Method and apparatus for film treatment of liquid to be treated

Abstract

To provide a membrane treatment method for a liquid to be treated, which allows membrane treatment using a NF membrane to be performed efficiently at a low cost.SOLUTION: There is provided a membrane treatment device 1 for liquid to be treated, including: a first NF membrane treatment device 10 that passes a liquid to be treated through a first NF membrane 12 to generate a first NF membrane permeated liquid that has permeated through the first NF membrane 12; a diluter 20 for diluting a first NF membrane concentrate by bringing the first NF membrane concentrate, which has been concentrated without passing through the first NF membrane 12 in the first NF membrane treatment device 10, into contact with a dilution liquid through a semipermeable membrane 22; and a second NF membrane treatment device 30 that passes the first NF membrane concentrate diluted in the diluter 20 through a second NF membrane 32 to generate a second NF membrane permeated liquid that has permeated through the second NF membrane 32.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] 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.

Background Art

[0002] Membrane treatment of a liquid to be treated using an NF membrane (nanofiltration membrane) has conventionally been performed, for example, as a pretreatment for desalination, salt production, concentration, etc. of seawater using an RO membrane (reverse osmosis membrane). That is, when seawater is directly supplied to the RO membrane, there is a risk that scale may precipitate and accumulate on the RO membrane due to scale-forming ions such as calcium carbonate and calcium sulfate in the seawater. Therefore, by reducing the scale-forming ions by NF membrane treatment before performing RO membrane treatment, scale risk is suppressed.

[0003] However, in the conventional membrane treatment method using an NF membrane, as the concentration of the liquid to be treated progresses, scale is likely to precipitate on the concentration side of the NF membrane, and membrane treatment at high pressure is required, resulting in an increase in energy cost. Therefore, it has been difficult to increase the water permeability of the NF membrane and improve the salt recovery rate.

[0004] Therefore, Patent Document 1 discloses that treated water having the same osmotic pressure is supplied to both sides of a semipermeable membrane, and pressure is applied to one side of the semipermeable membrane to make the treated water supplied to the other side of the semipermeable membrane rich in monovalent ions, and then this treated water is filtered through an NF membrane and used as treated water for a salt production process or a desalination process.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] While the membrane treatment method for the liquid to be treated disclosed in Patent Document 1 above can increase the monovalent ion concentration of the water to be treated that passes through the NF membrane, high pressure is still required to increase the permeability of monovalent ions to the NF membrane. Therefore, it cannot be said that the problems of energy cost and scale risk are sufficiently resolved.

[0007] Therefore, the present invention aims to provide a method and apparatus for membrane treatment of a liquid to be treated, which can perform membrane treatment with an NF membrane at low cost and in an efficient manner. [Means for solving the problem]

[0008] The object of the present invention is to provide a first NF membrane treatment step of passing a liquid to be treated through a first NF membrane to produce a first NF membrane permeate that has permeated through the first NF membrane; a dilution step of diluting the first NF membrane concentrate, which has been concentrated in the first NF membrane treatment step without permeating through the first NF membrane, by contacting it with a diluent via a semipermeable membrane; and a second NF membrane treatment step of passing the first NF membrane concentrate diluted in the dilution step through a second NF membrane to produce a second NF membrane permeate that has permeated through the second NF membrane. The process further comprises an RO membrane treatment step in which the first NF membrane permeate and the second NF membrane permeate are passed through an RO membrane to produce an RO membrane permeate that has permeated through the RO membrane, and the dilution step uses a portion of the produced RO membrane permeate as the dilution solution. This is achieved by a film treatment method for the liquid to be treated.

[0009] This method of treating a film with the liquid to be treated. In, The RO membrane processing step preferably includes a step of concentrating the first NF membrane permeate and the second NF membrane permeate in multiple stages using a plurality of RO membrane units equipped with the RO membrane. The dilution step may use the RO membrane permeate from at least the foremost RO membrane unit as the diluent. The RO membrane processing step may also include a step of pressurizing the RO membrane concentrate concentrated in the preceding RO membrane unit by recovering energy from the RO membrane concentrate concentrated in the subsequent RO membrane unit, in which case the dilution step preferably uses the RO membrane permeate generated in the subsequent RO membrane unit as the diluent.

[0011] The liquid to be treated is preferably seawater.

[0012] Furthermore, the present invention provides a first NF membrane processing apparatus that passes a liquid to be processed through a first NF membrane to produce a first NF membrane permeate that has permeated through the first NF membrane; a dilution apparatus that dilutes the first NF membrane concentrate, which has been concentrated in the first NF membrane processing apparatus without permeating through the first NF membrane, by contacting it with a dilution solution via a semipermeable membrane; and a second NF membrane processing apparatus that passes the first NF membrane concentrate diluted in the dilution apparatus through a second NF membrane to produce a second NF membrane permeate that has permeated through the second NF membrane. The RO membrane processing apparatus further comprises an RO membrane apparatus that passes the first NF membrane permeate and the second NF membrane permeate through an RO membrane to produce an RO membrane permeate that has permeated through the RO membrane, and the dilution apparatus uses a portion of the produced RO membrane permeate as the dilution solution. This is achieved by a membrane treatment device for the liquid to be treated. [Effects of the Invention]

[0013] According to the present invention, the film treatment method and apparatus for a liquid to be treated can be performed efficiently and at low cost using an NF film. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a membrane treatment device for a liquid to be treated according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of a membrane treatment apparatus for a liquid to be treated according to another embodiment of the present invention. [Figure 3] This is a schematic diagram of a membrane treatment apparatus for a liquid to be treated according to yet another embodiment of the present invention. [Figure 4] This is a schematic diagram of a membrane treatment apparatus for a liquid to be treated according to yet another embodiment of the present invention. [Figure 5] This is a schematic diagram of a membrane treatment apparatus for a liquid to be treated according to yet another embodiment of the present invention. [Figure 6] This is a schematic diagram of a membrane treatment apparatus for a liquid to be treated according to yet another embodiment of the present invention. [Figure 7] This is a schematic diagram of a membrane treatment apparatus for a liquid to be treated according to yet another embodiment of the present invention. [Figure 8] This figure shows a modified version of the main part of Figure 1. [Figure 9]It is a diagram showing another modification example of the main part of FIG. 1. [Figure 10] It is a diagram showing still another modification example of the main part of FIG. 1. [Figure 11] It is a diagram showing still another modification example of the main part of FIG. 1.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a basic configuration diagram of a membrane treatment apparatus for a liquid to be treated (hereinafter simply referred to as "membrane treatment apparatus") according to an embodiment of the present invention. As shown in FIG. 1, the membrane treatment apparatus 1-1 includes a first NF membrane treatment apparatus 10, a dilution apparatus 20, and a second NF membrane treatment apparatus 30.

[0016] The first NF membrane treatment apparatus 10 is composed of an NF membrane module having a first NF membrane (nanofiltration membrane) 12 in a casing. By passing the liquid to be treated through the first NF membrane 12, a first NF membrane permeate that has permeated through the first NF membrane 12 and a first NF membrane concentrate that has been concentrated without permeating through the first NF membrane 12 are generated. Examples of the shape of the first NF membrane 12 include a flat membrane and a hollow fiber membrane.

[0017] The dilution device 20 has a first chamber 24 and a second chamber 26 formed by partitioning the inside of the casing with a semipermeable membrane 22. A dilution liquid is introduced into the first chamber 24, while the first NF membrane concentrate generated by the first NF membrane treatment device 10 is introduced into the second chamber 26. The dilution liquid and the first NF membrane concentrate introduced into the first chamber 24 and the second chamber 26 respectively come into contact through the semipermeable membrane 22 and are then discharged to the outside. At this time, water moves from the first chamber 24 to the second chamber 26 through the semipermeable membrane 22, whereby the first NF membrane concentrate is diluted with the dilution liquid. The semipermeable membrane 22 can be appropriately selected in consideration of the pressure acting on the first chamber 24, the water permeability of the dilution liquid supplied to the second chamber 26, etc. For example, semipermeable membranes of the OARO (Osmotically Assisted Reverse Osmosis) method, PRO (Pressure Retarded Osmosis) membranes, FO (Forward Osmosis) membranes, etc. can be preferably cited, but the type thereof is not particularly limited. Examples of the shape of the semipermeable membrane 22 include a flat membrane and a hollow fiber membrane.

[0018] The second NF membrane treatment device 30 is composed of an NF membrane module provided with a second NF membrane (nanofiltration membrane) 32 in the casing. The first NF membrane concentrate diluted by the dilution device 20 is passed through the second NF membrane 32 to generate a second NF membrane permeate that has passed through the second NF membrane 32.

[0019] Next, a method for treating a liquid to be treated using the above-described membrane treatment device 1-1 will be described. First, a first NF membrane treatment step is performed in which the liquid to be treated is pressurized by the operation of the high-pressure pump 2 and supplied to the first NF membrane treatment device 10 and passed through the first NF membrane 12. Since the first NF membrane 12 has the property of mainly permeating monovalent ions while not permeating polyvalent ions of divalent or higher, by performing the first NF membrane treatment step on the liquid to be treated containing monovalent ions and polyvalent ions, the first NF membrane permeate containing monovalent ions can be selectively recovered. The liquid to be treated can preferably be exemplified by seawater, but may also be an inorganic salt solution other than seawater. When the liquid to be treated is seawater, it is preferably filtered seawater filtered by pretreatment after water intake.

[0020] Next, the first NF membrane concentrate generated in the first NF membrane processing step described above is supplied to the second chamber 26 of the dilution device 20, while a diluent is supplied to the first chamber 24 of the dilution device 20 by the operation of the supply pump 3. A dilution step is performed to dilute the first NF membrane concentrate by bringing it into contact with the diluent via the semipermeable membrane 22. The diluent supplied to the first chamber 24 is preferably a liquid with a lower osmotic pressure than the first NF membrane concentrate supplied to the second chamber 26, so as to promote the movement of water from the first chamber 24 to the second chamber 26 via the semipermeable membrane 22. For example, a low-concentration liquid such as fresh water or wastewater can be used. The diluent may also be the permeate of the RO membrane, as shown in each embodiment described later, and can be supplied to the first chamber 24 without using the supply pump 3 by the permeate pressure of the RO membrane. The diluent may have the same osmotic pressure as the first NF membrane concentrate. For example, the liquid to be treated can be supplied to the first chamber 24 as the diluent, and the first NF membrane concentrate supplied to the second chamber 26 can be diluted by applying pressure to the first chamber 24.

[0021] After this, the first NF membrane concentrate diluted in the above dilution step is supplied to the second NF membrane processing device 30, and a second NF membrane processing step is performed in which water is passed through the second NF membrane 32. The first NF membrane concentrate contains a small amount of monovalent ions that remain without permeating through the first NF membrane 12 in the first NF membrane processing step. By diluting it in the dilution step to lower the osmotic pressure and then passing water through the second NF membrane 32, the remaining monovalent ions can be more easily permeated through the second NF membrane 32 and recovered as the second NF membrane permeate. The second NF membrane permeate generated in the second NF membrane processing step is combined with the first NF membrane permeate generated in the first NF membrane processing step and sent to the next process as NF membrane permeate. The second NF membrane concentrate that is concentrated without permeating through the second NF membrane 32 is discharged as wastewater along with the dilution solution discharged from the first chamber 24 in the dilution step.

[0022] According to the membrane treatment method for the liquid to be treated according to this embodiment, by performing the second NF membrane treatment step after diluting the first NF membrane concentrate generated in the first NF membrane treatment step in the dilution step, the recovery rate of monovalent ions contained in the liquid to be treated can be easily increased without excessively increasing the operating pressure of the first NF membrane treatment apparatus 10 and the second NF membrane treatment apparatus 30, thus enabling low-cost and efficient membrane treatment with NF membranes.

[0023] Figure 2 is a schematic diagram of a membrane processing apparatus according to another embodiment of the present invention. The membrane processing apparatus 1-2 shown in Figure 2 is configured by adding an RO membrane processing apparatus 40 to the membrane processing apparatus 1-1 shown in Figure 1. In Figure 2, the same reference numerals are used for components similar to those in Figure 1, and detailed descriptions are omitted (the same applies to the following embodiments). In the following embodiments, including this embodiment, seawater is used as the liquid to be processed, but it is not necessarily limited to seawater.

[0024] The RO membrane processing apparatus 40 consists of an RO membrane module equipped with an RO membrane (reverse osmosis membrane) 42 inside a casing. The NF membrane permeate, which is a mixture of the first NF membrane permeate and the second NF membrane permeate, is passed through the RO membrane 42 by the operation of a high-pressure pump 4. The shape of the RO membrane 42 can be exemplified by a flat membrane or a hollow fiber membrane.

[0025] The membrane treatment method for a liquid to be treated using the membrane processing apparatus 1-2 shown in Figure 2 includes an RO membrane water flow step in which the NF membrane permeate generated by the first NF membrane treatment step, dilution step, and second NF membrane treatment step is passed through the RO membrane 42. The RO membrane permeate that has permeated through the RO membrane 42 can be used as fresh water, for example, while the RO membrane concentrate that has been concentrated without permeating through the RO membrane 42 can be used in other processes such as forward osmosis power generation or desalination by salt evaporation concentration. In this membrane treatment method for a liquid to be treated, it is preferable that in the dilution step, a portion of the generated RO membrane permeate is supplied to the first chamber 24 of the dilution apparatus 20 as a diluent. By utilizing the permeation pressure of the RO membrane 42, the first NF membrane concentrate can be efficiently diluted with a low-concentration diluent, thereby increasing the membrane treatment efficiency of the liquid to be treated and reducing the risk of scaling.

[0026] Figure 3 is a schematic diagram of a membrane processing apparatus according to yet another embodiment of the present invention. The membrane processing apparatus 1-3 shown in Figure 3 combines the diluent that has passed through the first chamber 24 of the diluent 20 with the liquid to be processed upstream of the high-pressure pump 2, as shown in the membrane processing apparatus 1-2 shown in Figure 2. This reduces the liquid pressure of the liquid to be processed and improves the permeability of monovalent ions in the first NF membrane 12. In Figure 3, the entire amount of diluent that has passed through the first chamber 24 is combined with the liquid to be processed, but only a portion of the diluent that has passed through the first chamber 24 may be combined with the liquid to be processed.

[0027] Figure 4 is a schematic diagram of a membrane processing apparatus according to yet another embodiment of the present invention. The membrane processing apparatus 1-4 shown in Figure 4 is configured in the same way as the membrane processing apparatus 1-2 shown in Figure 2, but with a plurality of dilution devices 20. One dilution device 20-1 dilutes the first NF membrane concentrate produced in the first NF membrane processing apparatus 10 by bringing it into contact with a diluent via a semipermeable membrane 22. Another dilution device 20-2 is located upstream of the first NF membrane processing apparatus 10 and dilutes the liquid to be processed by bringing it into contact with a diluent via a semipermeable membrane 22. In the membrane processing method of the liquid to be processed using the membrane processing apparatus 1-4 shown in Figure 4, the dilution step not only dilutes the first NF membrane concentrate but also dilutes the liquid to be processed, which allows the operating pressure of the first NF membrane processing apparatus 10 to be lowered, so that monovalent ions can easily permeate the first NF membrane 12 and the salt recovery rate can be increased. The dilution device 20-2, which is located upstream of the first NF membrane processing device 10, can be located downstream of the high-pressure pump 2 because it can dilute the liquid to be processed by utilizing the osmotic pressure difference between the liquid to be processed and the diluent. This allows for a reduction in the capacity of the high-pressure pump 2, thereby reducing costs and increasing the overall capacity of the device.

[0028] The membrane processing apparatus 1-4 shown in Figure 4 is configured to reliably maintain the desired high pressure in each of the first chambers 24 by supplying diluent to multiple diluent devices 20-1, 20-2 in parallel. However, as shown in the membrane processing apparatus apparatuses 1-5, 1-6 in Figures 5 and 6, the diluent may be supplied in series to each of the diluent devices 20-1, 20-2, so that the diluent passes through each of the first chambers 24 at the desired flow rate.

[0029] The membrane processing apparatus 1-7 shown in Figure 7 bypasses a portion of the diluent supplied to the first chamber 24 of the diluent 20 in the membrane processing apparatus 1-3 shown in Figure 3, and merges it with the liquid to be processed upstream of the high-pressure pump 2. This allows the liquid to be processed to be diluted without the need for multiple diluent 20s, thus reducing costs.

[0030] The RO membrane processing apparatus 40 in the membrane processing apparatus 1-2 to 1-7 shown in Figures 2 to 7 may be an RO membrane processing apparatus 40-8 equipped with a plurality of RO membrane units 41-1 and 41-2, as shown in Figure 8. The NF membrane permeate is concentrated by the RO membrane 42 of the preceding RO membrane unit 41-1 by the operation of the high-pressure pump 4, and then further concentrated by the RO membrane 42 of the subsequent RO membrane unit 41-2, thereby generating RO membrane permeate in each RO membrane unit 41-1 and 41-2.

[0031] The RO membrane processing process using the RO membrane processing apparatus 40-8 shown in Figure 8 allows for the concentration of NF permeate to a high degree by multiple RO membrane units 41-1 and 41-2. In the dilution step, it is preferable to use the high-purity RO membrane permeate produced by the preceding RO membrane unit 41-1 as the diluent. Applying back pressure can reduce the unevenness of the RO membrane flux and promote the dilution of the first NF membrane concentrate in the dilution step. The RO membrane unit 41 may be provided in three or more stages, and in this case, it is preferable to use the RO membrane permeate from at least the foremost RO membrane unit 41 as the diluent in the dilution step.

[0032] The RO membrane processing apparatus 40-8 shown in Figure 8 may also be configured to include an energy recovery device 50 between multiple RO membrane units 41-1 and 41-2, as shown in the RO membrane processing apparatus 40-9 shown in Figure 9. The energy recovery device 50 consists of, for example, a turbocharger, and rotates a turbine by recovering energy from the RO membrane concentrate concentrated in the downstream RO membrane unit 41-2. This power is then used to pressurize the RO membrane concentrate concentrated in the upstream RO membrane unit 41-1. The configuration of the energy recovery device 50 is not particularly limited, and may be a rotor type, piston type, or the like, in addition to a turbine type.

[0033] In the RO membrane treatment process using the RO membrane processing apparatus 40-9 shown in Figure 9, the RO membrane permeate generated in the subsequent RO membrane unit 41-2 is pressurized. Therefore, in terms of energy efficiency, it is preferable to use this RO membrane permeate as the diluent in the dilution process.

[0034] The RO membrane processing apparatus 40-10 shown in Figure 10 is configured with three RO membrane units 41-1, 41-2, and 41-3 in a multi-stage configuration, and includes an energy recovery device 50 between the second-stage RO membrane unit 41-2 and the third-stage RO membrane unit 41-3. In the RO membrane processing process using the RO membrane processing apparatus 40-10 shown in Figure 10, the flux of the RO membrane permeate generated in the first-stage RO membrane unit 41-1 is high, and it is desirable to apply back pressure. In addition, the pressure of the RO membrane permeate generated in the third-stage RO membrane unit 41-3 can be increased by the energy recovery device 50. In the dilution process, it is preferable from an energy efficiency standpoint to use the RO membrane permeates from these RO membrane units 41-1 and 41-3 as diluents.

[0035] The RO membrane processing apparatus 40-11 shown in Figure 11 recovers energy from the RO membrane concentrate of the downstream RO membrane unit 41-2 using an energy recovery device 50, as shown in the RO membrane processing apparatus 40-8 in Figure 8, and pressurizes a portion of the NF membrane permeate. The pressurized NF membrane permeate is further pressurized by the operation of the pressurization pump 5 and supplied to the upstream RO membrane unit 41-1 along with the remaining NF membrane permeate, thereby enabling more efficient RO membrane processing. [Explanation of Symbols]

[0036] 1. Membrane processing device 10. First NF film processing apparatus 12. First NF film 20 Dilution device 22 Semi-permeable membrane 30. Second NF film processing apparatus 32 Second NF film 40 RO membrane processing equipment 42 RO membrane 50 Energy recovery device

Claims

1. A first NF membrane treatment step involves passing the liquid to be treated through a first NF membrane to generate a first NF membrane permeate that has permeated through the first NF membrane, A dilution step is performed by bringing the first NF film concentrate, which has been concentrated in the first NF film processing step without permeating the first NF film, into contact with a diluent via a semipermeable membrane, thereby diluting the first NF film concentrate. The process includes a second NF membrane treatment step, in which the first NF membrane concentrate diluted in the dilution step is passed through a second NF membrane to generate a second NF membrane permeate that has permeated through the second NF membrane, The system further comprises an RO membrane processing step of passing the first NF membrane permeate and the second NF membrane permeate through an RO membrane to generate an RO membrane permeate that has permeated through the RO membrane, The aforementioned dilution step is a membrane treatment method for a liquid to be treated, in which a portion of the generated RO membrane permeate is used as the diluent.

2. The membrane treatment method for a liquid to be treated according to claim 1, further comprising the RO membrane treatment step of concentrating the first NF membrane permeate and the second NF membrane permeate in multiple stages using a plurality of RO membrane units equipped with the RO membrane.

3. The method for membrane treatment of a liquid to be treated according to claim 2, wherein the dilution step uses the RO membrane permeate of at least the foremost RO membrane unit as the dilution solution.

4. The RO membrane processing step includes a step of increasing the pressure of the RO membrane concentrate concentrated in the preceding RO membrane unit by recovering energy from the RO membrane concentrate concentrated in the subsequent RO membrane unit. The method for membrane treatment of a liquid to be treated according to claim 2 or 3, wherein the dilution step uses the RO membrane permeate generated by the RO membrane unit in the subsequent stage as the dilution solution.

5. The method for treating a film with a liquid to be treated according to claim 1, wherein the liquid to be treated is seawater.

6. A first NF membrane processing apparatus that passes a liquid to be processed through a first NF membrane to generate a first NF membrane permeate that has permeated through the first NF membrane, A dilution device for diluting the first NF membrane concentrate, which has been concentrated in the first NF membrane processing apparatus without permeating the first NF membrane, by bringing it into contact with a dilution solution via a semipermeable membrane, The apparatus comprises a second NF membrane apparatus which passes the first NF membrane concentrate, diluted in the dilution apparatus, through a second NF membrane to generate a second NF membrane permeate that has permeated through the second NF membrane, The RO membrane processing apparatus further comprises passing the first NF membrane permeate and the second NF membrane permeate through an RO membrane to generate an RO membrane permeate that has permeated through the RO membrane, The dilution apparatus is a membrane treatment apparatus for a liquid to be treated, which uses a portion of the generated RO membrane permeate as the dilution solution.

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