Water treatment device and method for operating same

Abstract

A water treatment device 1 has a plurality of unit devices that perform unit operations in water treatment. These unit devices include: a reverse osmosis membrane device 6 to which water to be treated is supplied; and an electric regeneration type deionization device 8 that receives permeated water from the reverse osmosis membrane device 6, produces treated water by removing ions present in the permeated water, and discharges a concentrated water that contains the removed ions. At least one unit device from among the plurality of unit devices, other than the electric regeneration type deionization device 8, is washed by using a wash water that contains the concentrated water discharged from the electric regeneration type deionization device 8.

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. In an RO-EDI system, water to be treated is supplied to an RO membrane device, and the permeate from the RO membrane device is treated by EDI. Typically, pretreatment processes such as sand filtration, coagulation, turbidity removal membrane treatment, activated carbon treatment, softening, ion exchange treatment, and decarbonation are performed upstream of the RO membrane device. Patent Document 1 describes an RO-EDI system that includes a brine RO membrane device that treats the concentrates from the RO membrane device and the EDI, and is configured to return the permeate from the brine RO membrane to the water to be treated. Patent Document 2 describes a technology for returning the concentrate from the EDI used to produce pure water to the water to be treated.

[0003] In the RO-EDI system described above, the unit equipment that performs the unit operations of water treatment (e.g., sand filtration equipment, activated carbon equipment, decarbonation equipment, RO membrane equipment, etc.) becomes contaminated with impurities (suspended matter, fine particles, organic matter, organisms, biological metabolites, scale components, etc.) during the treatment process. For this reason, the unit equipment must be washed with clear water or wash water containing added cleaning chemicals.

[0004] Although not an RO-EDI system, Patent Document 3 describes a technology in which a system is provided with multiple stages of RO membrane devices, permeated water 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.

[0005] JP 2020-146618 A JP 11-244854 A JP 2017-209654 A

[0006] In the RO-EDI system described above, when cleaning unit equipment that performs unit operations, if the cleaning water is neutral, sufficient cleaning effect may not be obtained. On the other hand, cleaning the unit equipment using separate cleaning water containing added chemicals can improve the cleaning effect. However, this method poses the problem of increased equipment costs and chemical costs.

[0007] When the permeate from the RO membrane device is used as the cleaning water, it is possible to suppress increases in equipment costs and chemical costs. However, even in this case, if the cleaning water is neutral, there is a problem that a sufficient cleaning effect cannot be obtained.

[0008] An object of the present invention is to provide a water treatment device and an operating method thereof that can solve the above problems, suppress increases in equipment costs and chemical costs, and improve the cleaning effect of unit devices that perform unit operations.

[0009] In order to achieve the above-mentioned object, according to one aspect of the present invention, there is provided a water treatment system having a plurality of unit devices that perform unit operations of water treatment, the plurality of unit devices including a reverse osmosis membrane device to which the water to be treated is supplied, and an electrodeionization device to which the permeate of the reverse osmosis membrane device is supplied, which removes ions from the permeate to produce treated water and discharges concentrated water containing the removed ions, and at least one unit device of the plurality of unit devices other than the electrodeionization device is washed using cleaning water containing the concentrated water discharged from the electrodeionization device.

[0010] According to another aspect of the present invention, there is provided a method for operating a water treatment system having a plurality of unit devices that perform unit operations of water treatment, wherein the plurality of unit devices include a reverse osmosis membrane device to which the water to be treated is supplied, and an electrodeionization device to which the permeate of the reverse osmosis membrane device is supplied, which removes ions from the permeate to produce treated water, and which discharges concentrated water containing the removed ions, and at least one unit device of the plurality of unit devices other than the electrodeionization device is washed using cleaning water containing the concentrated water discharged from the electrodeionization device.

[0011] According to the present invention, it is possible to suppress increases in facility costs and chemical costs and to improve the cleaning effect of unit devices.

[0012] 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 water treatment device according to a second embodiment of the present invention; Fig. 3 is a block diagram showing the configuration of a water treatment device according to a third embodiment of the present invention; Fig. 4 is a block diagram showing the configuration of a water treatment device according to an example of the present invention.

[0013] 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.

[0014] First Embodiment FIG. 1 is a block diagram showing the configuration of a water treatment system (ultrapure water production system) according to a first embodiment of the present invention. Referring to FIG. 1, the water treatment system 1 of this embodiment includes a pretreatment system 4, a primary pure water production system 12, and a secondary pure water production system (subsystem) 13. The pretreatment system 4 includes a sand filtration system 40, an intermediate tank 41, a pump 42, an activated carbon system 43, a softening system 44, and a decarbonation system 45. The pretreatment system 4 is not limited to this configuration. For example, some of the above-described components may be omitted, or other components may be added to the above-described configuration. In this embodiment, a raw water tank 2 and a pump 3a are provided upstream of the pretreatment system 4. The primary pure water production system 12 includes an RO-EDI system including a reverse osmosis (RO) membrane device 6 to which the water to be treated is supplied and an electrodeionization (EDI) device 8 to which the permeate from the RO membrane device 6 is supplied. The water to be treated may be pretreated to remove impurities before being supplied to the RO membrane device 6, depending on the raw water quality and the required water quality for primary pure water. In this embodiment, an RO raw water tank 5 and a pump 3b are provided upstream of the RO membrane device 6. Furthermore, in this embodiment, a demineralized water tank 14, an ultraviolet oxidation device 15, an ion exchange device 16, and a membrane degassing device 17 are provided downstream of the EDI 8. The primary pure water production system 12 is not limited to this configuration. For example, the ultraviolet oxidation device 15, the ion exchange device 16, and the membrane degassing device 17 provided downstream of the EDI 8 do not necessarily have to be provided in this order. Furthermore, an ultraviolet oxidation device, an ion exchange device, a membrane degassing device, etc. may be provided between the RO membrane device 6 and the EDI 8, as necessary. The secondary pure water production system 13 includes a primary pure water tank 18, a heat exchanger 19, an ultraviolet oxidation device 30, an ion exchange device 31, a membrane degassing device 32, and an ultrafiltration membrane device 33. Treated water (ultrapure water) produced in the secondary pure water production system 13 is supplied to a point of use 34. The primary pure water produced in the primary pure water production system is stored in the primary pure water tank 18. The ultraviolet oxidation system 30 irradiates the water to be treated, the temperature of which has been adjusted in the heat exchanger 19, with ultraviolet light to decompose organic matter contained in the water. The ion exchange system 31 removes ionic components from the water to be treated.The ion exchanger 31 is a non-regenerative cartridge polisher packed with a mixed bed of cation exchange resin and anion exchange resin. The membrane degassing device 32 removes gases such as dissolved oxygen and carbon dioxide from the water being treated. The ultrafiltration membrane device 33 removes fine particles from the water being treated. The secondary pure water production system 13 is not limited to the above-described configuration. For example, a hydrogen peroxide removal device that decomposes hydrogen peroxide generated in the ultraviolet oxidation device 30 may be provided between the ultraviolet oxidation device 30 and the ion exchanger 31. The RO membrane device 6, the electrodeionization deionization device (EDI) 8, the ultraviolet oxidation device 15, the ion exchanger 16, the membrane degassing device 17, the sand filtration device 40, the activated carbon device 43, the softening device 44, the decarbonation device 45, the heat exchanger 19, the ultraviolet oxidation device 30, the ion exchanger 31, the membrane degassing device 32, and the ultrafiltration membrane device 33 are examples of multiple unit devices that perform unit operations in water treatment.

[0015] The raw water tank 2 is connected to a sand filtration unit 40 via a pipe, and a pump 3a is provided on this pipe. The sand filtration unit 40 is connected to an intermediate tank 41 via a pipe. The intermediate tank 41 is connected to an activated carbon unit 43 via a pipe, and a pump 42 is provided on this pipe. The activated carbon unit 43 is connected to a softener 44 via a pipe. The softener 44 is connected to a decarbonator 45 via a pipe. The decarbonator 45 is connected to the RO raw water tank 5 via a pipe.

[0016] The water to be treated may be, for example, industrial water, well water, city water, surface water, wastewater provided from inside or outside a customer's factory, treated sewage, or desalinated seawater. One or more of these waters are stored in the raw water tank 2. By operating pumps 3a and 42, the water to be treated can be passed through the sand filter 40, intermediate tank 41, activated carbon device 43, softener 44, and decarbonator 45 at appropriate times. The sand filter 40 uses sand as a filter medium to filter the water to be treated. The activated carbon device 43 further filters the treated water from the sand filter 40 using activated carbon with a porous structure. The softener 44 uses an ion exchange resin that removes hardness components from the water to remove hardness components from the treated water from the activated carbon device 43. The decarbonator 45 degasses (removes) carbon dioxide from the treated water from the softener 44 using, for example, a gas-permeable decarbonation membrane. The unit equipment performing the pretreatment unit operations is not limited to the above-mentioned equipment. For example, a turbidity removal membrane device may be used to remove turbidity from raw water. Alternatively, an alkaline softening device may be used as a softening device, which adds an alkaline agent to remove hardness components. Alternatively, a decarbonation tower may be used as a decarbonation device, which removes carbon dioxide components from water by contacting water with an acidic pH with air.

[0017] The treated water from the decarbonation device 45 is stored in the RO raw water tank 5 as RO raw water (water to be treated and supplied to the RO membrane device 6). The RO raw water tank 5 is in communication with the RO membrane device 6 via a pipe, and a pump 3b is provided on this pipe. When the pump 3b is operated, the RO raw water (water to be treated) stored in the RO raw water tank 5 is supplied to the RO membrane device 6.

[0018] The RO membrane device 6 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 6 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 6 is in communication with an EDI raw water tank 7 via piping. The EDI raw water tank 7 stores the permeate from the RO membrane device 6 as EDI raw water. The EDI raw water tank 7 is in communication with an EDI 8 via piping, and a pump 3c is provided on this piping. By operating the pump 3c, the stored water in the EDI raw water tank 7 (EDI raw water) is supplied to the EDI 8.

[0020] The concentrated water discharge side of the RO membrane device 6 is in communication with a brine reverse osmosis (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 6 as B-RO raw water. The B-RO raw water tank 9 is in communication with the B-RO membrane device 10 via a pipe, and a pump 3d is provided on this pipe. By operating the pump 3d, the stored water in the B-RO raw water tank 9 (B-RO raw water) is supplied to the B-RO membrane device 10.

[0021] Like the RO membrane device 6, the B-RO membrane device 10 utilizes reverse osmosis to remove impurities from the concentrate of the RO membrane device 6. The B-RO membrane device 10 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 10 is supplied, for example, to an intermediate tank 41. The concentrate of the B-RO membrane device 10 is discharged (discarded) outside the system, for example. In the B-RO membrane device 10 and the RO membrane device 6, 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 8 removes ions from the permeate water supplied from the RO membrane device 6 via the EDI raw water tank 7 to produce treated water (pure water) and discharges concentrated water containing the removed ions. Specifically, the EDI 8 has alternately arranged deionization compartments and concentration compartments, which are separated by alternately arranged anion exchange membranes and cation exchange membranes. The deionization compartments contain ion exchange resins. Ions in the permeate water are trapped by the ion exchange resin and collected in the concentration compartments by an electric field, where they are discharged as concentrated water.

[0023] The water treatment device 1 of this embodiment is configured to wash at least one unit device, excluding the EDI 8, among a plurality of unit devices that perform unit operations of water treatment, using wash water containing concentrated water discharged from the EDI 8. Here, the unit devices (to be washed) to be washed using the wash water include, for example, the sand filtration device 40, the activated carbon device 43, the decarbonation device 45, and the B-RO membrane device 10, but are not limited to these. The RO membrane device 6 or other unit devices may also be to be washed.

[0024] The water treatment device 1 includes a control unit 21 and a cleaning water tank 22 as cleaning-related components 20. The cleaning water tank 22 is connected to the concentrated water discharge side of the EDI 8 via a pipe. The cleaning water tank 22 stores concentrated water from the EDI 8. The stored water in the cleaning water tank 22 is used as cleaning water to clean the unit devices. Here, the cleaning water tank 22 is connected to the sand filtration device 40, the activated carbon device 43, the decarbonation device 45, and the B-RO membrane device 10 via multiple pipes 23. Each pipe 23 is provided with a pump (not shown) for sending cleaning water. The control unit 21 controls these pumps to individually clean the sand filtration device 40, the activated carbon device 43, the decarbonation device 45, and the B-RO membrane device 10 at appropriate times. Cleaning of each unit device is preferably performed as needed. For example, a timer may be used to measure the operating time of the unit device, and the unit device may be cleaned when the measured operating time reaches a predetermined time. Furthermore, when the water flow pressure or flow rate of treated water passing through a unit device falls below an allowable value, the unit device may be cleaned. After cleaning the unit device, the cleaning water is discharged (discarded) from the system.

[0025] In the water treatment device 1 of this embodiment, adjustment is made so that alkaline concentrated water is discharged from the EDI 8. Preferably, the operating conditions of the EDI 8 are set so that the pH value of the concentrated water from the EDI 8 is higher than the pH value of the permeated water from the RO membrane device 6. More preferably, the operating conditions of the RO membrane device 6 and the EDI 8 are set so that the pH value of the permeated water from the RO membrane device 6 is 8.0 or higher and the pH value of the concentrated water from the EDI 8 is 9.0 or higher.

[0026] In order to satisfy the above-mentioned operating conditions, for example, the recovery rate of the RO membrane device 6 (recovery rate (%) = RO permeate water volume / feed water volume × 100) is set to 60% or more, preferably 75% or more, and more preferably 85% or more. The recovery rate of EDI8 (recovery rate (%) = EDI treated water volume / feed water volume × 100) is set to 90% or more, preferably 92% or more, and more preferably 95% or more. Increasing the recovery rate of the RO membrane device 6 increases the amount of alkali leaking to the permeate side, and increasing the recovery rate of EDI8 increases the alkaline component in the concentrate, thereby obtaining concentrate that is more suitable as washing water.

[0027] The RO membrane device 6 may be a two-stage RO device in which a first RO membrane device and a second RO membrane device are connected in series. In this case, the recovery rate per stage of the two-stage RO is set to 60% or more, preferably 75% or more, and more preferably 85% or more. The EDI 8 may also be a two-stage EDI device in which a first EDI and a second EDI are connected in series. In this case, the recovery rate per stage of the two-stage EDI is set to 90% or more, preferably 92% or more, and more preferably 95% or more. In the two-stage EDI configuration, only the concentrated water from the first EDI (first stage) may be supplied to the cleaning water tank 22, or the concentrated water from the first EDI (first stage) and the concentrated water from the second EDI (second stage) may be combined and supplied to the cleaning water tank 22.

[0028] In the water treatment device 1 of this embodiment, the control unit 21 adjusts the pH of the water to be treated that is supplied to the RO membrane device 6 so that the concentrated water from the EDI 8 becomes alkaline at a predetermined pH value or higher. Specifically, an alkali addition device 11 is provided that adds an alkaline agent to the water to be treated that flows between the RO raw water tank 5 and the pump 3b. The control unit 21 adjusts the amount of alkaline agent added, thereby making it possible to obtain alkaline concentrated water at a predetermined pH value or higher (9.0 in this case). The control unit 21 and the alkali addition device 11 are an example of an adjustment means that adjusts the pH upstream of the EDI 8.

[0029] To adjust the pH, the water treatment device 1 includes a pH meter 24. The pH meter 24 measures the pH of the concentrated water from the EDI 8. The control unit 21 adjusts the amount of alkaline agent added in the alkali addition device 11 so that the pH meter 24 reading is equal to or greater than a predetermined value. This allows the pH of the concentrated water to be adjusted to 9.0 or greater. In this embodiment, the control unit 21 continuously monitors the pH meter 24 reading (or monitors it at predetermined intervals) and automatically adjusts the amount of alkaline agent added. However, this is not limited to this. For example, the control unit 21 may manually check the pH meter 24 reading from time to time and adjust the amount of alkaline agent added so that the pH meter 24 reading is equal to or greater than a predetermined value.

[0030] The pH meter 24 may be arranged to measure the pH value of the permeate from the RO membrane device 6. In this case, the control unit 21 may adjust the amount of alkaline agent added based on the measurement value of the pH meter 24 so that the pH value of the permeate is 8.0 or higher. In a two-stage RO configuration, an alkaline agent may be added to the feed water of the second RO membrane device (second stage). In this case, the pH meter 24 may be arranged to measure the pH value of the permeate from the second RO membrane device, and an alkaline agent may be added to the feed water of the second RO membrane device (second stage) so that the pH is 8 or higher.

[0031] According to the water treatment device 1 of this embodiment described above, the unit devices are washed using the water (washing water) stored in the washing water tank 22. Because the washing water is alkaline, the washing effect of the unit devices can be enhanced. Furthermore, because the concentrated water (alkaline) from the EDI 8 is used as the washing water, there is no need to separately prepare alkaline washing water containing added chemicals. This makes it possible to suppress increases in equipment costs and chemical costs.

[0032] The cleaning water may contain EDI concentrated water having a pH of 9.0 or more, and other water may be replenished as needed. For example, a portion of RO concentrated water having a pH of 8.0 or more may be supplied to the cleaning water tank 22. In particular, in a two-stage RO configuration, the concentrated water from the second RO membrane device (second stage) is sufficiently free of impurities and is suitable as cleaning water. Furthermore, pure water, ultrapure water, recycled pure water, etc. may be replenished and mixed with the cleaning water.

[0033] Furthermore, since the alkaline components in the permeate from the RO membrane device 6 are concentrated in the EDI 8, the alkaline concentration of the concentrated water from the EDI 8 becomes even higher than that of the permeate. This makes it possible to provide wash water with an alkaline concentration more suitable for washing. Furthermore, in the water treatment device 1 of this embodiment, the B-RO membrane device 10, which is the most susceptible to contamination among multiple unit devices that perform unit operations in water treatment, is washed. This allows for more effective washing of the unit devices.

[0034] In the water treatment device 1 of this embodiment, a circulating cleaning water tank may be provided for each unit device to be cleaned. For example, a circulating cleaning water tank is provided in the pipe 23 that connects the B-RO membrane device 10 and the cleaning water tank 22. The circulating cleaning water tank stores cleaning water from the cleaning water tank 22. The cleaning water is supplied from the circulating cleaning water tank to the B-RO membrane device 10, and the cleaning water that has passed through the B-RO membrane device 10 returns to the circulating cleaning water tank. Circulating the cleaning water in this manner improves the utilization efficiency of the cleaning water.

[0035] A plurality of unit devices to be cleaned (e.g., the sand filtration device 40, the activated carbon device 43, the carbon dioxide removal device 45, and the B-RO membrane device 10) may be provided in parallel. In this case, when a unit device is stopped and cleaned, the processing of the unit device being cleaned can be covered by using other unit devices provided in parallel.

[0036] Second Embodiment Fig. 2 is a block diagram showing the configuration of a water treatment device according to a second embodiment of the present invention. A water treatment device 1A of this embodiment has the same configuration as the water treatment device 1 of the first embodiment, except that it is provided with a cleaning chemical addition device 25. To avoid duplication, detailed description of the same configuration as the water treatment device 1 will be omitted.

[0037] The water treatment device 1A has a cleaning chemical adding device 25 as a cleaning-related component 20. The cleaning chemical adding device 25 adds cleaning chemicals to the cleaning water discharged from the cleaning water tank 22. In this embodiment, the cleaning chemical adding device 25 can add cleaning chemicals to each pipe 23. Examples of cleaning chemicals include, but are not limited to, acidic agents, alkaline agents, oxidizing agents, dispersants, and slime control agents. The cleaning chemical adding device 25 can add one or more of these chemicals to the cleaning water. The control unit 21 can control the addition of chemicals to each pipe 23 by the cleaning chemical adding device 25. For example, the type and amount of chemicals added to each pipe 23 can be controlled.

[0038] In addition to the effects described in the first embodiment, the water treatment device 1A of this embodiment has the following effects.

[0039] 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.

[0040] According to the water treatment device 1A of this embodiment, the alkaline concentrated water discharged from the EDI 8 is used as cleaning water, and therefore the cleaning chemical adding device 25 adds cleaning chemicals to the alkaline cleaning water, thereby further enhancing the cleaning effect by adding chemicals.

[0041] In addition, the amount of chemicals added can be reduced. For example, the amount of alkaline agent added when alkaline water with a pH of 9.0 or higher is obtained by adding an alkaline agent to cleaning water with a low pH value is smaller than the amount of alkaline agent added when alkaline water with a pH of 9.0 or higher is obtained by adding an alkaline agent to cleaning water with a high pH value. According to this embodiment, the amount of alkaline agent added necessary to obtain the desired cleaning effect can be reduced because the pH value of the cleaning water is high. Similarly, the amount of chemicals other than alkaline agents added necessary to obtain the desired cleaning effect can be reduced because the pH value of the cleaning water is high.

[0042] In addition, in the water treatment device 1A of this embodiment, the cleaning-related configuration 20 may include, for example, only a configuration related to the addition of cleaning chemicals.

[0043] 3 is a block diagram showing the configuration of a water treatment device according to a third embodiment of the present invention. The water treatment device 1B of this embodiment has the same configuration as the water treatment device 1 of the first embodiment, except that it is provided with a first on-off valve 26a, a second on-off valve 26b, and a water level gauge 28. To avoid duplication, detailed description of the same configuration as the water treatment device 1 will be omitted.

[0044] Water treatment device 1B has, as cleaning-related components 20, a first on-off valve 26a, a second on-off valve 26b, and a water level gauge 28. Water level gauge 28 measures the level of cleaning water stored in cleaning water tank 22 and supplies the measurement value to control unit 21. First pipe 27a connects EDI 8 and cleaning water tank 22. First on-off valve 26a is provided on first pipe 27a. Second pipe 27b branches off from a portion of first pipe 27a between first on-off valve 26a and EDI 8 and connects to RO raw water tank 5. Second on-off valve 26b is provided on second pipe 27b.

[0045] The control unit 21 operates as a flow path switching means that switches the supply destination of the concentrated water discharged from the EDI 8 between the cleaning water tank 22 and the RO raw water tank 5, which is a storage tank, in accordance with the measurement value of the water level meter 28. Specifically, when the measurement value of the water level meter 28 is equal to or less than a threshold value, the control unit 21 opens the first on-off valve 26a and closes the second on-off valve 26b. As a result, the concentrated water of the EDI 8 is supplied to the cleaning water tank 22. Furthermore, when the measurement value of the water level meter 28 exceeds the threshold value, the control unit 21 closes the first on-off valve 26a and opens the second on-off valve 26b. As a result, the concentrated water of the EDI 8 is supplied to the RO raw water tank 5.

[0046] In addition to the effects described in the first embodiment, the water treatment device 1B of this embodiment has the following effects: The amount of wash water required to wash the unit devices is significantly smaller than the amount of concentrated water discharged from the EDI 8. If the excess concentrated water not used as wash water is discarded, the recovery rate of treated water will decrease.

[0047] In the water treatment device 1B of this embodiment, the excess concentrated water is returned to the RO raw water tank 5. This improves the recovery rate of treated water in the entire RO-EDI system. Note that the water treatment device 1B of this embodiment may have only a component related to the treatment of the excess concentrated water as the cleaning-related component 20, for example.

[0048] Furthermore, in the water treatment device 1B of this embodiment, the destination of the concentrated water discharged from the EDI 8 is switched between the cleaning water tank 22 and the RO raw water tank 5 based on the water level of the concentrated water in the cleaning water tank 22, but this is not limited to this. Instead of the RO raw water tank 5, the destination of the switch may be a storage tank (e.g., B-RO raw water tank 9, intermediate tank 41, etc.) provided at the inlet side of one of the unit devices located upstream of the EDI 8. Furthermore, instead of the water level in the cleaning water tank 22, the quality of the concentrated water from the EDI 8 (e.g., conductivity or TOC (total organic carbon) concentration) may be measured, and the destination of the supply may be switched based on the measured value. Specifically, a water quality measurement unit is provided that measures the quality of the concentrated water discharged from the EDI 8. The water quality measurement unit measures the quality of the concentrated water from the EDI 8 and supplies the measured value to the control unit 21. The control unit 21 operates as a flow path switching means that switches the supply destination of the concentrated water discharged from the EDI 8 between the cleaning water tank 22 and a storage tank provided on the inlet side of any unit device upstream of the EDI 8, depending on the measurement value of the water quality measurement unit. Specifically, when the measurement value of the water quality exceeds a threshold value, the control unit 21 switches the supply destination of the concentrated water discharged from the EDI 8 from the cleaning water tank 22 to a storage tank provided on the inlet side of any unit device upstream of the EDI 8. This makes it possible to prevent concentrated water with degraded water quality from being used as cleaning water.

[0049] (Embodiment) Fig. 4 is a block diagram showing one embodiment of a water treatment device of the present invention. For convenience, Fig. 4 shows only a part of the water treatment device (RO-EDI portion), and other parts are omitted.

[0050] The water treatment device of this embodiment includes a first RO membrane device 6a and a second RO membrane device 6b as the RO membrane device 6. The first RO membrane device 6a and the second RO membrane device 6b have basically the same structure, but have different recovery rates. The water to be treated is supplied from the RO raw water tank 5 to the first RO membrane device 6a. The first RO membrane device 6a uses reverse osmosis to remove impurities from the water to be treated and discharges permeated water that has passed through the reverse osmosis membrane and concentrated water containing impurities separated by the reverse osmosis membrane. The permeated water from the first RO membrane device 6a is supplied to the second RO membrane device 6b. The concentrated water from the first RO membrane device 6a is supplied to the B-RO raw water tank 9 (see FIG. 1, etc.).

[0051] The second RO membrane device 6b uses reverse osmosis to remove impurities from the permeated water of the first RO membrane device 6a and discharges the permeated water that has passed through the reverse osmosis membrane and the concentrated water containing the impurities separated by the reverse osmosis membrane. The permeated water of the second RO membrane device 6b is supplied to the EDI raw water tank 7. The concentrated water of the second RO membrane device 6b is supplied to the B-RO raw water tank 9 (see FIG. 1, etc.).

[0052] In the water treatment system of this example, the pH value of the feed water (water to be treated) for the first RO membrane device 6a was adjusted to 9.5, and the RO recovery rate was set to 85%. For the second RO membrane device 6b, the pH value of the feed water was left as is, and the RO recovery rate was set to 95%. The pH value of the permeate from the second RO membrane device 6b was 9.0.

[0053] For EDI8, the pH value of the feed water was left as is (=9.0), and the EDI recovery rate was set to 90%. The pH value of the concentrated water from EDI8 at this time was 10.2. When the concentrated water with a pH value of 10.2 was used as cleaning water to clean the unit equipment, a high cleaning effect was obtained.

[0054] The water treatment devices of the first to third embodiments described above are merely examples of the present invention, and the components of each embodiment can be modified as appropriate. For example, the cleaning configuration 20 (addition of cleaning chemicals) of the water treatment device 1A of the second embodiment may be combined with the cleaning configuration 20 (recovery of excess concentrated water) of the water treatment device 1B of the third embodiment. Furthermore, in each embodiment, the water treatment device can be realized by incorporating the cleaning configuration 20 into an existing RO-EDI system. In this case, too, the concentrated water discharged from the EDI is adjusted to be alkaline, and the unit equipment is cleaned with cleaning water containing the concentrated water.

[0055] In the water treatment apparatus of each embodiment, the unit equipment performing the unit operation downstream of the EDI 8 may be washed with wash water containing the concentrated water from the EDI 8, as necessary. Furthermore, some or all of the water obtained in or discharged from the unit equipment downstream of the EDI 8 may be mixed with the concentrated water from the EDI 8 as wash water. In particular, the final filter discharges a portion of the concentrated water for operation, and it is therefore preferable to mix this water as wash water. Furthermore, although each embodiment has been described using an ultrapure water production system as an example of the water treatment apparatus, the water treatment apparatus is not limited to an ultrapure water production system. For example, the water treatment apparatus may be composed of a pretreatment apparatus 4 and a primary pure water production apparatus 12, or may be composed of a primary pure water production apparatus 12.

[0056] 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.

[0057] This application claims priority based on Japanese Patent Application No. 2023-181976, filed October 23, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0058] 1 Water treatment device 6 Reverse osmosis membrane device 8 Electrodeionization device 20 Cleaning-related components

Claims

1. A water treatment device having a plurality of unit devices that perform unit operations of water treatment, the plurality of unit devices including: a reverse osmosis membrane device to which the water to be treated is supplied; and an electrodeionization device to which the permeate from the reverse osmosis membrane device is supplied, which removes ions from the permeate to produce treated water and discharges concentrated water containing the removed ions; and at least one of the plurality of unit devices, excluding the electrodeionization device, is washed using wash water containing the concentrated water discharged from the electrodeionization device.

2. The water treatment device according to claim 1, further comprising an adjusting means for adjusting the pH of the concentrated water discharged from the electrodeionization device in a stage upstream of the electrodeionization device so that the concentrated water is alkaline.

3. The water treatment device according to claim 2, wherein the operating conditions of the electrodeionization device are set so that the pH value of the concentrated water discharged from the electrodeionization device is higher than the pH value of the permeate from the reverse osmosis membrane device.

4. A method for operating a water treatment device as described in claim 3, wherein the operating conditions of the reverse osmosis membrane device and the electrical regenerative deionization device are set so that the pH value of the permeate from the reverse osmosis membrane device is 8 or higher, and the pH value of the concentrated water discharged from the electrical regenerative deionization device is 9 or higher.

5. The water treatment device according to claim 2, further comprising: an alkali addition device that adds an alkaline agent to the water to be treated; and a pH meter that measures the pH value of the permeate from the reverse osmosis membrane device or the concentrated water discharged from the electrical regenerator, and the amount of the alkaline agent added by the alkali addition device is adjusted so that the measured value of the pH meter is equal to or greater than a predetermined value.

6. The water treatment device described in claim 5, further comprising a control unit that adjusts the amount of alkaline agent added based on the measurement value of the pH meter so that the pH value of the permeate from the reverse osmosis membrane device is 8 or higher, or so that the pH value of the concentrated water discharged from the electrical regenerator deionization device is 9 or higher.

7. The water treatment device according to any one of claims 1 to 6, further comprising a chemical addition device for adding one or more of an acid agent, an alkaline agent, an oxidizing agent, a dispersing agent, and a slime control agent to the wash water.

8. A water treatment device as described in any one of claims 1 to 6, comprising: a cleaning water tank for storing the concentrated water discharged from the electrical deionization device as the cleaning water; a water quality measuring unit for measuring the water quality of the concentrated water discharged from the electrical deionization device; and a storage tank provided at the inlet side of any one of the plurality of unit devices that is located upstream of the electrical deionization device, wherein when the measurement value of the water quality measuring unit exceeds a threshold value, the supply destination of the concentrated water discharged from the electrical deionization device is switched from the cleaning water tank to the storage tank.

9. A water treatment device as described in any one of claims 1 to 6, comprising: a cleaning water tank for storing the concentrated water discharged from the electrical deionization device as the cleaning water; a water level gauge for measuring the water level of the cleaning water stored in the cleaning water tank; and a storage tank provided at the inlet side of any one of the plurality of unit devices that is located upstream of the electrical deionization device, wherein when the measured value of the water level gauge exceeds a threshold value, the supply destination of the concentrated water discharged from the electrical deionization device is switched from the cleaning water tank to the storage tank.

10. A method for operating a water treatment system having a plurality of unit devices that perform unit operations of water treatment, wherein the plurality of unit devices include a reverse osmosis membrane device to which the water to be treated is supplied, and an electrical deionization device to which the permeate from the reverse osmosis membrane device is supplied, which removes ions from the permeate to produce treated water, and which discharges concentrated water containing the removed ions, and wherein at least one unit device among the plurality of unit devices, excluding the electrical deionization device, is washed using cleaning water containing the concentrated water discharged from the electrical deionization device.