JP6740843B2 - Water treatment method and water treatment device - Google Patents

Description

The present invention relates to a water treatment method and a water treatment apparatus for extracting water from an aqueous solution containing water as a solvent.

Conventionally, seawater, river water, or industrial wastewater is treated water (containing water), and a liquid having a higher osmotic pressure than the treated water is used as an attractant solution (draw solution). There is known a water treatment system in which fresh water is allowed to permeate an attractant solution from water to be treated by bringing it into contact with treated water.

In Patent Document 1, seawater is supplied to a forward osmosis system that uses a draw solution as a solute having a cloud point, and the water in seawater is infiltrated by contacting the draw solution through a semipermeable membrane in the forward osmosis system. A technique is described in which a semipermeable membrane is permeated by pressure and transferred to a draw solution. In the water treatment device described in Patent Document 1, after heating a draw solution in which water in seawater has been moved, the draw solution is separated into a water-rich solution and a water-separating draw solution in a separation tank, and the water-separating draw solution is forwardly osmotic. It is circulated and used as a draw solution in the system.

In Patent Document 2, in the water treatment device described in Patent Document 1, a final treatment is further performed on the water-rich solution obtained in the separation tank to separate a separation treatment draw solution and produced water such as fresh water. After the treatment, the separated separation draw solution is introduced into the draw solution which is circulated in the forward osmosis system and reused.

U.S. Pat. No. 8021553 International Publication No. 2012/148864 International Publication No. 2015/156404

In the above-described conventional water treatment apparatus, the performance such as the filtration rate, which is the membrane permeation rate of water, changes depending on the concentrations of the aqueous solution and the draw solution supplied to the permeation means such as the membrane module. Therefore, in order to improve the water recovery rate, there has been a demand for a further technique capable of improving the filtration rate with respect to the concentrations of the aqueous solution and the draw solution.

In addition, in the water treatment device according to the conventional technique, there is a problem that the energy required for heating the draw solution increases as the amount of the draw solution used increases. Therefore, there has been a demand for the development of a technique capable of reducing the flow rate of the draw solution and reducing the energy consumed for heating by increasing the water recovery rate and reducing the amount of the draw solution used.

The present invention has been made in view of the above, and an object thereof is to increase the recovery rate of water, reduce the flow rate of the draw solution supplied to the permeation means, and reduce the energy consumed. And to provide a water treatment device.

In order to solve the above problems and achieve the object, a water treatment method according to one embodiment of the present invention transfers water from an aqueous solution containing water as a solvent through a semipermeable membrane to a draw solution having a cloud point. The first normal osmosis step to make a diluted draw solution, a heating step of heating the diluted draw solution to a temperature of the cloud point or higher, the diluted draw solution heated in the heating step, a water-rich solution and the A water treatment method comprising a water separation step of separating into a water separation draw solution having a lower water content than a water-rich solution, and a separation treatment step of separating the water-rich solution into generated water and a separation treatment draw solution, Before the first forward osmosis step, a diluted aqueous solution obtained by diluting water by moving water from a solution having a lower osmotic pressure than the aqueous solution through a semipermeable membrane is used as the aqueous solution in the first forward osmosis step. It further comprises a second forward osmosis step of:

In the water treatment method according to one aspect of the present invention, in the above invention, the separation treatment draw solution separated in the separation treatment step is used as the low osmotic pressure solution in the second forward osmosis step. And

In the water treatment method according to one aspect of the present invention, in the above invention, a solution in which the solution having a low osmotic pressure is concentrated in the second forward osmosis step is introduced into the diluted draw solution before the heating step. It is characterized by

In the water treatment method according to one aspect of the present invention, in the above invention, before the second forward osmosis step, the aqueous solution is branched into a part of the aqueous solution and the rest of the aqueous solution, and the part of the aqueous solution is branched. The second normal osmosis step is performed on the aqueous solution, and the remaining aqueous solution is introduced into the diluted aqueous solution obtained in the second normal osmosis step.

In the water treatment method according to one aspect of the present invention, in the above invention, the water separation draw solution separated in the water separation step is used as the draw solution in the normal osmosis step. In the water treatment method according to one aspect of the present invention, when the second forward osmosis step is included in this configuration, a solution obtained by concentrating the low osmotic pressure solution in the second forward osmosis step is added to the water separation step. It is characterized in that it is introduced into the separated water separation draw solution.

In the water treatment method according to one aspect of the present invention, in the above invention, the separation treatment step is performed using a coalescer, activated carbon, an ultrafiltration membrane, a nanofiltration membrane, or a reverse osmosis membrane. ..

In the water treatment method according to one aspect of the present invention, in the above invention, the draw solution is a solution mainly containing a temperature-sensitive water-absorbing agent having at least one cloud point.

In the water treatment method according to one aspect of the present invention, in the above invention, the aqueous solution is seawater, brackish water, brackish water, industrial wastewater, associated water, or sewage.

A water treatment apparatus according to an aspect of the present invention is a first forward osmosis unit that moves water from an aqueous solution containing water as a solvent to a draw solution having a cloud point through a semipermeable membrane to form a diluted draw solution. And a second forward osmosis unit that supplies water to the first forward osmosis unit after moving water from a solution having a lower osmotic pressure than the aqueous solution through the semipermeable membrane to form a diluted aqueous solution. , Heating means for heating the diluted draw solution to a temperature above the cloud point, the diluted draw solution heated by the heating means, a water-rich solution and a water separation draw solution having a lower water content than the water-rich solution. And a separation treatment means for separating the water-rich solution into produced water and a separation treatment draw solution.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, the separation treatment draw solution separated by the separation treatment means is supplied to the second forward osmosis means as the low osmotic pressure solution. Characterize.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, a concentrated solution obtained by concentrating the solution having a low osmotic pressure by the second normal osmosis unit is added in a flow direction of the heating unit or the diluted draw solution. And is introduced into the diluted draw solution upstream of the heating means.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, a part of the aqueous solution and the remaining part of the aqueous solution are contained upstream of the second forward osmosis unit along the flow direction of the aqueous solution. A branch part for branching into the aqueous solution is provided, and while the part of the aqueous solution is supplied to the second forward osmosis means, the remaining aqueous solution is added to the diluted aqueous solution obtained by the second forward osmosis means. It is characterized by introducing.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, the water separation draw solution separated by the water separation means is supplied to the first forward osmosis means as the draw solution. .. In the water treatment device according to one aspect of the present invention, in the case where the second forward osmosis unit is provided in this configuration, a solution obtained by concentrating the low osmotic pressure solution by the second forward osmosis unit is processed by the water separation unit. It is characterized in that it is introduced into the separated water separation draw solution.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, the separation treatment means is a coalescer, activated carbon, an ultrafiltration membrane, a nanofiltration, or a reverse osmosis membrane.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, the draw solution is a solution mainly containing a temperature-sensitive water absorbing agent having at least one cloud point.

In the water treatment apparatus according to one aspect of the present invention, in the above invention, the aqueous solution is seawater, brackish water, brackish water, industrial wastewater, associated water, or sewage.

According to the water treatment method and the water treatment apparatus of the present invention, it is possible to increase the recovery rate of water, reduce the flow rate of the draw solution supplied to the permeation means, and reduce the energy consumed.

FIG. 1 is a block diagram schematically showing a water treatment device according to a reference embodiment of the present invention. FIG. 2 is a block diagram schematically showing a water treatment device according to the first comparative example. FIG. 3 is a block diagram schematically showing a water treatment device according to the second comparative example. FIG. 4 is a block diagram schematically showing the water treatment device according to the first embodiment of the present invention. FIG. 5 is a block diagram schematically showing a water treatment device according to the second embodiment of the present invention. FIG. 6 is a block diagram schematically showing a water treatment device according to the third embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are designated by the same reference numerals. Moreover, the present invention is not limited to the embodiments described below.

First, the present inventor has conducted various studies in order to solve the above-mentioned problems of the conventional technique. Then, in the process in which the present inventor devises the present invention, after the water-rich solution and the water separation draw solution are separated in the separation tank, a draw solution generated when further separating the generated water from the water-rich solution, The method of introducing into the diluted draw solution after the water separation draw solution was diluted in the forward osmosis process was conceived. The reference embodiment described below is a water treatment method and a water treatment device which the present inventor has conceived in the process of devising the present invention.

(Reference embodiment)
(Water treatment device)
First, the water treatment device according to the reference embodiment will be described. FIG. 1 is a block diagram schematically showing a water treatment device 1 according to this reference embodiment. As shown in FIG. 1, the water treatment apparatus 1 according to this reference embodiment includes a membrane module 11, a heater 12, a separation tank 13, and a final treatment unit 14.

The membrane module 11 is provided with a semipermeable membrane 11a inside. The semipermeable membrane 11a is preferably one that can selectively permeate water, and a forward osmosis (FO) membrane is used, but a reverse osmosis (RO) membrane may also be used. The material of the separation layer of the semipermeable membrane 11a is not particularly limited, and examples thereof include cellulose acetate-based, polyamide-based, polyethyleneimine-based, polysulfone-based, and polybenzimidazole-based materials. The semipermeable membrane 11a may be composed of only one type (one layer) of material used for the separation layer, and has a support layer that physically supports the separation layer and does not substantially contribute to the separation. You may comprise from more than one layer. Examples of the support layer include polysulfone-based, polyketone-based, polyethylene-based, polyethylene terephthalate-based, and general nonwoven fabric materials. The form of the semipermeable membrane 11a is not limited, and various forms such as a flat membrane, a tubular membrane, or a hollow fiber can be used. The membrane module 11 is, for example, a cylindrical or box-shaped container, and the interior of the membrane module 11 is partitioned by the semipermeable membrane 11a into two chambers by installing the semipermeable membrane 11a therein. Examples of the form of the membrane module 11 include various forms such as a spiral module type, a laminated module type, and a hollow fiber module type. A known semipermeable membrane device can be used as the membrane module 11, and a commercially available product can also be used.

In the membrane module 11, an aqueous solution which is an aqueous solution can be made to flow in one chamber partitioned by the semipermeable membrane 11a, and a draw solution which is an aqueous solution can be made to flow in the other chamber. The introduction pressure of the draw solution into the membrane module 11 is 0.1 MPa or more and 0.5 MPa or less, and is 0.2 MPa in the reference embodiment, for example. The aqueous solution is, for example, seawater, brackish water, brackish water, industrial wastewater, associated water, or sewage, or an aqueous solution containing water as a solvent, which is obtained by subjecting these water to a filtration treatment. The aqueous solution is temperature-controlled at a predetermined temperature of, for example, about 50° C. by the treatment of the first stage.

As the draw solution, a solution mainly containing a temperature-sensitive water-absorbing agent (polymer) having at least one cloud point is used. A temperature-sensitive water-absorbing agent is hydrophilic at a low temperature and dissolves well in water to increase the amount of water absorption, while the amount of water absorption decreases as the temperature rises, and becomes hydrophobic when the temperature rises above a predetermined temperature and the solubility decreases. It is a substance. In this reference embodiment, the polymer is preferably a block or random copolymer containing at least a hydrophobic portion and a hydrophilic portion, and having a basic skeleton containing an ethylene oxide group and at least one group consisting of propylene oxide and butylene oxide. Examples of the basic skeleton include a glycerin skeleton and a hydrocarbon skeleton. Specifically, for example, a drug having a polymer of ethylene oxide and propylene oxide (GE1000-BBPP(A3), see Patent Document 3) was used. The temperature at which water solubility and water insolubility of such polymers change is called the cloud point. When the temperature of the draw solution reaches the cloud point, the hydrophobized temperature-sensitive water-absorbing agent aggregates and white turbidity occurs. The temperature-sensitive water absorbing agent is used as various surfactants, dispersants, emulsifiers and the like. In this reference embodiment, the draw solution is used as an attractant that attracts water from the aqueous solution.

The heater 12 as a heating means for the draw solution is provided on the upstream side of the separation tank 13 along the flow direction of the draw solution. The heater 12 heats the draw solution (diluted draw solution) diluted and discharged in the membrane module 11 to a temperature of the cloud point or higher.

The separation tank 13 as a water separating means is a water separation draw in which the diluted draw solution is phase-separated by heating in the heater 12 and which has water as a main component and a polymer as a main component and which has a lower water content than the water-rich solution. Phase separate into solution.

The final treatment unit 14 as a separation treatment means is composed of, for example, a coalescer, an activated carbon adsorption unit, an ultrafiltration membrane (UF membrane) unit, a nanofiltration membrane (NF membrane) unit, or a reverse osmosis membrane (RO membrane) unit. It The final treatment unit 14 separates the remaining polymer from the water-rich solution in the water-rich solution flowing out from the separation tank 13 to generate fresh water as produced water. The polymer solution containing the polymer separated by the final treatment unit 14 is introduced into the heater 12 together with the diluted draw solution as a separation treatment draw solution along the introduction path introduced from the final treatment unit 14 to the upstream side of the heater 12. To be done.

(Water treatment method)
Next, a water treatment method using the water treatment device 1 according to the reference embodiment will be described.

Forward Osmosis Step The forward osmosis step is performed in the membrane module 11 as the forward osmosis means. That is, in the membrane module 11, the water-containing solution and the draw solution are brought into contact with each other through the semipermeable membrane 11a, whereby the water in the aqueous solution passes through the semipermeable membrane 11a and moves to the draw solution due to the difference in osmotic pressure. From one of the chambers into which the water-containing solution flows, the concentrated water-containing solution, which has been concentrated due to the movement of water, flows out. Water moves from the other chamber into which the draw solution has flown, and the diluted diluted draw solution flows out. The temperature of the draw solution is adjusted by controlling the temperature of the aqueous solution and conducting heat during contact with the aqueous solution. In this reference embodiment, the temperature of the diluted draw solution is adjusted to 30° C. or higher and 50° C. or lower, specifically about 40° C., for example.

Heating Step In the heater 12, a heating step is performed. That is, the pre-separation draw solution in which the separation treatment draw solution obtained in the final treatment step described below is introduced into the diluted draw solution diluted by the movement of water from the aqueous solution in the forward osmosis step is clouded by the heater 12. By heating to a temperature above the point, at least a part of the polymer is aggregated and phase-separated. The heating temperature in the heating step can be adjusted by controlling the heater 12. The heating temperature is preferably 100° C. or lower, and in this reference embodiment, the heating temperature is, for example, 88° C., which is higher than the cloud point and lower than 100° C.

Water Separation Step In the separation tank 13, a water separation step is performed. That is, in the separation tank 13, the diluted draw solution is separated into a water-rich solution containing a large amount of water and a water separation draw solution as a concentrated draw solution containing a high concentration of polymer. The pressure in the separation tank 13 is atmospheric pressure. The phase separation between the water-rich solution and the water-separation draw solution can be carried out by allowing the solution to stand at a liquid temperature above the cloud point. The water separation draw solution separated from the diluted draw solution is supplied to the membrane module 11 as a draw solution. The draw concentration of the water separation draw solution is, for example, 60 to 95%. On the other hand, the water-rich solution separated from the diluted draw solution is supplied to the final processing unit 14. The water-rich solution has, for example, 99% water and a draw concentration of 1%.

Final Treatment Step In the final treatment unit 14, a final treatment step as a separation treatment step is performed. That is, the polymer may remain in the water-rich solution separated in the separation tank 13. Therefore, in the final treatment unit 14, the polymer solution to be the separation treatment draw solution is separated from the water-rich solution to generate generated water such as fresh water. Here, the processing temperature in the final processing unit 14 is, for example, 20° C. or more and 50° C. or less, preferably 35° C. or more and 45° C. or less, and in this reference embodiment, for example, 45° C. The produced water separated from the water-rich solution is released to the outside as a final product obtained from the aqueous solution. The separation treatment draw solution is a polymer solution having a draw concentration of about 0.5 to 25%, is introduced into the diluted draw solution on the upstream side of the heater 12, and is supplied to the heater 12.

(Reference Example and Comparative Example)
Next, a reference example of the water treatment device 1 configured as above and a comparative example according to a conventional technique will be described.

(Reference example)
The reference example is an example in which the water treatment device 1 according to the reference embodiment is used to generate 300 L of fresh water per hour from seawater having a salt concentration of 4%.

In order to compare with a reference example based on the reference embodiment, an example of a water treatment device that discards a separation-treated draw solution (see Patent Document 1) will be referred to as a first comparative example. FIG. 2 is a block diagram schematically showing the water treatment device 100 according to the first comparative example. Further, an example (see Patent Document 2) in which the separation-treated draw solution is introduced into the water separation draw solution in the latter stage of the separation tank is referred to as a second comparative example. FIG. 3 is a block diagram schematically showing a water treatment device 200 according to the second comparative example.

(First Comparative Example)
As shown in FIG. 2, the water treatment apparatus 100 according to the first comparative example is similar to the water treatment apparatus 1 according to the reference embodiment, a membrane module 101 having a semipermeable membrane 101a provided therein, a heater 102, and a separation tank. 103 and a final processing unit 104. The membrane module 101, the heater 102, the separation tank 103, and the final processing unit 104 are the same as the membrane module 11, the heater 12, the separation tank 13, and the final processing unit 14, respectively. On the other hand, unlike the water treatment device 1, in the water treatment device 100, the separation treatment draw solution after being separated from the water-rich solution in the final treatment unit 104 is discarded.

(Second Comparative Example)
As shown in FIG. 3, the water treatment apparatus 200 according to the second comparative example is similar to the water treatment apparatus 1 according to the reference embodiment, in which a semipermeable membrane 201a is provided inside the membrane module 201, a heater 202, and a separation tank. 203 and a final processing unit 204. The membrane module 201, the heater 202, the separation tank 203, and the final processing unit 204 are the same as the membrane module 11, the heater 12, the separation tank 13, and the final processing unit 14, respectively. On the other hand, unlike the water treatment apparatus 1, in the water treatment apparatus 200, the separation treatment draw solution separated from the water-rich solution in the final treatment unit 204 is introduced into the water separation draw solution on the downstream side of the separation tank 203 and mixed. It is supplied to the membrane module 201 as a draw solution.

Table 1 shows the water-containing solution and the concentrated water-containing solution, and the diluted draw solution, the water separation draw solution, the pre-separation draw solution, the separation treatment draw solution, and the mixing in the reference example, the first comparative example, and the second comparative example. The experimental result of each flow rate and concentration of the draw solution is shown. In addition, in the reference example, the first comparative example, and the second comparative example, the kind of the aqueous solution and the amount of fresh water produced per unit time of produced water such as fresh water are equal to each other. Specifically, the pressure introduced into the membrane module 11 was 34 atm above the osmotic pressure of seawater (about 25 atm), the draw concentration of the water-rich solution was 1%, the flow rate was 375 L/h, and the recovery rate in the final treatment unit 14 was 80%. %, the amount of fresh water produced finally per unit time is set to 300 L/h.

In the first comparative example, the separation treatment draw solution separated by the final treatment unit 104 is discarded. Therefore, not only the treatment cost becomes high, but also it is necessary to add the water separation draw solution at any time, so that there is a problem that cost reduction becomes extremely difficult.

In the second comparative example, the separation treatment draw solution is introduced into the water separation draw solution on the downstream side of the separation tank 203. As a result, although the separation treatment draw solution can be reused, the draw concentration of the mixed draw solution supplied to the membrane module 201 is lower than that of the water separation draw solution flowing out from the separation tank 203. Therefore, the filtration rate in the membrane module 201 to which the mixed draw solution is supplied is lower than the filtration rate in the membrane module 201 when the water separation draw solution is supplied. Along with this, the flow rate of the mixed draw solution supplied to the membrane module 201 increases, and the flow rate of the diluted draw solution flowing out of the membrane module 201 also increases. Therefore, there is a problem that the energy required for heating in the heater 202 increases.

It can be seen from Table 1 that the flow rate of the aqueous solution supplied to the water treatment device can be reduced in the reference example in comparison with the above-described first comparative example, when the final water production amount is the same. In other words, when the flow rate of the aqueous solution supplied to the water treatment apparatus 100 according to the first comparative example and the flow rate of the aqueous solution supplied to the water treatment apparatus 1 according to the reference example are the same, the amount of water produced is It can be seen that there are more water treatment devices 1 than the device 100. That is, in the water treatment device 1 according to the reference embodiment, it can be seen that the recovery rate of fresh water can be improved as compared with the conventional case.

Further, in contrast to the first and second comparative examples described above, in the reference example, as shown in FIG. 1, the separation treatment draw solution is introduced into the diluted draw solution on the upstream side of the heater 12. As a result, a decrease in the draw concentration of the water separation draw solution supplied to the membrane module 11 can be suppressed, and from Table 1, the draw concentration of the water separation draw solution becomes the same as that of the conventional technique (first and second comparative examples). You can see that it can be maintained.

Furthermore, it can be seen from Table 1 that the reference example can increase the filtration rate in the membrane module 11 as compared with the first comparative example. That is, it can be seen that in the reference example, the flow rate of the water separation draw solution is reduced as compared with the first and second comparative examples. Specifically, it can be seen from Table 1 that the reference example can reduce the flow rate of the water separation draw solution supplied to the membrane module 11 from 1249 L/h to 997 L/h, as compared with the first comparative example. Similarly, in the reference example, as compared with the second comparative example, the flow rate of the water separation draw solution (mixed draw solution in the second comparative example) supplied to the membrane module 11 is changed from 2075 L/h to 997 L/h. It can be seen that it can be reduced. The reduction of the flow rate of the water separation draw solution contributes to the reduction of the usage amount of the polymer contained in the draw solution, so that the cost of the polymer can be reduced.

Further, from Table 1, in the first comparative example, the diluted draw solution flows in the heater 102 at a flow rate of 1624 L/h, and in the second comparative example, the diluted draw solution is heated at a flow rate of 2375 L/h. It is flowing in 202. On the other hand, in the reference example, the draw solution before separation is flowing in the heater 12 at a flow rate of 1372 L/h. That is, it can be seen from Table 1 that in the reference example, the flow rate of the draw solution flown in the heater 12 is reduced. Here, since the specific heat and density of the aqueous polymer solutions used in the reference example and the first and second comparative examples were 3.2 kJ/kg·K and 1.05 kg/L, respectively, the draw solution was kept at 40° C. The energy required for heating to 88° C. above the cloud point is as follows. The specific heat does not depend on the concentration of the draw solution because the average specific heat of the polymer aqueous solution at 40 to 88° C. is used. Further, with respect to the density, since the contribution of the concentration and temperature of the draw solution is extremely small, the influence of the concentration and temperature is negligibly small.
Reference Example: (3.2 kJ/kg·K×1.05 kg/L×1372 L/h×(88° C.-40° C.)=) 2.21×10 ⁵ kJ/h
First comparative example: (3.2 kJ/kg·K×1.05 kg/L×1624 L/h×(88° C.-40° C.)=) 2.62×10 ⁵ kJ/h
Second comparative example: (3.2 kJ/kg·K×1.05 kg/L×2375 L/h×(88° C.-40° C.)=) 3.83×10 ⁵ kJ/h

That is, it can be seen that the reference example can reduce energy by about 16% as compared with the first comparative example, and can reduce energy by about 42% as compared with the second comparative example.

As described above, according to the reference embodiment, since the filtration rate of the membrane module 11 can be increased as compared with the conventional one, the flow rate of the draw solution supplied to the membrane module 11 can be reduced, and the heating rate can be increased accordingly. Since the draw solution flowing in the vessel 12 can be reduced, the cost required for the draw solution in the water treatment device 1 can be reduced and the energy consumed for heating can be reduced as compared with the conventional case.

The present inventor further diligently studied the water treatment apparatus and the water treatment method according to the above-described reference embodiment. Then, the present inventor has conceived a method of diluting an aqueous solution in advance using the separation treatment draw solution obtained in the above-described reference embodiment. That is, before introducing the aqueous solution into the membrane module that performs the forward osmosis step, devise a method of moving water from the separation treatment draw solution to the aqueous solution to obtain a diluted aqueous solution and introducing the diluted aqueous solution into the membrane module. Came to do.

(First embodiment)
(Water treatment device)
Next, a first embodiment of the present invention will be described based on the above-mentioned earnest studies by the present inventor. FIG. 4 is a block diagram schematically showing the water treatment device 2 according to the first embodiment. As shown in FIG. 4, the water treatment device 2 according to the first embodiment includes a first membrane module 21 having a semipermeable membrane 21a provided therein and a second membrane module 22 having a semipermeable membrane 22a provided therein. , A heater 23, a separation tank 24, and a final treatment unit 25. The first membrane module 21, the semipermeable membrane 21a, the heater 23, the separation tank 24, and the final treatment unit 25 in the water treatment apparatus 2 are the membrane module 11, the semipermeable membrane 11a, the heater 12, and the water treatment apparatus 1, respectively. It is similar to the separation tank 13 and the final processing unit 14.

The 2nd membrane module 22 and the semipermeable membrane 22a can employ|adopt the structure similar to the membrane module 11 and the semipermeable membrane 11a in the water treatment apparatus 1, respectively. That is, the inside of the second membrane module 22 is partitioned into two chambers by the semipermeable membrane 22a. Here, in the water treatment device 2, the first membrane module 21 as the first forward osmosis means and the second membrane module 22 as the second forward osmosis means may be membrane modules having the same structure, and Membrane modules having different configurations may be used. Further, the semipermeable membranes 21a and 22a may employ semipermeable membranes having the same configuration and type as each other, or may employ semipermeable membranes having configurations and types different from each other.

In the water treatment device 2 according to the first embodiment, unlike the reference embodiment, the second membrane module 22 is provided upstream of the first membrane module 21 along the flow direction of the draw solution and the aqueous solution. As a result, the aqueous solution supplied to the water treatment device 2 from the outside is supplied to one chamber of the second membrane module 22. The separation treatment draw solution separated in the final treatment unit 25 is supplied to the other chamber of the second membrane module 22. Other configurations are similar to those of the reference embodiment.

(Water treatment method)
(Second forward osmosis process)
Next, a water treatment method using the water treatment device 2 according to the first embodiment will be described. In the first embodiment, unlike the reference embodiment, the second forward osmosis step is performed in the second membrane module 22 as the second forward osmosis means. That is, in the second membrane module 22, the aqueous solution is brought into contact with the separation treatment draw solution having an osmotic pressure lower than that of the aqueous solution through the semipermeable membrane 22a. Here, since the osmotic pressure of the separation treatment draw solution is set to be lower than the osmotic pressure of the aqueous solution, the water in the separation treatment draw solution passes through the semipermeable membrane 22a and moves to the aqueous solution due to the difference in osmotic pressure. To do. As a result, from one of the chambers into which the aqueous solution flows, a diluted aqueous solution flows out of the separation-treated draw solution, which is diluted. From the other chamber into which the separation-processed draw solution flows, the concentrated separation-processed draw solution in which water has moved and is concentrated flows out. In the separation treatment draw solution supplied to the second membrane module 22, the temperature is set to 30°C or higher and 50°C or lower, for example, 40°C, and the pressure is set to 0.05 MPa or higher and 0.3 MPa or lower, for example, 0.1 MPa.

(First forward osmosis process)
The diluted aqueous solution flowing out from one chamber of the second membrane module 22 is supplied to one chamber of the first membrane module 21. In the first membrane module 21, the water separation draw solution and the dilute aqueous solution come into contact with each other through the semipermeable membrane 21a, and the first forward osmosis step is performed. The concentrate separation treatment draw solution that has flowed out from the other chamber of the second membrane module 22 is introduced to the upstream side of the heater 23 along the flow direction of the diluted draw solution. The diluted draw solution into which the concentrate separation treatment draw solution has been introduced is supplied to the heater 23 as a pre-separation draw solution. The other heating step, water separation step, and final treatment step are the same as in the reference embodiment. A first example based on the first embodiment will be described later.

(Second embodiment)
(Water treatment device)
Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram schematically showing the water treatment device 3 according to the second embodiment. As shown in FIG. 5, the water treatment device 3 according to the second embodiment includes the first membrane module 21 having the semipermeable membrane 21a and the semipermeable membrane 22a, as in the water treatment device 2 according to the first embodiment. The second membrane module 22, the heater 23, the separation tank 24, and the final treatment unit 25 are included. On the other hand, in the water treatment device 3, unlike the water treatment device 2 according to the first embodiment, the concentrated separation treatment draw solution flowing out from the second membrane module 22 is stored in the separation tank 24 along the flow direction of the water separation draw solution. It is configured to be introduced downstream. Other configurations are similar to those of the first embodiment.

(Water treatment method)
Next, a water treatment method using the water treatment device 3 according to the second embodiment will be described. In the second embodiment, the second forward osmosis step is performed by the second membrane module 22, and the water in the separation treatment draw solution passes through the semipermeable membrane 22a and moves to the aqueous solution. The diluted aqueous solution flows out from one chamber of the second membrane module 22 into which the aqueous solution flows, and is supplied to one chamber of the first membrane module 21. The concentrated separation treatment draw solution flows out from the other chamber into which the separation treatment draw solution flows in the second membrane module 22. The concentrated separation treatment draw solution is introduced into the water separation draw solution flowing out from the separation tank 24. The mixed draw solution obtained by introducing the concentrate separation treatment draw solution into the water separation draw solution is supplied to the other chamber of the first membrane module 21. In the first membrane module 21, the first forward osmosis step is performed between the diluted aqueous solution and the mixed draw solution, and water moves from the diluted aqueous solution to the mixed draw solution. The other heating step, water separation step, and final treatment step are the same as those in the reference embodiment and the first embodiment. A second example based on the second embodiment will be described later.

(Third Embodiment)
(Water treatment device)
Next, a third embodiment of the present invention will be described. FIG. 6 is a block diagram schematically showing the water treatment device 4 according to the third embodiment. As shown in FIG. 6, the water treatment device 4 according to the third embodiment includes the first membrane module 21 having the semipermeable membrane 21a and the semipermeable membrane 22a, similarly to the water treatment device 2 according to the first embodiment. The second membrane module 22, the heater 23, the separation tank 24, and the final treatment unit 25 are included. On the other hand, in the water treatment device 4, unlike the water treatment device 2 according to the first embodiment, the aqueous solution supplied from the outside to the water treatment device 4 is branched at the upstream side along the flow direction of the aqueous solution. Is composed of. In the water treatment device 4, a part of the branched aqueous solution is supplied to one chamber of the second membrane module 22, and the rest of the aqueous solution is on the downstream side of the second membrane module 22 and in the first membrane module 21. It is configured to be introduced upstream. Other configurations are similar to those of the first embodiment.

(Water treatment method)
Next, a water treatment method using the water treatment device 4 according to the third embodiment will be described. In the water treatment device 4 according to the third embodiment, a branch portion is provided on the upstream side supplied along the flow direction of the aqueous solution. At the branching portion, the aqueous solution supplied to the water treatment device 4 is branched into a part of the aqueous solution and the rest of the aqueous solution. Here, by adjusting the flow rate of a part of the aqueous solution supplied to the second membrane module 22, the flow rate of the remaining aqueous solution is adjusted. Part of the aqueous solution is supplied to one chamber of the second membrane module 22 and the second forward osmosis process is performed. In the second membrane module 22, the water in the separation treatment draw solution passes through the semipermeable membrane 22a and moves to a part of the aqueous solution. The diluted aqueous solution flows out from one chamber into which a part of the aqueous solution flows in the second membrane module 22, and after the remainder of the branched aqueous solution is introduced, the diluted aqueous solution of the first membrane module 21 is supplied. It is supplied to one chamber. From the other chamber of the second membrane module 22, the concentration separation treatment draw solution flows out, and is introduced into the diluted draw solution flowing out of the first membrane module 21 on the upstream side of the heater 23. Other first forward osmosis step, heating step, water separation step, and final treatment step are the same as those in the first and first embodiments. A third example based on the third embodiment will be described later.

(First, Second, Third Examples, and First, Second Comparative Examples)
Next, first to third examples based on the first to third embodiments will be described. The first, second and third examples are examples using water treatment devices 2, 3 and 4, respectively. The first comparative example is a comparative example using the water treatment apparatus 100 shown in FIG. 2 described above, and the second comparative example is a comparative example using the water treatment apparatus 200 shown in FIG. 3 described above.

Table 2 shows the flow rates and salt concentrations of the water-containing solution, the diluted water-containing solution, and the concentrated water-containing solution, and the water separation draw solution, the mixed draw solution, and the dilution in the first to third examples and the first and second comparative examples. The experimental results of flow rate and concentration of the draw solution, the pre-separation draw solution, the separation treatment draw solution, and the concentrated separation treatment draw solution are shown. In addition, in 1st-3rd Example, 1st, 2nd comparative example, the kind of aqueous solution and the amount of fresh water produced per unit time of produced|generated water, such as fresh water finally produced|generated, shall be equal. Specifically, the draw concentration of the water-rich solution is 1%, the flow rate is 375 L/h, the recovery rate in the final treatment unit 25 is 80%, and the amount of fresh water produced finally per unit time is 300 L/h. set to h. In the third embodiment, the flow rate of a part of the aqueous solution supplied to the second membrane module 22 is 75 L/h, and the flow rate of the remaining aqueous solution is 922 L/h. As a result, in the third embodiment, the salt concentration of the diluted aqueous solution before flowing out of the second aqueous solution module 22 and the remaining aqueous solution is 2.2%, and the flow rate is 135 L/h. In Table 2, the salt concentration and flow rate of the diluted aqueous solution of the third embodiment are the salt concentration and flow rate of the diluted aqueous solution after the remaining aqueous solution was introduced.

From Table 2, it is possible to reduce the flow rate of the aqueous solution supplied to the water treatment device in the first to third examples as compared with the above-described first comparative example, when the final fresh water production amount is the same. I understand. In other words, when the flow rate of the aqueous solution supplied to the water treatment device 100 according to the first comparative example and the flow rate of the aqueous solution supplied to the water treatment devices 2 to 4 according to the first to third examples are the same, It can be seen that the amount of water produced by the water treatment devices 2 to 4 is higher than that of the water treatment device 100. That is, it can be seen that the water treatment devices 2 to 4 according to the first to third embodiments can improve the recovery rate of fresh water as compared with the related art.

Further, as shown in FIGS. 4 and 5, in the water treatment devices 2 and 3 according to the first and second embodiments, the separation treatment is performed by the second membrane module 22 arranged on the upstream side of the first membrane module 21. Water is moved from the draw solution to the aqueous solution. Therefore, the concentration of the aqueous solution supplied to the first membrane module 21 is lower than the concentration of the aqueous solution supplied to the membrane module 101 in the water treatment device 100 according to the first comparative example. This increases the osmotic pressure difference between the diluted aqueous solution and the draw solution in the first membrane module 21. By increasing the osmotic pressure difference between the dilute aqueous solution and the draw solution in the first membrane module 21, the filtration rate and the water recovery rate can be increased and the flow rate of the draw solution supplied can be reduced as compared with the conventional case. Specifically, from Table 2, the first embodiment can reduce the flow rate of the water separation draw solution supplied to the first membrane module 21 from 1249 L/h to 700 L/h, as compared with the first comparative example. I understand. Similarly, in the second embodiment, the flow rate of the mixed draw solution supplied to the first membrane module 21 is 1249 L/in comparison with the flow rate of the water separation draw solution supplied to the membrane module 101 in the first comparative example. It can be seen that it can be reduced from h to 1100 L/h. The reduction of the flow rate of the water separation draw solution or the mixed draw solution contributes to the reduction of the amount of the polymer contained in the draw solution, and thus the cost of the polymer can be reduced.

Further, from Table 2, in the first comparative example, the diluted draw solution flows in the heater 102 at a flow rate of 1624 L/h, and in the second comparative example, the diluted draw solution is heated at a flow rate of 2375 L/h. It is flowing in 202. On the other hand, as shown in Table 2 and FIG. 4, in the first embodiment, the pre-separation draw solution flows in the heater 23 at a flow rate of 1075 L/h. Moreover, as shown in Table 2 and FIG. 5, in the second embodiment, the diluted draw solution is flowing in the heater 23 at a flow rate of 1460 L/h. That is, it can be seen from Table 2 that in the first and second examples, the flow rate of the draw solution flowing in the heater 23 is reduced as compared with the conventional case (first and second comparative examples). .. Here, since the specific heat and density of the aqueous polymer solutions used in the first and second examples and the first and second comparative examples are 3.2 kJ/kg·K and 1.05 kg/L, respectively, the draw solution The energy required for heating from 40° C. to 88° C. above the cloud point is as follows.
First Example: (3.2 kJ/kgK×1.05 kg/L×1075 L/h×(88° C.-40° C.)=) 1.73×10 ⁵ kJ/h
Second embodiment: (3.2 kJ/kgK*1.05 kg/L*1460 L/h*(88[deg.] C.-40[deg.] C.)=) 2.35*10< ⁵ > kJ/h
First comparative example: (3.2 kJ/kg·K×1.05 kg/L×1624 L/h×(88° C.-40° C.)=) 2.62×10 ⁵ kJ/h
Second comparative example: (3.2 kJ/kg·K×1.05 kg/L×2375 L/h×(88° C.-40° C.)=) 3.83×10 ⁵ kJ/h

That is, it can be seen that in the first example, the energy can be reduced by about 34% as compared with the first comparative example, and by about 55% as compared with the second comparative example. Similarly, in the second example, it can be seen that energy can be reduced by about 10% as compared with the first comparative example, and energy can be reduced by about 39% as compared with the second comparative example.

Furthermore, the reference example based on the reference embodiment described above (see Table 1) is compared with the first example according to the first embodiment of the present invention. The recovery rate of water in the membrane module 11 according to the reference example is ((997L/h-697L/h)/997L/h×100≈)30%, whereas in the first membrane module 21 according to the first example. The water recovery rate is ((1057L/h-697L/h)/1057L/h×100≈)34%. That is, according to the first embodiment, the water recovery rate is increased by 4 points as compared with the reference embodiment.

Further, the energy required for heating the draw solution from 40° C. to 88° C. above the cloud point is 2.21×10 ⁵ kJ/h in the reference example, whereas in the first example. Is 1.73×10 ⁵ kJ/h. As a result, it can be seen that the energy can be reduced by about 22% in the first embodiment compared to the reference embodiment.

That is, according to the water treatment apparatus 2 according to the first embodiment of the present invention, the water recovery rate in the first membrane module 21 is further increased and the energy consumed is higher than that in the water treatment apparatus 1 according to the reference embodiment. Can be further reduced.

In Table 2, comparing the first example and the third example, it can be seen that the same effect as the first example can be obtained in the third example. Further, the water-containing solution supplied to the water treatment devices 2 and 4 is 997 L/h in both cases, but as shown in FIG. 6, the supplied water-containing solution is branched by the branching portion to the second membrane module 22. The flow rate of the aqueous solution to be supplied is 75 L/h in the third embodiment, which is greatly reduced as compared with the first embodiment. As a result, the pressure loss in the second membrane module 22 can be reduced, so that the energy consumed in the water treatment device can be reduced in the third embodiment compared to the first embodiment.

As described above, according to the first, second, and third embodiments, the filtration rate of the first membrane module 21 can be increased as compared with the conventional one, and thus the draw supplied to the first membrane module 21 can be increased. Since the flow rate of the solution can be reduced and the draw solution flowing in the heater 23 can be reduced accordingly, the cost required for the draw solution in the water treatment devices 2, 3 and 4 can be reduced as compared with the conventional case. At the same time, the energy consumed for heating can be reduced. Furthermore, in the water treatment device 4, the energy consumed in the second membrane module 22 can be further reduced.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention. For example, the numerical values given in the above embodiments are merely examples, and different numerical values may be used as necessary, and the present invention will be described with reference to the description and drawings that form part of the disclosure of the present invention according to the present embodiment. Is not limited.

1, 2, 3, 4 Water treatment apparatus 11 Membrane module 11a, 21a, 22a Semipermeable membrane 12,23 Heater 13,24 Separation tank 14,25 Final treatment unit 21 First membrane module 22 Second membrane module

Claims (16)

A first forward osmosis step of moving water from an aqueous solution containing water as a solvent through a semipermeable membrane to a draw solution having a cloud point to obtain a diluted draw solution;
A heating step of heating the diluted draw solution to a temperature above the cloud point;
A water separation step of separating the diluted draw solution heated in the heating step into a water-rich solution and a water separation draw solution having a lower water content than the water-rich solution,
A separation treatment step of separating the water-rich solution into generated water and a separation treatment draw solution,
A water treatment method including
Before the first forward osmosis step, a diluted aqueous solution obtained by diluting water by moving water from the separation treatment draw solution having a lower osmotic pressure than the aqueous solution through the semipermeable membrane is used in the first forward osmosis step. Further including a second forward osmosis step of making a water-containing solution,
A water treatment method characterized by the above. Said second solution to said separation process draw solution is concentrated in the forward osmosis step, water treatment method according to claim 1, characterized in that introduced into the dilute draw solution before the heating step. Before the second forward osmosis step, the aqueous solution is branched into a part of the aqueous solution and the rest of the aqueous solution, the second forward osmosis step is performed on the part of the aqueous solution, and The water treatment method according to claim 1 or 2 , wherein an aqueous solution is introduced into the diluted aqueous solution obtained in the second forward osmosis step. The said water separation draw solution isolate|separated in the said water separation process is made into the said draw solution in the said 1st normal osmosis process. The water treatment method of any one of Claims 1-3 characterized by the above-mentioned. The solution in which the separation process draw solution is enriched in the second forward osmosis process, any one of the claims 1-4, characterized in that introduced into separate the water separating draw solution in the water separation process The water treatment method described in. Wherein the separation step, coalescers, activated carbon, ultrafiltration membranes, nanofiltration membranes or water treatment method according to any one of claims 1 to 5, be performed by using a reverse osmosis membrane, characterized in,. The draw solution, water treatment method according to any one of claims 1 to 6, characterized in that a solution consisting mainly of temperature sensitive water absorbing agent having at least one cloud point. The water solution is seawater, brine, brackish water, industrial wastewater, water treatment method according to any one of claims 1 to 7, wherein the produced water, or sewage. First forward osmosis means for moving water from an aqueous solution containing water as a solvent to a draw solution having a cloud point through a semipermeable membrane to obtain a diluted draw solution ;
Heating means for heating the dilute draw solution to a temperature above the cloud point,
The diluted draw solution heated by the heating means, a water separation means for separating a water-rich solution and a water separation draw solution having a lower water content than the water-rich solution,
Separation treatment means for separating the water-rich solution into generated water and a separation treatment draw solution,
Second normal osmosis in which water is moved from the separation treatment draw solution having a lower osmotic pressure than the aqueous solution through the semipermeable membrane to form a diluted aqueous solution, and then the diluted aqueous solution is supplied to the first forward osmosis unit. water treatment device, characterized in that it comprises a means. A solution in which the separation-treated draw solution is concentrated by the second normal osmosis means is introduced into the diluted draw solution on the upstream side of the heating means or the heating means along the flow direction of the diluted draw solution. The water treatment device according to claim 9 . A branch part for branching the aqueous solution into a part of the aqueous solution and the rest of the aqueous solution is provided on the upstream side of the second normal osmosis means along the flow direction of the aqueous solution, and the part of the aqueous solution. while supplying the second forward osmosis unit the water treatment according to claim 9 or 10, characterized in that introducing water solution of the remainder to the dilution water solution obtained by the second forward osmosis unit apparatus. The water separation draw solution separated by the water separation means is supplied to the first forward osmosis means as the draw solution, The water treatment apparatus according to any one of claims 9 to 12 . The solution to the separation process draw solution is concentrated by the second forward osmosis unit, any one of the claims 9-12, characterized in that introduced into the water separating draw solution separated by the water separator Water treatment device described in. Said separating means is, coalescers, activated carbon, ultrafiltration membrane, water treatment apparatus according to any one of claims 9-1 3, characterized in that it consists of nanofiltration or reverse osmosis membrane. The draw solution, water treatment apparatus according to any one of claims 9-1 4, characterized in that the temperature sensitive water absorbing agent is a solution mainly comprising at least one cloud point. The said water-containing solution is seawater, brackish water, brackish water, industrial waste water, associated water, or sewage. The water treatment apparatus of any one of Claims 9 to 15 characterized by the above-mentioned.

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