WO2018173329A1

WO2018173329A1 - Drawing agent for forward osmosis or pressure retarded osmosis and corresponding system

Info

Publication number: WO2018173329A1
Application number: PCT/JP2017/033657
Authority: WO
Inventors: Akiko Suzuki; Tomohito Ide; Kenji Sano; Toshihiro Imada
Original assignee: Kabushiki Kaisha Toshiba
Priority date: 2017-03-23
Filing date: 2017-09-19
Publication date: 2018-09-27
Also published as: JP6685960B2; JP2018158300A

Abstract

Embodiments provide a water treatment system capable of separating water at low cost and a working medium. A water treatment system of an embodiment includes: a first treatment container having an osmosis membrane to partition a first chamber for accommodating water to be treated and a second chamber for accommodating a working medium to induce osmotic pressure. The working medium is an aqueous solution containing a compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain or a compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain as a solute.

Description

[Title established by the ISA under Rule 37.2] DRAWING AGENT FOR FORWARD OSMOSIS OR PRESSURE RETARDED OSMOSIS AND CORRESPONDING SYSTEM

Embodiments described herein relate to a water treatment system and a working medium.

When a solution having a low solute concentration and a solution having a high solute concentration are isolated from each other by an osmosis membrane, the solvent of the low concentration solution permeates through the osmosis membrane and moves to the high concentration solution side. A desalination system which performs desalination such as seawater desalination and an osmotic power generation system which generates power by turning a turbine are known, and both of them utilize a phenomenon that the solvent moves. In addition, concentration systems which concentrate foods and sludge by utilizing this phenomenon are also known. At this time, the solution to be used on the higher concentration side is the working medium (draw solution), and various kinds of working mediums have been proposed so far.

As the solute of the draw solution, kitchen salt is generally used. Organic salts are also used as the solute of the draw solution. However, a draw solution of an organic salt has an inferior permeate flux of water to a draw solution of kitchen salt.

A draw solution in which two or more kinds of solutes are mixed has been proposed. A synergistic effect is observed in a mixture of plural inorganic salts, but the flux passing through the osmosis membrane may decrease due to an adverse effect in the case of a mixture of an inorganic salt with saccharose.

Patent JP2010-509540A

Embodiments provide a water treatment system capable of separating water at low cost and a working medium.

A water treatment system of an embodiment includes: a first treatment container having an osmosis membrane to partition a first chamber for accommodating water to be treated and a second chamber for accommodating a working medium to induce osmotic pressure. The working medium is an aqueous solution containing a compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain or a compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain as a solute.

Fig. 1 is a schematic diagram of a water treatment system according to an embodiment; Fig. 2 is chemical formulas of a solute according to an embodiment; Fig. 3 is a schematic diagram of a water treatment system according to an embodiment; Fig. 4 is a schematic diagram of a water treatment system according to an embodiment; and Fig. 5 is a schematic diagram of a water treatment system according to an embodiment.

Hereinafter, water treatment systems and working mediums to be used in the water treatment systems of embodiments will be described.
(First Embodiment)
A water treatment system according to a first embodiment will be described with reference to the schematic diagram illustrated in Fig. 1. In a water treatment system 100 according to the first embodiment illustrated in Fig. 1, a working medium B induces osmotic pressure in an osmotic pressure generator 1 including a first treatment container 11 equipped with an osmosis membrane 12 to partition a first chamber 13 for accommodating water to be treated A and a second chamber 14 for accommodating the working medium B.

According to such a water treatment system 100, water C in the water to be treated A in the first chamber 13 permeates through the osmosis membrane 12 and moves to the working medium B in the second chamber 14 by the osmotic pressure difference generated between the water to be treated A in the first chamber 13 and the working medium B in the second chamber 14.

The water treatment system of the embodiment is preferable from the viewpoint of being able to permeate the water C in the water to be treated A in the first chamber 13 through the osmosis membrane and to move the water C to the working medium B in the second chamber 14 at a high permeate flux by using the working medium B of the embodiment. The working medium B of the embodiment is used in a water treatment system which can be operated at low cost and a water treatment system.

The first treatment container 11 is partitioned into the first chamber 13 and the second chamber 14 by the osmosis membrane 12. The first treatment container 11 is a resin or metal container which accommodates the water to be treated A in the first chamber 13 and the working medium B in the second chamber 14.

The osmosis membrane 12 may be, for example, a forward osmosis membrane (FO membrane) or a reverse osmosis membrane (RO membrane). A preferred osmosis membrane is a FO membrane.

As the osmosis membrane 12, for example, a cellulose acetate membrane, a polyamide membrane, or the like can be used. The osmosis membrane preferably has a thickness of 45 micrometre or more and 250 micrometre or less.

The first chamber 13 is a region in the first treatment container 11 for accommodating the water to be treated A, and it is partitioned by the osmosis membrane 12. The first chamber 13 may be provided with an introduction and discharge path (not illustrated) through which the water to be treated A is introduced and discharged.

The water to be treated A is a liquid having a lower solute concentration than the working medium. Examples of the water to be treated A may include a salt water (seawater and the like), lake water, river water, marsh water, domestic wastewater, industrial wastewater, or a mixture thereof. When the water to be treated A is a salt water, the salt (sodium chloride) concentration of the salt water may be, for example, from 0.05% to 8%. The water to be treated A contains salts such as sodium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and potassium chloride and suspended substances, and substances other than water are concentrated.

The second chamber 14 is a region in the first treatment container 11 for accommodating the working medium B, and it is partitioned by the osmosis membrane 12. The second chamber 14 may be provided with an introduction and discharge path (not illustrated) through which the working medium B is introduced and discharged.

The working medium B of the first embodiment is an aqueous solution containing a compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and a compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain as a solute. The working medium B is an aqueous solution, and it thus contains water as a solvent. The working medium B containing such a solute is preferable since it exhibits a high osmotic pressure inducing action. Hence, it is possible to generate a high permeate flux (Jw L/m²h) when water in the water to be treated A in the first chamber 13 permeates through the osmosis membrane 12 and moves to the working medium B in the second chamber 14.

Consequently, in the embodiment, it is possible to provide a water treatment system which can be operated at low cost and can efficiently perform a treatment such as desalination and concentration of the water to be treated A. The water treatment system of the embodiment is also preferably utilized as a water treatment system which further includes a body of rotation and generates electricity by generating a water flow by induction of osmotic pressure and rotating the body of rotation by the water flow.

There is a phenomenon that the solute contained in the working medium B leaks out to the water to be treated A side via the osmosis membrane, and this loss of solute causes a decrease in quality of the water to be treated A and further increases the running cost of the forward osmosis system. Such a phenomenon is likely to occur in the case of a low molecular weight solute. In the case of a high molecular weight solute, reverse permeation via the osmosis membrane 12 is less likely to occur, but it is difficult to realize a high permeate flux since the solubility of the solute in water is low and the concentration of the high molecular weight working medium B is thus low.

It has been found that the solute reverse permeate flux (Js mmol/m²h) can be decreased by containing plural phosphonic acid groups (metal salt and ammonium salt) in the compound of the solute contained in the working medium B. This is the same even for a low molecular weight solute, and it is preferable to contain plural phosphonic acid groups (metal salt and ammonium salt) since the loss of solute decreases.

The compound (molecule) having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain of the embodiment are expressed by C_xH_yP_zO_wN_rCl_sBr_tM_u. M is a metal. It is preferable to satisfy 2 ≦(being less than or equal to) x ≦(being less than or equal to) 9, 8 ≦(being less than or equal to) y ≦(being less than or equal to) 28, 1 ≦(being less than or equal to) z ≦(being less than or equal to) 6, 3 ≦(being less than or equal to) w ≦(being less than or equal to) 18, 0 ≦(being less than or equal to) r ≦(being less than or equal to) 3, 0 ≦(being less than or equal to) s ≦(being less than or equal to) 1, 0 ≦(being less than or equal to) t ≦(being less than or equal to) 1, and 2 ≦(being less than or equal to) u ≦(being less than or equal to) 10 in order to increase the permeate flux. In addition, it is preferable to satisfy 2 ≦(being less than or equal to) x ≦(being less than or equal to) 15, 8 ≦(being less than or equal to) y ≦(being less than or equal to) 35, 2 ≦(being less than or equal to) z ≦(being less than or equal to) 5, 7 ≦(being less than or equal to) w ≦(being less than or equal to) 15, 0 ≦(being less than or equal to) r ≦(being less than or equal to) 5, 0 ≦(being less than or equal to) s ≦(being less than or equal to) 1, 0 ≦(being less than or equal to) t ≦(being less than or equal to) 1, and 2 ≦(being less than or equal to) u ≦(being less than or equal to) 10 in order to decrease the solute reverse permeate flux. Moreover, it is preferable to satisfy 2 ≦(being less than or equal to) x ≦(being less than or equal to) 9, 8 ≦(being less than or equal to) y ≦(being less than or equal to) 28, 2 ≦(being less than or equal to) z ≦(being less than or equal to) 5, 7 ≦(being less than or equal to) w ≦(being less than or equal to) 15, 0 ≦(being less than or equal to) r ≦(being less than or equal to) 3, 0 ≦(being less than or equal to) s ≦(being less than or equal to) 1, 0 ≦(being less than or equal to) t ≦(being less than or equal to) 1, and 2 ≦(being less than or equal to) u ≦(being less than or equal to) 10 in order to increase the permeate flux and to decrease the solute reverse permeate flux. The metal expressed by M is a metal of a metal salt of phosphonic acid. The metal of a metal salt is preferably an alkali metal or an alkaline earth metal. The metal of a metal salt is preferably at least one kinds selected from the group consisting of Na, K, Ca, Al, and Mg. The elements or structures contained in the solute of the embodiment can be determined by analyzing the solute by liquid chromatography, separating the compounds having the respective peaks, and analyzing the compounds by using a NMR or organic element analyzer.

The chemical formulas of the solute according to the embodiment are illustrated in Fig. 2. The compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain of the working medium B are preferably compounds in which a phosphonic acid group of compounds having structures expressed by Formulas (1), (2), and (3) in Fig. 2 has a metal salt structure or an ammonium salt structure. In the case of a metal salt, some or all of the phosphonic acid groups are a metal salt of a phosphonic acid group. In the case of an ammonium salt, some or all of the phosphonic acid groups are an ammonium salt of a phosphonic acid group. Some of the side chains contained in the compound of the solute may contain a phosphonic acid group which is not a salt.

X¹, X², and X³ in Formula (1) are one or more kinds selected from the group consisting of H and -(CH₂)_m1PO(OH)₂ (m1 is any integer from 1 to 3). It is preferable that two or more of X¹, X², and X³ are -(CH₂)_m1PO(OH)₂ (m1 is any integer from 1 to 3) since the loss of solute is minor. As the compound having a structure expressed by Formula (1) in Fig. 2, nitrilotris(methylenephosphonic acid)is preferable. Examples of the compound in which a phosphonic acid group of the compound having a structure expressed by Formula (1) in Fig. 2 has a metal salt structure may include nitrilotris(methylenephosphonic acid) sodium salt and nitrilotris(methylenephosphonic acid) potassium salt. Examples of the compound in which a phosphonic acid group of the compound having a structure expressed by Formula (1) in Fig. 2 has an ammonium salt structure may include nitrilotris(methylenephosphonic acid) ammonium salt.

Y¹ and Y² in Formula (2) are one or more kinds selected from the group consisting of OH, CH₃, Cl, Br, and CH₂CH₂NH₂. As the compound having a structure expressed by Formula (2) in Fig. 2, etidronic acid is preferable. Examples of the compound in which a phosphonic acid group of the compound having a structure expressed by Formula (2) in Fig. 2 has a metal salt structure may include etidronic acid sodium salt and etidronic acid potassium salt. Examples of the compound in which a phosphonic acid group of the compound having a structure expressed by Formula (2) in Fig. 2 has an ammonium salt structure may include etidronic acid ammonium salt.

Z¹, Z², Z³, and Z⁴ in Formula (3) are one or more kinds selected from the group consisting of H, -(CH₂)_m2PO(OH)₂ (m2 is any integer from 1 to 3), and -(CH₂)_m3N((CH₂)_m4PO(OH)₂)₂ (m3 is any integer from 1 to 3 and m4 is any integer from 1 to 3). In Formula (3) in Fig. 2, n is any integer of 2 or more and 10 or less. As the compound having the structure expressed by Formula (3) in Fig. 2, ethylenediaminetetramethylenephosphonic acid and diethylenetriaminepentamethylenephosphonic acid are preferable. Examples of the compound in which a phosphonic acid group of the compound having a structure expressed by Formula (3) in Fig. 2 has a metal salt structure may include ethylenediaminetetramethylenephosphonic acid sodium salt, diethylenetriaminepentamethylenephosphonic acid sodium salt, ethylenediaminetetramethylenephosphonic acid potassium salt, and diethylenetriaminepentamethylenephosphonic acid potassium salt. Examples of the compound in which a phosphonic acid group of the compound having a structure expressed by Formula (3) in Fig. 2 has an ammonium salt structure may include ethylenediaminetetramethylenephosphonic acid ammonium salt and diethylenetriaminepentamethylenephosphonic acid ammonium salt.

Consequently, the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain is preferably at least one kinds selected from the group consisting of ethidronic acid sodium salt, etidronic acid potassium salt, nitrilotris(methylenephosphonic acid) sodium salt, nitrilotris(methylenephosphonic acid) potassium salt, ethylenediaminetetramethylenephosphonic acid sodium salt, diethylenetriaminepentamethylenephosphonic acid sodium salt, ethylenediaminetetramethylenephosphonic acid potassium salt, and diethylenetriaminepentamethylenephosphonic acid potassium salt.

Consequently, the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain is preferably at least one kinds selected from the group consisting of ethidronic acid ammonium salt, nitrilotris(methylenephosphonic acid) ammonium salt, ethylenediamine tetramethylenephosphonic acid ammonium salt, and diethylenetriaminepentamethylenephosphonic acid ammonium salt.

The number of substitution of the alkali metal salt or ammonium salt changes depending on the pH. For example, etidronic acid 2Na salt is weakly acidic, and etidronic acid 4Na salt is alkaline. It is desirable to use the working medium B in the vicinity of a neutral pH range from the viewpoint of resistance of FO membrane, and it is preferable that the number of substitution is larger from the viewpoint of osmotic pressure. Hence, the pH of the working medium B in the embodiment is preferably 2 or more and 10 or less. The pH of the working medium B is measured by using the glass electrode type hydrogen ion densitometer manufactured by HORIBA, Ltd. and the method described in the manual.

The concentrations of the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain of a solute in the working medium B are desirably adjusted based on the concentration of the solute in the water to be treated A which is used, the kind of solute, and the properties of the solute. In general, it is desirable that the concentrations of the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain of a solute in the working medium B are set to 10% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and still more preferably 50% or more and 70% by mass or less. However, when a trouble such as an increase in the viscosity occurs, the adjustment is performed to decrease the concentration. The upper limit of the concentration depends on the specific solubility of the substance.

(Second Embodiment)
Next, a desalination system which is one example of a water treatment system will be described with reference to the schematic diagram illustrated in Fig. 3. In the second embodiment, the first chamber 13, the water to be treated A, the second chamber 14, the working medium B, and the osmosis membrane 12 are common to those in the first embodiment. The water to be treated A is a salt water (aqueous solution of sodium chloride) such as seawater. The working medium B to be used in the second embodiment is the working medium B of the first embodiment. In Fig. 3 and subsequent Figures, the reference numerals of water to be treated, working medium, and water in the water treatment system are not illustrated, but the reference numerals thereof are common to those in the water treatment system in Fig. 1.

A desalination system 200 is equipped with an osmotic pressure generator 1, a diluted working medium tank 2, a reverse osmosis membrane separator 3, and a concentrated working medium tank 4. The osmotic pressure generator 1, the diluted working medium tank 2, the reverse osmosis membrane separator 3, and the concentrated working medium tank 4 are connected in this order to form a loop. The working medium B (draw solution) which induces osmotic pressure circulates through this loop. In other words, the working medium B circulates through the osmotic pressure generator 1, the diluted working medium tank 2, the reverse osmosis membrane separator 3, and the concentrated working medium tank 4 in this order. Incidentally, the upper and the lower are the directions illustrated in the drawings, and for example, the concentrated working medium tank 4 is on the upper side of the diluted working medium tank 2, and the osmotic pressure generator 1 is on the left side of the reverse osmosis membrane separator 3.

A tank of water to be treated 15 is connected to the upper part of a treatment container 10 in which the first chamber 13 is located through a pipeline 101a. A first pump 16 is provided to the pipeline 101a. A pipeline 101b for discharging the concentrated water to be treated A is connected to the lower part of the first treatment container 11 in which the first chamber 13 is located.

The reverse osmosis membrane separator 3 is equipped with, for example, an airtight second treatment container 21. The second treatment container 21 is partitioned in, for example, the horizontal direction by a reverse osmosis membrane (RO membrane) 22, and a third chamber 23 is formed on the left side of the reverse osmosis membrane 22 and a fourth chamber 24 is formed on the right side thereof.

The diluted working medium tank 2 is connected to the lower part of the second treatment container 21 in which the third chamber 23 is located through a pipeline 101e. A third pump 25 is provided to the pipeline 101e. The upper part of the second treatment container 21 in which the third chamber 23 is located is connected to the concentrated working medium tank 4 through a pipeline 101f. The lower part of the second treatment container 21 in which the fourth chamber 24 is located is connected to a pure water tank 26 through a pipeline 101g. In the pure water tank 26, the water (fresh water) which has moved to the fourth chamber through the reverse osmosis membrane 22 when concentrating the working medium B is accommodated. A pipeline 101h for delivering pure water in the pure water tank 26 to the outside and recovering the pure water is connected to the pure water tank 26. An on-off valve 27 is provided to the pipeline 101h. For example, the on-off valve 27 is opened when pure water in the pure water tank 26 exceeds a certain amount.

The concentrated working medium tank 4 is connected to the upper part of the first treatment container 11 in which the second chamber 14 is located through a pipeline 101c. A second pump 17 is provided to the pipeline 101a. The lower part of the treatment container 10 in which the second chamber 14 is located is connected to the diluted working medium tank 2 through a pipeline 101d.

Next, the operation of desalination by the desalination system 200 illustrated in Fig. 3 will be described.

The first pump 16 is driven to supply the water to be treated A (for example, seawater) from the tank of water to be treated 15 into the first chamber 13 of the osmotic pressure generator 1 through the pipeline 101a. Before and after the supply of seawater, the second pump 17 is driven to supply the concentrated working medium B from the concentrated working medium tank 4 into the second chamber 14 of the osmotic pressure generator 1 through the pipeline 101c. At this time, the solute concentration of the concentrated working medium B supplied to the second chamber 14 is higher than the salt concentration of the seawater supplied to the first chamber 13. Hence, an osmotic pressure difference is generated between the seawater in the first chamber 13 and the concentrated working medium B in the second chamber 14, and water in the seawater permeates through the osmosis membrane 12 and moves into the second chamber 14. The concentrated working medium B in the second chamber 14 is an aqueous solution containing the solute of the first embodiment and exhibits a high osmotic pressure inducing action. Hence, a high permeate flux is generated when water in the seawater in the first chamber 13 permeates through the osmosis membrane 12 and moves to the concentrated working medium B in the second chamber 14. As a result, it is possible to move a large amount of water in the seawater in the first chamber 13 to the concentrated working medium B in the second chamber 14 and thus to perform a highly efficient desalination treatment for extracting water (pure water) from a salt water.

In the osmotic pressure generator 1, the seawater is discharged as condensed seawater from the first chamber 13 through the pipeline 101b and the concentrated working medium B is diluted with the water moved as the water in the seawater moves from the first chamber 13 to the concentrated working medium B in the second chamber 14.

The diluted working medium B in the second chamber 14 is delivered to the diluted working medium tank 2 through the pipeline 101d and stored therein. When the diluted working medium B is stored in the diluted working medium tank 2 to a predetermined water level, the third pump 25 is driven to supply the diluted working medium B in the diluted working medium tank 2 to the third chamber 23 of the second treatment container 21 of the reverse osmosis membrane separator 3 through the pipeline 101e at a desired pressure. The water in the diluted working medium B supplied to the third chamber 23 at a desired pressure forcibly permeates through the reverse osmosis membrane (RO membrane) 22 and moves to the fourth chamber 24. The diluted working medium B in the third chamber 23 is concentrated as water moves to the fourth chamber 24. The concentrated working medium B is delivered from the third chamber 23 to the concentrated working medium tank 4. The concentrated working medium B in the concentrated working medium tank 4 is supplied into the second chamber 14 of the osmotic pressure generator 1 as the second pump 17 is driven, and it is utilized in the desalination treatment for extracting water (pure water) from a salt water as described above.

Meanwhile, the water (pure water) moved to the fourth chamber 24 is delivered to the pure water tank 26 through the pipeline 101g. When the amount of water in the pure water tank 26 exceeds a certain amount, the on-off valve 27 is opened and the water is delivered to the outside through the pipeline 101h and recovered.

Consequently, it is possible to provide a desalination system which can be operated at low cost and can efficiently perform a desalination treatment of seawater (recovery of pure water).

Incidentally, in the desalination system 200 illustrated in Fig. 3, the first treatment container 11 of the osmotic pressure generator is partitioned in the horizontal direction by an osmosis membrane to form the first chamber 13 and the second chamber 14, but the first treatment container may be partitioned into upper and lower parts by an osmosis membrane to form the first chamber 13 and the second chamber 14.

It is preferable to add the solute to the concentrated working medium tank 4 and the like when the solute concentration in the working medium B is decreased by the desalination treatment.

In the desalination system 200 illustrated in Fig. 3, the concentration of the diluted working medium B is not only performed by using a reverse osmosis membrane separator equipped with a reverse osmosis membrane (RO membrane) but also may be performed by using any device as long as it can remove water in the diluted working medium B.

(Third Embodiment)
Next, a concentration system 300 which is one example of a water treatment system will be described with reference to the schematic diagram illustrated in Fig. 4. The working medium B to be used in the third embodiment is the working medium B of the first embodiment.

A concentration system 300 is equipped with an osmotic pressure generator 31, a diluted working medium tank 32, a membrane distillation and separation device 33, and a concentrated working medium tank 34. The osmotic pressure generator 31, the diluted working medium tank 32, the membrane distillation and separation device 33, and the concentrated working medium tank 34 are connected in this order to form a loop. The working medium B (draw solution) circulates through this loop. In other words, the working medium B circulates through the osmotic pressure generator 31, the diluted working medium tank 32, the membrane distillation and separation device 33, and the concentrated working medium tank 34 in this order.

The osmotic pressure generator 31 is equipped with, for example, an airtight first treatment container 41. The first treatment container 41 is partitioned in, for example, a horizontal direction by an osmosis membrane 42 (for example, a forward osmosis membrane: FO membrane), and a first chamber 43 is formed on the left side of the osmosis membrane 42 and a second chamber 44 is formed on the right side thereof. A tank of water to be treated 45 containing water to be treated A, for example, a stock solution such as industrial wastewater, is connected to the upper part of the first treatment container 41 in which the first chamber 43 is located through a pipeline 201a. A first pump 46 is provided to the pipeline 201a. A pipeline 201b for discharging the concentrated stock solution in the first chamber 43 to the outside is connected to the lower part of the first treatment container 41 in which the first chamber 43 is located.

The concentrated working medium tank 34 is connected to the upper part of the first treatment container 41 in which the second chamber 44 is located through a pipeline 201c. A second pump 47 is provided to the pipeline 201c. The diluted working medium tank 32 is connected to the lower part of the first treatment container 11 in which the second chamber 44 is located through a pipeline 201d.

The membrane distillation and separation device 33 is equipped with, for example, an airtight second treatment container 51. The second treatment container 51 is partitioned in, for example, a horizontal direction by a dehydration membrane 52 formed of, for example, a porous latex membrane, and a third chamber 53 is formed on the left side of the dehydration membrane 52 and a fourth chamber 54 is formed on the right side thereof.

The diluted working medium tank 32 is connected to the lower part of the second treatment container 51 in which the third chamber 53 is located through a pipeline 201e. A first on-off valve 61, a heat exchanger 62, and a third pump 63 are provided to the pipeline 201e along the flow direction of the working medium B in this order. The heat exchanger 62 intersects, for example, a pipeline 201f of exhaust heat gas, and the working medium B is heated by heat exchange between the working medium B flowing through the pipeline 201e and the exhaust heat gas. The upper part of the second treatment container 51 in which the third chamber 53 is located is connected to the upper part of a circulation tank 64 through a pipeline 201g. The circulation tank 64 is connected to the portion of the pipeline 201e located between the first on-off valve 61 and the heat exchanger 62 through a pipeline 201h. A second on-off valve 65 is provided to the pipeline 201h.

By such a conFiguration, a loop is formed by the third chamber 53 of the membrane distillation and separation device 33, the circulation tank 64, and the

pipelines

201e, 201g, and 201h which connect these members to each other. In other words, a diluted working medium circulation system is formed that the diluted working medium B which has been subjected to the dehydration treatment in the third chamber 53 to be described later and stored in the circulation tank 64 is circulated through the pipeline 201h, the pipeline 201e, the third chamber 53, and the pipeline 201g by opening the second on-off valve 65 and driving the third pump 63. Incidentally, in the circulation of the diluted working medium B, the diluted working medium circulation system is isolated from the diluted working medium tank 32 by closing the first on-off valve 61.

The circulation tank 64 is connected to the concentrated working medium tank 34 through a pipeline 201i. A fourth pump 66 is provided to the pipeline 201i.

A first pure water tank 71 is connected to the upper part of the second treatment container 51 in which the fourth chamber 54 is located through a pipeline 201j. The second pure water tank 72 is connected to the lower part of the second treatment container 51 in which the fourth chamber 54 is located through a pipeline 201k. A third on-off valve 73 is provided to the pipeline 201k and closed when pure water is not circulated to store the pure water in the fourth chamber 54. The second pure water tank 72 is connected to the first pure water tank 71 through a pipeline 201m. A fifth pump 74 is provided to the pipeline 201m. By such a conFiguration, a loop is formed by the first pure water tank 71, the fourth chamber 54 of the membrane distillation and separation device 33, the second pure water tank 72, and the

pipelines

201j, 201k, and 201m which connect these members to each other. In other words, a pure water circulation and cooling system is formed that the pure water in the second pure water tank 72 is circulated through the pipeline 201m, the first pure water tank 71, the pipeline 201j, the fourth chamber 54, and the pipeline 201k by opening the third on-off valve 73 and driving the fifth pump 74.

The second pure water tank 72 is connected to a pipeline 201n for delivering pure water in the second pure water tank 72 to the outside and recovering the pure water. A fourth on-off valve 75 is provided to the pipeline 201n. The fourth on-off valve 75 is closed when pure water is circulated described above, and it is opened when the pure water in the second pure water tank 72 exceeds a certain amount.

Next, the operation of concentration by the concentration system 300 illustrated in Fig. 4 will be described.

The first pump 46 is driven to supply the stock solution of the water to be treated A (for example, industrial wastewater) from the tank of water to be treated 45 into the first chamber 43 of the osmotic pressure generator 31 through the pipeline 201a. Before and after the supply of the stock solution, the second pump 47 is driven to supply the concentrated working medium B from the concentrated working medium tank 34 into the second chamber 44 of the osmotic pressure generator 31 through the pipeline 201c. The concentrated working medium B supplied to the second chamber 44 has a higher concentration than the stock solution supplied to the first chamber 43. Hence, an osmotic pressure difference is generated between the stock solution in the first chamber 43 and the concentrated working medium B in the second chamber 44, and water in the stock solution permeates through the osmosis membrane 42 and moves into the second chamber 44. At this time, the concentrated working medium B in the second chamber 44 is an aqueous solution containing the solute of the embodiment and exhibits a high osmotic pressure inducing action. Hence, a high permeate flux is generated when water in the stock solution in the first chamber 43 permeates through the osmosis membrane 42 and moves into the working medium B in the second chamber 44. As a result, it is possible to move a large amount of water in the stock solution in the first chamber 43 to the working medium B in the second chamber 44 and to highly efficiently perform the concentration treatment of the stock solution.

The stock solution is discharged from the first chamber 43 through the pipeline 201b and recovered as a concentrated stock solution as the water in the stock solution moves from the first chamber 43 to the concentrated working medium B in the second chamber 44 in the osmotic pressure generator 31. The concentrated working medium B is diluted with the water moved.

The diluted working medium B in the second chamber 44 is delivered to the diluted working medium tank 32 through the pipeline 201d and stored therein. When the diluted working medium B is stored in the diluted working medium tank 32 to a predetermined amount, the first on-off valve 61 provided to the pipeline 201e is opened, the second on-off valve 65 provided to the pipeline 201h is closed, and the third pump 63 is driven. By this, the diluted working medium B in the diluted working medium tank 32 is supplied to the third chamber 53 of the second treatment container 51 of the membrane distillation and separation device 33 through the pipeline 201e. While the diluted working medium B is supplied to the third chamber 53, the diluted working medium B flowing through the pipeline 201e is heated by heat exchange between the diluted working medium B and the exhaust heat gas flowing through the pipeline 201f in the heat exchanger 62 which intersects the pipeline 201f. In addition, by opening the third on-off valve 73 and driving the fifth pump 74, the pure water in the second pure water tank 72 is circulated through the pipeline 201m, the first pure water tank 71, the pipeline 201j, the fourth chamber 54, and the pipeline 201k, and the dehydration membrane 52 formed of a porous latex membrane of the membrane distillation and separation device 33 is cooled with pure water on the fourth chamber 54 side. In other words, the dehydration membrane 52 on the fourth chamber 54 side is cooled by the pure water circulation and cooling system.

By cooling the dehydration membrane 52 of the membrane distillation and separation device 33 with circulating pure water in the fourth chamber 54 while supplying the diluted working medium B thus heated to the third chamber 53 of the membrane distillation and separation device 33 through the pipeline 201e, the water in the diluted working medium B evaporates in the third chamber 53 and the vapor permeates through the dehydration membrane 52 formed of a porous latex membrane, moves to the fourth chamber 54, and is cooled and condensed with circulating pure water to be incorporated into the pure water. In other words, the diluted working medium B is subjected to the dehydration treatment in the third chamber 53. The diluted working medium B subjected to the dehydration treatment in the third chamber 53 is delivered to the circulation tank 64 through the pipeline 201g and stored therein. The diluted working medium B stored in the circulation tank 64 is concentrated to a certain concentration by the dehydration treatment.

However, the working medium B has a low concentration by the concentration to such an extent, and the working medium B is not suitable for use as the concentrated working medium B described above. Hence, when the diluted working medium B subjected to the dehydration treatment is stored in the circulation tank 64 in a certain amount, the second on-off valve 65 is opened and the diluted working medium B subjected to the dehydration treatment in the tank 64 is allowed to flow out to the pipeline 201h. At the same time, the first on-off valve 61 is closed to isolate the diluted working medium circulation system including the circulation tank 64, the pipeline 201h, the pipeline 201e, the third chamber 53, and the pipeline 201g from the diluted working medium tank 32.

In such a diluted working medium circulation system and the pure water circulation and cooling system, the diluted working medium B is concentrated so as to be used as the concentrated working medium B by repeatedly performing the dehydration treatment including the evaporation of water in the diluted working medium B in the third chamber 53, the permeation of the vapor through the dehydration membrane 52, the movement of the vapor to the fourth chamber 54, and the cooling and condensation of the vapor with the circulating pure water on the fourth chamber 54 side plural times. After such circulation and dehydration of the diluted working medium B, the second on-off valve 65 is closed to store the concentrated working medium B in the circulation tank 64. The water (pure water) moved to the fourth chamber 54 is delivered to the second pure water tank 72 together with the circulating pure water through the pipeline 201k.

After the concentrated working medium B at a concentration capable of being used as the concentrated working medium B is stored in the circulation tank 64, driving of the fifth pump 74 is stopped, circulation of pure water to the fourth chamber 54 is stopped, and the third on-off valve 73 is then closed. Incidentally, when the amount of pure water in the second pure water tank 72 exceeds a certain amount, the first on-off valve 61 is opened, and the pure water is delivered to the outside through the pipeline 201n and recovered.

The fourth pump 66 is driven to deliver the concentrated working medium B in the circulation tank 64 to the concentrated working medium tank 34 through the pipeline 201i. The concentrated working medium B in the concentrated working medium tank 34 is supplied into the second chamber 44 of the osmotic pressure generator 31 by driving the second pump 47, and it is utilized in the concentration treatment of the stock solution as described above.

Accordingly, in the osmotic pressure generator 31, the stock solution is supplied to the first chamber 43, the concentrated working medium B is supplied to the second chamber 44, the water in the stock solution is moved from the first chamber 43 to the concentrated working medium B in the second chamber 44 to concentrate the stock solution, and the stock solution is discharged from the first chamber 43 through the pipeline 201b and recovered. The concentrated working medium B is diluted with the water moved, and the diluted working medium B is delivered to the diluted working medium tank 32 and stored therein.

During the operation of stock solution concentration by the osmotic pressure generator 31, the diluted working medium B stored in the diluted working medium tank 32 is subjected to the operation of concentration by the diluted working medium circulation system including the third chamber 53 of the membrane distillation and separation device 33 and the pure water circulation and cooling system including the fourth chamber 54 of the membrane distillation and separation device 33 and delivered to the concentrated working medium tank 34 and the water (pure water) moved to the fourth chamber 54 is delivered from the second pure water tank 72 and recovered. In other words, it is possible to continuously perform the operation of stock solution concentration by the osmotic pressure generator 31 and the concentration of the diluted working medium B by the membrane distillation and separation device 33.

Consequently, it is possible to provide the concentration system 300 which can be operated at low cost and can efficiently perform the concentration treatment of a stock solution (water to be treated A) such as industrial wastewater and the recovery of water.

Incidentally, in the concentration system 300 illustrated in Fig. 4, the first treatment container 41 of the osmotic pressure generator is partitioned in the horizontal direction by an osmosis membrane to form the first chamber 43 and the second chamber 44, but the first treatment container may be partitioned into upper and lower parts by an osmosis membrane to form the first chamber 43 and the second chamber 44.

In the concentration system 300 illustrated in Fig. 4, the concentrated water to be treated A (for example, stock solution) in the first chamber 43 of the osmotic pressure generator 31 is delivered to the outside through the pipeline 201b, but the pipeline 201b may be connected to the tank of water to be treated 45 to form a loop by the tank of water to be treated 45, the pipeline 201a, the first chamber 43 of the osmotic pressure generator 31, and the pipeline 201b in the case of obtaining a stock solution concentrated to a higher concentration. In this case, it is desirable to determine the concentration degree of the stock solution in consideration of the osmotic pressure difference generated between the concentrated stock solution and the concentrated working medium B in the osmotic pressure generator 31.

In the concentration system 300 illustrated in Fig. 4, the dehydration membrane 52 of the membrane distillation and separation device 33 is not limited to a porous latex membrane, and any membrane may be used as long as it has the function of permeating vapor.

In the concentration system 300 illustrated in Fig. 4, the concentration of the diluted working medium B is not only performed by the membrane distillation and separation device 33 equipped with the dehydration membrane 52 but also may be performed by using any device as long as it can remove water from the diluted working medium B.

(Fourth Embodiment)
Next, a circulating osmotic power generation system 400 which is one example of a water treatment system according to the fourth embodiment will be described with reference to the schematic diagram illustrated in Fig. 5. Incidentally, in Fig. 5, the same members as those in Fig. 4 are denoted by the same reference numerals, and the description thereon is omitted. The working medium to be used in the fourth embodiment is the working medium B of the first embodiment.

The water treatment system according to the fourth embodiment is a circulating osmotic power generation system. The circulating osmotic power generation system 400 is equipped with an osmotic pressure generator 31 for generating a water flow and a body of rotation 82 for generating electricity by the water flow generated by the osmotic pressure generator 31.

The circulating osmotic power generation system 400 is equipped with the first chamber 43 for accommodating water, the second chamber 44 for accommodating the working medium B (draw solution) which induces osmotic pressure, the osmosis membrane 42 for partitioning the first chamber and the second chamber, a pressure exchanger 81 connected to the second chamber 44, and the body of rotation 82 connected to the pressure exchanger 81. According to such a water treatment system, by the osmotic pressure difference generated between the water in the first chamber 43 and the working medium B in the second chamber 44, the water in the first chamber 43 permeates through the osmosis membrane 42 and moves to the working medium B in the second chamber 44. The body of rotation 82 is rotated by the water flow accompanying the movement of water to the working medium B to generate electricity.

In the fourth embodiment, the working medium B is an aqueous solution containing the solute of the embodiment and exhibits a high osmotic pressure inducing action. Hence, it is possible to generate a high permeate flux when the water in the first chamber 43 permeates through the osmosis membrane 42 and moves to the working medium B in the second chamber 44. As a result, the working medium B containing water thus moved forms a water flow having a high pressure, and it is thus possible to rotate the body of rotation 82 at a higher speed to generate electricity. Consequently, it is possible to provide a water treatment system which can be operated at low cost and can efficiently rotate the body of rotation 82 to generate electricity.

As the body of rotation 82, for example, a turbine or a water wheel can be used.

In the circulating osmotic power generation system 400, the pressure exchanger 81 and the body of rotation 82 are provided to the pipeline 201b connected to the lower part (the exit side of the working medium B) of the first treatment container 41 in which the second chamber 44 of the osmotic pressure generator 31 is located along the flow direction of the working medium B in this order. In addition, in the pipeline 201c which connects the concentrated working medium tank 34 with the upper part of the first treatment container 41 in which the second chamber 44 is located, the portion of the pipeline 201c on the downstream side in the flowing direction of the working medium B of the second pump 47 is connected to the upper part of the first treatment container 41 in which the second chamber 44 is located via the pressure exchanger 81. In other words, in the osmotic pressure generator 31, the diluted working medium B having a flux generated when water has moved from the first chamber 43 to the second chamber 44 through the osmosis membrane 42 is allowed to flow out from the lower part of the first treatment container 41 in which the second chamber 44 is located through the pipeline 201b provided with the pressure exchanger 81. During this time, the pipeline 201c through which the concentrated working medium B flowed out from the concentrated working medium tank 34 flows passes through the pressure exchanger 81. Hence, the pressure of the diluted working medium B is lowered and the pressure of the concentrated working medium B is raised by pressure exchange between the concentrated working medium B and the diluted working medium B flowed out from the second chamber 44 in the pressure exchanger 81.

Incidentally, in the circulating osmotic power generation system 400, water is accommodated in the tank of water to be treated 45.

Next, the operation of power generation by the circulating osmotic power generation system 400 illustrated in Fig. 5 will be described. The first pump 46 is driven to supply water from the tank of water to be treated 45 into the first chamber 43 of the osmotic pressure generator 31 through the pipeline 201a. Before and after the supply of water, the second pump 47 is driven to supply the concentrated working medium B from the concentrated working medium tank 34 into the second chamber 44 of the osmotic pressure generator 31 through the pipeline 201c. The concentrated working medium B supplied to the second chamber 44 has a sufficiently higher concentration compared to the water only of the solvent supplied to the first chamber 43. Hence, the osmotic pressure difference is generated between the water in the first chamber 43 and the concentrated working medium B in the second chamber 44, and the water permeates through the osmosis membrane 42 and moves into the second chamber 44. At this time, the working medium B in the second chamber 44 is an aqueous solution containing the solute of the embodiment and exhibits a high osmotic pressure inducing action. Hence, a high permeate flux is generated when water in the first chamber 43 permeates through the osmosis membrane 42 and moves to the working medium B in the second chamber 44. As a result, a large amount of water in the first chamber 43 can move to the concentrated working medium B in the second chamber 44 and a diluted working medium B which has a high pressure and is diluted with water is produced. Incidentally, the water in the first chamber 43 is discharged through the pipeline 201b.

The diluted working medium B having a high pressure in the second chamber 44 is delivered to the diluted working medium tank 32 through the pipeline 201d and stored therein. The pressure exchanger 81 and the body of rotation 82 are provided to the pipeline 201d along the flow direction of the working medium B in this order.

Hence, the pressure of the diluted working medium B is lowered and the pressure of the concentrated working medium B is raised by pressure exchange between the concentrated working medium B which flows from the concentrated working medium tank 34 through the pipeline 201c and the diluted working medium B which has a high pressure and flows from the second chamber 44 (through the body of rotation 82) through the pipeline 201d in the pressure exchanger 81 as described above. The diluted working medium B having an appropriate pressure by pressure exchange flows to the body of rotation 82 and efficiently rotates it to generate electricity. In addition, the concentrated working medium B having an appropriate pressure by pressure exchange is supplied to the second chamber 44.

The diluted working medium B stored in the diluted working medium tank 32 is concentrated by the diluted working medium circulation system including the third chamber 53 of the membrane distillation and separation device 33 and the pure water circulation and cooling system including the fourth chamber 54 of the membrane distillation and separation device 33 in the same manner as the concentration system 300 illustrated in Fig. 4 described above. In other words, the diluted working medium B is stored in the circulation tank 64 as a working medium B (concentrated working medium B) at a concentration capable of being used as the concentrated working medium B by repeatedly performing the dehydration treatment including the evaporation of water in the diluted working medium B in the third chamber 53, the permeation of the vapor through the dehydration membrane 52, the movement of the vapor to the fourth chamber 54, and the cooling and condensation of the vapor with the circulating pure water on the fourth chamber 54 side plural times, and the concentrated working medium B is returned to the concentrated working medium tank 34. The concentrated working medium B in the concentrated working medium tank 34 is supplied into the second chamber 44 of the osmotic pressure generator 31 by driving the second pump 47 in order to rotate the body of rotation 82 and thus to generate electricity as described above.

Consequently, it is possible to continuously perform the operation of power generation by the rotation of the body of rotation 82 using the osmotic pressure generator 31 and the concentration of the diluted working medium B using the membrane distillation and separation device 33. Hence, it is possible to provide the circulating osmotic power generation system 400 which can be operated at low cost and can efficiently rotate the body of rotation 82 such as a turbine to generate electricity.

Incidentally, in the circulating osmotic power generation system 400 illustrated in Fig. 5, the first treatment container of the osmotic pressure generator is partitioned in the horizontal direction by an osmosis membrane to form the first chamber 43 and the second chamber 44, but the first treatment container may be partitioned into upper and lower parts by an osmosis membrane to form the first chamber 43 and the second chamber 44.

In the circulating osmotic power generation system 400 illustrated in Fig. 5, the water in the first chamber 43 of the osmotic pressure generator 31 is delivered to the outside through the pipeline 201b, but the pipeline 201b may be connected to the tank of water to be treated 45 to form a loop by the tank of water to be treated 45, the pipeline 201a, the first chamber 43 of the osmotic pressure generator 31, and the pipeline 201b.

In the circulating osmotic power generation system 400 illustrated in Fig. 5, the dehydration membrane 52 of the membrane distillation and separation device 33 is not limited to a porous latex membrane, and any membrane may be used as long as it has the function of permeating vapor.

In the circulating osmotic power generation system 400 illustrated in Fig. 5, the concentration of the diluted working medium B is not only performed by using the membrane distillation and separation device 33 equipped with the dehydration membrane 52 but also may be performed by using any device as long as it can remove water from the diluted working medium B.

Hereinafter, Examples will be described.

A forward osmosis test was performed as follows. The CTA-ES membrane manufactured by HTI Corporation was set in a FO cell, pure water was placed on the active face side of the membrane as water to be treated, and the working medium was then placed on the support layer side. The time when the working medium was completely placed was counted as 0 minute, and this state was left to stand for 20 minutes. After the test, the weight of the liquid on the active face side was measured, and the permeate flux (Jw) was calculated from the difference before and after the test by taking the specific gravity of the liquid as 1. In addition, the total organic carbon concentration in the liquid on the active face side after the test was measured by using a total organic carbon meter and the cation concentration was measured by ion chromatography to calculate the loss of solute (Js). The solute contained in the working medium and the concentration thereof and the experimental results are presented in Table 1.

As is apparent from Table 1, in Examples 1 to 7 in which a compound containing plural phosphonic acid groups is used as a draw solution, the loss of solute of an inorganic salt to be generally used is significantly minor. In addition, Comparative Examples in which a sodium salt having a carboxylic acid group is used as a solute is inferior to Examples in Js/Jw. It is possible to cut down the running cost of the water treatment system utilizing the osmotic pressure by using a working medium having such properties. In addition, it is possible to generate electricity at low cost by using the water flow generated by the osmotic pressure inducing action of these to generate electricity.
Here, some elements are expressed only by element symbols thereof.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

A Water to be treated,
B Working medium,
C Water
1, 31 Osmotic pressure generator,
2, 32 Diluted working medium tank,
3 Reverse osmosis membrane separator,
4, 34 Concentrated working medium tank,
11, 41 First treatment container,
12, 42 Osmosis membrane,
13, 43 First chamber,
14, 44 Second chamber,
15, 45 Tank of water to be treated,
16 First pump,
17 Second pump,
21, 51 Second treatment container,
22 Reverse osmosis membrane (RO membrane),
23, 53 Third chamber,
24, 54 Fourth chamber,
25 Third pump,
26 Pure water tank,
27 On-off valve,
33 Membrane distillation and separation device,
52 Dehydration membrane,
61 First on-off valve,
62 Heat exchanger,
64 Circulation tank,
65 Second on-off valve,
66 Fourth pump,
71 First pure water tank,
72 Second pure water tank,
73 Third on-off valve,
74 Fifth pump,
75 Fourth on-off valve,
81 Pressure exchanger,
82 Body of rotation,
100 Water treatment system,
101 Pipeline,
200 Desalination system,
201 Pipeline,
300 Concentration system, and
400 Circulating osmotic power generation system

Claims

A water treatment system comprising:
a first treatment container having an osmosis membrane to partition a first chamber for accommodating water to be treated and a second chamber for accommodating a working medium to induce osmotic pressure, wherein
the working medium is an aqueous solution containing a compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain or a compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain as a solute.
The system according to claim 1, wherein the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain are expressed by C_xH_yP_zO_wN_rCl_sBr_tM_u, wherein
M is an alkali metal or an alkaline earth metal and x, y, z, w, r, s, t, and u satisfy 2 ≦(being less than or equal to) x ≦(being less than or equal to) 9, 8 ≦(being less than or equal to) y ≦(being less than or equal to) 28, 1 ≦(being less than or equal to) z ≦(being less than or equal to) 6, 3 ≦(being less than or equal to) w ≦(being less than or equal to) 18, 0 ≦(being less than or equal to) r ≦(being less than or equal to) 3, 0 ≦(being less than or equal to) s ≦(being less than or equal to) 1, 0 ≦(being less than or equal to) t ≦(being less than or equal to) 1, and 2 ≦(being less than or equal to) u ≦(being less than or equal to) 10.
The system according to claim 1 or 2, wherein the compound has a plurality of ammonium salt structures or metal salt structures of a phosphonic acid group.
The system according to any one of claims 1 to 3, wherein the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain are a compound in which a phosphonic acid group of a compound having a structure expressed by Formula (1), (2), or (3) has an ammonium salt structure or a metal salt structure, wherein
X¹, X², and X³ in Formula (1) are one or more kinds selected from the group consisting of H and -(CH₂)_m1PO(OH)₂ (m1 is any integer from 1 to 3),
Y¹ and Y² in Formula (2) are one or more kinds selected from the group consisting of OH, CH₃, Cl, Br, and CH₂CH₂NH₂, and
Z¹, Z², Z³, and Z⁴ in Formula (3) are one or more kinds selected from the group consisting of H, -(CH₂)_m2PO(OH)₂ (m2 is any integer from 1 to 3), and -(CH₂)_m3N((CH₂)_m4PO(OH)₂)₂ (m3 is any integer from 1 to 3 and m4 is any integer from 1 to 3):

.
The system according to any one of claims 1 to 4, wherein the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain is at least one kinds selected from the group consisting of etidronic acid sodium salt, etidronic acid potassium salt, nitrilotris(methylenephosphonic acid) sodium salt, nitrilotris(methylenephosphonic acid) potassium salt, ethylenediaminetetramethylenephosphonic acid sodium salt, diethylenetriaminepentamethylenephosphonic acid sodium salt, ethylenediaminetetramethylenephosphonic acid potassium salt, and diethylenetriaminepentamethylenephosphonic acid potassium salt.
The system according to any one of claims 1 to 4, wherein the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain is at least one kinds selected from the group consisting of ethidronic acid ammonium salt, nitrilotris(methylenephosphonic acid) ammonium salt, ethylenediaminetetramethylenephosphonic acid ammonium salt, and diethylenetriaminepentamethylenephosphonic acid ammonium salt.
The system according to any one of claims 1 to 6, further comprising a body of rotation, wherein
a water flow is generated by induction of osmotic pressure, and
the body of rotation is rotated by the water flow to generate electricity.
A working medium to be used in the water treatment system according to any one of claims 1 to 7.
A working medium of an aqueous solution containing a compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain or a compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain as a solute.
The medium according to claim 9, wherein the compound having a metal salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain and the compound having an ammonium salt structure of a phosphonic acid group in a main chain, a side chain, or a main chain and a side chain are a compound in which a phosphonic acid group of a compound having a structure expressed by Formula (1), (2), or (3) has an ammonium salt structure or a metal salt structure, wherein
X¹, X², and X³ in Formula (1) are one or more kinds selected from the group consisting of H and -(CH₂)_m1PO(OH)₂ (m1 is any integer from 1 to 3),
Y¹ and Y² in Formula (2) are one or more kinds selected from the group consisting of OH, CH₃, Cl, Br, and CH₂CH₂NH₂, and
Z¹, Z², Z³, and Z⁴ in Formula (3) are one or more kinds selected from the group consisting of H, -(CH₂)_m2PO(OH)₂ (m2 is any integer from 1 to 3), and -(CH₂)_m3N((CH₂)_m4PO(OH)₂)₂ (m3 is any integer from 1 to 3 and m4 is any integer from 1 to 3):

.