JP2020014995A - Forward osmosis treatment method and forward osmosis treatment device - Google Patents

Abstract

To provide a forward osmosis treatment method and a forward osmosis treatment device which can reduce variation in a permeable water amount by forward osmosis treatment without changing supply amounts of a feed solution and a draw solution.SOLUTION: A forward osmosis treatment method includes a forward osmosis step of bringing a feed solution into contact with a draw solution having an osmotic pressure higher than that of the feed solution via a semi-permeable membrane to move water contained in the feed solution into the draw solution, in which the forward osmosis step includes adjusting a physical pressure difference between the feed solution and the draw solution so that variation in a permeable water amount that is an amount of water moving from the feed solution into the draw solution is reduced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a forward osmosis treatment method and a forward osmosis treatment apparatus.

  BACKGROUND ART A forward osmosis treatment method for recovering fresh water from a liquid to be treated (feed solution) such as seawater, river water, or wastewater using a forward osmosis phenomenon is known. The phenomenon of forward osmosis (hereinafter sometimes abbreviated as “FO”) is the phenomenon that water in a low-concentration solution moves through a semipermeable membrane toward a higher-concentration (high osmotic pressure) solution. It is a phenomenon that does.

  In the forward osmosis treatment, a draw solution (Draw Solution: sometimes abbreviated as “DS”) having a higher osmotic pressure than a feed solution (hereinafter sometimes abbreviated as “FS”) is used. In the forward osmosis module, when DS and FS are brought into contact via a semipermeable membrane, water moves from FS having low osmotic pressure to DS having high osmotic pressure. Then, fresh water can be recovered from the DS after passing through the forward osmosis module (that is, the DS from which water is recovered from the FS) using various methods.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-184403) discloses a method of increasing the amount of permeated water of a forward osmosis device by intermittently pressurizing FS and / or intermittently depressurizing DS. Is described. Patent Document 1 ([0010]) describes that the amount of permeated water can be increased by repeating pressure application and release.

JP 2014-184403 A

  For example, a change (seasonal fluctuation, daily fluctuation, etc.) may occur in the amount of permeated water of forward osmosis (FO) due to a change in viscosity and osmotic pressure of FS and DS due to a temperature change, a change in semipermeable membrane performance, and the like. is there. More specifically, for example, when the viscosity of FS and DS increases due to a decrease in temperature, the amount of FO permeated water may decrease. In addition, for example, the permeated water amount of the FO may gradually change due to a decrease in the performance of the semipermeable membrane after long-term operation.

  Here, for example, when an FO module is combined with an RO module or the like in order to recover water by reverse osmosis (RO) from DS from which FS water has been recovered by FO, if the amount of permeated water of FO fluctuates, The operating conditions of the RO module or the like designed according to the initial permeated water amount of the module may not be appropriate, and the operating conditions of the RO module or the like and equipment may need to be changed. Therefore, even when there is a fluctuation factor of the amount of permeated water such as a temperature change, it is desired to reduce the fluctuation of the amount of permeated water of the FO (preferably, the amount of permeated water of the FO is kept constant).

  As a method of reducing the fluctuation of the amount of permeated water of the FO, a method of changing the supply amounts of the FS and the DS in accordance with the change in the viscosity of the FS and the DS due to the temperature change or the like can be considered. However, the seasonal variation in the operation rates of the FS and DS pretreatment equipment causes a large loss from the viewpoint of economy, and it is commercially difficult to change the FS and DS supply amounts seasonally. Further, when the supply amounts of FS and DS are changed, complicated resetting of the operating conditions is required (especially in a system in which the FO and the peripheral equipment such as the RO module are combined), and the equipment such as the liquid feed pump is required. There is a problem that a change or the like is required.

  Therefore, an object of the present invention is to provide a forward osmosis treatment method and a forward osmosis treatment apparatus, which can reduce the fluctuation of the permeated water amount due to the forward osmosis treatment without changing the supply amounts of the feed solution and the draw solution. I do.

[1] By bringing a feed solution and a draw solution having a higher osmotic pressure than the feed solution into contact with each other through a semipermeable membrane, water contained in the feed solution is moved into the draw solution. Including an infiltration step,
In the forward osmosis step, a physical pressure difference between the feed solution and the draw solution is adjusted so that a fluctuation in a permeated water amount, which is an amount of water moving from the feed solution to the draw solution, is reduced. , Forward osmosis treatment method.

  [2] The forward osmosis treatment method according to [1], wherein the change in the amount of permeated water is a change caused by a change in temperature.

  [3] In the forward osmosis step, the physical pressure difference between the feed solution and the draw solution is adjusted by pressurizing the feed solution or by increasing or decreasing the pressure of the draw solution. The forward osmosis treatment method according to [1] or [2].

  [4] The forward osmosis treatment method according to any one of [1] to [3], wherein the semipermeable membrane is a hollow fiber membrane.

  [5] The forward osmosis treatment method according to [4], wherein the draw solution is supplied inside the hollow fiber membrane, and the feed solution is supplied outside the hollow fiber membrane.

[6] A forward osmosis treatment device used in the forward osmosis treatment method according to any one of [1] to [5],
The semipermeable membrane, and a first chamber to which the feed solution is supplied, and a second chamber to which the draw solution is supplied, wherein the first chamber and the second chamber are the semipermeable membrane. A separated forward osmosis module,
A pressure regulator for controlling the pressure of at least one of the feed solution and the draw solution,
By the pressure adjusting device, a physical pressure difference between the feed solution and the draw solution is adjusted so that a fluctuation in a permeated water amount, which is an amount of water moving from the feed solution into the draw solution, is reduced. , Forward osmosis treatment equipment.

  According to the present invention, in the forward osmosis process, the supply of the feed solution and the draw solution is controlled by adjusting the physical pressure difference between the feed solution and the draw solution so that the fluctuation of the amount of permeated water due to the forward osmosis process is reduced. Variations in the amount of permeated water due to forward osmosis can be reduced without changing the amount.

It is a mimetic diagram for explaining a forward osmosis processing method and a forward osmosis processing device of an embodiment. It is a cross section showing an example of a forward osmosis module (hollow fiber membrane module) used for a forward osmosis processing method and a forward osmosis processing device of an embodiment. It is a schematic graph which shows the relationship between the temperature change and the fluctuation | variation of the flow rate of DS in the outlet of FO module about the case where the forward osmosis processing method of embodiment is implemented, and the case where the conventional forward osmosis processing method is implemented. . It is a typical graph which shows the relationship between the temperature change and the fluctuation | variation of the density | concentration of DS in the outlet of FO module about the case where the forward osmosis processing method of embodiment is implemented, and the case where the conventional forward osmosis processing method is implemented. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

<Forward osmosis treatment device>
First, an example of a forward osmosis treatment apparatus that can be suitably used in the forward osmosis treatment method of the present embodiment will be described.

  Referring to FIG. 1, the forward osmosis treatment device of the present embodiment includes at least a forward osmosis module 1 and a pressure adjusting device 3.

[Forward osmosis module]
The forward osmosis module 1 has a semipermeable membrane 10, a first chamber 11 to which FS is supplied, and a second chamber 12 to which DS is supplied. The first chamber 11 and the second chamber 12 are separated by the semi-permeable membrane 10.

  The semipermeable membrane 10 is not particularly limited, and various known semipermeable membranes that can be used for forward osmosis can be used.

  The material constituting the semipermeable membrane is not particularly limited, and examples thereof include a cellulose resin, a polysulfone resin, and a polyamide resin. The semipermeable membrane is preferably made of a material containing at least one of a cellulose resin and a polysulfone resin.

  The cellulosic resin is preferably a cellulose acetate resin. Cellulose acetate resins have resistance to chlorine, which is a germicide, and can suppress the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and more preferably cellulose triacetate from the viewpoint of durability.

  The polysulfone resin is preferably a polyethersulfone resin. The polyethersulfone-based resin is preferably a sulfonated polyethersulfone.

  The shape of the semipermeable membrane is not particularly limited, and examples thereof include a flat membrane, a spiral membrane, and a hollow fiber membrane. In FIG. 1, a simplified flat film is depicted as the semipermeable film 10, but the invention is not limited to this. The hollow fiber membrane (hollow fiber type semipermeable membrane) is advantageous in that the membrane area per module can be increased and the efficiency of forward osmosis can be increased as compared with a flat membrane, a spiral membrane, or the like. is there.

  The form of the FO module 1 is not particularly limited, but when a hollow fiber membrane is used, a module in which a plurality of hollow fiber membranes are arranged straight or a cross-wind type in which a plurality of hollow fiber membranes are wound around a core tube. Modules and the like. When a flat membrane is used, a laminated module in which a plurality of flat membranes are stacked, a spiral module in which a plurality of flat membranes are enveloped and wound around a core tube, and the like are used.

(Hollow fiber membrane module)
Hereinafter, an example of an FO module (hollow fiber membrane module) using a hollow fiber membrane will be described with reference to FIG. The hollow fiber membrane module of FIG. 2 is a single element type hollow fiber membrane module in which one pressure vessel 100 is loaded with one hollow fiber membrane element. The feed solution (FS) flows outside the hollow fiber membrane 41 and the draw solution (DS) flows inside the hollow fiber membrane 41 (hollow portion). Thus, by taking out the fresh water in the FS to the DS, the DS can be diluted or the FS can be concentrated.

  The hollow fiber membrane element includes a porous distribution pipe 21 having a plurality of holes 21a disposed at the center, a plurality of hollow fiber membranes 41 disposed therearound, a porous distribution pipe 21 and a plurality of hollow fiber membranes 41. And resin walls 61 fixed at both ends. Each of the plurality of hollow fiber membranes 41 has openings at both ends.

  The hollow fiber membrane element has a DS supply port 111a and a discharge port 111b communicating with the inside of the plurality of hollow fiber membranes 41 and the outside of the hollow fiber membrane module, and the inflow side opening 41a of the hollow fiber membrane 41 has a DS supply port. The outlet 41b is connected to the DS outlet 111b.

  The porous pipe 21 is not particularly limited as long as it is a tubular body having a plurality of holes. By the porous distribution pipe 21, for example, FS supplied from the FS supply port 110a into the hollow fiber membrane module can be distributed to the outside 42 of the hollow fiber membrane. The holes are preferably provided radially in each direction with the central axis of the porous distribution pipe as a base point. Further, it is preferable that the porous distribution pipe is located at a substantially central portion of the hollow fiber membrane element.

  The DS flows into the hollow fiber membrane 41 from the inflow side opening 41a through the DS supply port 111a, flows out from the outflow side opening 41b, and flows out through the DS discharge port 111b.

  The FS flows into the inside of the porous distribution pipe 21 through the FS supply port 110a, flows out of the hole 21a, and is supplied to the outside 42 of the hollow fiber membrane 41. The FS that has passed through the outside 42 of the hollow fiber membrane 41 flows out through the FS outlet 110b.

  Note that, here, the description has been given of a mode in which FS is supplied to the outside of the hollow fiber membrane and DS is supplied to the inside of the hollow fiber membrane, but the present invention is not limited to this. That is, DS may be supplied outside the hollow fiber membrane, and FS may be supplied inside the hollow fiber membrane.

(Pressure adjusting device)
The pressure adjusting devices 3 and 3a are devices for controlling at least one pressure of the feed solution (FS) and the draw solution (DS). The physical pressure difference between the FS and the DS is adjusted by the pressure adjusting devices 3 and 3a such that the fluctuation in the amount of water (permeated water amount) moving from the FS into the DS is reduced.

  In the forward osmosis treatment device shown in FIG. 1, the pressure adjusting device 3 includes a pressurizing device (a boosting pump) 31 for pressurizing the FS, and a control device 32 for controlling the pressure of the pressurizing device 31. The pressure adjusting device 3a includes a pressing device 31a for pressing the DS, and a control device 32a for controlling the pressure of the pressing device 31. The pressure adjusting device is not particularly limited to such a form, and may be any device that can adjust the physical pressure difference between FS and DS so that the fluctuation in the amount of permeated water is reduced.

<Method of forward osmosis treatment>
The forward osmosis treatment method of the present embodiment is a method of separating and collecting water from a feed solution (FS: liquid to be treated) by forward osmosis using a semipermeable membrane.

  In the present embodiment, the feed solution is not particularly limited as long as it is a solution containing water, and examples thereof include seawater, river water, brackish water, and drainage. Examples of the wastewater include industrial wastewater, domestic wastewater, oilfield or gasfield wastewater, and the like. The feed solution may contain undissolved components.

  The draw solution is not particularly limited as long as it is a liquid having a higher osmotic pressure than the feed solution. Examples of the draw solution include an inorganic salt solution, a sugar solution, and a gas having high solubility in water (such as ammonia and carbon dioxide). , An organic substance, a liquid containing magnetic fine particles or an organic polymer. The draw solution may contain undissolved components.

The forward osmosis treatment method of the present embodiment includes at least the following forward osmosis step.
(Forward osmosis process)
In this step, FS is caused to flow into the first chamber 11 of the forward osmosis module 1, and FS is brought into contact with the first surface 10 a of the semipermeable membrane 10, and DS is introduced into the second chamber 12 of the forward osmosis module 1. Then, the DS is brought into contact with the second surface 10 b of the semipermeable membrane 10. In this state, due to the forward osmosis phenomenon, the water contained in the FS passes through the semipermeable membrane 10 from the first surface 10a side to the second surface 10b side, and moves into the DS.

  In this step, the physical pressure difference between the FS and the DS is adjusted so that the fluctuation of the amount of water (permeated water amount) moving from the FS to the DS is reduced. Preferably, the FS is adjusted so that the fluctuation rate of the permeated water amount is 20% or less, more preferably, the fluctuation rate of the permeated water amount is 5% or less, and even more preferably, the permeated water amount is substantially constant. The physical pressure difference with DS is adjusted. Note that the osmotic pressure is not included in the physical pressure. Such adjustment can be performed by, for example, the above-described pressure adjusting device.

  The variation in the amount of permeated water is preferably a variation caused by a temperature change such as a seasonal change. In this case, by adjusting the physical pressure difference between the FS and the DS according to the temperature change, the fluctuation of the permeated water amount can be reduced in the forward osmosis treatment apparatus exposed to the temperature change. For example, when the amount of permeated water of the FO decreases due to the increase in the viscosity of the FS and the DS due to the temperature decrease, the pressure difference of the FS with respect to the DS is appropriately increased by pressurizing the FS or reducing the pressure of the DS. The amount of water can be increased. As a result, it is possible to suppress a decrease in the amount of permeated water reduced by a temperature decrease, and to reduce a change in the amount of permeated water of the FO caused by a temperature change such as a seasonal change.

  In addition, for example, the permeated water amount of the FO may gradually change due to a decrease in the performance of the semipermeable membrane after long-term operation. Also in this case, by gradually (for example, gradually and gradually) increasing the physical pressure difference of the FS with respect to the DS, it is possible to suppress a decrease in the amount of permeated water and reduce a fluctuation in the amount of permeated water during long-term operation. .

  As described above, in the forward osmosis step, the physical pressure difference between FS and DS is adjusted so that the fluctuation of the permeated water amount (the amount of water recovered in FS by DS) due to the forward osmosis treatment is reduced. The change in the amount of permeated water due to the forward osmosis treatment can be reduced without changing the supply amounts of the feed solution and the draw solution.

  Adjustment of the physical pressure difference between FS and DS is performed by pressurizing FS or pressurizing or depressurizing DS (at least one of pressurizing FS, pressurizing DS, and depressurizing DS). Can be. Preferably, by pressurizing FS or DS, the physical pressure difference between FS and DS is adjusted. When depressurizing the DS, a general FO membrane is not designed to operate at a negative pressure in design, so care must be taken to avoid negative pressure, which complicates the depressurizing operation. More preferably, the physical pressure difference between FS and DS is adjusted by pressurizing FS. When pressurizing the DS, if the pressure of the DS exceeds the osmotic pressure difference between the FS and the DS, the permeation of water by forward osmosis does not occur, so that it is necessary to provide a complicated control mechanism. When pressurizing FS, the pressure is preferably 0.05 to 1.5 MPa, more preferably 0.1 to 1.0 MPa.

  Adjustment of the physical pressure difference between FS and DS can be performed, for example, by adjusting the pressure of a pump for supplying FS or DS to the FO module. Further, for example, the present invention can be implemented by externally applying pressure to the first chamber 11 to which FS of the FO module is supplied or the second chamber 12 to which DS is supplied.

  The pressurization or depressurization of FS or DS is preferably performed continuously in order to maintain a physical pressure difference between FS and DS in order to reduce fluctuations in the amount of permeated water.

  In the forward osmosis treatment, a method of increasing the amount of permeated water by simply pressurizing FS is known, and is called PAO (pressure-assisted osmosis). However, the use of PAO to reduce fluctuations in the amount of permeated water has not been studied so far.

  FIG. 3 is a schematic diagram showing a relationship between a temperature change and a change in the DS flow rate at the outlet of the FO module when the forward osmosis treatment method according to the embodiment is implemented and when the conventional forward osmosis treatment method is implemented. It is a simple graph. In FIG. 3, “dilution DS flow rate” means the flow rate of DS (seawater) at the outlet of the FO module.

  FIG. 4 is a schematic diagram showing the relationship between the temperature change and the change in the concentration of DS at the outlet of the FO module when the forward osmosis treatment method of the present embodiment is implemented and when the conventional forward osmosis treatment method is implemented. It is a typical graph. In FIG. 4, “diluted DS concentration” means the concentration of DS (seawater) at the outlet of the FO module per FO module.

  3 and 4 are graphs of forward osmosis processing in which water moves from FS (drainage: low osmotic pressure side) to DS (seawater: high osmotic pressure side).

  Referring to FIG. 3, in the conventional forward osmosis treatment method, the amount of permeated water tends to decrease at low temperatures (dotted line graph). In contrast, in the forward osmosis treatment method of the present embodiment, a decrease in the amount of permeated water can be suppressed by increasing the pressure on the FS side or increasing the pressure on the DS side at lower temperatures. . Also, at high temperatures, by reducing the pressure on the FS side or increasing the pressure on the DS side, fluctuations in the amount of permeated water can be reduced (graph indicated by the solid line).

  Referring to FIG. 4, in the conventional forward osmosis treatment method, the amount of permeated water decreases at low temperatures, so that the concentration of DS at the outlet of the FO module tends to increase (dotted line graph). On the other hand, in the forward osmosis treatment method of the present embodiment, fluctuations in the amount of permeated water can be reduced by increasing the pressure on the FS side or increasing the pressure on the DS side at lower temperatures. . Also, at high temperatures, by reducing the pressure on the FS side or increasing the pressure on the DS side, it is possible to reduce the fluctuation of the DS concentration at the outlet of the FO module (solid line graph).

(Treatment after forward osmosis treatment)
As a method for separating and recovering the water in the DS from the DS in which the water in the FS has been recovered by the forward osmosis phenomenon by passing through the second chamber 12 of the forward osmosis module 1, for example, reverse osmosis treatment, distillation And the like.

  In the reverse osmosis (RO) process, the diluted DS discharged from the FO module 1 is boosted to a pressure higher than the osmotic pressure of the diluted DS by the booster pump and supplied to the RO module. The diluted DS supplied to the RO module can pass through the RO membrane to obtain fresh water from the diluted DS. The remaining diluted DS that has not passed through the RO membrane is concentrated, and the concentrated diluted DS can be reused as DS.

  When the draw substance contained in the DS is an inorganic salt, a low-melting substance, or the like, water in the DS may be separated and recovered by crystallization. When the draw material is a gas having high solubility in water, the water in the DS may be separated and recovered by gas release. When the draw substance is magnetic fine particles, water in the DS may be separated and recovered by magnetic separation. If the draw material is a sugar solution, the water in the DS may be separated and recovered by ion exchange.

  As described above, when the FO module is used in combination with another device such as the RO module, if the amount of permeated water of the FO fluctuates, the operating conditions of the RO module or the like designed according to the initial permeated water amount of the FO module are appropriate. This may cause a problem that the operating conditions and facilities of the RO module and the like need to be changed. However, according to the forward osmosis treatment method of the present embodiment, even when there is a fluctuation factor of the permeated water amount such as a temperature change, the fluctuation of the permeated water amount of the FO can be reduced. Does not occur.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Reference Signs List 1 forward osmosis module, 10 semipermeable membrane, 10a first surface, 10b second surface, 11 first room, 12 second room, 100 pressure vessel, 110a FS supply port, 110b FS discharge port, 111a DS supply port, 111b DS outlet, 21 perforated pipe, 21a hole, 3 pressure regulator, 31 pressurizing device (pump), 32 controller, 41 hollow fiber membrane, 41a inlet opening, 41b outlet opening, 42 hollow fiber membrane Outside.

Claims (6)

A forward osmosis step of moving the water contained in the feed solution into the draw solution by contacting the feed solution and a draw solution having a higher osmotic pressure than the feed solution through a semipermeable membrane. Including
In the forward osmosis step, a physical pressure difference between the feed solution and the draw solution is adjusted so that a fluctuation in a permeated water amount, which is an amount of water moving from the feed solution to the draw solution, is reduced. , Forward osmosis treatment method.   The forward osmosis treatment method according to claim 1, wherein the change in the amount of permeated water is a change caused by a change in temperature.   The physical pressure difference between the feed solution and the draw solution is adjusted by pressurizing the feed solution or pressurizing or depressurizing the draw solution in the forward osmosis step. Or the forward osmosis treatment method according to 2.   The forward osmosis treatment method according to any one of claims 1 to 3, wherein the semipermeable membrane is a hollow fiber membrane.   The forward osmosis treatment method according to claim 4, wherein the draw solution is supplied inside the hollow fiber membrane, and the feed solution is supplied outside the hollow fiber membrane. A forward osmosis treatment device used in the forward osmosis treatment method according to any one of claims 1 to 5,
The semipermeable membrane, and a first chamber to which the feed solution is supplied, and a second chamber to which the draw solution is supplied, wherein the first chamber and the second chamber are the semipermeable membrane. A separated forward osmosis module,
A pressure regulator for controlling the pressure of at least one of the feed solution and the draw solution,
By the pressure adjusting device, a physical pressure difference between the feed solution and the draw solution is adjusted so that a fluctuation in a permeated water amount, which is an amount of water moving from the feed solution into the draw solution, is reduced. , Forward osmosis treatment equipment.

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