Pure water production system and method

Abstract

Provided are a pure water production system and method that can reduce the concentration of TOC components in the resulting pure water while suppressing a decrease in the water recovery rate of the entire system in pure water production that sequentially involves reverse osmosis membrane treatment, ion exchange treatment using ion exchange resins, and reverse osmosis membrane treatment. [Solution] A pure water production system 1 includes a first reverse osmosis membrane treatment device 16 that passes raw water through a first reverse osmosis membrane, an ion exchange treatment device 22 that performs ion exchange treatment on the first RO permeate using ion exchange resin, a second reverse osmosis membrane treatment device 26 that passes the ion-exchanged water through a second reverse osmosis membrane, and a return means that returns the second RO concentrated water to the upstream stage of the first reverse osmosis membrane treatment device 16.

Description

[Technical Field]

[0001] The present invention relates to a pure water production system and a pure water production method. [Background technology]

[0002] In pure water production systems, groundwater, industrial water, city water, etc. are used as raw water. In recent years, in order to make more efficient use of water resources, reclaimed water, which is treated and reused from sewage and other sources, has also come to be used as raw water. This raw water may contain scale components, such as hardness components and silica, which can cause scale formation.

[0003] In some pure water production systems, reverse osmosis membrane treatment and ion exchange resin treatment are used to remove ionic components from raw water containing scale components. In this method, the reverse osmosis membrane treatment separates most of the scale components into a concentrated water, and the components remaining in the permeate are adsorbed and removed by an ion exchange resin. The ion exchange resin is regenerated using regenerating chemicals, and the components adsorbed by the ion exchange resin are discharged from the system as regenerated wastewater.

[0004] In order to further remove trace amounts of organic matter and other TOC (Total Organic Carbon) components from ion-exchange treated water, a reverse osmosis membrane may be installed after the ion-exchange resin treatment. The permeate from this reverse osmosis membrane treatment is used as primary pure water, and the concentrated water is used for regenerating the ion-exchange resin or for washing.

[0005] As described above, when reverse osmosis membrane treatment is used in the stage preceding ion exchange resin treatment, concentrated water is produced, which poses a problem of a low water recovery rate for the system.

[0006] For example, Patent Document 1 describes an ultrapure water production system in which concentrated water from reverse osmosis membrane treatment, which follows ion exchange resin treatment, is introduced into a wastewater recovery system for miscellaneous water or a wastewater treatment system. If concentrated water from reverse osmosis membrane treatment, which follows ion exchange resin treatment, is recovered as miscellaneous water, a decrease in the water recovery rate of the entire system can be suppressed. However, if there is no other use for the miscellaneous water in other systems, the excess water must be discharged, and if the water quality does not meet the discharge standards, separate treatment equipment may be required.

[0007] Even when reverse osmosis membrane treatment is used in the upstream stage of ion exchange resin treatment, the concentrated water for the downstream reverse osmosis membrane treatment can be used to regenerate the ion exchange resin or to wash the ion exchange resin. However, when reverse osmosis membrane treatment is used in the upstream stage of ion exchange resin treatment, only small amounts of water are required for regenerating the ion exchange resin or to wash the ion exchange resin. This limits the places where the concentrated water for the downstream reverse osmosis membrane treatment can be recovered and used, resulting in surplus water. If the water quality does not meet the discharge standards, it has been necessary to install a separate treatment facility and treat the water before discharging it. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 3789619 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a pure water production system and method that can reduce the concentration of TOC components in the resulting pure water while suppressing a decrease in the water recovery rate of the entire system in the production of pure water by sequentially performing reverse osmosis membrane treatment, ion exchange treatment using an ion exchange resin, and reverse osmosis membrane treatment. [Means for solving the problem]

[0010] The present invention provides a pure water production system for producing pure water, comprising: a first reverse osmosis membrane treatment device that passes raw water through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrate; an ion exchange treatment device that performs ion exchange treatment on the first RO permeate with an ion exchange resin to obtain ion-exchanged water; a second reverse osmosis membrane treatment device that passes the ion-exchanged water through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrate; and a return means that returns the second RO concentrate to a stage upstream of the first reverse osmosis membrane treatment device. The permeability coefficient of the first reverse osmosis membrane is smaller than the permeability coefficient of the second reverse osmosis membrane. , a pure water production system.

[0012] In the pure water production system, it is preferable that the ion exchange resin is regenerated using regeneration water, and at least one of acid and alkali is recovered from the resulting regeneration waste liquid.

[0013] The pure water production system preferably further comprises at least one of an electrodialysis device and an electrical regeneration type demineralization device for recovering at least one of an acid and an alkali from the regeneration waste liquid.

[0014] In the pure water producing system, it is preferable that water from a plurality of water sources is used as the raw water, and that a portion of the raw water is bypassed through the first reverse osmosis membrane treatment device depending on the flow rate ratio of the water from each of the water sources.

[0015] In the pure water production system, it is preferable that the water from the multiple water sources is water that has permeated the reverse osmosis membrane and water that has not permeated the reverse osmosis membrane, and when the flow rate ratio of the water that has not permeated the reverse osmosis membrane is 50 vol% or less of the raw water, a portion of the raw water is bypassed through the first reverse osmosis membrane treatment device.

[0016] The present invention is a method for producing pure water, comprising: a first reverse osmosis membrane treatment step of passing raw water through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrate; an ion exchange treatment step of performing ion exchange treatment on the first RO permeate with an ion exchange resin to obtain ion-exchanged water; and a second reverse osmosis membrane treatment step of passing the ion-exchanged water through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrate, the permeability coefficient of the first reverse osmosis membrane is smaller than the permeability coefficient of the second reverse osmosis membrane; This is a method for producing pure water, in which the second RO concentrated water is returned to the stage before the first reverse osmosis membrane treatment step.

[0018] In the method for producing pure water, it is preferable to regenerate the ion exchange resin using regeneration water and recover at least one of the acid and the alkali from the resulting regeneration waste liquid.

[0019] The above-mentioned method for producing pure water preferably further comprises at least one of an electrodialysis step and an electrical regeneration demineralization step for recovering at least one of an acid and an alkali from the regeneration waste liquid.

[0020] In the method for producing pure water, it is preferable that the raw water is water from a plurality of water sources, and that a portion of the raw water is bypassed from the first reverse osmosis membrane treatment step depending on the flow rate ratio of the water from each of the water sources.

[0021] In the above-described method for producing pure water, it is preferable that when the water from the plurality of water sources is composed of water that has permeated the reverse osmosis membrane and water that has not permeated the reverse osmosis membrane, and the flow rate ratio of the water that has not permeated the reverse osmosis membrane is 50 vol% or less of the raw water, a portion of the raw water is bypassed from the first reverse osmosis membrane treatment step. [Effects of the Invention]

[0022] The present invention provides a pure water production system and method that can reduce the concentration of TOC components in the resulting pure water while suppressing a decrease in the water recovery rate of the entire system in the production of pure water by sequentially performing reverse osmosis membrane treatment, ion exchange treatment using an ion exchange resin, and reverse osmosis membrane treatment. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic configuration diagram illustrating an example of a pure water producing system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a schematic configuration diagram showing another example of a pure water producing system according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic configuration diagram showing another example of a pure water producing system according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing the water recovery rate of the entire system in the pure water producing system of Comparative Example 1. [Figure 5] FIG. 2 is a diagram showing the water recovery rate of the entire system in the pure water producing system of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0025] An example of a pure water production system according to an embodiment of the present invention is outlined in Fig. 1, and its configuration will be described below. The pure water production system 1 shown in Fig. 1 is an example of a pure water production system that sequentially performs reverse osmosis membrane treatment, ion exchange treatment using ion exchange resins, and reverse osmosis membrane treatment.

[0026] The pure water producing system 1 includes a first reverse osmosis membrane treatment device 16 that passes raw water through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrate, an ion exchange treatment device 22 that performs ion exchange treatment on the first RO permeate using ion exchange resin to obtain ion-exchanged water, a second reverse osmosis membrane treatment device 26 that passes the ion-exchanged water through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrate, and a return pipe 64 as return means for returning the second RO concentrate to the upstream stage of the first reverse osmosis membrane treatment device 16.

[0027] The pure water producing system 1 may include, upstream of the first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment), a raw water tank 10 for storing raw water, a filtration device 12 as a filtration means for performing turbidity treatment on the raw water, and a water tank 14 for storing clarified water obtained by the clarification treatment. The pure water producing system 1 may include, upstream of the ion exchange treatment device 22, a water tank 18 for storing first RO permeate obtained by the first reverse osmosis membrane treatment, and an activated carbon treatment device 20 as activated carbon treatment means for removing or reducing residual chlorine, organic matter, etc. from the first RO permeate. The pure water producing system 1 may include, upstream of the second reverse osmosis membrane treatment device 26, a water tank 24 for storing ion-exchanged water obtained by the ion exchange treatment. The pure water producing system 1 may include a water tank 28 for storing first RO concentrate obtained by the first reverse osmosis membrane treatment, and a third reverse osmosis membrane treatment device 30 for passing the first RO concentrate through a third reverse osmosis membrane to obtain third RO permeate and third RO concentrate.The pure water producing system 1 may also include a water tank 32 for diluting a regenerant for regenerating the ion exchange resin of the ion exchange treatment device 22 with a diluent such as water to obtain regeneration water, and a water tank 34 for storing regeneration waste liquid generated during the regeneration of the ion exchange resin.

[0028] In the pure water producing system 1 of FIG. 1 , a pipe 40 is connected to the raw water inlet of the raw water tank 10. The raw water outlet of the raw water tank 10 and the inlet of the filtration device 12 may be connected by a pipe (not shown). The clarified water outlet of the filtration device 12 and the clarified water inlet of the water tank 14 are connected by a pipe 42. The clarified water outlet of the water tank 14 and the clarified water inlet of the first reverse osmosis membrane treatment device 16 may be connected by a pipe (not shown). The first RO permeate outlet of the first reverse osmosis membrane treatment device 16 and the first RO permeate inlet of the water tank 18 are connected by a pipe 44. The first RO permeate outlet of the water tank 18 and the first RO permeate inlet of the activated carbon treatment device 20 may be connected by a pipe (not shown). The activated carbon-treated water outlet of the activated carbon treatment device 20 and the activated carbon-treated water inlet of the ion exchange treatment device 22 may be connected by a pipe (not shown). The ion exchange treated water outlet of the ion exchange treatment device 22 and the ion exchange treated water inlet of the water tank 24 are connected by piping 52. The ion exchange treated water outlet of the water tank 24 and the ion exchange treated water inlet of the second reverse osmosis membrane treatment device 26 may be connected by piping (not shown). A piping 62 is connected to the second RO permeate outlet of the second reverse osmosis membrane treatment device 26. A return piping 64 is connected to the second RO concentrate outlet of the second reverse osmosis membrane treatment device 26 and the second RO concentrate inlet of the raw water tank 10. A regeneration water outlet of the water tank 32 and the regeneration water inlet of the ion exchange treatment device 22 are connected by piping 54. A regeneration waste liquid outlet of the ion exchange treatment device 22 and the regeneration waste liquid inlet of the water tank 34 are connected by piping 56. A piping 58 is connected to the regeneration waste liquid outlet of the water tank 34. A piping 66 branching from the return piping 64 is connected to the second RO concentrate inlet of the water tank 32. The first RO concentrate outlet of the first reverse osmosis membrane treatment device 16 and the first RO concentrate inlet of the water tank 28 are connected by a pipe 46. The first RO concentrate outlet of the water tank 28 and the first RO concentrate inlet of the third reverse osmosis membrane treatment device 30 may be connected by a pipe (not shown). A pipe 48 is connected to the third RO permeate outlet of the third reverse osmosis membrane treatment device 30, and a pipe 50 is connected to the third RO concentrate outlet.

[0029] The operation of the pure water producing method and the pure water producing system 1 according to this embodiment will be described.

[0030] Raw water is stored in raw water tank 10 as needed via piping 40. The raw water is sent from raw water tank 10 to filtration device 12. As needed, the raw water is subjected to turbidity removal and other treatments in filtration device 12 (turbidity removal treatment process). The turbidity-removed water is stored in water tank 14 as needed via piping 42. The turbidity-removed water is sent from water tank 14 to first reverse osmosis membrane treatment device 16. In first reverse osmosis membrane treatment device 16, raw water (here, turbidity-removed raw water) is passed through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrate (first reverse osmosis membrane treatment process). The first RO permeate obtained by the first reverse osmosis membrane treatment is stored in water tank 18 as needed via piping 44. The first RO permeate is sent from water tank 18 to activated carbon treatment device 20. If necessary, the first RO permeate is treated with activated carbon in the activated carbon treatment device 20 to remove or reduce residual chlorine and organic matter from the first RO permeate (activated carbon treatment step). The activated carbon-treated water obtained by the activated carbon treatment is sent from the activated carbon treatment device 20 to the ion exchange treatment device 22. In the ion exchange treatment device 22, the first RO permeate (here, activated carbon-treated water, which is the first RO permeate that has been treated with activated carbon) is subjected to ion exchange treatment using an ion exchange resin to obtain ion-exchanged water (ion exchange treatment step). The ion-exchanged water obtained in the ion exchange treatment step is stored in the water tank 24 via piping 52 as necessary. The ion-exchanged water is sent from the water tank 24 to the second reverse osmosis membrane treatment device 26. In the second reverse osmosis membrane treatment device 26, the ion-exchanged water is passed through a second reverse osmosis membrane to obtain second RO permeate and second RO concentrate (second reverse osmosis membrane treatment step). The second RO permeate obtained by the second reverse osmosis membrane treatment is discharged as pure water via piping 62. At least a portion of the second RO concentrated water obtained by the second reverse osmosis membrane treatment is returned through the return pipe 64 to the raw water tank 10, which is the upstream stage of the first reverse osmosis membrane treatment device 16 (return process).

[0031] The first RO concentrate obtained by the first reverse osmosis membrane treatment is stored in the water tank 28 as needed via piping 46. The first RO concentrate is sent from the water tank 28 to the third reverse osmosis membrane treatment device 30. In the third reverse osmosis membrane treatment device 30, the first RO concentrate may be passed through a third reverse osmosis membrane to obtain third RO permeate and third RO concentrate (third reverse osmosis membrane treatment step). The third RO permeate obtained by the third reverse osmosis membrane treatment may be discharged via piping 48, or may be sent to the raw water tank 10 via piping 48 as needed. The third RO concentrate obtained by the third reverse osmosis membrane treatment is discharged as wastewater via piping 50.

[0032] The regenerant for regenerating the ion exchange resin is introduced into the water tank 32, for example, through a pipe 60. In the water tank 32, the regenerant is diluted with a diluent such as water to obtain regeneration water (regeneration water preparation process). At least a portion of the second RO concentrate is sent to the water tank 32 through a pipe 66 branched from the return pipe 64 and may be used as a diluent for diluting the regenerant. When it becomes necessary to regenerate the ion exchange resin in the ion exchange treatment device 22, the regeneration water containing the regenerant is sent to the ion exchange treatment device 22 through a pipe 54. The ion exchange resin is regenerated in the ion exchange treatment device 22 using the regeneration water (regeneration process). Regeneration waste liquid generated during the regeneration of the ion exchange resin is stored in the water tank 34 as needed through a pipe 56. The regeneration waste liquid is discharged from the water tank 34 through a pipe 58.

[0033] The inventors discovered that in a pure water production process that sequentially involves reverse osmosis membrane treatment (first reverse osmosis membrane treatment), ion exchange treatment using an ion exchange resin, and reverse osmosis membrane treatment (second reverse osmosis membrane treatment), a decrease in the water recovery rate of the entire system can be suppressed by returning the concentrated water from the second reverse osmosis membrane treatment (second RO concentrated water) to a stage (e.g., raw water tank 10) preceding the reverse osmosis membrane treatment (first reverse osmosis membrane treatment), which is a stage preceding the ion exchange treatment. Furthermore, if the second RO concentrated water is returned to a tank (e.g., tank 18) that stores water to be treated in the ion exchange treatment, trace amounts of TOC components eluted from the ion exchange resin are circulated and concentrated within the system, resulting in another problem of an increase in the TOC concentration of the primary pure water. However, by returning the second RO concentrated water to a stage preceding the first reverse osmosis membrane treatment, the TOC components eluted from the ion exchange resin are eliminated by the first reverse osmosis membrane treatment, thereby suppressing concentration within the system. Furthermore, since reverse osmosis membrane treatment (first reverse osmosis membrane treatment) is performed before the ion exchange treatment, there is also the effect of being able to extend the life of the activated carbon even when activated carbon treatment is performed before the ion exchange treatment.

[0034] In Patent Document 1, the concentrated water from the reverse osmosis membrane treatment subsequent to the ion exchange resin treatment in the pure water wastewater recovery system is recovered in a separate wastewater recovery system for general-purpose water or wastewater treatment. In contrast, in the pure water production method and system according to the present embodiment, the second RO concentrated water from the second reverse osmosis membrane treatment is returned to the upstream stage of the first reverse osmosis membrane treatment in the same system and recovered. This allows water to be recovered without causing excess recovered water, thereby preventing a decrease in the water recovery rate of the entire system. Furthermore, as described below, by setting the permeability coefficient of the first reverse osmosis membrane in the first reverse osmosis membrane treatment device 16 smaller than that of the second reverse osmosis membrane in the downstream second reverse osmosis membrane treatment device 26, TOC components eluted from the ion exchange resin in the system are prevented from being circulated and concentrated, allowing them to be efficiently discharged outside the system.

[0035] The raw water is not particularly limited, and may be, for example, groundwater, industrial water, or city water. The raw water is water containing components that can clog a reverse osmosis membrane, such as at least one of hardness components and silica. The raw water is stored in raw water tank 10 as needed. Water from multiple water sources may be used as the raw water. In some cases, the raw water may be partially mixed with water that has had its hardness components and silica reduced, such as reclaimed water or recovered water that has been treated once with a reverse osmosis membrane.

[0036] When the raw water contains hardness components, the concentration of the hardness components in the raw water is, for example, in the range of 1 to 100 mg / L.When the raw water contains silica, the concentration of silica in the raw water is, for example, in the range of 1 to 100 mg / L.

[0037] Raw water is sent to raw water tank 10 by means of a pump or the like, and is subjected to clarification treatment, such as sand filtration or turbidity membrane treatment, in filtration device 12 as needed, before being introduced into first reverse osmosis membrane treatment device 16. A reducing agent, a bactericide (slime inhibitor), a dispersant (scale inhibitor), or the like may be added before first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment step). Furthermore, a water tank 28 for storing first RO concentrate from first reverse osmosis membrane treatment device 16, a pump, and the like may be provided, and a third reverse osmosis membrane treatment device 30 may be provided as a brine reverse osmosis membrane treatment device that further concentrates the first RO concentrate. The third RO permeate from the brine reverse osmosis membrane treatment (third reverse osmosis membrane treatment) may be returned to raw water tank 10 or discharged outside the system.

[0038] The recovery rate of the first reverse osmosis membrane treatment (including brine reverse osmosis membrane treatment), expressed as (first RO permeate volume / inlet water volume) × 100, varies depending on the quality of the raw water, but is, for example, in the range of 30 to 95%, preferably in the range of 50 to 93%, and more preferably in the range of 60 to 90%. If the recovery rate of the first reverse osmosis membrane treatment is too high, the risk of scale deposition may increase, and if it is too low, the amount of raw water used may increase.

[0039] When using a portion of raw water that has been treated once with a reverse osmosis membrane, such as reclaimed water, the reclaimed water may be sent to a water tank 18 that stores water to be treated with activated carbon (first RO permeate) instead of the raw water tank 10.

[0040] The first RO permeate obtained in the first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment process) is sent to the subsequent stage, stored in a water tank 18 as needed, and then treated with activated carbon as needed before being sent to the ion exchange treatment device 22.

[0041] The ion exchange resin used in the ion exchange treatment device 22 is at least one of cation exchange resins, such as strongly acidic cation exchange resins or weakly acidic cation exchange resins, and anion exchange resins, such as strongly basic anion exchange resins or weakly basic anion exchange resins. The ion exchange treatment device 22 (ion exchange treatment step) may employ a known method, such as a two-bed, three-tower (2B3T) system equipped with a cation exchange tower containing a cation exchange resin, a decarbonation tower that removes or reduces carbon dioxide by blowing air or the like into the tower, and an anion exchange tower containing an anion exchange resin, or a mixed-bed system in which a cation exchange resin and an anion exchange resin are housed in a single tower. The ion-exchange-treated water obtained by the ion exchange treatment is sent to the second reverse osmosis membrane treatment device 26 in the downstream stage.

[0042] The ion exchange resin is periodically regenerated with a regenerant such as an acid such as hydrochloric acid, sulfuric acid, or nitric acid, or an alkali such as sodium hydroxide or potassium hydroxide. The regenerant used to regenerate the ion exchange resin is diluted with a diluent such as water in a water tank 32 before use.

[0043] The second RO permeate obtained in the second reverse osmosis membrane treatment device 26 (second reverse osmosis membrane treatment step) is used as primary pure water. A portion of the second RO concentrate may be used as a diluent for regenerating ion exchange resins or as water for rinsing the ion exchange resins, and the remaining portion is returned to the raw water tank 10 or other upstream portion of the first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment step). The second RO concentrate may be returned to the piping 40, piping 42, or water tank 14 upstream of the first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment step). In this case, if the second RO concentrate is returned to, for example, the water tank 18 or piping 44 storing the water to be treated (first RO permeate) for activated carbon treatment, TOC components eluted from the ion exchange resins may be circulated and concentrated within the system, potentially increasing the TOC content of the primary pure water. Therefore, the second RO concentrate is returned to the upstream portion of the first reverse osmosis membrane treatment device 16.

[0044] The recovery rate of the second reverse osmosis membrane treatment, expressed as (second RO permeate volume / inlet water volume) × 100, is, for example, in the range of 50 to 98%, preferably in the range of 60 to 96%, and more preferably in the range of 70 to 95%. If the recovery rate of the second reverse osmosis membrane treatment is too high, the risk of scale deposition may increase, and if it is too low, the amount of primary pure water obtained may decrease.

[0045] The entire amount of the second RO concentrate may be returned to the upstream stage of the first reverse osmosis membrane treatment device 16, or a portion may be used as a diluent for regenerating ion exchange resins or as water for washing the ion exchange resins. To increase the water recovery rate of the entire pure water production system, it is preferable to return 80% or more, and preferably 90% or more, of the second RO concentrate to the upstream stage of the first reverse osmosis membrane treatment device 16.

[0046] The second reverse osmosis membrane has a permeability coefficient (calculated as the amount of permeated water / membrane area / operating pressure when pure water is passed through at a temperature of 25°C and an operating pressure of 0.75 MPa) in the range of, for example, 0.2 m / d / MPa to 2.0 m / d / MPa, preferably 0.4 m / d / MPa to 1.8 m / d / MPa. In this case, the permeability coefficient of the first reverse osmosis membrane may be, for example, less than 1.0 m / d / MPa, and the permeability coefficient of the second reverse osmosis membrane may be, for example, 1.0 m / d / MPa or more, so that the permeability coefficient of the first reverse osmosis membrane is smaller than that of the second reverse osmosis membrane. Generally, a membrane with a high permeability coefficient has a low rejection rate of TOC components, and a membrane with a low permeability coefficient has a high rejection rate of TOC components. Therefore, by making the permeability coefficient of the first reverse osmosis membrane lower than that of the second reverse osmosis membrane, even if the TOC components eluted from the ion exchange resin are concentrated by the second reverse osmosis membrane and returned to the previous stage as components contained in the concentrated water, they can be effectively eliminated by the first reverse osmosis membrane, thereby suppressing cyclic concentration within the system.

[0047] The pure water producing method and pure water producing system according to this embodiment can achieve a water recovery rate of, for example, 85% or more, preferably 87% or more for the entire pure water producing system.

[0048] FIG. 2 shows another example of a pure water production method and system according to this embodiment, illustrating an example of a flow chart for recovering at least one of an acid and an alkali from regenerated wastewater of an ion exchange resin using at least one of an electrodialysis apparatus and an electrical regeneration demineralization apparatus.

[0049] The pure water production system 3 shown in FIG. 2 includes the components of FIG. 1, and further includes a recovery device 36 that recovers at least one of an acid and an alkali from the regeneration waste liquid.

[0050] In the pure water production system 3, the regeneration waste liquid outlet of the water tank 34 and the regeneration waste liquid inlet of the recovery device 36 are connected by a pipe 58. A pipe 68 is connected to the recovered acid / alkali outlet of the recovery device 36, and a pipe 70 is connected to the recovered liquid outlet.

[0051] The regeneration waste liquid generated during the regeneration of the ion exchange resin is stored in the water tank 34 as needed via a pipe 56. The regeneration waste liquid may be discharged from the water tank 34 via a pipe 58 as shown in Fig. 1, or may be recovered by separating the acid and alkali from the regeneration waste liquid using a recovery device 36 as shown in Fig. 2 (recovery step). The acid and alkali recovered by the recovery device 36 are discharged via a pipe 68, and the recovered liquid is discharged via a pipe 70.

[0052] As the recovery device 36, an electrodialysis (ED) device, an electrolysis demineralization (EDI) device, or the like is used, and a method such as electrodialysis (ED) or electrolysis demineralization is utilized. The recovered acid and alkali may be reused as a regenerant or may be used for another purpose. The recovered liquid from which the regenerant has been recovered may be discharged.

[0053] An electrodialysis (ED) device, for example, has cation exchange membranes and anion exchange membranes alternately arranged between a pair of electrodes to form a deionization compartment and a concentration compartment. In an electrodialysis device, when regeneration wastewater is supplied to the deionization compartment and a direct current is passed through, cations are attracted to the cathode, permeate the cation exchange membrane, and move to the concentration compartment, while anions are attracted to the anode, permeate the anion exchange membrane, and move to the concentration compartment. This removes or reduces ionic components from the regeneration wastewater in the deionization compartment, producing a recovered liquid, and the ionic components are recovered in the concentration compartment.

[0054] An electrical deionization (EDI) device is a device that combines electrophoresis and electrodialysis. An EDI device is configured, for example, with a deionization compartment separated by a pair of ion exchange membranes, disposed between an anode and a cathode. In an electrical deionization device, at least the deionization compartment is filled with an ion exchange resin, and regenerated wastewater is passed through the deionization compartment while a DC voltage is applied between the anode and the cathode. This causes the deionization process for the regenerated wastewater in the deionization compartment, and a recovered liquid with ionic components removed or reduced flows out of the deionization compartment.

[0055] In the pure water production method and pure water production system according to this embodiment, a first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment process) is provided before the ion exchange treatment device 22 (ion exchange treatment process) that uses ion exchange resin. This reduces the load of scale components on the ion exchange resin, thereby reducing the risk of the electrodialysis device or electrical regeneration demineralization device becoming clogged with scale, and the system can efficiently recover acids and alkalis and reduce the salt concentration in the regenerated waste liquid.

[0056] On the other hand, since the amount of water required as regeneration water or cleaning water for the ion exchange treatment device 22 is reduced, the use of the second RO concentrate water in the subsequent second reverse osmosis membrane treatment device 26 (second reverse osmosis membrane treatment process) is limited, so this method and system, which returns the second RO concentrate water to the upstream stage of the upstream first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment process), is effective.

[0057] If the first reverse osmosis membrane treatment device 16 is provided upstream of the ion exchange treatment device 22, there is a problem in that the first RO concentrated water is generated, reducing the water recovery rate of the entire system. However, as in the pure water production method and pure water production system of this embodiment, by returning the second RO concentrated water from the second reverse osmosis membrane treatment device 26 downstream of the ion exchange treatment device 22 to the upstream of the first reverse osmosis membrane treatment device 16, it is possible to provide a method and system that can reduce the salt concentration in the regeneration wastewater discharged from the system while suppressing a reduction in the water recovery rate of the entire system.

[0058] FIG. 3 shows another example of the pure water producing method and pure water producing system according to this embodiment, and is a diagram showing an example of the flow when water flows into the raw water tank 10 from a plurality of water sources.

[0059] 3, one or more pipes 72 for transporting raw water from another water source may be further connected to the raw water inlet of the raw water tank 10. In the pure water production system 5, a bypass pipe 74 may connect the clarified water outlet of the water tank 14 that stores the clarified water and the clarified water inlet of the water tank 18 that stores the first RO permeate.

[0060] When water from multiple sources is introduced into the raw water tank 10 as raw water, a portion of the raw water may be bypassed through the first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment step) depending on the flow rate ratio of each raw water. If the raw water contains a large proportion of reclaimed water that has passed through the reverse osmosis membrane once and has a low risk of scaling, the water recovery rate can be further increased by bypassing a portion of the raw water through the first reverse osmosis membrane treatment device 16 and sending the water, for example, from the water tank 14 to the water tank 18. If the proportion of water with a low risk of scaling is large, the recovery rate can be increased while sufficiently reducing the load on the ion exchange resin without passing the entire amount through the first reverse osmosis membrane. If the proportion of water that has passed through the reverse osmosis membrane and is supplied to the system decreases due to a lack of water supply or a decrease in the water supply volume due to some kind of trouble, the amount of water bypassed can be reduced and a high water recovery rate can be maintained while reducing the load on the ion exchange resin.

[0061] In particular, when water from multiple water sources includes water that has permeated the reverse osmosis membrane and water that has not permeated the reverse osmosis membrane, and the flow rate ratio of the water that has not permeated the reverse osmosis membrane is 50 vol% or less, preferably 30 vol% or less, of the raw water, it is preferable to bypass the first reverse osmosis membrane treatment device 16 (first reverse osmosis membrane treatment step).Since the water that has permeated the reverse osmosis membrane generally contains a small amount of scale components, bypassing some of the water can increase the water recovery rate.

[0062] The flow rate ratio of water from the multiple water sources may be determined based on the flow rate of each raw water measured by installing a flow rate measuring means such as a flow meter in each of the pipes 40, 72, etc.

[0063] The present specification includes the following embodiments. (1) A pure water production system for producing pure water, a first reverse osmosis membrane treatment device that passes raw water through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate; an ion exchange treatment device that performs ion exchange treatment on the first RO permeate with an ion exchange resin to obtain ion-exchanged water; a second reverse osmosis membrane treatment device that passes the ion-exchanged water through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate; a return means for returning the second RO concentrated water to a stage upstream of the first reverse osmosis membrane treatment device; A pure water production system comprising:

[0064] (2) The pure water producing system according to (1), A pure water production system, wherein the permeability coefficient of the first reverse osmosis membrane is smaller than the permeability coefficient of the second reverse osmosis membrane.

[0065] (3) The pure water production system according to (1) or (2), The ion exchange resin is regenerated using regeneration water, and at least one of acid and alkali is recovered from the resulting regeneration waste liquid.

[0066] (4) The pure water producing system according to (3), The pure water production system further comprises at least one of an electrodialysis device and an electrical regeneration demineralization device that recovers at least one of an acid and an alkali from the regeneration waste liquid.

[0067] (5) A pure water producing system according to any one of (1) to (4), A pure water producing system in which water from a plurality of water sources is used as the raw water, and a portion of the raw water is bypassed through the first reverse osmosis membrane treatment device depending on the flow rate ratio of the water from each of the water sources.

[0068] (6) The pure water producing system according to (5), A pure water production system in which the water from the multiple water sources is composed of water that has permeated a reverse osmosis membrane and water that has not permeated a reverse osmosis membrane, and when the flow rate ratio of the water that has not permeated the reverse osmosis membrane is 50 vol% or less of the raw water, a portion of the raw water is bypassed through the first reverse osmosis membrane treatment device.

[0069] (7) A method for producing pure water, comprising the steps of: a first reverse osmosis membrane treatment step of passing raw water through a first reverse osmosis membrane to obtain first RO permeate and first RO concentrate; an ion exchange treatment step of subjecting the first RO permeate to ion exchange treatment with an ion exchange resin to obtain ion-exchanged water; a second reverse osmosis membrane treatment step in which the ion-exchanged water is passed through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate; Including, A method for producing pure water, wherein the second RO concentrated water is returned to a stage preceding the first reverse osmosis membrane treatment step.

[0070] (8) The method for producing pure water according to (7), A method for producing pure water, wherein the permeability coefficient of the first reverse osmosis membrane is smaller than the permeability coefficient of the second reverse osmosis membrane.

[0071] (9) A method for producing pure water according to (7) or (8), A method for producing pure water, comprising regenerating the ion exchange resin using regeneration water and recovering at least one of acid and alkali from the resulting regeneration waste liquid.

[0072] (10) The method for producing pure water according to (9), The method for producing pure water further comprises at least one of an electrodialysis step and an electrical regeneration demineralization step for recovering at least one of an acid and an alkali from the regeneration waste liquid.

[0073] (11) A method for producing pure water according to any one of (7) to (10), A method for producing pure water, comprising the steps of: using water from a plurality of water sources as the raw water; and bypassing the first reverse osmosis membrane treatment step for a portion of the raw water according to a flow rate ratio of the water from each of the water sources.

[0074] (12) The method for producing pure water according to (11), A method for producing pure water, wherein the water from the multiple water sources is composed of water that has permeated a reverse osmosis membrane and water that has not permeated the reverse osmosis membrane, and when the flow rate ratio of the water that has not permeated the reverse osmosis membrane is 50 vol% or less of the raw water, a portion of the raw water is bypassed from the first reverse osmosis membrane treatment step. [Example]

[0075] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0076] <Comparative Example 1> As Comparative Example 1, the water balance under the following treatment conditions in a flow diagram shown in FIG. 4, which sequentially includes a first reverse osmosis membrane treatment device, a 2B3T ion exchange treatment device (a cation exchange tower (K ​​tower), a decarbonation tower (D tower), and an anion exchange tower (A tower)), and a second reverse osmosis membrane treatment device, is shown below.

[0077] (Processing conditions) The raw water flow rate is 12,000m 3 / d. In the sand filtration process, sand filtration treated water is used as backwash water, and the backwash wastewater is 150 m 3 / d is discharged. The recovery rate of the first reverse osmosis membrane treatment device is set at 90%, and 10% (1185m 3 / d) is discharged as the first RO concentrated water. *Reverse osmosis membrane recovery rate (%) = permeated water volume / inlet water volume x 100 (11850 / 10665 x 100) In the activated carbon tower, the first RO permeate is used as backwash water, and the backwash drainage is 50m 3 / d is discharged. In Tower K and Tower A, 40m of recycled wastewater is used. 3 / d is emitted. The recovery rate of the second reverse osmosis membrane treatment device is 95%, and 5% (531m 3 / d) is discharged as the second RO concentrated water, and a part of the second RO concentrated water (40m 3 / d each) is used as reclaimed water for towers K and A, and the remaining water (451m3 / d) is "excreted from the system." As a result, the water recovery rate of the entire pure water production system is (10084 / 12000) x 100 = 84.0%.

[0078] Example 1 As Example 1, the water balance under the following treatment conditions in a flow diagram shown in FIG. 5, which sequentially includes a first reverse osmosis membrane treatment device, 2B3T ion exchange treatment devices (a cation exchange tower (K ​​tower), a decarbonation tower (D tower), and an anion exchange tower (A tower)), and a second reverse osmosis membrane treatment device, is shown below.

[0079] (Processing conditions) The raw water flow rate is 12,000m 3 / d. In the sand filtration process, sand filtration treated water is used as backwash water, and the backwash wastewater is 150 m 3 / d is discharged. The recovery rate of the first reverse osmosis membrane treatment device is set at 90%, and 10% (1272m 3 / d) is discharged as the first RO concentrated water. In the activated carbon tower, the first RO permeate is used as backwash water, and the backwash drainage is 50m 3 / d is discharged. In Tower K and Tower A, 40m of regenerated waste liquid is discharged. 3 / d is emitted. The recovery rate of the second reverse osmosis membrane treatment device is 95%, and 5% (552m 3 / d) is discharged as the second RO concentrated water, and a part of the second RO concentrated water (40m 3 / d) is used as recycled water, and the remaining (472m 3 / d) is "circulated to the raw water tank." As a result, the water recovery rate of the entire pure water production system is (10488 / 12000) x 100 = 87.4%, and by returning the second RO concentrated water to the upstream stage of the first reverse osmosis membrane treatment device, a higher recovery rate can be achieved than in Comparative Example 1.

[0080] In this way, in the production of pure water by sequentially performing reverse osmosis membrane treatment, ion exchange treatment using ion exchange resin, and reverse osmosis membrane treatment, by returning the second RO concentrate to the upstream stage of the first reverse osmosis membrane treatment device as in the present embodiment, it is possible to suppress a decrease in the water recovery rate of the entire system and also to reduce the concentration of TOC components in the resulting pure water. [Explanation of symbols]

[0081] 1, 3, 5 Pure water production system, 10 Raw water tank, 12 Filtration device, 14, 18, 24, 28, 32, 34 Water tank, 16 First reverse osmosis membrane treatment device, 20 Activated carbon treatment device, 22 Ion exchange treatment device, 26 Second reverse osmosis membrane treatment device, 30 Third reverse osmosis membrane treatment device, 36 Recovery device, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 66, 68, 70, 72 Piping, 64 Return piping, 74 Bypass piping.

Claims

1. A pure water production system for producing pure water, a first reverse osmosis membrane treatment device that passes raw water through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate; an ion exchange treatment device that performs ion exchange treatment on the first RO permeate using an ion exchange resin to obtain ion-exchanged water; a second reverse osmosis membrane treatment device that passes the ion-exchanged water through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate; a return means for returning the second RO concentrated water to a stage upstream of the first reverse osmosis membrane treatment device; Equipped with A pure water producing system, characterized in that the permeability coefficient of the first reverse osmosis membrane is smaller than the permeability coefficient of the second reverse osmosis membrane.

2. 2. The pure water producing system according to claim 1, A pure water production system characterized in that the ion exchange resin is regenerated using regeneration water, and at least one of acid and alkali is recovered from the resulting regeneration waste liquid.

3. 3. The pure water producing system according to claim 2, The pure water production system further comprises at least one of an electrodialysis device and an electrical regeneration type demineralization device for recovering at least one of an acid and an alkali from the regeneration waste liquid.

4. 2. The pure water producing system according to claim 1, A pure water producing system characterized in that water from a plurality of water sources is used as the raw water, and a portion of the raw water is bypassed through the first reverse osmosis membrane treatment device depending on the flow rate ratio of the water from each of the water sources.

5. 5. The pure water producing system according to claim 4, a first reverse osmosis membrane treatment device that is configured to treat a portion of the raw water; a second reverse osmosis membrane treatment device that is configured to treat a portion of the raw water; a second reverse osmosis membrane treatment device that is configured to treat a portion of the raw water;

6. A method for producing pure water, comprising: a first reverse osmosis membrane treatment step of passing the raw water through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate; an ion exchange treatment step of performing ion exchange treatment on the first RO permeate using an ion exchange resin to obtain ion-exchanged water; a second reverse osmosis membrane treatment step of passing the ion-exchanged water through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate; Including, the permeability coefficient of the first reverse osmosis membrane is smaller than the permeability coefficient of the second reverse osmosis membrane; A method for producing pure water, characterized in that the second RO concentrated water is returned to a stage preceding the first reverse osmosis membrane treatment step.

7. 7. The method for producing pure water according to claim 6, A method for producing pure water, comprising the steps of: regenerating the ion exchange resin using regenerated water; and recovering at least one of an acid and an alkali from the resulting regeneration waste liquid.

8. 8. The method for producing pure water according to claim 7, The method for producing pure water further comprises at least one of an electrodialysis step and an electrical regeneration demineralization step for recovering at least one of an acid and an alkali from the regeneration waste liquid.

9. 7. The method for producing pure water according to claim 6, A method for producing pure water, characterized in that water from a plurality of water sources is used as the raw water, and a portion of the raw water is bypassed from the first reverse osmosis membrane treatment step depending on the flow rate ratio of the water from each of the water sources.

10. 10. The method for producing pure water according to claim 9, a first reverse osmosis membrane treatment step for treating a part of the raw water; a second reverse osmosis membrane treatment step for treating a part of the raw water; a first reverse osmosis membrane treatment step for treating a part of the raw water;

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