WO2018213929A1 - Switchable pressure retarded forward osmosis system and process thereof - Google Patents

Abstract

The present application provides provided a pressure retarded forward osmosis system, comprising : an aqueous draw solution having a draw solute concentration of ≥30 wt%, the draw solute comprising ionized trimethylamine; and at least one pressure retarded forward osmosis element, wherein the system generates energy. Also provided is a process for generating energy using a pressure retarded forward osmosis system based on an ionized trimethylamine containing draw solution.

Description

SWITCHABLE PRESSURE RETARDED FORWARD OSMOSIS SYSTEM AND

PROCESS THEREOF

FIELD OF THE INVENTION

[0001] The present application pertains to the field of water treatment and energy generation systems. More particularly, the present application relates to switchable pressure retarded forward osmosis systems and processes.

INTRODUCTION

[0002] Pressure retarded osmosis (PRO) is an osmotic process that has potential applications in power production, on the basis that energy can be derived from mixing solutions of varying concentrations (e.g., free energy of mixing). PRO can be considered an intermediary between osmosis, movement of water across a semi-permeable membrane due to a concentration gradient; and osmotic equilibrium, zero net movement of water across a semi-permeable membrane.

[0003] In PRO, as in forward osmosis, there is solvent flow (e.g., flux) across a membrane from a solution of low ionic concentration to high ionic concentration. In contrast to forward osmosis, however, hydraulic pressure is applied to the high concentration solution, such that the flux is retarded as it flows against the pressure gradient; if the hydraulic pressure is sufficiently high, the flux stops entirely (i.e., hydraulic pressure = osmotic pressure). It is this flow against a pressure gradient that allows PRO to harness the free energy of mixing, and potentially allow that energy to be converted into power [Loeb, S., Journal of Membrane Science, 1 , 49-63, 1976].

[0004] One way by which PRO can be applied to power production is via a power plant that uses diverted river water as a less concentrated osmotic feed solution, with diverted sea water as a more concentrated osmotic draw solution [F. Heifer et al., Journal of Membrane Science 453, 337-358, 2014]. In such power plants, river water is directed to one side of a membrane module as a feed solution, while pressurized seawater is directed to the other side as a draw solution. The two solutions are separated by a semi-permeable membrane that allows flow of water from the feed solution into the draw solution. This flow results in a high-pressure, diluted draw solution that is then directed to a turbine to generate power. Use of open water streams, however, can cause complications for such power plants; for example: membrane fouling; low differential osmotic pressures; and, placement at interfaces between natural streams.

[0005] An alternative is to apply PRO to power production via osmotic heat engines (OHE), which are closed-loop PRO processes, one example of which was described by McGinnis et al. in 2007 [R.L. McGinnis et al., Journal of Membrane Science, 305, 13-19, 2007].

McGinnis et al. described an OHE having a concentrated, pressurized ammonia-carbon dioxide draw solution separated from a deionized water feed solution by a semi-permeable membrane. The concentrated ammonia-carbon dioxide draw solution generated flux against a hydraulic pressure gradient; the resultant diluted draw solution was then diverted to a turbine to produce electrical power.

[0006] McGinnis et al. suggested that, after power generation, the diluted draw solution could be separated into its constituents (i.e., water, ammonia, and carbon dioxide) in the presence of heat, and that those constituents could then be used to reconstitute the draw and feed solutions for continued use within the system. However, ammonia-carbon dioxide draw solutions can be a more energy intensive option when compared to other available draw solutions, such as the amine-carbon dioxide draw solutions described by Jessop et al. in PCT application, PCT/CA201 1/050075; for example: deprotonation of an NH₄ ⁺ salt requires an energy input of 52.3 kJ/mol, versus only 36.9 kJ/mol for comparable NR₃H⁺ systems [Mucci, A.; Domain, R.; Benoit, R. L. Can. J. Chem. 1980, 58, 953-958].

[0007] The above information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide switchable pressure retarded forward osmosis system and process thereof. In accordance with an aspect of the present application, there is provided a pressure retarded forward osmosis system, comprising: an aqueous draw solution having a draw solute concentration of >30 wt%, the draw solute comprising ionized trimethylamine; and at least one pressure retarded forward osmosis element, comprising a semi-permeable membrane that is selectively permeable to water, having a first side and a second side; at least one port to bring a feed solution in fluid communication with the first side of the membrane (i.e. feed port); at least one port to bring the draw solution in fluid communication with the second side of the membrane (i.e. draw port); at least one pressure exchanger associated with the second side of the membrane (and in fluid communication with the draw solution) for pressurizing the draw solution in fluid communication with the second side of the membrane; and at least one energy generator in fluid communication with the pressure retarded forward osmosis element, downstream of the second side of the membrane, to permit flow of water from the feed solution through the semi-permeable membrane into the pressurized draw solution, to form a concentrated feed solution, a diluted draw solution, and to generate energy.

In accordance with another aspect, there is provided a pressure retarded forward s system, comprising: an aqueous draw solution having a draw solute concentration of > 10 wt%, the draw solute comprising ionized trimethylamine; and at least one pressure retarded forward osmosis element, comprising a semi-permeable membrane that is selectively permeable to water, having a first side and a second side; at least one port to bring a feed solution in fluid communication with the first side of the membrane; at least one port to bring the draw solution in fluid communication with the second side of the membrane; at least one pressure exchanger associated with the second side of the membrane for pressurizing the draw solution in fluid communication with the second side of the membrane; and at least one energy generator in fluid communication with the pressure retarded forward osmosis element, downstream of the second side of the membrane, to permit flow of water from the feed solution through the semi-permeable membrane into the pressurized draw solution, to form a concentrated feed solution, a diluted draw solution, and to generate energy.

[0010] In accordance with an embodiment of the present application, there is provided a pressure retarded forward osmosis system further comprising a system for regenerating the draw solution, comprising means for collecting the dilute draw solution; means for separating the draw solute from the dilute draw solution; means for reconstituting the draw solution; or any combination thereof.

[001 1] In accordance with another embodiment, there is provided a system wherein means for collecting the dilute draw solution comprise, for example, at least one first receptacle (e.g., storage tank) in fluid communication with the PRO system via pipes, pipelines, etc. which fluidly communicate the dilute draw solution via pumps or gravity-assisted set-ups to the at least one first receptacle.

[0012] In accordance with another embodiment, there is provided a system wherein means for separating the draw solute from the dilute draw solution comprises: a reverse osmosis system; centrifugation; filtration; volatilization; heating; a flushing gas; a vacuum or partial vacuum; agitation; or any combination thereof. In another embodiment, the means for separating the draw solute from the dilute draw solution comprises, for example, at least one second receptacle (e.g., storage tank) in fluid communication with the at least one first receptacle for collecting the dilute draw solution and/or the PRO system (for example: pipes, pipelines, etc. fluidly communicate the dilute draw solution via pumps or gravity-assisted setups to the at least one second receptacle, etc.), the at least one receptacle being in fluid communication with a column for separating the draw solution from the dilute draw solution. Non-limiting examples of columns include distillation columns, stripping columns, columns suitable for use under a vacuum or partial vacuum, columns suitable for use with a flushing gas, etc., or any combination thereof.

[0013] In accordance with another embodiment, there is provided a system wherein means for reconstituting the draw solution comprises, for example, at least one third receptacle

(e.g., storage tank) in communication with the at least one first receptacle for collecting the dilute draw solution, the PRO system, and/or the at least one second receptacle for separating the draw solute from the dilute draw solution (for example: pipes, pipelines, etc. communicate the draw solute via pumps to a receptacle, etc.), the at least one third receptacle being in communication with any one or more of: a bubble column, a packing bubble column, an absorbing column, a liquid-gas reactor/contactor (wherein, for example, said reactors comprise reactor set-ups or in-line set-ups), a falling-film column; a packing column, a spray tower, a gas-liquid agitated vessel, a stage-wise gas-liquid contactor (e.g., plate columns, rotating disc contactor, venturi tube, etc.)

[0014] In accordance with an embodiment of the application, there is provided a pressure retarded forward osmosis system further comprising a system for regenerating the draw solution, comprising a receptacle for collecting the dilute draw solution; an apparatus (such as, but not limited to, a separator) for separating the draw solute from the dilute draw solution; an apparatus (such as, but not limited to, a reactor) for reconstituting the draw solution; or any combination thereof.

[0015] In accordance with another embodiment, there is provided a system wherein an apparatus for separating the draw solute from the dilute draw solution comprises: a reverse osmosis element; a centrifuge; a filter (e.g., separation column, etc.); volatilizing system; heater; a source of a flushing gas; a vacuum or a source of a partial vacuum; an agitator; or any combination thereof.

[0016] In accordance with another embodiment, there is provided a system wherein the system is: closed; continuously cycled; or a combination thereof.

[0017] In accordance with another embodiment, there is provided a system wherein the pressure exchanger pressurizes the draw solution to a hydraulic pressure approximately 50% of the draw solution's osmotic pressure.

[0018] In accordance with another embodiment, there is provided a system wherein the feed solution: (i) has a Total Dissolved Solids (TDS) >3 - 3.5 wt%, or a TDS > 5 wt; or (ii) is an industrial wastewater, river water, or seawater; or (iii) comprises discharge from a reverse osmosis (RO) plant.

[0019] In accordance with another embodiment, there is provided a system wherein the draw solution has a draw solute concentration between > 30wt% and saturation; or, alternatively, between 30 - 70wt%; or, alternatively, between 30 - 60wt%; or, alternatively, between 30 - 50wt%; or, alternatively, between 30 - 40wt%. [0020] In another embodiment, the draw solution has a draw solute concentration between > 10wt% and saturation; or, alternatively, between 10 - 70wt%; or, alternatively, between 10 - 60wt%; or, alternatively, between 10 - 40wt%; or, alternatively, between 30 - 50wt%; or, alternatively, between 30 - 40wt%. In yet another embodiment, the draw solution has a draw solute concentration between 10 - 15wt%; or, 30 - 40wt%; or, alternatively, between 60 - 70wt%.

[0021] In accordance with an embodiment of the application, there is provided a pressure retarded forward osmosis system wherein the system is an apparatus.

[0022] In accordance with another aspect of the application, there is provided a process for generating energy, comprising: pressure retarded forward osmosis using a pressurized aqueous draw solution having a draw solute concentration of >30 wt%, the draw solute comprising ionized trimethylamine; the steps of pressure retarded forward osmosis comprising: introducing a feed solution to a first side of a semi-permeable membrane; introducing the pressurized draw solution to a second side of the semipermeable membrane; permitting flow of water from the feed solution across the semi-permeable membrane into the pressurized draw solution, to form a concentrated feed solution and a diluted draw solution; and inducing flow of the diluted draw solution through an energy generator for producing energy.

[0023] In accordance with another aspect, there is provided a process for generating energy, comprising: pressure retarded forward osmosis using a pressurized aqueous draw solution having a draw solute concentration of > 10 wt%, the draw solute comprising ionized trimethylamine; the steps of pressure retarded forward osmosis comprising: introducing a feed solution to a first side of a semi-permeable membrane; introducing the pressurized draw solution to a second side of the semipermeable membrane; permitting flow of water from the feed solution across the semi-permeable membrane into the pressurized draw solution, to form a concentrated feed solution and a diluted draw solution; and inducing flow of the diluted draw solution through an energy generator for producing energy.

[0024] In accordance with an embodiment of the application, there is provided a process further comprising: collecting the dilute draw solution after energy generation; separating the draw solute from the dilute draw solution; reconstituting the draw solution; or any combination thereof.

[0025] In accordance with another embodiment, there is provided a process wherein the pressurized draw solution is pressurized to a hydraulic pressure approximately 50% of the draw solution's osmotic pressure.

[0026] In accordance with another embodiment, there is provided a process wherein the process is performed as a: closed cycle; continuous cycle; or a combination thereof.

[0027] In accordance with another embodiment, there is provided a process wherein separating the draw solute from the dilute draw solution comprises: reverse osmosis;

centrifugation; filtration; volatilization; heating; a flushing gas; a vacuum or partial vacuum; agitation; or any combination thereof.

[0028] In accordance with another embodiment, there is provided a process wherein reconstituting the concentrated draw solution comprises: introducing an ionizing trigger, such as carbon dioxide, to an aqueous solution of trimethylamine; introducing trimethylamine to an aqueous solution of an ionizing trigger, such as carbon dioxide; simultaneously introducing trimethylamine and an ionizing trigger, such as carbon dioxide, to an aqueous solution; or any combination thereof. [0029] In accordance with another embodiment, there is provided a process wherein the feed solution: (i) has a TDS >3 - 3.5 wt%, or a TDS > 5 wt; or (ii) is an industrial wastewater, river water, or seawater; or (iii) comprises discharge from a reverse osmosis (RO) plant,

[0030] In accordance with another embodiment, there is provided a process wherein the draw solution has a draw solute concentration between > 30wt% to saturation; or, alternatively, between 30 - 70wt%; or, alternatively, between 30 - 60wt%; or, alternatively, between 30 - 50wt%; or, alternatively, between 30 - 40wt%.

[0031] In another embodiment, the draw solution has a draw solute concentration between > 10wt% and saturation; or, alternatively, between 10 - 70wt%; or, alternatively, between 10 - 60wt%; or, alternatively, between 10 - 40wt%; or, alternatively, between 30 - 50wt%; or, alternatively, between 30 - 40wt%. In yet another embodiment, the draw solution has a draw solute concentration between 10 - 15wt%; or, 30 - 40wt%; or, alternatively, between 60 - 70wt%.

[0032] In accordance with another embodiment, there is provided a process wherein the draw solution has a draw solute concentration between 30 - 40wt%; or, alternatively, between 60 - 70wt%. In yet another embodiment, the draw solution has a draw solute concentration between 5 - 10wt%; or, 30 - 40wt%; or, alternatively, between 60 - 70wt%.

BRIEF DESCRIPTION OF THE FIGURES AND TABLES

[0033] For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings and tables, where:

[0034] Figure 1A is a diagram of a demonstrative, non-limiting example of a forward osmosis (FO) flow cell, as described and used herein;

[0035] Figure 1 B is a diagram of a demonstrative, non-limiting example of a pressure- retarded forward osmosis (FO) flow cell, as described and used herein;

[0036] Figure 2 depicts a diagram of a demonstrative forward osmosis (FO) cell, as described and used herein;

[0037] Figure 3 depicts part of a custom-designed osmometer as described and used herein, comprising: (a) solution shell; (b) solvent shell; (c) pressure transducer; (d) compression screws; (e) static pressure cap; (f) dynamic pressure cap; (g) tin sealing washer; (h) solvent chamber cap; (i) tubing; (j) porous membrane support disk; (k) solvent chamber O-ring; (I) solution chamber O-rings; (m) supporting legs; (n) leg screws.

[0038] Figure 4 depicts pressure transducer (c) attached to a solution shell (a) used in conjunction with the custom-designed osmometer as described and used herein;

[0039] Figure 5A depicts a solution shell (a, left) and solvent shell (b, right) of the custom- designed osmometer as described and used herein;

[0040] Figure 5B depicts pressure transducer (c) and solution shell (a) and indicates aspects of the transducer's internal cavity;

[0041] Figure 5C depicts order of tightening compression screws to attach solvent shell (b) to pressure transducer (c) and solution shell (a);

[0042] Figure 5D depicts the custom-designed osmometer as described and used herein, assembled on support legs (m) using screws (n);

[0043] Figure 6A depicts top level (Level B) of an outer shell of the custom-designed osmometer as described and used herein, indicating the level to which solution was to be added to the osmometer;

[0044] Figure 6B depicts a static cap and its constituents, which were used with the custom- designed osmometer as described herein;

[0045] Figure 7A depicts a dynamic pressure cap and its constituents, used in conjunction with the custom-designed osmometer as described herein;

[0046] Figure 7B depicts a method for using the dynamic pressure cap in conjunction with the custom-designed osmometer as described herein;

[0047] Figure 8A depicts a graph delineating osmometer-measured osmotic pressures of 6.9 wt% to 69 wt% ionized trimethylamine (TMA) draw solutions;

[0048] Figure 8B depicts a graph delineating osmometer-measured osmotic pressures of a 34.5 wt% ionized trimethylamine (TMA) draw solution, completed in triplicate;

[0049] Figure 8C depicts a graph delineating osmotic pressures vs. concentration of ionized TMA draw solutions; [0050] Figure 9 depicts an embodiment of the herein described FO-PRO system;

[0051] Figure 10 depicts an embodiment of the herein described PR-FO system;

[0052] Figure 1 1 depicts an example of a river water / seawater based PRO power plant;

[0053] Figure 12 depicts an idealized arrangement for a PRO power plant with continuous, steady state flow;

[0054] Figures 13A - 20 depict an investigation into the use of ionized TMA as a draw solute for PRO Applications;

[0055] Figure 21A is a calibration curve for determining concentration of ionized TMA ([TMAH][HC03]).

[0056] Figure 21 B is a calibration curve for TMA over a calibration range of 0.17 mM to 170 mM, using methanol as an internal standard.

[0057] Table 1 delineates osmometer-measured osmotic pressures of ionized TMA draw solutions;

[0058] Table 2 delineates measured osmotic pressure of an ionized TMA-based draw solution;

[0059] Table 3 delineates concentration of ionized TMA (1 M) in various feed solutions (Membrane 2);

[0060] Table 4 delineates concentration of ionized TMA (3M) in various feed solutions (Membrane 2);

[0061] Table 5 delineates concentration of ionized TMA (5M) in various feed solutions (Membrane 2);

[0062] Table 6 delineates concentration of ionized TMA (1 M) in various feed solutions (Membrane 1);

[0063] Table 7 delineates concentration of ionized TMA (3M) in various feed solutions (Membrane 1); and [0064] Table 8 delineates concentration of ionized TMA (5M) in various feed solutions (Membrane 1).

DETAILED DESCRIPTION

[0065] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0066] As used in the specification and claims, the singular forms "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

[0067] The term "comprising" as used herein will be understood to mean that the list following is non-exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), component(s) and/or ingredient(s) as appropriate.

[0068] The term "switched" means that the physical properties have been modified - in particular ionic strength and osmotic pressure. "Switchable" means able to be converted from a first state with a first set of physical properties (in the present application, this refers to a first state of a given ionic strength) to a second state with a second set of physical properties (i.e., a state of higher ionic strength). A "trigger" is a change of conditions (e.g., introduction or removal of a gas, change in temperature) that causes the change in the physical properties, e.g., ionic strength. The term "reversible" means that the reaction can proceed in either direction (backward or forward).

[0069] As used herein, "carbonated water" or "aqueous C0₂" means a solution of water in which CO2 has been dissolved. "CO2 saturated water" means a solution of water in which C0₂ is dissolved to the maximum extent at that temperature.

[0070] As used herein, a "flushing gas" or "a gas that has substantially no carbon dioxide" means that the gas has insufficient C0₂ content to interfere with the removal of C0₂ from the solution, and is sufficiently inert such that it does not interfere with reversibly switching between a first state and a second state. For some applications, air may be a gas that has substantially no C0₂. Untreated air may be successfully employed, i.e., air in which the C0₂ content is unaltered from air that occurs naturally; this would provide a cost saving. For instance, air may be a gas that has substantially no CO2 because in some circumstances, the approximately 0.04% by volume of C0₂ present in air is insufficient to maintain an additive in a switched form, such that air can be a trigger used to remove C0₂ from a solution and cause switching. Similarly, "a gas that has substantially no C0₂, CS₂ or COS" has insufficient C0₂, CS2 or COS content to interfere with the removal of CO2, CS2 or COS from the solution.

[0071 ] The term "ionized trimethylamine", as used herein, refers to protonated or charged trimethylamine, wherein the trimethylamine has been protonated or rendered charged by exposure to an acid gas, such as but not limited to C0₂, COS, and/or CS₂, in the presence of water/aqueous solution.

[0072] The ionized form of trimethylamine may also be referred to as an "ammonium salt". When ionized trimethylamine is formed by exposure to the acid gas C0₂ in the presence of water or an aqueous solution, the ionic form of trimethylamine may comprise both carbonates and bicarbonates as counter ions. Consequently, although a draw solute is referred to herein as ionized trimethylamine, it should be understood that, when the ionizing trigger is C0₂, the draw solution may contain a mixture of carbonate and bicarbonate salts of the ionized trimethylamine. Although carbonic acid (C0₂ in water/aqueous solution) is mentioned and is used in the examples provided in this application, the nitrogen of trimethylamine could also be protonated by CS₂ in water/aqueous solution, and COS in water/aqueous solution. As such, this term is intended to denote the nitrogen's basicity and it is not meant to imply which of the three exemplary trigger gases (CO2, CS2 or COS) is used.

[0073] As would be readily appreciated by a worker skilled in the art, since few protonation / ionization reactions proceed to completion, when trimethylamine is referred to herein as being "protonated" or "ionized" it means that all, or only the majority, of the molecules of the compound are protonated / ionized. For example, more than about 90%, or about 95%, or more than about 95% of the molecules are protonated/ionized.

[0074] "Ionic" means containing or involving or occurring in the form of positively or negatively charged ions, i.e., charged moieties. "Nonionic" means comprising substantially of molecules with no formal charges. Nonionic does not imply that there are no ions of any kind, but rather that a substantial amount of basic nitrogens are in an unprotonated state. "Salts" as used herein are compounds with no net charge formed from positively and negatively charged ions.

[0075] "Ionic strength" of a solution is a measure of the concentration of ions in the solution. Ionic compounds (i.e., salts), which dissolve in water will dissociate into ions, increasing the ionic strength of a solution. The total concentration of dissolved ions in a solution will affect important properties of the solution such as its osmotic pressure. The ionic strength, I, of a solution is a function of the concentration of all ions present in the solution and is typically given by the equation (A),

² <=> (A) in which c, is the molar concentration of ion i in mol/dm³, z, is the charge number of that ion and the sum is taken over all ions dissolved in the solution. In non-ideal solutions, volumes are not additive such that it is preferable to calculate the ionic strength in terms of molality (mol/kg H₂0), such that ionic strength can be given by equation (B),

² « (B) in which m, is the molality of ion i in mol/kg H2O, and z, is as defined for equation (A).

[0076] As used herein, the term "osmotic pressure" refers to the pressure difference needed to stop a flow of fluid across a semipermeable membrane. The osmotic pressure of a solution is proportional to the molar concentration of the solute particles in solution; for example:

F\=nRTV=MMRT

[0077] where: Π is osmotic pressure; R is the ideal gas constant (0.0821 L atm / mol K); 7 is temperature in Kelvin; n is number of moles of solute present; V is volume of solution (nV is then molar concentration of the solute); and MM is the molar mass of the solute.

[0078] As used herein, 'means for' language is meant to denote practices known and applied in the art; or, practices that are readily modified through routine experimentation and optimization in view of the practices known and applied in the art, such that said practices suit the systems and/or process described herein. Said practices include, but are not limited to, academic, research and development, engineering, or industrial practices. [0079] Open-Loop PRO Power Plants

[0080] As described by Heifer, et al., one of the most studied applications of PRO technology for power generation involves pairing river water (feed solution) with seawater (draw solution) in a power-generating plant (Figure 1 1) [F. Heifer et al., Journal of Membrane Science 453 (2014) 337-358]. As depicted in Figure 1 1 , incoming river water and seawater are pumped into a forward osmosis membrane module, the solutions being separated by a semi-permeable membrane such that water from the river feed solution moves across the membrane, and into the seawater draw solution. Consequently, the volume of solution on the draw solution's side of the membrane increases, resulting in a high-pressure, brackish water solution that is split along two separate paths: one part of the increased water flow is diverted to a turbine for generating power; the other part is sent to a pressure exchanger designed to transfer pressure energy from the pressurized brackish water to any incoming sea water.

[0081 ] In 2009, a power-generating PRO plant prototype that operated using river and seawater was built by a Norwegian state-owned power company, Statkraft [Reuters News Agency, Norway Opens World's First Osmotic Power Plant, CNET. Available from:

<http://www.reuters.eom/article/2009/1 1/24/us-norway-osmotic-idUSTRE5A- N20Q20091 124> , 2009]. Although this prototype plant was projected to become a large- scale osmotic power production facility by 2015 [M. Gregory, Norway's Statkraft Opens First Osmotic Power Plant, BBC News. Available from: <http://news.bbc.co.Uk/2/hi/8377186.stm> , 24 November, 2009], Statkraft decided to stop pursuing electricity production from osmotic power due to a lack of competitiveness. The system was found not to be successful in efficient energy production.

[0082] Extractable Energy from PRO Systems

[0083] As described by Heifer, et al., [F. Heifer et al., Journal of Membrane Science 453 (2014) 337-358], Figure 12 depicts an idealized arrangement for a PRO power plant with continuous, steady state flow.

[0084] A draw solution of volume Vwith osmotic pressure n_D, (e.g. seawater), is pumped into a PRO power plant at a hydraulic pressure PD, wherein Input Power is the product of V and P_D. Concurrently, a feed solution (e.g. river water) enters a Permeator on one side of a membrane module, at osmotic and hydraulic pressures lower than the draw solution. Water flows from the feed solution, across a semi-permeable membrane, into the draw solution, generating a diluted draw solution at a rate of AV, acquiring a pressure of P_D (wherein

&V=JA_M, A_M is membrane area and J is water flux; wherein J is from =Α (Δπ-ΔΡ), where Δπ = UD-UF, and

with D and F referring to draw and feed solutions respectively). The diluted draw solution, a solution of brackish water of lower osmotic pressure (volume V+AV) , enters a hydroturbine in which hydraulic pressure P_D is reduced to zero, as it delivers power of magnitude P_D(V+ V).

[0085] As explained by Heifer et al., it therefore follows that maximum net power (PW_NET^MAX) that could be produced under such an idealized PRO system is a difference between quantity delivered by the hydroturbine, P_D(V+AV), and power input into the system, P_DV, such that:

PWNET^MAX = PD(V+AV)-P_DV = PDAV, where P_DA\ is the net power with 100% mechanical efficiency for all components, no energy losses, and a feed solution that enters the PRO system by gravity.

[0086] An ideal operating pressure for maximum power output is half the osmotic pressure differential between the feed and draw solution: for example, a river water vs. sea water PRO scheme, where an osmotic pressure differential is about 26 bar, an ideal operating pressure would be 13 bar, with a maximum net power output of 1 .3 MW/m³ s^~1 of permeate.

[0087] As further described by Heifer et al., for PRO systems having mechanical efficiencies less than 100%, as would be expected, net power would be:

PWNET^REAL = PoAV_n, where η is system's mechanical efficiency, dependent upon efficiencies of rotating components (e.g., pumps, motors, turbines and generators), friction losses in flow passages of the permeator, and configuration of plant equipment [S. Loeb, et al., J. Membr. Sci., 51 (1990), 323-335].

[0088] As such, it follows that the real net power of a PRO plant will be dependent upon: frictional pressure drops across the feed / draw solution sides of the permeator; configuration of plant equipment; inefficiencies of pumping and rotating components (e.g., hydroturbine- generator, freshwater pump-motor, seawater pump-motor, and the flushing solution pump- motor); system power inputs (e.g., pressurizing incoming fresh water and sea water); and current membranes being less than perfectly semipermeable [S. Loeb, et al., J. Membr. Sci., 51 (1990), 323-335; S. Loeb, et al., J. Membr. Sci., 1 (1976), 249-269)].

[0089] Extractable Energy from TMA-Based PR-FO Systems

[0090] As described below in Working Examples 1A and 1 B, it has now been found that an ionized TMA-based draw solution for use in PRO systems can be used to generate osmotic pressures on par with a saturated NaCI solution: 205 bar of osmotic pressure for a 66-69 wt% ionized TMA solution. As such, a power-generating PRO system using a concentrated ionized TMA draw solution can be used to extract energy and fresh water from feed solutions many times more concentrated than river, or brackish water.

[0091] Further, the Gibbs free energy of mixing was calculated for a 69 wt% ionized TMA solution being mixed with river water, said energy of mixing being representative of a thermodynamic maximum energy to be released from a mixing of two solutions of different salinities. It was found that the Gibbs free energy of mixing for an ionized TMA solution and river water translated into approximately 5.42 kWh/m³, wherein 5.4 kWh of energy is extracted from 1 m³ of feed solution processed.

[0092] In one example, based on an ionized TMA/river water PRO system, which processes 100 m³ of feed solution per day, the energy generated per day is 542 kWh. With an average home using an average of 909 kWh per month [US Energy Information Administration, EIA, http://www.eia. gov/tools/faqs/faq.cfm?id=97&t=3, 2013], or approximately 30 kWh per day, then a modestly sized ionized TMA-based PRO system provides power to approximately 18 homes per day. Scaling this system to process larger volumes of feed solution could generate enough electricity to power entire communities, towns, municipalities, or cities.

[0093] Detailed Description of TMA-Based PR-FO Power-Generating Systems

[0094] An aspect of this application provides a FO system in tandem with a PRO system (FO-PRO system), an embodiment of which is depicted in Figure 9.

[0095] With reference to Figure 9, there is provided a FO system comprising a FO flow cell comprising concentrated ionized trimethylamine (TMA) draw solution and feed solution having a concentration of > 0.5 - 3.5 wt% total dissolved solids (TDS), separated by a semipermeable membrane, wherein water flows from the feed solution, across the semipermeable membrane, into the concentrated draw solution, forming a diluted draw solution. [0096] In an embodiment, the draw solution has a concentration of >30 wt%; in another embodiment, it has a concentration between 66 - 69 wt%. In one embodiment, the feed solution has a TDS >3 - 3.5 wt%; in another embodiment, the feed solution has a TDS > 5 wt%. In yet another embodiment, the feed solution is an industrial wastewater, or the discharge from a reverse osmosis (RO) plant.

[0097] As depicted in Figure 9, there is also provided a means for reconstituting the concentrated draw solution, once it has been diluted via the above-described FO system. In one embodiment, the means for reconstituting the concentrated draw solution comprises removing ionized TMA from solution, in the form of its constituent gasses (C0₂ and TMA), via flushing with an inert gas (such as, but not limited to air, N₂, Ar, or any combination thereof) substantially devoid of CO2 or other acid gases; in another embodiment, these means comprise applying low-grade heating wherein, in one embodiment, the solution is heated to < 80°C, or to < 60°C. In another embodiment, these means comprise a combination of flushing with an inert gas and applying low-grade heating. Once ionized TMA is removed from the draw solution, generating fresh water, C0_{2 ,} and TMA, a portion of the fresh water is removed from the system for alterative use (e.g., agricultural use) or disposal, and the remaining portion is exposed to the constituent gasses C0₂ and TMA to regenerate the concentrated draw solution for continued use in the FO system.

[0098] With further reference to Figure 9, there is also provided a PRO system in fluid communication with the above-described FO system, wherein the system comprises a PR- FO flow cell comprising a draw solution composed of the concentrated feed solution from the FO system, and a relatively 'low' osmotic pressure feed solution, separated by a semipermeable membrane, wherein water flows from the feed solution, across the semipermeable membrane, and into the draw solution (wherein, in accordance with PRO practice, the draw solution is pressurized via a pressure exchanger - not shown), forming a second dilute draw solution. As water flows into the draw solution, internal pressures of the PR-FO flow cell increase, and said increased water volume is diverted towards an energy- generator to produce electricity. The then concentrated feed and diluted draw solutions are disposed of.

[0099] In an embodiment of the above-described PRO system, the relatively 'low' osmotic pressure feed solution comprises low salinity water, such as, but not limited to, fresh water, river water (e.g, brackish water), sea water, etc. In one embodiment, the energy-generator comprises a turbine; in another embodiment, disposal of the feed and draw solutions comprises discharge into waters of similar osmotic pressures, such as seawater.

[00100] In an embodiment of the above-described FO-PRO system, the electricity can be directed, in whole or in part, into an electrical grid for consumption by the public; in another embodiment, the electricity generated can be directed, in whole or in part, back into the FO-PRO system. In yet another embodiment, the electricity is stored, in whole or in part, for later use, such as, but not limited to, in a capacitor or a battery.

[00101 ] In an embodiment of the above-described FO-PRO system, the system is designed to function similar to a battery, such that the system is held in stasis until electricity generation is required. In one such embodiment, the FO-PRO system is used as a pumped storage system that vertically stores water; when electricity generation is required, the stored water is allowed to flow downhill through a generator, such as, but not limited to, a turbine. In another such embodiment, the feed and draw solutions are kept separated from the semipermeable membrane to prevent water flow until such a time that energy generation is required.

[00102] In an embodiment of the FO-PRO system, the system is a small-scale, portable unit, suitable for use, for example, in remote locations that may require a ready energy source. Such units have utility, for example, in disaster relief or during military operations. In another embodiment, the FO-PRO system is a large-scale power-generating plant, such as a municipal power-generating plant. In each case, the system can additionally be used for fresh water or agricultural water production simultaneously with energy production.

[00103] An aspect of this application provides a PR-FO system, one embodiment of which is depicted in Figure 10.

[00104] With reference to Figure 10, there is provided a PR-FO system comprising a FO flow cell comprising concentrated ionized trimethylamine (TMA) draw solution and a relatively 'low' osmotic pressure feed solution, separated by a semi-permeable membrane, wherein water flows from the feed solution, across the semi-permeable membrane, into the concentrated draw solution (wherein, in accordance with PRO practice, the draw solution is pressurized via a pressure exchanger - not shown), forming a diluted draw solution of increased volume. This increased water volume/flow is then diverted to an energy generator (such as, but not limited to, a turbine), in fluid communication with the FO flow cell, to produce electricity.

[00105] In an embodiment of the above-described PR-FO system, the relatively 'low' osmotic pressure feed solution comprises any solution having a lower osmotic pressure than the ionized TMA draw solution. In another embodiment, said feed solution comprises low salinity water, such as, but not limited to, fresh water, river water, etc.

[00106] As depicted in Figure 10, there is also provided means for reconstituting the concentrated draw solution, after it has been diluted via the above-described FO system, and diverted to the energy generator. In one embodiment, the diluted draw coming from the energy-generator is split into two paths, with X% being diverted down one path, and 100-X% being diverted down another. For the 100-X% path, dilute draw solution is sent to a means for draw solute removal, comprising removing ionized TMA from solution, in the form of its constituent gasses (C0₂ and TMA), via heating wherein, in one embodiment, the solution is heated using sources of available waste heat, such as, but not limited to, industrial waste heat, solar thermal waste heat, and/or geothermal waste heat. In another embodiment, said means comprises a combination of flushing with an inert gas (such as, but not limited to air, N₂, Ar, or any combination thereof), and heating using sources of available waste heat (e.g., industrial, solar, geothermal, or a combination thereof). Once ionized TMA is removed from the draw solution, generating fresh water, CO2, and TMA, the fresh water is looped back into the system, being recombined with the concentrated feed solution coming from the FO flow cell to regenerate the feed solution; and, the constituent gasses, C0₂ and TMA, are diverted to a means for draw regeneration, wherein the gasses are combined with the diverted X% of diluted draw solution to regenerate the concentrated draw solution for continued use in the PR-FO system.

[00107] In an embodiment of the above-described PR-FO system, the electricity can be directed, in whole or in part, into an electrical grid for consumption by the public; in another embodiment, the electricity generated can be directed, in whole or in part, back into the PR-FO system. In yet another embodiment, the electricity is stored, in whole or in part, for later use, such as, but not limited to, in a capacitor or a battery.

[00108] In an embodiment of the above-described PR-FO system, the system is designed to function similar to a battery, such that the system is held in stasis until electricity generation is required. In one such embodiment, the PR-FO system is used as a pumped storage system that vertically stores water; when electricity generation is required, the stored water is allowed to flow downhill through a generator, such as, but not limited to, a turbine. In another such embodiment, the feed and draw solutions are kept separated from the semipermeable membrane to prevent water flow until such a time that energy generation is required.

[00109] In an embodiment of the PR-FO system, the system is a small-scale, portable unit, suitable for use, for example, in remote locations that may require a ready energy source. Such units have utility, for example, in disaster relief or during military operations. In another embodiment, the PR-FO system is a large-scale power-generating plant, such as a municipal power-generating plant. In each case, the system can additionally be used for fresh water or agricultural water production simultaneously with energy production.

[001 10] In additional embodiments of the application, there is provided a pressure retarded forward osmosis system wherein the system generates a water flux (J_w; L/m²/h) between approximately 10 - 50; or, between approximately 10 - 20; or, between

approximately 20 - 30; or, between approximately 30 - 40. In another embodiment, the system generates a water flux (J_w; L/m²/H) between approximately 20 - 90; or, between approximately 30 - 40; or, between approximately 50 - 65; or, between approximately 65 - 80. In another embodiment, the system generates any one of the forgoing water fluxes when the hydraulic pressure (bar) is between approximately 2 - 12. In another embodiment, the system generates any one of the forgoing water fluxes when the concentration of the draw solute is between approximately 8 - 60wt%.

[001 1 1 ] In additional embodiments of the application, there is provided a pressure retarded forward osmosis system wherein the system generates a power density (W; w/m²) between approximately 1 - 10; or, between approximately 1 - 4; or, between approximately 3 - 7; or, between approximately 3 - 9. In another embodiment, the system generates a power density (W; w/m²) between approximately 2 - 20; or, between approximately 3 - 10; or, between approximately 6 - 15; or, between approximately 7 - 19. In another embodiment, the system generates any one of the forgoing power densities when the hydraulic pressure (bar) is between approximately 2 - 12. In another embodiment, the system generates any one of the forgoing power densities when the concentration of the draw solute is between approximately 8 - 60wt%.

[001 12] In additional embodiments of the application, there is provided a pressure retarded forward osmosis system wherein the system generates a reverse salt flux (J_s; mol/m²/h) between approximately 0.1 - 4; or, between approximately 0.3 - 2; or, between approximately 0.7 - 2; or, between approximately 1 - 3.5. In another embodiment, the system generates any one of the forgoing reverse salt fluxes when the hydraulic pressure (bar) is between approximately 2 - 12. In another embodiment, the system generates any one of the forgoing reverse salt fluxes when the concentration of the draw solute is between approximately 8 - 60wt%.

[001 13] Also see, for example, Figures 13A - 13E.

[001 14] To gain a better understanding of the invention described herein, the following examples are set forth. It should be understood that these examples are for illustrative purposes only. Therefore, they should not limit the scope of this invention in any way.

[001 15] EXAMPLES

[001 16] General Experimental

[001 17] Trimethylamine was purchased as a 45 wt% solution in water, and used as received from Sigma Aldrich. Coleman instrument grade carbon dioxide (99.99%) was purchased from Air Liquide. Deionized water (18 ΜΩ-cm) was provided using an Elga Purelab Pulse system. Stock feed solutions of sodium chloride at a given concentrations were prepared in advance by dissolving a requisite mass of sodium chloride in an appropriate volume of deionized water. Thin-film composite membranes were acquired from Porifera (Porifera, Inc., 3502 Breakwater Court, Hayward, CA 94545, (510) 695-2777) with a thickness of 0.07 mm.

[001 18] A 66 wt% ionized trimethylamine (TMA) draw solution was generated by carbonating an aqueous 45 wt% trimethylamine solution (2 L) in a chemineer reactor. The stock draw solution was sealed and stored in a glass bottle. Not all draw solution used came from the same batch of carbonated TMA solution.

[001 19] A feed solution of 3 wt% sodium chloride was prepared by dissolving a requisite mass of sodium chloride in an appropriate mass of deionized water (e.g. 3 g NaCI / 97 g water).

[00120] A Porifera membrane was conditioned and used as part of a forward osmosis (FO) flow cell (Figure 1 A-B). The membranes were shipped dry, with their active side labeled. Circles of membrane (4 cm in diameter) were cut from a membrane sheet, as needed, and were soaked in deionized water, for at least 30 min before use, to open their pores. After soaking, if not used immediately, the membrane circles were stored in water to be kept hydrated. The membranes were cut to fit within the flow cell's seal, to minimize leaking of liquid around the cell.

[00121] Example 1A: Determination of Expected Osmotic Pressure for Ionized TMA Draw Solution

[00122] General Experimental

[00123] Custom-built Osmometer, and Methods of Use Thereof:

[00124] A custom rapid membrane osmometer was built by Diffusomotics, LLC to allow for measurement of the ionized TMA draw solution's osmotic pressure. The custom osmometer comprised: i) custom stainless steel 316L membrane osmometer (volume 8 mL) ii) very high accuracy pressure transducer (Omega Engineering; pressure range 0-100 bar; output 0-5VDC)

iii) Sterlitech RO membranes

iv) stabilized power supply, Agilent E3643A (50 W, 0-35 V 1.4 A, 0-60 V 0.8 A)

v) Agilent 34401A Digital Multimeter, 6½ digit high performance

[00125] Use of such an osmometer has been described by A. Grattoni et al. [Grattoni, A. et al., Anal. Chem. 80, 2617-2622 (2008)].

[00126] Method for setting up the osmometer: i) Osmometer parts included:

(a) solution shell; (b) solvent shell; (c) pressure transducer; (d) compression screws; (e) static pressure cap; (f) dynamic pressure cap; (g) tin sealing washer; (h) solvent chamber cap; (i) tubing; (j) porous membrane support disk; (k) solvent chamber O-ring; (I) solution chamber O-rings; (m) supporting legs; (n) leg screws (Figure 3) ii) Cleaning procedure: Prior to use, all osmometer components (with exception of pressure transducer and membrane support disk (j)) were thoroughly cleaned. Cleaning procedure required use of a general use degreasing detergent and a brush. All components were rinsed with regular water and finally rinsed with deionized (Dl) water. The components were dried with compressed air or high purity nitrogen as necessary. To clean the pressure transducer, instructions from its manufacturer were followed (OMEGA Engineering). The cavity of the pressure transducer could be cleaned with water and organic solvents such as ethanol, isopropyl alcohol. Rigid objects could not be inserted within the cavity, nor could brush tools as they could damage the pressure sensitive diaphragm of the transducer. To clean the porous membrane support disc, it was immersed in acetone for 1 hour, and then rinse with Dl water; the disc was rapidly dried with compressed air or in oven.

Assembly of pressure transducer:

The pressure transducer (Figure 4) fit into a 1/4 inch threaded cavity in a lower side of the solution shell; prior to inserting the pressure transducer, its thread was wrapped with Teflon tape commercially available in any hardware store. Teflon tape also served as additional removable sealant for pressure transducer/solution shell assembly. The pressure transducer was tightened to the solution shell without exceeding torque indicated by the transducer manufacturer. The transducer was powered, and delivered output information, via an electrical connector positioned on opposite side of transducer thread. A female connector was provided with the osmometer, and instructions provided by the manufacturer were carefully followed to properly wire the female connector. The female connector received two conductor wires for powering the transducer through the Agilent stabilized power supply; and two conductor wires for delivering output to an Agilent multi-meter. Banana plug connectors could be used to connect to both power supply and multi-meter.

Assembly of the osmometer (Figure 5A/5B):

O-rings (I and k) were inserted into their respective groves machined into the solution shell and solvent shell. The porous membrane support disc and semipermeable membrane were wetted in solvent that were to be used during osmotic pressure measurement. The wetting procedure was fundamental for proper and rapid measurement of osmotic pressure. Users were instructed to verify chemical compatibility of selected semi-permeable membranes with solvent used in analysis. By means of a syringe and a plastic needle, the pressure transducer cavity was loaded, taking care to remove any air from the cavity. A plastic needle, shorter than the cavity itself, was used to avoid touching the transducer's sensing flat surface at its bottom. The cavity was filled until fluid levels approached the solution chamber (Level A; Figure 5B). The semipermeable membrane was placed on the support disc, making sure to face the membrane's support side toward the porous support disc. The wetted support disc and semi-permeable membrane was centered in the solution shell.

The semipermeable membrane needed to face the inside of the solution shell. The solvent shell (b) was lifted and positioned on the solution shell. A pin, threaded in the solution shell, allowed the two shells, and their holes for compression screws (d), to be accurately aligned. Compression screws were used to tighten the shells together. The screws were progressively tightened by following an order as indicated in Figure 5C. Care was taken to ensure the screws were tight before proceeding further with assembly. The osmometer's legs (m) were assembled using screws (n), as per Figure 5D.

Loading solution and solvent:

A syringe and G19 needle were used to load solution in the solution shell through a top loading duct, while slightly tilting the osmometer toward the solvent shell to ensure that air contained in the solution chamber escaped through the loading duct. The solution was carefully loaded up to the osmometer's outer shell top level (Level B; Figure 6A) to avoid formation of air bubbles within the liquid. Care was also taken to avoid scratching the semi-permeable membrane with the needle during loading. A clean syringe and long needle was used to load solvent in the solvent shell; solvent was loaded until the solvent level reached the equivalent of Level B for the solvent shell.

One end of a desired length of clear plastic tubing (i) was wrapped with Teflon tape, and inserted into the solvent chamber cap. Rubber-coated pliers were used to tight the solvent chamber cap on the solvent shell to ensure sufficient compression on the sealing O-ring. A portion of the clear tube was filled with solvent using the solvent syringe. This allowed monitoring of extent of solvent transport across the semi-permeable membrane during osmotic pressure measurements.

The pressure transducer was connected to the power supply and multi-meter, and output data collection was commenced. The static pressure cap was used to seal the solution chamber. The static solution cap was composed of a stainless steel screw, a tin washer, and a containment ring (Figure 6B). When the screw was tightened in the solution shell, it compressed soft tin washers. The washer was externally confined by the containment ring; as such, it deformed and filled all gaps in the thread, creating a tight seal against the solution chamber's external surface. Once properly tightened, the sealing cap could withstand pressures exceeding 200 bar.

By using the static pressure cap, the osmotic pressure was allowed to evolve naturally; solvent entered the solution chamber, and as a consequence, solution pressure increased. The pressure increase was expected to follow an exponential trend until a plateau was reached, equaling the solution's osmotic pressure; it was expected that this plateau would be reached within 8 to 24 hours, depending on solvent and solution utilized.

Dynamic pressure cap:

The dynamic pressure cap was composed of a stainless steel screw, a sealing nut, a tin sealing washer and a containment ring (Figure 7A). The dynamic pressure cap allowed for increasing the solution pressure to iteratively approach the osmotic pressure of the solution, while maintaining a tight seal on the solution chamber. Proper use of the dynamic pressure cap required: screwing screw (1) into the solution shell, allowing for excess fluid to be released from screw thread; tightening sealing nut (2) while keeping (1) fixed to achieve proper sealing of the chamber; further screwing in (1) while keeping (2) fixed, thus increasing the solution pressure to a desired level that is close to a predicted one; and, making additional iterative adjustments to the pressure (increasing and decreasing) by rotating (1) and maintaining (2) fixed (Figure 7B).

Method of measuring osmotic pressure: Instructions provided with osmometer were very carefully followed, to ensure the osmometer was correctly set-up and operated. It was found to be essential to fill the system without trapping any bubbles in the cell. To achieve a seal on the draw side of the system, larger O-rings were used than those provided with the system. A reverse osmosis (RO) membrane was used in the system to withstand high pressure. It was noted that when the osmometer's instructions (above) referred to solution cell, it was the side that the draw solution was introduced to, and the solvent cell was the side the feed solution was introduced to. To get accurate results, it was necessary to: i) tare the system once the draw solution was filled; and ii) start a timer at the same time as adding the feed solution - not after the feed solution has been added. It was found that dewatering occured as the feed solution was added, and that the feed solution needed to be added rapidly.

[00128] Forward Osmosis Flow Cell and Methods of Uses Thereof [00129] Materials:

[00130] Trimethylamine was purchased as a 45 wt% solution in water, and used as received from Sigma Aldrich. Coleman instrument grade carbon dioxide (99.99%) was purchased from Air Liquide. Deionized water (18 ΜΩ-cm) was provided using an Elga Purelab Pulse system. Stock feed solutions of sodium chloride at a given concentrations were prepared in advance by dissolving a required amount of sodium chloride in an appropriate amount of deionized water. Thin-film composite membranes were acquired from Porifera (Porifera, Inc., 3502 Breakwater Court, Hayward, CA 94545, (510) 695-2777). Membranes were cut for testing (4 cm diameter), and conditioned by soaking in deionized water for a minimum of 30 minutes before use. Once wet, all membranes were stored in deionized water for the duration of testing. Stock solutions of 66-69 wt% ionized

trimethylamine were produced by carbonating 2 L portions of a 45 wt% aqueous trimethylamine solution in a 1 gallon stainless steel Chemineer reactor, at 10 bar for 30 minutes.

[00131] Equipment and Analysis:

[00132] Forward osmosis flow cell used and described herein is depicted by Figure 1A. Typically, the flow cell comprised: (i) a pump to circulate feed and draw solutions; (ii) a membrane cartridge through which the solutions are circulated; (iii) separate reservoirs containing the feed and draw solutions; (iv) separate balances, upon which the reservoirs were placed, to measure mass changes with time; and, (v) connective tubing throughout.

[00133] Method of Operation:

[00134] Within the FO flow cell, as depicted in Figure 1A, the feed solution was circulated from the feed reservoir, through the pump, over the active/rejection side of the membrane, and back into the feed reservoir; the draw solution was simultaneously circulated from the draw reservoir, through the pump, over the support side of the membrane, and back into the draw reservoir; as the feed and draw solutions simultaneously passed over the membrane, water transferred from the feed solution across the membrane and into the draw solution; and, the reservoirs sat atop balances to record mass change of the solutions with time, via a computer. For each flow cell run, the mass change data were collected using Mettler Toledo PG2002-S balances, coupled to a computer with LabVIEW2012 software (National Instruments).

[00135] Representative Flow Cell Procedure for Forward Osmosis:

[00136] Conditioned membranes were loaded into a flow cell with the membrane's active/rejection layer orientated towards the feed solution. The cell was flushed with 3x100 mL portions of deionized water on both the feed and draw solution sides of the membrane. Glass bottles (250 mL) were used as reservoirs for the feed solution and draw solution. To run the cell under aerobic conditions, the bottles were left opened to air. Stock feed solutions of sodium chloride and draw solutions of 66-69 wt% ionized trimethylamine were prepared and used, as described above. Repeat runs were performed for each membrane at each salt concentration (two runs per feed/draw solution combination). A complete run was determined by length of time.

[00137] Feed solution (200 mL) was loaded into the feed reservoir, and aqueous 66- 69 wt% ionized trimethylamine (100 mL) was loaded into the draw reservoir. Tubing was lowered into each solution so that it did not touch the sides or bottom of the bottles. Data collection was initiated on the LabView software, followed by starting a circulating pump and timer. After 30 seconds, the balances were tared and any data points before this time were removed from analysis.

[00138] Results and Discussion: [00139] Using the above described rapid membrane osmometer, osmotic pressures were measured for four ionized TMA solutions, of concentrations varying from 6.9 wt% to 69 wt% (Figure 8A; Table 1). A plot of said osmotic pressures versus concentration was found to be approximately linear (Figure 8C).

[00140] Osmotic pressure measurements for ionized TMA solutions of concentrations 6.9 wt% to 34.5 wt% were completed in duplicate or triplicate to ensure reproducibility of results (Figure 8B). It was found that the osmotic pressure of an ionized TMA draw solution increased with increasing amounts of dissolved ionized TMA (Figure 8C); at a maximum draw concentration of 69 wt%, the osmotic pressure of ionized TMA was found to be comparable to saturated sodium chloride (approximately 200 bar; Table 1).

[00141] An assumption made during operation of the above described rapid membrane osmometer was that draw solute does not pass through the FO membrane; as such, it was considered that there may be a possible inherent error associated with osmotic pressure measurements of ionized TMA, as the salt, TMA, and/or C0₂ may pass from the solute-containing side to the solvent-containing side of the osmometer; at least to some extent [A. Grattoni, et al., Anal. Chem. 80, 2617-2622 (2008)].

[00142] However, after monitoring changes in osmotic pressure with respect to time for the various concentrations of ionized TMA (Figure 8A), solute movement did not appear to significantly affect osmotic pressure measurements: all samples exhibited a fast initial increase in osmotic pressure, with an eventual plateau at a maximum value (Figure 8A-B; Table 1). Considering the osmotic pressure of the ionized TMA solution having a concentration of 6.9 wt%, for example, the system reached a maximum pressure of 15 bar in 14 min; after an additional 90 min, a decrease in pressure of only 1 bar was measured. Consequently, only a 6 % drop in osmotic pressure was observed after allowing the forward osmosis to continue for over 5 times the equilibration time, further suggesting that solute movement did not significantly affect osmotic pressure.

[00143] To evaluate measurement accuracy, and support the postulation that ionized

TMA solutions were not losing solute through the osmometer's membrane, a further experiment was performed. Using a forward osmosis flow cell as described above and depicted in Figure 1 A, a saturated NaCI feed solution (26-28 wt%) was added to the feed reservoir, with a 66-69 wt% ionized TMA draw solution being added to the draw reservoir; after monitoring the weights of the solutions for 60 min, negligible (< 1 g) movement of water was observed. It was determined, based on an extrapolation from data provided by the membrane supplier Porifera, that a saturated NaCI solution has an osmotic pressure of approximately 208 bar - comparable to that obtained for the 66-69 wt% ionized TMA draw solution (205 bar); based on this, it was considered that the values measured with the osmometer for 66-69 wt% ionized TMA were relatively accurate.

[00144] EXAMPLE 1 B: Theoretical Maximum Work/Energy to be Derived from a Thermodynamically Reversible PR-FO System Comprising an Ionized TMA Draw Solute

[00145] As described by Elimelech et al., Gibbs free energy of mixing represents a thermodynamic maximum energy to be released from a mixing of two solutions of different salinities, which can only be attained via thermodynamically reversible processes. In a PRO system, a thermodynamically reversible process can be theoretically realized in a batch mode via application of a pressure infinitesimally smaller than the system's osmotic pressure difference throughout the entire PRO process. It has been shown that energy generated in such reversible PRO processes equals Gibbs free energy of mixing [Lin, S., et al., Energy Environ. Sci., 2014, 7, 2706].

[00146] As further described by Elimelech et al., Equation (1) can be used to calculate the Gibbs free energy of mixing of a thermodynamically reversible PRO system [Ngai Yin Yip, M. Elimelech, Environ. Sci. Technol. 2012, 46, 5230-5239]: G_miXiy_A C_M (1 - φ)

~—— In C i— c_A ln c& — c_Rln c_R

vRT φ φ

(1), wherein

0 is volume fraction of solution A (dilute/feed solution);

1 - 0 is volume fraction of solution B (concentrated draw solution); Assuming that two solutions are of equal volume, then 0 = 0.5; CM is molar salt concentration of the system;

CA is molar salt concentration of feed solution (solution A; approximately 0.002 M if feed solution is river water); c_B is molar salt concentration of draw solution (solution B; approximately 0.6 M if draw solution is seawater (35 g/L));

T = 298 K; R = 8.314 J/molK; v = number of ions salt dissociates into (e.g. 2 for NaCI);

[00147] For example, assuming that solutions A and B are of equal volume, and assuming river water on feed side and seawater on draw side, then Gibbs free energy of mixing is:

0 = 0.5 ; CM = (0.002 M + 0.6 M)/2 = 0.301 M

AG = -2 x 8.314 J/molK x 298 K x {(0.301 M x ln0.301)/0.5 - 0.002 M x ln(0.002) - (0.5/0.5)(0.6 M x In0.6)}

AG = -4955 J/mol x {-0.7228 + 0.0124 + 0.3065 mol/L}

= 2001 J/L = 2 kJ/L

[00148] With respect to the herein described system, the ionized TMA draw solution has a concentration between 66 - 69 wt%. Assuming a concentration of 69 wt%, said solution has molarity of approximately 5.7 M (69 g of the salt in 100 ml of solution, molarity of ionized TMA being calculated on the basis of [TMAH][HC03]).

[00149] Assuming that the draw solution of ionized TMA is paired with a feed solution of river water, and solutions are of equal volume, then energy of mixing is:

0 = 0.5 CM = (0.002 M + 5.7 M)/2 = 2.85 M

AG = -2 x 8.314 J/molK x 298 K x {(2.85 M x ln2.85)/0.5 - 0.002 M x In0.002 - (0.5/0.5)(5.7 M x In5.7)}

AG = -4955 J/mol x {5.970 + 0.0124 - 9.92 mol/L}

= 19,512 J/L = 19.5 kJ/L = 5.42 kWh/m³

[00150] As demonstrated by the above calculation, approximately 5.4 kWh of energy can be extracted from 1 m³ of feed solution processed. Applying this value, an ionized TMA- based PRO system that processes, for example, 100 m³ of feed solution per day, will generate 542 kWh of energy per day. With a typical home using an average of 909 kWh per month [US Energy Information Administration, EIA,

http://www.eia. gov/tools/faqs/faq.cfm?id=97&t=3, 2013], or approximately 30 kWh per day, then this ionized TMA-based PRO system can provide power to approximately 18 homes per day.

[00151] EXAMPLE 2A: Measuring Draw Solution Osmotic Pressure

[00152] Representative Flow Cell Procedure for Forward Osmosis Under Aerobic Conditions

[00153] Forward osmosis (FO) was undertaken using a flow cell as depicted in Figure 1 B. Conditioned membranes were loaded into a flow cell with the membrane's

active/rejection layer orientated towards the feed solution. The cell was flushed with 3x100 mL portions of deionized water on both the feed and draw solution sides of the membrane. Glass bottles (250 mL) were used as reservoirs for the feed solution and draw solution. To run the cell under aerobic conditions, the feed bottle was left opened to air; to measure osmotic pressure of the draw solution, the draw bottle was capped, and a pressure gauge was inserted through the cap to allow measurement of the reservoir's internal pressure.

[00154] Stock feed solutions of 3 wt% sodium chloride and draw solutions of 66 wt% ionized trimethylamine were prepared and used, as described above. The feed solution (200 mL) was loaded into the feed reservoir, and the draw solution (100 mL) was loaded into the draw reservoir. Tubing was lowered into each solution, and secured by metal supports, so that it did not touch the bottles' sides or bottom. The feed and draw reservoirs sat atop balances to record mass change of the solutions with time, via a computer.

[00155] Forward osmosis was initiated within the flow cell by circulating the feed solution from the feed reservoir (e.g. a glass bottle/container), through a pump, over the membrane's active/rejection side, and back into the feed reservoir; the draw solution was simultaneously circulated from a draw reservoir (e.g. glass bottle/container), through the pump, over the membrane's support side, and back into the draw reservoir; and, as the feed and draw solutions simultaneously passed over the membrane, water transferred from the feed solution across the membrane and into the draw solution. [00156] For each flow cell run, mass change data were collected using Mettler Toledo PG2002-S balances, coupled to a computer with LabVIEW2012 software (National

Instruments). Data collection was initiated on the LabView software, followed by starting a circulating pump and timer. After 30 seconds, the balances were tared and any data points before this time were removed from analysis. A complete flow cell run was determined by length of time length; initial run was 70 min, with pressure measurements being taken every 5 minutes.

[00157] As described above, the flow cell was modified such that the draw reservoir was capped, and a pressure gauge was inserted through the cap to allow measurement of the reservoir's internal pressure. This modification allowed for measurement of the draw solution's osmotic pressure: water drawn from the feed reservoir into the capped draw reservoir increased the draw reservoir's internal pressure, as air within the reservoir's headspace could not be displaced due to the cap; this increase in pressure was then measured by the pressure gauge, providing an indication of the draw solution's osmotic power.

[00158] Results

[00159] The foregoing work was undertaken to demonstrate the potential osmotic pressure of an ionized TMA draw solution to permit calculation of the power generating potential in FO systems comprising ionized TMA draw solutions.

[00160] As delineated in Table 2.0, measured pressure (i.e., osmotic pressure) increased from 0 psig to 5 psig over 30 min, and remained constant for an additional 40 min. The unexpectedly low pressure value, especially in view of the expected osmotic pressures determined for an ionized TMA draw solution (see below), was due to a leak in the FO system. However, the observed increase in the presence of a leak was indicative of significantly higher energy generation potential.

[00161] Example 2B: Calculating Power Generated from FO System with Ionized TMA Draw Solution

[00162] Representative Procedure for Forward Osmosis Cell Under Aerobic Conditions [00163] Forward osmosis (FO) was undertaken using a cell, as depicted in Figure 2. A large piece of conditioned membranes was loaded into the cell with the membrane's active/rejection layer orientated towards the feed solution. Tall glass reservoirs were used to house the feed and draw solutions. To run the cell under aerobic conditions, the reservoirs were left opened to air.

[00164] Stock feed solutions of 3 wt% sodium chloride and draw solutions of 66 wt% ionized trimethylamine were prepared and used, as described above. The feed and draw solutions were loaded into their respective reservoirs.

[00165] Forward osmosis was allowed to proceed for 30 min, with water moving through the membrane from the feed solution and into the draw solution. Change of height of the draw solution was measured with respect to time:

[00166] Column radius = 0.4 cm - Area = 0.503 cm²

[00167] Height at 30 min = 28 cm

[00168] Initial Draw Volume = 800 ml_

[00169] Results

[00170] The FO cell comprised long glass tubes from which the height of a column of draw solution could be measured over time. From this change in height, an amount of work required to raise the height of the draw solution a certain distance, in a certain period of time, was calculated.

[00171] In 30 min, the height of the column of draw solution was raised 28 cm;

therefore:

Pressure of a column of water = Density x Height x Gravity

= (0.28 m)(1 kg/m³)(9.8 m/s²) = 2.744 N/m² Force = Pressure x Area = Pressure*Crr)(r²)

= (2.744 Ν/ηι²)(π)(0.004ηι)² = (2.744 N/m²)(5.03 x10⁵ m²) = 1.379 x10⁴ N Work = Force x Distance x cos(0) = (1.379 x10^"4 N)(0.28 m)cos(O) =3.862 x 10 ⁵ Nm

Power = Work / time

= (3.862 x 10^"5 Nm) / (1800 s) = 2.146 x10⁸ J

[00172] As would be readily appreciated by one skilled in the art, the above Power calculation is based on results demonstrated herein; and that, in view of the experimentally determined osmotic pressure for a concentrated ionized TMA draw solution (205 bar), and the expectant Gibbs free energy of mixing (5.42 kWh/m³) delineated above, it is expected that further optimization of this system will result generate higher power outputs.

[00173] Example 3: Investigation of Ionized Trimethylamine as a Draw Solute for PRO Applications

[00174] Materials and Method

[00175] Membrane 1 and Membrane 2 were used in the below described PRO experiments. Prior to their use, membranes were immersed in deionized water for at least 1 hour to allow complete wetting, and then rinsed with deionized water. Intrinsic properties of Membrane 1 have been previously determined [J. Ren, J. R. McCutcheon, A new commercial thin film composite membrane for forward osmosis. Desalination, 343 (2014) 187-193]. Water permeability (A) was 0.87 Lm ²m ¹bar¹, salt permeability was 0.51 Lm ²h ¹, and structure parameter (S) was 454 μηι. Intrinsic properties of Membrane 2 have also been previously determined [J. Maisonneuve, C. B. Laflamme, P. Pillay, experimental investigation of pressure retarded osmosis for renewable energy conversion: Towards increased net power. Applied Energy, 164 (2016) 425-435]. Specifically, pure water and salt (NaCI) permeability coefficient were 4.2 L nr² h ¹ bar¹, and 1.4 Lm ²h ¹, respectively.

Structural parameter (S) was 454 μηι. See Figures 14C and 15A.

[00176] Draw Solution

[00177] Ionized TMA-C0₂ as a PRO draw solution was compared with draw solutions of NH3-CO₂ and sodium chloride (NaCI). Equivalent molar concentrations were used for all draw solutions (see, for example, Figures 15A - 15D)

[00178] Ionized TMA draw solutions were prepared by carbonation of TMA aqueous solution. 50 wt% TMA solution was obtained from Fisher Scientific (Pittsburgh, PA). Solutions were diluted using deionized water to achieve desired concentrations of 1 M, 3 M and 5 M, respectively. Carbonation reaction was conducted in a vessel that was pressurized to 100 psi by pure CO2 gas (see, for example, Figure 14A). Formation of ionized TMA was verified by ¹H NMR analysis (Bruker AVANCE 300 MHz): Chemical shift of TMA in solution is 2.23 ppm, while chemical shift of ionized TMA is 2.86 ppm, both in D₂0.

[00179] NH3-CO₂ draw solutions were prepared by dissolving ammonium bicarbonate (NH₄HCO3) (Fisher Scientific) in deionized water to form 1 M, 3 M and 5 M solutions with aid from ammonium hydroxide (NH₄OH) due to limited solubility of NH₄HCO3 in water. For comparison purposed, an ammonia and carbon ratio of 1 .75 to 1 was employed for all NH₃- C0₂ solutions. NaCI draw solutions of 1 M, 3 M, and 5 M were prepared by dissolving certain amount of NaCI (Fisher Scientific) in deionized water. See, for example, Figures 15B - 15D; 16A; 16D; 17A; 18A - 18C; 18E; 19C - 19E; and 19G - 19H.

[00180] Measurement of PRO Performance

[00181 ] A benchtop PRO system was used to measure water flux and salt flux under PRO conditions on a coupon scale (see, for example, Figure 14B). It was modified to be chemically resistant to ionized TMA.

[00182] Fresh membrane coupons with PRO orientation (selective layer (i.e.

active/rejection layer) facing draw solution, support layer facing feed solution) were tested at 20 °C of both draw and feed solutions. All three draw solutes were tested at 1.0 M, 3.0 M, and 5.0 M (see Figures 15A - 15D; 18A - 18C; and 18E). Feed stream was deionized water for all tests. Stream flow rates for the feed and draw solutions were maintained at 1 L/min (0.25 m/s) and 2 L/min (0.5 m/s), respectively. For each draw solution, there was a cycle ascending and a cycle descending operation. In cycle ascending, pressure was increased from 3.4 bar (50 psi) to 10.3 bar (150 psi) in 1.7 bar (25 psi) increments. Once maximum pressure was achieved, the pressure was reduced in 1 .7 bar increments to 3.4 bar (cycle descending). Each pressure was maintained for 10-15 min while data was collected.

[00183] Water flux, J_w, across each membrane was measured by monitoring a decrease in feed solution mass at 1 min intervals. Data collected after an initial water flux stabilized for 1 hour was averaged over each pressure period. Power density, W, was determined by the product of the hydraulic pressure, AP, and the water flux, as in equation [2] [K. L. Lee, R. W. Baker, H. K. Lonsdale, Membranes for power generation by pressure- retarded osmosis. Journal of membrane science, 8 (1981) 141 -171]: w = ΔΡ x y, (2)

[00184] Reverse solute flux, J_s, was determined by measuring concentration of draw solute in the feed solution at each moment when pressure changed. Concentration of NaCI was determined by a conductivity meter. Reversal flux of ammonium was measure by the ammonium ion-selective electrode purchased from Vernier Software & Technology

(Beaverton, OR). Samples were collected at the end of each pressure cycle, and were acidized before characterization.

[00185] Concentration of ionized TMA in the feed solution was quantified by way of the following:

[00186] FT-IR Measurements

[00187] Samples were stored in a sealed container in a fridge until analysis. Using an ATR-FT-IR , approximately 2 drops of solution were deposited onto the IR sensor. 32 scans were recorded over a spectrum range of 4000 cm ¹ to 650 cm ¹. A blank water spectrum was recorded and subtracted from resulting spectra. For analysis of TMA in solution, area under the resulting curve was integrated from 1290 to 1240 cm ¹, centered at 1265 cm ¹. For ionized TMA analysis, area under the resulting curve was integrated from 1440 to 1300 cm ¹, centered at 1365 cm ¹. The areas were then compare to a calibration curve to determine concentration (see Figure 21A; and Tables 3 - 5).

[00188] GC-FID Measurements

[00189] Samples were stored in a sealed container in a fridge until analysis. Using an Eppendorf pipette, 500 μΙ_ of aqueous solution was combined with 1000 μΙ_ of solvent (1 μΙ_/ηιΙ_ methanol in isopropanol) in a GC vial. The vial was mixed to combine the solutions. Each sample was run using the following GC-FID conditions, in triplicate:

[00190] Internal Standard: Methanol

[00191] Solvent: Isopropanol

[00192] Column: CP-volamine (Agilent CP7447)

[00193] Column Length: 30 m

[00194] Injector Temp: 250 °C [00195] Injection Volume: 1 μΙ_

[00196] Split Ratio: 1 : 10

[00197] Flow Rate: 2 mL/min

[00198] Oven Program: 75 °C hold 5 min, ramp @ 10 °C/min to 1 10 °C, hold for 1 .5 mins

[00199] Total Run Time: 10 mins [00200] Detector Temp: 300 °C

[00201 ] Resulting GC peaks were compared to a calibration curve below to determine concentration (see Figure 21 B; and Tables 6 - 8).

[00202] Ionized TMA as a thermolytic PRO draw solute was investigated relative to model draw solutes NaCI and NH₃-C0₂; see Figures 13A - 20.

[00203] Like other thermolytic draw solutes, such as NH3-CO₂, ionized TMA has a relatively high solubility in water and can generate high osmotic pressure (see Example 1A). It also has a comparable volatility to ammonia and low enthalpy of vaporization, indicating comparable or less energy would be consumed for draw solute regeneration. Further, relative to NH₃-C0₂ as a draw solute, ionized TMA has a larger molecular size, which decreases its likelihood to pass through a membrane.

[00204] As described above, and depicted in Figures 13A - 20, tests were conducted with up to 5 M solutions of ionized TMA using a lab-scale PRO test system. It was found that estimated power densities of up to 18.6 W nr² could be achieved at relatively low pressures (10 bar); it has thus been considered that higher hydraulic pressures could yield higher power densities, if a membrane housing is made to support a membrane without forming defects.

[00205] For comparison, NaCI and NH₃-C0₂ draw solutes were investigated for use in a PRO system. It was observed that water fluxes generated by ionized TMA draw solutions were about 20 % lower than that of NaCI, and comparable with that of NH₃-C0₂. Reverse solute fluxes of ionized TMA ranged from 0.5 to 3.5 mol nr² h^~\ which was lower than NH₃- C0₂ (4.0 to 51 mol nr² h^~1) and approximately half that of NaCI. This was not unexpected given ionized TMA's relatively larger molecular size. Table 1.0: Osmometer-measured osmotic pressures of ionized TMA draw

[00207] Table 2.0: Measured osmotic pressure of an ionized TMA draw solution

[00208] Table 3.0: Concentration of ionized TMA (1 M) in feed solution (Membrane 2)

[00209] Table 4.0: Concentration of ionized TMA (3M) in feed solution (Membrane 2)

[00210] Table 5.0: Concentration of ionized TMA (5M) in feed solution (Membrane 2)

[0021 1] Table 6.0: Concentration of ionized TMA (1 M) in feed solution (Membrane 1)

[00212] Table 7.0: Concentration of ionized TMA (3M) in feed solution (Membrane 1)

[00213] Table 8.0: Concentration of ionized TMA (5M) in feed solution (Membrane 1)

[00214] All publications, patents and patent applications mentioned in this

Specification are indicative of the level of skill of those skilled in the art to which this invention pertains and are herein incorporated by reference to the same extent as if each individual publication, patent, or patent applications was specifically and individually indicated to be incorporated by reference.

[00215] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 . A pressure retarded forward osmosis system, comprising:

an aqueous draw solution having a draw solute concentration of >30 wt%, the draw solute comprising ionized trimethylamine; and

at least one pressure retarded forward osmosis element, comprising

a semi-permeable membrane that is selectively permeable to water, having a first side and a second side;

at least one port to bring a feed solution in fluid communication with the first side of the membrane;

at least one port to bring the draw solution in fluid communication with the second side of the membrane;

at least one pressure exchanger associated with the second side of the membrane for pressurizing the draw solution in fluid communication with the second side of the membrane; and

at least one energy generator in fluid communication with the pressure retarded forward osmosis element, downstream of the second side of the membrane, to permit flow of water from the feed solution through the semi-permeable membrane into the pressurized draw solution, to form a concentrated feed solution, a diluted draw solution, and to generate energy.

2. The system of claim 1 , further comprising a system for regenerating the draw solution, comprising

a. means for collecting the dilute draw solution;

b. means for separating the draw solute from the dilute draw solution;

c. means for reconstituting the draw solution; or

d. any combination thereof.

3. The system of claim 1 or 2, wherein the system is:

i) closed;

ii) continuously cycled; or

iii) a combination thereof.

4. The system of any one of claims 1-3, wherein the pressure exchanger pressurizes the draw solution to a hydraulic pressure approximately 50% of the draw solution's osmotic pressure.

5. The system of claim 2, wherein means for separating the draw solute from the dilute draw solution comprises:

a reverse osmosis system; centrifugation; filtration; volatilization; heating; a flushing gas; a vacuum or partial vacuum; agitation; or any combination thereof.

6. The system of any one of claims 1 - 5, wherein the feed solution: (i) has a Total Dissolved Solids (TDS) >3 - 3.5 wt%, or a TDS > 5 wt; (ii) is an industrial wastewater, river water, or seawater; or (iii) comprises discharge from a reverse osmosis (RO) plant.

7. The system of any one of claims 1-6, wherein the draw solution has a draw solute concentration between > 30wt% and saturation; or, alternatively, between 30 - 70wt%; or, alternatively, between 30 - 60wt%; or, alternatively, between 30 - 50wt%; or, alternatively, between 30 - 40wt%.

8. The system of claim 7, wherein the draw solution has a draw solute concentration between 30 - 40wt%; or, alternatively, between 60 - 70wt%.

9. A process for generating energy, comprising

pressure retarded forward osmosis using a pressurized aqueous draw solution having a draw solute concentration of >30 wt%, the draw solute comprising ionized trimethylamine;

the steps of pressure retarded forward osmosis comprising:

introducing a feed solution to a first side of a semi-permeable membrane; introducing the pressurized draw solution to a second side of the semipermeable membrane;

permitting flow of water from the feed solution across the semi-permeable membrane into the pressurized draw solution, to form a concentrated feed solution and a diluted draw solution; and

inducing flow of the diluted draw solution through an energy generator for producing energy.

10. The process of claim 9, further comprising: collecting the dilute draw solution after energy generation;

separating the draw solute from the dilute draw solution;

reconstituting the draw solution; or

any combination thereof.

1 1. The process of claims 9 or 10, wherein the pressurized draw solution is pressurized to a hydraulic pressure approximately 50% of the draw solution's osmotic pressure.

12. The process of any one of claims 9-1 1 , wherein the process is performed as a: i) closed cycle

ii) continuous cycle; or

iii) a combination thereof.

13. The process of claim 10, wherein separating the draw solute from the dilute draw solution comprises:

reverse osmosis; centrifugation; filtration; volatilization; heating; a flushing gas; a vacuum or partial vacuum; agitation; or any combination thereof.

14. The process of claim 10, wherein reconstituting the concentrated draw solution comprises:

a. introducing an ionizing trigger, such as carbon dioxide, to an aqueous solution of trimethylamine;

b. introducing trimethylamine to an aqueous solution of an ionizing trigger, such as_carbon dioxide;

c. simultaneously introducing trimethylamine and an ionizing trigger, such as carbon dioxide, to an aqueous solution; or

d. any combination thereof.

15. The process of any one of claims 9 - 14, wherein the feed solution: (i) has a TDS >3 - 3.5 wt%, or a TDS > 5 wt; or (ii) is an industrial wastewater, river water, or seawater; or (iii) comprises discharge from a reverse osmosis (RO) plant,.

16. The process of any one of claims 9 - 15, wherein the draw solution has a draw solute concentration between > 30wt% to saturation; or, alternatively, between 30 - 70wt%; or, alternatively, between 30 - 60wt%; or, alternatively, between 30 - 50wt%; or, alternatively, between 30 - 40wt%.

17. The process of claim 16, wherein the draw solution has a draw solute concentration between 30 - 40wt%; or, alternatively, between 60 - 70wt%.