METHOD AND APPARATUS FOR MEMBRANE TREATMENT OF LIQUID TO BE TREATED

Abstract

To provide a membrane treatment apparatus for a treated liquid capable of efficiently concentrating the treated liquid at a high concentration.SOLUTION: A membrane treatment apparatus for a treated liquid includes: an NF membrane unit 10 which passes the treated liquid through a nanofiltration membrane 11 to generate permeated liquid; and a membrane concentrator 20 which concentrates the treated liquid by contacting at least a part of the generated permeated liquid with the treated liquid through a semipermeable membrane 21. The NF membrane unit 10 allows the treated liquid before concentrated with the membrane concentrator 20 to be passed through the nanofiltration membrane 11, and enables the treated liquid that has been concentrated without permeating through the nanofiltration membrane 11 to be concentrated with the membrane concentrator 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a membrane treatment method and apparatus for a liquid to be treated. [Background technology]

[0002] As an apparatus for performing membrane treatment on a liquid to be treated such as seawater, Patent Document 1 discloses a freshwater production system in which seawater is supplied to a first reverse osmosis membrane module to separate fresh water and discharge concentrated salt water, while low osmotic pressure water is supplied to a second reverse osmosis membrane module to separate fresh water and discharge concentrated low osmotic pressure water, and the discharged concentrated salt water and concentrated low osmotic pressure water are supplied to a forward osmosis membrane module, where the concentrated salt water is diluted with water supplied from the concentrated low osmotic pressure water via the forward osmosis membrane. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-176929 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned freshwater production system has as its main objective the increase in the amount of freshwater produced, and is configured to dilute the concentrated seawater produced in the first reverse osmosis membrane module in the forward osmosis membrane module. Therefore, there was room for consideration in increasing the concentration rate when concentrating and recovering the treated liquid.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS The present invention has an object to provide a membrane treatment method and apparatus for a liquid to be treated, which can efficiently concentrate the liquid to a high concentration. [Means for solving the problem]

[0006] The object of the present invention is to provide a process for passing a liquid to be treated through a nanofiltration membrane to generate a permeate, and , concentrated in the NF membrane water passing stepBy contacting the liquid to be treated through a semipermeable membrane , concentrated in the NF membrane water passing step A membrane concentration step for concentrating the liquid to be treated. In the membrane concentration step, the permeated liquid produced in the NF membrane water passing step is supplied to the low pressure chamber without being concentrated in a membrane concentration device in which a low pressure chamber and a high pressure chamber are separated by the semipermeable membrane, while the liquid to be treated that is concentrated in the NF membrane water passing step is supplied to the high pressure chamber, and the pressure in the high pressure chamber is maintained higher than the pressure in the low pressure chamber. This is achieved by a membrane treatment method for the liquid to be treated.

[0010] The above-mentioned membrane treatment method for the liquid to be treated may further include an RO membrane water passing step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane, and the NF membrane water passing step and the membrane concentration step may be performed on the liquid to be treated after being concentrated in the RO membrane water passing step.

[0012] The method may further include an additional concentration step of additionally concentrating the liquid to be treated that has been concentrated by the NF membrane water passing step and the membrane concentration step, and the additional concentration step may include a step of contacting a portion of the liquid to be treated after the additional concentration with the liquid to be treated before the additional concentration via a semipermeable membrane to perform additional concentration, and then merging the resulting liquid with the permeate used in the membrane concentration step.

[0014] The present invention can include a second NF membrane water passing step of passing the liquid to be treated concentrated in the membrane concentration step through a second nanofiltration membrane to generate a second permeated liquid, and a second membrane concentration step of concentrating the liquid to be treated concentrated in the second NF membrane water passing step by contacting at least a part of the generated second permeated liquid with the liquid to be treated concentrated in the second NF membrane water passing step via a second semipermeable membrane. The second NF membrane water passing step can include a step of reducing the pressure of the liquid to be treated concentrated in the membrane concentration step before passing it through the second nanofiltration membrane.

[0015] The membrane concentration step can include a step of bypassing a portion of the permeated liquid generated in the NF membrane water passing step without supplying it to the semipermeable membrane, and controlling the flow rate of the permeated liquid bypassing the semipermeable membrane by adjusting the flow rate of the permeated liquid supplied to the semipermeable membrane.

[0017] The membrane concentration step may include a step of increasing the pressure of the liquid to be treated before concentration. The increase in pressure of the liquid to be treated before concentration may be achieved by pressure exchange with the liquid to be treated after concentration.

[0018] The object of the present invention is to provide a nanofiltration membrane unit that generates a permeate by passing a liquid to be treated through the nanofiltration membrane, and a method for producing a permeate by contacting at least a part of the generated permeate with the liquid to be treated that has been concentrated in the NF membrane unit through a semipermeable membrane, thereby producing a permeate by the NF membrane unit. unitand a membrane concentrating device for concentrating the liquid to be treated that has been concentrated by the NF membrane unit, the membrane concentrating device having a low pressure chamber and a high pressure chamber separated by the semipermeable membrane, the permeated liquid produced by the NF membrane unit is supplied to the low pressure chamber without being concentrated, while the liquid to be treated that has been concentrated by the NF membrane unit is supplied to the high pressure chamber, and the pressure of the high pressure chamber is maintained higher than the pressure of the low pressure chamber. Effect of the Invention

[0019] According to the present invention, it is possible to provide a membrane treatment method and apparatus for a liquid to be treated, which can efficiently concentrate the liquid to a high concentration. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to another embodiment of the present invention. [Diagram 3] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 4] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Diagram 5] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 6] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 7] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 8] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 9] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 10] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 11] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 12] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 13] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 14] FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. [Figure 15] FIG. 13 is a schematic configuration diagram showing a main part of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a schematic diagram of a membrane treatment device for a liquid to be treated (hereinafter, simply referred to as "membrane treatment device") according to an embodiment of the present invention. As shown in Fig. 1, the membrane treatment device 1-1 includes an NF membrane unit 10 and a membrane concentration device 20 as main components.

[0022] The NF membrane unit 10 is composed of an NF membrane module equipped with an NF membrane (nanofiltration membrane) 11 inside a casing, and generates a permeate by passing a liquid to be treated through the NF membrane 11. Examples of the shape of the NF membrane include a flat membrane and a hollow fiber membrane.

[0023] In the membrane concentration device 20, a high pressure chamber 22 and a low pressure chamber 23 are formed by dividing the inside of a casing with a semipermeable membrane 21. The liquid to be treated that is concentrated in the NF membrane unit 10 without permeating the NF membrane 11 is introduced into the high pressure chamber 22, while the permeated liquid produced in the NF membrane unit 10 is introduced into the low pressure chamber 23. The liquid to be treated and the permeated liquid introduced into the high pressure chamber 22 and the low pressure chamber 23, respectively, are discharged to the outside after contacting each other via the semipermeable membrane 21. The semipermeable membrane may be a hollow fiber membrane other than a flat membrane. The semipermeable membrane may be an RO membrane (reverse osmosis membrane), but may be another semipermeable membrane such as an FO membrane (forward osmosis membrane).

[0024] Next, a membrane treatment method for a liquid to be treated using the membrane treatment device 1-1 having the above configuration (hereinafter, simply referred to as a "membrane treatment method") will be described. First, an NF membrane water passing step is performed in which the liquid to be treated, such as seawater, is supplied to the NF membrane unit 10 by the high-pressure pump 2, and the liquid to be treated is passed through the NF membrane 11 to generate a permeate. The high-pressure pump 2 can be, for example, an inverter-controlled pump to save energy.

[0025] The permeate produced in the NF membrane water passing step is supplied to the low pressure chamber 23 of the membrane concentration device 20, while the liquid to be treated concentrated in the NF membrane water passing step is boosted in the booster section 6 and then supplied to the high pressure chamber 22. By maintaining the pressure in the high pressure chamber 22 higher than the pressure in the low pressure chamber 23, the movement of water from the high pressure chamber 22 to the low pressure chamber 23 via the semipermeable membrane 21 is promoted, and the membrane concentration step of concentrating the liquid to be treated passing through the high pressure chamber 22 can be performed. Examples of the booster section 6 that boosts the pressure of the liquid to be treated before concentration in the membrane concentration step include a booster pump and an energy recovery device. The booster pump is preferably an inverter-controlled pump, which can easily control the flow rate and pressure of the liquid to be treated by controlling the motor rotation speed, and can save energy because it does not require throttling the flow path. The pressure difference required between the high pressure chamber 22 and the low pressure chamber 23 can be reduced, for example, by increasing the area of ​​the semipermeable membrane 21, and if the necessary pressure difference can be secured without the pressure booster 6, the configuration can be made without the pressure booster 6. The treated liquid concentrated by the NF membrane unit 10 and the membrane concentrator 20 can be recovered as a concentrated liquid and can be used in other processes, such as forward osmosis power generation and desalination by evaporation and concentration for salt production.

[0026] When an energy recovery device is used as the pressure increasing section 6, for example, the membrane treatment device 1-10 shown in FIG. 10 may be configured as such. The energy recovery device 8 shown in FIG. 10 is composed of a turbocharger in which pressure is exchanged between the pressure increasing section 6 and the pressure reducing section 7, and rotates a turbine using the liquid to be treated that has passed through the high pressure chamber 22 of the membrane concentrator 20 and been supplied to the pressure reducing section 7, and uses this power to increase the pressure of the liquid to be treated that is supplied to the pressure increasing section 6. According to the membrane treatment device 1-10 shown in FIG. 10, the liquid to be treated can be reduced in pressure reducing section 7 and recovered at low pressure. The configuration of the energy recovery device 8 is not particularly limited as long as it can recover the energy of the liquid to be treated that is supplied to the pressure reducing section 7 after concentration in the membrane concentrator 20, and can increase the pressure of the liquid to be treated that is supplied to the pressure increasing section 6 before concentration in the membrane concentrator 20. For example, it may be a rotor type, piston type, or other energy recovery device other than the turbine type.

[0027] 1, the NF membrane 11 suppresses the permeation of divalent or higher ions contained in the liquid to be treated, such as seawater, while easily passing monovalent ions, and therefore, the permeated liquid generated in the NF membrane unit 10 is particularly suppressed from decreasing in concentration of monovalent ions. Therefore, the osmotic pressure difference between the liquid to be treated and the permeated liquid supplied to the high-pressure chamber 22 and the low-pressure chamber 23 of the membrane concentration device 20, respectively, can be reduced, and the liquid to be treated can be reliably concentrated without excessively increasing the pressure in the high-pressure chamber 22.

[0028] A bypass line 4 is branched off from the supply line 3 that supplies the permeate from the NF membrane unit 10 to the membrane concentration device 20, and a flow control valve 5 is provided on the bypass line 4. The supply flow rate of the permeate to the membrane concentration device 20 can be controlled by adjusting the flow rate of the permeate bypassed to the bypass line 4 by changing the opening degree of the flow control valve 5, thereby ensuring the membrane concentration process. At least a part of the permeate produced in the NF membrane water passing process needs to be used in the membrane concentration process. When a desired pressure difference occurs between the high pressure chamber 22 and the low pressure chamber 23 even when the flow control valve 5 is fully closed, the entire amount of the permeate produced in the NF membrane unit 10 may be supplied to the membrane concentration device 20 without providing the bypass line 4 and the flow control valve 5.

[0029] In the membrane treatment method using the membrane treatment device 1-1 shown in Fig. 1, the NF membrane water passing step includes a step of passing the liquid to be treated before being concentrated in the membrane concentration step through the NF membrane 11, and the membrane concentration step is performed on the liquid to be treated that has been concentrated without passing through the NF membrane 11. In contrast, in the membrane treatment method using the membrane treatment device 1-2 shown in Fig. 2, the NF membrane water passing step can include a step of passing the liquid to be treated after being concentrated in the membrane concentration step through the NF membrane 11. In the following drawings, the same reference numerals are used for similar components between the drawings.

[0030] The membrane treatment device 1-2 shown in FIG. 2 includes an NF membrane unit 10 and a membrane concentration device 20, similar to the membrane treatment device 1-1 shown in FIG. 1, but unlike the membrane treatment device 1-1 shown in FIG. 1, the treated liquid such as seawater is supplied to the high-pressure chamber 22 of the membrane concentration device 20, and then depressurized in a pressure reducing section 7 consisting of a pressure reducing valve or the like, and supplied to the NF membrane unit 10. The pressure reducing section 7 may be an energy recovery device other than a pressure reducing valve. When an energy recovery device is used as the pressure reducing section 7, for example, it can be configured as the membrane treatment device 1-11 shown in FIG. 11. The energy recovery device 8-1 shown in FIG. 11 has a configuration in which pressure exchange is performed between the pressure increasing section 6-1 and the pressure reducing section 7-1, similar to the energy recovery device 8 shown in FIG. 10, and the treated liquid pressurized in the pressure increasing section 6-1 passes through the high-pressure chamber 22 of the membrane concentration device 20, and then is depressurized in the pressure reducing section 7-1. If the pressure of the liquid to be treated becomes too low due to the pressure reduction section 7-1, it is possible to restore the pressure of the liquid to be treated by appropriately providing a pressure boosting section 6' consisting of a booster pump or the like, and the liquid to be treated can be further pressurized in the pressure boosting section 6-2 of the energy recovery device 8-2 and supplied to the NF membrane unit 10. The liquid to be treated concentrated in the NF membrane unit 10 is reduced in pressure reduction section 7-2 and then recovered as a concentrated liquid.

[0031] A turbine having a power generating function can be used as the pressure reducing section 7 of the membrane treatment device 1-2 shown in FIG. 2, and the recovered electric energy can be used as the power source for the high-pressure pump 2 or the like. The permeate generated in the NF membrane unit 10 is supplied to the low-pressure chamber 23 of the membrane concentration device 20 to concentrate the liquid to be treated passing through the high-pressure chamber 22. The flow rate of the permeate supplied to the low-pressure chamber 23 can be controlled by adjusting the flow rate of the permeate bypassed to the bypass line 4 by changing the opening degree of the flow control valve 5. The bypass line 4 and the flow control valve 5 are not essential components, and the entire amount of the permeate generated in the NF membrane unit 10 may be supplied to the membrane concentration device 20. The pressure reducing section 7 can perform the desired pressure reduction according to the operating pressure of the NF membrane unit 10, while the pressure reducing section 7 can be omitted by applying back pressure to the downstream side of the NF membrane unit 10, for example. The operating pressure of the NF membrane unit 10 and the membrane concentrator 20 varies depending on the balance of monovalent ions and divalent ions contained in the liquid to be treated, and can be, for example, 10 to 30 bar, or can be boosted up to the maximum operating pressure of the NF membrane 11. The operating pressure of the membrane concentrator 20 is, for example, 40 to 70 bar. The pressurizing section 6 and the depressurizing section 7 are disposed as necessary so as to boost or depressurize the liquid to be treated in consideration of the operating pressure of the NF membrane unit 10 and the membrane concentrator 20 (the same applies to each of the following embodiments).

[0032] The membrane treatment device 1-3 shown in Fig. 3 is configured by combining the membrane treatment device 1-1 shown in Fig. 1 and the membrane treatment device 1-2 shown in Fig. 2, and includes a first NF membrane unit 10-1, a second NF membrane unit 10-2, and a membrane concentration device 20. The first NF membrane unit 10-1 and the second NF membrane unit 10-2 are configured similarly to the NF membrane unit 10 shown in Fig. 1 and Fig. 2, and include a first NF membrane 11-1 and a second NF membrane 11-2, respectively.

[0033] In the membrane treatment method using the membrane treatment device 1-3 shown in FIG. 3, the NF membrane water passing step can include a step of passing the liquid to be treated before being concentrated in the membrane concentration device 20 through the first NF membrane 11-1, and a step of passing the liquid to be treated after being concentrated in the membrane concentration device 20 through the second NF membrane 11-2, and the permeated liquid generated by passing the second NF membrane 11-2 can be supplied to the low-pressure chamber 23 of the membrane concentration device 20. The flow rate of the permeated liquid supplied to the membrane concentration device 20 can be controlled by adjusting the flow rate of the permeated liquid bypassed from the supply line 3 to the bypass line 4 by changing the opening degree of the flow control valve 5. The bypass line 4 and the flow control valve 5 are not essential components, and the entire amount of the permeated liquid generated in the second NF membrane unit 10-2 may be supplied to the membrane concentration device 20. The permeated liquid supplied to the low-pressure chamber 23 of the membrane concentration device 20 may be at least a part of the permeated liquid generated in the first NF membrane unit 10-1.

[0034] The liquid to be treated concentrated in the first NF membrane unit 10-1 is pressurized in the pressurization section 6-1 of the energy recovery device 8-1, where pressure exchange is performed between the pressurization section 6-1 and the depressurization section 7-1, passes through the high pressure chamber 22 of the membrane concentration device 20, and is depressurized in the depressurization section 7-1. The liquid to be treated depressurized in the depressurization section 7-1 has its pressure restored by the pressurization section 6', which is provided as necessary, and is then further pressurized in the pressurization section 6-2 of the energy recovery device 8-2 and supplied to the second NF membrane unit 10-2. The liquid to be treated concentrated in the second NF membrane unit 10-2 is depressurized in the depressurization section 7-2, and then recovered as a concentrated liquid.

[0035] A membrane treatment device 1-4 shown in FIG. 4 further includes an RO membrane unit 30 in addition to the membrane treatment device 1-1 shown in FIG. 1, and a liquid to be treated such as seawater is pressurized by a high-pressure pump 2 and supplied to the RO membrane unit 30. The RO membrane unit 30 is composed of an RO membrane module equipped with an RO membrane (reverse osmosis membrane) 31 in a casing, and generates produced water (fresh water) by passing the liquid to be treated through the RO membrane 31. The shape of the RO membrane 31 can be exemplified by a flat membrane or a hollow fiber membrane. The liquid to be treated that has not passed through the RO membrane 31 of the RO membrane unit 30 and has been concentrated is depressurized in a depressurization section 7 and then supplied to the NF membrane unit 10.

[0036] The membrane treatment method using the membrane treatment device 1-4 shown in Fig. 4 can include an RO membrane water passing step in which the liquid to be treated is pressurized and passed through an RO membrane, and an NF membrane water passing step and a membrane concentration step can be performed on the liquid to be treated after being concentrated in the RO membrane water passing step, so that the concentration rate of the concentrated liquid to be recovered can be further increased. The RO membrane unit 30 may be provided in the membrane treatment device 1-2 shown in Fig. 2, and in this case, the liquid to be treated concentrated in the RO membrane unit 30 can be configured to be supplied to the high-pressure chamber 22 of the membrane concentration device 20.

[0037] The membrane treatment device 1-5 shown in FIG. 5 is the membrane treatment device 1-2 shown in FIG. 2, further including an RO membrane unit 30, and a plurality of membrane concentrators 20 are arranged to include a first membrane concentrator 20-1 and a second membrane concentrator 20-2. The liquid to be treated concentrated in the RO membrane unit 30 passes through the high-pressure chambers 22-1 and 22-2 of the first membrane concentrator 20-1 and the second membrane concentrator 20-2 in series, and is then depressurized in the depressurizing section 7 and supplied to the NF membrane unit 10. The permeate produced in the NF membrane unit 10 passes through the low-pressure chambers 23-1 and 23-2 of the first membrane concentrator 20-1 and the second membrane concentrator 20-2 in parallel, and is then merged with the liquid to be treated and supplied to the RO membrane unit 30 again.

[0038] In the membrane treatment method using the membrane treatment device 1-5 shown in Fig. 5, the membrane concentration step can include a step of supplying the liquid to be treated in series and the permeate in parallel to the first membrane concentration device 20-1 and the second membrane concentration device 20-2, and the liquid to be treated can be concentrated in each of the membrane concentration devices 20-1 and 20-2. The flow rate of the permeate supplied to the low pressure chambers 23-1 and 23-2 can be individually controlled by adjusting the flow rate of the permeate bypassing the low pressure chambers 23-1 and 23-2 by changing the opening degree of the flow control valves 5-1 and 5-2, and the concentration of the permeate passing through the low pressure chamber 23-1 can also be controlled. The permeate generated in the NF membrane unit 10 may be supplied in series to the low pressure chambers 23-1 and 23-2, and in this case, it is preferable that the permeate passes through the low pressure chambers 23-2 and 23-1 in this order. Alternatively, the low pressure chambers 23-1, 23-2 may not be bypassed and the entire amount of the permeated liquid may be supplied in series or in parallel to the low pressure chambers 23-1, 23-2. The number and arrangement of the flow control valves 5-1, 5-2 are not particularly limited and may be appropriately set so as to easily control the flow rate and concentration of the low pressure chambers 23-1, 23-2.

[0039] The first membrane concentrating apparatus 20-1 and the second membrane concentrating apparatus 20-2 shown in FIG. 5 can also be applied to the membrane treatment apparatus 1-1 shown in FIG. 1, and a configuration in which multiple membrane concentrating apparatuses 20 are arranged in the membrane treatment apparatus 1-1 shown in FIG. 1 can be configured.

[0040] The RO membrane unit 30 shown in Fig. 5 can be provided in, for example, the membrane treatment device 1-11 shown in Fig. 11 to form the membrane treatment device 1-12 shown in Fig. 12. The membrane treatment device 1-12 in Fig. 12 is configured such that the liquid to be treated, which has been pressurized in the pressurization section 6-1 of the energy recovery device 8-1, is supplied to the RO membrane unit 30 and concentrated, and then passes through the high-pressure chamber 22 of the membrane concentration device 20 and is depressurized in the depressurization section 7-1.

[0041] The membrane treatment device 1-13 shown in Figure 13 uses an energy recovery device 8 in the pressure reduction section 7 of the membrane treatment device 1-5 shown in Figure 5, and the pressure increase section 6 of this energy recovery device 8 is used to increase the pressure of the treated liquid before it is supplied to the high-pressure chambers 22-1, 22-2 of the first membrane concentrating device 20-1 and the second membrane concentrating device 20-2.

[0042] A membrane treatment device 1-6 shown in Fig. 6 is the membrane treatment device 1-1 shown in Fig. 1, further including an additional concentrator 40 that further concentrates the liquid to be treated concentrated by the membrane concentrator 20. In the additional concentrator 40, a high-pressure chamber 42 and a low-pressure chamber 43 are formed by dividing the inside of a casing with a semipermeable membrane 41. The shape of the semipermeable membrane 41 can be, for example, a flat membrane or a hollow fiber membrane.

[0043] The membrane treatment method using the membrane treatment device 1-6 shown in Fig. 6 can include an additional concentration step in which the liquid to be treated concentrated in the NF membrane unit 10 and the membrane concentration device 20 is supplied to the high pressure chamber 42 of the additional concentration device 40, and a part of the liquid to be treated that has passed through the high pressure chamber 42 is supplied to the low pressure chamber 43, thereby performing additional concentration of the liquid to be treated by utilizing the pressure difference generated between the high pressure chamber 42 and the low pressure chamber 43. The additional concentration step can include a step in which a part of the liquid to be treated that has passed through the high pressure chamber 42 and been additionally concentrated is brought into contact with the liquid to be treated before being additionally concentrated in the high pressure chamber 42 via the semipermeable membrane 41, and then the part is merged with the permeated liquid to be supplied to the membrane concentration device 20. The remaining part of the liquid to be treated that has been additionally concentrated in the high pressure chamber 42 is recovered as a concentrated liquid.

[0044] The additional concentrator 40 can also be applied to the membrane treatment device 1-2 shown in Fig. 2. That is, in the membrane treatment device 1-2 shown in Fig. 2, the liquid to be treated concentrated in the membrane concentrator 20 can be supplied to the high-pressure chamber 42 of the additional concentrator 40, and a part of the liquid to be treated that has passed through the high-pressure chamber 42 and been further concentrated passes through the low-pressure chamber 43 and joins the permeated liquid supplied to the membrane concentrator 20. The remainder of the liquid to be treated that has been further concentrated in the high-pressure chamber 42 can be supplied to the NF membrane unit 10 to recover the concentrated liquid.

[0045] The membrane treatment device 1-7 shown in Fig. 7 is the same as the membrane treatment device 1-5 shown in Fig. 5, except that a plurality of NF membrane units 10 are provided, that is, a first NF membrane unit 10-1 and a second NF membrane unit 10-2, and a third membrane concentrator 20-3 is added. The liquid to be treated concentrated in the first membrane concentrator 20-1 and the second membrane concentrator 20-2 is supplied to the first NF membrane unit 10-1 and concentrated there, and then supplied to the third membrane concentrator 20-3 and the second NF membrane unit 10-2 and further concentrated there.

[0046] The membrane treatment method using the membrane treatment device 1-7 shown in Fig. 7 may include a membrane concentration step in which a part of the liquid to be treated concentrated in the second NF membrane unit 10-2 is depressurized in a pressure reducing section 7' ​​consisting of a pressure reducing valve or the like, and then the part is merged with the permeated liquid produced in the second NF membrane unit 10-2 and supplied to a third membrane concentration device 20-3 for use in concentrating the liquid to be treated. The flow rate and concentration of the permeated liquid can be controlled by adjusting the flow rate of the liquid to be treated merged with the permeated liquid.

[0047] As described above, in the membrane concentration step, the step of concentrating the liquid to be treated by merging a part of the liquid to be treated concentrated in the NF membrane water passing step with the permeate can be performed in other membrane treatment devices than the membrane treatment device 1-7 shown in FIG. 7. For example, in the membrane treatment device 1-1 shown in FIG. 1 and the membrane treatment device 1-2 shown in FIG. 2, a part of the liquid to be treated concentrated in the NF membrane unit 10 can be merged with the permeate produced in the NF membrane unit 10 and supplied to the membrane concentration device 20. In the membrane treatment device 1-1 shown in FIG. 1, a part of the liquid to be treated concentrated in the NF membrane unit 10 may be merged with the permeate before being supplied to the membrane concentration device 20, or may be merged with the permeate after passing through the membrane concentration device 20.

[0048] The membrane treatment device 1-7 shown in Fig. 7 supplies the permeate generated in the first NF membrane unit 10-1 to the first membrane concentrator 20-1, and supplies the permeate generated in the second NF membrane unit 10-2 to the second membrane concentrator 20-2 and the third membrane concentrator 20-3, but for example, the permeate of the first NF membrane unit 10-1 may be supplied to the first membrane concentrator 20-1 and the second membrane concentrator 20-2, and the permeate of the second NF membrane unit 10-2 may be supplied to the third membrane concentrator 20-3. Alternatively, the permeate of the second NF membrane unit 10-2 may be supplied to the first membrane concentrator 20-1, the second membrane concentrator 20-2, and the third membrane concentrator 20-3.

[0049] In the membrane treatment device 1-7 shown in Fig. 7, the number of NF membrane units 10 and membrane concentrators 20 to be arranged is not particularly limited. In this case, the membrane concentrator 20 to which the permeate generated in each NF membrane unit 10 is supplied is also not particularly limited, but it is preferable to supply the permeate from each NF membrane unit 10 to the membrane concentrator 20 on the upstream side (i.e., the membrane concentrator 20 through which the liquid to be treated used to generate the permeate in the NF membrane unit 10 passed before being introduced into the NF membrane unit 10). The supply of the permeate from the NF membrane unit 10 to the multiple membrane concentrators 20 may be in parallel or in series, or a combination of parallel and series may be used.

[0050] The membrane treatment device 1-8 shown in FIG. 8 includes a first NF membrane unit 10-1, a second NF membrane unit 10-2, a first membrane concentrator 20-1, and a second membrane concentrator 20-2, and is a unit in which the membrane treatment device 1-1 shown in FIG. 1 is arranged in two stages as one unit. That is, the liquid to be treated concentrated in the first NF membrane unit 10-1 is pressurized in the pressurizing section 6-1 and concentrated in the first membrane concentrator 20-1, then depressurized in the depressurizing section 7 and further concentrated in the second NF membrane unit 10-2, pressurized in the pressurizing section 6-2, and further concentrated in the second membrane concentrator 20-2, and recovered as a concentrated liquid. The pressurizing section 6-2 and depressurizing section 7 shown in FIG. 8 may use an energy recovery device 8 that performs pressure exchange between the pressurizing section 6 and the depressurizing section 7, as in the membrane treatment device 1-9 shown in FIG. 9. The concentrated liquid recovered by the membrane treatment devices 1-8, 1-9 shown in Figures 8 and 9 is pressurized in the pressure boosting section (6-2 or 6) to a high pressure, and can therefore be suitably used for applications such as osmotic pressure power generation.

[0051] The membrane treatment device 1-14 shown in Fig. 14 uses energy recovery devices 8-1 and 8-2 in both of the boosting sections 6-1 and 6-2 shown in Fig. 8, and the liquid to be treated after concentration in the first membrane concentrator 20-1 and the second membrane concentrator 20-2 is supplied to the pressure reducing sections 7-1 and 7-2 of the energy recovery devices 8-1 and 8-2, respectively. In order to obtain the desired operating pressures of the first membrane concentrator 20-1, the NF membrane unit 10, and the second membrane concentrator 20-2, boosting sections 6'-1, 6'-2, and 6'-3 may be provided upstream of each of them as necessary.

[0052] The membrane treatment method using the membrane treatment device 1-8 shown in Fig. 8 can efficiently increase the concentration rate of the recovered concentrated liquid by alternately repeating the NF membrane water passing step and the membrane concentration step. The unit consisting of the membrane treatment device 1-1 shown in Fig. 1 may be arranged in three or more stages to further increase the concentration rate. Also, the membrane treatment device 1-2 shown in Fig. 2 and the membrane treatment device 1-3 shown in Fig. 3 can be arranged in two or more stages as one unit.

[0053] The permeate generated in the NF membrane unit 10 arranged in the last stage (in FIG. 8, the second NF membrane unit 10-2) has the highest concentration among the permeates generated in each NF membrane unit 10. By supplying this permeate in series to each membrane concentrator 20 from the rear stage (in FIG. 8, it is supplied to the second membrane concentrator 20-2 and then to the first membrane concentrator 20-1), the concentration of the treated liquid in each membrane concentrator 20 can be easily and reliably performed.

[0054] The permeate produced in the second NF membrane unit 10-2 and passed through the second membrane concentrator 20-2 may be combined with either or both of the permeate produced in the first NF membrane unit 10-1 and the permeate produced in the second NF membrane unit 10-2 before passing through the second membrane concentrator 20-2. The flow rate and concentration of the permeate supplied to the first membrane concentrator 20-1 can be controlled by changing the mixing ratio of these permeates by adjusting the opening of the flow control valves 5-1 and 5-2.

[0055] The booster 6 in each of the above embodiments can adopt various configurations. For example, the booster 6 shown in FIG. 15 can be applied to the booster 6'-2 shown in FIG. 14. The booster 6 shown in FIG. 15 is equipped with a pressure conversion type energy recovery device 6a called a PX type, and a part of the liquid to be treated supplied to the NF membrane unit 10 is boosted by pressure exchange with the liquid to be treated concentrated in the NF membrane unit 10 in the energy recovery device 6a, and is further boosted by the booster pump 6b and merged with the remaining liquid to be treated boosted by the booster pump 6c. The operation of the booster pump 6b is preferably performed by precisely adjusting the flow rate by inverter control. In this embodiment, the booster pump 6c is not inverter controlled, but is pressure controlled by a pressure control valve 9 arranged between the downstream side of the booster pump 6c and the merger from the booster pump 6b to adjust the flow rate. However, the booster pump 6c may also be inverter controlled, in which case the configuration can be configured without the pressure control valve 9. [Explanation of symbols]

[0056] 1. Membrane treatment equipment 5 Flow Control Valve 6 Booster 7 Pressure reduction section 10 NF membrane unit 11 Nanofiltration Membranes 20 Membrane concentrator 21 Semi-permeable membrane 30 RO membrane unit 31 Reverse osmosis membrane 40 Additional concentrator

Claims

1. a NF membrane water passing step in which the liquid to be treated is passed through a nanofiltration membrane to generate a permeate; and a membrane concentration step of concentrating the liquid to be treated concentrated in the NF membrane water passing step by contacting at least a part of the produced permeate with the liquid to be treated concentrated in the NF membrane water passing step via a semipermeable membrane, The membrane concentration process is a membrane treatment method for a liquid to be treated, in which a permeated liquid produced in the NF membrane water passing process is supplied to the low-pressure chamber without being concentrated in a membrane concentration device in which a low-pressure chamber and a high-pressure chamber are separated by the semipermeable membrane, while the liquid to be treated concentrated in the NF membrane water passing process is supplied to the high-pressure chamber, and the pressure of the high-pressure chamber is maintained higher than the pressure of the low-pressure chamber.

2. The method further includes a RO membrane water passing step of pressurizing the liquid to be treated and passing the liquid through a reverse osmosis membrane, The membrane treatment method for a liquid to be treated according to claim 1 , wherein the NF membrane water passing step and the membrane concentration step are carried out on the liquid to be treated after being concentrated in the RO membrane water passing step.

3. The method further includes a step of further concentrating the liquid to be treated that has been concentrated by the NF membrane passing step and the membrane concentration step, 3. The membrane treatment method for a liquid to be treated according to claim 1 or 2, wherein the additional concentration step comprises a step of contacting a portion of the liquid to be treated after the additional concentration with the liquid to be treated before the additional concentration via a semipermeable membrane to perform additional concentration, and then merging the portion with the permeated liquid used in the membrane concentration step.

4. a second NF membrane passing step of passing the liquid to be treated concentrated in the membrane concentration step through a second nanofiltration membrane to generate a second permeate; 3. The membrane treatment method for the liquid to be treated according to claim 1 or 2, further comprising a second membrane concentration step of concentrating the liquid to be treated concentrated in the second NF membrane water passing step by contacting at least a portion of the produced second permeate liquid with the liquid to be treated concentrated in the second NF membrane water passing step via a second semipermeable membrane.

5. 5. The membrane treatment method for a liquid to be treated according to claim 4, wherein the second NF membrane water passing step comprises a step of reducing the pressure of the liquid to be treated concentrated in the membrane concentration step before the liquid to be treated is passed through the second nanofiltration membrane.

6. 6. The membrane treatment method for a liquid to be treated according to claim 1, wherein the membrane concentration step includes a step of bypassing a portion of the permeated liquid generated in the NF membrane water passing step without supplying it to the semipermeable membrane, and adjusting a flow rate of the permeated liquid bypassing the semipermeable membrane to control a supply flow rate of the permeated liquid to the semipermeable membrane.

7. 7. The membrane treatment method for a liquid to be treated according to claim 1, wherein the membrane concentration step includes a step of increasing the pressure of the liquid to be treated before concentration.

8. 8. The membrane treatment method for a liquid to be treated according to claim 7, wherein the pressurization of the liquid to be treated before being concentrated in the membrane concentration step is carried out by pressure exchange with the liquid to be treated after being concentrated in the membrane concentration step.

9. an NF membrane unit that passes a liquid to be treated through a nanofiltration membrane to generate a permeate; a membrane concentrator for concentrating the liquid to be treated concentrated in the NF membrane unit by contacting at least a portion of the produced permeate with the liquid to be treated concentrated in the NF membrane unit via a semipermeable membrane; The membrane concentration device is a membrane treatment device for treated liquid in which a low pressure chamber and a high pressure chamber are separated by the semipermeable membrane, and the permeated liquid produced in the NF membrane unit is supplied to the low pressure chamber without being concentrated, while the treated liquid concentrated in the NF membrane unit is supplied to the high pressure chamber, and the pressure of the high pressure chamber is maintained higher than the pressure of the low pressure chamber.

Images