JP2019155289A - Water treatment method and apparatus - Google Patents

Abstract

To make it possible to quickly separate layers, in a process in which water to be treated and an attracting solution in which a temperature-sensitive drug is dissolved are brought into contact with each other through a semipermeable membrane, and a diluted attractant solution is heated to separate a concentrated and dilute phase solutions of temperature-sensitive drugs into two layers, the diluted attracting solution being generated by transferring water in the treated water to the attracting solution.SOLUTION: A water treatment method includes: a gravity separation step of gravity-separating a concentrated phase solution 7 mainly composed of temperature-sensitive drug phase-separated in a heating step and a dilute phase solution 6 mainly composed of water and containing a small amount of temperature-sensitive drug; and a cooling and circulating step of circulating the concentrated phase solution separated by the gravity separation step to a forward osmosis step after cooling to a temperature below a lower critical temperature of the attracting solution 4, to reuse as the attracting solution. pH is adjusted by adding alkali to the diluted attraction solution 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water treatment 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, seawater and salt solution with a higher concentration than seawater are brought into contact with each other through a semipermeable membrane, and water in seawater is transferred to this salt solution by osmotic pressure without being pressurized, and separated and recovered to produce fresh water. A method has been developed. (Patent Documents 1 to 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 the water in the seawater is moved to the salt solution through the semipermeable membrane. The obtained diluted salt solution is separated into ammonium ions and carbonate ions individually using an ion exchange membrane, a distillation tower, etc. to obtain purified water, and the separated ammonium ions and carbonate ions are dissolved in the salt solution. It is a method of returning to the original room of the permeable membrane.

  The method of Patent Document 2 uses an attraction solution in which a substance having a cloud point (temperature-sensitive drug) is used as a solute, and sends seawater 21 to a forward osmosis (FO) membrane system 30 as shown in FIG. From there, it is brought into contact with the attracting solution 24 through the semipermeable membrane, and the water in the seawater 21 is allowed to permeate the semipermeable membrane by osmotic pressure and move to the attracting solution 24. The concentrated seawater 22 remaining after the water has moved to the attracting solution 24 flows out of the FO membrane 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, where the diluted attraction solution 25 that has undergone phase separation or precipitation is pressurized by a pump 37 and filtered. Sent to. At that time, a liquid 29 having a temperature lower than the cloud point of the solute can be added. The attraction solution 24 concentrated in the filtration system 32 is returned to the FO membrane system 30. On the other hand, the filtered membrane filtrate 28 is further purified by the post-processing unit 33 to become drinking water. An amphiphilic polymer mainly composed of polyethylene glycol or polypropylene glycol is used for a solute having a cloud point, and a nanofiltration membrane or a reverse osmosis membrane is used for a filter medium of a filtration system.

  However, 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 enormous, requiring enormous energy and cost. high. Furthermore, when ammonium carbonate is used, it easily leaks from the FO membrane and is discharged into the environment through membrane concentrated water, which causes eutrophication.

  The method of patent document 2 can reduce membrane filtration energy by aggregating a part of attractant using the temperature sensitivity of an attractant solution. In this method, the diluted attracting solution in which the attracting substance is aggregated is sent to the filtration system as it is to separate the aggregate by filtration. However, if the aggregated particles having a temperature higher than the cloud point temperature are filtered at a high concentration, clogging due to accumulation on the membrane surface is caused, and much time and energy are required for filtration and separation.

  As a means for solving this problem, the present inventor does not directly send the diluted attraction solution in which the attracting substance is aggregated to the filtration system as it is, but once mainly uses the attracting substance that is a temperature-sensitive drug in the phase separation tank. The lower layer liquid is separated into an upper layer liquid mainly composed of water, and the lower layer liquid is cooled below the cloud point and circulated to the forward osmosis step as an attracting solution, and only the upper layer liquid is filtered through a nanofiltration membrane or the like. Disclosure.

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

  In this way, in the phase separation tank, the dilution attraction solution is continuously separated by gravity into a concentrated phase solution having a high concentration of the temperature-sensitive drug and a dilute phase solution having a low concentration, and each is recovered. When the concentration of the temperature-sensitive drug in the concentrated phase solution is low, the osmotic pressure of the attracting solution is lowered, and the speed of permeating fresh water from the treated water in the FO membrane is lowered. There is a problem that the number of FO films increases.

  The object of the present invention is to bring the water to be treated and an attracting solution in which the temperature sensitive drug is dissolved in water through a semipermeable membrane, and move the water in the treated water to the attracting solution through the semipermeable membrane. The concentration of the temperature-sensitive drug in the concentrated phase solution in the gravity separation step, in which the concentrated solution and the diluted phase solution of the temperature-sensitive drug are separated into two layers. It is to provide a means capable of enhancing the above.

  As a result of intensive studies to solve the above problems, the present inventor can increase the concentration of the temperature-sensitive drug in the concentrated phase solution by adjusting the pH of the dilution attraction solution supplied to the phase separation tank. I found it.

  Therefore, the present invention provides a semipermeable membrane comprising water to be treated and an attracting solution in which a temperature-sensitive drug having a lower critical temperature, which is a temperature at which the hydrophobized temperature-sensitive drug precipitates and causes clouding, is dissolved in water. A forward osmosis step of obtaining a diluted attraction solution diluted with water and membrane concentrated water, and transferring the diluted attraction solution to the attraction solution through the semipermeable membrane with respect to the water in the water to be treated. A heating step of heating the attracting solution to a temperature equal to or higher than the lower critical temperature, a concentrated phase solution mainly composed of a temperature-sensitive drug phase-separated in the heating step, and a small amount of temperature sensitivity mainly composed of water. Gravity separation step of gravity separation into a dilute phase solution containing a drug, and after cooling the concentrated phase solution separated in the gravity separation step to a temperature below the lower critical temperature of the attracting solution, to the forward osmosis step Circulate and reuse as an attractant solution In the water treatment process and a cooling and circulation process, by adding an alkali to the diluted attractant solution is to provide a water treatment method characterized by adjusting the pH.

  The present invention further includes a membrane treatment step in which the diluted phase solution separated in the gravity separation step is subjected to membrane treatment to obtain membrane filtrate water and membrane concentrated water in the above water treatment method, The concentration of the temperature-sensitive drug in the concentrated phase solution obtained from the phase separation tank by adding the obtained membrane concentrated water to the dilution attraction solution and adjusting the pH of the dilution attraction solution after the addition of the membrane concentration water It is intended to provide a method that can enhance the above.

  According to the present invention, in a water treatment method by a forward osmosis method using an aqueous solution of a temperature-sensitive drug having a lower critical temperature as an attractant solution, the temperature-sensitive drug produced by heating the diluted attractant solution diluted with water The concentration of the concentrated phase solution mainly composed of can be increased, and the number of FO films can be reduced.

It is a block diagram which shows one embodiment of this invention typically. It is a block diagram which shows the outline of a well-known water treatment method.

  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 or brine. Brine includes associated water from wells that mine shale gas, oil sand, CBM (coal bed methane), oil, and the like. The pH of seawater is usually about 8.

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 (oil or added chemicals) Etc.) in the range of 10 to 1,000 mg / L as the TOC and the suspended substance in the range of 100 to 10,000 mg / L. The pH is 5 to 7 as an example.

  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, as a pretreatment, the water to be treated is first subjected to a filtration treatment 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.

  In addition to filtration, pH adjustment is performed as necessary. This is to prevent scaling of the water to be treated in the next forward osmosis step. Another purpose is to prevent deterioration depending on the material of the forward osmosis membrane used. For example, in the case of seawater, an acid is added to adjust the pH to about 5.5 to 6.5. Although the kind of acid is not ask | required, hydrochloric acid, a sulfuric acid, etc. are used normally.

<Normal osmosis process>
In the forward osmosis step, the pretreated water is brought into contact with a high osmotic pressure attraction solution obtained by dissolving a temperature-sensitive drug in water through a semipermeable membrane, and the semipermeable membrane is made of water in the treated water. To the attraction solution, and a diluted attraction solution diluted with water and membrane concentrated water are obtained.

  A temperature-sensitive drug is a substance that is hydrophilic and well soluble in water at low temperatures, but becomes hydrophobic and decreases in solubility at a certain temperature or higher, and the temperature at which it changes from water-soluble to water-insoluble is called a cloud point. When this temperature is reached, the hydrophobized temperature-sensitive drug precipitates and white turbidity occurs.

  This temperature-sensitive drug is used as various nonionic surfactants, dispersants, emulsifiers and the like. For example, alcohol or fatty acid and ethylene oxide compound, alcohol or fatty acid and propylene oxide compound, acrylamide and A compound of an alkyl group, ethylene glycol fatty acid ester, glycerin fatty acid ester, sorbitan fatty acid ester ethylene oxide adduct, amino acid and derivatives thereof, preferably a block copolymer of polyethylene glycol and polypropylene / polybutylene glycol, glycerol ethoxy butyrate Rate, trimethylolpropane ethoxybutoxylate and the like. Particularly preferred is ethylene oxide (molecular weight of about 1,000 to 10,000) for an alkyl chain or glycerin.

  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 75 ° C are preferable.

  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. Specifically, about 80 to 200 atm is appropriate.

  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.

  The apparatus to which this semipermeable membrane is attached usually has a semipermeable 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 A known semipermeable membrane device can be used, and a commercially available product can be used.

  In the forward osmosis step, when the water to be treated is brought into contact with the attracting solution through the semipermeable membrane, the water in the treated water moves to the attracting solution through the semipermeable membrane due to the difference in osmotic pressure, and becomes a diluted attracting solution. The treated water is thereby concentrated and discharged as membrane concentrated water.

<Warming process>
In the forward osmosis step, the dilution attraction solution diluted by moving water from the water to be treated 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 phase solution of a temperature sensitive drug.

  An electric heater, a heat exchanger, or the like can be used as the heater in the heating step, and the heating temperature can be controlled by adjusting the flow rate of the heat medium introduced into the heat exchanger, for example.

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

<Gravity separation process>
Gravity-separated into a concentrated phase solution mainly composed of the temperature-sensitive drug phase-separated in the heating step and a dilute phase solution mainly composed of water and containing a small amount of the temperature-sensitive drug. This gravitational separation can be performed in a liquid temperature state equal to or higher than the lower critical temperature, while standing or continuously flowing in a phase separation tank. At that time, the concentrated phase solution of the temperature-sensitive drug aggregated in the heating step is in the form of fine droplets. And if it puts into a phase separation tank in this state, the specific droplet whose gravity is heavier than water, the fine droplet of a concentrated phase solution settles quickly, the droplets unite, and the concentrated phase solution below Layers are formed. On the other hand, the portion of the dilute phase solution containing mainly a small amount of temperature-sensitive drug, which is mainly composed of water generated from the heated dilution attraction solution, rises, and a layer of the dilute phase solution is formed on the inside of the phase separation tank. Is done. Finally, each solution separated into the upper and lower parts is pulled out from the upper and lower parts in the phase separation tank and sent to the next step.

<Cooling and circulation process>
The concentrated phase 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 the phases are separated and the osmotic pressure is lost.

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

<Membrane treatment process>
On the other hand, the diluted phase solution separated in the gravity separation step is preferably subjected to membrane filtration with a nanofiltration membrane, a reverse osmosis membrane or the like to remove the temperature sensitive drug remaining therein. Membrane filtrate is fresh water and can be used for drinking water and the like. Since the membrane-concentrated water remaining without being membrane-filtered contains a temperature-sensitive drug, it 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.

  The present invention is based on the finding that in such a method, the concentration of the concentrated phase solution obtained by the sedimentation separation in the phase separation tank depends on the pH of the liquid supplied to the phase separation tank. Therefore, the present invention is characterized in that the pH is adjusted by adding alkali to the liquid supplied to the phase separation tank. The kind of alkali to be added is preferably NaOH from the viewpoint of availability and cost. As an example, the pH to be adjusted is preferably pH 6.0 or more, and more preferably 6.5 or more. Even if the pH is raised above a certain level, the time required for sedimentation separation is not shortened and the chemical cost increases, so it is practically 9 or less, preferably 8 or less. This pH is a value inherent to the temperature sensitive drug, and it is desirable to obtain it in advance by a beaker test or the like. The alkali is preferably added before the heating step.

  This method of the present invention is shown schematically in FIG. As shown in the figure, treated water 1 such as seawater is sent to a forward osmosis membrane device 10, and water is permeated through the semipermeable membrane 3 into the opposite chamber and the remaining membrane concentrated water 2 is discharged. Is done. 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 is heated through a heat exchanger (heating means) 11 and enters a phase separation tank 12.

  The dilute phase solution 6 separated in the phase separation tank 12 is cooled by a heat exchanger 13 and then filtered by a membrane filtration device 14, and the obtained membrane filtrate 8 is taken out as fresh water. Membrane concentrated water 9 that has not been filtered by the membrane filtration device 14 is returned to the phase separation tank 12, warmed by the heat exchanger 11 together with the dilution attraction solution, and phase-separated in the phase separation tank 12.

  In the present invention, an alkali supply pipe from the alkali storage tank 16 is disposed on the downstream side where the membrane concentrated water 9 of the line for sending the dilution attraction solution 5 to the phase separation tank is joined, and a pH meter 17 is further disposed on the downstream side thereof. And the alkali supply pump 19 is operated according to instructions from the controller 18 based on the measurement data. With this alkali supply device, the pH of the combined solution of the dilution attraction solution 5 and the membrane concentrated water 9 supplied to the phase separation tank 12 is adjusted to a predetermined value.

  On the other hand, the concentrated phase solution 7 separated in the gravity separation tank 12 is cooled by the heat exchanger (cooling means) 15 and returned to the forward osmosis device 10 as the attraction solution 4.

  The apparatus shown in FIG. 1 was used. A cellulose acetate FO membrane was used for the semipermeable membrane of the forward osmosis membrane device 10, and a nanofiltration membrane was used for the membrane filtration device 14.

  To the attracting solution, water was added to polyoxyethylene / polyoxypropylene / alkyl ether to prepare an 80% by weight solution. The lower critical temperature of this solution was 65 ° C. This lower critical temperature varies depending on the drug concentration.

  Seawater filtered through a UF membrane and adjusted to pH 6.5 by adding sulfuric acid was made to flow into the forward osmosis membrane device 10 at a flow rate of 15 L / min as treated water 1. The dilution attraction solution 5 was heated to 88 ° C. by the heat exchanger 11 and was allowed to flow into the phase separation tank 12. In the phase separation tank 12, the temperature sensitive drug aggregated and was gravity separated into a concentrated phase solution 7 having a concentration of 80% by weight and a diluted phase solution 6 having a concentration of 1%. The concentrated phase solution 7 as the lower layer was cooled to 40 ° C. by the heat exchanger 15 and again flowed into the forward osmosis membrane device 10. The dilute phase solution 6 as the upper layer was introduced into a membrane filtration device 14 and separated into membrane filtrate 8 and membrane concentrate 9. The pH of the membrane concentrated water 9 was 5.0, and the pH of the diluted attraction solution in which the membrane concentrated water 9 was combined was 5.5, so that NaOH was added to this to adjust the pH to 6.5. It put into the separation tank.

  Membrane filtrate 8 obtained fresh water through a post-treatment device. This fresh water could be used as drinking water.

  Table 1 shows the pH of the dilution-induced solution flowing into the phase separation tank and the concentration of the concentrated phase solution obtained from the phase separation tank when the NaOH addition amount is intentionally adjusted.

  The method of the present invention can be widely used for production of fresh water from seawater, treatment of associated water from a well, and the like.

DESCRIPTION OF SYMBOLS 1 Water to be treated 2 Membrane concentrated water 3 Semipermeable membrane 4 Attraction solution 5 Dilution attraction solution 6 Dilute phase solution 7 Concentrated phase solution 8 Membrane filtrate 9 Membrane concentrated water 10 Forward osmosis membrane device 11 Heat exchanger (heating means)
12 phase separation tank 13 heat exchanger 14 membrane filtration device 15 heat exchanger (cooling means)
16 Alkali storage tank 17 pH meter 18 Controller 19 Alkali supply pump

Claims (6)

  The water to be treated and an attraction solution in which a temperature-sensitive drug having a lower critical temperature is dissolved in water are brought into contact with each other through a semipermeable membrane, and the water in the water to be treated is brought into the attraction solution through the semipermeable membrane. A forward osmosis step for obtaining a diluted attraction solution and membrane-concentrated water diluted by water, a heating step for heating the diluted attraction solution to a temperature equal to or higher than the lower critical temperature of the attraction solution, and the heating Gravity separation step of gravity separation into concentrated phase solution mainly composed of temperature sensitive drug phase-separated in process and dilute phase solution mainly composed of water and containing a small amount of temperature sensitive drug, and separated by said gravity separation step In the water treatment step, the cooled concentrated phase solution is cooled to a temperature below the lower critical temperature of the attracting solution and then circulated to the forward osmosis step and reused as the attracting solution. Alkali in the attractant solution Ete water treatment method characterized by adjusting the pH.   The dilute phase solution separated in the gravity separation step is further subjected to membrane treatment to obtain membrane filtration water and membrane concentrated water, and the membrane concentrated water obtained in the membrane treatment step is added to the dilution attraction solution. The water treatment method according to claim 1, wherein the pH is adjusted by adding an alkali to the dilution attraction solution after adding the membrane concentrated water.   The water treatment method according to claim 1 or 2, wherein a pH of the dilution attraction solution to which the alkali is added is 6 or more and 9 or less.   The water treatment method according to any one of claims 1 to 3, wherein the temperature-sensitive drug is a polymer in which ethylene oxide or ethylene oxide and propylene oxide are added to an alkyl chain.   The water to be treated and an attraction solution in which a temperature-sensitive drug having a lower critical temperature is dissolved in water are brought into contact with each other through a semipermeable membrane, and the water in the water to be treated is brought into the attraction solution through the semipermeable membrane. A forward osmosis membrane treatment device for obtaining a diluted attraction solution and membrane concentrated water that is moved and diluted with water, a heating means for heating the diluted attraction solution to a temperature equal to or higher than the lower critical temperature of the attraction solution, and A phase separation tank that gravity-separates into a concentrated phase solution mainly composed of a temperature-sensitive drug heated by a heating means and phase-separated, and a dilute phase solution mainly composed of water and containing a small amount of the temperature-sensitive drug; After cooling the concentrated phase solution separated in the phase separation tank to a temperature equal to or lower than the lower critical temperature of the attracting solution, it is circulated to the forward osmosis membrane treatment device and reused as an attracting solution, Membrane treatment of dilute phase solution separated in phase separation tank Circulate, having a membrane treatment device for obtaining membrane filtrate and membrane concentrate, and adding the membrane concentrate separated by the membrane treatment device to the dilute attraction solution discharged from the forward osmosis membrane treatment device and sent to the heating means A line, a pH meter for measuring the pH of the diluted attraction solution to which the membrane concentrated water is added, and means for supplying alkali to the diluted attraction solution to which the membrane concentrated water is added. Processing equipment.   6. The water treatment apparatus according to claim 5, wherein the means for supplying alkali comprises a controller that sends a command to the alkali supply pump in accordance with a measurement result of the alkali supply pump and the pH meter.

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