JP6521077B2 - Water treatment method and water treatment system - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment system.

  Forward osmosis (FO) means a solution (draw solution) with high concentration (high osmotic pressure) of water on the low concentration (low osmotic pressure) side of treated water (feed solution) through a semipermeable membrane It is a phenomenon that moves toward. On the other hand, in the field of water treatment, a water treatment method using a reverse osmosis (RO) process is conventionally known. The reverse osmosis step is a step of moving water from the high concentration treated water to the low concentration solution side contrary to the forward osmosis by artificially applying a strong pressure.

  However, the reverse osmosis process requires a strong pressure, so the energy consumption is very high and the energy efficiency is low. Therefore, in order to increase the energy efficiency of water treatment, a water treatment system using a forward osmosis phenomenon that does not require manual pressure has been proposed in recent years. For example, Japanese Patent Application Laid-Open No. 2014-184402 (Patent Document 1) discloses a forward osmosis water treatment system using a hollow fiber type semipermeable membrane.

  Moreover, although various things are known as a draw solution for forward osmosis used for a water treatment system, for example, it is highly responsive to temperature as a draw solution in Unexamined-Japanese-Patent No. 2015-47541 (patent document 2) It is disclosed to use relatively high viscosity solutions such as molecules.

JP, 2014-184402, A JP, 2015-47541, A

  Treated water such as seawater usually contains scale components. Therefore, when the water to be treated is allowed to flow into the hollow portion of the hollow fiber type semipermeable membrane and the high viscosity draw solution is allowed to flow to the outside of the hollow fiber type semipermeable membrane, the scale component is formed on the inner wall of the hollow portion of the hollow fiber type semipermeable membrane. Is easy to deposit. On the other hand, since the flow velocity is relatively high on the outside of the hollow fiber type semipermeable membrane, even if the scale component adheres to the outer periphery of the hollow fiber type semipermeable membrane, it easily peels off, and the scale component does not easily deposit. From such reasons, it is necessary to flow the water to be treated to the outer peripheral surface side of the hollow fiber type semipermeable membrane and to flow the draw solution into the hollow portion of the hollow fiber type semipermeable membrane.

  However, when flowing a high viscosity draw solution such as a temperature responsive polymer disclosed in Patent Document 2 into the hollow portion of the existing hollow fiber semipermeable membrane for forward osmosis, the pressure loss is large. Therefore, the flow rate of the draw solution required to maintain a sufficient effective osmotic pressure difference between the inside and the outside of the hollow fiber type semipermeable membrane can not be secured, and the efficiency of water treatment is lowered.

  An object of the present invention is to provide a water treatment method and a water treatment system capable of improving the efficiency of water treatment when using a high viscosity draw solution in view of the above-mentioned problems.

[1] A water treatment method for obtaining purified water from treated water containing water and components other than water,
The water in the water to be treated is moved into the first draw solution by bringing the water to be treated into contact with the first draw solution having an osmotic pressure higher than the water to be treated via the first semipermeable membrane. 1 Forward penetration process,
The first draw solution diluted in the first forward osmosis step is brought into contact with the second draw solution having a higher osmotic pressure than the diluted first draw solution through the second semipermeable membrane. A second forward osmosis step of transferring water in the first draw solution into the second draw solution;
Including a water producing step of obtaining purified water from the second draw solution diluted in the second forward osmosis step;
Reusing the first draw solution concentrated in the second forward osmosis step in the first forward osmosis step;
Reuse the second draw solution concentrated in the water making process in the second forward osmosis process,
In the first forward osmosis step, the first semipermeable membrane is a hollow fiber type semipermeable membrane, and water to be treated is brought into contact with the outer peripheral surface of the hollow fiber type semipermeable membrane, and inside the hollow portion of the hollow fiber type semipermeable membrane Water treatment method, flowing the first draw solution.

  [2] The water treatment method according to [1], wherein the second draw solution contains a temperature responsive polymer having a property of changing hydrophilicity with a predetermined temperature as a critical point.

  [3] The first forward osmosis step is carried out in the state in which the immersion type hollow fiber membrane module in which the hollow fiber type semipermeable membrane is exposed is immersed in the water to be treated in the treatment tank, to [1] or [2] Water treatment method described.

  [4] The water treatment method according to any one of [1] to [3], wherein the water to be treated is brine concentrated by reverse osmosis treatment.

  [5] In the second forward osmosis step, the second semipermeable membrane is a hollow fiber semipermeable membrane, the second draw solution is brought into contact with the outer peripheral surface of the hollow fiber semipermeable membrane, and the hollow fiber semipermeable membrane The water treatment method according to any one of [1] to [4], wherein the first draw solution diluted in the first forward osmosis step is allowed to flow in the hollow portion of

[6] A water treatment system for obtaining purified water from treated water containing water and components other than water,
The water in the water to be treated is moved into the first draw solution by bringing the water to be treated into contact with the first draw solution having an osmotic pressure higher than the water to be treated via the first semipermeable membrane. 1 positive penetration module,
The first draw solution diluted in the first forward osmosis module is brought into contact with the second draw solution having a higher osmotic pressure than the diluted first draw solution through the second semipermeable membrane. A second forward osmosis module to move water in the one draw solution into the second draw solution;
Including a freshwater generator for obtaining purified water from the second draw solution diluted in the second forward osmosis module;
Reusing the first draw solution concentrated in the second forward osmosis module in the first forward osmosis module;
The second draw solution concentrated in the fresh water generator is reused in the second forward osmosis module,
In the first forward osmosis module, the first semipermeable membrane is a hollow fiber type semipermeable membrane, and water to be treated is brought into contact with the outer peripheral surface of the hollow fiber type semipermeable membrane, and in the hollow portion of the hollow fiber type semipermeable membrane Water treatment method, flowing the first draw solution.

  [7] The water treatment system according to [6], wherein the second draw solution contains a temperature responsive polymer having a property of changing hydrophilicity with a predetermined temperature as a critical point.

  ADVANTAGE OF THE INVENTION According to this invention, when using a high viscosity draw solution, the water treatment method and water treatment system which can improve the efficiency of water treatment can be provided.

It is a schematic diagram which shows an example of the water treatment method (water treatment system) of this invention. It is a partial transmission perspective view showing roughly an example of composition of an immersion type hollow fiber membrane module. It is a schematic diagram which shows an example of the conventional water treatment method (water treatment system).

  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.

<Water treatment method>
The water treatment method of this embodiment is a method of obtaining purified water from treated water, and includes at least a first forward osmosis step, a second forward osmosis step, and a fresh water generation step.

  In the present embodiment, the first forward osmosis step and the second forward osmosis step are combined, and by using a high viscosity draw solution in the second forward osmosis step, hollow fiber type semipermeability in the first forward osmosis step is achieved. Since the pressure loss by the membrane is reduced, the flow rate of the draw solution flowing in the hollow portion of the hollow fiber type semipermeable membrane can be increased. As a result, the flow rate necessary to maintain a sufficient effective osmotic pressure difference between the inside and the outside of the hollow fiber type semipermeable membrane can be secured, and a high viscosity draw solution is obtained in the water treatment process until finally obtaining purified water. Even when used, the efficiency of water treatment can be improved.

  On the other hand, conventionally, as shown in FIG. 3, since the forward osmosis process is one step, when the water 203 to be treated containing the scale component is flowed into the hollow portion of the hollow fiber type semipermeable membrane 1, the hollow fiber type There is a problem that the scale component is easily deposited on the inner wall of the hollow portion of the permeable membrane. Therefore, it is desirable that the water to be treated be brought into contact with the outer peripheral surface side of the hollow fiber type semipermeable membrane which has a relatively high flow velocity and in which the scale component is not easily deposited.

  However, when a high viscosity draw solution (second draw solution) 206 is allowed to flow in the hollow portion of the hollow fiber type semipermeable membrane 1, pressure is applied to the draw solution 206 by the pump 4 because the pressure loss is large. However, the flow rate of the draw solution 206 flowing in the hollow portion decreases. Generally, when the flow rate of the draw solution flowing in the hollow portion of the hollow fiber type semipermeable membrane decreases, the amount of water permeating to the draw solution side increases while the draw solution flows in the hollow portion. As a result, the overall osmotic pressure of the draw solution flowing in the hollow portion is reduced, and the osmotic pressure difference between the draw solution and the water to be treated (feed solution) is reduced, whereby the water recovery efficiency is reduced. When a high viscosity draw solution such as a temperature responsive polymer is allowed to flow in the hollow portion of the hollow fiber type semipermeable membrane, the pressure loss is large, the necessary draw solution flow rate can not be secured, and the efficiency of water treatment decreases. There was a problem that you

  In addition, in FIG. 3, the to-be-processed water 203 is the brine 201 concentrated by the reverse osmosis process. That is, the brine 201 flows into the first chamber 101 of the reverse osmosis module 10, and the water in the brine 201 moves to the second chamber 102 through the semipermeable membrane 100 by the reverse osmosis to become the produced water 202. On the other hand, the brine 201 is concentrated in the first chamber 101 to be treated water 203. The water to be treated in the present embodiment also includes salt water concentrated by such reverse osmosis treatment.

Hereinafter, each process of the water treatment method of this embodiment is demonstrated with reference to FIG.
(First positive penetration process)
In the first forward osmosis step, the water in the water to be treated is firstly contacted by bringing the water to be treated into contact with the first draw solution having an osmotic pressure higher than that of the water to be treated via the first semipermeable membrane. It is a process of moving into a draw solution.

  Referring to FIG. 1, the first semipermeable membrane 1 is a hollow fiber type semipermeable membrane (hollow fiber membrane), and the first forward osmosis module 11 is an immersion type hollow fiber membrane in which the hollow fiber type semipermeable membrane 1 is exposed. It is a module. In the first penetration step, the outer peripheral surface of the hollow fiber type semipermeable membrane 1 is brought into contact with the water to be treated 203 by immersing the immersion type hollow fiber membrane module in the water to be treated in the treatment tank 3 The first draw solution 204 is flowed into the hollow portion of the semipermeable membrane 1.

  Water to be treated is a liquid containing water and components other than water. Examples of the water to be treated include seawater, brackish water, brine, associated well water, lake water, river water, industrial wastewater and the like. When the water to be treated is a solution having a high salt concentration, the evaporation residue concentration (TDS) of the water to be treated is preferably 0.7 to 14% by mass. The water to be treated is preferably brine concentrated by reverse osmosis treatment. In this case, the TDS of the water to be treated is preferably 0.5 to 14% by mass.

  The first draw solution is not particularly limited as long as it is a solution having an osmotic pressure higher than that of the water to be treated, but it reduces the pressure loss of the hollow fiber semipermeable membrane in the first forward osmosis step to reduce the pressure of the first draw solution. From the viewpoint of securing a sufficient flow rate, a solution having a viscosity lower than that of the second draw solution is preferable. Examples of the solute of the first draw solution include inorganic salts such as sodium chloride, potassium chloride, potassium nitrate and sodium hydrogencarbonate, sugars such as glucose and fructose, ammonium carbonate, ammonium hydrogencarbonate and butanol.

  Referring to FIG. 2, the immersion type hollow fiber membrane module 11 is provided with the above-described straight type hollow fiber membrane element 2 (a bundle of hollow fiber type semipermeable membranes 1). In addition, the immersion type hollow fiber membrane module 11 is provided with fixing resins 21 and 22 for fixing the plurality of hollow fiber type semipermeable membranes 1 at predetermined intervals at both ends of the hollow fiber membrane element 2. In addition, in order to maintain the whole shape of the immersion type hollow fiber membrane module 11, two fixed resin 21 and 22 may be mutually connected by the support body which is not shown in figure.

  The fixed resin 21 is connected to the distribution chamber 21 a having an internal space communicating with the hollow portions of the plurality of hollow fiber type semipermeable membranes 1 through the opening at one end of the hollow fiber type semipermeable membrane 1. The distribution chamber 21a has an inlet 21b communicating with the inner space thereof. Accordingly, the inflow port 21 b communicates with the hollow portions of the plurality of hollow fiber semi-permeable membranes 1 at one end of the hollow fiber membrane element 2.

  The fixed resin 22 is connected to the collecting chamber 22 a having an internal space communicating with the hollow portions of the plurality of hollow fiber type semipermeable membranes 1 through the opening of the other end of the hollow fiber type semipermeable membrane 1. . The collecting chamber 22a has an outlet 22b communicating with the inner space thereof. Accordingly, the outlet 22 b communicates with the hollow portions of the plurality of hollow fiber semi-permeable membranes 1 at the other end of the hollow fiber membrane element 2.

  As shown in FIG. 2, in the immersion type hollow fiber membrane module 11, the plurality of hollow fiber type semipermeable membranes 1 are exposed. The plurality of hollow fiber type semipermeable membranes 1 may have at least a part of the outer surface exposed. In FIG. 1, one of the hollow fiber type semipermeable membranes 1 drawn in the fixed resins 21 and 22 is shown. The part is covered with resin and not exposed, but the other part of the hollow fiber type semipermeable membrane 1 is exposed. In FIG. 2, the fixed resins 21 and 22, the distribution chamber 21 a, and the collecting chamber 22 a are drawn through, but it is not necessary to be actually transparent.

  Such a straight type submerged hollow fiber membrane module can be manufactured using a conventionally known method, and can be manufactured by a method disclosed in, for example, JP-A-10-192661.

  The inner diameter of the hollow fiber semipermeable membrane 1 of the present invention is not particularly limited, but is preferably 50 to 250 μm, and more preferably 80 to 200 μm.

The hollow ratio [(inner diameter / outer diameter) ² × 100 (%)] of the hollow fiber type semipermeable membrane is preferably 30 to 60%, more preferably 35 to 55%. The hollow ratio is the ratio of the area of the hollow portion in the cross section of the hollow fiber type semipermeable membrane.

  The length of the hollow fiber type semipermeable membrane is not particularly limited, but is preferably 15 to 400 cm, more preferably 20 to 350 cm.

  The hollow fiber type semipermeable membrane preferably has a pore diameter of 100 nm or less. As such hollow fiber type semipermeable membrane, for example, reverse osmosis membrane (RO membrane: Reverse Osmosis Membrane), forward osmosis membrane (FO membrane: Forward Osmosis Membrane), nanofiltration membrane (NF membrane: Nanofiltration Membrane), limit What is called an ultrafiltration membrane (UF membrane: Ultrafiltration Membrane) is mentioned.

  Generally, the pore size of RO and FO membranes is less than or equal to about 2 nm and the pore size of UF membranes is about 2 to 100 nm. The NF membrane is a RO membrane having a relatively low rejection rate of ions and salts, and the pore diameter of the NF membrane is usually about 1 to 2 nm.

  Although it does not specifically limit as a material which comprises the hollow fiber type | mold semipermeable membrane 1, For example, a cellulose resin, a polysulfone type resin, a polyamide-type resin etc. are mentioned. The hollow fiber type semipermeable membrane is preferably made of a material containing at least one of a cellulose resin and a polysulfone resin.

  The cellulose-based resin is preferably a cellulose acetate-based resin. Cellulose acetate based resins are resistant to chlorine, which is a bactericidal agent, and are characterized in that they can suppress the growth of microorganisms. The cellulose acetate resin is preferably cellulose acetate, and from the viewpoint of durability, more preferably cellulose triacetate.

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

  An example of a specific hollow fiber type semipermeable membrane is a membrane having a single layer structure which is entirely composed of a cellulose-based resin. However, the single layer structure mentioned here does not have to be a uniform film throughout the layer, and for example, as disclosed in Patent Document 1, it has a dense layer near the outer peripheral surface, and this dense layer is substantially It is preferable that the separation active layer defines the pore diameter of the hollow fiber type semipermeable membrane.

  As another example of a specific hollow fiber type semipermeable membrane, a dense layer made of polyphenylene resin (for example, sulfonated polyether sulfone) is formed on the outer peripheral surface of a support layer (for example, a layer made of polyphenylene oxide) 2 Layered films can be mentioned. Another example is a film having a two-layer structure having a dense layer made of a polyamide-based resin on the outer peripheral surface of a support layer (for example, a layer made of polysulfone or polyethersulfone).

(2nd positive penetration process)
The water treatment method of the present embodiment includes a second forward osmosis step subsequent to the first forward osmosis step. In the second forward osmosis step, the first draw solution diluted in the first forward osmosis step and the second draw solution having a higher osmotic pressure than the first drawn solution diluted through the second semipermeable membrane This is a step of moving the water in the first draw solution into the second draw solution by bringing into contact with each other.

  That is, the first draw solution 205 diluted in the first forward osmosis process flows into the first chamber 121 of the second forward osmosis module 12. By forward osmosis, the water in the first draw solution 205 flows through the second semipermeable membrane 120 into the second chamber 122 (having a higher osmotic pressure than the diluted first draw solution 205). Move to the solution 206 side. The first draw solution 204 concentrated in the second forward osmosis step is reused in the first forward osmosis step.

  Although the second semipermeable membrane is not particularly limited in the second forward osmosis step, when the second semipermeable membrane is a hollow fiber semipermeable membrane, the second draw solution is applied to the outer peripheral surface of the hollow fiber semipermeable membrane. It is preferable that the first draw solution diluted in the first forward osmosis step is made to flow into the hollow portion of the hollow fiber type semipermeable membrane while making contact. If a high viscosity second draw solution is allowed to flow into the hollow portion of the hollow fiber type semipermeable membrane, a sufficient flow rate can not be flowed due to pressure loss, and the efficiency of water treatment may decrease.

  The second draw solution is not particularly limited as long as it has a higher osmotic pressure than the diluted first draw solution, but preferably contains a temperature responsive polymer. The temperature responsive polymer is a polymer having a property (temperature responsive) in which the hydrophilicity changes with a predetermined temperature as a critical point. The temperature response is, in other words, the property of becoming hydrophilic or hydrophobic depending on the temperature. Here, the change in hydrophilicity is preferably reversible. In this case, the temperature responsive polymer can be dissolved in water or phase separated from water by adjusting the temperature.

  The temperature responsive polymer is a polymer composed of a plurality of structural units derived from a monomer, and preferably has a hydrophilic group in the side chain.

  The temperature responsive polymers include a lower critical solution temperature (LCST) type and an upper critical solution temperature (UCST) type. In the LCST type, when a polymer dissolved in low temperature water reaches a temperature higher than its own temperature (LCST), it separates from water. Conversely, in the UCST type, when the polymer dissolved in high temperature water becomes lower than the inherent temperature (UCST) of the polymer, it separates from water (see Sugihara et al. Development, see SEN'I GAKKAISHI (Fiber and Industrial), Vol. 62, No. 8, 2006). When the semipermeable membrane is made of a material that is easily deteriorated at high temperature, it is preferable to contact the low temperature water in which the temperature responsive polymer is dissolved, so the temperature responsive polymer used in the present invention is The LCST type is preferred. Moreover, when using the semipermeable membrane comprised with the raw material which does not deteriorate easily by high temperature, a UCST type other than LCST type can also be used.

  As a hydrophilic group, a hydroxyl group, a carboxyl group, an acetyl group, an aldehyde group, an ether bond, an ester bond is mentioned, for example. The hydrophilic group is preferably at least one selected from these.

  The temperature responsive polymer preferably has at least one hydrophilic group in at least a part or all of the structural units. In addition, the temperature responsive polymer may have a hydrophobic group in a part of structural units while having a hydrophilic group. In addition, in order for a thermoresponsive polymer to have thermoresponsiveness, it is considered that the balance between the hydrophilic group and the hydrophobic group contained in the molecule is important.

  Specific examples of the temperature responsive polymer include polyvinyl ether polymers, polyvinyl acetate polymers, and (meth) acrylic acid polymers.

  The viscosity of the second draw solution is preferably 0.50 Pa · s or less, more preferably 0.20 Pa · s or less. When such a high viscosity solution is allowed to flow into the hollow portion of the hollow fiber type semipermeable membrane as a draw solution, the efficiency of forward osmosis treatment tends to decrease, so the water treatment method of the present embodiment is particularly useful.

  The osmotic pressure of the second draw solution is preferably 0.5 to 20 MPa, more preferably 1 to 18 MPa, still more preferably 2 to 15 MPa, although it depends on the molecular weight of the solute (temperature responsive polymer), etc. It is.

(Water-making process)
The water treatment method of this embodiment further includes a water making process after the second forward osmosis process. In the fresh water production process, purified water is obtained from the second draw solution diluted in the second forward osmosis process.

  When the draw solute of the second draw solution is a temperature responsive polymer, the draw solute included in the second draw solution by flowing the second draw solution into another chamber and changing the temperature in the chamber. (The thermoresponsive polymer) can be separated from water.

  In this case, the temperature responsive polymer can be easily separated from water and recovered only by changing the temperature of the second draw solution. In addition, since the temperature responsive polymer has high separability from water, it is advantageous in that purified water with high purity can be obtained. Furthermore, the draw solute after recovery can be easily reused (redissolved in a draw solution or the like). In this manner, the second draw solution concentrated in the water making process can be reused in the second forward osmosis process.

  Note that the draw solute recovery process may be divided into multiple stages and repeated so as to obtain pure water, and after the draw solute recovery, a process may be performed to further improve the quality of the purified water.

<Water treatment system>
The water treatment system of the present embodiment is a system for obtaining purified water from treated water containing water and components other than water. Referring to FIG. 1, the water treatment system includes at least a first forward osmosis module 11, a second forward osmosis module 12, and a fresh water generator 13.

  In the first forward osmosis module 11, the to-be-treated water 203 and the first draw solution 204 having an osmotic pressure higher than the to-be-treated water 203 are separated via the first semipermeable membrane 1 (hollow fiber type semipermeable membrane) The contact causes the water in the treated water to move into the first draw solution. Specifically, the water to be treated 203 is brought into contact with the outer peripheral surface of the hollow fiber semipermeable membrane 1, and the first draw solution 204 is allowed to flow in the hollow portion of the hollow fiber semipermeable membrane 1.

  In the second forward osmosis module 12, the first draw solution 205 diluted in the first forward osmosis module 11 and the second draw solution 206 having a higher osmotic pressure than the diluted first draw solution 205 are The contact through the semipermeable membrane 120 moves the water in the first draw solution 205 into the second draw solution 206. The first draw solution 204 concentrated in the second forward osmosis module 12 is reused in the first forward osmosis module 11.

  In the fresh water generator 13, the purified water 208 is obtained from the second draw solution 207 diluted by the second forward osmosis module 12. The second draw solution 206 concentrated by the fresh water generator 13 is reused in the second forward osmosis module 12.

  Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to these examples.

[Examples 1 to 16]
As Examples 1 to 16, it is assumed that the water treatment method includes the two-step forward osmosis process (first forward osmosis process and second forward osmosis process) described in the above embodiment under the following conditions and the water making process. The simulation calculation of the amount of water production described later was performed.

(First positive penetration process)
Immersion type hollow fiber membrane module (hollow fiber membrane arrangement: straight)
Diameter of hollow fiber membrane element: 10 inches Packing ratio of hollow fiber membrane: 50%
Effective length of hollow fiber membrane: 120 cm
Water to be treated: 5000 ppm NaCl aqueous solution First draw solution: 10 mass% NaCl aqueous solution The simulation was carried out so that the injection pressure of the first draw solution into the hollow portion of the hollow fiber semipermeable membrane was 0.2 MPa.

(2nd positive penetration process)
Hollow fiber membrane module (with crosswind type housing)
Diameter of hollow fiber membrane element: 10 inches Packing ratio of hollow fiber membrane: 50%
Effective length of hollow fiber membrane: 115 cm
Water to be treated: First draw solution diluted in the first treatment step Second draw solution: 85% by mass of poly (ethylene oxide) / poly (propylene oxide) / poly (ethylene oxide) triblock copolymer aqueous solution The simulation was performed by adjusting the operating conditions such that the outlet concentration was 10% by mass and the flow pressure loss of the second draw solution was 0.075 MPa.

  As the second draw solution, a poly (ethylene oxide) / poly (propylene oxide) / poly (ethylene oxide) triblock copolymer aqueous solution having a concentration of 85% by mass was assumed. The viscosity of the second draw solution was assumed to be 0.200 Pa · s. The osmotic pressure of the second draw solution was 15.4 MPa. The osmotic pressure is 28 bar (2.8 MPa) of seawater having a sodium chloride concentration of 40% by mass, and a relational expression is created with reference to a curve showing the relationship between the concentration of the pluronic and the osmotic pressure, and the relational expression It is an osmotic pressure in case the density | concentration of the calculated | required poly (ethylene oxide) / poly (propylene oxide) / poly (ethylene oxide) triblock copolymer aqueous solution is 85 mass%.

The hollow fiber type semipermeable membrane is classified into an FO membrane having a dense layer thickness of about 2 μm, a pressure difference water permeability of 150 (L / m ² / day) and a pressure difference salt removal rate of 99.6%. used. The above-mentioned filling factor is [π (outer diameter / 2) ² × (number of fillings)] / [π (module inner diameter / 2) ² ].

  The pressure difference water permeability and the pressure difference salt removal rate are, for example, parameters of the hollow fiber semi-permeable membrane measured as follows.

[Pressure differential permeability]
The hollow fiber type semipermeable membrane was bundled and inserted into a plastic sleeve, and then a thermosetting resin was injected into the sleeve, cured and sealed. The open surface of the hollow fiber type semipermeable membrane is obtained by cutting the end of the hollow fiber type semipermeable membrane cured with a thermosetting resin, and the membrane area based on the outer diameter is for evaluation of about 0.1 m ² A module was made. This evaluation module was connected to a membrane performance test apparatus consisting of a feed water tank and a pump, and the performance was evaluated. Specifically, a feed aqueous solution having a sodium chloride concentration of 1500 mg / L is filtered at a temperature of 25 ° C. and a pressure of 1.5 MPa from the outside to the inside of the hollow fiber semipermeable membrane and operated for 1 hour. Thereafter, the membrane-permeated water was collected from the opening surface of the hollow fiber type semipermeable membrane, and the weight of the permeated water was measured with an electronic balance (LIBROR EB-3200D, manufactured by Shimadzu Corporation). The pressure differential permeability (FR) is the following formula:
FR [L / m ² / day] = permeated water weight [L] / outer diameter reference membrane area [m ² ] / collection time [minutes] × (60 [minutes] × 24 [hours])
Calculated.

[Pressure differential salt removal rate]
The sodium chloride concentration is measured using a conductivity meter (CM-25R manufactured by Toa DK Co., Ltd.) for the permeated membrane water collected in the water permeability measurement and the sodium chloride concentration 1500 mg / L supplied aqueous solution similarly used in the water permeability measurement. Pressure difference salt removal rate is the following formula:
Pressure difference salt removal rate [%] = (1− permeate water salt concentration [mg / L] / feed aqueous solution salt concentration [mg / L]) × 100
Calculated.

Comparative Examples 1 to 5
As Comparative Examples 1 to 5, simulation calculation of the amount of water production to be described later was performed, assuming a water treatment method including one-step forward osmosis process and water production process under the following conditions.

(Forward penetration process)
Immersion type hollow fiber membrane module (hollow fiber membrane arrangement: straight)
Diameter of hollow fiber membrane element: 10 inches Packing ratio of hollow fiber membrane: 50%
Effective length of hollow fiber membrane: 120 cm
Water to be treated: an aqueous solution of evaporation residue concentration (TDS) 5000 ppm draw solution: 85 mass% pluronic aqueous solution (same as the second draw solution of the example)
The injection pressure of the first draw solution into the hollow part of the hollow fiber membrane is fixed at 0.2 MPa. <Simulation calculation of the amount of water production (1)>
Assuming the first forward osmosis process and the second forward osmosis process of the above example and the forward osmosis process of the comparative example, characteristic values such as the water production amount were determined by calculation. In addition, about the assumed module of the said Example and comparative example, the temperature of 25 degreeC and the case where it reached a steady state at the temperature of 25 degreeC were calculated, and the amount of water production was calculated | required by simulation calculation. The calculation results of the example are shown in Table 2, and the calculation results of the comparative example are shown in Table 3. In addition, the number of modules required to obtain the amount of water production 100 m ³ / day obtained from the amount of water production is also shown.

[Method of calculation]
Calculation program to calculate DS inlet flow rate, DS outlet flow rate, DS outlet density, total amount of water permeated through hollow fiber type semipermeable membrane (water production amount: ΔV) when DS inlet concentration is input based on the above parameters The calculations were performed using In these calculations, the virtual module (hollow fiber type semipermeable membrane) was divided into equal minute sections in the flow direction, and the material balance in each section was calculated.

Specifically, using the DS inlet concentration and the DS inlet flow rate, the amount of water permeating the hollow fiber type semipermeable membrane in the first section (the section on the most inlet side) of the virtual module is represented by the A 'value (cm ³ / Cm ² / s / (kgf / cm ² ) (assumed constant value) × membrane area (cm ² ) × 60 × [effective osmotic pressure-effective pressure (hydrostatic pressure)] (kgf / cm ² ) Calculate the outlet concentration and outlet flow rate of DS in the first section. Assuming that the outlet side concentration and outlet side flow rate of this first section are the inlet side concentration and inlet side flow rate of DS of the next section, the same calculation is repeated sequentially from the inlet side to the outlet side of the virtual module. Calculation of the DS outlet concentration and DS outlet flow rate of a virtual module (hollow fiber type semipermeable membrane). The total amount of water that has permeated through the hollow fiber type semipermeable membrane in each section is the total amount (ΔV) of water that has permeated through the hollow fiber type semipermeable membrane in the virtual module, [DS outlet flow rate-DS inlet flow rate It can be calculated by

  Moreover, A 'value (water permeability) was computed from the following formula using the film evaluation result in the laboratory level using the draw solution of the said viscosity and density | concentration, and it utilized for the simulation supposing 10 inch module. The A 'values used are shown in Table 1 below.

A 'value (cm ³ / cm ² / s / (kgf / cm ² )) = amount of water permeated through the membrane: ΔV (cm ³ ) / membrane area (cm ² ) / hour (s) / [effective osmotic pressure-effective Pressure (hydrostatic pressure)] (kgf / cm ² )

From the results shown in Tables 2 and 3, in the case of using the high viscosity draw solution, the forward osmosis step is one step, and in the comparative example in which the high viscosity draw solution flows in the hollow portion of the hollow fiber type semipermeable membrane. However, the efficiency of water treatment (water production) is low, and an unrealistic number of modules are required to obtain the desired water production (100 m ³ / day). On the other hand, in the embodiment in which the forward osmosis process is in two stages and the high viscosity draw solution is not flowed into the hollow portion of the hollow fiber type semipermeable membrane, the efficiency (the amount of water production) of water treatment is extremely improved. The number of modules required to obtain the desired water production (100 m ³ / day) can also be significantly reduced. From the results shown in Table 3, it is considered that when the inner diameter of the hollow fiber type semipermeable membrane is in the range of about 100 to 250 μm, the effects of the present invention can be exhibited.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims.

  1 first semipermeable membrane (hollow fiber type semipermeable membrane), 10 reverse osmosis module, 100 semipermeable membrane, 101 first chamber, 102 second chamber, 11 first forward osmosis module (immersion type hollow fiber membrane module), 12 second forward osmosis module, 120 second semipermeable membrane, 121 first chamber, 122 second chamber, 13 water producing apparatus, 2 hollow fiber membrane element, 201 brine, 202 production water, 203 treated water, 204 first Draw solution, 205 diluted first draw solution, 206 second drawn solution, 207 diluted second draw solution, 208 purified water, 21 and 22 fixed resin, 21a distribution chamber, 21b inlet, 22a collecting chamber, 22b Discharge port, 3 treatment tank.

Claims (5)

A water treatment method for obtaining purified water from treated water containing water and components other than water,
The water in the water to be treated is contained in the first draw solution by bringing the water to be treated into contact with the first draw solution having an osmotic pressure higher than the water to be treated via the first semipermeable membrane. First forward osmosis process to move to
Contacting the first draw solution diluted in the first forward osmosis step with a second draw solution having a higher osmotic pressure than the diluted first draw solution via a second semipermeable membrane A second forward osmosis step of transferring water in the first draw solution into the second draw solution;
Including a water producing step of obtaining the purified water from the second draw solution diluted in the second forward osmosis step;
Reusing the first draw solution concentrated in the second forward osmosis step in the first forward osmosis step;
The second draw solution concentrated in the water making process is reused in the second forward osmosis process,
In the first forward osmosis step, the first semipermeable membrane is a hollow fiber type semipermeable membrane, and the treated water is brought into contact with the outer peripheral surface of the hollow fiber type semipermeable membrane, and the hollow fiber type semipermeable membrane the first draw solution flow into the hollow portion,
The second draw solution comprises a temperature responsive polymer having a property of changing hydrophilicity with a predetermined temperature as a critical point . The water treatment according to claim 1 , wherein the first forward osmosis step is carried out in a state in which the immersion type hollow fiber membrane module in which the hollow fiber type semipermeable membrane is exposed is immersed in the water to be treated in a treatment tank. Method. The water to be treated is a salt, which is concentrated by reverse osmosis treatment, water treatment method according to claim 1 or 2. In the second forward osmosis step, the second semipermeable membrane is a hollow fiber type semipermeable membrane, and the outer surface of the hollow fiber type semipermeable membrane is brought into contact with the second draw solution, and the hollow fiber type semipermeable membrane The water treatment method according to any one of claims 1 to 3 , wherein the first draw solution diluted in the first forward osmosis step is allowed to flow in the hollow portion of the membrane. A water treatment system for obtaining purified water from treated water containing water and components other than water, comprising:
The water in the water to be treated is contained in the first draw solution by bringing the water to be treated into contact with the first draw solution having an osmotic pressure higher than the water to be treated via the first semipermeable membrane. First forward osmosis module, to be moved to
Contacting the first draw solution diluted by the first forward osmosis module with a second draw solution having a higher osmotic pressure than the diluted first draw solution through a second semipermeable membrane A second forward osmosis module for transferring water in the first draw solution into the second draw solution;
Including a fresh water generator for obtaining the purified water from the second draw solution diluted by the second forward osmosis module;
Reusing the first draw solution concentrated in the second forward osmosis module in the first forward osmosis module;
Reusing the second draw solution concentrated by the fresh water generator in a second forward osmosis module;
In the first forward osmosis module, the first semipermeable membrane is a hollow fiber type semipermeable membrane, and the treated water is brought into contact with the outer peripheral surface of the hollow fiber type semipermeable membrane, and the hollow fiber type semipermeable membrane the first draw solution flow into the hollow portion,
The water treatment system, wherein the second draw solution contains a temperature responsive polymer having a property that hydrophilicity changes with a predetermined temperature as a critical point .

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