Concentration system

Abstract

This concentration system includes at least one semipermeable membrane module, and uses the osmotic pressure assisted reverse osmosis method to separate a solvent from a target solution containing a target component, thus obtaining the concentrated liquid in which the target component is concentrated. The semipermeable membrane module has a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane. The concentration system further includes a filtration device for filtering the target solution supplied to the first chamber. The filtration device is periodically cleaned by using at least some of the concentrated liquid.

Description

Concentration System

[0001] The present invention relates to a concentration system.

[0002] A known membrane separation method (osmotically assisted reverse osmosis (OARO) method: brine concentration) involves passing a high-pressure target solution through the first chamber of a semipermeable membrane module having a semipermeable membrane and first and second chambers separated by the semipermeable membrane, and passing a low-pressure auxiliary solution (such as the target solution) through the second chamber, causing the solvent (such as water) contained in the target solution in the first chamber to migrate through the semipermeable membrane into the auxiliary solution in the second chamber, thereby discharging a concentrated target solution (concentrate) from the first chamber and a diluted auxiliary solution (diluted solution) from the second chamber. The OARO method makes it possible to reduce the energy required for membrane separation (concentration) processing using reverse osmosis (RO) and to obtain a more highly concentrated concentrate.

[0003] For example, International Publication No. 2018 / 084246 (Patent Document 1), Japanese Patent Application Laid-Open No. 2019-188330 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2018-515340 (Patent Document 3) disclose the use of a multistage membrane separation system in which a plurality of semipermeable membrane modules are connected in series in an osmotic-assisted reverse osmosis (OARO) method.

[0004] International Publication No. 2018 / 084246 Japanese Patent Application Laid-Open No. 2019-188330 Japanese Patent Application Laid-Open No. 2018-515340

[0005] The target solution supplied to such a concentration system using the osmotic pressure-assisted reverse osmosis (OARO) method may be filtered by a filtration device such as an ultrafiltration module and then supplied to a semipermeable membrane module. In the filtration device, suspended solids and the like contained in the target solution are removed by a semipermeable membrane such as an ultrafiltration membrane, but the semipermeable membrane may become clogged with suspended solids and the like over time. For this reason, the filtration device (semipermeable membrane) must be periodically cleaned by backwashing, in which a liquid is passed in the opposite direction. Generally, the liquid used for backwashing is the liquid filtered by the filtration device (filtrate).

[0006] However, when filtrate is used to clean the filtration device, the target components to be concentrated are also consumed during backwashing, resulting in a problem of a decrease in the amount of OARO concentrate recovered. Furthermore, mixing the cleaning liquid with the OARO concentrate reduces the concentration, making it impossible to ensure the required concentrate concentration. These aspects pose a problem of a decrease in concentration efficiency. While it is possible to supply backwashing liquid from a separate system, this requires the post-cleaning water to be discharged outside the concentration system, which poses a problem of requiring additional equipment.

[0007] Therefore, an object of the present invention is to perform efficient concentration in a concentration system using an osmotic pressure-assisted reverse osmosis (OARO) method, even when cleaning of the filtration device is performed.

[0008] [1] A concentration system comprising at least one semipermeable membrane module, which uses osmotic pressure-assisted reverse osmosis to separate a solvent from a target solution containing a target component, thereby obtaining a concentrated solution in which the target component is concentrated, wherein the semipermeable membrane module has a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, and the concentration system further comprises a filtration device for filtering the target solution supplied to the first chamber, and the filtration device is periodically cleaned using at least a portion of the concentrated solution.

[0009] [2] The concentration system according to [1], wherein the target solution is filtered by the filtration device, concentrated using reverse osmosis, and then supplied to the first chamber.

[0010] [3] The concentration system according to [1] or [2], wherein the membrane separation system includes a plurality of the semipermeable membrane modules.

[0011] [4] The concentration system according to any one of [1] to [3], wherein the target solution at high pressure is passed through the first chamber and the auxiliary solution at low pressure is passed through the second chamber, and the solvent contained in the target solution in the first chamber is transferred to the auxiliary solution in the second chamber via the semipermeable membrane, whereby the concentrated solution, which is the concentrated target solution, is discharged from the first chamber and the diluted solution, which is the diluted auxiliary solution, is discharged from the second chamber, and the diluted solution is supplied to the first chamber of the semipermeable membrane module.

[0012] [5] The concentration system according to any one of [1] to [4], wherein the concentrated liquid is supplied to the second chamber of the semipermeable membrane module.

[0013] According to the present invention, in a concentration system using an osmotic pressure-assisted reverse osmosis (OARO) method, efficient concentration can be achieved even when cleaning of the filtration device is performed.

[0014] Fig. 1 is a flow chart showing the flow of information processing of an example of a design tool according to an embodiment. Fig. 2 is a schematic diagram showing another example of a membrane separation system according to an embodiment. Fig. 3 is a schematic diagram showing another example of a membrane separation system according to an embodiment.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding parts.

[0016] <Concentration System> The concentration system of this embodiment is a system that includes at least one semipermeable membrane module and separates a solvent from a target solution containing a target component using osmotic pressure-assisted reverse osmosis to obtain a concentrated solution in which the target component is concentrated.

[0017] The concentration system uses at least an osmotic pressure-assisted reverse osmosis (OARO) method, and may further use a membrane separation method other than the OARO method (e.g., reverse osmosis (RO) method, forward osmosis (FO) method, ultrafiltration method, etc.).

[0018] An example of the concentration system of the present embodiment is shown in Fig. 1. Another example of the concentration system of the present embodiment is shown in Fig. 2 and Fig. 3.

[0019] The concentration system includes at least one semipermeable membrane module 1. The semipermeable membrane module 1 has a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 separated by the semipermeable membrane 10.

[0020] A target solution (OARO feed solution) is passed through the first chamber 11, and an auxiliary solution (OARO auxiliary solution) having an osmotic pressure is passed through the second chamber 12. The target solution has a higher pressure (hydrostatic pressure) than the auxiliary solution. That is, in each semipermeable membrane module 1, the liquid in the first chamber 11 (target solution) has a higher pressure than the liquid in the second chamber 12 (auxiliary solution). As a result, in each semipermeable membrane module, the solvent (e.g., water) contained in the target solution in the first chamber 11 migrates through the semipermeable membrane 10 to the auxiliary solution in the second chamber 12, concentrating the target solution to obtain a concentrated liquid (OARO concentrate). The concentrated liquid (OARO concentrate) is discharged from the first chamber, and a diluted liquid (OARO diluted liquid) is discharged from the second chamber.

[0021] The pressure of the target solution is increased by a pressurizing device or the like. An example of the pressurizing device is a high-pressure pump that can pressurize the target solution while feeding it into the first chamber 11. The pressurizing device may be a device other than a pump, and may be, for example, a device that pressurizes the liquid in the first chamber 11 from outside the semipermeable membrane module 1.

[0022] In each semipermeable membrane module, the flow directions of the liquids on both sides of the semipermeable membrane (between the first and second chambers) may be in any direction, and may be opposite directions (counterflow system) or parallel directions (parallel flow system).

[0023] The concentration system of this embodiment may be a multistage concentration system equipped with a plurality of semipermeable membrane modules 1. In this case, a concentration flow path is provided in which the first chambers of a plurality of semipermeable membrane modules are connected. The concentration flow path is composed of the first chambers and a flow path connecting them. In at least some of the plurality of semipermeable membrane modules, the first chambers are preferably connected in series. In some of the plurality of semipermeable membrane modules, the first chambers may be connected in parallel.

[0024] In addition, a dilution flow path is provided in which the second chambers of multiple semipermeable membrane modules are connected. The dilution flow path consists of the second chambers and a flow path connecting them. In at least a portion of the multiple semipermeable membrane modules, the second chambers are preferably connected in series. In a portion of the multiple semipermeable membrane modules, the second chambers may be connected in parallel. For example, as disclosed in Japanese Patent No. 7020512, in a multi-stage concentration system, all of the first chambers of the semipermeable membrane modules may be connected in series, and a first dilution flow path in which the second chambers of a first module group (semipermeable membrane modules in odd-numbered stages from the downstream side of the concentration flow path) are connected in series may be connected in parallel with a second dilution flow path in which the second chambers of a second module group (semipermeable membrane modules in even-numbered stages from the downstream side of the concentration flow path) are connected in series.

[0025] The target solution flows through the concentration flow path, and the auxiliary solution having an osmotic pressure flows through the dilution flow path. The directions in which the target solution and the auxiliary solution flow are not particularly limited.

[0026] As shown in FIG. 1 , the filtered target solution (UF permeate) may be directly concentrated by the OARO method (semipermeable membrane module 1). Alternatively, as shown in FIG. 2 , the target solution may be concentrated by the RO method (reverse osmosis module 2) and then further concentrated by the OARO method (semipermeable membrane module 1). That is, the concentration system may include a reverse osmosis module 2 used in the RO method in addition to the semipermeable membrane module 1 used in the OARO method. The reverse osmosis module 2 has a semipermeable membrane 20 and a first chamber 21 and a second chamber 22 separated by the semipermeable membrane 20. When a high-pressure liquid is passed through the first chamber 21, the solvent (e.g., water) contained in the liquid migrates through the semipermeable membrane 20 into the second chamber 22, and the concentrated liquid is discharged from the first chamber 21.

[0027] 3, the diluted solution discharged from the second chamber 12 of the semipermeable membrane module 1a may be supplied to the first chamber 11 of the semipermeable membrane module 1a (see FIG. 3). Note that in FIG. 3, the diluted solution is supplied to the first chamber 11 of the semipermeable membrane module 1a via the reverse osmosis module 2, but the diluted solution may also be supplied to the first chamber 11 of the semipermeable membrane module 1a without passing through the reverse osmosis module 2.

[0028] Furthermore, the concentrated solution discharged from the first chamber 11 of the semipermeable membrane module 1c may be supplied to the second chamber 12 of the semipermeable membrane module 1c (see FIG. 3). That is, as shown in FIG. 3, a portion of the target solution (concentrated solution) concentrated in the first chamber 11 of the semipermeable membrane module 1c may be supplied to the second chamber 12 of the semipermeable membrane module 1c as an auxiliary solution (OARO auxiliary solution).

[0029] In this case, it is preferable to provide a mechanism (for example, a flow rate control valve 57) for adjusting the ratio of the concentrated liquid supplied as an auxiliary solution to the second chamber 12 of the semipermeable membrane module 1 relative to the total amount of the concentrated liquid. Note that it is preferable to provide a mechanism for reducing the pressure of the liquid in the flow path for supplying a portion of the concentrated liquid as an auxiliary solution to the second chamber 12 of the semipermeable membrane module 1c. Examples of such a mechanism include a device such as the pressure control valve 58 that keeps the pressure high on the upstream side and reduces the pressure on the downstream side, and an energy recovery device that has a mechanism for converting energy recovered from a pressurized supply liquid into auxiliary energy for driving a pump or the like.

[0030] (Filtration Device) In addition to the semipermeable membrane module described above, the concentration system of this embodiment further includes a filtration device (ultrafiltration module 3) for filtering the target solution supplied to the first chamber 11 of the semipermeable membrane module 1. That is, the target solution is supplied to the first chamber 11 of the semipermeable membrane module 1 after being filtered by the filtration device (ultrafiltration module 3).

[0031] A filtration device is a device that can remove foreign matter such as suspended matter contained in a target solution by filtering the target solution through solid-liquid separation using a semipermeable membrane or the like. Examples of filtration devices include ultrafiltration (UF) modules, microfiltration (MF) modules, reverse osmosis (RO) modules, and nanofiltration (NF) modules. Examples of semipermeable membranes used in filtration devices include ultrafiltration (UF) membranes, microfiltration (MF) membranes, reverse osmosis (RO) membranes, and nanofiltration (NF) membranes.

[0032] For example, the ultrafiltration (UF) module 3 has an ultrafiltration (UF) membrane 30, and a first chamber 31 and a second chamber 32 separated by the UF membrane 30. When a target solution is supplied to the first chamber 31, the filtered target solution (UF permeate) is discharged from the second chamber 32, and the target solution (UF concentrate) containing suspended matter and the like (filtration residue) is discharged from the first chamber 31.

[0033] In addition, in Figures 1 to 3, the UF membrane module has three ports: a feed liquid inlet, a permeate liquid outlet, and a concentrate outlet. The cleaning liquid inlet is shown as being used in combination with the permeate outlet, and the cleaning liquid outlet is shown as being used in combination with the concentrate outlet. However, there is no limitation on the number of ports, and for example, there may be a separate port for the cleaning liquid inlet.

[0034] In the filtration device, suspended matter and the like contained in the target solution are removed by a semipermeable membrane such as a UF membrane, but over time the semipermeable membrane may become clogged with suspended matter and the like. For this reason, the filtration device (UF module 3, UF membrane 30) must be periodically cleaned by backwashing, in which a liquid is passed in the reverse direction.

[0035] In the concentration system of this embodiment, the filtration device (ultrafiltration module 3) is periodically cleaned using at least a portion of the concentrate (OARO concentrate) discharged from the first chamber 11 of the semipermeable membrane module 1.

[0036] In the past, when the filtered liquid from a filtration device was used as the cleaning liquid for backwashing, the target components to be concentrated were consumed during the backwashing, resulting in a decrease in the amount of recovered OARO concentrate. Furthermore, mixing the used cleaning liquid with the OARO concentrate also reduces the concentration. These aspects led to the problem of reduced concentration efficiency.

[0037] In contrast, in the concentration system of this embodiment, by using OARO concentrate as the backwash cleaning liquid, mixing used cleaning liquid with the OARO concentrate does not result in a decrease in concentration, and the amount of OARO concentrate recovered is not reduced. Therefore, in a concentration system using osmotic pressure-assisted reverse osmosis (OARO) technology, efficient concentration can be achieved even when cleaning a filtration device. Furthermore, if backwash cleaning liquid is supplied from a separate system, a separate facility is required to discharge used cleaning liquid outside the concentration system. However, in the concentration system of this embodiment, such a problem does not arise because the cleaning liquid is not supplied from a separate system.

[0038] The opening of valves 52 and 54 may be controlled so that a portion of the concentrated liquid used as a cleaning liquid is maintained at a predetermined flow rate. Alternatively, the opening of valves 52 and 54 may be controlled so that the collected concentrated liquid is maintained at a predetermined flow rate. Furthermore, the pressure of a portion of the concentrated liquid used as a cleaning liquid may be controlled by adjusting the flow rate of pump 41 or the opening of valve 57 to ensure a predetermined flow rate or concentration.

[0039] Furthermore, the concentrated solution used as a cleaning solution for the filtration device (OARO concentrated solution) is a liquid with a higher concentration than a solution obtained by reverse osmosis, etc., and is therefore excellent in eliminating clogging of the filtration device (semipermeable membrane). Note that a chemical solution may be added to the concentrated solution used as a cleaning solution for the filtration device (OARO concentrated solution) to enhance the cleaning effect.

[0040] 1 to 3, solid arrows indicate the flow of liquid during normal operation of the concentration system, and dotted arrows indicate the flow of liquid during cleaning (backwashing) of the filtration device (UF module 3).

[0041] During normal operation of the concentration system, the opening and closing of valves 51 to 56 is controlled so that liquid flows in the direction of the solid arrows. That is, valves 51, 52, and 53 are opened, valves 54, 55, and 56 are closed, and high-pressure pump 41 is operated (pump 42 is stopped). On the other hand, during cleaning of the filtration device, the opening and closing of valves 51 to 56 is controlled so that liquid flows in the direction of the dotted arrows. That is, valves 51, 52, and 53 are closed, valves 54, 55, and 56 are opened, and pump 42 is operated (high-pressure pump 41 is stopped).

[0042] When cleaning the filtration device, the OARO concentrate (UF cleaning solution) containing foreign matter such as suspended matter will be mixed into the OARO concentrate recovery path. However, if the OARO concentrate is subjected to a further concentration process such as evaporation, the foreign matter can be easily separated during recovery of useful materials, so it is not a problem if the foreign matter such as suspended matter is mixed into the OARO concentrate.

[0043] (Target Solution, Auxiliary Solution) The target solution is not particularly limited as long as it is a liquid in which the target component is dissolved in a solvent. Examples of the solvent include water, and the target component is any component that dissolves in the solvent. For example, salt water (brine, seawater, brackish water, etc.), industrial wastewater (aqueous solution containing inorganic salts, aqueous solution containing water-soluble organic solvents, etc.), etc. can be used. The concentration system described above is particularly suitable for further concentrating the target solution when it is a highly concentrated (high osmotic pressure) solution such as brine.

[0044] The target solution, etc. may be subjected to pretreatment to remove fine particles, microorganisms, scale components, etc. contained in the solution. Pretreatment may involve various known pretreatments used in seawater desalination technologies, etc., such as filtration using an NF membrane, UF membrane, MF membrane, etc., addition of sodium hypochlorite, addition of a coagulant, activated carbon adsorption treatment, and ion exchange resin treatment. Such pretreatment is preferably carried out before the target solution, etc. is supplied to the semipermeable membrane module. In this embodiment, as described above, the target solution is filtered by at least the filtration device (UF module 3) before being supplied to the first chamber 11 of the semipermeable membrane module 1, 1a, but other pretreatments may also be performed on the target solution, etc.

[0045] The auxiliary solution is not particularly limited as long as it has osmotic pressure, but it preferably contains the same components as the target components of the target solution. In theory, membrane separation (concentration of the target solution) using OARO is possible if the osmotic pressure difference (absolute value) between the target solution (concentrated solution) flowing through the first chamber 11 (high-pressure side) and the auxiliary solution (diluted solution) flowing through the second chamber 12 (low-pressure side) is smaller than the pressure of the target solution. In this case, the difference between the osmotic pressure of the target solution and the osmotic pressure of the auxiliary solution is preferably 30% or less of the pressure of the target solution.

[0046] In the concentration process (membrane separation process) by OARO using the semipermeable membrane module 1, osmotic pressure acting in the opposite direction to the direction in which the solvent moves from the first chamber 11 to the second chamber 12 is unlikely to be generated, and therefore concentration can be carried out at a lower pressure (pump pressure) than in the reverse osmosis (RO) method. Therefore, in the concentration system of this embodiment, which mainly performs concentration by OARO, the amount of power consumed by pumps, etc. can be reduced, and the energy efficiency of concentration can be improved.

[0047] Furthermore, in concentration by the RO method, the osmotic pressure of the concentrated target solution on one side of the semipermeable membrane is generated in the opposite direction to the pressing force of the pump. Therefore, when the osmotic pressure of the concentrated target solution reaches the pressure of the pump, the pressing force of the pump and the osmotic pressure of the target solution acting in the opposite direction are balanced, and water does not pass through the semipermeable membrane any further, and concentration does not proceed.

[0048] In contrast, in a membrane separation process (concentration method) using the OARO method, the difference in concentration (osmotic pressure difference) between the liquids supplied to the first and second compartments in each semipermeable membrane module is small, and the osmotic pressure that inhibits the concentration process, as in the RO method, is unlikely to occur. Therefore, a concentration system using the OARO method can increase the final concentration of the target solution compared to a concentration system using only the RO method. In principle, it is thought that the target solution can be concentrated to a saturated concentration.

[0049] (Semipermeable Membrane) Examples of the semipermeable membrane used in this embodiment include semipermeable membranes called reverse osmosis membranes (RO membranes), forward osmosis membranes (FO membranes), nanofiltration membranes (NF membranes), and ultrafiltration membranes (UF membranes). The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane. When a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane is used as the semipermeable membrane, the pressure of the liquid (target solution) in the first chamber is preferably 0.5 to 10.0 MPa.

[0050] Typically, RO membranes and FO membranes have pore sizes of approximately 2 nm or less, and UF membranes have pore sizes of approximately 2 to 100 nm. NF membranes have a relatively low rejection rate for ions and salts compared to RO membranes, and typically have pore sizes of approximately 1 to 2 nm. When an RO membrane, FO membrane, or NF membrane is used as the semipermeable membrane, the salt rejection rate of the RO membrane, FO membrane, or NF membrane is preferably 90% or higher.

[0051] The material constituting the semipermeable membrane is not particularly limited, but examples thereof include cellulose-based resins, polysulfone-based resins, polyamide-based resins, etc. The semipermeable membrane is preferably made of a material containing at least one of a cellulose-based resin and a polysulfone-based resin.

[0052] The cellulose-based resin is preferably a cellulose acetate-based resin. Cellulose acetate-based resins are resistant to chlorine, a disinfectant, and have the characteristic of being able to inhibit the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and from the viewpoint of durability, more preferably cellulose triacetate.

[0053] The polysulfone-based resin is preferably a polyethersulfone-based resin. The polyethersulfone-based resin is preferably a sulfonated polyethersulfone.

[0054] In the drawings, the semipermeable membranes of the semipermeable membrane modules are depicted as flat membranes for simplification, but the shape of the semipermeable membranes is not particularly limited. The semipermeable membranes may be flat membranes such as spiral membranes (spiral-type semipermeable membranes) or hollow fiber membranes (hollow fiber-type semipermeable membranes), but hollow fiber membranes are preferred. Hollow fiber membranes are advantageous in that they have a smaller membrane thickness than flat membranes and can increase the membrane area per module, thereby increasing permeation efficiency.

[0055] When the semipermeable membrane is a hollow fiber membrane, it is preferable that in each semipermeable membrane module, the first chamber is outside the hollow fiber membrane and the second chamber is inside the hollow fiber membrane (hollow portion). This is because even if the solution flowing inside the hollow fiber membrane is pressurized, the pressure loss may become large and it may be difficult to pressurize sufficiently, and further, although hollow fiber membranes generally easily maintain their structure against external pressure, high internal pressure may damage the hollow fiber membrane.

[0056] A specific example of a hollow fiber membrane is a membrane with a single layer structure composed entirely of a cellulose-based resin. However, the single layer structure referred to here does not necessarily mean a membrane with a uniform layer throughout; for example, it may be a membrane that is non-uniform in the thickness direction. Specifically, the membrane may have a dense layer on the outer surface, which serves as a separation active layer that essentially determines the pore size of the hollow fiber membrane, and the inner surface side may have a lower density than the dense layer. Since the dense layer essentially serves as a separation active layer that determines the pore size of the hollow fiber membrane, when the solution outside the hollow fiber membrane is pressurized, having a dense layer on the outer surface of the hollow fiber membrane allows for more accurate control of the movement of molecules from the outside to the inside of the hollow fiber membrane.

[0057] Another specific example of a hollow fiber membrane is a two-layer membrane having a dense layer of a polyphenylene resin (e.g., sulfonated polyethersulfone) on the outer surface of a support layer (e.g., a layer made of polyphenylene oxide). Another example is a two-layer membrane having a dense layer of a polyamide resin on the outer surface of a support layer (e.g., a layer made of polysulfone or polyethersulfone).

[0058] 1, 1a, 1b, 1c semipermeable membrane module, 10 semipermeable membrane, 11 first chamber, 12 second chamber, 2 reverse osmosis module, 20 semipermeable membrane, 21 first chamber, 22 second chamber, 3 ultrafiltration module, 30 ultrafiltration membrane, 31 first chamber, 32 second chamber, 41 high-pressure pump, 42 pump, 51 to 56 valves, 57 flow rate control valve, 58 pressure control valve.

Claims

1. A concentration system comprising at least one semipermeable membrane module, which uses osmotic pressure-assisted reverse osmosis to separate a solvent from a target solution containing a target component, thereby obtaining a concentrated solution in which the target component is concentrated, wherein the semipermeable membrane module has a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, and the concentration system further comprises a filtration device for filtering the target solution supplied to the first chamber, and the filtration device is periodically cleaned using at least a portion of the concentrated solution.

2. The concentration system according to claim 1, wherein the target solution is filtered by the filtration device and concentrated using reverse osmosis before being supplied to the first compartment.

3. The concentration system according to claim 1 or 2, comprising a plurality of the semipermeable membrane modules.

4. A concentration system according to any one of claims 1 to 3, wherein the target solution at high pressure is passed through the first chamber and the auxiliary solution at low pressure is passed through the second chamber, and the solvent contained in the target solution in the first chamber is transferred to the auxiliary solution in the second chamber via the semipermeable membrane, thereby discharging the concentrated solution, which is the concentrated target solution, from the first chamber and discharging the diluted solution, which is the diluted auxiliary solution, from the second chamber, and the diluted solution is supplied to the first chamber of the semipermeable membrane module.

5. The concentration system according to any one of claims 1 to 4, wherein the concentrated liquid is supplied to the second chamber of the semipermeable membrane module.

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