JP6980992B2 - Water treatment method and water treatment equipment - 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, industrial wastewater, etc. are used as treated water (feed solution), and a liquid having a higher osmotic pressure than the treated water is used as an attracting solution (draw solution), and the draw solution and the subject are covered through a semi-permeable membrane. A water treatment system is known in which fresh water is permeated into an attracting solution from the water to be treated by contacting it with the treated water.

In Patent Document 1, seawater is supplied to a forward osmosis system using a draw solution as a solute having a cloud point, and the water in the seawater is infiltrated by contacting the forward osmosis system with the draw solution via a semipermeable membrane in the forward osmosis system. A technique for permeating a semipermeable membrane by pressure and transferring it to a draw solution is described. In the water treatment apparatus described in Patent Document 1, after the draw solution to which water in seawater is transferred is heated, it is separated into a water-rich solution and a water-separated draw solution in a separation tank, and the water-separated draw solution is directly permeated. It is circulated and used as a draw solution in the system.

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

U.S. Pat. No. 821553 International Publication No. 2012/148864 International Publication No. 2015/156404

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

Further, in the water treatment apparatus according to the prior art, there is a problem that when the amount of the draw solution to be introduced increases, the energy required for heating the draw solution also increases. Therefore, a technology that can reduce the flow rate of the draw solution and reduce the energy consumed for heating by increasing the filtration rate in the infiltration means to increase the recovery rate of water and reducing the amount of the draw solution to be introduced. Development was required.

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

In order to solve the above-mentioned problems and achieve the object, the water treatment method according to one aspect of the present invention is to add water from a water-containing solution containing water as a solvent to a draw solution having a cloud point via a translucent film. The positive permeation step of moving the diluted draw solution to a diluted draw solution, the heating step of heating the diluted draw solution to a temperature equal to or higher than the cloud point, and the diluted draw solution heated in the heating step are divided into a water-rich solution and the water. A water treatment method comprising a water separation step of separating into a water-separated draw solution having a lower water content than a rich solution, and a separation treatment step of separating the water-rich solution into a generated water and a separation-treated draw solution. The separation-treated draw solution is introduced into the diluted draw solution prior to the heating step.

The water treatment method according to one aspect of the present invention is characterized in that, in the above invention, the water separation draw solution separated in the water separation step is used as the draw solution in the forward osmosis step.

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

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

The water treatment method according to one aspect of the present invention is characterized in that, in the above invention, the aqueous solution is seawater, brackish water, steam water, industrial wastewater, accompanying water, or sewage.

The water treatment apparatus according to one aspect of the present invention comprises a direct permeation means for moving water from an aqueous solution containing water as a solvent to a draw solution having a cloud point via a translucent film to obtain a diluted draw solution. The heating means for heating the diluted draw solution to a temperature higher than the cloud point and the diluted draw solution heated by the heating means are separated into a water-rich solution and a water-separated draw solution having a lower water content than the water-rich solution. The water separation means and the separation treatment means for separating the water-rich solution into the generated water and the separation treatment draw solution are provided, and the separation treatment draw solution is provided along the flow direction of the heating means or the diluted draw solution. It is characterized in that it is introduced to the upstream side of the heating means.

The water treatment apparatus according to one aspect of the present invention is characterized in that, in the above invention, the water separation draw solution separated by the water separation means is supplied to the forward osmosis means as the draw solution.

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

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

The water treatment apparatus according to one aspect of the present invention is characterized in that, in the above invention, the aqueous solution is seawater, brackish water, steam water, industrial wastewater, accompanying water, or sewage.

According to the water treatment method and the water treatment apparatus according to 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 apparatus according to the first embodiment of the present invention. FIG. 2 is a block diagram schematically showing a water treatment apparatus according to the first comparative example. FIG. 3 is a block diagram schematically showing the water treatment apparatus according to the second comparative example. FIG. 4 is a block diagram schematically showing a water treatment apparatus according to a second embodiment of the present invention. FIG. 5 is a block diagram schematically showing a water treatment apparatus according to a third embodiment of the present invention. FIG. 6 is a block diagram schematically showing a water treatment apparatus according to a fourth 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. Further, the present invention is not limited to the embodiments described below.

(First Embodiment)
(Water treatment equipment)
First, the water treatment apparatus according to the first embodiment of the present invention will be described. FIG. 1 is a block diagram schematically showing a water treatment apparatus 1 according to the first embodiment. As shown in FIG. 1, the water treatment apparatus 1 according to the first 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 semi-permeable 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 materials such as cellulose acetate-based, polyamide-based, polyethyleneimine-based, polysulfone-based, and polybenzimidazole-based. The semipermeable membrane 11a may be composed of only one type (one layer) of the material used for the separation layer, and has a support layer that physically supports the separation layer and does not substantially contribute to separation2. It may be composed of layers or more. Examples of the support layer include materials such as polysulfone-based, polyketone-based, polyethylene-based, polyethylene terephthalate-based, and general non-woven fabric. The form of the semipermeable membrane 11a is not limited, and various forms of membranes such as flat membranes, tubular membranes, and hollow fibers can be used. The membrane module 11 is, for example, a cylindrical or box-shaped container, and the inside is divided into two chambers by the semipermeable membrane 11a by installing the semipermeable membrane 11a inside. 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. As the membrane module 11, a known semipermeable membrane device can be used, and a commercially available product can also be used.

In the membrane module 11, an aqueous solution-containing solution can be flowed into one chamber partitioned by the semipermeable membrane 11a, and a draw solution which is an aqueous absorption solution can be flowed into the other chamber. The pressure for introducing the draw solution into the membrane module 11 is 0.1 MPa or more and 0.5 MPa or less, and in the first embodiment, for example, 0.2 MPa. The aqueous solution-containing solution is, for example, seawater, brackish water, steam water, industrial wastewater, accompanying water, or sewage, or an aqueous solution containing water as a solvent obtained by filtering these waters, if necessary. The temperature of the aqueous solution-containing solution is controlled to a predetermined temperature of, for example, about 50 ° C. by the treatment in the previous stage.

As the draw solution, a solution mainly composed of a temperature-sensitive water-absorbing agent (polymer) having at least one cloud point is used. A temperature-sensitive water absorbent is hydrophilic at low temperatures and dissolves well in water to increase the amount of water absorption, while the amount of water absorption decreases as the temperature rises, and when the temperature rises above a predetermined temperature, it becomes hydrophobic and the solubility decreases. It is a substance. In this first embodiment, the polymer is preferably a block or random copolymer containing at least a hydrophobic part and a hydrophilic part, and the basic skeleton contains at least one group consisting of ethylene oxide group and 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. In such polymers, the temperature at which water solubility and water insolubility change is called the cloud point. When the temperature of the draw solution reaches the cloud point, the hydrophobic temperature-sensitive water absorbent aggregates and becomes cloudy. The temperature-sensitive water absorbent is used as various surfactants, dispersants, emulsifiers and the like. In this first embodiment, the draw solution is used as an attractant to attract water from the aqueous solution.

The heater 12 as a means for heating 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 drawn solution (diluted draw solution) diluted and discharged in the membrane module 11 to the temperature of the cloud point or higher.

The separation tank 13 as a water separation means is a water separation draw in which the diluted draw solution is phase-separated by heating in the heater 12, and the water content is lower than that of the water-rich solution mainly composed of water and the water-rich solution mainly composed of polymer. Phase-separate with solution.

The final treatment unit 14 as the separation treatment means is composed of, for example, a corelesser, an activated charcoal adsorption unit, an ultrafiltration membrane (UF membrane) unit, a nanofiltration membrane (NF membrane) unit, or a reverse osmosis membrane (RO membrane) unit. To. In the water-rich solution flowing out of the separation tank 13, the final treatment unit 14 separates the remaining polymer from the water-rich solution 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 at least the upstream side of the heater 12. be introduced.

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

Forward osmosis step In the membrane module 11 as a forward osmosis means, a forward osmosis step is performed. That is, in the membrane module 11, when the aqueous solution and the draw solution are brought into contact with each other via the semipermeable membrane 11a, the water in the aqueous solution passes through the semipermeable membrane 11a and moves to the draw solution due to the osmotic pressure difference. Water moves from one of the chambers into which the aqueous solution-containing solution flows, and the concentrated aqueous solution-containing solution flows out. Water moves from the other chamber into which the draw solution flows, and the diluted draw solution flows out. The temperature of the draw solution is adjusted by temperature control with respect to the aqueous solution and heat conduction at the time of contact with the aqueous solution. In this first embodiment, the temperature of the diluted draw solution is adjusted to a temperature of 30 ° C. or higher and 50 ° C. or lower, specifically, for example, about 40 ° C.

Heating step In the heater 12, a heating step is performed. That is, the pre-separation draw solution in which the separation-treated draw solution obtained in the final treatment step described later is introduced into the diluted draw solution diluted by moving 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 portion 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 first embodiment, the heating temperature is, for example, 88 ° C., which is 100 ° C. or higher at the cloud point or higher.

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-separated 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-separated draw solution can be performed by allowing the solution to stand at a liquid temperature equal to or higher than the cloud point. The water-separated 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-separated 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 treatment unit 14. The water-rich solution is, for example, 99% water and 1% draw concentration.

Final processing step In the final processing unit 14, a final processing step as a separation processing 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 produced water such as fresh water. Here, the treatment temperature in the final treatment unit 14 is, for example, 20 ° C. or higher and 50 ° C. or lower, preferably 35 ° C. or higher and 45 ° C. or lower, and in this first embodiment, for example, 45 ° C. The product water separated from the water-rich solution is released to the outside as the final product obtained from the aqueous solution. The separation-treated 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.

(Examples and comparative examples)
Next, a first embodiment of the water treatment apparatus 1 configured as described above and a comparative example according to the prior art will be described.

(First Example)
The first embodiment is an example of producing 300 L of fresh water per hour from seawater having a salinity of 4% by using the water treatment apparatus 1 according to the first embodiment.

In order to compare with the first embodiment based on the first embodiment, an example of a water treatment apparatus for discarding the separation-treated draw solution (see Patent Document 1) is referred to as a first comparative example. FIG. 2 is a block diagram schematically showing the water treatment apparatus 100 according to the first comparative example. Further, an example of introducing the separation-treated draw solution into the water-separated draw solution at the subsequent stage of the separation tank (see Patent Document 2) will be referred to as a second comparative example. FIG. 3 is a block diagram schematically showing the water treatment apparatus 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 includes a membrane module 101 having a semipermeable membrane 101a inside, a heater 102, and the same as the water treatment apparatus 1 according to the first embodiment. It is configured to include a separation tank 103 and a final treatment unit 104. The membrane module 101, the heater 102, the separation tank 103, and the final treatment unit 104 are the same as the membrane module 11, the heater 12, the separation tank 13, and the final treatment 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 device 200 according to the second comparative example has a membrane module 201 provided with a semipermeable membrane 201a inside, a heater 202, and the same as the water treatment device 1 according to the first embodiment. It is configured to include a separation tank 203 and a final treatment unit 204. The membrane module 201, the heater 202, the separation tank 203, and the final treatment unit 204 are the same as the membrane module 11, the heater 12, the separation tank 13, and the final treatment unit 14, respectively. On the other hand, unlike the water treatment device 1, in the water treatment device 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 aqueous solution-containing solution and the concentrated aqueous solution-containing solution, as well as the diluted draw solution, the water-separated draw solution, the pre-separation draw solution, the separation-treated draw solution, and the separation-treated draw solution in the first example, the first comparative example, and the second comparative example. The experimental results of the respective flow rates and concentrations of the mixed draw solution are shown. In the first example, the first comparative example, and the second comparative example, the types of the aqueous solution and the amount of water produced per unit time of the finally produced fresh water such as fresh water are assumed to be equal to each other. Specifically, the introduction pressure to the membrane module 11 is 34 atm, which is equal to or higher than the osmotic pressure of seawater (about 25 atm), the draw concentration of the water-rich solution is 1%, the flow rate is 375 L / h, and the recovery rate in the final treatment unit 14 is 80. %, The amount of fresh water finally produced 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 processing cost becomes high, but also the draw solution needs to be added at any time, which causes a problem that it becomes extremely difficult to reduce the cost.

In the second comparative example, the separation-treated draw solution is introduced into the water-separated draw solution on the downstream side of the separation tank 203. As a result, the separation-treated draw solution can be reused, but the draw concentration of the mixed draw solution supplied to the membrane module 201 is lower than that of the water-separated draw solution flowing out of the separation tank 203. Therefore, the filtration rate of the membrane module 201 to which the mixed draw solution is supplied is lower than the filtration rate of the membrane module 201 when the water-separated draw solution is supplied. Along with this, the flow rate of the mixed draw solution supplied to the membrane module 201 also 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 becomes large.

From Table 1, it can be seen that in the first embodiment as compared with the first comparative example described above, when the final amount of water produced is the same, the flow rate of the aqueous solution supplied to the water treatment apparatus 1 can be reduced. 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 first embodiment are set to the same flow rate, the amount of water produced is water. It can be seen that the number of the water treatment device 1 is larger than that of the treatment device 100. That is, it can be seen that in the water treatment apparatus 1 according to the first embodiment, the recovery rate of fresh water can be improved as compared with the conventional case.

Further, in contrast to the above-mentioned first and second comparative examples, in the first embodiment, as shown in FIG. 1, the separation-treated draw solution is introduced into the diluted draw solution on the upstream side of the heater 12. As a result, it is possible to suppress a decrease in the draw concentration of the water-separated draw solution supplied to the membrane module 11, and from Table 1, the draw concentration of the water-separated draw solution is set to the same concentration as that of the prior art (first and second comparative examples). It turns out that it can be maintained.

Further, from Table 1, it can be seen that in the first embodiment, the filtration rate in the membrane module 11 can be increased as compared with the first comparative example. That is, it can be seen that in the first embodiment, the flow rate of the water-separated draw solution is reduced as compared with the first and second comparative examples. Specifically, from Table 1, it can be seen that in the first embodiment, the flow rate of the water separation draw solution supplied to the membrane module 11 can be reduced from 1249 L / h to 997 L / h as compared with the first comparative example. .. Similarly, in the first embodiment, the flow rate of the water separation draw solution (mixed draw solution in the second comparative example) supplied to the membrane module 11 is from 2075 L / h to 997 L / h as compared with the second comparative example. It can be seen that it can be reduced to. Since the reduction of the flow rate of the water-separated draw solution contributes to the reduction of the amount of the polymer used in the draw solution, 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 flows in the heater 102 at a flow rate of 2375 L / h. It is flowing in 202. On the other hand, in the first embodiment, the pre-separation draw solution is flowing in the heater 12 at a flow rate of 1372 L / h. That is, from Table 1, it can be seen that in the first embodiment, the flow rate of the draw solution to be flowed in the heater is reduced. Here, since the specific heat and density of the polymer aqueous solution used in the first example and the first and second comparative examples are 3.2 kJ / kg · K and 1.05 kg / L, respectively, 40 draw solutions are used. The energy required for heating from ° C to 88 ° C above the cloud point is as follows. As for the specific heat, since the average specific heat at 40 to 88 ° C. is used as the polymer aqueous solution, it does not depend on the concentration of the draw solution. As for the density, the influence of the concentration and the temperature is negligibly small because the contribution of the concentration and the temperature of the draw solution is extremely small.
First 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 in the first embodiment, the energy can be reduced by about 16% as compared with the first comparative example, and the energy can be reduced by about 42% as compared with the second comparative example.

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

(Second embodiment)
(Water treatment equipment)
Next, a second embodiment of the present invention will be described. FIG. 4 shows the water treatment device 2 according to the second embodiment. As shown in FIG. 4, the water treatment apparatus 2 according to the second embodiment has a first membrane module 21 having a semipermeable membrane 21a inside and a second membrane module 22 having a semipermeable membrane 22a inside. , 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, and the heater 12 in the water treatment apparatus 1, respectively. This is the same as the separation tank 13 and the final treatment unit 14.

The second membrane module 22 and the semipermeable membrane 22a can adopt the same configurations as 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 divided into two chambers by the semipermeable membrane 22a. Here, in the water treatment apparatus 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 may be mutually exclusive. Membrane modules with different configurations may be used. Further, the semipermeable membranes 21a and 22a may adopt semipermeable membranes having the same configuration and type as each other, or may adopt semipermeable membranes having different configurations and types from each other.

In the water treatment apparatus 2 according to the second embodiment, unlike the first embodiment, the second membrane module 22 is provided on the upstream side of the first membrane module 21 along the flow direction of the draw solution and the aqueous solution-containing solution. Be done. As a result, the aqueous solution containing water supplied from the outside to the water treatment device 2 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 the same as those of the first embodiment.

(Water treatment method)
(Second forward osmosis step)
Next, a water treatment method using the water treatment device 2 according to the second embodiment will be described. In the second embodiment, unlike the first 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 and the separation-treated draw solution having a lower osmotic pressure than the aqueous solution are brought into contact with each other via the semipermeable membrane 22a. Here, since the osmotic pressure of the separation-treated draw solution is lower than the osmotic pressure of the aqueous solution-containing solution, the water in the separation-treated draw solution passes through the semipermeable membrane 22a and moves to the aqueous solution-containing solution due to the difference in osmotic pressure. As a result, the diluted aqueous solution, which is diluted by moving water from the separation-treated draw solution, flows out from one of the chambers into which the aqueous solution-containing solution flows. Water moves from the other chamber into which the separation-treated draw solution flows, and the concentrated separation-treated draw solution flows out. In the separation-treated 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.

(1st forward osmosis step)
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-separated draw solution and the diluted aqueous solution are brought into contact with each other via the semipermeable membrane 21a, and the first forward osmosis step is performed. The concentrated separation treated draw solution flowing 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 concentrated separation treatment draw solution has been introduced is supplied to the heater 23 as a pre-separation draw solution. The other heating step, the water separation step, and the final treatment step are the same as those in the first embodiment. A second embodiment based on the second embodiment will be described later.

(Third embodiment)
(Water treatment equipment)
Next, a third embodiment of the present invention will be described. FIG. 5 shows the water treatment device 3 according to the third embodiment. As shown in FIG. 5, the water treatment apparatus 3 according to the third embodiment has the first membrane module 21 and the semipermeable membrane 22a having the semipermeable membrane 21a, similarly to the water treatment apparatus 2 according to the second embodiment. It is configured to include a second membrane module 22, a heater 23, a separation tank 24, and a final treatment unit 25. On the other hand, unlike the water treatment device 2 according to the second embodiment, the water treatment device 3 has the concentrated separation treatment draw solution flowing out from the second membrane module 22 in the separation tank 24 along the flow direction of the water separation draw solution. It is configured to be introduced on the downstream side. Other configurations are the same as those of the second embodiment.

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

(Fourth Embodiment)
(Water treatment equipment)
Next, a fourth embodiment of the present invention will be described. FIG. 6 shows the water treatment device 4 according to the fourth embodiment. As shown in FIG. 6, the water treatment apparatus 4 according to the fourth embodiment has the first membrane module 21 and the semipermeable membrane 22a having the semipermeable membrane 21a, similarly to the water treatment apparatus 2 according to the second embodiment. It is configured to include a second membrane module 22, a heater 23, a separation tank 24, and a final treatment unit 25. On the other hand, unlike the water treatment device 2 according to the second embodiment, the water treatment device 4 is such that the aqueous solution supplied to the water treatment device 4 from the outside is branched on the upstream side along the flow direction of the aqueous solution. It is composed of. In the water treatment apparatus 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 the first membrane module 21. It is configured to be introduced on the upstream side. Other configurations are the same as those of the second embodiment.

(Water treatment method)
Next, a water treatment method using the water treatment device 4 according to the fourth embodiment will be described. In the water treatment apparatus 4 according to the fourth embodiment, a branch portion is provided on the upstream side where the aqueous solution-containing solution is supplied along the flow direction. At the branching portion, the aqueous solution-containing solution supplied to the water treatment apparatus 4 is branched into a partial aqueous solution-containing solution and the remaining aqueous solution-containing solution. Here, the flow rate of the remaining aqueous solution is adjusted by adjusting the flow rate of a part of the aqueous solution supplied to the second membrane module 22. A part of the aqueous solution is supplied to one chamber of the second membrane module 22 to perform the second forward osmosis step. In the second membrane module 22, the water in the separation-treated draw solution passes through the semipermeable membrane 22a and moves to a part of the aqueous solution-containing solution. The diluted aqueous solution flows out from one of the chambers in which the aqueous solution-containing solution flows in in the second membrane module 22, and after the balance of the branched aqueous solution is introduced, one chamber of the first membrane module 21 is used as the diluted aqueous solution. Is supplied to. The concentrated separation-treated draw solution flows out from the other chamber of the second membrane module 22, and is introduced into the diluted draw solution flowing out of the first membrane module 21 on the upstream side of the heater 23. The other first forward osmosis step, heating step, water separation step, and final treatment step are the same as those of the first and second embodiments. A fourth embodiment based on the fourth embodiment will be described later.

(2nd, 3rd, 4th Examples, and 1st, 2nd Comparative Examples)
Next, the second to fourth embodiments based on the respective second to fourth embodiments will be described. The second, third, and fourth embodiments are examples using the water treatment devices 2, 3, and 4, respectively. The first comparative example is a comparative example using the water treatment device 100 shown in FIG. 2 described above, and the second comparative example is a comparative example using the water treatment device 200 shown in FIG. 3 described above.

Table 2 shows the flow rates and salt concentrations of the aqueous solution-containing solution, the diluted aqueous solution-containing solution, and the concentrated aqueous solution, as well as the water-separated draw solution, the mixed draw solution, and the diluted solution in the second to fourth examples and the first and second comparative examples. The experimental results of the flow rates and concentrations of the draw solution, the pre-separation draw solution, the separation-treated draw solution, and the concentrated separation-treated draw solution are shown. In the second to fourth examples and the first and second comparative examples, the types of the aqueous solution and the amount of water produced per unit time of the finally produced fresh water such as fresh water are assumed to be equal to each other. 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 finally produced per unit time is 300 L / h. Set to h. In the fourth 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 containing water is 922 L / h. As a result, in the fourth embodiment, the salt concentration of the diluted aqueous solution before flowing out from the second membrane module 22 and introducing the remaining aqueous solution is 2.2%, and the flow rate is 135 L / h. In Table 2, the salt concentration and the flow rate of the diluted aqueous solution of the fourth example are the salt concentration and the flow rate of the diluted aqueous solution after the remaining aqueous solution is introduced.

From Table 2, in the second to fourth embodiments as compared with the first comparative example described above, when the final amount of fresh water produced is the same, the flow rate of the aqueous solution supplied to the water treatment apparatus can be reduced. 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 second to fourth embodiments are set to the same flow rate, It can be seen that the amount of water produced in the water treatment devices 2 to 4 is larger than that in the water treatment device 100. That is, it can be seen that in the water treatment devices 2 to 4 according to the second to fourth embodiments, the recovery rate of fresh water can be improved as compared with the conventional case.

Further, as shown in FIGS. 4 and 5, in the water treatment devices 2 and 3 according to the second and third 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 being transferred 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 apparatus 100 according to the first comparative example. As a result, the osmotic pressure difference between the diluted aqueous solution and the draw solution in the first membrane module 21 becomes large. By increasing the osmotic pressure difference between the diluted aqueous solution and the draw solution in the first membrane module 21, the filtration rate and the water recovery rate can be increased as compared with the conventional case, and the flow rate of the supplied draw solution can be reduced. Specifically, from Table 2, in the second embodiment, the flow rate of the water separation draw solution supplied to the first membrane module 21 can be reduced from 1249 L / h to 700 L / h as compared with the first comparative example. I understand. Similarly, in the third embodiment, the flow rate of the mixed draw solution supplied to the first membrane module 21 is 1249 L / L / 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. Reducing the flow rate of the water-separated draw solution or the mixed draw solution contributes to the reduction of the amount of the polymer used in the draw solution, so that 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 flows in the heater 102 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 second embodiment, the pre-separation draw solution flows in the heater 23 at a flow rate of 1075 L / h. Further, as shown in Table 2 and FIG. 5, in the third embodiment, the diluted draw solution flows in the heater 23 at a flow rate of 1460 L / h. That is, from Table 2, it can be seen that in the second and third embodiments, the flow rate of the draw solution to be flowed 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 polymer aqueous solution used in the second, third embodiment 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.
Second Example: (3.2 kJ / kg · K × 1.05 kg / L × 1075 L / h × (88 ° C − 40 ° C) =) 1.73 × 10 ⁵ kJ / h
Third Example: (3.2 kJ / kg · K × 1.05 kg / L × 1460 L / h × (88 ° C − 40 ° 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 second embodiment, the energy can be reduced by about 34% as compared with the first comparative example, and the energy can be reduced by about 55% as compared with the second comparative example. Similarly, it can be seen that in the third embodiment, the energy can be reduced by about 10% as compared with the first comparative example, and the energy can be reduced by about 39% as compared with the second comparative example.

In Table 2, when the second embodiment and the fourth embodiment are compared, it can be seen that the same effect as that of the second embodiment can be obtained in the fourth embodiment. Further, the aqueous solution supplied to the water treatment devices 2 and 4 is 997 L / h, but as shown in FIG. 6, the supplied aqueous solution is branched by the branch portion to the second membrane module 22. The flow rate of the water-containing aqueous solution to be supplied is 75 L / h in the fourth embodiment, which is significantly reduced as compared with the second 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 apparatus 4 can be reduced in the fourth embodiment as compared with the second embodiment.

As described above, according to the second, third, and fourth embodiments, the filtration rate of the first membrane module 21 can be increased as compared with the conventional case, so that 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 can be reduced in the water treatment devices 2, 3 and 4 as compared with the conventional case. At the same time, the energy consumed for heating can be reduced. Further, in the water treatment apparatus 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 based on the technical idea of the present invention are possible. For example, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used if necessary, and the present invention is based on the description and drawings which form a part of the disclosure of the present invention according to the present embodiment. Is not limited.

1,2,3,4 Water treatment equipment 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 (18)

A forward osmosis step in which water is transferred from an aqueous solution containing water as a solvent to a draw solution having a cloud point via a semipermeable membrane to obtain a diluted draw solution.
A heating step of heating the diluted draw solution to a temperature of 100 ° C. or higher above the cloud point, and
A water separation step of separating the diluted draw solution heated in the heating step into a water-rich solution and a water-separated draw solution having a lower water content than the water-rich solution.
A water treatment method comprising a separation treatment step of separating the water-rich solution into a generated water and a separation treatment draw solution.
The separation-treated draw solution was introduced into the diluted draw solution prior to the heating step.
The temperature of the diluted draw solution obtained in the forward osmosis step is adjusted to 30 ° C. or higher and 50 ° C. or lower by controlling the temperature of the aqueous solution and conducting heat with the aqueous solution.
Prior to the forward osmosis step, the aqueous solution and the separation-treated draw solution are brought into contact with each other via a second semi-permeable membrane, and the water in the separation-treated draw solution is transferred to the aqueous solution to be diluted. A second forward osmosis step was performed in which the separated aqueous solution was prepared and the separation-treated draw solution was concentrated to obtain a concentrated separation-treated draw solution.
A water treatment method comprising performing the forward osmosis step on the diluted aqueous solution. The water treatment method according to claim 1, wherein the water separation draw solution separated in the water separation step is used as the draw solution in the forward osmosis step. The water treatment method according to claim 1 or 2, wherein the separation treatment step is performed using a corelesser, activated carbon, an ultrafiltration membrane, a nanofiltration membrane, or a reverse osmosis membrane. The water treatment method according to any one of claims 1 to 3, wherein the draw solution is a solution mainly composed of a temperature-sensitive water-absorbing agent having at least one cloud point. The water treatment method according to any one of claims 1 to 4, wherein the aqueous solution contains seawater, brackish water, brackish water, industrial wastewater, accompanying water, or sewage. The water treatment method according to any one of claims 1 to 5, wherein the cloud point is more than 50 ° C and 100 ° C or less. The water treatment method according to any one of claims 1 to 6, wherein the concentrated separation treated draw solution is introduced into the diluted draw solution before the heating step. The aqueous solution is branched into a partial aqueous solution and a remaining aqueous solution, the second positive osmosis step is performed on the partial aqueous solution, and the positive osmosis step is performed on the remaining aqueous solution. The water treatment method according to any one of claims 1 to 7, wherein the water treatment method is performed. The water treatment method according to any one of claims 1 to 6, wherein the concentrated separation treated draw solution is introduced into the water separated draw solution after the water separation step. A forward osmosis means for moving water from an aqueous solution containing water as a solvent to a draw solution having a cloud point via a semipermeable membrane to obtain a diluted draw solution.
A heating means for heating the diluted draw solution to a temperature above the cloud point and below 100 ° C.
A water separation means for separating the diluted draw solution heated by the heating means into a water-rich solution and a water-separated draw solution having a lower water content than the water-rich solution.
A separation treatment means for separating the water-rich solution into the generated water and the separation treatment draw solution is provided.
The separation-treated draw solution is introduced to the upstream side of the heating means or the heating means along the flow direction of the diluted draw solution.
The temperature of the diluted draw solution obtained by the forward osmosis means is adjusted to 30 ° C. or higher and 50 ° C. or lower by temperature control with respect to the aqueous solution and heat conduction with the aqueous solution .
The aqueous solution and the separation-treated draw solution are brought into contact with each other via a second translucent film, and the water in the separation-treated draw solution is moved to the aqueous solution to obtain a diluted diluted aqueous solution, and the separation is made. processing the draw solution second forward osmosis unit to concentration and separation process draw solution was concentrated, water treatment apparatus, characterized in that Ru is provided on an upstream side of the forward osmosis unit along the flow direction of the water-containing solution. Has been the water separating draw solution separated by the water separator, the water treatment apparatus according to claim 1 0, characterized in that to supply as the draw solution to the forward osmosis unit. Said separating means is, coalescers, activated carbon, ultrafiltration membrane, water treatment apparatus according to claim 1 0 or 1 1, characterized in that it consists nanofiltration membrane or reverse osmosis membrane. The draw solution, water treatment apparatus according to any one of claims 1 0 to 1 2, characterized in that the temperature sensitive water absorbing agent is a solution mainly comprising at least one cloud point. The water solution is seawater, brine, brackish water, industrial waste water, produced water, or water treatment device according to any one of claims 1 0 to 1 3, characterized in that the sewage. Water treatment device according to any one of claims 1 0-1 4, wherein the cloud point is equal to or less than 100 ° C. exceed 50 ° C.. The water according to any one of claims 10 to 15, wherein the concentrated separation treated draw solution is configured to be introduced to the upstream side of the heating means along the flow direction of the diluted draw solution. Processing device. The aqueous solution supplied from the outside is configured to be branched into a partial aqueous solution and the remaining aqueous solution on the upstream side along the flow direction of the aqueous solution, and the partial aqueous solution is formed. The water treatment apparatus according to any one of claims 10 to 16, wherein the water treatment apparatus is introduced into the second forward osmosis means and the aqueous solution containing the balance is introduced into the forward osmosis means. A claim characterized in that the concentrated separation treated draw solution flowing out of the second forward osmosis means is configured to be introduced downstream of the water separation means along the flow direction of the water separation draw solution. The water treatment apparatus according to any one of 10 to 15.

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