JP7644948B2 - METHOD AND APPARATUS FOR MEMBRANE TREATMENT OF LIQUID TO BE TREATED - Google Patents

Description

The present invention relates to a membrane treatment method and device for a liquid to be treated.

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.

JP 2017-176929 A

The main purpose of the above-mentioned freshwater production system is to increase the amount of freshwater produced, and since it is configured to dilute the concentrated seawater produced in the first reverse osmosis membrane module in the forward osmosis membrane module, there was room for consideration in increasing the concentration rate when concentrating and recovering the treated liquid.

The present invention aims to provide a membrane treatment method and device for treating a liquid that can efficiently concentrate the liquid to a high concentration.

The object of the present invention is achieved by a membrane treatment method for a liquid to be treated, which comprises an NF membrane water passing step of passing the liquid to be treated through a nanofiltration membrane to produce a permeated liquid , and a membrane concentration step of concentrating the liquid to be treated concentrated in the NF membrane water passing step by bringing at least a part of the produced permeated liquid into contact with the liquid to be treated concentrated in the NF membrane water passing step via a semipermeable membrane, wherein the membrane concentration step supplies the permeated liquid produced in the NF membrane water passing step to the low pressure chamber without concentrating it, while supplying the liquid to be treated concentrated in the NF membrane water passing step to the high pressure chamber, and maintaining the pressure of the high pressure chamber higher than the pressure of the low pressure chamber, in a membrane concentration device having a low pressure chamber and a high pressure chamber separated by the semipermeable membrane.

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

It is possible to further include an additional concentration step in which the liquid to be treated that has been concentrated by the NF membrane water passing step and the membrane concentration step is further concentrated, and the additional concentration step can include a step in which a portion of the liquid to be treated after the additional concentration is brought into contact with the liquid to be treated before the additional concentration via a semipermeable membrane to perform additional concentration, and then the portion is merged with the permeate used in the membrane concentration step.

The present invention may 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 through a second semipermeable membrane. The second NF membrane water passing step may 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.

The membrane concentration process can include a process of bypassing a portion of the permeate produced in the NF membrane water passing process without supplying it to the semipermeable membrane, and adjusting the flow rate of the permeate bypassing the semipermeable membrane to control the supply flow rate of the permeate to the semipermeable membrane.

The membrane concentration process can include a process of pressurizing the liquid to be treated before concentration. Pressurization of the liquid to be treated before concentration can be achieved by pressure exchange with the liquid to be treated after concentration.

The above-mentioned object of the present invention is also achieved by a membrane treatment device for a liquid to be treated, which comprises an NF membrane unit for passing a liquid to be treated through a nanofiltration membrane to produce a permeated liquid, and a membrane concentrating device for concentrating the liquid to be treated concentrated in the NF membrane unit by bringing at least a portion of the produced permeated liquid into contact with the liquid to be treated concentrated in the NF membrane unit via a semipermeable membrane, wherein the membrane concentrating device has a low pressure chamber and a high pressure chamber 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 liquid to be treated concentrated in the NF membrane unit 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.

The present invention provides a membrane treatment method and device for treating a liquid that can efficiently concentrate the liquid to a high concentration.

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. FIG. 11 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to another embodiment of the present invention. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.

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

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 the 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.

In the membrane concentration device 20, a high-pressure chamber 22 and a low-pressure chamber 23 are formed by dividing the inside of the casing with a semipermeable membrane 21. The liquid to be treated that has been concentrated in the NF membrane unit 10 without passing through 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 preferably be an RO membrane (reverse osmosis membrane), but may also be another semipermeable membrane such as an FO membrane (forward osmosis membrane).

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 the "membrane treatment method") will be described. First, the liquid to be treated, such as seawater, is supplied to the NF membrane unit 10 by the high-pressure pump 2, and an NF membrane water passing process is performed in which the liquid to be treated is passed through the NF membrane 11 to produce a permeate liquid. The high-pressure pump 2 can be, for example, an inverter-controlled pump, to achieve energy savings.

The permeate produced in the NF membrane water passing process is supplied to the low pressure chamber 23 of the membrane concentration device 20, while the treated liquid concentrated in the NF membrane water passing process 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 treated liquid passing through the high pressure chamber 22 can be concentrated in the membrane concentration process. Examples of the booster section 6 that boosts the treated liquid before concentration in the membrane concentration process 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 treated liquid 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. If the necessary pressure difference can be secured without the booster section 6, the booster section 6 may not be provided. The treated liquid concentrated by the NF membrane unit 10 and the membrane concentrator 20 can be recovered as a concentrated liquid and used in other processes, such as forward osmosis power generation and desalination by evaporation and concentration for salt production.

When an energy recovery device is used as the boosting section 6, for example, the membrane treatment device 1-10 shown in FIG. 10 can 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 boosting section 6 and the decompression section 7, and rotates a turbine using the liquid to be treated that passes through the high-pressure chamber 22 of the membrane concentration device 20 and is supplied to the decompression section 7, and uses this power to boost the liquid to be treated that is supplied to the boosting section 6. According to the membrane treatment device 1-10 shown in FIG. 10, the liquid to be treated can be decompressed in the decompression 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 decompression section 7 after concentration in the membrane concentration device 20 and can boost the liquid to be treated that is supplied to the boosting section 6 before concentration in the membrane concentration device 20, and may be, for example, a rotor type, piston type, or other energy recovery device other than the turbine type.

In the membrane treatment device 1-1 shown in FIG. 1, the NF membrane 11 suppresses the permeation of divalent or higher ions contained in the treated liquid such as seawater, while allowing monovalent ions to easily permeate, so that the permeate generated by the NF membrane unit 10 is particularly suppressed from decreasing in concentration of monovalent ions. Therefore, the osmotic pressure difference between the treated liquid and the permeate supplied to the high-pressure chamber 22 and low-pressure chamber 23 of the membrane concentration device 20, respectively, can be reduced, so that the treated liquid can be reliably concentrated without excessively increasing the pressure in the high-pressure chamber 22.

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 of the flow control valve 5, thereby ensuring the membrane concentration process. At least a portion of the permeate generated in the NF membrane water passing process needs to be used in the membrane concentration process. If 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 generated 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.

In the membrane treatment method using 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 through NF membrane 11 before it is concentrated in the membrane concentration step, and the membrane concentration step is performed on the liquid to be treated that has been concentrated without passing through NF membrane 11. In contrast, the membrane treatment method using 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 through NF membrane 11 after it has been concentrated in the membrane concentration step. In the following figures, similar components are given the same reference numerals between the figures.

The membrane treatment device 1-2 shown in FIG. 2 is equipped with 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 reduction section 7 consisting of a pressure reduction valve or the like, and supplied to the NF membrane unit 10. The pressure reduction section 7 may be an energy recovery device other than a pressure reduction valve. When an energy recovery device is used as the pressure reduction 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 is configured in such a way that pressure exchange is performed between the pressure boosting section 6-1 and the pressure reduction section 7-1, similar to the energy recovery device 8 shown in FIG. 10, and the treated liquid pressurized in the pressure boosting section 6-1 passes through the high-pressure chamber 22 of the membrane concentration device 20 and is then depressurized in the pressure reduction section 7-1. If the pressure of the liquid being treated becomes too low due to the pressure reduction section 7-1, the pressure of the liquid being treated can be restored by appropriately providing a pressure boosting section 6' consisting of a booster pump or the like, and the liquid being 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 being treated that has been concentrated in the NF membrane unit 10 is reduced in pressure reduction section 7-2 and then recovered as a concentrated liquid.

As the pressure reducing section 7 of the membrane treatment device 1-2 shown in FIG. 2, a turbine having a power generating function can be used, and the recovered electric energy can be used as the power for the high-pressure pump 2, etc. 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 treated liquid 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 a configuration without the pressure reducing section 7 can be achieved 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 concentration device 20 varies depending on the balance of monovalent ions and divalent ions contained in the liquid to be treated, but for example, the operating pressure of the NF membrane unit 10 can be set to 10 to 30 bar, or can be increased to the maximum operating pressure of the NF membrane 11. The operating pressure of the membrane concentration device 20 is, for example, 40 to 70 bar. The pressure increase section 6 and the pressure reduction section 7 are arranged as necessary to increase or decrease the pressure of the liquid to be treated taking into account the operating pressure of the NF membrane unit 10 and the membrane concentration device 20 (the same applies to each of the following embodiments).

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.

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 permeate 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 permeate supplied to the membrane concentration device 20 can be controlled by adjusting the flow rate of the permeate 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 permeate generated in the second NF membrane unit 10-2 may be supplied to the membrane concentration device 20. The permeate supplied to the low-pressure chamber 23 of the membrane concentration device 20 may be at least a part of the permeate generated in the first NF membrane unit 10-1.

The treated liquid 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, and then passes through the high-pressure chamber 22 of the membrane concentration device 20 and is depressurized in the depressurization section 7-1. The treated liquid 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 treated liquid concentrated in the second NF membrane unit 10-2 is depressurized in the depressurization section 7-2 and then recovered as a concentrated liquid.

The membrane treatment device 1-4 shown in FIG. 4 is the membrane treatment device 1-1 shown in FIG. 1, further equipped with an RO membrane unit 30, and the 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 produces 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 is concentrated is depressurized in a depressurization section 7 and then supplied to the NF membrane unit 10.

The membrane treatment method using the membrane treatment device 1-4 shown in FIG. 4 can include an RO membrane water passing process in which the liquid to be treated is pressurized and passed through the RO membrane, and the NF membrane water passing process and membrane concentration process can be performed on the liquid to be treated after being concentrated in the RO membrane water passing process, so that the concentration rate of the concentrated liquid 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.

The membrane treatment device 1-5 shown in FIG. 5 is the membrane treatment device 1-2 shown in FIG. 2, further equipped with an RO membrane unit 30, and multiple membrane concentrators 20 are arranged to provide 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, is depressurized in the depressurizing section 7, and is 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, is merged with the liquid to be treated, and is supplied again to the RO membrane unit 30.

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 that order. In addition, the entire amount of the permeate may be supplied to each low-pressure chamber 23-1, 23-2 in series or parallel without bypassing 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 set appropriately so that flow control and concentration control for each low-pressure chamber 23-1, 23-2 can be easily performed.

The first membrane concentrator 20-1 and the second membrane concentrator 20-2 shown in FIG. 5 can also be applied to the membrane treatment device 1-1 shown in FIG. 1, and multiple membrane concentrators 20 can be arranged in the membrane treatment device 1-1 shown in FIG. 1.

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

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

The membrane treatment device 1-6 shown in FIG. 6 is the membrane treatment device 1-1 shown in FIG. 1, further comprising an additional concentrator 40 that further concentrates the liquid to be treated that has been concentrated by the membrane concentrator 20. The additional concentrator 40 has a casing that is divided by a semipermeable membrane 41 to form a high-pressure chamber 42 and a low-pressure chamber 43. The shape of the semipermeable membrane 41 can be, for example, a flat membrane or a hollow fiber membrane.

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 portion of the liquid to be treated that has passed through the high-pressure chamber 42 is supplied to the low-pressure chamber 43, thereby utilizing the pressure difference between the high-pressure chamber 42 and the low-pressure chamber 43 to perform additional concentration of the liquid to be treated. The additional concentration step can include a step in which a portion 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 merged with the permeated liquid to be supplied to the membrane concentration device 20. The remaining portion of the liquid to be treated that has been additionally concentrated in the high-pressure chamber 42 is recovered as a concentrated liquid.

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 that has been concentrated in the membrane concentrator 20 can be supplied to the high-pressure chamber 42 of the additional concentrator 40, and a portion of the liquid to be treated that has been further concentrated by passing through the high-pressure chamber 42 passes through the low-pressure chamber 43 and joins the permeated liquid supplied to the membrane concentrator 20. The remaining portion 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.

The membrane treatment device 1-7 shown in FIG. 7 is the membrane treatment device 1-5 shown in FIG. 5, with multiple NF membrane units 10 provided, including a first NF membrane unit 10-1 and a second NF membrane unit 10-2, and with the addition of a third membrane concentrator 20-3. The treated liquid 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.

The membrane treatment method using the membrane treatment device 1-7 shown in FIG. 7 can include a membrane concentration step in which a portion 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 merged with the permeated liquid produced in the second NF membrane unit 10-2 and supplied to the 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 that is merged with the permeated liquid.

As described above, in the membrane concentration step, the step of combining a portion of the treated liquid concentrated in the NF membrane water passing step with the permeate liquid to concentrate the treated liquid can be performed in devices other 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 portion of the treated liquid concentrated in the NF membrane unit 10 can be combined with the permeate liquid generated 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 portion of the treated liquid concentrated in the NF membrane unit 10 may be combined with the permeate liquid before being supplied to the membrane concentration device 20, or may be combined with the permeate liquid after passing through the membrane concentration device 20.

The membrane treatment device 1-7 shown in FIG. 7 supplies the permeate produced in the first NF membrane unit 10-1 to the first membrane concentrator 20-1, and supplies the permeate produced in the second NF membrane unit 10-2 to the second membrane concentrator 20-2 and the third membrane concentrator 20-3. However, 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.

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, there is no particular limit to the membrane concentrator 20 to which the permeate generated in each NF membrane unit 10 is supplied, 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 treated liquid 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.

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 pressure booster 6-1 and concentrated in the first membrane concentrator 20-1, then depressurized in the pressure booster 7 and further concentrated in the second NF membrane unit 10-2, and pressurized in the pressure booster 6-2 and further concentrated in the second membrane concentrator 20-2, and recovered as a concentrated liquid. The pressure booster 6-2 and pressure booster 7 shown in FIG. 8 may use an energy recovery device 8 that exchanges pressure between the pressure booster 6 and pressure booster 7, as in the membrane treatment device 1-9 shown in FIG. 9. The concentrated liquid recovered by the membrane treatment devices 1-8 and 1-9 shown in Figures 8 and 9 is pressurized in the pressure boosting section (6-2 or 6) to a high pressure, so it can be suitably used for applications such as osmotic power generation.

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 reduction sections 7-1 and 7-2 of the energy recovery devices 8-1 and 8-2, respectively. Boosting sections 6'-1, 6'-2, and 6'-3 may be provided upstream of the first membrane concentrator 20-1, NF membrane unit 10, and second membrane concentrator 20-2 as necessary to obtain the desired operating pressures.

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

The permeate produced by the NF membrane unit 10 located at the last stage (in FIG. 8, the second NF membrane unit 10-2) is the most concentrated of the permeates produced by each NF membrane unit 10, and by supplying this permeate to each membrane concentrator 20 in series 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 treated liquid can be concentrated easily and reliably in each membrane concentrator 20.

The permeate produced in the second NF membrane unit 10-2 and passed through the second membrane concentrator 20-2 may be mixed 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. By adjusting the opening of the flow control valves 5-1 and 5-2 to change the mixing ratio of these permeates, the flow rate and concentration of the permeate supplied to the first membrane concentrator 20-1 can be controlled.

The booster unit 6 in each of the above embodiments can adopt various configurations. For example, the booster unit 6 shown in FIG. 15 can be applied to the booster unit 6'-2 shown in FIG. 14. The booster unit 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. It is preferable that the operation of the booster pump 6b is performed by precisely adjusting the flow rate by inverter control. In this embodiment, the booster pump 6c is not inverter controlled, and the flow rate is adjusted by pressure control using a pressure control valve 9 arranged between the downstream side of the booster pump 6c and the merger part from the booster pump 6b. However, the booster pump 6c may also be inverter controlled, in which case the configuration can be configured without the pressure control valve 9.

REFERENCE SIGNS LIST 1 Membrane treatment device 5 Flow control valve 6 Pressure increase section 7 Pressure reduction section 10 NF membrane unit 11 Nanofiltration membrane 20 Membrane concentration device 21 Semipermeable membrane 30 RO membrane unit 31 Reverse osmosis membrane 40 Additional concentration device

Claims (9)

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. 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. 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. 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. The membrane treatment method for a liquid to be treated according to claim 4, wherein the second NF membrane water passing step includes a step of reducing the pressure of the liquid to be treated concentrated in the membrane concentration step before passing the liquid through the second nanofiltration membrane. The membrane treatment method for the liquid to be treated according to any one of claims 1 to 5, wherein the membrane concentration step includes a step of bypassing a portion of the permeate produced in the NF membrane water passing step without supplying it to the semipermeable membrane, and adjusting the flow rate of the permeate bypassing the semipermeable membrane to control the supply flow rate of the permeate to the semipermeable membrane. The membrane treatment method for a liquid to be treated according to any one of claims 1 to 6, wherein the membrane concentration process includes a process of increasing the pressure of the liquid to be treated before concentration. The membrane treatment method for the liquid to be treated according to claim 7, wherein the pressure of the liquid to be treated before being concentrated in the membrane concentration process is increased by pressure exchange with the liquid to be treated after being concentrated in the membrane concentration process. 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.

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