Water treatment device and method for operating same

Abstract

This water treatment device 1 includes: a reverse osmosis membrane device 4 to which water to be treated is supplied; an electric regeneration type deionization device 6 that separates water that has passed through the reverse osmosis membrane device 4 into desalinated water, concentrated water, and electrode water; and a washing mechanism 20 that passes the washing water containing the electrode water separated by the electric regeneration type deionization device 6 through the reverse osmosis membrane device 4 for a predetermined time.

Description

Water treatment device and method for operating same

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

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

[0003] Typically, RO membrane devices become contaminated with impurities (such as suspended solids, fine particles, organic matter, living organisms, biological metabolites, and scale components) 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 need to be cleaned with clear water or cleaning water containing added cleaning chemicals.

[0004] Patent Document 2 describes a technique for a primary pure water production system equipped with multiple stages of RO membrane devices, in which 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.

[0005] JP 2020-146618 A JP 2017-209654 A

[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. This causes a problem of a reduced water recovery rate from the primary pure water production system. While it is possible to clean the RO membrane device using demineralized water or concentrated water from EDI, this also causes a problem of a reduced 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.

[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.

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

[0011] Fig. 1 is a block diagram showing the configuration of a water treatment device according to a first embodiment of the present invention. Fig. 2 is a block diagram showing the configuration of a primary pure water production device of a comparative example. Fig. 3 is a block diagram showing the configuration of a water treatment device according to a second embodiment of the present invention. Fig. 4 is a block diagram showing the configuration of a water treatment device according to a fourth embodiment of the present invention. Fig. 5 is a block diagram showing the configuration of a water treatment device according to a fifth embodiment of the present 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] 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 water to be treated is supplied, and an electrodeionization system (EDI) 6 to which permeated water from 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 permeated water and concentrated water, and a brine RO membrane device (B-RO membrane device) 41 that separates the concentrated water separated by the RO membrane device 40 into permeated water and concentrated water.

[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 a 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 a pipe, and a pump 3d is provided in this pipe. The water to be treated may be, for example, industrial water, well water, city water, surface water, wastewater provided inside or outside a customer's factory, treated sewage, or desalinated seawater. One or more of these types of water are stored in the raw water tank 30. The pump 3d supplies the stored water 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 a pipe. The pretreatment device 31 is composed of, for example, a sand filter, an activated carbon device, a softener, a decarbonator, and tanks (water tanks) for storing the feed water 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 other devices may be added to the components. 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 35.

[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 containing 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 (EDI raw water) in the EDI raw water tank 5 is supplied to the EDI 6.

[0020] The concentrated water discharge side of the RO membrane device 40 is in communication with a brine reverse osmosis (B-RO) membrane raw water tank (B-RO raw water tank) 9 via a pipe. 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 in communication with the B-RO membrane device 41 via a pipe 10, to which a valve 11 and a pump 3c are attached. 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 utilizes 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. In the B-RO membrane device 41 and the RO membrane device 40, the configuration, 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 permeated water supplied from the RO membrane device 40 via the EDI raw water tank 5. The EDI 6 separates the permeated water from the RO membrane device 40 into desalinated water (pure water), concentrated water containing the removed ions, and electrode water.

[0023] Specifically, the EDI 6 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 EDI 6 is not limited to the configuration described here. The EDI 6 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 with respect to the structure of the ion exchange membrane disposed between the deionization compartment and the concentration compartment, the water flow paths between the deionization compartment, the concentration compartment, and the electrode compartment, and the like.

[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 a 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 includes 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 to be stored in the cleaning water tank 22 is preferably determined based on the predetermined cleaning interval and required water amount 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 production system 1 of this 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 production 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. Figure 2 is a block diagram for explaining the primary pure water production system 101 of the 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 Figure 1 except that the cleaning-related component (cleaning mechanism) 20 has been removed. The components other than the component 20 are basically the same as those of the primary pure water production system 1.

[0031] The primary pure water production system 101 of this comparative example employs three cleaning routes A to C (indicated by dashed arrows in FIG. 2 ) for cleaning the B-RO membrane device 41. In cleaning route A, the B-RO membrane device 41 is cleaned at low pressure and high flow rate using stored water in the B-RO raw water tank 9 as cleaning water. In cleaning route B, the B-RO membrane device 41 is cleaned using stored water in the EDI raw water tank 5 as cleaning water. In cleaning route C, the B-RO membrane device 41 is cleaned using stored water in the demineralized water tank 7 as cleaning water. In cleaning route C, a cleaning water tank for storing demineralized water may be provided, and the B-RO membrane device 41 may be cleaned using stored water in the cleaning water tank as cleaning water, and the cleaned water may be 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 decrease in the water recovery rate. In contrast, in the primary pure water production system 1 of this embodiment, the electrode water of EDI 6 that was not used to produce primary pure water is used as cleaning water, which prevents a decrease in the water recovery rate.

[0033] The electrode water of the EDI 6 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 the RO membrane, the electrode water containing hydrogen peroxide is suitable as cleaning water for the RO membrane.

[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 supplies cleaning water to the B-RO membrane device 41 by controlling the water supply operation of the pump provided in the pipe 25. If the amount of storage in 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 is somewhat reduced, but the amount of cleaning water required to clean the B-RO membrane device 41 can be reliably secured.

[0035] Second Embodiment Figure 3 is a block diagram showing the configuration of a water treatment device according to a second embodiment of the present invention. Figure 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 Figure 1 in that multiple B-RO membrane devices 41-1 to 41-n are connected in parallel. Components that are the same as those in the primary pure water production system 1 are given the same reference numerals, and descriptions of those components will be omitted here.

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

[0037] A pipe 10 connected to the B-RO raw water tank 9 is branched into a plurality of branch pipes 10-1 to 10-n. The plurality of branch pipes 10-1 to 10-n are connected to a plurality of 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 a plurality of branch pipes 25-1 to 25-n. The branch pipe 25-1 is connected to a portion between the valve 11-1 and the pump 3c-1 of the branch pipe 10-1 connected to the inlet side of the B-RO membrane device 41-1. 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, the cleaning of the B-RO membrane device 41-1 is performed as follows.

[0040] The control unit 21 closes the valve 11-1 and opens the valve 24-1, controls the water supply operation of the pump 3c-1 to provide a flow rate (or flow velocity) 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 the valves 11-2 to 11-n and closes the valves 24-2 to 24-n, and controls the water supply operation of the pumps 3c-2 to 3c-n to provide a flow rate (or flow velocity) 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 the 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) Figure 4 is a block diagram showing the configuration of a water treatment device according to a third embodiment of the present invention. Figure 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 Figure 1, except that a cleaning chemicals addition device 26 is provided in the component 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 producing apparatus 1B of this embodiment has the following effects.

[0045] In general, alkaline agents can achieve a high cleaning effect. Oxidizing agents (sodium hypochlorite, hydrogen peroxide, etc.) 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 the cleaning effect, but making the cleaning water alkaline can further enhance the cleaning effect of adding chemicals. In other words, the cleaning effect when chemicals are added to alkaline cleaning water with a high pH value is higher than the cleaning effect when chemicals are added 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 system 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) Figure 5 is a block diagram showing the configuration of a water treatment device according to a fourth embodiment of the present invention. Figure 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 Figure 1, except that it is provided with a cleaning chemicals addition device 26 and has a configuration 20 for circulating cleaning water. 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 adding 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 provide 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 apparatus 1C of this embodiment, in addition to achieving the effects described in the first embodiment, the utilization 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. A valve 14b is provided on a pipe 13b connecting the B-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 provide a flow rate (or flow velocity) 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. 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 supply operation of the pump 3a to provide a flow rate (or flow velocity) suitable for operating the RO membrane device 40. This allows the water stored in the RO raw water tank 2 to flow through the RO membrane device 40.

[0056] According to the primary pure water production apparatus 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 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 systems of each embodiment can be modified 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 cleaning 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 of the primary pure water production systems 1, 1A, 1B, and 1C of the first to fourth embodiments may be combined with the configuration of the primary pure water production system 1D of the fifth embodiment. Furthermore, the configuration of the primary pure water production system 1B of the third embodiment (addition of cleaning chemicals) or the configuration of the primary pure water production system 1C of the fourth embodiment (circulation mechanism) may be applied to the primary pure water production system 1A of the second embodiment or the primary pure water production system 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 each other. 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 of the second embodiment may 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, in which multiple stages are installed in series. In a two-stage configuration, the quality of the RO-treated water can be improved by further treating the treated water obtained in the first-stage RO membrane device in the second-stage RO membrane device. While there are no particular restrictions on the RO membranes to be cleaned with EDI electrode water, it is preferable to use the EDI electrode water to clean the first-stage RO membranes, given the susceptibility of RO membranes to contamination.

[0060] Furthermore, in the primary pure water production systems 1, 1A, 1B, 1C, and 1D of the first to fifth embodiments, a plurality of EDIs 6 may be provided in series or in parallel with one another. 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 a water treatment device that is an existing RO-EDI system, and the RO membrane device can be cleaned with cleaning water containing electrode water discharged from the EDI.

[0062] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0063] This application claims priority based on Japanese Patent Application No. 2024-026732, filed February 26, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0064] 1 Primary pure water production device 4, 40 Reverse osmosis membrane device 41 Brine reverse osmosis membrane device 6 Electrodeionization device 20 Cleaning-related configuration (cleaning mechanism)

Claims

1. A water treatment device comprising: a reverse osmosis membrane device to which 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; 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.

2. The water treatment device according to claim 1, wherein the reverse osmosis membrane device comprises: a first reverse osmosis membrane device that separates the water to be treated into a first permeate and a first concentrated water; and 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; and 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. The water treatment device according to claim 2, comprising a plurality of the first or second reverse osmosis membrane devices, the plurality of first or second reverse osmosis membrane devices being connected in parallel with each other, and the cleaning mechanism passing the cleaning water containing the electrode water through the plurality of first or second reverse osmosis membrane devices in sequence.

4. A water treatment device according to any one of claims 1 to 3, further comprising a gas-liquid separator that separates the electrode water separated by the electrical regeneration deionization device into gas and liquid, and 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 any one of claims 1 to 3, 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 any one of claims 1 to 3, further comprising an oxidant removal device for removing oxidants contained in the cleaning water containing the electrode water.

7. The water treatment device according to any one of claims 1 to 3, comprising a plurality of electrodeionization devices connected in series or in parallel with one another, and a cleaning water tank for storing the electrode water separated by 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 the permeate water from the reverse osmosis membrane device into desalinated water, concentrated water, and electrode water, the method comprising passing wash water containing the electrode water separated by the electrodeionization device through the reverse osmosis membrane device for a predetermined period of time.

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