JP2023181602A - Membrane treatment method and device of liquid to be treated - Google Patents

Abstract

To provide a membrane treatment method of liquid to be treated which can perform membrane treatment of the liquid to be treated efficiently at low cost.SOLUTION: A membrane treatment method of liquid to be treated which includes an NF membrane treatment step of passing the liquid to be treated through an NF membrane 11, and an RO membrane treatment step of passing NF membrane permeating liquid which has permeated into the NF membrane 11 at the NF membrane treatment step through an RO membrane 21 includes: a dilution step of causing, as diluent, at least a part of RO membrane permeating liquid which has permeated into the RO membrane 21 to merge into the liquid to be treated before passing through the NF membrane 11, and diluting the liquid; and a salt concentration regulation step of increasing a flow rate of the diluent to the liquid to be treated as electric conductivity of the liquid to be treated after the dilution increases.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and apparatus for membrane treatment of a liquid to be treated, and more particularly to a method and apparatus for membrane treatment of a liquid to be treated using an NF membrane and an RO membrane.

As a conventional membrane treatment device for a liquid to be treated, Patent Document 1 describes a first membrane filtration device having an NF membrane (nanofiltration membrane) or an RO membrane (reverse osmosis membrane) and a raw water tank in a second membrane filtration device. An apparatus for manufacturing pure water by sequentially passing raw water through the water is disclosed. A portion of the pure water that has passed through the second membrane filtration device is returned to the raw water tank along with a portion of the concentrated water from the first membrane filtration device, and the amount of concentrated water returned is the same as the amount of purified water returned. By reducing the amount of water, the scale risk of the first membrane filtration device is suppressed.

JP 2019-89018 Publication

The device disclosed in Patent Document 1 cannot cope with changes in the concentration of raw water supplied to the raw water tank, so if the salt concentration of the raw water increases, scale will form on the membrane surface of the first membrane filtration device. Not only is this easy to occur, but it also requires membrane treatment at high pressure, leading to problems such as increased energy costs, increased membrane load, and reduced durability.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method and apparatus for membrane treatment of a liquid to be treated, which can perform membrane treatment of a liquid to be treated efficiently at low cost.

The object of the present invention is to provide an NF membrane treatment step in which a liquid to be treated is passed through an NF membrane, and an RO membrane treatment step in which an NF membrane permeated liquid that has passed through the NF membrane in the NF membrane treatment step is passed through an RO membrane. A method for membrane treatment of a liquid to be treated, comprising: diluting at least a part of the RO membrane permeate that has passed through the RO membrane by joining the liquid to be treated as a diluent before passing through the NF membrane; This is achieved by a method for membrane treatment of a liquid to be treated, which includes a dilution step of increasing the electrical conductivity of the liquid to be treated after dilution, and a salt concentration adjustment step of increasing the flow rate of the diluent to the liquid to be treated as the electrical conductivity of the diluted liquid increases.

Preferably, the RO membrane treatment step includes a step of arranging a plurality of RO membrane units each including the RO membrane, and sequentially passing the RO membrane concentrate from the preceding RO membrane unit to the subsequent RO membrane unit. Preferably, in the dilution step, at least a portion of the RO membrane permeate of the last stage RO membrane unit is used as a diluent.

Further, the object of the present invention is to provide an NF membrane treatment device for passing a liquid to be treated through an NF membrane, and an RO membrane for passing an NF membrane permeated liquid that has passed through the NF membrane of the NF membrane treatment device to an RO membrane. A membrane treatment device for a liquid to be treated, comprising: a treatment device, wherein at least a part of the RO membrane permeate that has passed through the RO membrane is combined with the liquid to be treated as a diluted liquid before passing through the NF membrane. A dilution channel that dilutes the liquid to be treated, an electrical conductivity meter that measures the electrical conductivity of the liquid to be treated after dilution, and an electric conductivity meter that measures the flow rate of the diluted liquid to the liquid to be treated when the electrical conductivity of the liquid to be treated after dilution increases. This is achieved by a membrane treatment device for the liquid to be treated, which is equipped with a control device for increasing the amount of water.

Preferably, the membrane treatment device for the liquid to be treated further includes a high-pressure pump that pressurizes the diluted liquid to be treated and supplies it to the NF membrane treatment device, and the control device is configured to control the membrane treatment device for supplying the diluted liquid to the NF membrane treatment device. Preferably, the flow rate of the high-pressure pump is controlled by an inverter based on the pressure of the processing liquid.

According to the method and apparatus for membrane treatment of a liquid to be treated of the present invention, membrane treatment of a liquid to be treated can be performed efficiently at low cost.

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

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a membrane treatment apparatus for a liquid to be treated (hereinafter simply referred to as a "membrane treatment apparatus") according to an embodiment of the present invention. As shown in FIG. 1, the membrane treatment device 1 includes an NF membrane treatment device 10 that passes a liquid to be treated through an NF membrane (nanofiltration membrane), and an NF membrane permeated liquid that has passed through the NF membrane of the NF membrane treatment device 10. An RO membrane treatment device 20 that passes water through an RO membrane (reverse osmosis membrane) by the operation of a high-pressure pump 2, and dilutes at least a portion of the RO membrane permeate that has passed through the RO membrane of the RO membrane treatment device 20 into a liquid to be treated. It is provided with a dilution flow path 30 for diluting the liquid by merging it as a liquid, and is configured such that the liquid to be treated diluted by the diluent is supplied to the NF membrane processing apparatus 10 by the operation of the high-pressure pump 3. A flow rate adjustment valve 40 is provided in the dilution channel 30, and the flow rate of the diluent can be adjusted by operating the flow rate adjustment valve 40.

The NF membrane processing apparatus 10 includes a single NF membrane unit in which an NF membrane 11 is disposed within a casing, and a non-permeated liquid that does not pass through the NF membrane 11 is discharged as an NF membrane concentrated liquid. A flow rate adjustment valve 41 is provided in the discharge line for discharging the NF membrane concentrate. The NF membrane processing device 10 can also include two or more stages of NF membrane units, and the NF membrane concentrate that does not pass through the NF membrane in the NF membrane unit in the former stage is transferred to the NF membrane in the NF membrane unit in the latter stage. It may be configured such that water is passed through the NF membrane unit and the NF membrane permeated liquid from each stage of the NF membrane unit is supplied to the RO membrane processing apparatus 20.

The RO membrane processing apparatus 20 includes two stages of RO membrane units 20-1 and 20-2. Each RO membrane unit 20-1, 20-2 is equipped with an RO membrane 21-1, 21-2 inside the casing, and the RO membrane unit 20-1 in the previous stage is a non-permeable membrane that does not pass through the RO membrane 21-1. The liquid is passed through the RO membrane 21-2 of the RO membrane unit 20-2 at the subsequent stage, and the RO membrane permeated liquid is discharged from the RO membrane units 20-1 and 20-2 at each stage. The non-permeate liquid that does not pass through the subsequent RO membrane 21-2 is recovered as an RO membrane concentrate. The recovered RO membrane concentrate can be used for salt production, for example, by evaporation or membrane concentration. The RO membrane processing apparatus 20 may be configured with a single RO membrane unit, or may be configured with three or more stages of RO membrane units.

The materials for the NF membrane 11 and the RO membranes 21-1 and 21-2 are not particularly limited, and known materials can be used as appropriate. The shapes of the NF membrane 11 and the RO membranes 21-1 and 21-2 are not particularly limited either, and examples include flat membranes and hollow fiber membranes.

The membrane processing apparatus 1 further includes electrical conductivity meters 50 and 51, flowmeters 60, 61, 62, and 63, and a control device 70. The electrical conductivity meters 50 and 51 measure the electrical conductivity of the diluted liquid (RO membrane permeated liquid) passing through the dilution channel 30 and the diluted liquid to be treated, respectively. The flowmeters 60, 61, 62, and 63 measure the flow rates of the diluted liquid, the diluted liquid to be treated, the NF membrane concentrated liquid, and the NF membrane permeated liquid, respectively. The measured values of the electrical conductivity meters 50, 51 and the flow meters 60, 61, 62, 63 are input to the control device 70. The control device 70 controls the operation of the flow rate regulating valves 40 and 41 and the high pressure pumps 2 and 3.

Next, a method for membrane treatment of a liquid to be treated using the membrane treatment apparatus 1 having the above configuration will be described. First, the NF membrane treatment step of increasing the pressure of the liquid to be treated by operating the high pressure pump 3 and supplying it to the NF membrane treatment device 10 and passing water through the NF membrane 11 is performed. It is preferable that the high-pressure pump 3 is a pump capable of inverter control that can easily control the flow rate and pressure with power saving, and the pressure of the liquid to be treated passing through the NF membrane 11 is controlled on the downstream side of the high-pressure pump 3. The NF membrane treatment process can be performed safely by detecting the pressure with the pressure gauge 4 installed in the pressure gauge 4 and controlling the inverter by the control device 70 so that the detected pressure of the pressure gauge 4 is maintained below a predetermined value.

The NF membrane 11 mainly allows monovalent ions to pass through it, but does not allow multivalent ions of two or more valences to pass through. Therefore, the NF membrane treatment is not possible for the liquid to be treated containing monovalent ions and multivalent ions. By performing this step, the NF membrane permeate containing monovalent ions can be selectively recovered. Preferred examples of the liquid to be treated include seawater and brine, but other inorganic salt solutions may also be used. In this embodiment, filtered seawater obtained by filtering seawater after water intake through pretreatment is used as the liquid to be treated.

Next, the NF membrane permeate that has passed through the NF membrane 11 in the above NF membrane treatment step is pressurized by the operation of the high-pressure pump 2 and is supplied to the RO membrane treatment device 20, and water is passed through the RO membranes 21-1 and 21-2. Perform the RO membrane treatment step.

After this, a part of the RO membrane permeate that has passed through the RO membranes 21-1 and 21-2 in the above RO membrane treatment process is passed through the dilution flow path 30 to be treated before passing through the NF membrane 11. A dilution process is performed in which the liquid is combined with the liquid as a diluent to dilute the liquid. The remainder of the RO membrane permeate that is not used as a diluent can be used, for example, as manufactured water. In the dilution step, the entire RO membrane permeate generated in the RO membrane treatment step may be used as a diluent, if necessary. The dilution process reduces the salt concentration of the liquid to be treated, which not only suppresses scale generation on the NF membrane 11 in the NF membrane treatment process described above, but also enables membrane treatment at low pressure, reducing energy costs. It is possible to achieve longer life by reducing the amount of carbon dioxide, improving membrane permeability, and reducing membrane load.

In this embodiment, the diluted liquid to be combined with the liquid to be treated through the dilution channel 30 is the combined permeate of the two RO membranes 21-1 and 21-2. , 21-2 may be used. Normally, the water quality of the permeate through the rear RO membrane 21-2 is worse than the water quality of the permeate through the front RO membrane 21-1. It is preferable to include. When the RO membrane processing apparatus 20 includes three or more stages of RO membrane units, it is preferable that the diluent contains at least the RO membrane permeate of the last stage RO membrane unit.

The flow rate ratio of the diluted liquid to the treated liquid passing through the dilution channel 30 is kept constant at all times by being calculated in real time by the control device 70 using necessary measured values from the outputs of the flow meters 60, 61, 62, and 63. It can be controlled so that However, if the salt concentration of the liquid to be treated increases, there is a possibility that the above flow control may not be able to sufficiently reduce the salt concentration of the liquid to be treated that is supplied to the NF membrane processing apparatus 10.

Therefore, the membrane treatment method for a liquid to be treated according to the present embodiment includes a salt concentration adjustment step of increasing the flow rate ratio of the diluent to the liquid to be treated when the electrical conductivity of the liquid to be treated increases after being diluted with the diluent. As a result, even if the salt concentration of the liquid to be treated increases, it is possible to suppress the increase in the salt concentration of the liquid to be treated that is supplied to the NF membrane processing apparatus 10. In the above salt concentration adjustment step, when the electrical conductivity of the liquid to be treated after dilution with the diluent decreases, it is preferable to reduce the flow rate ratio of the diluted liquid to the liquid to be treated, so that the RO membrane outside the system is reduced. The utilization rate of permeate can be increased.

In this embodiment, the control device 70 adjusts the opening degree of the flow rate regulating valve 40 based on the detection of the electrical conductivity of the diluted liquid to be treated by the electrical conductivity meter 51, thereby controlling the salt concentration. The adjustment process can be performed automatically. Adjustment of the flow rate ratio of the diluted liquid by operating the flow rate adjustment valve 40 is performed by detecting the electric conductivity meter 51 in addition to the detection by the electric conductivity meter 51 so that the electric conductivity of the diluted liquid to be treated becomes a desired value. The method may also be based on detection of the electrical conductivity of the diluent using the method 50.

Further, the control device 70 may adjust the opening degree of the flow rate regulating valve 41 based on the electrical conductivity of the diluted liquid to be treated detected by the electrical conductivity meter 51, and The flow rate of the NF membrane concentrate can be controlled to a desired value. For example, when the electrical conductivity of the diluted liquid to be treated increases, the opening degree of the flow rate adjustment valve 41 is increased to reduce the flow rate of the NF membrane permeated liquid, while the electrical conductivity of the diluted liquid to be treated decreases. Then, the opening degree of the flow rate regulating valve 41 can be reduced to increase the flow rate of the NF membrane permeate liquid.

The membrane treatment method and device for a liquid to be treated of the present invention are suitable for uses such as seawater desalination, salt production, and concentration, but are not necessarily limited to these uses. It can be used for various purposes such as recovering materials and reducing the volume of liquid to be treated.

1 Membrane treatment device 10 NF membrane treatment device 11 NF membrane 20 RO membrane treatment device 21-1, 21-2 RO membrane 30 Dilution channel 50, 51 Electrical conductivity meter 60, 61, 62, 63 Flow meter 70 Control device

Claims (4)

an NF membrane treatment step of passing the liquid to be treated through the NF membrane;
An RO membrane treatment step of passing the NF membrane permeated liquid that has passed through the NF membrane in the NF membrane treatment step through an RO membrane, the method comprising:
a dilution step of diluting at least a portion of the RO membrane permeate that has passed through the RO membrane by combining it with the liquid to be treated as a diluent before passing through the NF membrane;
A method for membrane treatment of a liquid to be treated, comprising a salt concentration adjustment step of increasing the flow rate ratio of the diluent to the liquid to be treated when the electrical conductivity of the liquid to be treated increases after dilution. The RO membrane treatment step includes a step of arranging a plurality of RO membrane units including the RO membrane and sequentially passing the RO membrane concentrate of the RO membrane unit in the preceding stage to the RO membrane unit in the succeeding stage,
2. The method for membrane treatment of a liquid to be treated according to claim 1, wherein the dilution step uses at least a portion of the RO membrane permeate of the last stage RO membrane unit as a diluent. an NF membrane treatment device that passes the liquid to be treated through the NF membrane;
A membrane treatment device for a liquid to be treated, comprising: an RO membrane treatment device for passing the NF membrane permeated liquid that has permeated through the NF membrane of the NF membrane treatment device to an RO membrane;
a dilution channel for diluting at least a portion of the RO membrane permeate that has passed through the RO membrane by joining it as a diluent with the liquid to be treated before passing through the NF membrane;
an electrical conductivity meter that measures the electrical conductivity of the liquid to be treated after dilution;
A membrane treatment device for a liquid to be treated, comprising: a control device that increases the flow rate ratio of the diluent to the liquid to be treated when the electrical conductivity of the diluted liquid increases. further comprising a high-pressure pump that pressurizes the diluted liquid to be treated and supplies it to the NF membrane treatment device,
4. The membrane treatment apparatus for a liquid to be treated according to claim 3, wherein the control device controls the flow rate of the high-pressure pump using an inverter based on the pressure of the liquid to be treated passing through the NF membrane.

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