Device of treating water and method of operating the same

Abstract

To provide a device of treating water, capable of suppressing the water recovery rate from decreasing and of washing an RO membrane device.SOLUTION: A water treatment device 1 comprises a reverse osmosis membrane device 4 to which water to be treated is fed, an electric deionization device 6 separating water permeating the reverse osmosis membrane device 4 into desalted water, concentrated water and electrode water, and a cleaning mechanism 20 allowing cleaning water including the electrode water separated by the electric deionization device 6 to flow through the reverse osmosis membrane device 4 for a predetermined period of time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment device and a method for operating the same. [Background technology]

[0002] A water treatment device for producing primary pure water is known to have an RO-EDI system that includes a reverse osmosis (RO) membrane device and an electrodeionization (EDI) device. This RO-EDI system may include multiple RO membrane devices. For example, a brine RO membrane device that treats the concentrated water from the RO membrane device may be installed (see Patent Document 1).

[0003] Typically, RO membrane devices become contaminated with impurities (turbidity, fine particles, organic matter, living organisms, biological metabolites, scale components, etc.) contained in the water being treated as they are used. For this reason, RO membrane devices that have been in use for a long time must be cleaned using clear water or cleaning water containing cleaning chemicals.

[0004] Patent Document 2 describes a technology in which, in a primary pure water production system equipped with multiple stages of RO membrane devices, permeate from each RO membrane device is stored in a tank and the stored water in the tank is used as cleaning water to clean each RO membrane device. In this primary pure water production system, the water used for cleaning is discharged outside the system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-146618 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-209654 Summary of the Invention [Problem to be solved by the invention]

[0006] In the primary pure water production system described in Patent Document 2, the permeate water from the RO membrane device used to produce pure water is used as cleaning water, and the water used for cleaning is discharged outside the system, which causes a problem of a reduced water recovery rate in the primary pure water production system. It is also possible to use desalinated water or concentrated water from EDI to clean the RO membrane device, but this also creates the problem of a decrease in water recovery rate.

[0007] An object of the present invention is to provide a water treatment device and an operating method thereof that can suppress a decrease in water recovery rate and clean an RO membrane device. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, according to one aspect of the present invention, a water treatment device is provided, comprising: a reverse osmosis membrane device to which water to be treated is supplied; an electrodeionization device that separates the permeate water of the reverse osmosis membrane device into desalinated water, concentrated water, and electrode water; and a cleaning mechanism that passes cleaning water containing the electrode water separated by the electrodeionization device through the reverse osmosis membrane device for a predetermined period of time.

[0009] According to another aspect of the present invention, there is provided a method for operating a water treatment device having a reverse osmosis membrane device to which water to be treated is supplied and an electrodeionization device that separates the permeate water from the reverse osmosis membrane device into desalinated water, concentrated water, and electrode water, in which cleaning water containing the electrode water separated by the electrodeionization device is passed through the reverse osmosis membrane device for a predetermined period of time. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent a decrease in the water recovery rate and clean the RO membrane device. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a configuration of a water treatment device according to a first embodiment of the present invention. [Figure 2]FIG. 1 is a block diagram showing the configuration of a primary pure water manufacturing apparatus of a comparative example. [Figure 3] FIG. 4 is a block diagram showing the configuration of a water treatment device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a block diagram showing the configuration of a water treatment device according to a third embodiment of the present invention. [Figure 5] FIG. 10 is a block diagram showing the configuration of a water treatment device according to a fourth embodiment of the present invention. [Figure 6] FIG. 10 is a block diagram showing the configuration of a water treatment device according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] (First embodiment) Fig. 1 is a block diagram showing the configuration of a water treatment device according to a first embodiment of the present invention. Fig. 1 shows an ultrapure water production system 100 including a primary pure water production system 1, which is the water treatment device of this embodiment. In Fig. 1, solid arrows indicate piping (or flow paths), and solid open arrows indicate signal lines for transmitting control signals and the like.

[0014] As shown in FIG. 1, the ultrapure water production system 100 includes a raw water tank 30, a pretreatment device 31, a primary pure water production system 1, and a secondary pure water production system (subsystem) 32. The primary pure water production system 1 has an RO-EDI system including a reverse osmosis (RO) membrane device 4 to which the water to be treated is supplied, and an electrodeionization (EDI) device 6 to which the permeated water of the RO membrane device 4 is supplied. The RO membrane device 4 includes an RO membrane device 40 that separates the water to be treated into permeate and concentrate, and a brine RO membrane device (B-RO membrane device) 41 that separates the concentrate separated by the RO membrane device 40 into permeate and concentrate.

[0015] The water to be treated may be pretreated to remove impurities before being supplied to the RO membrane device 40, depending on the raw water quality and the required water quality as primary pure water. In this embodiment, an RO raw water tank 2 and a pump 3a are provided upstream of the RO membrane device 40. The RO raw water tank 2 is connected to the RO membrane device 40 via a pipe, and the pipe is provided with the pump 3a. When the pump 3a is operated, the RO raw water (water to be treated) stored in the RO raw water tank 2 is supplied to the RO membrane device 40. In this embodiment, a desalinated water tank 7 and a group of unit operation devices 8 that perform various water treatments are provided downstream of the EDI 6. The group of unit operation devices 8 may be composed of, for example, an ultraviolet oxidation device, an ion exchange device, a membrane degassing device, etc. However, the group of unit operation devices 8 is not limited to the components listed here. For example, some of the components may be omitted, or other devices may be further provided in the components. If necessary, an ultraviolet oxidation device, an ion exchange device, a membrane degassing device, etc. may be provided between the RO membrane device 40 and the EDI 6.

[0016] The raw water tank 30 and the pretreatment device 31 are connected via piping, and a pump 3d is provided in this piping. The water to be treated is, for example, industrial water, well water, city water, surface water, wastewater provided from inside or outside a customer factory, treated sewage water, desalinated seawater, etc., and one or more of these waters are stored in the raw water tank 30. The pump 3d supplies the water stored in the raw water tank 30 to the pretreatment device 31. The pretreatment device 31 is connected to the RO raw water tank 2 via piping. The pretreatment device 31 is composed of, for example, a sand filtration device, an activated carbon device, a softening device, a decarbonation device, and a tank (water tank) for storing the water supplied to these devices and the treated water. However, the pretreatment device 31 is not limited to the components listed here. For example, some of the components may be omitted, or the components may further include other devices. The treated water treated in the pretreatment device 31 is stored in the RO raw water tank 2 as RO raw water (water to be treated and supplied to the RO membrane device 40).

[0017] The secondary pure water production system 32 includes a primary pure water tank 33 and a group of unit operation devices 34 that perform various water treatments. The primary pure water tank 33 and the group of unit operation devices 34 are connected via piping. The primary pure water tank 33 stores the primary pure water produced by the primary pure water production system 1. The group of unit operation devices 34 is composed of, for example, a heat exchanger, an ultraviolet oxidation device, an ion exchange device, a membrane degassing device, and an ultrafiltration membrane device. However, the group of unit operation devices 34 is not limited to the components listed here. For example, some of the components may not be included, or the components may further include other devices. The treated water (ultrapure water) treated by the group of unit operation devices 34 is supplied to, for example, a point of use 34.

[0018] In the primary pure water production system 1, the RO membrane device 40 includes one or more reverse osmosis membrane elements and is configured to remove impurities from the RO raw water (water to be treated) by utilizing reverse osmosis. The RO membrane device 40 discharges permeate that has passed through the reverse osmosis membrane and concentrated water that contains impurities separated by the reverse osmosis membrane.

[0019] The permeate discharge side of the RO membrane device 40 is in communication with the EDI raw water tank 5 via a pipe. The EDI raw water tank 5 stores the permeate from the RO membrane device 40 as EDI raw water. The EDI raw water tank 5 is in communication with the EDI 6 via a pipe, and a pump 3b is provided on this pipe. By operating the pump 3b, the stored water in the EDI raw water tank 5 (EDI raw water) is supplied to the EDI 6.

[0020] The concentrated water discharge side of the RO membrane device 40 is connected via piping to a brine reverse osmosis (B-RO) membrane raw water tank (B-RO raw water tank) 9. The B-RO raw water tank 9 stores the concentrated water from the RO membrane device 40 as B-RO raw water. The B-RO raw water tank 9 is connected to the B-RO membrane device 41 via piping 10, which is provided with a valve 11 and a pump 3c. The valve 11 is located on the inlet side of the pump 3c. By operating the pump 3c with the valve 11 open, the stored water in the B-RO raw water tank 9 (B-RO raw water) is supplied to the B-RO membrane device 41.

[0021] Like the RO membrane device 40, the B-RO membrane device 41 uses reverse osmosis to remove impurities from the concentrate of the RO membrane device 40. The B-RO membrane device 41 discharges permeate that has passed through the reverse osmosis membrane and concentrate containing impurities separated by the reverse osmosis membrane. The permeate of the B-RO membrane device 41 may be supplied to, for example, the pretreatment device 31. The concentrate of the B-RO membrane device 41 is discharged (discarded) outside the system, for example. The configuration of the B-RO membrane device 41 and the RO membrane device 40, such as the number and tier arrangement of reverse osmosis membrane elements, is determined depending on the quality of the raw water, the desired quality of the treated water, and the amount of treated water.

[0022] The EDI 6 removes ions from the permeate water supplied from the RO membrane device 40 via the EDI raw water tank 5. The EDI 6 separates the permeate water from the RO membrane device 40 into desalinated water (pure water), concentrated water containing the removed ions, and electrode water.

[0023] Specifically, the EDI6 has deionization compartments and concentration compartments alternately arranged between an anode and a cathode. The deionization compartments and concentration compartments are partitioned by alternating anion-exchange membranes and cation-exchange membranes. Electrode compartments are arranged on both sides of the area containing the deionization compartments and concentration compartments (i.e., the anode side and the cathode side). The deionization compartments contain ion exchange resins. Ions in the permeate are trapped by the ion exchange resin and collected in the concentration compartments by an electric field, where they are discharged as concentrated water. Concentrated water is discharged from each concentration compartment, and deionized water is discharged from each deionization compartment. A portion of the permeate is supplied to each electrode compartment, and electrode water is discharged from each electrode compartment. Note that the EDI6 is not limited to the configuration described here. The EDI6 may have any structure as long as it can separate the permeate into deionized water, concentrated water, and electrode water. For example, various modifications are possible regarding the structure of the ion exchange membranes arranged between the deionization compartments and concentration compartments, and the water flow paths between the deionization compartments, concentration compartments, and electrode compartments.

[0024] The EDI 6 discharges desalinated water, concentrated water, and electrode water. The desalinated water is supplied to the desalinated water tank 7. The concentrated water is supplied, for example, to the RO raw water tank 2. The electrode water is supplied to the cleaning water tank 22 via the gas-liquid separator 23. In the EDI 6, electrolysis of water generates oxygen and other substances in the anode-side electrode chamber, and hydrogen and other substances in the cathode-side electrode chamber. The gas-liquid separator 23 removes gases (dissolved gases) such as hydrogen and oxygen contained in the electrode water. The cleaning water tank 22 stores cleaning water containing electrolyzed water from which hydrogen has been removed.

[0025] The primary pure water production system 1 is configured to clean the B-RO membrane device 41 using cleaning water containing electrode water discharged from the EDI 6. Here, the cleaning water may contain only electrode water, or may further contain other water that can be used for cleaning. The primary pure water production system 1 has a cleaning-related configuration (cleaning mechanism) 20 including the gas-liquid separator 23 and cleaning water tank 22, as well as a control unit 21, a valve 24, and piping 25. One end of the piping 25 is connected to the cleaning water tank 22, and the other end of the piping 25 is connected to a portion of the piping 10 connected to the inlet side of the B-RO membrane device 41 between the valve 11 and the pump 3c. The piping 25 is provided with a valve 24.

[0026] The control unit 21 controls the water supply operation of the pump 3c and the opening and closing operations of the valves 11 and 24. During a predetermined period (flushing period), the control unit 21 closes the valve 11 and opens the valve 24, controlling the water supply operation of the pump 3c to achieve a flow rate (or flow speed) suitable for cleaning the B-RO membrane device 41. In other words, the configuration 20 passes cleaning water containing electrode water through the B-RO membrane device 41 for a predetermined period. After cleaning the B-RO membrane device 41, the cleaning water is discharged (discarded) outside the system.

[0027] Outside the flushing period, the control unit 21 opens the valve 11 and closes the valve 24, and controls the water supply operation of the pump 3c to provide a flow rate (or flow velocity) suitable for operating the B-RO membrane device 41. This allows the concentrated water from the RO membrane device 40 to pass through the B-RO membrane device 41.

[0028] The amount of water stored in the cleaning water tank 22 is preferably determined based on the predetermined cleaning interval and required water volume of the B-RO membrane device 41. The cleaning interval of the B-RO membrane device 41 can be determined using a timer or based on changes in the operating conditions of the B-RO membrane device 41, such as the pressure, flow rate, and treated water quality.

[0029] The primary pure water manufacturing system 1 of the present embodiment described above provides the following advantageous effects. The electrode water of the EDI 6 contains oxygen, hydrogen, hydrogen peroxide, and the like. For this reason, the electrode water is generally discharged (discarded) outside the system. In the primary pure water manufacturing system 1 of this embodiment, the electrode water of the EDI 6, which is normally discarded, is used as cleaning water to clean the B-RO membrane device 41. This makes it possible to clean the B-RO membrane device 41 while suppressing a decrease in the water recovery rate. In particular, since the B-RO membrane device 41 has a higher raw water load than the RO membrane device 40 and is therefore more susceptible to contamination, cleaning the B-RO membrane device 41 is preferable.

[0030] Next, the effects of the primary pure water production system 1 of this embodiment will be specifically described in comparison with a primary pure water production system 101 of a comparative example. 2 is a block diagram for explaining a primary pure water production system 101 of a comparative example. The primary pure water production system 101 of this comparative example is the same as the primary pure water production system 1 shown in FIG. 1 except for the cleaning-related component (cleaning mechanism) 20. The components other than the component 20 are basically the same as those of the primary pure water production system 1.

[0031] In the primary pure water production system 101 of this comparative example, three cleaning paths A to C (indicated by dashed arrows in FIG. 2) are used to clean the B-RO membrane device 41. In cleaning path A, the B-RO membrane device 41 is cleaned at low pressure and high flow rate using the stored water in the B-RO raw water tank 9 as cleaning water. In cleaning path B, the B-RO membrane device 41 is cleaned using the stored water in the EDI raw water tank 5 as cleaning water. In cleaning path C, the B-RO membrane device 41 is cleaned using the stored water in the desalinated water tank 7 as cleaning water. In cleaning path C, a cleaning water tank for storing desalinated water may be provided, and the stored water in the cleaning water tank may be used to clean the B-RO membrane device 41, with the cleaned water being returned to the cleaning water tank for circulating cleaning.

[0032] In any of the above cleaning routes A to C, the stored water that can be used to produce primary pure water is used as cleaning water, which causes a problem of a reduced water recovery rate. In contrast, in the primary pure water production system 1 of this embodiment, the electrode water of EDI 6 that has not been used for producing primary pure water is used as cleaning water, so that a decrease in the water recovery rate can be suppressed.

[0033] The electrode water of EDI6 contains hydrogen peroxide. The concentration of hydrogen peroxide is, for example, about 0.1 to 1.0 ppm. Because hydrogen peroxide has the effect of suppressing organic fouling of RO membranes, the electrode water containing hydrogen peroxide is suitable as cleaning water for RO membranes.

[0034] The pipe 25 may also be connected between the pump 3c and the B-RO membrane device 41. In this case, a new pump is provided in the pipe 25. The control unit 21 controls the water supply operation of the pump provided in the pipe 25 to supply cleaning water to the B-RO membrane device 41. If the storage volume of the cleaning water tank 22 is insufficient, desalinated water from the EDI raw water tank 5 or the EDI 6 may be temporarily added. In this case, the water recovery rate will be somewhat lower, but the amount of cleaning water required to clean the B-RO membrane device 41 can be reliably secured.

[0035] (Second embodiment) Fig. 3 is a block diagram showing the configuration of a water treatment device according to a second embodiment of the present invention. Fig. 3 shows an ultrapure water production system 100 including a primary pure water production system 1A, which is the water treatment device of this embodiment. The primary pure water production system 1A differs from the primary pure water production system 1 shown in Fig. 1 in that a plurality of B-RO membrane devices 41-1 to 41-n are connected in parallel. The same components as those in the primary pure water production system 1 are given the same reference numerals, and a description of those components will be omitted here.

[0036] The primary pure water production system 1A has multiple valves 11-1 to 11-n, multiple valves 24-1 to 24-n, multiple pumps 3c-1 to 3c-n, and multiple B-RO membrane devices 41-1 to 41-n instead of the valves 11 and 24, pump 3c, and B-RO membrane device 41 shown in Figure 1. All of the multiple B-RO membrane devices 41-1 to 41-n have the same configuration as the B-RO membrane device 41 shown in Figure 1.

[0037] A pipe 10 connected to the B-RO raw water tank 9 branches into multiple branch pipes 10-1 to 10-n. The multiple branch pipes 10-1 to 10-n are connected to multiple B-RO membrane devices 41-1 to 41-n, respectively. The branch pipe 10-1 is provided with a valve 11-1 and a pump 3c-1. Similarly, the branch pipes 10-2 to 10-n are provided with valves 11-2 to 11-n and pumps 3c-2 to 3c-n.

[0038] A pipe 25 connected to the cleaning water tank 22 branches into multiple branch pipes 25-1 to 25-n. The branch pipe 25-1 is connected to a portion of the branch pipe 10-1 connected to the inlet side of the B-RO membrane device 41-1 between the valve 11-1 and the pump 3c-1. Similarly, the branch pipes 25-2 to 25-n are connected to the branch pipes 10-2 to 10-n connected to the inlet sides of the B-RO membrane devices 41-2 to 41-n. The branch pipes 25-1 to 25-n are provided with valves 24-1 to 24-n.

[0039] In the primary pure water manufacturing system 1A of this embodiment, the control unit 21 sequentially cleans the B-RO membrane devices 41-1 to 41-n. For example, cleaning of the B-RO membrane device 41-1 is performed as follows.

[0040] The control unit 21 closes valve 11-1 and opens valve 24-1, controls the water supply operation of pump 3c-1 to provide a flow rate (or flow speed) suitable for cleaning the B-RO membrane device 41-1, and passes cleaning water through the B-RO membrane device 41-1 for a predetermined time. During the cleaning period (flushing period) of the B-RO membrane device 41-1, the control unit 21 opens valves 11-2 to 11-n and closes valves 24-2 to 24-n, and controls the water supply operation of pumps 3c-2 to 3c-n to provide a flow rate (or flow speed) suitable for operating the B-RO membrane devices 41-2 to 41-n. The remaining B-RO membrane devices 41-2 to 41-n are sequentially cleaned using the same procedure as above.

[0041] In addition to the effects described in the first embodiment, the primary pure water production system 1A of this embodiment can sequentially clean multiple B-RO membrane devices 41-1 to 41-n, and while the B-RO membrane devices are being cleaned, the other B-RO membrane devices can operate normally. At this time, the other B-RO membrane devices can cover the processing of the B-RO membrane device being cleaned.

[0042] (Third embodiment) Fig. 4 is a block diagram showing the configuration of a water treatment device according to a third embodiment of the present invention. Fig. 4 shows an ultrapure water production system 100 including a primary pure water production system 1B, which is the water treatment device of this embodiment. The primary pure water production system 1B has the same configuration as the primary pure water production system 1 shown in Fig. 1, except that a cleaning chemicals addition device 26 is provided in the structure 20. To avoid duplication, detailed description of the same configuration as the primary pure water production system 1 will be omitted.

[0043] The cleaning chemical dosing device 26 adds cleaning chemicals to the cleaning water discharged from the cleaning water tank 22. Examples of cleaning chemicals include, but are not limited to, acidic agents, alkaline agents, oxidizing agents, dispersants, slime control agents, etc. The cleaning chemical dosing device 26 can add one or more of these chemicals to the cleaning water. The control unit 21 can control the addition of chemicals by the cleaning chemical dosing device 26. For example, the control unit 21 can control the type and amount of chemicals added by the cleaning chemical dosing device 26.

[0044] In addition to the effects described in the first embodiment, the primary pure water manufacturing system 1B of this embodiment has the following effects.

[0045] In general, alkaline agents can achieve a high cleaning effect. Oxidizing agents (such as sodium hypochlorite and hydrogen peroxide) are effective in removing biofouling and sterilizing. Dispersants are effective in dispersing RO scale. Slime control agents are effective in removing RO biofouling and sterilizing. All of these chemicals can be added to cleaning water to enhance their cleaning effect, but making the cleaning water alkaline can further enhance the cleaning effect of adding chemicals. In other words, the cleaning effect of adding chemicals to alkaline cleaning water with a high pH value is higher than the cleaning effect of adding chemicals to neutral cleaning water with a low pH value. For example, the dispersion effect and slime control effect of dispersants and slime control agents are greater when added to alkaline cleaning water than when added to neutral cleaning water.

[0046] According to the primary pure water manufacturing apparatus 1B of this embodiment, in addition to achieving the effects described in the first embodiment, the cleaning chemicals adding device 26 adds cleaning chemicals to the cleaning water, thereby further enhancing the cleaning effect of the B-RO membrane device 41.

[0047] (Fourth embodiment) Fig. 5 is a block diagram showing the configuration of a water treatment device according to a fourth embodiment of the present invention. Fig. 4 shows an ultrapure water production system 100 including a primary pure water production system 1C, which is the water treatment device of this embodiment. The primary pure water production system 1C has the same configuration as the primary pure water production system 1 shown in Fig. 1, except that it is provided with a cleaning chemicals addition device 26 and is configured with a cleaning water circulating configuration 20. To avoid duplication, detailed description of the same configuration as the primary pure water production system 1 will be omitted.

[0048] A branch pipe 27 branching off from the pipe 12 on the concentrated water side of the B-RO membrane device 41 is connected to the cleaning water tank 22. A valve 28 is provided on the pipe 12, and a valve 29 is provided on the branch pipe 27. The cleaning chemical addition device 26 has the same configuration as that described in the third embodiment, but in this embodiment, cleaning chemicals are added to the cleaning water tank 22.

[0049] The control unit 21 controls the water supply operation of the pump 3c and the opening and closing operations of the valves 11, 24, 28, and 29. During a predetermined period (flushing period), the control unit 21 closes the valves 11 and 28 and opens the valves 24 and 29, controlling the water supply operation of the pump 3c to achieve a flow rate (or flow speed) suitable for cleaning the B-RO membrane device 41. As a result, cleaning water is supplied from the cleaning water tank 22 to the B-RO membrane device 41, and the cleaning water that has passed through the B-RO membrane device 41 returns to the cleaning water tank 22.

[0050] Outside the flushing period, the control unit 21 opens the valves 11 and 28 and closes the valves 24 and 29, and controls the water supply operation of the pump 3c to provide a flow rate (or flow velocity) suitable for operating the B-RO membrane device 41. This allows the concentrated water from the RO membrane device 40 to pass through the B-RO membrane device 41.

[0051] According to the primary pure water manufacturing system 1C of this embodiment, in addition to achieving the effects described in the first embodiment, the use efficiency of the cleaning water is improved by circulating the cleaning water.

[0052] (Fifth embodiment) Fig. 6 is a block diagram showing the configuration of a water treatment device according to a fifth embodiment of the present invention. Fig. 6 shows an ultrapure water production system 100 including a primary pure water production system 1D, which is the water treatment device of this embodiment. The primary pure water production system 1D has the same configuration as the primary pure water production system 1 shown in Fig. 1, except that a configuration 20 is configured to clean the RO membrane device 40 instead of the B-RO membrane device 41. To avoid duplication, detailed descriptions of the same configuration as the primary pure water production system 1 will be omitted.

[0053] A pump 3a and a valve 14a are provided on a pipe 13a connecting the RO raw water tank 2 and the RO membrane device 40. The valve 14a is located between the RO raw water tank 2 and the pump 3a. A pipe 25 connected to the cleaning water tank 22 is connected between the valve 14a of the pipe 13a and the pump 3a. A valve 24a is provided on the pipe 25. B-A valve 14b is provided on a pipe 13b connecting the RO raw water tank 9 and the RO membrane device 40. A branch pipe 13c branches off from a portion of the pipe 13b between the RO membrane device 40 and the valve 14b, and a valve 24b is provided on this branch pipe 13c.

[0054] The control unit 21 controls the water supply operation of the pump 3a and the opening and closing operations of the valves 14a, 14b, 24a, and 24b. During a predetermined period (flushing period), the control unit 21 closes the valves 14a and 14b and opens the valves 24a and 24b, controlling the water supply operation of the pump 3a to achieve a flow rate (or flow speed) suitable for cleaning the RO membrane device 40. In other words, the configuration 20 passes cleaning water containing electrode water through the RO membrane device 40 for a predetermined period of time. After cleaning the RO membrane device 40, the cleaning water is discharged (discarded) outside the system.

[0055] Outside the flushing period, the control unit 21 opens the valves 14a and 14b and closes the valves 24a and 24b, and controls the water conveying operation of the pump 3a to achieve a flow rate (or flow velocity) suitable for operating the RO membrane device 40. This allows the stored water in the RO raw water tank 2 to pass through the RO membrane device 40.

[0056] According to the primary pure water manufacturing system 1D of this embodiment, the RO membrane device 40 can be cleaned while suppressing a decrease in the water recovery rate, based on the same principle as the operational effects described in the first embodiment.

[0057] The primary pure water production systems 1, 1A, 1B, 1C, and 1D of the first to fifth embodiments described above are examples of the present invention, and the components of the primary pure water production system of each embodiment can be changed as appropriate. For example, any of the primary pure water production systems 1, 1A, 1B, 1C, and 1D of the first to fifth embodiments may be provided with an oxidant removal device that removes oxidants contained in the wash water containing electrode water. Hydrogen peroxide contained in the electrode water of the EDI 6 causes deterioration of the RO membrane, so removing it using an oxidant removal device can extend the life of the RO membrane. Examples of methods for removing oxidants in the oxidant removal device include adding activated carbon or a reducing agent.

[0058] Furthermore, the configuration of any one of the primary pure water production systems 1, 1A, 1B, and 1C according to the first to fourth embodiments may be combined with the configuration of the primary pure water production system 1D according to the fifth embodiment. Furthermore, the configuration of the primary pure water manufacturing apparatus 1B of the third embodiment (addition of cleaning chemicals) or the configuration of the primary pure water manufacturing apparatus 1C of the fourth embodiment (circulation mechanism) may be applied to the primary pure water manufacturing apparatus 1A of the second embodiment or the primary pure water manufacturing apparatus 1D of the fifth embodiment. Furthermore, in the primary pure water production system 1D of the fifth embodiment, multiple RO membrane devices 40 may be provided in parallel with one another. In this case, the multiple RO membrane devices 40 may be cleaned sequentially. For example, the cleaning structure of the B-RO membrane devices 41 connected in parallel in the second embodiment can be applied to multiple RO membrane devices 40 connected in parallel.

[0059] The RO membrane device 40 may also be configured in a multi-stage configuration, with multiple stages installed in series. In a two-stage configuration, the treated water obtained in the first stage RO membrane device is further treated in the second stage RO membrane device, thereby improving the quality of the RO treated water. While there are no particular restrictions on the RO membrane to be cleaned with EDI electrode water, it is preferable to use it to clean the first stage RO membrane, given the susceptibility of RO membranes to fouling.

[0060] Furthermore, in the primary pure water production systems 1, 1A, 1B, 1C, and 1D of the first to fifth embodiments, multiple EDIs 6 may be provided in series or in parallel with each other. In this case, the electrode water of each EDI 6 may be supplied to the cleaning water tank 22 via the gas-liquid separator 23.

[0061] The configuration (cleaning mechanism) 20 described in the first to fifth embodiments can be incorporated into an existing water treatment device that is an RO-EDI system, and the RO membrane device can be cleaned with cleaning water containing electrode water discharged from the EDI. [Explanation of symbols]

[0062] 1 Primary water purification equipment 4, 40 Reverse osmosis membrane device 41 Brine reverse osmosis membrane equipment 6. Electrodeionizer 20 Cleaning-related configuration (cleaning mechanism)

Claims

1. a reverse osmosis membrane device to which the water to be treated is supplied; an electrodeionization device that separates the permeate water from the reverse osmosis membrane device into desalinated water, concentrated water, and electrode water; a cleaning mechanism that passes cleaning water containing the electrode water separated in the electrodeionization device through the reverse osmosis membrane device for a predetermined period of time.

2. The reverse osmosis membrane device is a first reverse osmosis membrane device that separates the water to be treated into a first permeate and a first concentrate; a second reverse osmosis membrane device that separates the first concentrated water separated by the first reverse osmosis membrane device into a second permeate and a second concentrated water, The water treatment device according to claim 1 , wherein the cleaning mechanism passes the cleaning water containing the electrode water through at least one of the first and second reverse osmosis membrane devices.

3. a plurality of the first or second reverse osmosis membrane devices are provided, and the plurality of first or second reverse osmosis membrane devices are connected in parallel with each other; The water treatment device according to claim 2 , wherein the cleaning mechanism passes the cleaning water containing the electrode water through the plurality of first or second reverse osmosis membrane devices in sequence.

4. a gas-liquid separator that separates the electrode water separated by the electrodeionization device into gas and liquid, The water treatment device according to claim 1 , wherein the cleaning mechanism passes cleaning water containing the electrode water separated into gas and liquid by the gas-liquid separator.

5. The water treatment device according to claim 1 , further comprising a chemical addition device that adds cleaning chemicals to the cleaning water containing the electrode water.

6. The water treatment device according to claim 1 , further comprising an oxidant removal device that removes an oxidant contained in the cleaning water containing the electrode water.

7. a plurality of the electrodeionization devices, the plurality of electrodeionization devices being connected in series or in parallel with each other; The water treatment device according to claim 1 , further comprising a cleaning water tank for storing the electrode water separated in each of the plurality of electrodeionization devices as the cleaning water.

8. A method for operating a water treatment system having a reverse osmosis membrane device to which water to be treated is supplied and an electrodeionization device that separates permeated water from the reverse osmosis membrane device into desalinated water, concentrated water, and electrode water, comprising: A method for operating a water treatment device, comprising: passing wash water containing the electrode water separated in the electrodeionization device through the reverse osmosis membrane device for a predetermined period of time.

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