JP2018143970A - Concentration system and concentration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concentration system and a concentration method capable of concentrating a high-concentration target liquid which easily causes fouling by using membrane separation. A concentration system for concentrating a target solution containing water and a component other than water, a treatment tank containing the target solution and an immersion type forward osmosis module immersed in the target solution in the treatment tank. The immersion type forward osmosis module has a semi-transparent film, one surface of the semi-transparent film is in contact with the target liquid, and the other surface of the semi-transparent film contains a draw solute. The membrane separation module, which is configured to be in contact with the solution, has a separation membrane and first and second chambers separated by the separation membrane, and a part of the draw solution is poured into the first chamber, and the second chamber is used. By flowing another part of the draw solution through the chamber and pressurizing the draw solution in the first chamber, the water contained in the draw solution in the first chamber is transferred to the draw solution in the second chamber via the separation membrane. A concentration system configured to drain the concentrated draw solution from the first chamber and drain the diluted draw solution from the second chamber. [Selection diagram] Fig. 1

Description

  The present invention relates to a concentration system and a concentration method.

  In the field of water treatment, a water treatment method using reverse osmosis (RO) is conventionally known. Reverse osmosis is a phenomenon in which water in the target liquid permeates the other side of the separation membrane through the separation membrane by artificially applying high pressure to the target liquid flowing on one side of the separation membrane. . Thereby, water is taken out from the target liquid and the target liquid is concentrated. However, in reverse osmosis, it is necessary to apply a pressure higher than the osmotic pressure of the target liquid. For this reason, in an actual RO system, there is an upper limit to the concentration of the target liquid that can be concentrated, depending on the pressurization capability of the pump.

  Therefore, in recent years, the target liquid of the same concentration (liquid with the same osmotic pressure) is flowed on both sides of the separation membrane, and the target liquid on one side of the separation membrane is pressurized, so that There has been proposed a method (hereinafter referred to as “isobaric membrane separation method”) in which water is permeated through the separation membrane to the other side of the separation membrane to concentrate the target liquid on one side of the separation membrane (hereinafter referred to as “isobaric membrane separation method”). , Patent Document 1 (see US Patent Application Publication No. 2016/0339390). According to this isobaric membrane separation method, even if the concentration of the target liquid increases, the osmotic pressure difference between the two sides of the separation membrane does not basically occur. It is also possible to concentrate a high concentration target liquid.

  However, for example, when the isobaric membrane separation method is applied to a high-concentration target liquid (waste liquid, fruit juice, milk, etc.) that is likely to cause fouling of the separation membrane and contains a large amount of scale components, fouling ( The separation membrane is likely to be clogged due to scale generation. For this reason, it is difficult to apply the isobaric membrane separation method as it is to a target liquid that easily causes fouling.

  On the other hand, it is known to perform a process using a submerged forward osmosis module on a target liquid that easily causes fouling (see, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2011-173040)). In the immersion type forward osmosis module, since the target liquid side of the semipermeable membrane is opened, it is easy to remove the scale generated in the semipermeable membrane and maintain the performance of the semipermeable membrane by a backwash operation or the like. .

  However, when a high concentration target liquid is processed by the immersion type forward osmosis module, a very high concentration draw solution (DS) having a higher osmotic pressure than the target liquid is required. The DS is normally concentrated and reused. However, in Patent Document 2, an RO module is used to reuse (reconcentrate) a high concentration DS. However, it is considered difficult to reconcentrate a high concentration DS by the RO module due to the limitation of the pressurization capacity of the pump used for the RO.

US Patent Application Publication No. 2016/0339390 JP 2011-173040 A

  Therefore, the subject of this invention is providing the concentration system and the concentration method which can concentrate the high concentration object liquid which is easy to generate | occur | produce a fouling using membrane separation.

  The inventors of the present invention concentrate a high concentration target liquid that is likely to generate fouling with an immersion type forward osmosis module, and concentrate and reuse the high concentration draw solution used at that time by an isobaric membrane separation method. As a result, the present inventors have found that the above problems can be solved, and have reached the present invention. That is, the present invention is as follows.

[1] A concentration system for concentrating a target liquid containing water and components other than water,
A treatment tank containing the target liquid, an immersion type forward osmosis module immersed in the target liquid in the treatment tank, and a membrane separation module,
The immersion type forward osmosis module has a semipermeable membrane, one surface of the semipermeable membrane is in contact with the target liquid, and the other surface of the semipermeable membrane is configured to be in contact with the draw solution containing the draw solute,
The membrane separation module has a separation membrane, and a first chamber and a second chamber partitioned by the separation membrane,
By flowing a part of the draw solution into the first chamber, flowing another part of the draw solution into the second chamber, and pressurizing the draw solution in the first chamber, water contained in the draw solution in the first chamber is discharged. A concentration system configured to transfer to a draw solution in a second chamber through a separation membrane, discharge the concentrated draw solution from the first chamber, and discharge the diluted draw solution from the second chamber.

[2] A method for concentrating a target liquid using the concentration system according to [1],
By immersing the immersion type forward osmosis module in the target liquid in the treatment tank and flowing the draw solution containing the draw solute on the opposite side of the target liquid of the semipermeable membrane, the water contained in the target liquid is semipermeable. A target liquid concentration step, which is transferred to a draw solution through a membrane;
In the membrane separation module, a part of the draw solution is allowed to flow in the first chamber, the other part of the draw solution is allowed to flow in the second chamber, and the draw solution in the first chamber is pressurized, thereby allowing the draw solution in the first chamber to be pressurized. The concentration of the water contained in the water is transferred to the draw solution in the second chamber through the separation membrane, the concentrated draw solution is discharged from the first chamber, and the diluted draw solution is discharged from the second chamber. When,
Reusing the concentrated draw solution in a submerged forward osmosis module;
Concentration method.

  ADVANTAGE OF THE INVENTION According to this invention, the concentration system and concentration method which can concentrate the high concentration target liquid which is easy to generate | occur | produce a fouling using membrane separation can be provided.

It is a mimetic diagram showing one embodiment of the concentration system of the present invention. It is a flowchart which shows each process of the concentration method of this invention.

<Concentration system>
The concentration system of this embodiment is a concentration system for concentrating a target liquid. The target liquid is a liquid containing water and components other than water. The target liquid is preferably a high-concentration liquid that easily causes fouling. Examples of such target liquids include industrial and domestic wastewater, liquids for beverages such as fruit juice and milk, river water, and the like. Examples of the fouling component (foulant) include clayey components such as silica, aluminum, iron, calcium, and manganese, organic materials such as proteins, and slime.

  With reference to FIG. 1, the concentration system of the present embodiment includes a processing tank 1 that stores a target liquid (feed solution: FS), a submerged forward osmosis module 2 that is immersed in the target liquid in the processing tank 1, A membrane separation module 3.

(Immersion type forward osmosis module)
The immersion type forward osmosis module 2 has a semipermeable membrane 21. Referring to FIG. 1, in immersion type forward osmosis module 2, one surface of semipermeable membrane 21 (the outer surface of a plurality of hollow fiber membranes) is in contact with the target liquid (FS), and the other surface of semipermeable membrane 21 is The surface (inner wall surfaces of the hollow portions of the plurality of hollow fiber membranes) is configured to contact a draw solution (DS) containing a draw solute.

  As the semipermeable membrane, for example, usually a reverse osmosis membrane (RO membrane: Reverse Osmosis Membrane), a forward osmosis membrane (FO membrane: Forward Osmosis Membrane), a nanofiltration membrane (NF membrane: Nanofiltration Membrane), an ultrafiltration membrane ( Examples thereof include a semipermeable membrane called a UF membrane (Ultrafiltration Membrane) and a microfiltration membrane (MF membrane: Microfiltration Membrane). The semipermeable membrane is preferably an RO membrane, FO membrane, NF membrane or UF membrane. Usually, the pore size of the RO membrane and the FO membrane is about 2 nm or less, the pore size of the UF membrane is about 2 to 100 nm, and the pore size of the MF membrane is about 0.1 to 10 μm. The NF membrane has a relatively low rejection rate of ions and salts among the RO membrane, and the pore size of the NF membrane is usually about 1 to 2 nm.

  The shape of the semipermeable membrane is not particularly limited, and examples thereof include a hollow fiber membrane, a spiral membrane, and a flat membrane. In FIG. 1, a thread-like semipermeable membrane (hollow fiber membrane) having a hollow portion is depicted as the semipermeable membrane 21, but is not particularly limited to such a shape. The hollow fiber membrane is advantageous in that the membrane area per module can be increased and the permeation efficiency can be increased as compared with a spiral membrane, a flat membrane, and the like. When the semipermeable membrane 21 is a hollow fiber membrane as shown in FIG. 1, the hollow fiber membrane is a hollow on both ends opening type having openings communicating with the hollow portions at both ends in order to allow the DS to flow in the hollow portions. A thread membrane is preferred.

  When the semipermeable membrane is a hollow fiber membrane, the immersion type forward osmosis module is preferably a parallel arrangement type hollow fiber membrane module (relative to the crosswind type). In the parallel arrangement type hollow fiber membrane module, a plurality of hollow fiber membranes are arranged in parallel at predetermined intervals. By using a parallel-arranged hollow fiber membrane module, the target liquid in the treatment tank can easily reach the inside of the hollow fiber membrane module, and the processing efficiency is increased. Such a parallel-arranged hollow fiber membrane module can be manufactured by a conventionally known method, for example, by a method as disclosed in JP-A-10-192661. .

  In FIG. 1, an immersion type forward osmosis module 2 is the parallel arrangement type hollow fiber membrane module. The immersion type forward osmosis module 2 includes fixing resins 22a and 22b for fixing a plurality of hollow fiber membranes at predetermined intervals at both ends of the hollow fiber membrane (semipermeable membrane 21). The fixing resin 22a has a distribution chamber that communicates with the hollow portions of the plurality of hollow fiber membranes through an opening at one end of the hollow fiber membrane. The distribution chamber has an inlet. The fixing resin 22b has a collecting chamber that communicates with the hollow portions of the plurality of hollow fiber membranes through an opening at one end of the hollow fiber membrane. The gathering chamber has an outlet. Therefore, DS can flow into the hollow part of the hollow fiber membrane by allowing DS to flow into the inlet of the fixing resin 22a, and the DS diluted by forward osmosis by passing through the hollow part of the hollow fiber membrane, It is discharged from the outlet of the fixed resin 22b.

  Although it does not specifically limit as a material which comprises a semipermeable membrane, For example, a cellulose resin, a polysulfone resin, a polyamide resin etc. are mentioned. The semipermeable membrane is preferably composed of a material containing at least one of a cellulose resin and a sulfonated polysulfone resin.

  The cellulose resin is preferably a cellulose acetate resin. Cellulose acetate resin is resistant to chlorine, which is a bactericidal agent, and has a feature that it can suppress the growth of microorganisms. The cellulose acetate 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 resin is preferably a sulfonated polyethersulfone.

(Membrane separation module)
The membrane separation module 3 includes a separation membrane 30 and a first chamber 31 and a second chamber 32 partitioned by the separation membrane 30.

  In the membrane separation module 3, a part of DS (DS diluted by the immersion type forward osmosis module 2) is allowed to flow in the first chamber 31, and another part of the DS is allowed to flow in the second chamber 32. The DS in 31 is pressurized. Thereby, the water contained in the DS in the first chamber 31 is transferred to the DS in the second chamber 32 through the separation membrane. The concentrated DS is discharged from the first chamber 31, and the diluted DS is discharged from the second chamber 32.

  Pressurization (pressure increase) of the DS in the first chamber 31 can be performed by pressurizing the first chamber 31 from the outside (FIG. 1). In addition to the pump 4 (liquid feeding pump), a pressurizing pump is installed in the flow path near the upstream side of the first chamber 31, and the DS in the first chamber 31 is pressurized by this pressurizing pump. Also good.

  As the separation membrane 30, a membrane similar to the semipermeable membrane 21 of the forward osmosis module 2 can be used. For example, a reverse osmosis membrane (RO membrane), a forward osmosis membrane (FO membrane), a nanofiltration membrane ( NF membranes), ultrafiltration membranes (UF membranes), and membranes called microfiltration membranes (MF membranes). The separation membrane 30 is preferably an RO membrane, FO membrane, NF membrane, or UF membrane. When an RO membrane, FO membrane, NF membrane, or UF membrane is used as the separation membrane 30, the pressure applied to the DS in the first chamber 31 is preferably 0.5 to 6.5 MPa.

  The shape of the separation membrane is the same as that of the semipermeable membrane 21 of the forward osmosis module 2, and examples thereof include a hollow fiber membrane, a spiral membrane, and a flat membrane. In FIG. 1, a flat membrane is simplified as the separation membrane 30, but is not particularly limited to such a shape. The hollow fiber membrane is advantageous in that the membrane area per module can be increased and the permeation efficiency can be increased as compared with a spiral membrane, a flat membrane, and the like.

  When the separation membrane is a hollow fiber membrane, the outside of the hollow fiber membrane is usually the first chamber, and the inside of the hollow fiber membrane (inside the hollow portion) is the second chamber. This is because even if the fluid inside the hollow fiber membrane is pressurized, the pressure loss is large, so that the pressurization does not work sufficiently.

<Concentration method>
The concentration method of the present embodiment is a method for concentrating a target liquid using the above-described concentration system. Referring to FIG. 2, the concentration method of the present invention includes a target liquid concentration step (forward osmosis step), a draw solution concentration step (isobaric membrane separation step), and a draw solution reuse step described below. Including at least. In addition, you may advance these each process simultaneously in said concentration system.

(Target liquid concentration process)
Referring to FIG. 1, in the target liquid concentration process (forward osmosis process), the immersion type forward osmosis module 2 is immersed in the target liquid (FS) in the treatment tank 1 and is opposite to the target liquid in the semipermeable membrane 21. By flowing a draw solution (DS) containing a draw solute on the side (hollow part of the hollow fiber membrane), water contained in the target liquid is moved to the DS through the semipermeable membrane 21. Thereby, the target liquid is concentrated.

  The target liquid (FS) may be processed in a continuous manner or a batch manner. That is, the concentrated FS may be collected while continuously supplying FS to the treatment tank 1, or the target liquid concentration process is performed by filling the treatment tank 1 with a predetermined amount of FS, and for a predetermined time. You may repeat operation which collect | recovers all the target liquid concentrated in the processing tank 1 after completion | finish of a target liquid concentration process.

  In the target liquid concentration step, the foulant adhering to the semipermeable membrane, the clogged foulant, etc. are removed by performing a physical operation such as backwashing or vibration on the semipermeable membrane 21, The performance of the permeable membrane can be maintained (recovered). Further, as shown in FIG. 1, bubbles 1 a may be generated in the target liquid by blowing out gas from an air blowing port (not shown) provided in the upper part of the bottom wall of the processing tank 1. Thereby, the bubble 1a stirs the target liquid and also shakes the hollow fiber membrane, thereby preventing foulant from adhering to the hollow fiber membrane and clogging of the hollow fiber membrane, and the performance of the hollow fiber membrane. The decrease can be suppressed.

  A part of the diluted DS by the above process is concentrated by the draw solution concentration process. The DS concentrated in the draw solution concentration step is reused in the immersion type forward osmosis module 2 in the draw solution reuse step.

  The osmotic pressure of the draw solution (DS) is preferably 0.5 to 20 MPa, although it depends on the molecular weight of the solute. Examples of the draw solute include saccharides, proteins, and synthetic polymers. Since draw solutes (especially low molecular draw solutes) may penetrate into the target solution, it is desirable to select the type of draw solute to be used in consideration of this point. For example, when the target liquid is a liquid for beverages such as fruit juice, it is preferable to select a saccharide or the like as the draw solute because salt may be used when the salt is used as the draw solute.

(Draw solution concentration process)
In the draw solution concentration step (isobaric membrane separation step), in the membrane separation module 3, a part of DS (the DS after being diluted in the target liquid concentration step) is allowed to flow in the first chamber 31, and the DS is passed to the second chamber 32. The other part is flowed to pressurize the DS in the first chamber 31. Thereby, the water contained in the DS in the first chamber 31 is transferred to the DS in the second chamber 32 through the separation membrane. Therefore, the DS in the first chamber 31 is concentrated, and the concentrated DS is discharged from the first chamber 31. On the other hand, the DS in the second chamber 32 is diluted, and the diluted DS is discharged from the second chamber 32.

  Here, in the membrane separation module 3, since the DS flowing into one side (first chamber 31) and the other side (second chamber 32) of the separation membrane 30 is the same, the osmotic pressure is basically equal. Therefore, unlike the RO method, a high pressure for causing reverse osmosis against a high osmotic pressure difference is not necessary, and a high concentration DS can be concentrated by a relatively low pressure (one DS). Part can be concentrated and other part of DS can be diluted).

  However, the DS flowing to one side (first chamber 31) of the separation membrane 30 and the DS flowing to the other side (second chamber 32) do not necessarily have to be the same liquid. If the osmotic pressure difference (absolute value) between the DS flowing into the first chamber 31 and the DS flowing into the second chamber 32 is about 10% or less of the pressure for pressurizing the first chamber, the membrane separation step can be performed. It is.

  The membrane separation process may be a one-stage process using one membrane separation module 3 as shown in FIG. 1, or may be a multi-stage process using a plurality of membrane separation modules. . In the membrane separation process, the difference in the osmotic pressure of the DS on both sides of the final separation membrane does not exceed the pressure of the pressure applied to the first chamber of the membrane separation module, and therefore the one-stage process (one membrane separation module) There is a limit to the DS concentration rate. For this reason, it is possible to further increase the DS concentration rate by making the membrane separation step into two or more steps.

(Draw solution reuse process)
In the draw solution reuse step, the concentrated draw solution is reused in the immersion forward osmosis module 2. Specifically, referring to FIG. 1, in the membrane separation step, the concentrated DS discharged from the first chamber 31 of the membrane separation module 3 is converted into an inlet ( It is supplied as DS into the hollow part of the hollow fiber membrane (on the side opposite to the target liquid FS of the semipermeable membrane 21) via the collecting chamber.

(Other processes)
In the draw solution concentration step, the diluted DS discharged from the second chamber 32 may be concentrated using a reverse osmosis (RO) method. The diluted DS discharged from the second chamber 32 is a liquid obtained by further diluting the DS diluted in the target liquid concentration step (primary dilution DS) (secondary dilution DS), and is more than the primary dilution DS. Low osmotic pressure. Therefore, even when the osmotic pressure of the primary dilution DS is high and exceeds the osmotic pressure that can be concentrated by the RO method (for example, about 1 to 6 MPa), the osmotic pressure of the secondary dilution DS is concentrated by the RO method. Can be concentrated by the RO method.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. 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.

  DESCRIPTION OF SYMBOLS 1 Treatment tank, 1a bubble, 2 immersion type forward osmosis module, 21 semipermeable membrane, 22a, 22b fixing resin, 3 membrane separation module, 30 separation membrane, 31 1st chamber, 32 2nd chamber, 4 pumps.

Claims (2)

A concentration system for concentrating a target liquid containing water and components other than water,
A treatment tank containing the target liquid, a submerged forward osmosis module immersed in the target liquid in the treatment tank, and a membrane separation module,
The immersion type forward osmosis module has a semipermeable membrane, and one surface of the semipermeable membrane is in contact with the target liquid, and the other surface of the semipermeable membrane is in contact with a draw solution containing a draw solute. And
The membrane separation module includes a separation membrane, and a first chamber and a second chamber partitioned by the separation membrane,
By flowing a part of the draw solution into the first chamber, flowing another part of the draw solution into the second chamber, and pressurizing the draw solution in the first chamber, Water contained in the draw solution is transferred to the draw solution in the second chamber through the separation membrane, the concentrated draw solution is discharged from the first chamber, and the diluted draw solution is discharged from the first chamber. Configured to drain from two chambers,
Concentration system. A method for concentrating the target liquid using the concentration system according to claim 1,
Included in the target liquid by immersing the immersion type forward osmosis module in the target liquid in a treatment tank and flowing a draw solution containing a draw solute on the side opposite to the target liquid of the semipermeable membrane. A target liquid concentration step of transferring the water to be drawn to the draw solution through the semipermeable membrane;
In the membrane separation module, by flowing a part of the draw solution into the first chamber, flowing another part of the draw solution into the second chamber, and pressurizing the draw solution in the first chamber The water contained in the draw solution in the first chamber is transferred to the draw solution in the second chamber through the separation membrane, and the concentrated draw solution is discharged from the first chamber and diluted. A draw solution concentration step of discharging the draw solution from the second chamber;
Reusing the concentrated draw solution in the immersion forward osmosis module;
Concentration method.

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