JP7621835B2 - Water treatment method and water treatment device - Google Patents

Description

The present invention relates to a water treatment method and a water treatment device for concentrating water containing total dissolved solids (TDS) and the like.

In recent years, efforts have been made to reduce the amount of wastewater discharged from factories as much as possible, and methods have been adopted in which the wastewater is concentrated using reverse osmosis membranes and the permeate is recovered to reduce the volume of the wastewater. There is a tendency to increase the water recovery rate as much as possible, and an increasing number of factories are even using methods such as evaporation concentration to recover almost the entire amount of water and solidify all dissolved solids before discharging it (Zero Liquid Discharge).

Methods such as evaporation and concentration that heat water require a large amount of energy and increase costs, so there is a demand for a method to highly concentrate wastewater with minimal heating. The reverse osmosis membrane method consumes less energy than the evaporation and concentration method, but the effect of osmotic pressure can result in insufficient concentration, and the volume of water may not be reduced to the desired amount.

Patent Document 1 describes a method for concentrating water by passing raw water or concentrated water through a first space and a second space separated by a semipermeable membrane of a multi-stage semipermeable membrane module and pressurizing the first space. The method of Patent Document 1 is a method for concentrating water to a high concentration with less pressurizing power, i.e., less energy, by reducing the concentration difference (osmotic pressure difference) between the first and second spaces of the semipermeable membrane module.

The concentration method described in Patent Document 1 requires control of the flow rate and concentration not only in the first space of the semipermeable membrane module but also in the second space, so compared to the reverse osmosis membrane method, the water balance is more likely to be disrupted by fluctuations in the quality of the raw water (water to be treated), making it difficult to stably reduce the volume of wastewater. In addition, when using a method of concentrating to such a high concentration, the quality of the recovered water may deteriorate, making it unsuitable for recovery.

JP 2018-069198 A

The object of the present invention is to provide a water treatment method and water treatment device that enables stable treatment in a water concentration treatment using a semipermeable membrane module, even when the water quality of the water to be treated (raw water) fluctuates.

The present invention is a water treatment method including a pressurizing step of pressurizing water to be treated containing total dissolved solid components to 0.1 MPa or more, a first reverse osmosis membrane treatment step of passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate, a semipermeable membrane treatment step of passing the first RO concentrate through the first space using a semipermeable membrane module having a first space and a second space partitioned by a semipermeable membrane, pressurizing the first space by pressurizing in the pressurizing step to cause the water contained in the first RO concentrate to permeate through the semipermeable membrane to obtain a concentrate, and passing a part of the first RO concentrate or at least a part of the concentrate through the second space to obtain dilution water, and a flow rate adjustment step of measuring the flow rate of the concentrate and the flow rate of the dilution water, and automatically adjusting the flow rate of the first RO concentrate so that the recovery rate of the water to be treated based on the measured values of the flow rate of the concentrate and the measured values of the flow rate of the dilution water (recovery rate = measured value of the flow rate of the dilution water / (measured value of the flow rate of the concentrate + measured value of the flow rate of the dilution water) × 100) is constant .

The present invention includes a pressurizing step of pressurizing water to be treated, which contains total dissolved solids, to 0.1 MPa or more; a first reverse osmosis membrane treatment step of passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate; and a method of treating a first RO concentrate by passing the first RO concentrate through a first space of a semipermeable membrane module of a first stage using a semipermeable membrane module having a first space and a second space partitioned by a semipermeable membrane, and pressurizing the first space by pressurizing in the pressurizing step to cause water contained in the first RO concentrate to permeate through the semipermeable membrane to obtain concentrate, and further treating the concentrate by using a semipermeable membrane module of a subsequent stage or later to obtain concentrate. and a flow rate adjusting step of measuring the flow rate of the concentrated water and the flow rate of the dilution water and automatically adjusting the flow rate of the first RO concentrated water so that a recovery rate of the water to be treated (recovery rate = measured value of the flow rate of the dilution water / (measured value of the flow rate of the concentrated water + measured value of the flow rate of the dilution water) × 100) based on the measured value of the flow rate of the concentrated water and the measured value of the flow rate of the dilution water is constant .

In the water treatment method, it is preferable that the first reverse osmosis membrane has a pure water permeation flux in the range of 0.2 to 0.7 ^m3 / ^m2 /day under conditions of a membrane surface effective pressure of 1 MPa and 25°C, and has a NaCl removal rate of 99.5% or more (under conditions of NaCl 32,000 mg/L) at standard operating pressure.

In the water treatment method, it is preferable that the permeation flux of the semipermeable membrane module in the semipermeable membrane treatment step is in the range of 0.005 m/d to 0.05 m/d under conditions of an effective membrane surface pressure of 1 MPa and 25°C.

In the water treatment method, it is preferable that the pressure of the first RO concentrated water immediately after the first reverse osmosis membrane process is 7 MPa or more, and the method further includes a depressurization process in which the pressure of the first RO concentrated water is reduced to less than 7 MPa prior to the semipermeable membrane treatment process.

The water treatment method preferably further includes a second reverse osmosis membrane treatment step in which the diluted water is passed through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate.

It is preferable that the water treatment method further includes a third reverse osmosis membrane treatment step in which at least one of the first RO permeate and the second RO permeate is passed through a third reverse osmosis membrane to obtain a third RO permeate and a third RO concentrated water.

In the water treatment method, it is preferable that the first RO concentrated water has a sulfate ion concentration of 20,000 mg/L or more and a concentration of at least one of sodium ions and ammonium ions of 10,000 mg/L or more.

The present invention is a water treatment device comprising: a pressurizing means for pressurizing water to be treated, including total dissolved solid components, to 0.1 MPa or more; a first reverse osmosis membrane treatment means for passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate; a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the first RO concentrate through the first space by pressurizing the first space by the pressurizing means to cause the water contained in the first RO concentrate to permeate through the semipermeable membrane to obtain concentrate, and passing a part of the first RO concentrate or at least a part of the concentrate through the second space to obtain dilution water; and a flow rate adjustment means for measuring the flow rate of the concentrate and the flow rate of the dilution water, and automatically adjusting the flow rate of the first RO concentrate so that the recovery rate of the water to be treated (recovery rate = measured value of the dilution water / (measured value of the concentrate flow rate + measured value of the dilution water flow rate) × 100) based on the measured value of the flow rate of the concentrate and the measured value of the flow rate of the dilution water is constant.

The present invention relates to a method for treating water containing total dissolved solid components, comprising: a pressurizing means for pressurizing water to be treated containing 0.1 MPa or more; a first reverse osmosis membrane treatment means for passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate; and a semipermeable membrane module having a first space and a second space partitioned by a semipermeable membrane, connected in a plurality of stages, in which the first RO concentrate is passed through the first space of the semipermeable membrane module of the first stage, the first space is pressurized by the pressurizing means to cause the water contained in the first RO concentrate to permeate through the semipermeable membrane to obtain concentrate, and the concentrate is further treated using a semipermeable membrane module of a subsequent stage or later to obtain concentrate. and a semipermeable membrane treatment means for passing a portion of the first RO permeate water, at least a portion of the concentrated water, or at least a portion of the dilution water obtained from another semipermeable membrane module through a second space of the semipermeable membrane module of each stage to obtain dilution water; and a flow rate adjustment means for measuring the flow rate of the concentrated water and the flow rate of the dilution water, and automatically adjusting the flow rate of the first RO concentrated water so that a recovery rate of the treated water (recovery rate = measured value of the flow rate of the dilution water / (measured value of the flow rate of the concentrated water + measured value of the flow rate of the dilution water) × 100) based on the measured value of the flow rate of the concentrated water and the measured value of the flow rate of the dilution water is constant .

In the water treatment device, the first reverse osmosis membrane preferably has a pure water permeation flux in the range of 0.2 to 0.7 ^m3 / ^m2 /day under conditions of a membrane surface effective pressure of 1 MPa and 25°C, and has a NaCl removal rate of 99.5% or more (under conditions of NaCl 32,000 mg/L) at standard operating pressure.

It is preferable that the water treatment device further includes a permeation flux adjustment means for adjusting the permeation flux of the semipermeable membrane module in the semipermeable membrane treatment means to be in the range of 0.005 m/d to 0.05 m/d under conditions of an effective membrane surface pressure of 1 MPa and 25°C.

In the water treatment device, it is preferable that the pressure of the first RO concentrated water immediately after the first reverse osmosis membrane means is 7 MPa or more, and that the water treatment device further includes a pressure reducing means for reducing the pressure of the first RO concentrated water to less than 7 MPa upstream of the semipermeable membrane treatment means.

It is preferable that the water treatment device further includes a second reverse osmosis membrane treatment means for passing the diluted water through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrated water.

It is preferable that the water treatment device further includes a third reverse osmosis membrane treatment means for passing at least one of the first RO permeate and the second RO permeate through a third reverse osmosis membrane to obtain a third RO permeate and a third RO concentrated water.

In the water treatment device, it is preferable that the first RO concentrated water has a sulfate ion concentration of 20,000 mg/L or more and a concentration of at least one of sodium ions and ammonium ions of 10,000 mg/L or more.

The present invention provides a water treatment method and water treatment device that enables stable treatment in the water concentration treatment using a semipermeable membrane module, even when there is a change in the water quality of the water to be treated (raw water).

1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

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

The water treatment device 1 shown in FIG. 1 includes a pressure pump 26 as a pressurizing means for pressurizing the water to be treated, including all dissolved solid components, to 0.1 MPa or more; a first reverse osmosis membrane treatment device 100 as a first reverse osmosis membrane treatment means for passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrated water; and a single-stage or multi-stage semipermeable membrane module having a first space (concentrated side) and a second space (permeation side) separated by a semipermeable membrane, for passing the first RO concentrated water through the first space, pressurizing the first space by pressurizing the pressure pump 26 to cause the water contained in the first RO concentrated water to permeate through the semipermeable membrane to obtain concentrated water, and passing a portion of the first RO concentrated water or at least a portion of the concentrated water through the second space to obtain dilution water. The semipermeable membrane treatment means includes, for example, a first-stage membrane module unit 12, a second-stage membrane module unit 14, a third-stage membrane module unit 16, a fourth-stage membrane module unit 18, and a fifth-stage membrane module unit 20. The water treatment device 1 is equipped only with a pressure pump upstream of the first reverse osmosis membrane treatment device 100 as a pressurizing means for pressurizing the water to be treated, including all dissolved solid components, to 0.1 MPa or more.

The first-stage membrane module unit 12 includes, for example, six membrane modules connected in parallel, the second-stage membrane module unit 14 includes, for example, five membrane modules connected in parallel, the third-stage membrane module unit 16 includes, for example, four membrane modules connected in parallel, the fourth-stage membrane module unit 18 includes, for example, three membrane modules connected in parallel, and the fifth-stage membrane module unit 20 includes, for example, three membrane modules connected in parallel. Each membrane module has a first space 11 and a second space 13 separated by a semipermeable membrane 15. The water treatment device 1 may include a treated water tank 10 for storing treated water, a concentrated water tank 22 for storing concentrated water from the final-stage membrane module unit (in the example of FIG. 1, concentrated water from the fifth-stage membrane module unit 20), and a first dilution water tank 24 for storing dilution water from the first-stage membrane module unit (in the example of FIG. 1, dilution water from the first-stage membrane module unit 12).

In the water treatment device 1 of FIG. 1, a pipe 38 is connected to the treated water inlet of the treated water tank 10. The outlet of the treated water tank 10 and the inlet of the first reverse osmosis membrane treatment device 100 are connected by a pipe 40 via a pressure pump 26. The concentrated water outlet of the first reverse osmosis membrane treatment device 100 and the first space inlet of each membrane module of the first stage membrane module unit 12 are connected in parallel by a first RO concentrated water pipe 106. The permeated water outlet of the first reverse osmosis membrane treatment device 100 is connected to a first RO permeated water pipe 108. The first space outlet of each membrane module of the first stage membrane module unit 12 and the first space inlet of each membrane module of the second stage membrane module unit 14 are connected in parallel by a pipe 42. The first space outlet of each membrane module of the second stage membrane module unit 14 and the first space inlet of each membrane module of the third stage membrane module unit 16 are connected in parallel by a pipe 44. The first space outlet of each membrane module of the third membrane module unit 16 and the first space inlet of each membrane module of the fourth membrane module unit 18 are connected in parallel by a pipe 46. The first space outlet of each membrane module of the fourth membrane module unit 18 and the first space inlet and the second space inlet of each membrane module of the fifth membrane module unit 20 are connected in parallel by a pipe 48. The first space outlet of each membrane module of the fifth membrane module unit 20 and the inlet of the concentrated water tank 22 are connected by a pipe 50 via a valve 32. A pipe 52 is connected to the outlet of the concentrated water tank 22 via a pump 28. The second space outlet of each membrane module of the fifth membrane module unit 20 and the second space inlet of each membrane module of the fourth membrane module unit 18 are connected in parallel by a pipe 54. The second space outlet of each membrane module of the fourth membrane module unit 18 and the second space inlet of each membrane module of the third membrane module unit 16 are connected in parallel by a pipe 56. The second space outlets of each membrane module of the third-stage membrane module unit 16 and the second space inlets of each membrane module of the second-stage membrane module unit 14 are connected in parallel by a pipe 58. The second space outlets of each membrane module of the second-stage membrane module unit 14 and the second space inlets of each membrane module of the first-stage membrane module unit 12 are connected in parallel by a pipe 60. The second space outlets of each membrane module of the first-stage membrane module unit 12 and the inlet of the first dilution water tank 24 are connected by a pipe 62. A pipe 64 is connected to the outlet of the first dilution water tank 24. The water treatment device 1 may or may not include a concentrated water tank 22, a pump 28, and a pipe 52. The water treatment device 1 may or may not include a first dilution water tank 24 and a pipe 64.

The booster pump 26 is provided in front of the first reverse osmosis membrane treatment device 100, and is driven, for example, at a rotational speed corresponding to an input drive frequency, and is a booster pump that draws in the water to be treated and discharges it to the first reverse osmosis membrane treatment device 100. The booster pump 26 is provided with a first inverter 30 that outputs a drive frequency corresponding to an input command signal to the booster pump 26. A first flow rate measuring device 34 is provided between the valve 32 in the piping 50 and the inlet of the concentrated water tank 22 as a first flow rate measuring means for measuring the flow rate of the concentrated water that has passed through the first space of the final membrane module unit (in the example of FIG. 1, the fifth membrane module unit 20). A second flow rate measuring device 36 is provided in the piping 62 as a second flow rate measuring means for measuring the flow rate of the diluted water that has passed through the second space of the first membrane module unit (in the example of FIG. 1, the first membrane module unit 12). The valve 32 is provided after the final membrane module unit (in the example of FIG. 1, the fifth membrane module unit 20) and is, for example, a proportional control valve that adjusts the opening based on the measured values of the first flow measuring device 34 and the second flow measuring device 36. The water treatment device 1 includes a control device 66, which is connected to the first inverter 30, the first flow measuring device 34, and the second flow measuring device 36 by wired or wireless electrical connections, etc. The control device 66 may also be connected to the valve 32 by wired or wireless electrical connections, etc.

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

The water treatment device 1 uses, for example, a multi-stage membrane module having a first space 11 and a second space 13 separated by a semipermeable membrane 15, and the first RO concentrated water obtained in the first reverse osmosis membrane treatment device 100 that performs reverse osmosis membrane treatment of water to be treated containing all dissolved solid components is passed in series through the first space 11 of the multi-stage membrane module, and the concentrated water of the previous membrane module unit (in the example of FIG. 1, the fourth membrane module unit 18) is distributed to the first space 11 and second space 13 of the final membrane module unit (in the example of FIG. 1, the fifth membrane module unit 20), and the dilution water of the final membrane module is returned and passed in series to the second space 13 of the previous membrane module, and the first space 11 is pressurized to permeate the water contained in the first space 11 into the second space 13, concentrating the water. That is, in the water treatment device 1, the first RO concentrated water is concentrated using the semipermeable membrane 15, and the concentrated water is further concentrated using the semipermeable membrane 15 of the next stage. The first RO concentrated water is supplied to the first space 11 of the first-stage membrane module unit (in the example of FIG. 1, the first-stage membrane module unit 12), and the concentrated water of the previous stage (in the example of FIG. 1, the fourth-stage membrane module unit 18) is supplied to both the first space 11 and the second space 13 of the final-stage membrane module. The dilution water that has passed through the second space 13 of the final-stage membrane module is then supplied to the second space 13 of the upstream membrane module, and the first space 11 of each stage membrane module is pressurized to allow the water contained in the first space 11 to permeate into the second space 13.

Specifically, in the water treatment device 1, the water to be treated, which contains all dissolved solid components, is stored in the water tank 10 as necessary through the pipe 38, and is pressurized from the water tank 10 to 0.1 MPa or more by the pressure pump 26 (pressurization process), and is sent through the pipe 40 to the first reverse osmosis membrane treatment device 100. In the first reverse osmosis membrane treatment device 100, the pressurized water to be treated is passed through the first reverse osmosis membrane to obtain the first RO permeate and the first RO concentrated water (first reverse osmosis membrane treatment process). The first RO permeate is discharged through the first RO permeate pipe 108. At least a portion of the first RO permeate may be further sent to the third reverse osmosis membrane treatment device 104, as described below, and reverse osmosis membrane treatment may be performed in the third reverse osmosis membrane treatment device 104 (third reverse osmosis membrane treatment process).

The first RO concentrated water is sent through the first RO concentrated water pipe 106 to the first space 11 of each membrane module of the first-stage membrane module unit 12. Meanwhile, dilution water returned from the fifth-stage membrane module unit 20 (the final stage described later) via the second space 13 of the fourth-stage membrane module unit 18, the second space 13 of the third-stage membrane module unit 16, and the second space 13 of the second-stage membrane module unit 14 is sent through the pipe 60 to the second space 13 of each membrane module of the first-stage membrane module unit 12. In each membrane module of the first-stage membrane module unit 12, the first space 11 is pressurized by the pressure pump 26, and the water contained in the first space 11 is permeated into the second space 13 (concentration process (first stage)).

The concentrated water from the first-stage membrane module unit 12 is sent through the pipe 42 to the first space 11 of each membrane module of the second-stage membrane module unit 14. Meanwhile, the dilution water returned from the fifth-stage membrane module unit 20 (the final stage described later) via the second space 13 of the fourth-stage membrane module unit 18 and the second space 13 of the third-stage membrane module unit 16 is sent through the pipe 58 to the second space 13 of each membrane module of the second-stage membrane module unit 14. As in the first stage, the first space 11 is pressurized in each membrane module of the second-stage membrane module unit 14, and the water contained in the first space 11 is permeated into the second space 13 (concentration process (second stage)).

The concentrated water from the second-stage membrane module unit 14 is sent through the pipe 44 to the first space 11 of each membrane module of the third-stage membrane module unit 16. Meanwhile, the dilution water returned from the fifth-stage membrane module unit 20 (the final stage, described later) via the second space 13 of the fourth-stage membrane module unit 18 is sent through the pipe 56 to the second space 13 of each membrane module of the third-stage membrane module unit 16. As in the first and second stages, the first space 11 is pressurized in each membrane module of the third-stage membrane module unit 16, and the water contained in the first space 11 is permeated into the second space 13 (concentration process (third stage)).

The concentrated water from the third-stage membrane module unit 16 is sent through piping 46 to the first space 11 of each membrane module of the fourth-stage membrane module unit 18. Meanwhile, the dilution water returned from the fifth-stage membrane module unit 20 (the final stage, described later) is sent through piping 54 to the second space 13 of each membrane module of the fourth-stage membrane module unit 18. As in the first, second, and third stages, in each membrane module of the fourth-stage membrane module unit 18, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fourth stage)).

The concentrated water from the fourth-stage membrane module unit 18 is distributed and sent through the pipe 48 to the first space 11 and the second space 13 of each membrane module in the fifth-stage membrane module unit 20, which is the final stage. As in the first to fourth stages, in the fifth-stage membrane module unit 20, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fifth stage)). Here, the pressure pump 26, the pipe 48, etc. function as a supply means for supplying the concentrated water from the previous stage to both the first space and the second space of the final-stage semipermeable membrane module.

With valve 32 open, the concentrated water from the fifth membrane module unit 20 is sent through piping 50 to the concentrated water tank 22 as necessary and stored there. At least a portion of the concentrated water is discharged from the concentrated water tank 22 to the outside of the system through piping 52 by pump 28 as treated water. At least a portion of the concentrated water is sent to the treated water tank 10 and may be mixed with the treated water in the treated water tank 10.

The dilution water from the fifth-stage membrane module unit 20 is sent to the second space 13 of each membrane module of the fourth-stage membrane module unit 18 through the pipe 54. As described above, in each membrane module of the fourth-stage membrane module unit 18, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fourth stage)).

The dilution water from the fourth-stage membrane module unit 18 is sent through the pipe 56 to the second space 13 of each membrane module of the third-stage membrane module unit 16. As described above, in each membrane module of the third-stage membrane module unit 16, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (third stage)).

The dilution water from the third-stage membrane module unit 16 is sent through the pipe 58 to the second space 13 of each membrane module of the second-stage membrane module unit 14. As described above, in each membrane module of the second-stage membrane module unit 14, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (second stage)).

The dilution water from the second-stage membrane module unit 14 is sent through the pipe 60 to the second space 13 of each membrane module of the first-stage membrane module unit 12. As described above, in each membrane module of the first-stage membrane module unit 12, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (first stage)).

The dilution water from the first-stage membrane module unit 12 is sent to the first dilution water tank 24 through the piping 62 as necessary, and after being stored there, is discharged outside the system through the piping 64. At least a portion of the dilution water may be sent to the water tank 10 to be treated and mixed with the water to be treated there. At least a portion of the dilution water may be further sent to the second reverse osmosis membrane treatment device 102 as described below, and may be subjected to reverse osmosis membrane treatment in the second reverse osmosis membrane treatment device 102 (second reverse osmosis membrane treatment process).

In this way, treated water containing total dissolved solids and other substances (final stage concentrated water) is obtained, and dilution water is obtained from the treated water, which is the target of treatment, and the volume of the treated water is reduced.

In the water treatment method and water treatment device 1 according to this embodiment, the flow rate of the concentrated water that has passed through the first space of the semipermeable membrane module of the final stage is measured (first flow rate measurement process), and the flow rate of the dilution water that has passed through the second space of the semipermeable membrane module of the first stage is measured (second flow rate measurement process), and the flow rate of the first RO concentrated water supplied to the first space of the semipermeable membrane module of the first stage is adjusted (flow rate adjustment process) so that the measured flow rate of the concentrated water of the final stage and the measured flow rate of the dilution water of the first stage are the preset target flow rate values.

For example, the control device 66 functions as a flow rate adjusting means for adjusting the flow rate of the first RO concentrated water supplied to the first space of the first-stage semipermeable membrane module so that the measured value of the flow rate of the concentrated water of the final-stage membrane module unit (in the example of FIG. 1, the fifth-stage membrane module unit 20) measured by the first flow rate measuring device 34 and the measured value of the flow rate of the dilution water of the first-stage membrane module unit (in the example of FIG. 1, the first-stage membrane module unit 12) measured by the second flow rate measuring device 36 become the preset target flow rate value. The control device 66 calculates the drive frequency using an arbitrary arithmetic expression, for example, so that the measured values of the first flow rate measuring device 34 and the second flow rate measuring device 36 become the preset target flow rate value, and outputs a command signal corresponding to this calculated value to the first inverter 30 to control the pressure pump 26, thereby adjusting the flow rate of the first RO concentrated water supplied to the first space 11 of the first-stage membrane module unit (in the example of FIG. 1, the first-stage membrane module unit 12).

As a result, in the water concentration process using a semipermeable membrane module, the volume of wastewater is reduced compared to the reverse osmosis membrane method, and stable treatment is possible even when the water quality of the treated water (raw water) fluctuates.

Specifically, for example, the booster pump 26 is started, the valve 32 is fully opened (100% open), and the output value of the first inverter 30 associated with the booster pump 26 is gradually increased. When the measurement value of the first flow measuring device 34 reaches the target flow rate, the valve 32 is closed, for example, at a predetermined arbitrary rate (for example, 10% of the fully open opening). Since the measurement value of the first flow measuring device 34 decreases, the output of the first inverter 30 of the booster pump 26 is increased until the measurement value of the first flow measuring device 34 reaches the target flow rate. When the valve 32 is closed, the measurement value of the second flow measuring device 36 increases. After that, the following operation is repeated: increase the output of the first inverter 30 → increase the measurement value of the first flow measuring device 34 → close the valve 32 → decrease the measurement value of the first flow measuring device 34 and increase the measurement value of the second flow measuring device 36, and the measurements of the first flow measuring device 34 and the second flow measuring device 36 can be adjusted to the target flow rate.

When the recovery rate of the water to be treated changes, the output value of the first inverter 30 and the opening of the valve 32 are automatically controlled, for example, so that the recovery rate of the water to be treated based on the measurement values of the first flow measurement device 34 and the measurement values of the second flow measurement device 36 (recovery rate = second flow measurement value / (first flow measurement value + second flow measurement value) x 100) is as constant as possible, and the flow rate of the first RO concentrated water is changed. When the flow rate of the first space measured by the first flow measurement device 34 becomes less than the set flow rate, the output value of the first inverter 30 can be fixed and the opening of the valve 32 can be increased (i.e., the valve is opened). The opening of the valve 32 can be adjusted, for example, by opening it to a predetermined arbitrary ratio (for example, 10% of the opening rate relative to full opening) and repeating the process of observing the state of the flow rate of the first space measured by the first flow measurement device 34 for a predetermined time (for example, 1 minute). Alternatively, the opening of the valve 32 can be fixed and the output value of the first inverter 30 can be increased to increase the flow rate of the first space.

When the flow rate in the first space measured by the first flow rate measuring device 34 becomes larger than the set flow rate, the opening of the valve 32 is fixed and the output of the first inverter 30 is reduced. However, when the pressure pump 26 reaches the lower output limit value for which operation is guaranteed, the opening of the valve 32 is reduced (the valve is closed). The opening of the valve 32 can be adjusted, for example, by closing it at a predetermined arbitrary rate (for example, 10% of the opening rate compared to full opening) and repeating the process of observing the state of the flow rate in the first space measured by the first flow rate measuring device 34 for a predetermined time (for example, 1 minute). Alternatively, the output value of the first inverter 30 may be fixed and the opening of the valve 32 may be reduced to reduce the flow rate in the first space.

When the flow rate in the second space measured by the second flow measuring device 36 becomes smaller than the set flow rate, the flow rate in the first space increases, so the output value of the first inverter 30 can be fixed and the opening of the valve 32 can be reduced. Alternatively, the opening of the valve 32 can be fixed and the output value of the first inverter 30 can be increased. When the flow rate in the second space measured by the second flow measuring device 36 becomes larger than the set flow rate, the flow rate in the first space decreases, so the output value of the first inverter 30 can be fixed and the opening of the valve 32 can be increased. Alternatively, the opening of the valve 32 can be fixed and the output value of the first inverter 30 can be reduced.

In addition to the valve 32, one or more proportional control valves that adjust the opening based on the measured values of the first flow measuring device 34 and the second flow measuring device 36 may be provided in the piping of the first space 11, for example, in the piping 106, 42, 44, 46, and 48, and the opening of the valve may be adjusted manually or automatically by the control device 66.

In addition to the first flow rate measuring device 34 that measures the flow rate of the concentrated water that has passed through the first space of the final-stage membrane module unit, one or more flow rate measuring devices that measure the flow rate in the first space 11 may be provided in the piping of the first space 11, for example, in the pipings 106, 42, 44, 46, and 48.

In addition to the second flow rate measuring device 36 that measures the flow rate of the dilution water that has passed through the second space of the first-stage membrane module unit, one or more flow rate measuring devices that measure the flow rate in the second space 13 may be provided in the piping of the second space 13, for example, in the piping 54, 56, 58, and 60.

In the water treatment device 1, the flow rate of the dilution water that has passed through the second space of the membrane module unit in the final stage may be further measured, and the flow rate of the first RO concentrated water supplied to the first space of the membrane module unit in the first stage and the flow rate of the dilution water supplied to the second space in the stage preceding the final stage may be adjusted so that the measured flow rate of the concentrated water in the final stage, the measured flow rate of the dilution water in the first stage, and the measured flow rate of the dilution water in the final stage reach preset target flow rate values. A water treatment device with such a configuration is shown in Figure 2.

The water treatment device 2 shown in FIG. 2 further includes a second dilution water tank 68 for storing dilution water from the final stage membrane module unit (in the example of FIG. 2, dilution water from the fifth stage membrane module unit 20). In the water treatment device 2, the second space outlet of each membrane module of the fifth stage membrane module unit 20 and the dilution water inlet of the second dilution water tank 68 are connected by a pipe 76. The outlet of the second dilution water tank 68 and the second space inlet of each membrane module of the fourth stage membrane module unit 18 are connected in parallel by a pipe 78 via a second pressure pump 70. The water treatment device 2 may or may not include a concentrated water tank 22, a pump 28, and a pipe 52. The water treatment device 2 may or may not include a first dilution water tank 24 and a pipe 64.

The dilution water from the fifth-stage membrane module unit 20 is pumped through the pipe 76 to the second dilution water tank 68, where it is stored. The second pressurizing pump 70 then pumps the dilution water from the second dilution water tank 68 through the pipe 78 to the second space 13 of each membrane module of the fourth-stage membrane module unit 18. As described above, in each membrane module of the fourth-stage membrane module unit 18, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fourth stage)).

A third flow rate measuring device 74 is installed in the piping 76 as a third flow rate measuring means for measuring the flow rate of the dilution water passing through the second space of the final membrane module unit (in the example of FIG. 2, the fifth membrane module unit 20). The second pressure pump 70 is provided in the rear of the final membrane module unit (in the example of FIG. 2, the fifth membrane module unit 20), and is driven at a rotation speed corresponding to the input drive frequency, for example, and is a second pressure pump that sucks in the dilution water of the final membrane module unit (in the example of FIG. 2, the fifth membrane module unit 20) and discharges it to the previous membrane module unit (in the example of FIG. 2, the fourth membrane module unit 18). The second pressure pump 70 is installed with a second inverter 72 that outputs a drive frequency corresponding to the input command signal to the second pressure pump 70. The locations of the second dilution water tank 68, the second pressure pump 70, and the flow rate measuring device 74 are not limited to the locations shown in FIG. 2, and may be installed in any of the dilution water piping along the way, for example, in any of the piping 56, 58, and 60. The water treatment device 2 includes a control device 66, which is connected to the first inverter 30, the second inverter 72, the first flow rate measuring device 34, the second flow rate measuring device 36, and the third flow rate measuring device 74 by wired or wireless electrical connections, etc. The control device 66 may also be connected to the valve 32 by wired or wireless electrical connections, etc.

In the water treatment method and water treatment device 2 according to this embodiment, the flow rate of the concentrated water that has passed through the first space of the membrane module unit of the final stage is measured (first flow rate measurement process), the flow rate of the dilution water that has passed through the second space of the membrane module unit of the first stage is measured (second flow rate measurement process), and the flow rate of the dilution water that has passed through the second space of the membrane module unit of the final stage is measured (third flow rate measurement process), and the flow rate of the first RO concentrated water supplied to the first space of the membrane module unit of the first stage and the flow rate of the dilution water supplied to the second space of the membrane module unit before the final stage are adjusted (flow rate adjustment process) so that the measured values of the flow rate of the concentrated water of the final stage, the measured value of the flow rate of the dilution water of the first stage, and the measured value of the flow rate of the dilution water of the final stage are preset target flow rate values.

For example, the control device 66 functions as a flow rate adjusting means for adjusting the flow rate of the first RO concentrated water supplied to the first space of the first stage membrane module unit and the flow rate of the dilution water supplied to the second space of the membrane module unit preceding the final stage so that the measured value of the flow rate of the concentrated water of the final stage membrane module unit (in the example of Figure 2, the fifth stage membrane module unit 20) measured by the first flow rate measuring device 34, the measured value of the flow rate of the dilution water of the first stage membrane module unit (in the example of Figure 2, the first stage membrane module unit 12) measured by the second flow rate measuring device 36, and the measured value of the flow rate of the dilution water of the final stage membrane module unit measured by the third flow rate measuring device 74 become predetermined target flow rate values. The control device 66 calculates the drive frequency using an arbitrary calculation formula so that the measured values of the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 74 become the preset target flow value, outputs a command signal corresponding to this calculated value to the first inverter 30 to control the pressure pump 26, and outputs a command signal to the second inverter 72 to control the second pressure pump 70, and adjusts the flow rate of the first RO concentrated water supplied to the first space 11 of the first stage membrane module unit (in the example of FIG. 2, the first stage membrane module unit 12) and the dilution water supplied to the second space 13 of the membrane module unit before the final stage (in the example of FIG. 2, the fourth stage membrane module unit 18).

As a result, in the water concentration treatment using the semipermeable membrane module, the amount of wastewater is reduced compared to the reverse osmosis membrane method, and more stable treatment is possible even when the water quality of the water to be treated (raw water) fluctuates. By storing the diluted water that has passed through the second space of the final stage in the second dilution water tank 68, it becomes easier to adjust the flow rate even if the water balance between the first space and the second space is disrupted due to fluctuations in the water quality of the water to be treated. In addition, by using the second pressure pump 70 as the second pressure pump that sucks in the diluted water from the membrane module unit of the final stage and discharges it to the membrane module unit of the previous stage, the load on the pressure pump 26 can be reduced and the pressure shortage required for water flow can be suppressed even if the number of stages of the membrane module units increases and the pressure required for water flow is insufficient with the pressure pump 26 alone.

Specifically, for example, the pressure pump 26 is started, the valve 32 is fully opened (100% open), and the output value of the first inverter 30 associated with the pressure pump 26 is gradually increased. When the measurement value of the first flow measurement device 34 reaches the target flow rate, the valve 32 is closed, for example, at a predetermined arbitrary rate (for example, 10% of the fully open opening). Since the measurement value of the first flow measurement device 34 decreases, the output of the first inverter 30 of the pressure pump 26 is increased until the measurement value of the first flow measurement device 34 reaches the target flow rate. When the valve 32 is closed, the measurement value of the third flow measurement device 74 increases. After that, the following operation is repeated: increase the output of the first inverter 30 → increase the measurement value of the first flow measurement device 34 → close the valve 32 → decrease the measurement value of the first flow measurement device 34 and increase the measurement value of the third flow measurement device 74, and the measurements of the first flow measurement device 34 and the third flow measurement device 74 can be adjusted to the target flow rate. In addition, the output value may be set by a second inverter 72 associated with the second pressure pump 70, and the measurement value of the second flow measuring device 36 may be adjusted to the desired flow rate.

When the recovery rate of the treated water changes, the output value of the first inverter 30, the output value of the second inverter 72, and the opening of the valve 32 are automatically controlled, for example, so that the recovery rate of the treated water based on the measured values of the first flow measuring device 34 and the second flow measuring device 36 is as constant as possible, and the flow rate of the first RO concentrated water and the flow rate of the dilution water are changed. When the flow rate of the first space measured by the first flow measuring device 34 becomes less than the set flow rate, the output value of the first inverter 30 is fixed and the opening of the valve 32 is increased (i.e., the valve is opened). The opening of the valve 32 can be adjusted, for example, by closing it by a predetermined arbitrary percentage (for example, 10% of the opening relative to full opening) and repeating the process of observing the state of the flow rate of the first space measured by the first flow measuring device 34 for a predetermined time (for example, 1 minute). Alternatively, the opening of the valve 32 may be fixed and the output value of the first inverter 30 increased to increase the flow rate of the first space.

When the flow rate in the first space measured by the first flow rate measuring device 34 becomes larger than the set flow rate, the opening of the valve 32 is fixed and the output of the first inverter 30 is reduced. However, when the pressure pump 26 reaches the lower output limit value for which operation is guaranteed, the opening of the valve 32 is reduced (the valve is closed). The opening of the valve 32 can be adjusted, for example, by closing it at a predetermined arbitrary rate (for example, 10% of the opening rate compared to full opening) and repeating the process of observing the state of the flow rate in the first space measured by the first flow rate measuring device 34 for a predetermined time (for example, 1 minute). Alternatively, the output value of the first inverter 30 may be fixed and the opening of the valve 32 may be reduced to reduce the flow rate in the first space.

If the flow rate in the second space measured by the second flow measuring device 36 becomes less than the set flow rate, the opening of the valve 32 can be fixed and the output value of the second inverter 720 can be increased. If the flow rate in the second space measured by the second flow measuring device 36 becomes greater than the set flow rate, the opening of the valve 32 can be fixed and the output value of the second inverter 720 can be decreased.

When the flow rate in the second space measured by the third flow measuring device 74 becomes smaller than the set flow rate, the flow rate in the first space increases, so the output value of the first inverter 30 can be fixed and the opening of the valve 32 can be reduced. Alternatively, the opening of the valve 32 can be fixed and the output value of the first inverter 30 can be increased. When the flow rate in the second space measured by the third flow measuring device 74 becomes larger than the set flow rate, the flow rate in the first space decreases, so the output value of the first inverter 30 can be fixed and the opening of the valve 32 can be increased. Alternatively, the opening of the valve 32 can be fixed and the output value of the first inverter 30 can be reduced.

In addition to the valve 32, one or more proportional control valves that adjust the opening based on the measured values of the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 74 may be provided in the piping of the first space 11, for example, the piping 106, 42, 44, 46, and 48, and the opening of the valve may be adjusted manually or automatically by the control device 66.

In addition to the first flow rate measuring device 34 that measures the flow rate of the concentrated water that has passed through the first space of the final-stage membrane module unit and the third flow rate measuring device 74 that measures the flow rate of the dilution water that has passed through the second space of the final-stage membrane module unit, one or more flow rate measuring devices that measure the flow rate in the first space 11 may be provided in the piping of the first space 11, for example, in the pipings 106, 42, 44, 46, and 48.

In addition to the second flow rate measuring device 36 that measures the flow rate of the dilution water that has passed through the second space of the first-stage membrane module unit, one or more flow rate measuring devices that measure the flow rate in the second space 13 may be provided in the piping of the second space 13, for example, in the piping 78, 56, 58, and 60.

One or more proportional control valves may be provided in the piping of the first space 11, for example, in the piping 106, 42, 44, 46, and 48, to adjust the opening based on the measured values of the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 74.

The water treatment device 2 does not need to have a second dilution water tank 68. A water treatment device with such a configuration is shown in Figure 3.

In the water treatment device 3 shown in FIG. 3, a third flow rate measuring device 84 is installed in the piping 54 as a third flow rate measuring means for measuring the flow rate of dilution water passing through the second space of the final membrane module unit (in the example of FIG. 3, the fifth membrane module unit 20). The second space outlets of each membrane module of the fifth membrane module unit 20 and the second space inlets of each membrane module of the fourth membrane module unit 18 are connected in parallel by the piping 54 via the second pressure pump 80. The water treatment device 3 may or may not include the concentrated water tank 22, the pump 28, and the piping 52. The water treatment device 3 may or may not include the first dilution water tank 24 and the piping 64.

The second booster pump 80 is provided with a second inverter 82 that outputs a drive frequency corresponding to the input command signal to the second booster pump 80. The water treatment device 3 includes a control device 66, which is connected to the first inverter 30, the second inverter 82, the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 84 by wired or wireless electrical connections, etc. The control device 66 may also be connected to the valve 32 by wired or wireless electrical connections, etc.

In the water treatment method and water treatment device 3 according to this embodiment, the flow rate of the concentrated water passing through the first space of the membrane module unit of the final stage is measured (first flow rate measurement process), the flow rate of the dilution water passing through the second space of the membrane module unit of the first stage is measured (second flow rate measurement process), and the flow rate of the dilution water passing through the second space of the membrane module unit of the final stage is measured (third flow rate measurement process), and the flow rate of the first RO concentrated water supplied to the first space of the membrane module unit of the first stage and the flow rate of the dilution water supplied to the second space of the membrane module unit before the final stage are adjusted (flow rate adjustment process) so that the measured flow rate of the concentrated water of the final stage, the measured flow rate of the dilution water of the first stage, and the measured flow rate of the dilution water of the final stage are preset target flow rate values.

For example, the control device 66 functions as a flow rate adjusting means for adjusting the flow rate of the first RO concentrated water supplied to the first space of the first stage membrane module unit and the flow rate of the dilution water supplied to the second space of the membrane module unit preceding the final stage so that the measured value of the flow rate of the concentrated water of the final stage membrane module unit (in the example of Figure 2, the fifth stage membrane module unit 20) measured by the first flow rate measuring device 34, the measured value of the flow rate of the dilution water of the first stage membrane module unit (in the example of Figure 2, the first stage membrane module unit 12) measured by the second flow rate measuring device 36, and the measured value of the flow rate of the dilution water of the final stage membrane module unit measured by the third flow rate measuring device 84 become predetermined target flow rate values. The control device 66 calculates the drive frequency using an arbitrary calculation formula so that the measured values of the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 84 become the preset target flow value, outputs a command signal corresponding to this calculated value to the first inverter 30 to control the pressure pump 26, and outputs a command signal to the second inverter 82 to control the second pressure pump 80, and adjusts the flow rate of the first RO concentrated water supplied to the first space 11 of the first stage membrane module unit (in the example of FIG. 2, the first stage membrane module unit 12) and the dilution water supplied to the second space 13 of the membrane module unit before the final stage (in the example of FIG. 2, the fourth stage membrane module unit 18).

As a result, in the water concentration treatment using a multi-stage semipermeable membrane module, the amount of wastewater is reduced compared to the reverse osmosis membrane method, and more stable treatment is possible even when the water quality of the water to be treated (raw water) fluctuates. In addition, by using the second pressure pump 80 as a second pressure pump that sucks in dilution water from the final stage membrane module unit and discharges it to the previous stage membrane module unit, the load on the pressure pump 26 can be reduced and the pressure shortage required for water flow can be suppressed even if the number of stages of membrane module units increases and the pressure required for water flow is insufficient with the pressure pump 26 alone.

An outline of another example of a water treatment device according to an embodiment of the present invention is shown in Figure 4.

The water treatment device 4 shown in FIG. 4 differs from the water treatment device 1 shown in FIG. 1 in that the first space outlets of each membrane module of the fourth-stage membrane module unit 18 and the first space inlets of each membrane module of the fifth-stage membrane module unit 20 are connected in parallel by piping 88, and the downstream side of the pump 28 in piping 52 and the second space inlets of each membrane module of the fifth-stage membrane module unit 20 are connected in parallel by piping 90 via valves 86.

The water treatment device 4 uses a multi-stage membrane module having a first space 11 and a second space 13 separated by a semipermeable membrane 15, passes the first RO concentrated water in series through the first space 11 of the multi-stage membrane module, distributes the concentrated water of the final stage membrane module unit to the second space 13 of the final stage membrane module unit (in the example of FIG. 4, the fifth stage membrane module unit 20), returns and passes the dilution water of the final stage membrane module in series to the second space 13 of the membrane module in the previous stage, and pressurizes the first space 11 to permeate the water contained in the first space 11 into the second space 13 to concentrate the water. That is, in the water treatment device 4, the first RO concentrated water is concentrated using the semipermeable membrane 15, and the concentrated water is further concentrated using the semipermeable membrane 15 of the next stage. The first RO concentrated water is supplied to the first space 11 of the first stage membrane module unit (in the example of FIG. 4, the first stage membrane module unit 12), and after the concentrated water passes through the first space 11 of the final stage membrane module unit (in the example of FIG. 1, the fifth stage membrane module unit 20), at least a portion of the concentrated water of the final stage is supplied to the second space 13 of the final stage membrane module. Then, the dilution water that has passed through the second space 13 of the final stage membrane module is supplied to the second space 13 of the upstream membrane module, and the first space 11 of each stage membrane module is pressurized to allow the water contained in the first space 11 to permeate into the second space 13.

Specifically, in the water treatment device 4, the water to be treated, which contains all dissolved solid components, is stored in the water tank 10 as necessary through the pipe 38, and is pressurized from the water tank 10 to 0.1 MPa or more by the pressure pump 26 (pressurization process), and is sent through the pipe 40 to the first reverse osmosis membrane treatment device 100. In the first reverse osmosis membrane treatment device 100, the pressurized water to be treated is passed through the first reverse osmosis membrane to obtain the first RO permeate and the first RO concentrated water (first reverse osmosis membrane treatment process). The first RO permeate is discharged through the first RO permeate pipe 108. At least a portion of the first RO permeate may be further sent to the third reverse osmosis membrane treatment device 104, as described below, and reverse osmosis membrane treatment may be performed in the third reverse osmosis membrane treatment device 104 (third reverse osmosis membrane treatment process).

The first RO concentrated water is sent to the first space 11 of each membrane module of the first-stage membrane module unit 12 through the first RO concentrated water pipe 106. Meanwhile, dilution water returned from the fifth-stage membrane module unit 20 (the final stage described later) via the second space 13 of the fourth-stage membrane module unit 18, the second space 13 of the third-stage membrane module unit 16, and the second space 13 of the second-stage membrane module unit 14 is sent to the second space 13 of each membrane module of the first-stage membrane module unit 12 through the pipe 60. In each membrane module of the first-stage membrane module unit 12, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (first stage)).

The concentrated water from the first-stage membrane module unit 12 is sent through the pipe 42 to the first space 11 of each membrane module of the second-stage membrane module unit 14. Meanwhile, the dilution water returned from the fifth-stage membrane module unit 20 (the final stage described later) via the second space 13 of the fourth-stage membrane module unit 18 and the second space 13 of the third-stage membrane module unit 16 is sent through the pipe 58 to the second space 13 of each membrane module of the second-stage membrane module unit 14. As in the first stage, the first space 11 is pressurized in each membrane module of the second-stage membrane module unit 14, and the water contained in the first space 11 is permeated into the second space 13 (concentration process (second stage)).

The concentrated water from the second-stage membrane module unit 14 is sent through the pipe 44 to the first space 11 of each membrane module of the third-stage membrane module unit 16. Meanwhile, the dilution water returned from the fifth-stage membrane module unit 20 (the final stage, described later) via the second space 13 of the fourth-stage membrane module unit 18 is sent through the pipe 56 to the second space 13 of each membrane module of the third-stage membrane module unit 16. As in the first and second stages, the first space 11 is pressurized in each membrane module of the third-stage membrane module unit 16, and the water contained in the first space 11 is permeated into the second space 13 (concentration process (third stage)).

The concentrated water from the third-stage membrane module unit 16 is sent through piping 46 to the first space 11 of each membrane module of the fourth-stage membrane module unit 18. Meanwhile, dilution water returned from the fifth-stage membrane module unit 20 (the final stage, described later) is sent through piping 92 to the second space 13 of each membrane module of the fourth-stage membrane module unit 18. As in the first, second, and third stages, in each membrane module of the fourth-stage membrane module unit 18, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fourth stage)).

The concentrated water from the fourth-stage membrane module unit 18 is sent through piping 88 to the first space 11 of each membrane module in the fifth-stage membrane module unit 20 (the final stage). Meanwhile, the concentrated water returned from the fifth-stage membrane module unit 20 (the final stage, described later) is sent through piping 90 to the second space 13 of each membrane module in the fifth-stage membrane module unit 20. As in the first to fourth stages, in the fifth-stage membrane module unit 20, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fifth stage)).

When valve 32 is open, the concentrated water from the fifth membrane module unit 20 is sent through piping 50 to the concentrated water tank 22 as necessary and stored there. When valve 86 is closed, at least a portion of the concentrated water is discharged from the concentrated water tank 22 to the outside of the system through piping 52 by pump 28 as treated water. At least a portion of the concentrated water is sent to the treated water tank 10 and may be mixed with the treated water in the treated water tank 10.

With valve 86 open, at least a portion of the concentrated water from the fifth-stage membrane module unit 20 is pumped from the concentrated water tank 22 through pipes 52 and 90 by pump 28 to the second space 13 of each membrane module of the fifth-stage membrane module unit 20. As described above, in each membrane module of the fifth-stage membrane module unit 20, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fifth stage)). Here, pump 28, pipes 52, 90, etc. function as a supply means for supplying at least a portion of the concentrated water from the final stage to the second space of the semipermeable membrane module of the final stage. As shown in the water treatment device 17 of FIG. 10, instead of providing the concentrated water tank 22 and the pump 28, a pipe 50 from the first space outlet of each membrane module of the fifth-stage membrane module unit 20 branches off at the upstream side of the valve 32, and a pipe 91 via a valve 87 is connected to the second space inlet of each membrane module of the fifth-stage membrane module unit 20, and the concentrated water of the fifth-stage membrane module unit 20 may be sent to the second space 13 of each membrane module of the fifth-stage membrane module unit 20 through the pipes 50 and 91 with the valve 87 open. The water treatment device 4 may or may not include a first dilution water tank 24 and a pipe 64.

The dilution water from the fifth-stage membrane module unit 20 is sent through the pipe 92 to the second space 13 of each membrane module of the fourth-stage membrane module unit 18. As described above, in each membrane module of the fourth-stage membrane module unit 18, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fourth stage)).

The dilution water from the fourth-stage membrane module unit 18 is sent through the pipe 56 to the second space 13 of each membrane module of the third-stage membrane module unit 16. As described above, in each membrane module of the third-stage membrane module unit 16, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (third stage)).

The dilution water from the third-stage membrane module unit 16 is sent through the pipe 58 to the second space 13 of each membrane module of the second-stage membrane module unit 14. As described above, in each membrane module of the second-stage membrane module unit 14, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (second stage)).

The dilution water from the second-stage membrane module unit 14 is sent through the pipe 60 to the second space 13 of each membrane module of the first-stage membrane module unit 12. As described above, in each membrane module of the first-stage membrane module unit 12, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (first stage)).

The dilution water from the first-stage membrane module unit 12 is sent to the first dilution water tank 24 through the piping 62 as necessary, and after being stored there, is discharged outside the system through the piping 64. At least a portion of the dilution water may be sent to the water tank 10 to be treated and mixed with the water to be treated there. At least a portion of the dilution water may be further sent to the second reverse osmosis membrane treatment device 102 as described below, and may be subjected to reverse osmosis membrane treatment in the second reverse osmosis membrane treatment device 102 (second reverse osmosis membrane treatment process).

In this way, treated water containing total dissolved solids and other substances (final stage concentrated water) is obtained, and dilution water is obtained from the treated water, which is the target of treatment, and the volume of the treated water is reduced.

For example, the control device 66 functions as a flow rate adjusting means for adjusting the flow rate of the first RO concentrated water supplied to the first space of the first-stage membrane module unit so that the measured value of the flow rate of the concentrated water of the final-stage membrane module unit (in the example of FIG. 1, the fifth-stage membrane module unit 20) measured by the first flow rate measuring device 34 and the measured value of the flow rate of the dilution water of the first-stage membrane module unit (in the example of FIG. 1, the first-stage membrane module unit 12) measured by the second flow rate measuring device 36 become the preset target flow rate value. The control device 66, for example, calculates the drive frequency using an arbitrary arithmetic expression so that the measured values of the first flow rate measuring device 34 and the second flow rate measuring device 36 become the preset target flow rate value, outputs a command signal corresponding to this calculated value to the first inverter 30 to control the pressure pump 26, and adjusts the flow rate of the first RO concentrated water supplied to the first space 11 of the first-stage membrane module unit (in the example of FIG. 1, the first-stage membrane module unit 12).

As a result, in water concentration treatment using a semipermeable membrane module, the volume of wastewater is reduced compared to the reverse osmosis membrane method, and stable treatment is possible even when the water quality of the water to be treated (raw water) fluctuates.

In the water treatment device 4, similar to the water treatment device 2 shown in FIG. 2, the flow rate of the dilution water that has passed through the second space of the membrane module unit in the final stage may be further measured, and the flow rate of the first RO concentrated water supplied to the first space of the membrane module unit in the first stage and the flow rate of the dilution water supplied to the second space in the stage preceding the final stage may be adjusted so that the measured flow rate of the concentrated water in the final stage, the measured flow rate of the dilution water in the first stage, and the measured flow rate of the dilution water in the final stage reach preset target flow rate values. A water treatment device having such a configuration is shown in FIG. 5.

The water treatment device 5 shown in FIG. 5 further includes a second dilution water tank 68 for storing dilution water from the final stage membrane module unit (in the example of FIG. 5, dilution water from the fifth stage membrane module unit 20). In the water treatment device 5, the second space outlet of each membrane module of the fifth stage membrane module unit 20 and the dilution water inlet of the second dilution water tank 68 are connected by piping 94. The outlet of the second dilution water tank 68 and the second space inlet of each membrane module of the fourth stage membrane module unit 18 are connected in parallel by piping 78 via a second pressure pump 70. As in the water treatment device 17 of FIG. 10, instead of providing the concentrated water tank 22 and the pump 28, a pipe 50 from the first space outlet of each membrane module of the fifth-stage membrane module unit 20 branches off at the upstream side of the valve 32, and a pipe 91 via a valve 87 is connected to the second space inlet of each membrane module of the fifth-stage membrane module unit 20, and the concentrated water of the fifth-stage membrane module unit 20 may be sent to the second space 13 of each membrane module of the fifth-stage membrane module unit 20 through the pipes 50 and 91 with the valve 87 open. The water treatment device 5 may or may not include a first dilution water tank 24 and a pipe 64.

The dilution water from the fifth-stage membrane module unit 20 is sent to the second dilution water tank 68 through the pipe 94, where it is stored. The second pressurizing pump 70 then sends the dilution water from the second dilution water tank 68 through the pipe 78 to the second space 13 of each membrane module of the fourth-stage membrane module unit 18. As described above, in each membrane module of the fourth-stage membrane module unit 18, the first space 11 is pressurized and the water contained in the first space 11 is permeated into the second space 13 (concentration process (fourth stage)).

A third flow rate measuring device 74 is installed in the piping 94 as a third flow rate measuring means for measuring the flow rate of the dilution water passing through the second space of the final membrane module unit (in the example of FIG. 5, the fifth membrane module unit 20). The second pressure pump 70 is provided in the rear of the final membrane module unit (in the example of FIG. 2, the fifth membrane module unit 20), and is driven at a rotation speed corresponding to the input drive frequency, for example, and is a second pressure pump that sucks in the dilution water of the final membrane module unit (in the example of FIG. 2, the fifth membrane module unit 20) and discharges it to the previous membrane module unit (in the example of FIG. 2, the fourth membrane module unit 18). The second pressure pump 70 is installed with a second inverter 72 that outputs a drive frequency corresponding to the input command signal to the second pressure pump 70. The locations of the second dilution water tank 68, the second pressure pump 70, and the flow rate measuring device 74 are not limited to the locations shown in FIG. 5, and may be installed in any of the dilution water piping along the way, for example, in any of the piping 56, 58, and 60. The water treatment device 5 includes a control device 66, which is connected to the first inverter 30, the second inverter 72, the first flow rate measuring device 34, the second flow rate measuring device 36, and the third flow rate measuring device 74 by wired or wireless electrical connections, etc. The control device 66 may also be connected to the valve 32 by wired or wireless electrical connections, etc.

In the water treatment method and water treatment device 5 according to this embodiment, the flow rate of the concentrated water passing through the first space of the membrane module unit of the final stage is measured (first flow rate measurement process), the flow rate of the dilution water passing through the second space of the membrane module unit of the first stage is measured (second flow rate measurement process), and the flow rate of the dilution water passing through the second space of the membrane module unit of the final stage is measured (third flow rate measurement process), and the flow rate of the first RO concentrated water supplied to the first space of the membrane module unit of the first stage and the flow rate of the dilution water supplied to the second space of the membrane module unit before the final stage are adjusted (flow rate adjustment process) so that the measured flow rate of the concentrated water of the final stage, the measured flow rate of the dilution water of the first stage, and the measured flow rate of the dilution water of the final stage are preset target flow rate values.

For example, the control device 66 functions as a flow rate adjusting means for adjusting the flow rate of the first RO concentrated water supplied to the first space of the first-stage membrane module unit and the flow rate of the dilution water supplied to the second space of the membrane module unit preceding the final stage so that the measured value of the flow rate of the concentrated water of the final-stage membrane module unit (in the example of Figure 5, the fifth-stage membrane module unit 20) measured by the first flow rate measuring device 34, the measured value of the flow rate of the dilution water of the first-stage membrane module unit (in the example of Figure 5, the first-stage membrane module unit 12) measured by the second flow rate measuring device 36, and the measured value of the flow rate of the dilution water of the final-stage membrane module unit measured by the third flow rate measuring device 74 become predetermined target flow rate values. The control device 66 calculates the drive frequency using an arbitrary calculation formula so that the measured values of the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 74 become the preset target flow value, outputs a command signal corresponding to this calculated value to the first inverter 30 to control the pressure pump 26, and outputs a command signal to the second inverter 72 to control the second pressure pump 70, and adjusts the flow rate of the first RO concentrated water supplied to the first space 11 of the first stage membrane module unit (in the example of FIG. 5, the first stage membrane module unit 12) and the dilution water supplied to the second space 13 of the membrane module unit before the final stage (in the example of FIG. 5, the fourth stage membrane module unit 18).

As a result, in the water concentration treatment using the semipermeable membrane module, the amount of wastewater is reduced compared to the reverse osmosis membrane method, and more stable treatment is possible even when the water quality of the water to be treated (raw water) fluctuates. By storing the diluted water that has passed through the second space of the final stage in the second dilution water tank 68, it becomes easier to adjust the flow rate even if the water balance between the first space and the second space is disrupted due to fluctuations in the water quality of the water to be treated. In addition, by using the second pressure pump 70 as the second pressure pump that sucks in the diluted water from the membrane module unit of the final stage and discharges it to the membrane module unit of the previous stage, the load on the pressure pump 26 can be reduced and the pressure shortage required for water flow can be suppressed even if the number of stages of the membrane module units increases and the pressure required for water flow is insufficient with the pressure pump 26 alone.

In the water treatment device 5, as in the water treatment device 3 shown in FIG. 3, the second dilution water tank 68 may not be provided. A water treatment device with such a configuration is shown in FIG. 6.

In the water treatment device 6 shown in FIG. 6, a third flow rate measuring device 84 is installed in the pipe 92 as a third flow rate measuring means for measuring the flow rate of the dilution water passing through the second space of the final membrane module unit (in the example of FIG. 6, the fifth membrane module unit 20). The second space outlet of each membrane module of the fifth membrane module unit 20 and the second space inlet of each membrane module of the fourth membrane module unit 18 are connected in parallel by the pipe 92 via the second pressure pump 80. As in the water treatment device 17 of FIG. 10, the concentrated water tank 22 and the pump 28 are not provided, and the pipe 50 from the first space outlet of each membrane module of the fifth membrane module unit 20 is branched on the upstream side of the valve 32, and the pipe 91 via the valve 87 is connected to the second space inlet of each membrane module of the fifth membrane module unit 20, and the concentrated water of the fifth membrane module unit 20 may be sent to the second space 13 of each membrane module of the fifth membrane module unit 20 through the pipe 50 and the pipe 91 with the valve 32 open. Additionally, the water treatment device 6 may or may not include a first dilution water tank 24 and piping 64.

The second booster pump 80 is provided with a second inverter 82 that outputs a drive frequency corresponding to the input command signal to the second booster pump 80. The water treatment device 6 includes a control device 66, which is connected to the first inverter 30, the second inverter 82, the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 84 by wired or wireless electrical connections, etc. The control device 66 may also be connected to the valve 32 by wired or wireless electrical connections, etc.

In the water treatment method and water treatment device 6 according to this embodiment, the flow rate of the concentrated water passing through the first space of the membrane module unit of the final stage is measured (first flow rate measurement process), the flow rate of the dilution water passing through the second space of the membrane module unit of the first stage is measured (second flow rate measurement process), and the flow rate of the dilution water passing through the second space of the membrane module unit of the final stage is measured (third flow rate measurement process), and the flow rate of the first RO concentrated water supplied to the first space of the membrane module unit of the first stage and the flow rate of the dilution water supplied to the second space of the membrane module unit before the final stage are adjusted (flow rate adjustment process) so that the measured values of the flow rate of the concentrated water of the final stage, the measured value of the flow rate of the dilution water of the first stage, and the measured value of the flow rate of the dilution water of the final stage are preset target flow rate values.

For example, the control device 66 functions as a flow rate adjusting means for adjusting the flow rate of the first RO concentrated water supplied to the first space of the first stage membrane module unit and the flow rate of the dilution water supplied to the second space of the membrane module unit preceding the final stage so that the measured value of the flow rate of the concentrated water of the final stage membrane module unit (in the example of Figure 6, the fifth stage membrane module unit 20) measured by the first flow rate measuring device 34, the measured value of the flow rate of the dilution water of the first stage membrane module unit (in the example of Figure 6, the first stage membrane module unit 12) measured by the second flow rate measuring device 36, and the measured value of the flow rate of the dilution water of the final stage membrane module unit measured by the third flow rate measuring device 84 become predetermined target flow rate values. The control device 66 calculates the drive frequency using an arbitrary calculation formula so that the measured values of the first flow measuring device 34, the second flow measuring device 36, and the third flow measuring device 84 become the preset target flow value, outputs a command signal corresponding to this calculated value to the first inverter 30 to control the pressure pump 26, and outputs it to the second inverter 82 to control the second pressure pump 80, and adjusts the flow rate of the first RO concentrated water supplied to the first space 11 of the first stage membrane module unit (in the example of FIG. 6, the first stage membrane module unit 12) and the dilution water supplied to the second space 13 of the membrane module unit before the final stage (in the example of FIG. 6, the fourth stage membrane module unit 18).

As a result, in the water concentration treatment using the semipermeable membrane module, the amount of wastewater is reduced compared to the reverse osmosis membrane method, and more stable treatment is possible even when the water quality of the water to be treated (raw water) fluctuates. In addition, by using the second pressure pump 80 as the second pressure pump that sucks in the dilution water of the final stage membrane module unit and discharges it to the previous stage membrane module unit, the load on the pressure pump 26 can be reduced and the pressure shortage required for water flow can be suppressed even if the number of stages of membrane module units increases and the pressure required for water flow is insufficient with the pressure pump 26 alone.

In the water treatment method and water treatment device according to this embodiment, the number of stages of the membrane module units may be determined according to the concentration of the target treated water, etc. For example, if it is desired to obtain treated water with a higher concentration from treated water with a lower concentration, the number of stages of the membrane module units may be increased.

The number of membrane modules in each membrane module unit can be determined based on factors such as the flow rate of the first RO permeate.

In the water treatment method and water treatment device according to this embodiment, it is preferable to provide a pressure pump as a pressure means for pressurizing the water to be treated, including all dissolved solid components, to 0.1 MPa or more, only in the upstream of the first reverse osmosis membrane treatment device 100. In other words, it is preferable not to provide a pressure means (pump, etc.) between the first reverse osmosis membrane treatment device 100 and the first-stage membrane module unit 12, and to pass the first RO concentrate of the first reverse osmosis membrane treatment device 100 directly through the first-stage membrane module unit 12 by pressurization by the pressure pump 26. By operating the reverse osmosis membrane device and the semipermeable membrane module with a single pressure pump, it is possible to reduce equipment costs, power costs, equipment space, etc.

The first reverse osmosis membrane used in the first reverse osmosis membrane treatment device 100 preferably has a pure water permeation flux in the range of 0.2 to 0.7 m ³ /m ² /day under conditions of an effective membrane surface pressure of 1 MPa and 25° C., and has a NaCl removal rate of 99.5% or more (under conditions of NaCl 32,000 mg/L) at standard operating pressure. It is more preferable that the first reverse osmosis membrane has a pure water permeation flux in the range of 0.3 to 0.6 ^{m 3} /m ² /day under conditions of an effective membrane surface pressure of 1 MPa and 25° C., and has a NaCl removal rate of 97% or more at standard operating pressure. When the pure water permeation flux is less than 0.2 ^m3 / ^m2 /day under conditions of a membrane surface effective pressure of 1 MPa and 25°C, a sufficient RO permeate amount may not be obtained, whereas when it exceeds 0.7 ^m3 / ^m2 /day, the RO permeate amount becomes excessive, which may cause clogging of the membrane.

The first reverse osmosis membrane treatment device 100 may be a multi-stage reverse osmosis membrane treatment device. In this case, the RO concentrate of each stage is passed through the reverse osmosis membrane treatment device of the next stage to undergo reverse osmosis membrane treatment, and the RO concentrate of the final stage is sent as the first RO concentrate to the first space 11 of each membrane module of the first stage membrane module unit 12. The RO permeate of each stage may be discharged, or at least a portion of the RO permeate may be further sent to the third reverse osmosis membrane treatment device 104 as described below, where reverse osmosis membrane treatment may be performed (third reverse osmosis membrane treatment process).

The permeation flux of the semipermeable membrane module in the semipermeable membrane treatment process is preferably in the range of 0.005 m/d to 0.05 m/d under conditions of an effective membrane surface pressure of 1 MPa and 25°C, and more preferably in the range of 0.015 m/d to 0.04 m/d. If the permeation flux of the semipermeable membrane module is less than 0.005 m/d under conditions of an effective membrane surface pressure of 1 MPa and 25°C, the number of semipermeable membrane modules required may increase, and if it exceeds 0.05 m/d, clogging of the membrane may occur.

In the water treatment method and water treatment device according to this embodiment, it is preferable that the pressure of the first RO concentrated water immediately after the first reverse osmosis membrane process is 7 MPa or more, and that the device further includes a depressurization process in which the first RO concentrated water is depressurized to less than 7 MPa before the semipermeable membrane treatment process (first-stage membrane module unit 12). An example of such a configuration is shown in FIG. 7.

In the water treatment device 7 of FIG. 7, the concentrated water outlet of the first reverse osmosis membrane treatment device 100 and the first space inlet of each membrane module of the first-stage membrane module unit 12 are connected in parallel by the first RO concentrated water pipe 106 via a pressure reducing valve 118, which is a pressure reducing means. The other configuration is the same as that of the water treatment device 1 of FIG. 1. In the water treatment devices 2 to 6, 17 of FIG. 2 to 6 and FIG. 10, the pressure reducing valve 118 may be provided in the first RO concentrated water pipe 106. With this configuration, the first RO concentrated water can be reduced in pressure to less than 7 MPa, which is the upper limit of the semipermeable membrane module pressure resistance, in the previous stage of the semipermeable membrane treatment process. In the water treatment device 7, no pressurizing means (pump, etc.) is provided between the first reverse osmosis membrane treatment device 100 and the first-stage membrane module unit 12, and the first RO concentrated water of the first reverse osmosis membrane treatment device 100 is preferably passed directly through the first-stage membrane module unit 12 after the pressure applied by the pressure pump 26 is reduced by the pressure reducing valve 118. The water treatment device 7 may or may not include a concentrated water tank 22, a pump 28, and a pipe 52. The water treatment device 7 may or may not include a first dilution water tank 24 and a pipe 64.

The pressure of the first RO concentrated water immediately after the first reverse osmosis membrane process is preferably 7 MPa or more, more preferably in the range of 7 MPa to 12 MPa, and even more preferably in the range of 7 MPa to 10 MPa. If the pressure of the first RO concentrated water immediately after the first reverse osmosis membrane process is 7 MPa, it may not be possible to efficiently concentrate to a high concentration, so the upper limit is preferably 12 MPa in terms of the pressure resistance of the reverse osmosis membrane, etc.

From the standpoint of the pressure resistance of the semipermeable membrane module, it is preferable to reduce the pressure of the first RO concentrated water to less than 7 MPa before the semipermeable membrane treatment process (first-stage membrane module unit 12), and it is more preferable to reduce the pressure to the range of 3.0 MPa to 6.9 MPa.

The pressure reducing means is not particularly limited as long as it can reduce the pressure of the first RO concentrated water, but examples include a pressure reducing valve, an orifice, etc.

The water treatment method and water treatment device according to this embodiment may further include a second reverse osmosis membrane treatment step in which the dilution water is passed through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate. An example of such a configuration is shown in FIG. 8.

In the water treatment device 8 of FIG. 8, the outlet of the first dilution water tank 24 and the inlet of the second reverse osmosis membrane treatment device 102 are connected by a pipe 64 via a pump 120. The second RO concentrated water pipe 110 is connected to the concentrated water outlet of the second reverse osmosis membrane treatment device 102, and the second RO permeate pipe 112 is connected to the permeate outlet. The other configuration is the same as that of the water treatment device 1 of FIG. 1. The second reverse osmosis membrane treatment device 102 may be provided in the water treatment devices 2 to 7 and 17 of FIG. 2 to 7 and FIG. 10. The water treatment device 8 may or may not include the concentrated water tank 22, the pump 28, and the pipe 52. The water treatment device 8 may or may not include the first dilution water tank 24. In this case, the pipe 62 and the pipe 64 are connected, and the pump 120 may or may not be installed in the pipe 62 or the pipe 64.

At least a portion of the dilution water is sent by the pump 120 through the pipe 64 to the second reverse osmosis membrane treatment device 102, where reverse osmosis membrane treatment is performed to obtain second RO concentrated water and second RO permeate water (second reverse osmosis membrane treatment process). The second RO permeate water obtained by the second reverse osmosis membrane treatment device 102 is discharged outside the system through the second RO permeate water pipe 112. The third RO concentrated water obtained by the reverse osmosis membrane treatment may be discharged outside the system through the second RO concentrated water pipe 110, or may be sent to the water tank 10 to be treated and mixed with the water tank 10. With this configuration, the dilution water can be reused as the second RO permeate water.

The water treatment method and water treatment device according to this embodiment may further include a third reverse osmosis membrane treatment step in which at least one of the first RO permeate and the second RO permeate is passed through a third reverse osmosis membrane to obtain a third RO permeate and a third RO concentrated water. An example of such a configuration is shown in FIG. 9.

In the water treatment device 9 of FIG. 9, the permeate outlet of the first reverse osmosis membrane treatment device 100 and the inlet of the third reverse osmosis membrane treatment device 104 are connected by the first RO permeate pipe 108. The concentrated water outlet of the third reverse osmosis membrane treatment device 104 is connected to the third RO concentrated water pipe 114, and the permeate outlet is connected to the third RO permeate pipe 116. The rest of the configuration is the same as that of the water treatment device 1 of FIG. 1. The third reverse osmosis membrane treatment device 104 may be provided in the water treatment devices 2 to 8 and 17 of FIGS. 2 to 8 and 10. The water treatment device 9 may or may not include the concentrated water tank 22, the pump 28, and the pipe 52. The water treatment device 9 may or may not include the first dilution water tank 24 and the pipe 64.

At least a portion of the first RO permeate is sent to the third reverse osmosis membrane treatment device 104 through the first RO permeate pipe 108, where reverse osmosis membrane treatment is performed to obtain third RO concentrated water and third RO permeate (third reverse osmosis membrane treatment process). The third RO permeate obtained by the third reverse osmosis membrane treatment device 104 is discharged outside the system through the third RO permeate pipe 116. The third RO concentrated water obtained by the reverse osmosis membrane treatment may be discharged outside the system through the third RO concentrated water pipe 114, or may be sent to the water tank 10 and mixed with the water to be treated in the water tank 10. With this configuration, the third RO permeate can be reused.

The water treatment device 8 in FIG. 8 may further include a reverse osmosis membrane treatment step in which the second RO permeate is passed through a reverse osmosis membrane to obtain RO permeate and RO concentrated water.

The semipermeable membrane 15 provided in the membrane module may be, for example, a reverse osmosis membrane (RO membrane), a forward osmosis membrane (FO membrane), a nanofiltration membrane (NF membrane), or 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 target solution in the first space 11 is preferably 0.5 to 10.0 MPa.

The material constituting the semipermeable membrane 15 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 15 is preferably a cellulose acetate-based resin.

The shape of the semipermeable membrane 15 can be a flat membrane, a hollow fiber membrane, a spiral membrane, etc.

The water to be treated may be any water containing substances such as total dissolved solids (TDS), and is not particularly limited. Examples include industrial wastewater, salt water, seawater, chemical wastewater, and concentrated wastewater after reverse osmosis membrane treatment. The water treatment method and water treatment device according to this embodiment are suitable for use when the TDS (total dissolved solids) concentration of the water to be treated is, for example, 50,000 mg/L or more, preferably 60,000 mg/L or more, and more preferably 100,000 mg/L or more. TDS (total dissolved solids) is composed of, for example, chlorides such as sodium chloride, carbonates such as calcium carbonate and magnesium carbonate, and sulfates such as calcium sulfate and magnesium sulfate.

The water treatment method and water treatment device according to this embodiment are preferably applicable when the sulfate ion concentration of the first RO concentrated water is 20,000 mg/L or more, and the concentration of at least one of the sodium ions and ammonium ions is 10,000 mg/L or more. The sulfate ion concentration of the first RO concentrated water is preferably 40,000 mg/L or more, and more preferably in the range of 40,000 to 250,000 mg/L. The concentration of at least one of the sodium ions and ammonium ions of the first RO concentrated water is preferably 20,000 mg/L or more, and more preferably in the range of 20,000 to 100,000 mg/L.

1, 2, 3, 4, 5, 6, 7, 8, 9, 17 Water treatment device, 10 Water tank to be treated, 11 First space, 12 First stage membrane module unit, 13 Second space, 14 Second stage membrane module unit, 15 Semipermeable membrane, 16 Third stage membrane module unit, 18 Fourth stage membrane module unit, 20 Fifth stage membrane module unit, 22 Concentrated water tank, 24 First dilution water tank, 26 Pressure pump, 28, 120 Pump, 30 First inverter, 32, 86, 87 Valve, 34 First flow rate measuring device, 36 Second flow rate measuring device, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 76, 78, 88, 90, 91, 92, 94 Piping, 66 Control device, 68 Second dilution water tank, 70, 80 Second pressure pump, 72, 82 Second inverter, 74, 84 Third flow rate measuring device, 100 First reverse osmosis membrane device, 102 Second reverse osmosis membrane device, 104 Third reverse osmosis membrane device, 106 First RO concentrated water pipe, 108 First RO permeate water pipe, 110 Second RO concentrated water pipe, 112 Second RO permeate water pipe, 114 Third RO concentrated water pipe, 116 Third RO permeate water pipe, 118 Pressure reducing valve.

Claims (10)

A pressurizing step of pressurizing the water to be treated containing total dissolved solid components to 0.1 MPa or more;
a first reverse osmosis membrane treatment step of passing the pressurized water through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate;
a semipermeable membrane treatment step in which, using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, the first RO concentrate is passed through the first space, and the first space is pressurized by pressurization in the pressurization step to cause water contained in the first RO concentrate to permeate through the semipermeable membrane to obtain concentrated water, and a part of the first RO concentrate or at least a part of the concentrate is passed through the second space to obtain dilution water;
A flow rate adjusting step of automatically adjusting the flow rate of the first RO concentrated water so that a recovery rate of the treated water based on the measured flow rate of the concentrated water and the measured flow rate of the dilution water (recovery rate = measured flow rate of the dilution water / (measured flow rate of the concentrated water + measured flow rate of the dilution water) x 100) is constant ;
A water treatment method comprising the steps of: A pressurizing step of pressurizing the water to be treated containing total dissolved solid components to 0.1 MPa or more;
a first reverse osmosis membrane treatment step of passing the pressurized water through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate;
a semipermeable membrane treatment step in which the first RO concentrate is passed through a first space of a first-stage semipermeable membrane module using a semipermeable membrane module connected in a plurality of stages, the first space being pressurized in the pressurizing step to cause the water contained in the first RO concentrate to permeate through the semipermeable membrane, and the concentrate is further obtained using a semipermeable membrane module in a subsequent stage or later to obtain concentrate, and dilution water is obtained by passing a portion of the first RO permeate, at least a portion of the concentrate, or at least a portion of dilution water obtained from another semipermeable membrane module through a second space of the semipermeable membrane module in each stage;
A flow rate adjusting step of automatically adjusting the flow rate of the first RO concentrated water so that a recovery rate of the treated water based on the measured flow rate of the concentrated water and the measured flow rate of the dilution water (recovery rate = measured flow rate of the dilution water / (measured flow rate of the concentrated water + measured flow rate of the dilution water) x 100) is constant ;
A water treatment method comprising the steps of: The water treatment method according to claim 1 or 2,
The water treatment method is characterized in that the first reverse osmosis membrane has a pure water permeation flux in the range of 0.2 to 0.7 ^m3 / ^m2 /day under conditions of a membrane surface effective pressure of 1 MPa and 25°C, and has a NaCl removal rate (under conditions of NaCl 32,000 mg/L) of 99.5% or more at standard operating pressure. The water treatment method according to any one of claims 1 to 3,
The water treatment method is characterized in that the pressure of the first RO concentrated water immediately after the first reverse osmosis membrane process is 7 MPa or more, and further comprises a depressurization process of depressurizing the first RO concentrated water to less than 7 MPa prior to the semipermeable membrane treatment process. The water treatment method according to any one of claims 1 to 4,
The water treatment method further comprises a second reverse osmosis membrane treatment step of passing the dilution water through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate. A pressurizing means for pressurizing the water to be treated containing total dissolved solid components to 0.1 MPa or more;
a first reverse osmosis membrane treatment means for passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate;
a semipermeable membrane treatment means for using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the first RO concentrate through the first space, pressurizing the first space by pressurizing with the pressurizing means to cause water contained in the first RO concentrate to permeate through the semipermeable membrane to obtain concentrated water, and passing a part of the first RO concentrate or at least a part of the concentrate through the second space to obtain dilution water;
a flow rate adjusting means for automatically adjusting the flow rate of the first RO concentrated water so that a recovery rate of the treated water (recovery rate = measured value of the dilution water flow rate / (measured value of the concentrated water flow rate + measured value of the dilution water flow rate) x 100) based on the measured value of the concentrated water flow rate and the measured value of the dilution water flow rate is constant ;
A water treatment device comprising: A pressurizing means for pressurizing the water to be treated containing total dissolved solid components to 0.1 MPa or more;
a first reverse osmosis membrane treatment means for passing the pressurized water to be treated through a first reverse osmosis membrane to obtain a first RO permeate and a first RO concentrate;
a semipermeable membrane treatment means for using a semipermeable membrane module connected in a plurality of stages, each having a first space and a second space separated by a semipermeable membrane, passing the first RO concentrate through the first space of the semipermeable membrane module in the first stage, pressurizing the first space by the pressurizing means to cause the water contained in the first RO concentrate to permeate through the semipermeable membrane, thereby obtaining concentrated water, and further obtaining concentrated water from the concentrated water using a semipermeable membrane module in the next stage or later, and passing a part of the first RO permeate, at least a part of the concentrated water, or at least a part of dilution water obtained from another semipermeable membrane module through the second space of the semipermeable membrane module in each stage to obtain dilution water;
a flow rate adjusting means for automatically adjusting the flow rate of the first RO concentrated water so that a recovery rate of the treated water (recovery rate = measured value of the dilution water flow rate / (measured value of the concentrated water flow rate + measured value of the dilution water flow rate) x 100) based on the measured value of the concentrated water flow rate and the measured value of the dilution water flow rate is constant ;
A water treatment device comprising: The water treatment device according to claim 6 or 7,
The water treatment device is characterized in that the first reverse osmosis membrane has a pure water permeation flux in the range of 0.2 to 0.7 ^m3 / ^m2 /day under conditions of a membrane surface effective pressure of 1 MPa and 25°C, and has a NaCl removal rate of 99.5% or more (under conditions of NaCl 32,000 mg/L) at standard operating pressure. The water treatment device according to any one of claims 6 to 8,
The water treatment device is characterized in that the pressure of the first RO concentrated water immediately after the first reverse osmosis membrane means is 7 MPa or more, and further comprises a pressure reducing means for reducing the pressure of the first RO concentrated water to less than 7 MPa upstream of the semipermeable membrane treatment means. The water treatment device according to any one of claims 6 to 9,
The water treatment device further comprises a second reverse osmosis membrane treatment means for passing the dilution water through a second reverse osmosis membrane to obtain a second RO permeate and a second RO concentrate.