raw water tank 53 is connected to the EDI 54 via piping, and a pump 51b is installed in this piping. By operating the pump 51b, the stored water (EDI raw water) from the EDI raw water tank 53 is supplied to the EDI 54. The concentrated water discharge side of the RO membrane unit 52b is connected to the RO raw water tank 50 via piping.

[0032] The EDI 54 removes ions from the permeate supplied from the RO membrane unit 52b via the EDI raw water tank 53 to produce treated water (primary pure water), and also discharges concentrated water and electrode water containing the removed ions. Specifically, the EDI 54 has alternating desalination chambers and concentration chambers, which are separated by alternating anion exchange membranes and cation exchange membranes. The desalination chambers contain ion exchange resin. Ions in the permeate are trapped by the ion exchange resin and collected in the concentration chamber by an electric field, and then discharged as concentrated water. The concentrated water discharge side of the EDI 54 is connected to the RO raw water tank 50 via piping.

[0033] In addition, the unit devices used for unit operations in the pretreatment system 4 and the primary pure water system 5 are not limited to the configuration shown in the diagram. For example, unit devices such as activated carbon units, 2B3T (two-bed, three-column ion exchange system), ultraviolet irradiation units, multi-bed pure water systems (SBP), and deaeration units may be used as needed. Furthermore, the K column 44 and decarboxylation unit 45 shown in the diagram are not necessarily required and can be selected as appropriate depending on the required water quality. For example, if the K column 44 is bypassed, the decarboxylation efficiency can be increased by adding an acidifying agent at the inlet of the decarboxylation unit 45 to adjust the pH to 2-4. Furthermore, a subsystem for producing ultrapure water from primary pure water may be provided downstream of the primary pure water system 5. Subsystem 1b can remove trace amounts of ions and TOC (total organic carbon) that could not be removed by the primary pure water system 5, as well as ions and TOC eluted from system components after the primary pure water system 5.

[0034] In addition to the above configuration, the water treatment apparatus 1 of this embodiment includes a conductivity meter 8 and a control unit 10. The conductivity meter 8 is installed in the piping between the raw water tank 2 and the filtration device 40. The conductivity meter 8 detects the conductivity of the raw water (first mixed water obtained by mixing tap water and recycled water) discharged from the raw water tank 2. The conductivity meter 8 can be called a first concentration detection means that detects the concentration of a specific component contained in the first mixed water. In the operation method of the water treatment apparatus 1, the control unit 10 controls the operating conditions of the reverse osmosis membrane device 52 based on the detected value of the conductivity meter 8. Here, the control unit 10 controls the operating conditions of the B-RO membrane device 52c based on the detected value of the conductivity meter 8.

[0035] The control of the operating conditions of the B-RO membrane apparatus 52c by the control unit 10 will be described in detail below. Figure 3 is a schematic diagram showing the detailed configuration of the area enclosed by the dashed line A, including the B-RO membrane device 52c shown in Figure 2. As shown in Figure 3, in addition to the pump 51c, pressure regulating automatic valves 11a to 11c and a chemical injection device 12 are provided as elements related to the operating conditions of the B-RO membrane device 52c. Pressure regulating automatic valve 11a is provided in the piping between the B-RO membrane device 52c and the pump 51c. One end of a branch pipe is connected to the piping between the pressure regulating automatic valve 11a and the pump 51c. The other end of the branch pipe is connected to the piping connected to the concentrated water discharge side of the B-RO membrane device 52c. This branch pipe is a bypass pipe and is equipped with a pressure regulating automatic valve 11c. Pressure regulating automatic valve 11b is provided in the piping connected to the concentrated water discharge side of the B-RO membrane device 52c. The chemical injection device 12 injects chemicals into the B-RO raw water supplied to the B-RO membrane device 52c. The chemicals used include dispersants and acidulants.

[0036] The control unit 10 can individually control the operation of the pressure regulating automatic valves 11a to 11c, the pump 51c, and the chemical dispensing device 12. When the value detected by the conductivity meter 8 exceeds a first threshold, the control unit 10 controls the operating conditions of the B-RO membrane system 52c by controlling the necessary elements among the pressure regulating automatic valves 11a to 11c, the pump 51c, and the chemical dispensing device 12. The first threshold is preferably set appropriately considering the risk of RO membrane blockage and appropriate operating conditions for the B-RO membrane system 52c.

[0037] Adjusting the operating conditions of the B-RO membrane system 52c includes the following operational controls. (1) Recovery rate of B-RO membrane system 52c Under normal conditions, the pressure regulating automatic valves 11a and 11b are open, and the pressure regulating automatic valve 11c is closed, and B-RO raw water is supplied to the B-RO membrane device 52c at a predetermined flow rate (Flux). When the value detected by the conductivity meter 8 exceeds a first threshold, the control unit 10 determines that the proportion of tap water has increased and reduces the recovery rate of the B-RO membrane device 52c. The recovery rate can be reduced by increasing the discharge rate of concentrated water from the B-RO membrane device 52c. For example, to reduce the recovery rate, the control unit 10 controls the opening degree and opening / closing time of the pressure regulating automatic valves 11a and 11b to increase the discharge rate of concentrated water. Alternatively, the control unit 10 may control the inverter of the pump 51c to increase the pressure of the supplied water to reduce the recovery rate. Note that the operation of the pressure regulating automatic valves and inverter control may be performed simultaneously (for example, by adjusting the pressure regulating automatic valve 11b and the inverter).

[0038] (2) Bypass Under normal operation as described above, B-RO raw water is supplied to the B-RO membrane device 52c at a predetermined flow rate (Flux). When the value detected by the conductivity meter 8 exceeds a first threshold, the control unit 10 determines that the proportion of tap water has increased and bypasses the B-RO membrane device 52c. Specifically, the control unit 10 opens the pressure regulating automatic valves 11a and 11b and closes the pressure regulating automatic valve 11c. As a result, the B-RO raw water flows through the branch piping where the pressure regulating automatic valve 11c is installed and is not supplied to the B-RO membrane device 52c.

[0039] (3) Shutdown of B-RO membrane unit 52c Under the normal operation described above, B-RO raw water is supplied to the B-RO membrane unit 52c at a predetermined flow rate (Flux). When the value detected by the conductivity meter 8 exceeds a first threshold, the control unit 10 determines that the proportion of tap water has increased and stops the operation of the B-RO membrane unit 52c. Specifically, the control unit 10 stops the pump 51c.

[0040] (4) Amount of drug injection During the normal operation described above, B-RO raw water is supplied to the B-RO membrane device 52c at a predetermined flow rate (Flux). When the conductivity meter 8 detects a value exceeding a first threshold, the control unit 10 determines that the proportion of tap water has increased and increases the amount of chemical supplied by the chemical dispenser 12.

[0041] By controlling the operating conditions using one or more of the above operating control methods (1) to (4), the risk of RO membrane blockage in the B-RO membrane system 52c can be reduced. This operating control may also be performed manually.

[0042] In the water treatment apparatus 1 of this embodiment, the conductivity meter 8 is located downstream of the raw water tank 2 and upstream of the pretreatment system 4. Therefore, it is possible to detect the conductivity of the first mixed water, which is a mixture of tap water and recycled water, before it is affected by dilution or changes in conductivity in the pretreatment system 4. Consequently, the operating conditions of the B-RO membrane apparatus 52c can be appropriately controlled by detecting changes in the mixing ratio of the first mixed water.

[0043] In this embodiment, the water treatment apparatus 1 is an example of a first concentration detection means. As the first concentration detection means, a measuring instrument capable of detecting the concentration of a specific component (silica, aluminum, TOC, hydrogen ions, etc.) of the first mixed water (for example, a calcium meter, TOC meter, silica meter, pH meter, etc.) may be used.

[0044] Furthermore, in this embodiment, the first mixed water stored in the raw water tank 2 is a mixture of tap water and recycled water, but it is not limited to this. The first mixed water may be, for example, a mixture of two or more types of water with different water qualities.

[0045] Furthermore, although the control unit 10 controls the operating conditions of the B-RO membrane system 52c, it is not limited to this. The control unit 10 may also control the operating conditions of the RO membrane system 52a instead of the B-RO membrane system 52c. In this case, the control of the operating conditions of the RO membrane system 52a is basically the same as the control of the operating conditions of the B-RO membrane system 52c.

[0046] (Second embodiment) Figure 4 is a block diagram showing the configuration of a water treatment apparatus according to a second embodiment of the present invention. In Figure 4, solid arrows indicate piping (or flow paths), and dashed arrows indicate signal lines (or signals). At the intersection of two pipes, for convenience, the solid line representing one of the pipes is shown as broken.

[0047] The water treatment apparatus 1A shown in Figure 4 is configured such that the control unit 10 controls the operating conditions of the B-RO membrane apparatus 52c based on the detected value of the conductivity meter 13. In this respect, it differs from the water treatment apparatus 1 of the first embodiment, but the other configurations are basically the same as the water treatment apparatus 1 of the first embodiment. Below, the configurations that differ from the water treatment apparatus 1 will be described in detail, and the descriptions of the same configurations will be omitted.

[0048] The conductivity meter 13 is installed in the piping between the pump 42 and the K tower 44. The conductivity meter 13 detects the conductivity of the stored water supplied from the filtered water layer 41 to the K tower 44. The conductivity meter 13 can be called a second concentration detection means that detects the concentration of specific components (silica, aluminum, TOC, etc.).

[0049] When the value detected by the conductivity meter 8 exceeds a first threshold, the control unit 10 changes the operating conditions of the B-RO membrane apparatus 52c by the operation control (1) to (4) described above. Subsequently, when the value detected by the conductivity meter 13 falls below a second threshold, the control unit 10 controls the operating conditions of the B-RO membrane apparatus 52c to return them to their previous state. The second threshold is smaller than the first threshold. It is preferable to set the second threshold appropriately, taking into consideration the risk of RO membrane blockage, appropriate operating conditions for the B-RO membrane apparatus 52c, the placement of the conductivity meter 13, etc.

[0050] For example, when the conductivity meter 8 detects a value exceeding a first threshold, the control unit 10 determines that the proportion of tap water has increased and reduces the recovery rate of the B-RO membrane device 52c. Subsequently, when the conductivity meter 13 detects a value below a second threshold, the control unit 10 determines that the proportion of tap water has decreased and the mixing ratio has returned to its original state, and controls the recovery rate of the B-RO membrane device 52c to return it to its original state. This control uses the inverter of the pressure regulating automatic valves 11a, 11b or the pump 51c.

[0051] Furthermore, when the conductivity meter 8 detects a value exceeding a first threshold, the control unit 10 determines that the proportion of tap water has increased and bypasses the B-RO membrane device 52c. Subsequently, when the conductivity meter 13 detects a value below a second threshold, the control unit 10 determines that the proportion of tap water has decreased and the mixing ratio has returned to its original state and releases the bypass. Pressure regulating automatic valves 11a to 11c are used in this control.

[0052] Furthermore, when the conductivity meter 8 detects a value exceeding a first threshold, the control unit 10 determines that the proportion of tap water has increased and stops the operation of the B-RO membrane device 52c. Subsequently, when the conductivity meter 13 detects a value below a second threshold, the control unit 10 determines that the proportion of tap water has decreased and the mixing ratio has returned to its original state and restarts the operation of the B-RO membrane device 52c. Pump 51c is used in this control.

[0053] Furthermore, when the conductivity meter 8 detects a value exceeding a first threshold, the control unit 10 determines that the proportion of tap water has increased and increases the amount of chemical dispensed by the chemical dispenser 12. Subsequently, when the conductivity meter 13 detects a value below a second threshold, the control unit 10 determines that the proportion of tap water has decreased and the mixing ratio has returned to its original state and controls the chemical dispenser 12 to return the amount of chemical dispensed to its original state.

[0054] In addition to the effects of the water treatment device 1 described in the first embodiment, the water treatment device 1A of this embodiment provides the following effects. In the path from the raw water tank 2 to the B-RO membrane device 52c, changes in the mixing ratio of the first mixed water stored in the raw water tank 2 gradually affect the system from upstream to downstream. For example, if the proportion of tap water in the raw water stored in the raw water tank 2 increases, it will gradually be replaced by mixed water with a higher proportion of tap water from upstream to downstream. Similarly, if the proportion of tap water in the raw water decreases, it will gradually be replaced by mixed water with a lower proportion of tap water from upstream to downstream. Due to this time lag, if the proportion of tap water in the raw water decreases after the entire path has been replaced by mixed water with a higher proportion of tap water, and the decision to return the operating conditions of the B-RO membrane device 52c to their previous state is made based on the conductivity immediately after discharge from the raw water tank 2, there is a risk of RO membrane blockage because mixed water with a high proportion of tap water remains in the path from the filtered water layer 41 to the B-RO membrane device 52c.

[0055] In this embodiment, taking the above-mentioned time lag into consideration, the conductivity meter 13 is installed in the piping between the filtered water layer 41 and the K tower 44. This reduces the risk of RO membrane blockage. The conductivity meter 13 may be placed at any position in the path from the filtered water layer 41 to the B-RO membrane device 52c. Since the risk of RO membrane blockage due to the above-mentioned time lag decreases further downstream, it is preferable to place the conductivity meter 13 immediately before the B-RO membrane device 52c from the viewpoint of blockage risk. On the other hand, considering the problem that it becomes difficult to detect changes in the proportion of tap water due to the influence of changes in conductivity in the K tower 44, it is preferable to place the conductivity meter 13 upstream of the K tower 44.

[0056] In the water treatment apparatus 1 of the first embodiment and the water treatment apparatus 1A of the second embodiment described above, the raw water tank 2 can be called a first confluence section where two or more types of water merge and discharge a first mixed water. The filtered water tank 41 can be called a second confluence section where two or more types of water, including the first mixed water discharged from the first confluence section, merge and discharge a second mixed water.

[0057] Furthermore, the first confluence is not limited to a storage tank that stores a first mixed water obtained by mixing two or more types of water, such as the raw water tank 2. The first confluence can have any configuration as long as it can obtain the first mixed water from two or more types of water. For example, the first confluence may have a first storage tank (tank) to which tap water is supplied, a second storage tank (tank) to which recycled water is supplied, and a third storage tank (tank) to which tap water discharged from the first storage tank and recycled water discharged from the second storage tank are supplied.

[0058] Furthermore, the second confluence is not limited to a storage tank that stores a second mixed water, which is a mixture of two or more types of water including the first mixed water, such as a filtration tank 41. The second confluence can have any configuration as long as it can obtain the second mixed water from two or more types of water including the first mixed water. For example, the second confluence may have a first storage tank to which the first mixed water is supplied, a second storage tank to which other water such as recovered water is supplied, and a third storage tank to which the stored water from the first storage tank and the stored water from the second storage tank are supplied. The reverse osmosis membrane device 52 is configured to separate the water containing the second mixed water discharged from the second confluence into permeate and concentrated water. Here, "water containing the second mixed water" includes water in which other water has been combined with the second mixed water before the reverse osmosis membrane device 52, and water in which the second mixed water has been treated. [Explanation of Symbols]

[0059] 1. 1A Water Treatment System 2 Raw water tank 3, 42, 51a~51c Pumps 4. Pre-processing system 5. Primary pure water system 40 Filtration device 41 Filtration tank 44k tower 45 Decarboxylation equipment 50 RO raw water tanks 52 Reverse osmosis membrane equipment 53 EDI raw water tank 54 Electroregenerative deionizer 55 B-RO raw water tank 52a, 52b Reverse osmosis membrane equipment 52c Brine reverse osmosis apparatus

Claims

1. A first confluence where two or more types of water merge and discharge the first mixed water, Two or more types of water, including the first mixed water discharged from the first confluence, merge into a second confluence that discharges a second mixed water, A reverse osmosis membrane apparatus for separating the water containing the second mixed water discharged from the second confluence into permeate water and concentrated water, A first concentration detection means is located upstream of the second confluence and detects the concentration of a specific component contained in the first mixed water, A water treatment apparatus comprising: a control unit that controls the operating conditions of the reverse osmosis membrane apparatus based on the detection value of the first concentration detection means.

2. The reverse osmosis membrane apparatus is, A first reverse osmosis membrane apparatus for separating the second mixed water into a first permeate and a first concentrated water, The system includes a second reverse osmosis membrane apparatus that separates the first concentrated water from the first reverse osmosis membrane apparatus into a second permeate and a second concentrated water, The water treatment apparatus according to claim 1, characterized in that the control unit changes the operating conditions of the second reverse osmosis membrane apparatus when the detected value of the first concentration detection means exceeds a first threshold.

3. The system includes a second concentration detection means provided on the path between the second confluence and the second reverse osmosis membrane apparatus, which detects the concentration of the specific component contained in the second mixed water flowing through the path, The water treatment apparatus according to claim 2, characterized in that the control unit returns the operating conditions of the second reverse osmosis membrane apparatus to the state before the change when the detected value of the second concentration detection means falls below a second threshold.

4. The water treatment apparatus according to claim 3, characterized in that the first and second concentration detection means are conductivity meters.

5. The water treatment apparatus according to any one of claims 1 to 4, characterized in that it has a water quality adjustment means arranged downstream of the second confluence and upstream of the reverse osmosis membrane apparatus for adjusting the water quality of the second mixed water.

6. The water treatment apparatus according to any one of claims 1 to 4, characterized in that the concentration of the specific component contained in the second mixed water is lower than the concentration of the specific component contained in the first mixed water.

7. A method for operating a water treatment apparatus having: a first confluence where two or more types of water merge and discharge a first mixed water; a second confluence where two or more types of water, including the first mixed water discharged from the first confluence, merge and discharge a second mixed water; and a reverse osmosis membrane apparatus that separates the water, including the second mixed water discharged from the second confluence, into permeate and concentrated water, The concentration of a specific component contained in the first mixed water is detected upstream of the second confluence. A method for operating a water treatment device, characterized by controlling the operating conditions of the reverse osmosis membrane device based on the detected concentration of the specific component.

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