JP2016041411A - Water desalination processing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for treating water by forward osmosis method that can separate, in the gravity separation process, a layer that has a temperature-responsive chemical material as the main body, at a predetermined solute concentration or water concentration.SOLUTION: Provided is a water desalination processing method and apparatus comprising a forward osmosis process 10 for contacting a salts-containing to-be-processed water 1 and an inducing solution 4 in which a temperature-responsive chemical material having a lower critical temperature is dissolved into water, through a semi-permeable membrane 3; a warming process 14; a gravity separation process 11; a cooling and recirculation process for cooling a concentrated solution 7 separated in the gravity separation process 11 to a temperature below the lower critical temperature of the inducing solution 4 and then recirculating it to the forward osmosis process 10 to be reused as the inducing solution 4; and a membrane-treatment process 12 for membrane-treating a diluted solution 6 separated in the gravity separation process 11 to produce a membrane-filtered water 8, in which the lower critical temperature of a diluted inducing solution 5 is measured and when the measured value is higher than a set value a hydrophobic material is added to the diluted inducing solution 5, and when the measured value is lower than the set value a hydrophilic material is added to the diluted inducing solution 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water desalting method and apparatus for producing fresh water from water to be treated such as seawater and brine.

  Various methods for producing fresh water from seawater using a semipermeable membrane are known, but a reverse osmosis method for forcibly permeating water by applying a pressure higher than the osmotic pressure to seawater has been mainly developed. However, since this method needs to be pressurized to a high pressure, there is a problem that the equipment cost and the operation cost are high. Therefore, a method of producing fresh water by contacting seawater and a solution having a higher concentration than seawater through a semipermeable membrane, transferring water in seawater to this solution by osmotic pressure without applying pressure, and separating and recovering the solution. Has been developed. (Patent Documents 1-3).

  In the method of Patent Document 1, a salt solution obtained by dissolving ammonia and carbon dioxide is passed through a semipermeable membrane on the side opposite to seawater, and water in the seawater is passed through the semipermeable membrane into the salt solution. The resulting diluted salt solution is separated into ammonium ions and carbonate ions individually using an ion exchange membrane or distillation tower to obtain purified water, and the separated ammonium ions and carbonate ions are dissolved in the salt solution. This is the method of returning to the original room of the semipermeable membrane.

  The method of Patent Document 2 uses an attraction solution having a substance having a lower critical temperature as a solute. As shown in FIG. 4, seawater 21 is sent to a forward osmosis system 30 where it is attracted through a semipermeable membrane. The water in the seawater 21 is brought into contact with the solution 24 and permeated through the semipermeable membrane by osmotic pressure to move to the attracting solution 24. The concentrated seawater 22 remaining after the water has moved to the attracting solution flows out of the forward osmosis system 30. On the other hand, the diluted attraction solution 25 diluted with water in seawater is sent to a precipitation system 34 equipped with a heater, and the diluted attraction solution that has undergone phase separation or precipitation is pressurized by a pump 37 to the filtration system 32. Sent. At that time, a liquid 29 having a temperature lower than the lower critical temperature of the solute can be added. The attraction solution 24 concentrated in the filtration system 32 is returned to the forward osmosis system 30. On the other hand, the filtered membrane filtrate 28 is further purified by the post-processing unit 33 to become drinking water. Polyethylene glycol or polypropylene glycol is used as a solute having a lower critical temperature, and a nanofiltration membrane or a reverse osmosis membrane is used as a filter medium of a filtration system.

  Patent Document 3 discloses an induced solute for forward osmosis having a specific structure. This induced solute has a lower critical temperature and becomes self-aggregated and separated from the solution above that temperature. A method for producing fresh water using a semipermeable membrane using this property is disclosed.

JP 2011-83663 A US Pat. No. 8,021,553B2 JP 2012-170954 A

In the method of Patent Document 1, the attracting substance (for example, ammonium carbonate) is separated and recovered by an evaporation method. At that time, the latent heat of vaporization of ammonia and accompanying water is great, enormous energy is required, and the cost is high. Furthermore, the size of the evaporation facility is extremely large, and is not suitable for producing a large amount (for example, 100,000 m ³ / day) of drinking water. Moreover, since the input energy is large, the size of the heat exchanger is also large, which is not suitable for mass processing. Furthermore, when ammonium carbonate is used, the attracting substance that leaks into the environment through the membrane concentrated water by backflow from the semipermeable membrane contains nitrogen, which causes eutrophication.

  In the methods of Patent Documents 2 and 3, membrane filtration energy can be reduced by aggregating a part of the attracting substance by utilizing the temperature sensitivity of the attracting solution.

  However, if the attractant solution is repeatedly recycled over a long period of time, salt and organic substances that slightly permeate through the semi-permeable membrane accumulate due to fluctuations in the water temperature and outside air temperature, and the diluted attractant solution obtained in the forward osmosis process is accumulated. It was found that the solute concentration of a concentrated solution mainly composed of a temperature-sensitive drug changes due to a change in the gravity separation characteristics at the time of gravity separation. When separating a concentrated solution of a temperature-sensitive drug, the higher the temperature is above the lower critical temperature, the greater the concentration difference between the concentrated solution and the diluted solution during separation, and when filtering through a semipermeable membrane. When the temperature is lower than the lower critical temperature, the osmotic pressure increases and a high filtration rate is obtained. Therefore, when controlling the temperature of heating and cooling during gravity separation or forward osmosis to a constant value, an increase in the lower critical temperature causes a decrease in separation efficiency in the gravity separation process, and a decrease in the lower critical temperature occurs in the forward osmosis process. Causes a decrease in filtration efficiency.

  Accordingly, it is essential for stable operation of the forward osmosis method to maintain a constant solute concentration or water concentration of a concentrated solution mainly composed of a temperature-sensitive drug separated by gravity.

  The object of the present invention is to treat a layer mainly composed of a temperature-sensitive drug in a gravity separation step in a method of water treatment by a forward osmosis method, regardless of the accumulation of salts and organic substances in the attracting solution. It is to provide a method and an apparatus that can be separated with each other.

  As a result of intensive studies to solve the above problems, the present inventor measured the lower critical temperature of the dilution-induced solution separated in the gravity separation step, and when the measured value is higher than a preset value, A hydrophobic substance is added to the diluted attracting solution, and if the measured value is lower than a preset value, a hydrophilic substance is added to the diluted attracting solution to lower the lower limit of the attracting solution. It was found that the forward osmosis method can be stably operated while keeping the critical temperature constant.

  The lower critical temperature of a temperature-sensitive drug is determined by the balance between the hydrophilic group and the hydrophobic group of the drug, and is higher when there are more hydrophilic groups and lower when there are more hydrophobic groups. A similar tendency is observed in the aqueous solution of the mixture, and a phenomenon in which the lower critical temperature rises is observed when a substance having a high lower critical temperature containing many hydrophilic groups is mixed with a substance having a lower lower critical temperature. The degree of change in the lower critical temperature varies depending on the mixing amount of the substance having a high lower critical temperature containing many hydrophilic groups and the degree of hydrophilic group / hydrophobic group of the mixed substance. On the other hand, when the water in which the temperature-sensitive drug is dissolved contains a large amount of salt, the lower critical temperature decreases, and when the water contains a large amount of a hydrophilic substance such as alcohol, the lower critical temperature increases. Such a phenomenon is seen when the forward osmosis method which performs membrane filtration as a finishing treatment after gravity separation is operated for a long time. That is, this occurs when the rejection rate of salt or alcohol is higher in the finished membrane than in the forward osmosis membrane.

  The surfactant is composed of a hydrophobic substance and a hydrophilic substance, and the effect of changing the lower critical temperature is smaller than that of the hydrophobic substance or the hydrophilic substance itself. For example, although the lower critical temperature changes even when a surfactant composed of hydrophobic butylene glycol and hydrophilic ethylene glycol is added, the lower critical temperature per weight added is more when butylene glycol or ethylene glycol itself is added. The effect of temperature change is great.

The present invention has been made on the basis of these findings, contact water to be treated containing salts and an attraction solution in which a temperature-sensitive drug having a lower critical temperature is dissolved in water through a semipermeable membrane. A normal osmosis step of transferring water in the water to be treated to the attraction solution through the semipermeable membrane to obtain a diluted attraction solution diluted with water and membrane concentrated water, and the lower limit of the attraction solution. A heating step for heating to a temperature above the critical temperature, a concentrated solution layer mainly composed of the temperature-sensitive agent phase-separated in the heating step, and a dilute solution mainly containing water and containing a small amount of the temperature-sensitive agent. Gravity separation step that separates into layers, and after cooling the concentrated solution separated in the gravity separation step to a temperature below the lower critical temperature of the attracting solution, it is circulated to the forward osmosis step and reused as the attracting solution Cooling and circulation process, and The dilute solution that has been separated by the force separation process and membrane treatment, a desalination treatment method for water having a film processing step of obtaining a membrane filtration water,
When the lower critical temperature of the dilution attraction solution is measured and the measured value is higher than a preset set value, a hydrophobic substance is added to the dilution attraction solution, and the set value is set at a preset value. If lower than the above, the present invention provides a desalting treatment method characterized by adding a hydrophilic substance to the dilution-inducing solution, and an apparatus related thereto.

  According to the present invention, in a water treatment method by a forward osmosis method using a temperature sensitive agent having a lower critical solution temperature, water treatment is performed by stabilizing the solute concentration or water concentration of the layer mainly composed of the temperature sensitive agent separated by gravity. Can be carried out stably over a long period of time.

It is a block diagram which shows one embodiment of this invention typically. It is the figure which showed typically the membrane filtration by the semipermeable membrane, and the isolation | separation in a gravity separation tank. 3 is a curve showing the relationship between the lower critical temperature and the drug concentration. It is a block diagram which shows the outline of a well-known water treatment method.

  FIG. 1 schematically shows an embodiment of the present invention.

  The water to be treated to be treated by the method of the present invention is a solution using water as a solvent, such as seawater, brine, sewage, industrial wastewater, or the like. Brine includes associated water from wells that mine shale gas, oil sand, CBM (coal bed methane), oil, and the like.

Accompanying water is water that is discharged along with the object to be mined from the well, and includes salt, organic matter, suspended matter, and the like. Concentrations of pollutants include, for example, evaporation residues (mainly Na ⁺ , K ⁺ , Ca ²⁺ , Cl ⁻ , SO ₄ ^2−, etc.) of 1,000 to 100,000 mg / L, organic substances (such as oil and added chemicals) Is contained in a range of 10 to 1,000 mg / L as TOC and suspended material in a range of 100 to 10,000 mg / L.

  There is no limitation on the means for separating oil and associated water, but oil-water separation is performed, for example, by sedimentation.

Although not shown in FIG. 1, the water to be treated is first filtered if necessary. This filtration treatment is performed, for example, with a filter using a microfiltration membrane, and a normal membrane used as a microfiltration membrane can be used as the filtration membrane. For example, in addition to cellulose acetate, polytetrafluoroethylene, polysulfone, polyvinyl chloride, etc., ceramic membranes and porous glass membranes can also be used. In the micromembrane filtration treatment, membrane filtrate water that has passed through the microfiltration membrane and membrane concentrated water remaining without passing through the membrane are obtained.
In addition to precision membrane filtration, filtration treatment such as ultramembrane filtration and sand filtration can be used. The material for the ultrafiltration is the same as that for precision membrane filtration.

Forward osmosis process The forward osmosis process is a process in which filtered water to be treated is brought into contact with a high osmotic pressure attraction solution in which a temperature-sensitive drug is dissolved in water through a semipermeable membrane, and the water in the treated water is mixed with the semi-permeable water. It is a step of moving to the attraction solution through a permeable membrane to obtain a diluted attraction solution diluted with water and membrane concentrated water.

  Temperature-sensitive drugs are substances that are hydrophilic and well soluble in water at low temperatures, but become hydrophobic and their solubility decreases at a certain temperature or higher.The temperature at which they change from hydrophilic to hydrophobic is the lower critical temperature or cloud point. be called. When this temperature is reached, a hydrophobized temperature-sensitive drug is precipitated, resulting in white turbidity or phase separation. When gradually warming, there are those that become cloudy by the drug but not phase-separated, those that become cloudy and then further heated and phase-separated, and those that phase-separate without passing through the cloudy state, the drug used in the present invention Means that the phases are separated, and the lower critical temperature here means the temperature at which the phases are separated.

  This temperature-sensitive agent is used as various surfactants, dispersants, emulsifiers, and the like. For example, alcohols, alkyl groups, glycols, or fatty acid and ethylene glycol compounds (water-soluble polyalkylene glycol derivatives, Polyoxyethylene polyoxypropylene alkyl ether, polyoxytetramethylene polyoxyethylene glycol, polyoxyethylene polyoxypropylene trimethylolpropane, polyoxyethylene polyoxypropylene glyceryl ether, polyoxyethylene polyoxypropylene pentaerythritol ether, etc.) alkyl group Or fatty acid and propylene oxide compound, acrylamide and alkyl group compound, ethylene glycol fatty acid ester, glycerin fatty acid ester, sorbi Fatty acid ester ethylene oxide adducts, amino acids and derivatives thereof, glycols such as butyl glycol and hexyl glycol, preferably block copolymers of polyethylene glycol and polypropylene / polybutylene glycol, glycerol ethoxylate butoxylate, trimethylol Propane ethoxybutoxylate and the like. As the temperature-sensitive drug used in the present invention, those having a lower critical temperature in the range of 30 ° C to 80 ° C, particularly in the range of 40 ° C to 60 ° C are preferable. Therefore, a method is adopted in which the lower critical temperature is adjusted to the above range by combining a nonionic surfactant having an HLB value of 10 or more and a nonionic surfactant having a lower HLB value, a fatty acid or an alcohol. You can also.

  The concentration of the attracting solution must be adjusted so that the osmotic pressure of the attracting solution is sufficiently higher than the osmotic pressure of the liquid to be treated.

  Aggregating solid particles may be added to the attracting solution. As the solid particles for aggregation, bentonite, kaolin, activated carbon powder and the like can be used, and an inorganic adsorbent is more desirable. The average particle size is preferably about 0.1 to 10 μm. The amount of solid particles added is suitably about 0.1 to 10% by weight with respect to the temperature sensitive drug. However, these are preferably determined in consideration of the affinity between the temperature sensitive drug and the solid particles.

  The semipermeable membrane is preferably one that can selectively permeate water, and a forward osmosis membrane is preferable, but a reverse osmosis membrane can also be used. The material is not particularly limited, and examples thereof include cellulose acetate-based, polyamide-based, polyethyleneimine-based, polysulfone-based, and polybenzimidazole-based materials. The form of the semipermeable membrane is not particularly limited and may be any of a flat membrane, a tubular membrane, a hollow fiber, and the like.

  A device for mounting this semipermeable membrane is usually a semi-permeable membrane installed in a cylindrical or box-shaped container, and water to be treated flows into one chamber partitioned by this semipermeable membrane, and the other chamber is filled with water. An attracting solution can be flowed, and a known semipermeable membrane device can be used, and a commercially available product can also be used.

  A chamber where treated water flows into the attracting solution through the semipermeable membrane due to the difference in osmotic pressure when the treated water is brought into contact with the attracting solution through the semipermeable membrane in the forward osmosis process. From the membrane concentrate and from the chamber into which the attraction solution flows, the dilute attraction solution flows out.

  The present invention measures the lower critical temperature of the dilution attraction solution, and when the measured value is higher than a preset set value, a hydrophobic substance is added to the dilution attraction solution, and the measured value is If it is lower than the set value, there is a feature in that a hydrophilic substance is added to the dilution attraction solution.

  In principle, the lower critical temperature of the dilution attraction solution may be measured somewhere between the outlet of the semipermeable membrane device and the gravity separation tank. The lower critical temperature can be measured by collecting the dilution-inducing solution, visually warming it and gradually observing the temperature at which phase separation begins. Some drugs may have a cloud point at a temperature slightly lower than the phase separation temperature. In this case, the cloud point may be observed visually, but it can also be measured as a temperature at which the absorbance of visible light rapidly increases. .

  Instead of the lower critical temperature itself, the lower critical temperature may be obtained from another index. For example, when the lower critical temperature increases, the moisture concentration of the temperature sensitive drug in the gravity separation tank increases, and as a result, the interface increases.

  That is, as shown in FIG. 3, the water concentration of the concentrated solution layer mainly composed of the temperature-sensitive drug separated by gravity is lower as the temperature at the time of gravity separation is higher than the lower critical temperature and higher as it is closer to the lower critical temperature. Become. Therefore, the lower critical temperature can be measured by measuring the interface height in the gravity separation tank.

  The set value for comparing the measured values is set within an allowable range, and whether or not it is within the range is compared. The allowable range of the lower critical temperature should be set for each plant according to the allowable range of changes in the performance of the thermosensitive drug (forward osmosis filtration rate and concentrated concentration after gravity separation) accompanying the fluctuation of the lower critical temperature. For example, ± 2 ° C. can be set within the allowable range with respect to the initial value of operation.

  Then, when the measured value exceeds the upper limit of the allowable range of the set value, a hydrophobic substance is added to the dilution attraction solution. As the hydrophobic substance, a glycol compound having 3 or more carbon atoms, preferably about 6 to 60, a fatty acid (salt), a sorbitan compound, or the like can be used. Examples of glycol compounds include polypropylene glycol, examples of fatty acids (salts) include oleic acid, lauric acid, alkali metal salts of caprylic acid, and examples of sorbitan compounds include sorbitan and sorbitan fatty acid esters (sorbitan monocaprylate). Etc.). The addition form of these hydrophobic substances is usually added as an aqueous solution, but may be added as it is when the dispersibility is good. The hydrophobic substance may be added all at once, or may be added continuously or intermittently. The addition is performed until the lower critical temperature of the dilution-inducing solution falls within the range of the set value, and it is preferable to add to the vicinity of the center of the range.

  On the other hand, when the measured value falls below the lower limit of the allowable range of the set value, a hydrophilic substance is added to the dilution attraction solution. As the hydrophilic substance, alcohol, an ethylene glycol-containing compound, a glycerin compound, or the like can be used. Examples of alcohol include butanol and propanol, examples of ethylene glycol-containing compounds include polyethylene glycol and polymers thereof with polybutylene glycol and polypropylene glycol, and examples of glycerol compounds include glycerol and polymers thereof (triglycerol, decaglycerol) Etc.). The addition form of these hydrophilic substances is also added as it is or in an aqueous solution. The hydrophilic substance may be added all at once, or may be added continuously or intermittently. The addition is performed until the lower critical temperature of the dilution-inducing solution falls within the range of the set value, and it is preferable to add to the vicinity of the center of the range.

Heating step The dilution attraction solution diluted by moving water from the water to be treated in the forward osmosis step is heated to a temperature equal to or higher than the lower critical temperature to aggregate at least a part of the temperature-sensitive drug. This agglomeration is a phase separation of a concentrated solution of a temperature sensitive drug.

  The heating temperature in the heating step can be controlled, for example, by adjusting the flow rate of the heat medium introduced into the heat exchanger.

  It is preferable to use the sensible heat of the concentrated solution separated in the next gravity separation step as the heat source for this heating step.

Gravity separation step Gravity-separated into a concentrated solution layer mainly composed of the temperature-sensitive drug phase-separated in the heating step and a dilute solution layer mainly composed of water and containing a small amount of the temperature-sensitive drug. This gravitational separation can be performed by standing in a gravity separation tank at a liquid temperature equal to or higher than the lower critical temperature. At this time, the concentrated solution of the temperature-sensitive drug aggregated in the heating step is in the form of fine droplets having the aggregation solid particles as a core. And when it is put into the gravity separation tank in this state, if the specific gravity of the temperature sensitive drug is heavier than water, the fine droplets of the concentrated solution will settle quickly, and the droplets will coalesce and concentrate underneath. A solution layer is formed. Most of the agglomerating solid particles collect in the concentrated solution layer or only a small part remains in the upper diluted solution layer. The solid particles for agglomeration have the effect of promoting the aggregation of the temperature-sensitive drug. The concentration of the upper layer drug (for example, 2 to 6% ⇒ 0.5 to 1.5%) and the lower layer drug concentration (for example, 60 to 70%) are increased. ⇒ 80-85%). Furthermore, the effect of shortening the separation time (for example, 30 minutes to 15 minutes) can be obtained. On the other hand, when the specific gravity of the temperature sensitive drug is lighter than water, for example, when butyl glycol or hexyl glycol is used as the temperature sensitive drug, the concentrated solution layer becomes the upper layer and the diluted solution layer becomes the lower layer.

Cooling / circulation step The concentrated solution separated in the gravity separation step is cooled to a temperature lower than the lower critical temperature of the attracting solution to be dissolved in water and regenerated into the attracting solution. Although this temperature can be employed in a wide range, considering the economy, a temperature of room temperature or higher is preferable. As this cooling heat source, it is preferable from the viewpoint of efficient use of energy to use the water to be treated or the dilution attraction solution obtained in the forward osmosis step. If this cooling is insufficient, the concentration is lowered by the water moving from the water to be treated in the forward osmosis process, so that the lower critical temperature is developed and phase separation occurs, and the osmotic pressure is lost.

  The regenerated attractant solution can be circulated and reused as it is.

Membrane treatment step On the other hand, the dilute solution separated in the gravity separation step is subjected to membrane filtration with a nanofiltration membrane, a reverse osmosis membrane or the like to remove the temperature-sensitive drug and solid particles for aggregation remaining therein. Membrane filtrate is fresh water and can be used for drinking water and the like. The membrane concentrated water remaining without being membrane filtered contains a temperature sensitive drug and solid particles for aggregation, and therefore should be circulated in the gravity separation step. Alternatively, it can be concentrated and returned directly to the forward osmosis process as an attractant solution.

  On the other hand, since the membrane concentrated water obtained in the forward osmosis step contains a high concentration of salt, it can be concentrated to precipitate and separate the salt for effective use.

  This method of the present invention is shown schematically in FIG. As shown in the figure, the treated water 1 such as seawater is fed into the forward osmosis membrane device 10, and the remaining membrane concentrated water 2 is discharged through the semipermeable membrane 3 by passing water through the opposite chamber. . The attracting solution 4 flows into the chamber on the opposite side of the forward osmosis membrane device 10, where it is diluted with the water transferred from the treated water 1 in countercurrent contact with the treated water 1 through the semipermeable membrane 3. And exit the forward osmosis membrane device 10. The dilution attraction solution 5 exiting the forward osmosis membrane device 10 has its lower critical temperature measured by the lower critical temperature measuring means 17 (takes a sample periodically and measured in the laboratory), and is input to the computer 18 in advance. Compared with the measured value. When the measured value exceeds the upper limit of the set value, the hydrophobic substance is added from the hydrophobic substance tank 19 to the dilution attraction solution. When the measured value is lower than the lower limit of the set value, the hydrophilic substance tank 20 is added. The hydrophilic substance is added to the dilution attraction solution. Then, the heat is exchanged with the concentrated solution 7 separated by gravity through the heat exchanger 16 and heated, and further heated by the heater 14 and enters the gravity separation tank 11.

  An interface meter 111 for measuring the interface between the lower layer and the upper layer is attached to the gravity separation tank 11, and the interface height is constantly measured. The value is also sent to the computer 18, and deviates from the set value range. A signal is sent to the hydrophobic substance tank 19 or the hydrophilic substance tank 20 to input them.

  The dilute solution 6 separated in the gravity separation tank 11 is filtered by a membrane filtration device 12, and the obtained membrane filtrate 8 is further purified by a post-treatment device 13 such as activated carbon to obtain purified water. Membrane concentrated water 9 that has not been filtered by the membrane filtration device 12 is returned to the gravity separation tank 11 and phase-separated together with the dilution attraction solution.

  On the other hand, the concentrated solution 7 separated in the gravity separation tank 11 is cooled by the cooler 15 via the heat exchanger 16 and returned to the forward osmosis device 10 as the attracting solution 4.

  The apparatus shown in FIG. 1 was used. A cellulose acetate FO membrane was used as the semipermeable membrane of the forward osmosis membrane device 10, and a nanofiltration membrane was used as the membrane filtration device 13.

  As the attracting solution, water was added to glycerol ethoxypropoxylate to make an 80% by weight solution. The lower critical temperature of this solution was 55 ° C. This lower critical temperature varies depending on the drug concentration. The results of examining the relationship between the drug concentration and the lower critical temperature are shown in FIG.

  Seawater pretreated with a UF membrane was flowed into the forward osmosis membrane device 10 as a treated water 1 at a flow rate of 3 L / min. The amount of the membrane permeated water was 1.5 L / min, and the amount of the dilution attraction solution 5 flowing out from the forward osmosis membrane device 10 was 3.8 L / min. Since the flow rate of the membrane permeated water mainly changes depending on the osmotic pressure of the concentrated attracting solution, when the flow rate is increased, the concentration temperature of the concentrated attracting solution is increased by increasing the separation temperature of the gravity separation tank. It is also possible to increase the membrane permeate flow rate by increasing the flow rate of the concentrated attracting solution to suppress the concentration drop. In order to reduce the membrane permeate flow rate, the reverse operation may be performed. The dilution attraction solution 5 was heated to 60 ° C. by the heater 14 through the heat exchanger 16 and flowed into the gravity separation tank 11. In the gravity separation tank 11, the temperature-sensitive drug was aggregated and separated into a concentrated solution 7 having a concentration of 80% by weight and a diluted solution 6 having a concentration of 1%. The concentrated solution 7 as the lower layer was cooled to 40 ° C. by the cooler 15 through the heat exchanger 16 and again flowed into the forward osmosis membrane device 10. The upper diluted solution 6 was introduced into the membrane filtration device 12 and separated into membrane filtrate 8 and membrane concentrate 9. The membrane concentrated water 9 was again flowed into the gravity separation tank 11. Membrane filtrate 8 obtained fresh water of 1.5 L / min via post-treatment device 13. This fresh water could be used as drinking water.

  The method of the present invention can be widely used for the production of fresh water from seawater, the treatment of associated water from wells, and the treatment of sewage and industrial wastewater.

DESCRIPTION OF SYMBOLS 1 Water to be treated 2 Membrane concentrated water 3 Semipermeable membrane 4 Attraction solution 5 Dilution attraction solution 6 Dilute solution 7 Concentrated solution 8 Membrane filtrate 9 Membrane concentrate 10 Forward osmosis membrane device 11 Gravity separation tank 111 Interface meter 12 Membrane filtration device 13 Post-processing device 14 Heater 15 Cooler 16 Heat exchanger 17 Lower critical temperature measuring means 18 Computer 19 Hydrophobic substance tank 20 Hydrophilic substance tank

Claims (8)

Water to be treated containing salts is brought into contact with an attraction solution in which a temperature-sensitive drug having a lower critical temperature is dissolved in water through a semipermeable membrane, and the water in the water to be treated is attracted through the semipermeable membrane. A normal osmosis step of transferring the solution to the solution to obtain a diluted attraction solution and membrane concentrated water diluted with water, a heating step for heating the diluted attraction solution to a temperature equal to or higher than a lower critical temperature of the attraction solution, and the addition A gravity separation step of gravity separating into a concentrated solution layer mainly composed of a temperature-sensitive drug phase-separated in a temperature step and a dilute solution layer mainly containing water and containing a small amount of the temperature-sensitive drug; The separated concentrated solution is cooled to a temperature below the lower critical temperature of the attracting solution, then circulated to the forward osmosis step, and reused as the attracting solution, and the diluted solution separated in the gravity separation step Membrane treatment of the solution, membrane filtered water A desalination treatment method for water having obtained film processing step,
When the lower critical temperature of the dilution attraction solution is measured and the measured value is higher than a preset set value, a hydrophobic substance is added to the dilution attraction solution, and the set value is set at a preset value. If lower than that, a hydrophilic substance is added to the dilution attraction solution.   The method for desalinating water according to claim 1, wherein the hydrophilic substance is a substance containing a substance selected from alcohol, an ethylene glycol-containing compound, and a glycerin compound.   The water desalting method according to claim 1, wherein the hydrophobic substance is a substance containing a substance selected from a glycol compound having 3 or more carbon atoms, a fatty acid (salt), and a sorbitan compound.   The method for desalinating water according to claim 1, wherein the lower critical temperature is measured based on the interface height of the gravity separation tank. Water to be treated containing salts is brought into contact with an attraction solution in which a temperature-sensitive drug having a lower critical temperature is dissolved in water through a semipermeable membrane, and the water in the water to be treated is attracted through the semipermeable membrane. A forward osmosis membrane treatment device that moves to the solution and obtains a diluted attraction solution diluted with water and membrane concentrated water, and a heating means for heating the diluted attraction solution to a temperature equal to or higher than a lower critical temperature of the attraction solution; A gravity separation tank that gravity-separates into a concentrated solution layer mainly composed of a temperature-sensitive drug heated and phase-separated by the heating means, and a dilute solution layer mainly composed of water and containing a small amount of the temperature-sensitive drug; Cooling / circulation means for cooling the concentrated solution separated in the gravity separation tank to a temperature equal to or lower than the lower critical temperature of the attracting solution, circulating to the forward osmosis step, and reusing as the attracting solution, and the gravity separating step Membrane treatment of the diluted solution separated by A desalination apparatus of water having a film processing apparatus for obtaining a membrane filtration water,
An apparatus for desalinating water, comprising: a lower critical temperature measuring means for the dilution-inducing solution; and a hydrophobic substance adding means and / or a hydrophilic substance-adding means to the dilution-inducing solution.   The water desalting apparatus according to claim 5, wherein the hydrophilic substance is a substance containing a substance selected from alcohol, an ethylene glycol-containing compound, and a glycerin compound.   The water desalting apparatus according to claim 5, wherein the hydrophobic substance is a substance containing a substance selected from a glycol compound having 3 or more carbon atoms, a fatty acid (salt), and a sorbitan compound.   6. The water desalination apparatus according to claim 5, wherein the lower critical temperature measuring means is means for setting an interface height of a gravity separation tank and measuring the lower critical temperature based on the set value. .

Images