CA3108312A1 - Systems and methods for forward osmosis - freeze concentration (fo-fc) purification of contaminated aqueous solutions - Google Patents

Abstract

Forward osmosis - freeze concentration (FO-FC) hybrid purification systems and methods are described to economically recover water from a contaminated liquid, such as a contaminated aqueous solution. For instance, the system and method can enable subjecting the contaminated aqueous solution to forward-osmosis (FO) using a concentrated draw solution (CDS) to cause water to pass into the CDS and thus obtain a diluted draw solution (DDS), and then subjecting the DDS to a freeze concentration (FC) operation to produce a recovered frozen fraction and a regenerated solution reused as at least part of the CDS. This FO-FC method facilitates efficient purification of contaminated streams compared to conventional methods.

Description

SYSTEMS AND METHODS FOR FORWARD OSMOSIS - FREEZE CONCENTRATION
(FO-FC) PURIFICATION OF CONTAMINATED AQUEOUS SOLUTIONS
RELATED APPLICATION
This application claims priority under applicable laws to United States provisional application No. 62/717.083 filed on August 10, 2018, the contents of which are incorporated herein by reference in their entirety for all purposes.
TECHNICAL FIELD
The technical field generally relates to the purification of contaminated aqueous solutions, and more particularly to methods and systems for the purification of streams such as contaminated water from industrial effluents using a combination of forward osmosis (FO) and freeze concentration (FC).
BACKGROUND
Every year in Ontario, approximately 2 million m3 of industrial effluents are disposed of at an average cost of $115/m3. If the amount of water contained in these effluents was recovered, the disposed waste volume would be significantly reduced.
Furthermore, the recovered cleaner water could then be reused in industrial operations, thereby minimizing the freshwater intakes.
Traditional water purification processes are often complex, expensive, relatively inefficient, limited in their application and energy intensive. Non-limiting examples of conventional water purification processes include evaporative processes, reverse osmosis (RO), and electrodialysis (ED). FO, also known as engineered osmosis, may be considered as one of the emerging techniques in membrane technology which may simplify water purification, for example, by being able to treat contaminated water from industrial effluents (e.g., waste water from desalination plants) at lower energy requirements compared to other traditional processes.
In FO, a concentrated draw solution (COS) is used to recover water from a feed solution, i.e., a contaminated effluent. These two solutions are separated by a semi-permeable membrane that selectively allows water molecules to pass through its pores.
The driving force in FO is a spontaneous osmotic pressure gradient generated between the feed

2 solution and the CDS rather than hydraulic pressure (as is the case in RO).
Therefore, using FO allows for the recovery of water without any external energy input to the membrane.
The CDS contains dissolved draw solutes to generate solutions of high osmotic pressure, allowing for the recovery of water from the effluent. Eventually, the CDS gets diluted and has to be treated, usually thermally via thermal evaporation, to separate the purified water recovered from the draw solutes, which may be recovered and reused to regenerate the CDS. For example, an engineered CDS comprising a 13.5 molal (i.e., mol of solute per kg of water) aqueous carbonated trimethylamine (TMAH:HCO3) solution (up to 370 atm osmotic pressure) may recover at least 90 % of the water existing in typical industrial effluents. Subsequently, water is recovered from the resulting diluted draw solution (DDS) via thermal evaporation of the draw solutes, i.e., TMA and 002.
Commonly used CDS are however often toxic or noxious and require thermal energy to allow separation from the DDS and for the CDS to regenerate. Aqueous inorganic salt solutions, such as chloride salt solutions, have been identified as promising CDS
candidates. To date, the main limitation that prevented their use in FO
applications was not having an energy efficient way of separating them from the diluted draw solution (DDS), which in turn would allow for the CDS to regenerate and clean water to be recovered.
Accordingly, there is a need for technologies that overcome one or more of the disadvantages encountered with conventional purification processes.
SUMMARY
According to a first aspect, the present technology relates to a method for purifying a contaminated aqueous solution including dissolved contaminants, including:
providing a feed stream including the contaminated aqueous solution to contact a first side of a semi-permeable forward osmosis (FO) membrane;
providing a concentrated draw solution including dissolved draw solutes to contact a second side of the semi-permeable FO membrane, thereby causing water to diffuse from the feed stream through the semi-permeable FO membrane and into

3 the concentrated draw solution to produce a diluted draw solution and a water-depleted contaminated stream;
cooling at least a portion of the diluted draw solution to cause freezing of water present in the diluted draw solution to produce a frozen water fraction; and recovering the frozen water fraction that is depleted in draw solutes and a regenerated solution that is enriched in the draw solutes and is reused as at least part of the concentrated draw solution.
In one embodiment, the contaminated aqueous solution includes industrial effluents.
In another embodiment, the dissolved contaminant includes a salt. For example, the salt includes sodium chloride. For instance, the contaminated aqueous solution is brackish water, saline water or briny water.
In another embodiment, the contaminated aqueous solution has a concentration of dissolved contaminants between 1 000 and 250 000 ppm, limits included. For example, the contaminated aqueous solution has a concentration of dissolved contaminants between 60 000 and 240 000 ppm, limits included.
In another embodiment, the draw solute includes or is a soluble inorganic salt or a mixture of soluble inorganic salts. For example, the soluble inorganic salt is a soluble chloride salt.
For example, the soluble chloride salt is selected from the group consisting of sodium chloride, magnesium chloride, potassium chloride, lithium chloride, calcium chloride and a mixture of at least two thereof. For example, the soluble inorganic salt is a soluble sulfate salt. For instance, the soluble sulfate salt is selected from the group consisting of magnesium sulfate, lithium sulfate, potassium sulfate, ammonium sulfate, sodium sulfate and a mixture of at least two thereof.
In another embodiment, the concentrated draw solution has a draw solute concentration of at least 0.5 mol/kg. For example, the concentrated draw solution has a draw solute concentration of up to the saturation concentration. Alternatively, the concentrated draw solution has a draw solute concentration higher than the saturation concentration. For instance, the concentrated draw solution has a draw solute concentration between 0.5 mol/kg and 7 mol/kg, or between 0.5 mol/kg and 4 mol/kg, or between 1.5 mol/kg and

4 mol/kg, limits included.

5 In another embodiment, the regenerated solution is separated from the frozen water fraction by gravity separation.
In another embodiment, all the regenerated solution is reused as at least part of the concentrated draw solution.
In another embodiment, the at least a portion of the diluted draw solution is cooled down at a temperature between the freezing point and the eutectic temperature thereof.
In another embodiment, the cooling is performed using a single-stage process.
Alternatively, the cooling is performed using a multi-stage process.
In another embodiment, at least 90 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction. Alternatively, less than 90 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction. For example, up to 98 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction.
In another embodiment, the frozen water fraction includes below 1 000 ppm of draw solutes.
In another embodiment, the method as defined herein, further includes melting the frozen water fraction to obtain liquid phase purified water. For example, the melting is performed by using low-grade heat. For instance, the low-grade heat is heat waste derived from a plant that produces the contaminated aqueous solution.
In another embodiment, the method as defined herein, further includes reusing the liquid phase purified water in an industrial process.
In another embodiment, the method as defined herein, further includes subjecting the liquid phase purified water to additional purification to produce a further purified water. For example, the additional purification comprises reverse osmosis.
In another embodiment, the method as defined herein, further includes controlling the frozen water fraction recovery. For example, controlling the frozen water fraction recovery includes controlling the amount of water diffused from the feed stream to be equivalent to the amount of water recovered in the frozen water fraction.

According to another aspect, the present technology relates to a purified water produced by the method as defined herein.
According to another aspect, the present technology relates to a forward osmosis - freeze concentration (FO-FC) hybrid purification system, comprising:
a forward osmosis (FO) unit comprising a first chamber and a second chamber separated by a semi-permeable membrane, the first chamber having an inlet being configured to receive a feed stream comprising a contaminated aqueous solution that contacts a first side of the semi-permeable membrane, and the second chamber having an inlet being configured to receive a concentrated draw solution that contacts a second side of the semi-permeable membrane, thus causing water to diffuse from the feed stream, through the semi-permeable membrane and into the concentrated draw solution, thereby producing a diluted draw solution and a water-depleted contaminated stream, the first chamber comprising an outlet configured to release the water-depleted contaminated stream and the second chamber comprising an outlet configured to release the diluted draw solution; and a freeze concentration (FC) unit having an inlet in fluid communication with the outlet of the second chamber of the forward osmosis (FO) unit, a freezing chamber for receiving and cooling the diluted draw solution to cause freezing of water present in the diluted drawn solution to produce a frozen water fraction and a regenerated solution, and a liquid outlet for releasing the regenerated solution and being in fluid communication with the inlet of the second chamber for supplying the regenerated solution as at least part of the concentrated draw solution.
In another embodiment, the semi-permeable membrane is a polymeric membrane.
For example, the polymeric membrane is a cellulosic membrane or a polyamide-based membrane.
In another embodiment, the system, as defined herein, further includes a first optional reservoir configured to hold the contaminated aqueous solution and provide the feed stream to the forward osmosis unit.
In another embodiment, the system as defined herein, further includes a heating unit to receive and melt the frozen water fraction and produce a liquid phase purified water.

6 In another embodiment, the system as defined herein, further includes a second optional reservoir unit in fluid communication with the heating unit configured to hold the liquid phase purified water.
In another embodiment, the system as defined herein, further includes a reverse osmosis unit configured for further purification of the liquid phase purified water.
In another embodiment, the system as defined herein, further includes a controller unit in fluid communication with at least one of the forward osmosis (FO) unit, the freeze concentration (FC) unit, the heating unit, the first optional reservoir and the second optional reservoir unit. For example, the controller unit includes a flow controller configured to control the flow rate of the feed stream. The controller unit may also include a multi-scale weight controller configured to control that the amount water diffused from the feed stream is equivalent to the amount of water recovered in the frozen water fraction. The controller unit may further include a concentration controller configured to control the concentration of the concentrated draw solution. The controller unit yet further includes a temperature controller configured to control the cooling of the temperature.
According to another aspect, the present technology relates to the system as defined herein for use in the purification treatment of water derived from an industrial effluent.
According to another aspect, the present technology relates to a method for purifying a contaminated aqueous solution comprising dissolved contaminants, comprising:
subjecting the contaminated aqueous solution and a concentrated draw solution to forward osmosis (FO) to produce a diluted draw solution and a water-depleted contaminated stream; and subjecting the diluted draw solution to freeze concentration (FC) to produce a recovered frozen fraction and a regenerated solution reused as at least part of the concentrated draw solution.
According to a further aspect, the present technology relates to a method for purifying a contaminated liquid comprising dissolved contaminants, comprising:

7 subjecting the contaminated liquid and a concentrated draw stream to forward osmosis (FO) to produce a diluted draw solution and a liquid depleted contaminated stream; and subjecting the diluted draw solution to freeze concentration (FC) to produce a recovered frozen fraction of the liquid and a regenerated stream reused as at least part of the concentrated draw stream.
According to yet a further aspect, the present technology relates to the use of a freeze concentration (FC) unit for converting a diluted draw solution produced by forward osmosis (FO) into a recovered frozen fraction and a regenerated stream reusable as at least part of a concentrated draw stream in FO.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a schematic representation of a process for the purification of a contaminated aqueous solution according to one embodiment.
Figure 2 is a phase diagram of an aqueous CaCl2 solution, showing a multi-stage FC
process, effectively a graph of the temperature (in C) versus the concentration of the draw solution (an aqueous solution of CaCl2).
Figure 3 is a schematic representation of a laboratory-scale FO-FC hybrid purification system as described in Example 1 (a).
Figure 4 is a graph of the osmotic pressure versus the concentration of aqueous solutions of KCI, NaCI, LiCI, CaCl2 and MgCl2 as described in Example 2 (a).
Figure 5 is a phase diagram of an aqueous NaCI solution, effectively a graph of the temperature versus the concentration of the draw solution (an aqueous solution of NaCI) as described in Example 2 (c).
Figure 6 is a phase diagram of an aqueous CaCl2 solution, effectively a graph of the temperature versus the concentration of the draw solution (an aqueous solution of CaCl2) as described in Example 2 (c).

8 Figure 7 is a phase diagram of an aqueous MgC12 solution, effectively a graph of the temperature versus the concentration of the draw solution (an aqueous solution of MgCl2) as described in Example 2 (c).
Figure 8 is a graph of the water flux (in L/m2/h) versus the concentration of the draw solution (an aqueous solution of NaCI) as described in Example 3 (a).
Previously reported values are also shown for comparative purposes.
Figure 9 is a graph of the water flux (in L/m2/h) versus the concentration of the draw solution (an aqueous solution of CaCl2) as described in Example 3 (a).
Previously reported values are also shown for comparative purposes.
Figure 10 is a graph of the water flux (in L/m2/h) versus the concentration of the draw solution (an aqueous solution of MgCl2) as described in Example 3 (a).
Previously reported values are also shown for comparative purposes.
Figure 11 is a graph of the water flux (in L/m2/h) versus the concentration of the draw solution for three different aqueous draw solutions (aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (a).
Figure 12 is a graph of the reverse solute flux (in mol/m2/h) versus the concentration of the draw solution (an aqueous solution of NaCI) as described in Example 3 (b).
Previously reported values are also shown for comparative purposes.
Figure 13 is a graph of the reverse solute flux (in mol/m2/h) versus the concentration of the draw solution (an aqueous solution of CaCl2) as described in Example 3 (b). Previously reported values are also shown for comparative purposes.
Figure 14 is a graph of the reverse solute flux (in mol/m2/h) versus the concentration of the draw solution (an aqueous solution of MgCl2) as described in Example 3 (b). Previously reported values are also shown for comparative purposes.
Figure 15 is a graph of the reverse solute flux (in mol/m2/h) versus the concentration of the draw solution for three different aqueous draw solutions (aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (b).

9 Figure 16 is a graph of the water flux (in L/m2/h) versus the temperature (in C) for three different 1 m aqueous draw solutions (1 m aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (c).
Figure 17 is a graph of the water flux (in L/m2/h) versus the temperature (in C) for three different 3 m aqueous draw solutions (3 m aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (c).
Figure 18 is a graph of the reverse solute flux (in mol/m2/h) versus the temperature (in C) for three different 1 m aqueous draw solutions (1 m aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (d).
Figure 19 is a graph of the reverse solute flux (in mol/m2/h) versus the temperature (in C) for three different 3 m aqueous draw solutions (3 m aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (d).
Figure 20 is a graph of the specific water flux (in L of water/mol of draw solute) versus the temperature (in C) for three different 1 m aqueous draw solutions (1 m aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (e).
Figure 21 is a graph of the specific water flux (in L of water/mol of draw solute) versus the temperature (in C) for three different 3 m aqueous draw solutions (3 m aqueous solutions of NaCI, CaCl2 and MgCl2) as described in Example 3 (e).
Figure 22 is a graph of the temperature versus the concentration of the draw solution (an aqueous solution of NaCI) as described in Example 4 (a).
Figure 23 is a graph of the temperature versus the concentration of the draw solution (an aqueous solution of CaCl2) as described in Example 4 (a).
Figure 24 is a graph of the temperature versus the concentration of the draw solution (an aqueous solution of MgCl2) as described in Example 4 (a).
Figure 25 is a graph of the experimental and theoretical water recovery yield (%) as a function of the temperature (results presented for -10 C, -15 C and -20 C) for an aqueous NaCI DDS as described in Example 4 (b). Data obtained during single-stage and multi-stage operations is also shown for comparative purposes.

Figure 26 is a graph of the experimental and theoretical water recovery yield (%) as a function of the temperature (results presented for -10 C, -20 C, -30 C and -40 C) for an aqueous CaCl2 DDS as described in Example 4 (b). Data obtained during single-stage and multi-stage operations is also shown for comparative purposes.
Figure 27 is a graph of the experimental and theoretical water recovery yield (%) as a function of the temperature (results presented for -10 C, -20 C and -30 C) for an aqueous MgCl2 DDS as described in Example 4 (b). Data obtained during single-stage and multi-stage operations is also shown for comparative purposes.
Figure 28 is a graph of the concentration of impurities in the water recovered using an aqueous NaCI draw solution as described in Example 4 (c). Data obtained during single-stage and multi-stage operations is also shown for comparative purposes.
Figure 29 is a graph of the concentration of impurities in the water recovered using an aqueous CaCl2 draw solution as described in Example 4 (c). Data obtained during single-stage and multi-stage operations is also shown for comparative purposes.
Figure 30 is a graph of the concentration of impurities in the water recovered using an aqueous MgCl2 draw solution as described in Example 4 (c). Data obtained during single-stage and multi-stage operations is also shown for comparative purposes.
Figure 31 is a graph of the water recovery from a DDS in wt. % as a function of the freeze time in hours (results presented for 2 h, 3 h, 4 h, 24 h, and 48 h) for different concentrations of DDS (1 mol/kg, 1.5 mol/kg and 2 mol/kg) as described in Example 5.
Theoretical (i.e., equilibrium) data is also shown for comparative purposes.
Figure 32 is a graph of the concentration of dissolved contaminants (mol/kg) in the water recovered as ice versus the different concentrations of DDS (1 mol/kg, 1.5 mol/kg and 2 mol/kg) as described in Example 5.
Figure 33 is a graph of the concentration of the regenerated CaCl2 CDS versus the freeze time in hours (results presented for 2 h, 3 h, 4 h, 24 h, and 48 h) for different concentrations of CaCl2 DDS (1 mol/kg, 1.5 mol/kg and 2 mol/kg) as described in Example 5.
Theoretical (i.e., equilibrium) data is also shown for comparative purposes.

DETAILED DESCRIPTION
The following detailed description and examples are illustrative and should not be interpreted as further limiting the scope of the invention.
All technical and scientific terms and expressions used herein have the same definitions as those commonly understood by the person skilled in the art when relating to the present technology. The definitions of some terms and expressions used herein are nevertheless provided below for clarity purposes.
When the term "approximately" or its equivalent term "about" are used herein, it means in the region of, and around. When the terms "approximately" or "about" are used in relation to a numerical value, they modify such numerical value. For example, the use of such terms could mean above and below its nominal value by a variation of 10%. Such terms may also take into account the probability of random errors in experimental measurements or rounding.
When the expression "substantially free" is used herein in relation to a concentration, it means a concentration that is lower than 5 % by weight (wt. %), unless otherwise indicated.
When a range of values is mentioned in the present application, the lower and upper limits of the range are, unless otherwise indicated, always included in the definition. When a range of values is mentioned in the present application, for instance, a composition range or a concentration range, then all intermediate ranges and subranges, as well as individual values included in the ranges, are intended to be included in the present application.
When the term "comprising" or its equivalent terms "including," "containing", or expression "characterized by" are used herein, such are inclusive or open-ended and do not exclude additional, unrecited elements or process steps. When the expression "consisting of" is used herein, it excludes any element, step, or ingredient not specified in the present application.
When an indefinite or definite article is used when referring to a singular noun, e.g., "a", "an" or "the", these also include a plural of that noun, unless anything else is specifically stated.

Various techniques are described herein related to the purification of a contaminated stream by leveraging a hybrid process that includes both forward osmosis (FO) and freeze concentration (FC). For example, water can be removed from the contaminated stream into a draw solution using FO, and the resuting diluted draw solution can be subjected to FC in order to recover purified water and regenerate the draw solution. A
hybrid FO-FC
process can faciliate efficient purification of contaminated streams, such as contaminated industrial effluents.
For a more detailed understanding of the disclosure, reference is first made to Figure 1, which provides a schematic representation of a forward osmosis - freeze concentration (FO-FC) hybrid purification system 10 in accordance with a possible embodiment. The FO-FC hybrid purification system 10 includes a FO unit 12 and a FC unit 14.
In accordance with one embodiment, the FO-FC hybrid purification system 10 may further include a first optional reservoir 16 configured to hold a contaminated aqueous solution 18 and provide a feed stream 20 comprising the contaminated aqueous solution 18 to the FO unit 12. The reservoir 16 may receive the contaminated aqueous solution 18, for example from an industrial effluent line (not shown in Figure 1).
Alternatively, the FO unit 12 may receive the feed stream 20 directly from the industrial effluent line (not shown in Figure 1).
The contaminated aqueous solution 18 comprises an aqueous solution and one or more dissolved contaminant(s). In at least one embodiment, the feed stream comprises between 1 000 ppm and 250 000 ppm, or between 35 000 ppm and 250 000 ppm, or between 35 000 ppm and 60 000 ppm, or between 35 000 ppm and 160 000 ppm, or between 160 000 ppm and 250 000 ppm, or between 60 000 ppm and 240 000 ppm, of dissolved contaminants. Of course, the feed stream can also include other organic or inorganic substances, such as suspended materials, as well as other materials that are typically derived when using an industrial process from which such a contaminated solution could be derived.
It is to be noted that, although aqueous contaminated solutions are typically used when treating contaminated streams using the techniques described herein, other types of contaminated liquid streams can also be treated using the FO-FC hybrid process in order to generate a purified liquid. Any type of compatible contaminated liquid is considered.

As illustrated in Figure 1, the FO unit 12 includes a first chamber 22 and a second chamber 24, which are separated by a semi-permeable membrane 26, or FO membrane. In a preferred embodiment, the semi-permeable membrane 26 is an osmotic membrane allowing water to pass from the first chamber 22 to the second chamber 24.
For example, the semi-permeable membrane 26 may be made from a material which is permeable to water and substantially impermeable to at least one or more dissolved contaminant(s) in the feed stream 20. Any type of compatible semi-permeable membrane material is considered. For example, the semi-permeable membrane material may be selected for their properties, such as water permeability coefficient, salt permeability coefficient, structural parameters (e.g., the thickness and the porosity); all of which may affect the process performances. For instance, the semi-permeable membrane material may be a polymer and polymer composite. Non-limiting examples of semi-permeable membrane materials include aquaporin, cellulose acetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetyl propionate, cellulose diacetate, cellulose dibutyrate, cellulose tributyrate, blends of cellulosic materials, polyurethane and polyamides. In one variant of interest, the semi-permeable membrane 26 is an asymmetric cellulose triacetate (CTA) membrane. In one embodiment, the semi-permeable membrane material is casted on a support material.
Still referring to Figure 1, the first chamber 22 includes an inlet 28 configured to receive a feed stream 20 comprising the contaminated aqueous solution 18 that contacts a first side of the semi-permeable membrane 26. As illustrated in Figure 1, the inlet 28 is in fluid communication with an outlet 30 of the reservoir 16 supplying the feed stream 20, the outlet 30 being configured to release the contaminated aqueous solution 18.
Alternatively, the inlet 28 may receive the feed stream 20 directly from the industrial effluent line (not shown in Figure 1). The inlet 28 is illustratively located at the top of the first chamber 22.
However, it is possible for the inlet 28 to be located on other sides or locations of the first chamber 22.
As illustrated in Figure 1, the second chamber 24 includes an inlet 32 configured to receive a concentrated draw solution 34 that contacts a second side of the semi-permeable membrane 26, thus causing water to diffuse from the feed stream 20, through the semi-permeable membrane 26 and into the concentrated draw solution 34, thereby producing a diluted draw solution 36 and a water-depleted contaminated stream 38. The inlet 32 is illustratively located at the bottom of the second chamber 24. However, it is possible for the inlet 36 to be located on other sides or locations of the second chamber 24.
In some embodiments, the concentrated draw solution 34 comprises dissolved draw solutes in water. Any compatible type of draw solutes is considered. The draw solutes may be selected for their properties, such as their being non-hazardous, as well as for their osmotic pressure, water solubility, speciation, pH, toxicity, compatibility with the semi-permeable membrane 26, and specifically associated costs, which may also come into play and affect process sustainability or performances. For instance, the draw solutes may have a substantially high solubility in water to generate a concentrated draw solution of high osmotic pressure and/or may substantially readily separate to produce water and to regenerate the concentrated draw solution with a substantially low energy input. Non-limiting examples of draw solutes include thermolytic inorganic or organic salts (e.g.
thermolytic ammonium salts or trimethylammonium salts), sugar-based solutes (e.g.
fructose, sucrose, or glucose), fertilisers, 2-methylimidazole-based compounds, magnetic nanoparticles (MNPs), hydrogels, potassium citrate, citric acid, potassium ascorbate, sodium ascorbate, ascorbic acid, and low molecular weight inorganic salts and a combination of the above as well as any of the draw solute when compatible.
For example, the inorganic salt with low molecular weight is a sulfate salt or a chloride salt. For instance, the sulfate salt is selected from magnesium sulfate (MgSO4), lithium sulfate (Li2SO4), potassium sulfate (K2SO4), ammonium sulfate ((NE14)2SO4), and sodium sulfate (Na2SO4).
For instance, the chloride salt is selected from sodium chloride (NaCI), magnesium chloride (MgCl2), potassium chloride (KCI), lithium chloride (LiCI) and calcium chloride (CaCl2). According to one variant of interest, the draw solute is a chloride salt selected from NaCI, MgCl2 and CaCl2. For instance, NaCI, MgCl2 and CaCl2 may be considered as non-toxic and highly soluble in water and may generate environmentally benign solutions of high osmotic pressure and water draw capability. Although, the most common chloride and sulfate salts have been listed here, other chloride and sulfate salts may serve as draw solutes when compatible with the FO-FC hybrid purification system 10 as described herein.
In some embodiments, the concentrated draw solution 34 has a concentration of at least 0.5 mol/kg. In some embodiments, the concentrated draw solution 34 has a concentration of up to the saturation concentration of the selected dissolved draw solute in water at the operating temperature. Alternatively, the concentrated draw solution 34 has a concentration above the saturation concentration of the selected dissolved draw solute in water at the operating temperature. For instance, when the concentration is above the saturation concentration, the osmotic driving force may be constantly at its maximum.
Using a concentration of concentrated draw solution 34 above the saturation concentration may also prevent the dilution of the concentrated draw solution 34. For example, the concentrated draw solution 34 can have a concentration between 0.5 mol/kg and 7.0 mol/kg, or between 0.5 mol/kg and 6.0 mol/kg, between 0.5 mol/kg and 5.0 mol/kg, or between 0.5 mol/kg and 4.0 mol/kg, or between 0.5 mol/kg and 3.5 mol/kg, or between 1.0 mol/kg and 7.0 mol/kg, or between 1.0 mol/kg and 6.0 mol/kg, between 1.0 mol/kg and 5.0 mol/kg, or between 1.0 mol/kg and 4.0 mol/kg, or between 1.5 mol/kg and 7.0 mol/kg, or between 1.5 mol/kg and 6.0 mol/kg, between 1.5 mol/kg and 5.0 mol/kg, or between 1.5 mol/kg and 4.0 mol/kg, or between 2.0 mol/kg and 7.0 mol/kg, or between 2.0 mol/kg and 6.0 mol/kg, between 2.0 mol/kg and 5.0 mol/kg, or between 2.0 mol/kg and 4.0 mol/kg, or between 3.0 mol/kg and 7.0 mol/kg, or between 3.0 mol/kg and 6.0 mol/kg, between 3.0 mol/kg and 5.0 mol/kg, or between 3.0 mol/kg and 4.0 mol/kg, or between 4.0 mol/kg and 7.0 mol/kg, or between 4.0 mol/kg and 6.0 mol/kg, between 4.0 mol/kg and 5.0 mol/kg, between 5.0 mol/kg and 7.0 mol/kg, or between 5.0 mol/kg and 6.0 mol/kg, between 6.0 mol/kg and 7.0 mol/kg, or preferably between 1.5 mol/kg and 4.0 mol/kg;
limits included depending on the choice of dissolved draw solute and the operating temperature.
For instance, the selection of the draw solutes and the level of concentration in the concentrated draw solution 34 directly affects the water flux through the semi-permeable membrane 26. Such a selection may be made in accordance with the type of contaminated stream to be treated.
Still referring to Figure 1, in accordance with one embodiment, the first chamber 22 may further include an outlet 40 configured to release the water-depleted contaminated stream 38. Illustratively, the outlet 40 is located at the bottom of the first chamber 22. However, it is possible for the outlet 40 to be located on other sides or locations of the first chamber 22.
As illustrated in Figure 1, the second chamber 24 includes an outlet 42 configured to release the diluted draw solution. Illustratively, the outlet 42 is located at the top of the second chamber 24. However, it is possible for the outlet 42 to be located on other sides or locations of the second chamber 24.

Still referring to Figure 1, the FC unit 14 comprises an inlet 44 in fluid communication with the outlet 42 of the second chamber 24 of the FO unit 12. The inlet 44 is configured to receive the diluted draw solution. In this embodiment, there is a direct line from the outlet 42 of the second chamber 24 to the inlet 44 in of the FC unit 14, and the diluted draw solution is not subjected to intervening processing or unit operation.
However, in other examples, the diluted draw solution may undergo processing or treatment in advance of the FC unit 14; for example, to prepare it for the FC operation. It is also noted that all or part of the diluted draw solution can be sent to the FC unit 14.
As illustrated in Figure 1, the FC unit 14 comprises a freezing chamber 46 configured to receive and cool the diluted draw solution, thereby freezing the water present in the diluted drawn solution to produce a frozen water fraction and a regenerated solution.
As illustrated in Figure 1, the FC unit 14 further comprises a liquid outlet 48 configured to release the regenerated solution. The liquid outlet 48 is in fluid communication with the inlet 32 of the second chamber 24 for supplying the regenerated solution, and thus, at least part of the regenerated solution forms at least part of the concentrated draw solution.
It is noted that there can be a direct line from the liquid outlet 48 to the inlet 32 in the second chamber 24, where the solution is not subjected to intervening processing or unit operation. However, in other examples, the concentrated draw solution may undergo processing or treatment in advance of the FO unit 12; for example, to prepare it for the FO
operation. It is also noted that all or part of the regenerated draw solution can be sent to the FO unit 12.
As illustrated in Figure 1, in accordance with one embodiment, the freezing chamber 46 may further comprise an outlet 50 configured to release the frozen water fraction. This outlet 50 can thus be configured for solids handling and can release the frozen fraction from the freezing chamber 46 so that it can be melted in another unit or in another compartment of the FC unit 14.
In accordance with one embodiment, the FO-FC hybrid purification system 10 may further comprise a heating unit 52 configured to receive and melt the frozen water fraction and recover a liquid phase purified water. For example, the heating unit 52 may depend on the availability of a low-grade heat; for example, it could be waste heat derived from a plant that produces the contaminated aqueous solution. The melting can therefore leverage low-value heat (e.g., warm condensate or heat from various process streams) to produce the liquid phase purified water.
In accordance with one embodiment, the FO-FC hybrid purification system 10 may further include a second optional reservoir unit 54 configured to hold a liquid phase purified water and provide a feed stream of liquid phase purified water. For instance, the second optional reservoir unit 54 may be in fluid communication with the fresh/treated water intake unit (not shown in Figure 1) of the industrial process. For example, the liquid phase purified water may be produced using the industrial process. For instance, the liquid phase purified water produced using the industrial process may be employed during washing or cooling steps of industrial processes. Other non -limiting examples of industries that use the liquid phase purified water include hydrometallurgical, mineral processing, mining, pulp and paper, oil and gas, operations and the food industry. For instance, the second optional reservoir unit 54 may be in fluid communication with the heating unit 52.
In accordance with one embodiment, the FO-FC hybrid purification system 10 may further comprise a reverse osmosis unit (not shown in Figure 1) configured to further purify the liquid phase purified water and thereby produce a further purified liquid phase water.
Indeed, FO may be used to recover water from industrial effluent solutions containing between 1 000 ppm to 250,000 ppm of dissolved contaminants. FO operates at and beyond the RO operational cut-off, which is less than about 35 000 ppm of dissolved contaminants. Even though reverse osmosis (RO) cannot be used to recover water efficiently from such highly concentrated solutions, due to membrane fouling and the resulting very high energy requirements and maintenance costs, it is a viable treatment option which can be implemented after reaching its operational cut-off. Thus, RO can be efficiently used to further treat purified water produced by the FC unit. In addition, the further purified liquid phase water produced by RO may be potable water that is safe for human consumption. According to one embodiment, the RO unit may be in fluid communication with the heating unit 52 to receive and treat the liquid phase purified water derived from the FC unit.
In accordance with one embodiment, the FO-FC hybrid purification system 10 may further comprise a controller unit 56. The controller unit 56 may comprise a flow controller configured to control the flow rate of the feed stream 20, comprising the contaminated aqueous solution 18 to be received by the FO unit 12. The controller unit 56 may also comprise a multi-scale weight controller configured to evaluate the water recovery from the DDS in wt. %, meaning effectively ensuring that the weight water removed from the feed stream 20 is substantially equivalent to that of the weight of the water recovered in the frozen water fraction. The controller unit 56 may also comprise a concentration configured to control the concentration of the concentrated draw solution (CDS). The controller unit 56 may further comprise a temperature controller configured to control the cooling temperature. According to one embodiment, the controller unit 56 may be in fluid communication with the FO unit 12, or the freeze concentration (FC) unit 14, or both. The controller unit 56 may also be in fluid communication with at least one of the heating unit 52, the second optional reservoir unit 54 and the first optional reservoir 16.
In accordance to one embodiment, the FO unit 12 of the FO-FC hybrid purification system may be place inside a cooling unit (not shown in Figure 1) provided to control the cooling temperature of the FO unit 12. Alternatively, the FO unit 12 of the FO-FC hybrid purification system 10 may be partially place inside a cooling unit (not shown in Figure 1).
For instance, the cooling unit may be a refrigerator such as a high-performance laboratory refrigerator.
The present technology also relates to a method for purifying a contaminated stream, such as a contaminated aqueous solution comprising dissolved contaminants.
In some embodiments, the method includes providing the feed stream 20 comprising the contaminated aqueous solution 18 to contact a first side of the semi-permeable membrane 26 or FO membrane. The method also includes providing the concentrated draw solution 34 comprising dissolved draw solutes as described herein to contact the second side of the semi-permeable membrane 26, thereby causing water to diffuse from the feed stream through the semi-permeable membrane 26 and into the concentrated draw solution 34, to produce a diluted draw solution and a water-depleted contaminated stream. The method further includes cooling at least a portion of the diluted draw solution to cause the water present in the diluted draw solution to produce a frozen water fraction. The method also includes recovering the frozen water fraction that is depleted in draw solutes and a regenerated solution that is enriched in the draw solutes and reused as at least part of the concentrated draw solution.

In one embodiment, the contaminated aqueous solution 18 is derived from industrial effluents. For example, the industrial effluent may be a contaminated aqueous stream from the chemical, mining, oil, food, or pharmaceutical industry. Alternatively, the contaminated aqueous solution 18 may be leachates or agricultural wastes. For example, the contaminated aqueous solution 18 may be brackish water, saline water or briny water. In one embodiment, the dissolved contaminant may include a salt (e.g., sodium chloride (NaCI)). For instance, the contaminated aqueous solution may be briny water or brine produced in a desalination plant.
In some embodiments, depending on the FO-FC hybrid purification system 10, the FO
process may be carried out at about room temperature. Alternatively, the FO
process may be carried out at a temperature of less than about 25 C. For instance, the FO
process may be carried out at a temperature in the range of from about 0 C to about 25 C, or from about 5 C to about 25 C, or from about 5 C to about 10 C, or from about 5 C to about 15 C, or from about 5 C to about 10 C.
In some embodiments, depending on the FO-FC hybrid purification system 10, the water flux (in L/m2/h), the specific water flux (in L of water/mol of draw solute), the reverse draw solute flux (in mol/m2/h) all depend on the FO process temperature. For example, the water flux and the reverse draw solute flux may decrease by up to about 47 %
and about 64%, respectively with a decrease in FO operating temperature of from about 25 C to about 5 C. For example, the water flux may decrease by about 31.6 % to about 46.8 %
with a decrease in FO operating temperature from about 25 C to about 5 C.
In some embodiments, depending on the FO-FC hybrid purification system 10, when the draw solution is aqueous solution of NaCI the water flux obtained using a FO
process carried out at room temperature may be in the range of from about 6.4 L/m2/h to about 19.7 L/m2/h for CDS concentrations between about 0.5 m to about 4 m. In one example, the water flux is in the range of from about 6.4 L/m2/h to about 16.2 L/m2/h using an aqueous NaCI solution having a concentration in the range of from about 0.5 m to about 3.5 m.
In some embodiments, depending on the FO-FC hybrid purification system 10, when the draw solution is aqueous solution of CaCl2 the water flux obtained using a FO
process carried out at room temperature may be in the range of from about 6.7 L/m2/h to about 16.9 Um2/h for CDS concentrations between about 0.4 m to about 3.5 m. In one example, the water flux is in the range of from about 7.9 Um2/h to about 16.9 Um2/h using an aqueous CaCl2 solution having a concentration in the range of from about 0.5 m to about 3.5 m.
In some embodiments, depending on the FO-FC hybrid purification system 10, when the draw solution is aqueous solution of MgC12 the water flux obtained using a FO
process carried out at room temperature may be in the range of from about 6.1 Um2/h to about 16.9 Um2/h for CDS concentrations between about 0.35 m to about 3.5 m. In one example, the water flux is in the range of from about 8.6 Um2/h to about 16.9 Um2/h using an aqueous MgCl2 solution having a concentration in the range of from about 0.5 m to about 3.5 m.
In some embodiments, depending on the FO-FC hybrid purification system 10, when the draw solution is aqueous solution of NaCI the reverse draw solute flux obtained using a FO process carried out at room temperature may be in the range of from about 0.13 mol/m2/h to about 0.34 mol/m2/h for draw solute concentrations between about 0.5 m to about 3.5 m.
In some embodiments, depending on the FO-FC hybrid purification system 10, when the draw solution is aqueous solution of CaCl2 the reverse draw solute flux obtained using a FO process carried out at room temperature may be in the range of from about 0.07 mol/m2/h to about 0.22 mol/m2/h for CDS concentration between about 0.5 m to about 3.5 m.
In some embodiments, depending on the FO-FC hybrid purification system 10, when the draw solution is aqueous solution of MgCl2 the reverse draw solute flux obtained using a FO process carried out at room temperature may be in the range of from about 0.09 mol/m2/h to about 0.18 mol/m2/h for CDS concentration between about 0.5 m to about 3.5 m.
In some embodiments, depending on the FO-FC hybrid purification system 10, less than 90 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction. For example, at least 66 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction. For example, between 66 wt.% and 96 wt.%, or between 80 wt.% and 96 wt.%. Alternatively, in a preferred embodiment, at least 90 wt.%

of the water in the contaminated aqueous solution is recovered in the frozen water fraction.
For example, between 90 wt.% and 100 wt.%, or between 90 wt.% and 99 wt.%, or between 90 wt.% and 98 wt.%, or between 90 wt.% and 97 wt.%, or between 90 wt.% and 96 wt.%, or between 90 wt.% and 95 wt.%, or between 90 wt.% and 94 wt.%, or between 93 wt.% and 92 wt.%, or between 90 wt.% and 91 wt.%, or preferably up to 98 wt.%, limits included, of the water in the contaminated aqueous solution is recovered in the frozen water fraction. For instance, the water recovery depends on both the type of process (i.e., single-stage FC process and multi-stage FC process) and the FO operating temperature.
In some embodiments, the diluted draw solution is cooled down at a temperature between the freezing point and the eutectic temperature of the DDS. For example, when the DDS
is a 2 mol/kg aqueous solution of CaCl2, the diluted draw solution may be cooled down at a temperature of about -15 C to about -50 C, or of about -15 C to about -45 C, or of about -20 C to about -45 C, or of about -20 C to about -40 C, or of about -25 C to about -35 C
or of about -25 C to about -30 C. For instance, when the DDS is a 2 mol/kg aqueous solution of CaCl2 the diluted draw solution may be cooled down at a temperature of about -27 C. In another example, the draw solution is selected from aqueous solutions of NaCI, CaCl2, MgCl2 and a mixture of at least two thereof and the solution may be cooled down at a temperature of about -5 C to about -50 C. For example, of about -5 C to about -40 C, or of about -5 C to about -35 C, or of about -5 C to about -30 C, or of about -5 C to about -20 C or of about -5 C to about -10 C.
In some embodiments, the cooling of the at least a portion of the diluted draw solution is performed in a single-stage process. Alternatively, the cooling can be performed in a multi-stage process. A multi-stage FC unit could therefore also be used. For example, FC
separation is analogous to distillation separation in that temperature is the driving force for the selective separation. Consequently, to achieve high or about 100 %
separation of the frozen water fraction and the regeneration of CDS, a multi-stage FC
process is proposed. Reference is now made to Figure 2, which illustrates a multi-stage FC process on the CaCl2 phase diagram and thus illustrates a graph of the temperature (in C) versus the concentration of the DDS; in this case, an aqueous solution of CaCl2. The multi-stage FC process may include several temperature steps for a given period of time.
In some embodiments, the frozen water fraction comprises up to 1 000 ppm, limits included of dissolved draw solutes. In such an example, the water from the frozen water fraction is considered purified water. For example, the purified water comprises between 500 ppm to 1 000 ppm, or between 500 ppm and 900 ppm, or between 500 ppm and 800 ppm, or between 500 ppm and 700 ppm, or between 500 ppm and 600 ppm, limits included of dissolved draw solutes. For example, the purified water is fresh water comprising between 0 ppm and 500 ppm, or between 0 ppm and 400 ppm, or between ppm and 300 ppm, or between 0 ppm and 200 ppm, limits included of dissolved draw solutes. For example, the purified water is drinking water comprising below 100 ppm, limits included of dissolved draw solutes. For example, fresh and drinking water may obtain further purification, for instance, by RD. In some embodiments, the frozen water fraction comprises a concentration of impurities of less than about 0.20 m. For example, less than about 0.18 m, or between about 0.06 m and about 0.18 m, or between about 0.06 m and about 0.14 m. In some embodiments, the frozen water fraction comprises an average concentration of impurities of 0.12 m 0.05 m. For instance, when the draw solution comprises a divalent aqueous solution (e.g. CaCl2 and MgCl2) the frozen water fraction comprises an average concentration of impurities of 0.14 m 0.03 m. For instance, when the draw solution comprises a monovalent aqueous solution (e.g. NaCI) the frozen water fraction comprises an average concentration of impurities of 0.06 m 0.02 m.
For instance, the frozen water fraction obtained in a single-stage process comprises a substantially superior concentration of impurities when compared to water fraction obtained in a multi-stage process.
According to another aspect, the present technology relates to a method for purifying a contaminated aqueous solution comprising dissolved contaminants. The method comprises subjecting the contaminated aqueous solution and a concentrated draw solution to FO to produce a diluted draw solution and a water-depleted contaminated stream, and then subjecting the diluted draw solution to FC, thereby producing a recovered frozen fraction and a regenerated solution that can be reused as, at least, part of the concentrated draw solution.
In some embodiments, the concentration of regenerated CDS is substantially greater than that of the DDS. For example, the concentration of regenerated CDS is greater than that of the DDS by a factor of at least 2.8. For example, the concentration of regenerated CDS
is greater than that of the DDS by a factor in the range of from about 2.8 to about 4 (i.e., the concentration of regenerated CDS is about 2.8 to about 4 x higher compared to the DDS).

According to another aspect, the present technology relates to a method for purifying a contaminated liquid comprising dissolved contaminants. The method comprises subjecting the contaminated liquid and a concentrated draw stream to FO, thereby producing a diluted draw solution and a liquid depleted contaminated stream, and then subjecting the diluted draw solution to FC, thus producing a recovered frozen fraction of the liquid and a regenerated stream that can be reused as, at least, part of the concentrated draw stream.
The purification of water from industrial effluents reduces the volume of liquid waste to be disposed, leading to cost savings and environmental benefits.
Another advantage of the technology described herein is that inorganic salts solutions may be advantageously used in FO. Furthermore, FO water diffuses spontaneously due to an osmotic pressure gradient, and therefore does not require an external energy input. For instance, the technology described herein may energetically outperform commonly used water recovery processes also leading to cost savings and environmental benefits. As described by Williams et al. (see Williams et al., Desalination, 356 (2015) 314-327), FC
may energetically outperform processes operating on the evaporation concept requiring up to about 7 times less energy input.
Further advantages include the recovery of cleaner water through FC while efficiently regenerating the CDS. The cleaner water recovered as ice may then be melted by using low-grade waste plant heat. FC is a low-energy process able to effectively recover clean water from aqueous solutions with up to seven times less energy input (on a thermodynamic basis) than current processes operating on the evaporation concept.
Moreover, the application of FO before FC is highly beneficial. For instance, it facilitates modeling, monitoring, and control over water recovery. For instance, by selecting the appropriate concentration difference between the concentrated draw solution 34 and the contaminated aqueous solution 18 in the FO unit 12, a control over the water flux through the semi-permeable membrane 26 value may be achieved. Afterwards, the water that is passed through the semi-permeable membrane 26 in the concentrated draw solution 34 is recovered in the FC unit 14, allowing for clean water recovery and simultaneous concentrated draw solution regeneration. For instance, the monitoring is performed using the controller unit 56 which may, for example, comprise sensors for measuring and monitoring relevant process parameters, such as temperatures, flows, levels, concentration and water recovery.
In some embodiments, the FC unit 14 may be a semi-automated FC unit able to run in batch or continuous mode. Alternatively, the FC unit 14 may be a fully automated industrial scale units with a continuous operating mode. In some embodiments, FC unit 14 may be paired with a refrigeration system. For instance, the outer walls of the FC
unit 14 may comprise a cooling jacket and may be cooled by circulation of at least one refrigerant. The ice production and ice crystal growth take place inside the FC unit 14. For example, the FC unit 14 may comprise cooled wall portions (not shown in Figure 1) and at least one raking or scraping element(s) for scraping the recovered frozen fraction from the cooled wall portions (not shown in Figure 1).
The technology described herein may be useful in several industries and industrial sectors. For example, the technology described herein may be useful in the industrial wastewater sector, the oil and gas industry, the mining industry and the agriculture industry to stabilize their often-challenging aqueous waste streams through natural dewatering, minimizing at the same time the risks and severity of potential catastrophic accidents related to them.
EXAMPLES
The following non-limiting examples are illustrative and should not be construed as limiting the scope of the present invention. These examples will be better understood with reference to the accompanying Figures.
Example 1: FO-FC hybrid purification system laboratory set-up and experimental conditions (a) Laboratory-scale FO-FC hybrid purification system The experiments were performed using a laboratory-scale FO-FC hybrid purification system as illustrated in Figure 3. The laboratory-scale FO-FC hybrid purification system comprises a rectangular stainless steel CF042 FO unit having an active area of 42 cm2 (purchased from SterlitechTm). The experiments were performed using an asymmetric cellulose triacetate (CTA) semi-permeable membrane having a CTA active layer on one side from Fluid Technology SolutionsTM. The CTA semi-permeable membrane was oriented so that the CTA active layer was facing the feed stream including the contaminated aqueous solution. The laboratory-scale FO-FC hybrid purification system further comprises a control unit provided to control metrics, such as flowrates. The control unit of the laboratory-scale FO-FC hybrid purification system comprises a Thermo-Fischer Easy LoadTM II peristaltic pump. The laboratory-scale FO-FC hybrid purification system further comprises a FC unit comprising a Thermo ScientificTM FormaTM FRGL1204A
high-performance laboratory refrigerator. The laboratory-scale FO-FC hybrid purification system also comprises a reservoir contaminated solution to be purified and a draw solution reservoir, both configured to hold the solutions and provide the feed to the FO unit.
(b) FO-FC experimental conditions FO experiments were performed using the laboratory-scale FO-FC hybrid purification system, as described in Example 1 (a). The FO unit was operated counter-currently and the flowrates were controlled using the peristaltic pump. Experiments were performed at a temperature of 5, 15, and 25 C. The temperature was controlled using the high-performance laboratory refrigerator. For the experiments performed at a temperature of 5 C, the entire FO set-up was placed inside the refrigerator. For the experiments performed at a temperature of 15 C, the concentrated draw solution and the stream, including the contaminated aqueous solution, were both placed outside of the refrigerator while the FO unit was placed inside the refrigerator. The experiments performed at a temperature of 25 C were carried out outside of the refrigerator.
Example 2: Selection of draw solutes and laboratory-scale batch experiments This example illustrates the selection of the draw solutes. Chloride salts were investigated as draw solutes for the hybrid FO-FC process. These salts are highly soluble in water, and thus generate solutions of high ionic strength and high osmotic pressure.
(a) Simulated osmotic pressure Figure 4 presents the osmotic pressure generated by aqueous solutions of KCI
(line A), NaCI (line B), LiCI (line C), CaCl2 (line D), and MgCl2 (line E) versus their concentration.
The data presented in Figure 4 was obtained using OLI TM system simulation software and the MSE model. The simulated osmotic pressure recorded with these solutions at a concentration of 4 mol/kg, which is below the solubility for these salts, was between about 185 to about 850 atm depending on the salts.
(b) FO laboratory-scale batch experiments FO lab-scale batch experiments were performed using 0.5 mol/kg, 1 mol/kg, 2 mol/kg, 3 mol/kg, 3.5 mol/kg NaCI, CaCl2, MgCl2 CDS and deionized (DI) water as the feed solution. The CDS were prepared by dissolving the appropriate amount of salt in DI water to obtain the desired concentrations. Both the draw and feed solutions were circulated in a closed loop system. The volume of both reservoirs was large enough to ensure a substantially constant concentration throughout the experiment. The experiments were carried out at a mass flowrate of 8,000 g/h (2.1 cm/s crossflow velocity) for both streams.
The mass of each reservoir was digitally recorded every 30 s using a Mettler-ToledoTm balance. Both the draw and feed solution samples were taken at a steady rate 15 min), and again approximatively 1 hour after the experiment. Both the draw and feed solution cation concentrations were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Prior to the analysis, the samples were diluted with 5 % (V/V) nitric acid (H NO3) (50x for the feed samples; and 1000x for the draw solution samples).
The water flux was determined based on the draw solution mass variation with time (i.e., the draw solution mass variation rate per unit of membrane area, expressed, for example in L/m2/h), while the reverse salt flux was determined using the final solute concentration in the feed. The laboratory-scale batch experiments were performed in triplicates.
(c) FC laboratory-scale batch experiments The diluted draw solutions used in the FC experiments were prepared by dissolving the appropriate amount of each salt in DI water. The initial concentration of the solutions prepared was measured by ICP-OES. The diluted draw solutions were placed in beakers (150 mL) inside a Thermo ScientificTM FormaTM 8600 Series Chest Freezer Model freezer. The diluted draw solutions were exposed to the targeted temperature inside the freezer for 24 hours, until they reached equilibrium. The resulting slurry was then vacuum filtered for about 2 min to about 7 min to separate the solid phase from the liquid phase, after which the CDS and ice samples were collected and weighed. The final ice products were washed with about 10 g to about 15 g of chilled DI water (about 4 C).
The samples were diluted using DI water to known volumes of 100 mL and 200 mL for the ice and CDS, respectively. Finally, the above diluted samples were further diluted by a factor of 1000x using 5 % (V/V) HNO3 and were analyzed by ICP-OES to determine their cation content.
The FC experiments described above were also carried out in triplicates.
Detailed information concerning the FC experimental matrix is presented in Table 1.
Table 1. FC experimental matrix Solute Concentration Tern peratu re Operation 0.5 -20 Single-Stage NaCI 0.5 -10 2.5 -15 Multi-Stage 3.5 -20 0.5 -40 Single-Stage 0.5 -10 CaCl2 1.5 -20 2.0 -30 Multi-Stage 2.5 -40 0.5 -30 Single-Stage 0.5 -10 MgCl2 1.5 -20 Multi-Stage 2.0 -30 FC temperatures were selected by referring to the phase diagram of each of the NaCI, CaCl2 and MgCl2 solutions, which were obtained using the using OLI TM system simulation software and the MSE model, which are respectively presented in Figures 5 to 7. Detailed information concerning the eutectic composition and temperature as calculated by the OLI-MSE software for each solution is presented in Table 2.
Table 2. Eutectic composition and temperature for the NaCI, CaCl2, and MgCl2 solutions Inorganic Draw Solution Eutectic Composition (m) Eutectic Temperature ( C) NaCI 5.17 -21.4 CaCl2 3.68 -51.7 MgCl2 2.74 -33.6 Example 3: Characterization of the FO laboratory-scale batch experiments (a) Water flux at room temperature As described in Example 2 (b) the water flux was determined from the rate of change of the draw solutions mass per unit of membrane area (L/m2/h). The experimental water flux data obtained in Example 2 (b) using a NaCI, CaCl2, and MgCl2 CDS and DI water as the feed solution was compared to values previously reported (see Achilli et al., Journal of Membrane Science, 364 (2010) 233-241; Boo etal., Journal of Membrane Science, (2015) 302-309; Phillip etal., Environmental Science & Technology, 44 (2010) 5170-5176;
Phuntsho etal., Journal of Membrane Science, 453 (2014) 240-252; Su etal., Journal of Membrane Science, 376 (2011) 214-224; and Hancock et al., Environmental Science &
Technology, 43 (2009) 6769-6775).
Figure 8 presents a graph of the experimental water flux versus the concentration of the NaCI CDS (circles and discontinued line) compared to values reported by Achilli et al.
(diamonds), Phillip et al. (plus) and Boo et al. (squares with a diagonal line). The water flux values previously reported were in the range of from 9.6 to 19.7 L/m2/h for NaCI CDS
concentrations of 0.6 to 4 m. As can be seen in Figure 8, the experimental water flux data was in substantially good agreement with the above reported values, indicating water flux values in the range of from about 6.4 L/m2/h to about16.2 L/m2/h for NaCI CDS
concentrations in the range of from about 0.5 m to about 3.5 m.
Figure 9 presents a graph of the experimental water flux versus the concentration of the CaCl2 CDS (triangles and dotted line) compared to the values reported by Achilli et a/.
(diamonds) and Phuntsho etal. (squares). Water flux values reported by Achilli etal. were in the range from 9.5 to 11.6 L/m2/h for CaCl2 CDS concentrations of 0.4 to 0.6 m, while water flux values estimated by Phuntsho et al. were in the range from 6.7 to 11.5 L/m2/h for CaCl2 CDS concentrations of 1 to 3 m. As can be seen in Figure 9, the experimental water flux data was substantially similar to the above reported values for CaCl2 CDS
concentrations of up to about 2 m and appeared to be above the values reported by Phuntsho et a/. for higher CaCl2 CDS concentrations.
Figure 10 presents a graph of the experimental water flux versus the concentration of the MgCl2 CDS (squares and solid line) compared to values reported by Achilli et a/.
(diamonds), Hancock et a/. (triangles) and Su etal. (stars). Water flux values reported by both Hancock et al. and Su et a/. were in the range from 6.1 to 8.3 L/m2/h for MgCl2 CDS
concentrations of 0.5 to 2 m, while Achilli et al. reported higher water flux values ranging from 8.3 to 9.7 L/m2/h using lower MgCl2 CDS concentrations (in the range of 0.35 to 0.5 m). As can be seen in Figure 10, the experimental water flux values were in the range of from about 8.6 Um2/h to about 16.9 L/m2/h for MgCl2 CDS concentrations that are in the range of from about 0.5 m to about 3.5 m. The experimental water flux values were in substantially good agreement with the values reported by Achilli et al. for MgCl2 CDS
concentrations of about 0.5 m but were significantly higher using greater MgCl2 CDS
concentrations.
Overall, the experimental water flux results were substantially in agreement with water flux values previously reported. As expected, water flux increases with increasing CDS
concentrations, which may be attributed to the increased driving force for water transfer across the semi-permeable membrane. However, the increase in water flux with increasing CDS concentrations appears to be non-linear, which may suggest an increase in the concentration polarization effects found at higher CDS concentrations.
The experimental water flux results obtained with the three different CDS
solutions were also compared to each other. Figure 11 presents a graph of the experimental water flux versus the concentration of the MgCl2 CDS (squares and solid line), the CaCl2 CDS
(triangles and dotted line) and of the NaCl2 CDS (circles and discontinued line). As can be seen in Figure 11, the experimental water flux results were substantially similar to those for the three different CDS solutions, with the CaCl2 CDS solution displaying a greater increase in water flux at higher draw solution concentrations.
(b) Reverse draw solute flux at room temperature The reverse draw solute flux was determined from the rate of change of the feed solute concentration per unit of membrane area, expressed in units of mol/m2/h. The experimental reverse draw solute flux data obtained using the NaCI, CaCl2, and MgCl2 draw solutions obtained in Example 2 (b) were compared to values previously reported (see above).
Figure 12 presents a graph of the experimental reverse solute flux versus the concentration of the NaCI draw solution (circles and discontinued line) compared to values reported by Achilli et al. (diamonds), Phillip et al. (plus) and Boo et a/.
(squares with a diagonal line). The experimental water flux results were in the range of from about 0.13 mol/m2/h to about 0.34 mol/m2/h depending on the concentration of the NaCI draw solution. As can be seen in Figure 12, the experimental water flux data is in substantially good agreement with the reported values for NaCI draw solution concentrations, meaning in the range of from about 0.5 m to about 1 m, but were significantly higher for greater concentrations.
Figure 13 presents a graph of the experimental reverse solute flux versus the concentration of the CaCl2 draw solution (triangles and dotted line) compared to values reported by Achilli et al. (diamonds) and Phuntsho et al. (squares). As can be seen in Figure 13, the experimental water flux data follows a trend substantially similar to the values reported by both Achilli etal. and Phuntsho et al. However, higher absolute reverse solute flux values were estimated. The experimental reverse solute flux values were in the range of from about 0.07 mol/m2/h to about 0.22 mol/m2/h.
Figure 14 presents a graph of the experimental reverse solute flux versus the concentration of the MgCl2 draw solution (squares and solid line) compared to the values reported by Achilli etal. (diamonds), Hancock etal. (triangles) and Su etal.
(stars). As can be seen in Figure 14, the experimental reverse solute flux values were in the range of from about 0.09 mol/m2/h to about 0.18 mol/m2/h, depending on the concentration of the MgCl2 draw solution, and were in substantially excellent agreement with the previously reported values.
Overall, greater experimental reverse draw solute flux values were observed when compared to the previously reported values, which correlates with the increased experimental water flux values, as they increase simultaneously with the concentration of the draw solution. For each draw solution, the water flux increases with increasing draw solution's concentration, which may be attributed to an increased driving force for the transport of the draw solute. Figure 15 presents a graph of the experimental reverse draw solute flux versus the concentration of the MgCl2 draw solution (squares and solid line), the CaCl2 draw solution (triangles and dotted line) and of the NaCl2 draw solution (circles and discontinued line). As can be seen in Figure 15, the NaCI and MgCl2 draw solutions respectively display the highest and lowest reverse draw solute flux, which may suggest that the membrane has a greater selectivity for divalent draw solutes.
(c) Effect of the temperature on the water flux The effect of lowering the FO operating temperature during process performance was investigated.

Figures 16 and 17 present the effect of lowering the temperature on the water flux, respectively using 1 m and 3 m aqueous NaCI (circles and discontinued line), CaCl2 (triangles and dotted line) and MgCl2 (squares and solid line) draw solutions and DI water as the feed solution.
As can be seen in Figures 16 and 17, the water flux decreased from about 31.6 to about 46.8% for systems at a temperature of 5 C, compared to systems at room temperature.
This decrease also appears exacerbated when using draw solutions of higher concentrations. This may be attributed to a decrease in the draw solute diffusivity and an increase in the draw solution viscosity at lower temperatures, which may hinder the transport of the draw solute to the active layer of the membrane, leading to a decrease of the osmotic driving force. Although the magnitude of the water flux decrease appeared to be substantially similar for the three different draw solutions, the largest decrease for both draw solution concentrations (i.e., 1 m and 3m) were observed using NaCI draw solutions.
This may likely be due to a greater decrease in diffusivity when the temperature is decreased, as opposed to MgCl2 and CaCl2 draw solutions. As expected, the water flux is greater for more concentrated draw solutions due to the increased osmotic driving force for water transfer across the membrane. Substantially similar water fluxes were observed for all draw solutions, with CaCl2 and MgCl2 draw solutions displaying slightly superior water fluxes.
(d) Effect of the temperature on the reverse draw solute flux The effect of temperature on the experimental reverse draw solute flux data was evaluated. Results using aqueous NaCI (circles and discontinued line), CaCl2 (triangles and dotted line) and MgCl2 (squares and solid line) draw solutions were compared at 2 concentrations 1 m and 3 m. The result for the 1 m and 3 m draw solutions are respectively presented in Figures 18 and 19.
As can be seen in Figures 18 and 19, the reverse draw solute flux decreases with its temperature, which may be due to an increase in mass transfer resistance and a decrease in solute permeation capacity. Similar to the water flux, NaCI draw solutions observe the largest reduction in reverse draw solute flux with temperature, approaching the values obtained with the divalent salts at a temperature of 5 C. As expected, the reverse draw solute flux increases with the draw solution concentration due to an increased driving force for the transport of the draw solute.
(e) Effect of the temperature on the specific water flux The effect of temperature on the specific water flux was evaluated. The specific water flux was determined from the ratio of the water flux to that of the reverse draw solute flux for a given draw solute, expressed in units of L of water per mol of draw solute.
The effect of temperature on the specific water flux data using aqueous NaCI (circles and discontinued line), CaCl2 (triangles and dotted line), and MgCl2 (squares and solid line) draw solutions were compared at concentrations of 1 m and 3 m and the results presented in Figures 20 and 21, respectively.
As can be seen in Figures 20 and 21, the specific water flux displays an inverse relationship with temperature which may indicate an increase in the selectivity of the membrane for water over the draw solute at lower temperatures. As such, while lower temperatures may reduce the amount of water recovered, less draw solute may be released into the feed solution during operation. The latter may reduce the overall operating expenditure. As can also be seen in Figures 20 and 21, NaCI and MgCl2 draw solutions display the lowest and highest specific water flux; respectively, with MgCl2 exhibiting the largest increase in specific water flux associated to decreasing temperature.
Notably, only a minor increase in the specific water flux was observed for CaCl2 at lower temperatures, which may suggest substantially negligible benefits to operating at temperatures below 25 C for this draw solution.
In summary, based on the water and reverse draw solute flux results the use of MgCl2 draw solutes produces a substantially higher water flux with less draw solution permeation across all temperatures and concentrations examined compared to the two other draw solutes.
Example 4: Characterization of the FC laboratory-scale batch experiments (a) CDS regeneration The CDS concentrations produced in FC starting from 0.5 m DDS as the feed, are reported in Table 3.

Table 3. Regenerated CDS concentration for NaCI, CaCl2, and MgCl2 both in single-stage and multi-stage FC operation Inorganic Draw Solution Single-Stage CDS (m) Multi-Stage CDS (m) NaCI 1.42 1.98 CaCl2 1.83 2.03 MgCl2 1.74 1.42 The multi-stage FC experimental results obtained for the simultaneous CDS
regeneration and water recovery as ice are presented in Figures 22 to 24. While the ice impurities increased in correlation with the increase in initial DDS concentration, the resulting regenerated CDS concentrations stayed substantially close to the liquidus line in the phase diagram of each solute. In Figures 22 to 24, concentrations of fresh water recovery are represented by blue circles; while concentration of CDS are represented by orange triangles. As described by Stefanescu, pure ice and CDS are produced only when planar ice grows; however, in practice, the constitutional undercooling of the liquid immediately adjacent to the advancing ice front results in dendritic ice growth, cause liquid CDS
pockets to trap between the grain boundaries of ice crystals and decrease the ice purity (see Stefanescu. Science and engineering of casting solidification. Springer, 2015).
(b) Fresh water recovery as ice The single-stage ice recovery yield for each DDS was measured and compared with the cumulative ice recovery yield from the multi-stage operation. In both operations, the yield was found to be in the range of from about 66 % to about 77 % with an average ice recovery efficiency in the range of from about 80 % to about 96 %. These results are summarized in Figures 25 to 27. The ice recovery efficiency was calculated using the following equation:
Experimental ice recovery yield (%) Ice recovery efficiency (%) = ___________________________ 100 Theoretical ice recovery yield (%) wherein the theoretical ice recovery yield (%) was obtained using the OLI-MSE
software.
(c) Freshwater quality and level of impurities in the ice product As mentioned above, the fresh water recovered as ice from the FC experiments can be recycled to industrial circuits; however, further purification treatments, such as RO, may be necessary. The concentration of impurities in the ice produced using both single-stage and multi-stage operations was measured to be less than about 0.18 m, averaging at 0.12 m 0.05 m considering all experimental runs and the results are presented in Figures 28 to 30. The ice produced from the divalent DDS (i.e., CaCl2 and MgCl2 DDS) contained an average concentration of impurities of 0.14 m 0.03 m, which is more than 2x higher than the 0.06 m 0.02 m concentration of impurities found in the ice produced from the monovalent DDS (i.e., NaCI). The higher error reported in the multi-stage operation results was expected due to the error addition from all the sequential experiments performed.
Overall, the two operational modes (i.e., single-stage and multi-stage) yield substantially comparable freshwater recovery and quality of the final product. Multi-stage FC did not show any significant advantage; however, it could provide such an advantage in a continuous FC unit operation.
Example 5: Water recovery from CaCl2 This example illustrates the effectiveness of the FC process to recover water from CaCl2, MgCl2, and NaCI diluted draw solutions and to regenerate the concentrated draw solution.
In this example, a 1.5 to 2 times dilution factor was assumed in the FO cell;
thus, 1, 1.5, and 2 mol/kg diluted draw solutions were tested.
The objective of the present example was to regenerate the concentrated draw solutions back to the initial concentrations of at least 1.5 to 2 times the diluted draw solution concentration as well as to recover water as a frozen water fraction with a low concentration of dissolved contaminants or impurities.
The water recovery from a DDS in wt. % was evaluated by cooling a mass of DDS
with different concentrations (1 mol/kg, 1.5 mol/kg and 2 mol/kg) to cause freezing of water present in the DDS at a temperature of -27 C for 2 h, 4 h, and 24 h in a single-stage process. The DDS, the recovered frozen water fraction, the regenerated CDS, and the remaining filtrates were analyzed by ICP-OES.
Figure 31 shows a graph of the water recovery from a CaCl2 DDS in wt. % as a function of the freeze time (in hour) for different concentrations of CaCl2 DDS (1 mol/kg, 1.5 mol/kg and 2 mol/kg). Theoretical data corresponding to equilibrium at -27 C is also shown for comparative purposes.
Figure 32 shows a graph of the concentrations of dissolved contaminants in the water recovered as ice as a function of the DDS concentration for different concentrations of CaCl2 DDS (1 mol/kg, 1.5 mol/kg and 2 mol/kg). From the results presented in Figure 32, the concentration of dissolved contaminants in the water recovered is such that the water from the FC process may directly be reused in some industrial process.
However, as described above, it would require further treatment, such as RO, if the intent for the recovered water was to be used for human consumption.
Figure 33 shows a graph of the concentration of the regenerated CDS as a function of the freeze time in hours for different concentrations of CaCl2 DDS (1 mol/kg, 1.5 mol/kg and 2 mol/kg). Theoretical data corresponding to equilibrium at -27 C is also shown for comparative purposes. From the results presented in Figure 33, the concentration of the regenerated CaCl2 CDS after a freezing time of 24 hours is about 2 times higher than the initial CaCl2 DDS (1 mol/kg).
Referring to Figures 31 and 33, for example, the CaCl2 CDS may be regenerated, after removing about 40-50 wt.% of the water from the 1 mol/kg 0a012 DDS.
Although, the results presented herein are for 0a012 DDS, similar results were obtained with MgCl2 and NaCI DDS.
Example 6: Thermodynamic energy In conventional processes, two different steps (i.e., stripping and absorption) are required to separate water from the DDS and regenerate the CDS and this is where the main costs of the process may arise. In the proposed processes described herein, these steps are reduced to one step (i.e., freezing), which means that the capital cost expenditure for equipment and infrastructure is significantly reduced. The thermodynamic energy advantage in freezing, compared to stripping and adsorption, is estimated to be more than 50 % using OLI-MSE simulation. For example, the total enthalpy change per kg was estimated for two solutions of similar osmotic pressure (130 atm) (i.e., a 4.5 mol/kg TMAH:HCO3 DDS and a 1.5 mol/kg CaCl2 DOS). For example, the absolute enthalpy change was estimated to be about 152,000 cal kg-1 and about 62,000 cal kg-1 respectively for the TMAH:HCO3 DDS and the CaCl2 DDS. For the TMAH:HCO3 DDS, the separation was performed using the existing 2 steps process by heating the DDS from 25 C
to 75 C in order to separate the draw solutes from the water and for the CaCl2 DDS to use the process as described herein by freezing from 25 C to - 25 C to separate the draw solutes from the frozen water fraction.
Numerous modifications could be made to any of the embodiments described above without distancing from the scope of the present invention. Any references, patents or scientific literature documents referred to in the present application are incorporated herein by reference in their entirety for all purposes.

Claims (52)

37

1. A method for purifying a contaminated aqueous solution comprising dissolved contaminants, comprising:
providing a feed stream comprising the contaminated aqueous solution to contact a first side of a semi-permeable forward osmosis (FO) membrane;
providing a concentrated draw solution comprising dissolved draw solutes to contact a second side of the semi-permeable FO membrane, thereby causing water to diffuse from the feed stream through the semi-permeable FO membrane and into the concentrated draw solution to produce a diluted draw solution and a water-depleted contaminated stream;
cooling at least a portion of the diluted draw solution to cause freezing of water present in the diluted draw solution to produce a frozen water fraction;

and recovering the frozen water fraction that is depleted in draw solutes and a regenerated solution that is enriched in the draw solutes and is reused as at least part of the concentrated draw solution.

2. The method of claim 1, wherein the contaminated aqueous solution comprises industrial effluents.

3. The method of either claim 1 or 2, wherein the dissolved contaminant comprises a salt.

4. The method of claim 3, wherein the salt comprises sodium chloride.

5. The method of any one of claims 1 to 4, wherein the contaminated aqueous solution is brackish water, saline water or briny water.

6. The method of any one of claims 1 to 5, wherein the contaminated aqueous solution has a concentration of dissolved contaminants between 1 000 and 250 000 ppm, limits included.

7. The method of claim 6, wherein the contaminated aqueous solution has a concentration of dissolved contaminants between 60 000 and 240 000 ppm, limits included.

8. The method of any one of claims 1 to 7, wherein the draw solute comprises or is a soluble inorganic salt or a mixture of soluble inorganic salts.

9. The method of claim 8, wherein the soluble inorganic salt is a soluble chloride salt.

10. The method of claim 9, wherein the soluble chloride salt is selected from the group consisting of sodium chloride, potassium chloride, lithium chloride magnesium chloride, calcium chloride and a mixture of at least two thereof.

11. The method of claim 8, wherein soluble inorganic salt is a soluble sulfate salt.

12. The method of claim 11, wherein the soluble sulfate salt is selected from the group consisting of magnesium sulfate, lithium sulfate, potassium sulfate, ammonium sulfate, sodium sulfate and a mixture of at least two thereof.

13. The method of any one of claims 1 to 12, wherein the concentrated draw solution has a draw solute concentration of at least 0.5 mol/kg.

14. The method of any one of claims 1 to 13, wherein the concentrated draw solution has a draw solute concentration of up to the saturation concentration.

15. The method of any one of claims 1 to 13, wherein the concentrated draw solution has a draw solute concentration higher than the saturation concentration.

16. The method of claim 13, wherein the concentrated draw solution has a draw solute concentration between 0.5 mol/kg and 7 mol/kg, limits included.

17. The method of claim 16, wherein the concentrated draw solution has a draw solute concentration between 0.5 mol/kg and 4 mol/kg, limits included.

18. The method of claim 17, wherein the concentrated draw solution has a draw solute concentration between 1.5 mol/kg and 4 mol/kg, limits included.

19. The method of any one of claims 1 to 18, wherein the regenerated solution is separated from the frozen water fraction by gravity separation.

20. The method of any one of claims 1 to 19, wherein all of the regenerated solution is reused as at least part of the concentrated draw solution.

21. The method of any one of claims 1 to 20, wherein the at least a portion of the diluted draw solution is cooled down at a temperature between the freezing point and the eutectic temperature of the diluted draw solution thereof.

22. The method of any one of claims 1 to 21, wherein the cooling is performed in a single-stage process.

23. The method of any one of claims 1 to 21, wherein the cooling is performed in a multi-stage process.

24. The method of any one of claims 1 to 23, wherein at least 90 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction.

25. The method of any one of claims 1 to 24 wherein up to 98 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction.

26. The method of any one of claims 1 to 23, wherein less than 90 wt.% of the water in the contaminated aqueous solution is recovered in the frozen water fraction.

27. The method of any one of claims 1 to 26, wherein the frozen water fraction comprises below 1 000 ppm of draw solutes.

28. The method of any one of claims 1 to 27, further comprising melting the frozen water fraction to obtain liquid phase purified water.

29. The method of claim 28, wherein the melting is performed by using low-grade heat.

30. The method of claim 29, wherein the low-grade heat is waste heat derived from a plant that produces the contaminated aqueous solution.

31. The method of any one of claims 28 to 30, further comprising reusing the liquid phase purified water in an industrial process.

32. The method of any one of claims 28 to 30, further comprising subjecting the liquid phase purified water to additional purification to produce further purified water.

33. The method of claim 32, wherein the additional purification comprises reverse osmosis.

34. The method of any one of claims 1 to 33, further comprising controlling the frozen water fraction recovery.

35. The method of claim 34, wherein controlling the frozen water fraction recovery comprises controlling that the amount water diffused from the feed stream is equivalent to the amount of water recovered in the frozen water fraction.

36. A purified water produced by the method as defined in any one of claims 1 to 35.

37. A forward osmosis - freeze concentration (FO-FC) hybrid purification system, comprising:
a forward osmosis (FO) unit comprising a first chamber and a second chamber separated by a semi-permeable membrane, the first chamber having an inlet being configured to receive a feed stream comprising a contaminated aqueous solution that contacts a first side of the semi-permeable membrane, and the second chamber having an inlet being configured to receive a concentrated draw solution that contacts a second side of the semi-permeable membrane, thus causing water to diffuse from the feed stream, through the semi-permeable membrane and into the concentrated draw solution, thereby producing a diluted draw solution and a water-depleted contaminated stream, the first chamber comprising an outlet configured to release the water-depleted contaminated stream and the second chamber comprising an outlet configured to release the diluted draw solution; and a freeze concentration (FC) unit having an inlet in fluid communication with the outlet of the second chamber of the forward osmosis (FO) unit, a freezing chamber for receiving and cooling the diluted draw solution to cause freezing of water present in the diluted drawn solution to produce a frozen water fraction and a regenerated solution, and a liquid outlet for releasing the regenerated solution and being in fluid communication with the inlet of the second chamber for supplying the regenerated solution as at least part of the concentrated draw solution.

38. The system of claim 37, wherein the semi-permeable membrane is a polymeric membrane.

39. The system of claim 38, wherein the polymeric membrane is a cellulosic membrane or a polyamide-based membrane.

40. The system of any one of claims 37 to 39, further comprising a first optional reservoir configured to hold the contaminated aqueous solution and provide the feed stream to the forward osmosis unit.

41. The system of any one of claims 37 to 40, further comprising a heating unit to receive and melt the frozen water fraction and produce a liquid phase purified water.

42. The system of claim 41, further comprising a second optional reservoir unit in fluid communication with the heating unit configured to hold the liquid phase purified water.

43. The system of any one of claims 41 to 42, further comprising a reverse osmosis unit configured for further purification of the liquid phase purified water.

44. The system of any one of claims 37 to 43, further comprising a controller unit in fluid communication with at least one of the forward osmosis (FO) unit, the freeze concentration (FC) unit, the heating unit, the first optional reservoir and the second optional reservoir unit.

45. The system of claim 44, wherein the controller unit comprises a flow controller configured to control the flow rate of the feed stream.

46. The system of claim 44 or 45, wherein the controller unit comprises a multi-scale weight controller configured to control that the amount water diffused from the feed stream is equivalent to the amount of water recovered in the frozen water fraction.

47. The system of any one of claims 44 to 46, wherein the controller unit comprises a concentration controller configured to control the concentration of the concentrated draw solution.

48. The system of any one of claims 44 to 47, wherein the controller unit comprises a temperature controller configured to control the cooling temperature.

49. The system of any one of claims 37 to 48 for use in the purification treatment of water derived from an industrial effluent.

50. A method for purifying a contaminated aqueous solution comprising dissolved contaminants, comprising:
subjecting the contaminated aqueous solution and a concentrated draw solution to forward osmosis (FO) to produce a diluted draw solution and a water-depleted contaminated stream; and subjecting the diluted draw solution to freeze concentration (FC) to produce a recovered frozen fraction and a regenerated solution, which can be reused as at least part of the concentrated draw solution.

51. A method for purifying a contaminated liquid comprising dissolved contaminants, comprising:
subjecting the contaminated liquid and a concentrated draw stream to forward osmosis (FO) to produce a diluted draw solution and a liquid depleted contaminated stream; and subjecting the diluted draw solution to freeze concentration (FC) to produce a recovered frozen fraction of the liquid and a regenerated stream reused as at least part of the concentrated draw stream.

52. Use of a freeze concentration (FC) unit for converting a diluted draw solution produced by forward osmosis (FO) into a recovered frozen fraction and a regenerated stream that is reusable as at least part of a concentrated draw stream in FO.