Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device which can reduce an influence of concentration polarization in concentration treatment of water using a semipermeable membrane module.SOLUTION: A water treatment method comprises: a semipermeable membrane treatment step of using a semipermeable membrane module 12 having a first space 16 and a second space 18 divided by a semipermeable membrane 14 to pass water to be treated including a dissolved solid component through the first space 16 and pressurize the first space 16 to cause the water included in the water to be treated to penetrate the semipermeable membrane 14 to thereby obtain concentrated water while passing a part of the concentrated water through the second space 18, obtaining diluted water; and a circulation step of returning an additional part of the concentrated water to the side of the water to be treated of the semipermeable membrane module 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment method and a water treatment apparatus for concentrating water containing total dissolved solids (TDS) and the like. [Background technology]

[0002] 2. Description of the Related Art In recent years, methods for reducing the volume of wastewater from factories and the like have become known, including an evaporation method using an evaporator and a reverse osmosis method in which a reverse osmosis membrane is used to recover permeate and reduce the volume of wastewater.

[0003] Also, a method is known in which the water to be treated or its concentrate is passed through a first space and a second space separated by a semipermeable membrane of a semipermeable membrane module, and the first space is pressurized, as in Patent Document 1. This type of concentration method using a semipermeable membrane reduces the osmotic pressure difference between the first space and the second space, and thus can highly concentrate wastewater and reduce its volume with less energy consumption, compared to a general reverse osmosis method.

[0004] However, in such a concentration method using a semipermeable membrane, especially when concentrating high-concentration water to be treated, the liquid is concentrated on the membrane surface of the semipermeable membrane, and is affected by a phenomenon in which a larger osmotic pressure is applied (i.e., concentration polarization), and the amount of water permeating from the first space to the second space of the membrane may be reduced. In addition, when a multi-stage semipermeable membrane module is used as in Patent Document 1, the concentration of water passing through the first space of the membrane becomes higher toward the rear of the membrane unit, and the effect of concentration polarization becomes greater, so the amount of water permeating from the first space to the second space of the membrane decreases. As a result, a high pressure is required to obtain concentrated water, and the number of membrane units required for concentration increases, leading to increased initial costs and running costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-069198 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a water treatment method and water treatment apparatus capable of reducing the influence of concentration polarization in water concentration treatment using a semipermeable membrane module. [Means for solving the problem]

[0007] The present invention relates to a semipermeable membrane treatment process in which a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane is used, and water to be treated that contains dissolved solid components is passed through the first space, and the first space is pressurized to cause the water contained in the water to permeate through the semipermeable membrane to obtain concentrated water, and a part of the concentrated water is passed through the second space to obtain dilution water. The water to be treated The semipermeable membrane module Pipe for sending liquid to the first space and a circulating step of returning the waste water to the Measure a flow rate (FI1) of the water to be treated supplied to the first space in the pipe; When the concentration of the dissolved solid components in the treated water exceeds a predetermined concentration value, The flow rate of the circulating concentrated water is 200% or more relative to the flow rate of the water to be treated (FI1). and controlling the flow rate of the circulating concentrated water so as to reduce the amount of the concentrated water.

[0008] The present invention relates to a semipermeable membrane treatment process in which a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane is used, and water to be treated that contains dissolved solid components is passed through the first space, and the first space is pressurized to cause the water contained in the water to permeate through the semipermeable membrane to obtain concentrated water, and a part of the water to be treated is passed through the second space to obtain dilution water. The water to be treated The semipermeable membrane module Pipe for sending liquid to the first space and a circulation step of returning the waste water to the Measure a flow rate (FI1) of the water to be treated supplied to the first space in the pipe; When the concentration of the dissolved solid components in the treated water exceeds a predetermined concentration value, The flow rate of the circulating concentrated water is 200% or more relative to the flow rate of the water to be treated (FI1). and controlling the flow rate of the circulating concentrated water so as to reduce the amount of the concentrated water.

[0011] In the water treatment method, the predetermined concentration value is preferably a concentration value at which the osmotic pressure of the water to be treated is 5 MPa or more.

[0012] The present invention relates to a semipermeable membrane treatment means for obtaining dilution water by passing water to be treated that contains dissolved solid components through the first space and pressurizing the first space to cause the water contained in the water to permeate through the semipermeable membrane, and for passing a portion of the concentrated water through the second space, using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane. The water to be treated The semipermeable membrane module Pipe for sending liquid to the first space A circulation means for returning the waste to the recycling facility; a water-to-be-treated flow rate measuring means for measuring a flow rate (FI1) of the water to be treated supplied to the first space in the piping; When the concentration of the dissolved solid components in the treated water exceeds a predetermined concentration value, The flow rate of the circulating concentrated water is 200% or more relative to the flow rate of the water to be treated (FI1). and a control means for controlling the flow rate of the circulating concentrated water so as to control the flow rate of the circulating concentrated water.

[0013] The present invention relates to a semipermeable membrane treatment means for obtaining dilution water by passing water to be treated that contains dissolved solid components through the first space and pressurizing the first space to cause the water contained in the water to permeate through the semipermeable membrane, and for obtaining dilution water by passing a portion of the water to be treated through the second space, using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane. The water to be treated The semipermeable membrane module Pipe for sending liquid to the first space A circulation means for returning the waste to the recycling facility; a water-to-be-treated flow rate measuring means for measuring a flow rate (FI1) of the water to be treated supplied to the first space in the piping; When the concentration of the dissolved solid components in the treated water exceeds a predetermined concentration value, The flow rate of the circulating concentrated water is 200% or more relative to the flow rate of the water to be treated (FI1). and a control means for controlling the flow rate of the circulating concentrated water so as to control the flow rate of the circulating concentrated water.

[0016] In the water treatment device, the predetermined concentration value is preferably a concentration value at which the osmotic pressure of the water to be treated is 5 MPa or more. Effect of the Invention

[0017] According to the present invention, it is possible to provide a water treatment method and a water treatment apparatus capable of reducing the influence of concentration polarization in a water concentration treatment using a semipermeable membrane module. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. [Diagram 5] FIG. 1 is a schematic diagram showing the configuration of a water treatment device used in Comparative Example 1. [Figure 6] 1 is a graph showing the first space side (primary side) flow rate (L / min) and the increase rate (%) of the permeated water amount in Examples 2 to 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0020] An example of a water treatment apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0021] 1 includes, for example, a membrane module 12 as a semipermeable membrane treatment means for concentrating water to be treated that contains total dissolved solids (TDS) and the like using a semipermeable membrane module having a first space (concentrated side) and a second space (permeated side) separated by a semipermeable membrane. The membrane module 12 includes a first space 16 and a second space 18 separated by a semipermeable membrane 14. The water treatment device 1 may include a water tank 10 to be treated that stores the water to be treated.

[0022] In the water treatment device 1 of Figure 1, a pipe 22 is connected to the inlet of the water to be treated of the water tank 10. The outlet of the water tank 10 to be treated and the first space inlet of the membrane module 12 are connected by a pipe 24 via a pump 20. A pipe 26 is connected to the first space outlet of the membrane module 12. A pipe 28 branching off from the pipe 26 is connected to the second space inlet of the membrane module 12. A pipe 30 is connected to the second space outlet of the membrane module 12. A pipe 32 branching off from the pipe 26 is connected to the circulating water inlet of the water tank 10 to be treated.

[0023] The water treatment device 1 of FIG. 1 uses a membrane module 12 having a first space 16 and a second space 18 separated by a semipermeable membrane 14, and passes water to be treated from the first space inlet of the membrane module 12 to the first space 16, and passes a part of concentrated water discharged from the first space outlet of the first space 16 of the membrane module 12 to the second space 18 from the second space inlet of the membrane module 12, and pressurizes the first space 16, thereby causing the water contained in the water to be treated in the first space 16 to permeate into the second space 18 through the semipermeable membrane 14, thereby concentrating the water. That is, in the water treatment device 1, the water to be treated is concentrated using the semipermeable membrane 14. The water treatment device 1 is a device that supplies the water to be treated to the first space 16 of the membrane module 12, and supplies a part of the concentrated water obtained from the outlet of the first space 16 to the second space 18 of the membrane module 12 to perform a concentration treatment.

[0024] The water treatment method and the operation of the water treatment device 1 according to this embodiment will be described.

[0025] In the water treatment device 1, the water to be treated containing total dissolved solids (TDS) is stored in the water tank 10 as necessary through the pipe 22, and then pressurized and fed from the water tank 10 to the first space 16 of the membrane module 12 through the pipe 24 by the pump 20. A part of the water contained in the pressurized water to be treated permeates from the first space 16 to the second space 18 through the semipermeable membrane 14. At this time, most of the dissolved solids cannot permeate the semipermeable membrane 14, so the water in the first space 16 that did not permeate the semipermeable membrane 14 is concentrated. Meanwhile, in the second space 18, a part of the concentrated water fed through the pipe 28 and the permeated water with a low TDS concentration that permeated the semipermeable membrane 14 are merged, so that a dilution effect is produced. The concentrated water obtained in the first space 16 is discharged through the pipe 26 from the first space outlet, and a part of the concentrated water is fed through the pipe 28 branched from the pipe 26 to the second space 18 from the second space inlet of the membrane module 12 and fed. The dilution water obtained in the second space 18 is discharged from the second space outlet through the pipe 30. Here, in the membrane module 12, the first space 16 is pressurized, and the water contained in the water to be treated in the first space 16 is permeated through the semipermeable membrane 14 into the second space 18, so that concentrated water is obtained in the first space 16 (concentration process), and dilution water is obtained in the second space 18 (dilution process). A part of the concentrated water obtained in the first space 16 may be discharged to the outside of the system through the pipe 26. A part of the concentrated water is sent and passed through the pipes 26 and 28 to the second space 18 of the membrane module 12 as described above, and a further part of the concentrated water is returned as circulating water through the pipe 32 to the water to be treated side of the membrane module 12, for example, the water to be treated tank 10, and circulated (circulation process). The circulating water may be returned to the pipe 24.

[0026] Here, the pump 20, piping 24, 26, 28, etc. function as a supply means for supplying the treated water to the first space 16 of the semipermeable membrane module 12 and supplying at least a portion of the concentrated water obtained from the outlet of the first space 16 to the second space 18 of the semipermeable membrane module 12.

[0027] The diluted water obtained in the second space 18 may be discharged outside the system through the pipe 30, or may be sent to a dilution water tank and stored there as necessary, and then discharged outside the system. At least a part of the diluted water may be sent to the water tank 10 to be treated and mixed with the water to be treated in the water tank 10. At least a part of the diluted water may be further sent to a reverse osmosis membrane treatment device, where reverse osmosis membrane treatment is performed (reverse osmosis membrane treatment step). The RO permeate obtained by the reverse osmosis membrane treatment is discharged outside the system. The RO concentrated water obtained by the reverse osmosis membrane treatment may be sent to the water tank 10 to be treated and mixed with the water to be treated in the water tank 10.

[0028] In this manner, treated water (concentrated water) in which substances such as dissolved solid components are concentrated, and dilution water are obtained from the treated water, which is the target of treatment and contains dissolved solid components, thereby reducing the volume of the treated water.

[0029] In the water treatment method and water treatment device 1 according to this embodiment, a pipe 32 is provided as a circulation means for returning and circulating a portion of the concentrated water to the water to be treated side of the membrane module 12. By returning and circulating a portion of the concentrated water to the water to be treated side of the membrane module 12 and increasing the amount of water supplied to the first space 16 of the semipermeable membrane module 12, it is possible to reduce the influence of concentration polarization. As a result, the operating power for applying pressure to obtain concentrated water can be reduced, which leads to reductions in initial costs and running costs, and a low-cost water treatment method and water treatment device can be provided.

[0030] Another example of a water treatment device according to an embodiment of the present invention is shown generally in FIG. 2, and its configuration will be described.

[0031] 2 includes, for example, a membrane module 12 as a semipermeable membrane treatment means for concentrating water to be treated that contains total dissolved solids (TDS) and the like using a semipermeable membrane module having a first space (concentrated side) and a second space (permeated side) separated by a semipermeable membrane. The membrane module 12 includes a first space 16 and a second space 18 separated by a semipermeable membrane 14. The water treatment device 2 may include a water tank 10 to be treated that stores the water to be treated.

[0032] In the water treatment device 2 in Fig. 2, a pipe 22 is connected to the inlet of the water tank 10 to be treated. The outlet of the water tank 10 to be treated and the first space inlet of the membrane module 12 are connected by a pipe 24 via a pump 20, and a pipe 34 branching off from the pipe 24 on the downstream side of the pump 20 in the pipe 24 is connected to the second space inlet of the membrane module 12. A pipe 26 is connected to the first space outlet of the membrane module 12, and a pipe 36 is connected to the second space outlet of the membrane module 12. A pipe 32 branching off from the pipe 26 is connected to the circulating water inlet of the water tank 10 to be treated.

[0033] The water treatment device 2 in Fig. 2 uses a membrane module 12 having a first space 16 and a second space 18 separated by a semipermeable membrane 14, and is an apparatus in which the water to be treated is passed from the first space inlet of the membrane module 12 to the first space 16 and from the second space inlet to the second space 18, and the first space 16 is pressurized, thereby causing the water contained in the water to be treated in the first space 16 to permeate into the second space 18 via the semipermeable membrane 14, thereby concentrating the water. That is, in the water treatment device 2, the water to be treated is concentrated using the semipermeable membrane 14. The water treatment device 2 is an apparatus in which the water to be treated is supplied to both the first space 16 and the second space 18 of the membrane module 12 to perform a concentration treatment.

[0034] In the water treatment device 2, the water to be treated containing total dissolved solids (TDS) is stored in the water tank 10 as necessary through the pipe 22, and then pressurized and fed from the water tank 10 to the first space 16 of the membrane module 12 through the pipe 24 by the pump 20. The water to be treated is also fed from the second space inlet of the membrane module 12 to the second space 18 through the pipe 34 branched from the pipe 24. The concentrated water obtained in the first space 16 is discharged from the first space outlet through the pipe 26, and the diluted water obtained in the second space 18 is discharged from the second space outlet through the pipe 36. Here, in the membrane module 12, the first space 16 is pressurized and the water contained in the water to be treated in the first space 16 is permeated through the semipermeable membrane 14 into the second space 18, so that concentrated water is obtained in the first space 16 (concentration process) and diluted water is obtained in the second space 18 (dilution process). A part of the concentrated water obtained in the first space 16 may be discharged to the outside of the system through the pipe 26. At least a part of the concentrated water is returned as circulating water through the pipe 32 to the water side of the membrane module 12, for example, to the water tank 10 (circulation step). The circulating water may be returned upstream of the branch point of the pipe 24 with the pipe 34.

[0035] Here, the pump 20 , the pipes 24 , 34 , etc. function as a supply means for supplying the water to be treated to both the first space 16 and the second space 18 of the semipermeable membrane module 12 .

[0036] The diluted water obtained in the second space 18 may be discharged outside the system through the pipe 36, or may be sent to a dilution water tank and stored there as necessary, and then discharged outside the system. At least a part of the diluted water may be sent to the water tank 10 to be treated and mixed with the water to be treated in the water tank 10. At least a part of the diluted water may be further sent to a reverse osmosis membrane treatment device, where reverse osmosis membrane treatment is performed (reverse osmosis membrane treatment step). The RO permeate obtained by the reverse osmosis membrane treatment is discharged outside the system. The RO concentrated water obtained by the reverse osmosis membrane treatment may be sent to the water tank 10 to be treated and mixed with the water to be treated in the water tank 10.

[0037] In this manner, treated water (concentrated water) in which substances such as dissolved solid components are concentrated, and dilution water are obtained from the treated water, which is the target of treatment and contains dissolved solid components, thereby reducing the volume of the treated water.

[0038] In the water treatment method and water treatment device 2 according to this embodiment, a pipe 32 is provided as a circulation means for returning and circulating at least a portion of the concentrated water to the water to be treated side of the membrane module 12. By returning and circulating at least a portion of the concentrated water to the water to be treated side of the membrane module 12 and increasing the amount of water supplied to the first space 16 of the semipermeable membrane module 12, it is possible to reduce the influence of concentration polarization. As a result, the operating power for applying pressure to obtain concentrated water can be reduced, which leads to reductions in initial costs and running costs, and a low-cost water treatment method and water treatment device can be provided.

[0039] In the water treatment method and water treatment device according to this embodiment, it is preferable to measure the TDS concentration of the water to be treated at the inlet of the first space 16 of the membrane module 12, and when the measured TDS concentration exceeds a predetermined concentration value, control the flow rate of the circulating concentrated water (circulating water) so that the amount of permeated water permeating through the semipermeable membrane 14 from the first space 16 to the second space 18 falls within a predetermined range. An example of a water treatment device configured in this way is shown in Figure 3.

[0040] The water treatment device 3 shown in FIG. 3 includes, in addition to the same configuration as the water treatment device 2 shown in FIG. 2, a concentration measuring device 44 as a concentration measuring means for measuring the concentration of dissolved solid components in the water to be treated at the inlet of the first space 16 of the membrane module 12, and a water to be treated flow rate measuring device 46 as a first space water to be treated flow rate measuring means for measuring the flow rate (FI1) of the water to be treated at the inlet of the first space 16 of the membrane module 12, on the upstream side of the pump 20 in the piping 24. A circulation flow rate measuring device 56 is provided in the piping 32 as a circulation flow rate measuring means for measuring the flow rate (FI2) of the circulating concentrated water (circulating water). A blow flow rate measuring device 54 is provided downstream of the branch point of the piping 26 with the piping 32 as a blow flow rate measuring means for measuring the flow rate (FI3) of the concentrated water to be blown at the outlet of the first space 16 of the membrane module 12. An additional configuration similar to that of the water treatment device 3 may be added to the water treatment device 1 shown in FIG. 1.

[0041] The pump 20 is, for example, a pressure pump that is driven at a rotation speed corresponding to an input drive frequency, sucks in the water to be treated, and discharges it to the membrane module 12. The pump 20 is provided with, for example, an inverter 42 that outputs to the pump 20 a drive frequency corresponding to an input command signal. A valve 60 is provided downstream of the branch point with the pipe 32 in the pipe 26 and upstream of the blow flow rate measuring device 54. The valve 60 is, for example, a proportional control valve that adjusts the opening based on the measured values ​​of the water to be treated flow rate measuring device 46 and the blow flow rate measuring device 54. An inlet pressure measuring device 48 is provided downstream of the pump 20 in the pipe 24 as an inlet pressure measuring means for measuring the pressure at the inlet of the first space 16, and an outlet pressure measuring device 58 may be provided upstream of the branch point with the pipe 32 in the pipe 26 as an outlet pressure measuring means for measuring the pressure at the outlet of the first space 16. Pipe 34 branching off from pipe 24 is connected to the inlet of the second space 18 of the membrane module 12 via pump 52, and a treated water flow rate measuring device 50 may be installed upstream of pump 52 as a second space treated water flow rate measuring means for measuring the flow rate (FI4) of the treated water at the inlet of the second space 18 of the membrane module 12.

[0042] The water treatment device 3 may include a control device 40 as a control means for controlling the flow rate of the circulating concentrated water so that the amount of permeate falls within a predetermined range when the concentration of dissolved solid components exceeds a predetermined concentration value, and the control device 40 may be electrically connected to the inverter 42, the concentration measuring device 44, the treated water flow rate measuring device 46, the blow flow rate measuring device 54, the circulation flow rate measuring device 56, and the valve 62. The control device 40 may be electrically connected to the valve 60. The control device 40 is composed of a microcomputer and an electronic circuit, which are composed of a calculation means such as a CPU that calculates a program, and a storage means such as a ROM and RAM that store the program and the calculation results, and has a function of controlling the flow rate of the pump 20, the opening and closing degree of the valve 62, etc.

[0043] In the water treatment device 3, similarly to the water treatment device 2, treated water (concentrated water) in which substances such as dissolved solid components are concentrated and dilution water are obtained from the treated water, which is the target of treatment and contains dissolved solid components, etc., thereby reducing the volume of the treated water.

[0044] Here, for example, the concentration measuring device 44 measures the concentration of dissolved solid components in the water to be treated at the inlet of the first space 16 of the membrane module 12 (concentration measurement process), the water to be treated flow rate measuring device 46 measures the flow rate (FI1) of the water to be treated at the inlet of the first space 16 of the membrane module 12 (first space water to be treated flow rate measuring process), the circulation flow rate measuring device 56 measures the flow rate (FI2) of the circulating concentrated water (circulation flow rate measuring process), and the blow flow rate measuring device 54 measures the flow rate (FI3) of the blown concentrated water at the outlet of the first space 16 of the membrane module 12 (blow flow rate measuring process). Then, when the concentration of dissolved solid components measured in the concentration measurement process exceeds a predetermined concentration value, the flow rate of the circulating concentrated water is controlled so that, for example, the amount of permeated water passing from the first space 16 to the second space 18 (=FI1-(FI2+FI3)), which is calculated from the respective flow rates (FI1, FI2, FI3) measured in the first space treated water flow rate measurement process, the circulation flow rate measurement process, and the blow flow rate measurement process, falls within a predetermined range (control process).

[0045] For example, when the concentration of dissolved solids measured by concentration measuring device 44 exceeds a predetermined concentration value, control device 40 may calculate the drive frequency using an arbitrary arithmetic expression so that the permeate amount=FI1-(FI2+FI3) calculated from the flow rates (FI1, FI2, FI3) measured by treated water flow rate measuring device 46, circulation flow rate measuring device 56, and blow flow rate measuring device 54 falls within a predetermined range, output a command signal corresponding to this calculated value to inverter 42 to control pump 20, and control the opening / closing degree of valve 62 to control the flow rate of the circulating concentrated water. Note that the method of calculating the permeate amount is not limited to the method of "calculating the permeate amount=FI1-(FI2+FI3) from FI1, FI2, FI3". For example, a permeate flow rate measuring device 51 may be installed as a permeate flow rate measuring means in the piping 36 which is the outlet of the second space 18, and the flow rate of the water to be treated (FI4) at the inlet of the second space 18 may be measured (second space water to be treated flow rate measuring process), and the flow rate of the permeate (FI5) at the outlet of the second space 18 may be measured (permeate flow rate measuring process). The flow rate of the circulating concentrated water may be controlled so that the permeate amount calculated from the respective flow rates (FI4, FI5) = FI5 - FI4 falls within a predetermined range.

[0046] In the water treatment method and water treatment device 3 according to this embodiment, the TDS concentration of the water to be treated at the inlet of the first space 16 of the membrane module 12 is measured, and when the TDS concentration exceeds a predetermined concentration value, the opening of the valve 62 is adjusted, and at least a portion of the concentrated water is returned and circulated to the water to be treated side of the membrane module 12 where the TDS concentration has exceeded the predetermined concentration value, thereby increasing the amount of water supplied to the first space 16 of the semipermeable membrane module 12. As a result, in water concentration treatment using a semipermeable membrane module, the effects of concentration polarization can be reduced even when the concentration of dissolved solids in the water to be treated exceeds a predetermined concentration value.

[0047] For example, when the TDS concentration of the water to be treated exceeds a predetermined concentration value, it is preferable to control the flow rate of the circulating concentrated water so that the flow rate of the circulating concentrated water is 200% or more, and more preferable to control the flow rate of the circulating concentrated water so that the flow rate of the circulating concentrated water is 250% or more, relative to the flow rate of the water to be treated supplied to the first space 16 of the membrane module 12. If the flow rate of the circulating concentrated water is less than 200%, it may not be possible to reduce the effect of concentration polarization.

[0048] For example, the pump 20 is started, and the water to be treated is passed from the water tank 10 to the first space 16 of the membrane module 12. At this time, the valve 62 is fully closed, and the valve 60 is open, and the device is operated. When the TDS concentration of the water to be treated exceeds a predetermined concentration value (for example, 6%), the output value of the inverter 42 is increased by a predetermined ratio (for example, 10%). Since the measurement value (FI3) by the blow flow rate measurement device 54 and the permeate amount (FI1-(FI2+FI3)) increase, the valve 60 is opened, the valve 62 is opened, and the opening degree of the valve 60 and the valve 62 is adjusted so that the permeate amount falls within a predetermined range. The operation may be repeated until the measurement value (FI2) by the circulation flow rate measurement device 56 indicates that the circulation amount is a predetermined value (for example, 200% or more) relative to the supply flow rate of the first space 16. If the TDS concentration of the water to be treated is below a predetermined concentration value, the valve 62 can be closed and the flow rate of the circulating concentrated water can be adjusted to gradually reduce it, or the valve 62 can be fully closed and the concentrated water does not need to be circulated.

[0049] The "predetermined concentration value" of the TDS concentration of the water to be treated is, for example, preferably a concentration value at which the osmotic pressure of the water to be treated is 5 MPa or more, and more preferably a concentration value at which the osmotic pressure of the water to be treated is 8 MPa or more. When the concentration value at which the osmotic pressure of the water to be treated is less than 5 MPa, the effect of concentration polarization is small and the decrease in the amount of permeated water is slight. For example, when the dissolved solid component is sodium chloride (NaCl), the "predetermined concentration value" of the TDS concentration of the water to be treated is "6 mass%". The osmotic pressure is calculated by the following formula. Osmotic pressure (MPa) = molar concentration (mol / L) × gas constant (Pa L / (mol K)) × absolute temperature (K) × 10-6

[0050] In the water treatment method and water treatment device according to this embodiment, a multi-stage semipermeable membrane module may be used. An example of a water treatment device having such a configuration is shown in FIG.

[0051] The water treatment device 4 shown in FIG. 4 is equipped with, for example, a first-stage membrane module 12a, a second-stage membrane module 12b, and a third-stage membrane module 12c as semipermeable membrane treatment means for concentrating water to be treated containing total dissolved solids (TDS) and the like using a semipermeable membrane module having a first space (concentration side) and a second space (permeation side) separated by a semipermeable membrane, and further concentrating the concentrated water using a semipermeable membrane module. Each membrane module has a first space 16 and a second space 18 separated by a semipermeable membrane 14. The water treatment device 4 may be equipped with a water tank 10 to be treated that stores concentrated water from the second-stage membrane module 12b, i.e., water to be treated from the third-stage membrane module 12c. The water treatment device 4 is an apparatus that supplies water to be treated to the first space of the first-stage membrane module, and after the concentrated water passes through the first space of the semipermeable membrane module of the final stage, supplies a part of the concentrated water of the final stage to the second space of the semipermeable membrane module of the final stage to perform concentration treatment.

[0052] In the water treatment device 4 of FIG. 4, a pipe 68 is connected to the first space inlet of the first-stage membrane module 12a via a pump 66. A pipe 70 is connected to the first space outlet of the first-stage membrane module 12a and the first space inlet of the second-stage membrane module 12b. A pipe 72 is connected to the first space outlet of the second-stage membrane module 12b and the concentrated water inlet of the water tank 10 to be treated. A pipe 24 is connected to the outlet of the water tank 10 to be treated and the first space inlet of the third-stage membrane module 12c via a pump 20. A pipe 26 is connected to the first space outlet of the third-stage membrane module 12c via a valve 60. A pipe 28 branched from the upstream side of the valve 60 in the pipe 26 is connected to the second space inlet of the third-stage membrane module 12c via a valve 64. A pipe 32 branched from the upstream side of the valve 60 in the pipe 26 and downstream of the branch point of the pipe 28 is connected to the circulating water inlet of the water tank 10 to be treated via a valve 62. The second space outlet of the third-stage membrane module 12c and the second space inlet of the second-stage membrane module 12b are connected by a pipe 74. The second space outlet of the second-stage membrane module 12b and the second space inlet of the first-stage membrane module 12a are connected by a pipe 76. A pipe 78 is connected to the outlet of the first-stage membrane module 12a.

[0053] The water treatment device 4 shown in Fig. 4 is provided with a concentration measuring device 44 as a concentration measuring means for measuring the concentration of dissolved solid components in the water to be treated at the inlet of the first space 16 of the third-stage membrane module 12c, and a water to be treated flow rate measuring device 46 as a first-space water to be treated flow rate measuring means for measuring the flow rate (FI1) of the water to be treated at the inlet of the first space 16 of the third-stage membrane module 12c, on the downstream side of the pump 20 in the piping 24. A circulation flow rate measuring device 56 is provided in the piping 32 as a circulation flow rate measuring means for measuring the flow rate (FI2) of the circulating concentrated water (circulating water). A blow flow rate measuring device 54 is provided downstream of the valve 60 in the piping 26 as a blow flow rate measuring means for measuring the flow rate (FI3) of the concentrated water to be blown at the outlet of the first space 16 of the third-stage membrane module 12c. A branched concentrated water flow rate measuring device 53 is provided downstream of the valve 64 in the piping 28 as a branched concentrated water flow rate measuring means for measuring the flow rate of the branched concentrated water. These configurations may be applied to an apparatus that supplies treated water to both the first space and the second space of a first-stage semipermeable membrane module, or to an apparatus that supplies concentrated water from the previous stage to both the first space and the second space of a final-stage semipermeable membrane module.

[0054] The pump 20 is, for example, a pressure pump that is driven at a rotation speed corresponding to an input drive frequency, sucks in concentrated water from the second-stage membrane module 12b, i.e., the water to be treated in the third-stage membrane module 12c, and discharges it to the third-stage membrane module 12c. The pump 20 is equipped with, for example, an inverter 42 that outputs a drive frequency corresponding to an input command signal to the pump 20. The valve 60 is, for example, a proportional control valve that adjusts the opening based on the measured values ​​of the water to be treated flow rate measuring device 46 and the blow flow rate measuring device 54.

[0055] The water treatment device 4 may include a control device 40 as a control means for controlling the flow rate of the circulating concentrated water so that the amount of permeate falls within a predetermined range when the concentration of the dissolved solid components exceeds a predetermined concentration value, and the control device 40 may be electrically connected to the inverter 42, the concentration measuring device 44, the treated water flow rate measuring device 46, the branched concentrated water flow rate measuring device 53, the blow flow rate measuring device 54, the circulation flow rate measuring device 56, and the valve 62. The control device 40 may be electrically connected to the valve 60. The control device 40 is composed of a microcomputer and an electronic circuit, which are composed of a calculation means such as a CPU that calculates a program, and a storage means such as a ROM and RAM that store the program and the calculation results, and has a function of controlling the flow rate of the pump 20, the opening and closing degree of the valve 62, etc.

[0056] The water treatment device 4 is a device that uses a multistage membrane module having a first space 16 and a second space 18 separated by a semipermeable membrane 14, passes water to be treated in series through the first space 16 of the multistage membrane module, sends concentrated water of the membrane module unit of the final stage to the second space 18 of the membrane module unit of the final stage (in the example of FIG. 4, the third-stage membrane module 12c), passes dilution water of the membrane module of the final stage in series through the second space 18 of the membrane module of the preceding stage, and pressurizes the first space 16 to cause the water contained in the first space 16 to permeate into the second space 18 through the semipermeable membrane 14, thereby concentrating the water. That is, in the water treatment device 4, the water to be treated is concentrated using the semipermeable membrane 14, and the concentrated water is further concentrated using the semipermeable membrane 14 of the next stage. The water to be treated is supplied to the first space 16 of the first-stage membrane module unit (first-stage membrane module 12a in the example of FIG. 4), and concentrated water from the previous stage (second-stage membrane module 12b in the example of FIG. 4) is supplied to the first space 16 of the membrane module of the final stage. Then, the diluted water that has passed through the second space 18 of the membrane module of the final stage is supplied to the second space 18 of the membrane module of each stage, and the first space 16 of the membrane module of each stage is pressurized to allow the water contained in the first space 16 to permeate into the second space 18.

[0057] Specifically, in the water treatment device 4, the water to be treated containing total dissolved solids (TDS) is sent by a pump 66 through a pipe 68 to the first space 16 of the first-stage membrane module 12a. Meanwhile, dilution water sent via the second space 18 of the third-stage membrane module 12c and the second space 18 of the second-stage membrane module 12b, which will be described later, is sent to the second space 18 of the first-stage membrane module 12a through a pipe 76. In the first-stage membrane module 12a, the first space 16 is pressurized, and the water contained in the first space 16 is permeated into the second space 18 (concentration process (first stage)).

[0058] The concentrated water obtained in the first space 16 of the first-stage membrane module 12a is sent to the first space 16 of the second-stage membrane module 12b through the piping 70. Meanwhile, the dilution water sent via the second space 18 of the third-stage membrane module 12c, which will be described later, is sent to the second space 18 of the second-stage membrane module 12b through the piping 74. As in the first stage, in the second-stage membrane module 12b, the first space 16 is pressurized and the water contained in the first space 16 is permeated into the second space 18 (concentration process (second stage)).

[0059] The concentrated water obtained in the first space 16 of the second-stage membrane module 12b is stored in the water tank 10 to be treated as necessary through the pipe 72, and then pumped from the water tank 10 to the first space inlet of the third-stage membrane module 12c through the pipe 24 by the pump 20 and passed through the first space 16. The concentrated water obtained in the first space 16 is discharged from the first space outlet through the pipe 26, and a part of the concentrated water is pumped from the second space inlet of the third-stage membrane module 12c through the pipe 28 branched from the pipe 26 to the second space 18 and passed through. The dilution water obtained in the second space 18 is pumped from the second space outlet through the pipe 74 to the second space 18 of the second-stage membrane module 12b. Here, in the third-stage membrane module 12c, the first space 16 is pressurized, and the water contained in the first space 16 is permeated into the second space 18, and concentrated water is obtained in the first space 16 (concentration step (third stage)), and dilution water is obtained in the second space 18 (dilution step (third stage)). When the valves 60 and 64 are open and the valve 62 is fully closed, a part of the concentrated water obtained in the first space 16 is discharged to the outside of the system through the pipe 26, and a part of the concentrated water is sent and passed through the pipes 26 and 28 to the second space 18 of the third-stage membrane module 12c as described above. When the valves 60 and 64 are open and the valve 62 are open, a part of the concentrated water is returned as circulating water through the pipe 32 to the water-to-be-treated side of the membrane module 12, for example, the water-to-be-treated tank 10, and circulated (circulation step). The circulating water may be returned to the pipe 24.

[0060] Here, the pump 20, pipes 24, 26, 28, etc. function as a supply means for supplying the treated water to the first space 16 of the third-stage membrane module 12c and supplying at least a portion of the concentrated water obtained from the outlet of the first space 16 to the second space 18 of the third-stage membrane module 12c.

[0061] The dilution water obtained in the second space 18 of the third-stage membrane module 12c is sent to the second space 18 of the second-stage membrane module 12b through the pipe 74. As described above, in the second-stage membrane module 12b, the first space 16 is pressurized and the water contained in the first space 16 is permeated into the second space 18 (concentration process (second stage)).

[0062] The dilution water obtained in the second space 18 of the second-stage membrane module 12b is sent to the second space 18 of the first-stage membrane module 12a through the pipe 76. As described above, in the first-stage membrane module 12a, the first space 16 is pressurized and the water contained in the first space 16 is permeated into the second space 18 (concentration process (first stage)).

[0063] The dilution water obtained in the second space 18 of the first-stage membrane module 12a may be discharged outside the system through the pipe 78, or may be sent to a dilution water tank and stored therein as necessary, and then discharged outside the system. At least a portion of the dilution water may be mixed with the water to be treated in the first-stage membrane module 12a. At least a portion of the dilution water may be further sent to a reverse osmosis membrane treatment device, where reverse osmosis membrane treatment may be performed (reverse osmosis membrane treatment step). The RO permeate obtained by the reverse osmosis membrane treatment is discharged outside the system. The RO concentrated water obtained by the reverse osmosis membrane treatment may be mixed with the water to be treated in the first-stage membrane module 12a.

[0064] In this manner, treated water containing dissolved solid components and the like is treated to obtain treated water (final stage concentrated water) in which substances such as dissolved solid components are concentrated, and diluted water (first stage diluted water), thereby reducing the volume of the treated water.

[0065] Here, for example, the concentration measuring device 44 measures the concentration of dissolved solid components in the water to be treated at the inlet of the first space 16 of the third-stage membrane module 12c (concentration measuring process), the water to be treated flow rate measuring device 46 measures the flow rate (FI1) of the water to be treated at the inlet of the first space 16 of the third-stage membrane module 12c (water to be treated flow rate measuring process), the circulation flow rate measuring device 56 measures the flow rate (FI2) of the circulating concentrated water (circulation flow rate measuring process), the blow flow rate measuring device 54 measures the flow rate (FI3) of the blown concentrated water at the outlet of the first space 16 of the third-stage membrane module 12c (blow flow rate measuring process), and the branch concentrated water flow rate measuring device 53 measures the flow rate (FI6) of the branch concentrated water at the inlet of the second space 18 of the third-stage membrane module 12c (branch concentrated water flow rate measuring process). Then, for example, when the concentration of dissolved solid components measured in the concentration measurement process exceeds a predetermined concentration value, the flow rate of the circulating concentrated water is controlled so that the amount of permeated water passing from the first space 16 to the second space 18 (=FI1-(FI2+FI3+FI6)), which is calculated from the respective flow rates (FI1, FI2, FI3, FI6) measured in the treated water flow rate measurement process, the circulation flow rate measurement process, the blow flow rate measurement process, and the branch concentrated water flow rate measurement process, is within a predetermined range (control process).

[0066] For example, when the concentration of dissolved solids measured by concentration measuring device 44 exceeds a predetermined concentration value, control device 40 calculates a drive frequency using an arbitrary formula so that the permeate volume = FI1 - (FI2 + FI3 + FI6) calculated from the flow rates (FI1, FI2, FI3, FI6) measured by treated water flow rate measuring device 46, circulation flow rate measuring device 56, blow flow rate measuring device 54, and branch concentrated water flow rate measuring device 53 falls within a predetermined range, and outputs a command signal corresponding to this calculated value to inverter 42 to control pump 20, and controls the opening and closing degree of valve 62 to control the flow rate of the circulating concentrated water.

[0067] In the water treatment method and water treatment device 4 according to this embodiment, the TDS concentration of the water to be treated at the inlet of the first space 16 of the third-stage membrane module 12c is measured, and when the TDS concentration exceeds a predetermined concentration value, the opening of the valve 62 is adjusted, and at least a part of the concentrated water is returned and circulated to the water to be treated of the third-stage membrane module 12c whose TDS concentration has exceeded the predetermined concentration value, thereby increasing the amount of water supplied to the first space 16 of the third-stage membrane module 12c. As a result, in a water concentration treatment using a multi-stage semipermeable membrane module, the water passing through the first space of the membrane becomes highly concentrated, and even if the concentration of the dissolved solid components of the water to be treated exceeds a predetermined concentration value in the final-stage membrane module where the effect of concentration polarization is likely to be large, the effect of concentration polarization can be reduced.

[0068] When a multi-stage membrane module is used, the number of stages of the membrane module may be determined depending on the concentration of the target treated water, etc. For example, when it is desired to obtain treated water of a higher concentration from water to be treated of a lower concentration, the number of stages of the membrane module unit may be increased. The water treatment method and water treatment device according to the present embodiment can be suitably applied when a multi-stage membrane module is used.

[0069] As the membrane module of each stage, a membrane module unit having a plurality of membrane modules connected in parallel may be used. The number of membrane modules in each membrane module unit may be determined depending on the flow rate of the water to be treated, etc.

[0070] A pipe for transferring the concentrated water from the first space 16 to the second space 18 may be provided to each stage of the membrane module.

[0071] A treated water tank and a dilution water tank may be provided in each stage of the membrane module.

[0072] Examples of the semipermeable membrane 14 included in the membrane module include a reverse osmosis membrane (RO membrane), a forward osmosis membrane (FO membrane), a nanofiltration membrane (NF membrane), and the like. 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 water to be treated in the first space 16 is preferably 0.5 to 10.0 MPa.

[0073] The material constituting the semipermeable membrane 14 is not particularly limited, but examples thereof include cellulose-based resins such as cellulose acetate-based resins, polysulfone-based resins such as polyethersulfone-based resins, polyamide-based resins, etc. The material constituting the semipermeable membrane 14 is preferably a cellulose acetate-based resin.

[0074] The shape of the semipermeable membrane 14 may be a flat membrane, a hollow fiber membrane, a spiral membrane, or the like.

[0075] As the concentration measuring means, for example, a conductivity meter, a density meter, an ion concentration meter, etc. can be used.

[0076] The water to be treated is not particularly limited as long as it contains substances such as total dissolved solids (TDS), but examples include industrial wastewater, salt water, seawater, chemical wastewater, and concentrated wastewater after reverse osmosis membrane treatment.

[0077] TDS (dissolved solids) includes, for example, chlorides such as sodium chloride, carbonates such as calcium carbonate and magnesium carbonate, and sulfates such as calcium sulfate and magnesium sulfate. EXAMPLES

[0078] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0079] <Example 1> Treatment was carried out using the water treatment device 3 shown in FIG. 3. A single 5-inch membrane (HP5255SI) manufactured by Toyobo Co., Ltd. was used as the membrane module. Sodium chloride (NaCl) was used as the TDS component. Sodium chloride was added to pure water to prepare test water with a TDS concentration of 6% by mass. The pumps 20 and 52 were started, and operation was started so that the flow rate (FI1) at the first space inlet of the membrane module 12 was 5 L / min and the flow rate (FI4) at the second space inlet was 1 L / min. The inverter 42 value of the pump 20 and the opening of the valve 62 were adjusted so that the measured values ​​of the pressure (PI1) at the first space inlet and the pressure (PI2) at the first space outlet were as constant as possible (increasing the inverter 42 value increases the pressure, so the opening of the valve 62 was increased to reduce the pressure), and the concentrated water was circulated until the flow rate (FI1) at the first space inlet became 10 L / min. The concentration ratio (FI1 / FI3) and the amount of permeated water (FI1-(FI2+FI3)) were calculated from the flow rate at the first space inlet (FI1), the flow rate of the circulating water (FI2), and the flow rate of the concentrated water to be blown (FI3). The results are shown in Table 1.

[0080] <Comparative Example 1> Treatment was carried out using the water treatment device 5 shown in FIG. 5. The water treatment device 5 differs from the water treatment device 3 in that it does not have the piping 32, the circulation flow rate measuring device 56, and the valve 62, which are circulation means. Sodium chloride (NaCl) was used as the TDS component. Sodium chloride was added to pure water to prepare test water with a TDS concentration of 6 mass%. The pumps 20 and 52 were started and operated so that the flow rate (FI1) at the inlet of the first space of the membrane module 12 was 10 L / min and the flow rate (FI4) at the inlet of the second space was 1 L / min. The concentration ratio (FI1 / FI3) and the permeate amount (FI1-FI3) were calculated from the values ​​of the flow rate (FI1) at the inlet of the first space and the flow rate (FI3) of the concentrated water to be blown. The results are shown in Table 1.

[0081] [Table 1]

[0082] In this way, by circulating the concentrated water and increasing the flow rate on the first space side as in Example 1, the effects of concentration polarization could be reduced compared to when the concentrated water was not circulated as in Comparative Example 1, and operation could be performed while maintaining a high concentration ratio.

[0083] <Example 2> Treatment was carried out using the water treatment device 3 shown in FIG. 3. Sodium chloride (NaCl) was used as a TDS component. Pure water and sodium chloride were added to the water tank 10 to be treated, and the conductivity was measured with a conductivity meter. Test water was successively prepared so that the converted NaCl concentration was 6% by mass. The pumps 20 and 52 were started, and operation was started so that the flow rate (FI1) at the first space inlet of the membrane module 12 was 5 L / min and the flow rate (FI4) at the second space inlet was 1 L / min. The inverter 42 value of the pump 20 and the opening degree of the valve 62 were adjusted so that the measured values ​​of the pressure (PI1) at the first space inlet and the pressure (PI2) at the first space outlet were as constant as possible, and the concentrated water was circulated until the flow rate (FI1) at the first space inlet became 10 L / min. The permeate amount (FI1-(FI2+FI3)) was calculated from the values ​​of the flow rate (FI1) at the first space inlet, the flow rate (FI2) of the circulating water, and the flow rate (FI3) of the concentrated water to be blown at this time. The same operation was repeated until the flow rate (FI1) at the inlet of the first space reached 20 L / min, and the amount of permeated water was calculated from the flow rate (FI1) at the inlet of the first space, the flow rate (FI2) of the circulating water, and the flow rate (FI3) of the concentrated water to be blown. The results are shown in Figure 6.

[0084] <Example 3> Except for the NaCl concentration being 3 mass %, the operation was carried out in the same manner as in Example 2. The results are shown in FIG.

[0085] <Example 4> Except for the NaCl concentration being 10 mass %, the operation was carried out in the same manner as in Example 2. The results are shown in FIG.

[0086] <Example 5> Except for the NaCl concentration being 15% by mass, the operation was carried out in the same manner as in Example 2. The results are shown in FIG.

[0087] Figure 6 shows the increase in the permeate volume relative to the permeate volume (100%) when the flow rate (FI1) at the first space inlet was 5 L / min. In particular, when the TDS concentration of the water to be treated was 6 mass% or more, circulating concentrated water reduced the effect of concentration polarization and allowed a larger permeate volume to be obtained. When the NaCl concentration was 3 mass%, circulating concentrated water reduced the effect of concentration polarization, but only slightly.

[0088] In this way, the water treatment apparatus and water treatment method of the examples were able to reduce the effects of concentration polarization in the water concentration treatment using the semipermeable membrane module. [Explanation of symbols]

[0089] 1,2,3,4,5 water treatment device, 10 treated water tank, 12 membrane module, 12a first stage membrane module, 12b second stage membrane module, 12c third stage membrane module, 14 semipermeable membrane, 16 first space, 18 second space, 20,52,66 pump, 22,24,26,28,30,32,34,36,68,70,72,74,76,78 piping, 40 control device, 42 inverter, 44 concentration measuring device, 46,50 treated water flow rate measuring device, 48 inlet pressure measuring device, 51 permeate flow rate measuring device, 53 branched concentrated water flow rate measuring device, 54 blow flow rate measuring device, 56 circulation flow rate measuring device, 58 outlet pressure measuring device, 60,62,64 valve.

Claims

1. a semipermeable membrane treatment step in which a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane is used, and a water to be treated containing dissolved solid components is passed through the first space, and the first space is pressurized to cause the water contained in the water to permeate through the semipermeable membrane to obtain concentrated water, and a part of the concentrated water is passed through the second space to obtain dilution water; A circulation step of returning and circulating a further portion of the concentrated water to a pipe that sends the water to be treated to the first space of the semipermeable membrane module; Including, Measure a flow rate (FI1) of the water to be treated supplied to the first space in the pipe; A water treatment method characterized by controlling the flow rate of the circulating concentrated water so that the flow rate of the circulating concentrated water is 200% or more of the flow rate of the water to be treated (FI1) when the concentration of dissolved solid components in the water to be treated exceeds a predetermined concentration value.

2. a semipermeable membrane treatment step in which a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane is used to pass water to be treated that contains dissolved solid components through the first space, and the first space is pressurized to cause the water contained in the water to permeate through the semipermeable membrane to obtain concentrated water, and a part of the water to be treated is passed through the second space to obtain dilution water; A circulation step of returning and circulating at least a portion of the concentrated water to a pipe that sends the water to be treated to the first space of the semipermeable membrane module; Including, Measure a flow rate (FI1) of the water to be treated supplied to the first space in the pipe; A water treatment method characterized by controlling the flow rate of the circulating concentrated water so that the flow rate of the circulating concentrated water is 200% or more of the flow rate of the water to be treated (FI1) when the concentration of dissolved solid components in the water to be treated exceeds a predetermined concentration value.

3. The water treatment method according to claim 1 or 2, A water treatment method, characterized in that the predetermined concentration value is a concentration value at which the osmotic pressure of the water to be treated is 5 MPa or more.

4. a semipermeable membrane treatment means for passing water to be treated, which contains dissolved solid components, through the first space using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, pressurizing the first space to cause the water contained in the water to permeate through the semipermeable membrane to obtain concentrated water, and passing a portion of the concentrated water through the second space to obtain dilution water; A circulation means for returning and circulating a further portion of the concentrated water to a pipe that sends the water to be treated to the first space of the semipermeable membrane module; a water-to-be-treated flow rate measuring means for measuring a flow rate (FI1) of the water to be treated supplied to the first space in the piping; A control means for controlling the flow rate of the circulating concentrated water so that the flow rate of the circulating concentrated water is 200% or more of the flow rate (FI1) of the water to be treated when the concentration of the dissolved solid components in the water to be treated exceeds a predetermined concentration value; A water treatment device comprising:

5. a semipermeable membrane treatment means for passing water to be treated that contains dissolved solid components through the first space using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, pressurizing the first space to cause the water contained in the water to permeate through the semipermeable membrane to obtain concentrated water, and passing a portion of the water to be treated through the second space to obtain dilution water; A circulation means for returning and circulating at least a portion of the concentrated water to a pipe that sends the water to be treated to the first space of the semipermeable membrane module; a water-to-be-treated flow rate measuring means for measuring a flow rate (FI1) of the water to be treated supplied to the first space in the piping; A control means for controlling the flow rate of the circulating concentrated water so that the flow rate of the circulating concentrated water is 200% or more of the flow rate (FI1) of the water to be treated when the concentration of the dissolved solid components in the water to be treated exceeds a predetermined concentration value; A water treatment device comprising:

6. The water treatment device according to claim 4 or 5, The water treatment device according to claim 1, wherein the predetermined concentration value is a concentration value at which the osmotic pressure of the water to be treated is 5 MPa or more.

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