Patent Publication Number: US-2017369337-A1

Title: Enhanced brine concentration with osmotically driven membrane systems and processes

Description:
FIELD OF THE TECHNOLOGY 
     Generally, the invention relates to osmotically driven membrane systems and processes and more particularly to increased brine concentration for zero liquid discharge (ZLD) using osmotically driven membrane systems and processes. The invention also relates to related draw solute recovery techniques for the osmotically driven membrane systems and processes. 
     BACKGROUND 
     In general, osmotically driven membrane processes involve two solutions separated by a semi-permeable membrane. One solution may be, for example, seawater, while the other solution is a concentrated solution that generates a concentration gradient between the seawater and the concentrated solution. This gradient draws water from the seawater across the membrane, which selectively permits water to pass, but not salts, into the concentrated solution. Gradually, the water entering the concentrated solution dilutes the solution. The solutes then need to be removed from the dilute solution to generate potable water. Traditionally, the potable water was obtained, for example, via distillation; however, the solutes were typically not recovered and recycled. 
     In certain prior art systems that use distillation and low grade heat to recover draw solutes, it is necessary to perform condensation and absorption steps under vacuum in an attempt to maximize draw solute recovery. For example, a knock-out pot and an eductor (using air as a driving medium) are disposed downstream of the condensation and/or absorption processes in an attempt to improve draw solute recovery. However, this arrangement requires the venting of the non-condensable gases, which can also result in a loss of draw solutes and possible environmental issues. Additionally, the prior art systems for recovering draw solutes require considerable energy input (e.g., direct steam or electricity) that makes the recovery process inefficient and expensive. 
     Furthermore, many existing technologies for concentrating a feed stream are not capable of removing substantially all of the water, or other solvent, (i.e., ZLD) from the stream generally, and in particular without the use of complicated and/or very energy intensive equipment making it expensive and impractical to maximize the concentration of the feed stream to meet ZLD requirements. 
     SUMMARY 
     The invention generally relates to systems and methods for increasing brine concentration to ZLD or near ZLD conditions and for recovering/recycling the draw solutions used in those systems and methods. The draw solutions are used in various osmotically driven membrane systems and methods, for example; forward osmosis (FO), pressure retarded osmosis (PRO), osmotic dilution (OD), direct osmotic concentration (DOC), or other processes that rely on the concentration (or variability thereof) of solutes in a solution. The systems and methods for draw solute recovery may be incorporated in various osmotically driven membrane systems/processes. Examples of osmotically driven membrane systems/processes are disclosed in U.S. Pat. Nos. 6,391,205, 7,560,029, and 9,039,899; U.S. Patent Publication Nos. 2011/0203994, 2012/0273417, and 2012/0267306; and PCT Publication No. WO2015/157031; the disclosures of which are hereby incorporated herein by reference in their entireties. In addition, a variety of draw solute recovery systems are disclosed in U.S. Pat. Nos. 8,246,791 and 9,044,711; the disclosures of which are also hereby incorporated herein by reference in their entireties. 
     Generally, the draw solution(s) used are aqueous solutions, i.e., the solvent is water; however, in some embodiments the draw solution is a non-aqueous solution using, for example, an organic solvent. The draw solution is intended to contain a higher concentration of solute relative to a feed or first solution so as to generate an osmotic pressure within the osmotically driven membrane system. The osmotic pressure may be used for a variety of purposes, including desalination, water treatment, solute concentration, power generation, and other applications. In some embodiments, the draw solution may include one or more removable solutes. In at least some embodiments, thermally removable (thermolytic) solutes may be used. For example, the draw solution may comprise a thermolytic salt solution, such as that disclosed in U.S. Pat. No. 7,560,029. Other possible thermolytic salts include various ionic species, such as chloride, sulfate, bromide, silicate, iodide, phosphate, sodium, magnesium, calcium, potassium, nitrate, arsenic, lithium, boron, strontium, molybdenum, manganese, aluminum, cadmium, chromium, cobalt, copper, iron, lead, nickel, selenium, silver, and zinc. 
     Generally, the feed or first solution may be any solution containing solvent and one or more solutes for which separation, concentration, purification, or other treatment is desired. In some embodiments, the first solution may be non-potable water such as seawater, salt water, brackish water, gray water, and some industrial water. In other embodiments, the first solution may be a process stream containing one or more solutes, such as target species, which it is desirable to concentrate, isolate, or recover. Such streams may be from an industrial process, such as a pharmaceutical or food grade application. Target species may include pharmaceuticals, salts, enzymes, proteins, catalysts, microorganisms, organic compounds, inorganic compounds, chemical precursors, chemical products, colloids, food products, or contaminants. The first solution may be delivered to a forward osmosis membrane treatment system from an upstream unit operation such as an industrial facility, or any other source, such as the ocean. 
     In one aspect, the invention relates to an osmotically driven membrane system and related process. Generally, the system includes one or more forward osmosis membrane modules including one or more membranes in each, a source of feed solution in fluid communication with one side of the one or more membranes, a source of concentrated draw solution in fluid communication with an opposite side of the one or more membranes, and a draw solution recovery system in fluid communication with the forward osmosis membrane module(s). 
     In another aspect, the invention relates to a system for concentrating a feed stream and recovering draw solution solutes from an osmotically driven membrane system. The system includes one or more forward osmosis modules, each having one or more membranes having first sides and second sides, the first side(s) of the membrane(s) fluidly coupled to a source of a first solution and the second side(s) of the membrane(s) fluidly coupled to a source of a concentrated draw solution, wherein the membrane(s) is configured for osmotically separating a solvent from the first solution, thereby forming a more concentrated first solution on the first side(s) of the membrane(s) and a dilute draw solution on the second side(s) of the membrane(s) and a separation system in fluid communication with the forward osmosis module(s) and configured for receiving the concentrated first solution and the dilute draw solution from the forward osmosis module(s). The separation system includes a first separation apparatus and a second separation apparatus. The first separation apparatus is in fluid communication with the osmotically driven membrane system and includes a first thermal recovery device, a first heat transfer means (e.g., a heat exchanger or other type of condenser) in fluid communication with the forward osmosis module(s) for receiving the dilute draw solution and coupled to a first inlet of the first thermal recovery device for preheating and introducing the dilute draw solution into the first thermal recovery device, a second heat transfer means coupled to the first thermal recovery device and having an inlet coupled to a first source of thermal energy and an outlet coupled to the first thermal recovery device for directing thermal energy to the first thermal recovery device to cause solutes within the dilute draw solution in the first thermal recovery device to vaporize, a first outlet for removing the vaporized dilute draw solution solutes from the first thermal recovery device, wherein the first outlet is in fluid communication with the first heat transfer means for providing the vaporized draw solution solutes as a source of thermal energy thereto for preheating the dilute draw solution (and partially condensing the vaporized draw solution into at least an intermediary concentrated draw solution), and a second outlet for removing a bottoms product from the first thermal recovery device. 
     The second separation apparatus is in fluid communication with the osmotically driven membrane system and includes a second thermal recovery device, a first heat transfer means in fluid communication with the forward osmosis module(s) for receiving the concentrated first solution and coupled to a first inlet of the second thermal recovery device for preheating and introducing the concentrated first solution into the second thermal recovery device, a second heat transfer means coupled to the second thermal recovery device and having an inlet coupled to a second source of thermal energy and an outlet coupled to the second thermal recovery device for directing thermal energy to the second thermal recovery device to cause solutes within the concentrated first solution in the second thermal recovery device to vaporize, a first outlet for removing the vaporized solutes from the second thermal recovery device, wherein the first outlet is in fluid communication with the first heat transfer means for providing the vaporized solutes as a source of thermal energy thereto for preheating the concentrated first solution, and a second outlet for removing a bottoms product from the second thermal recovery device. 
     In another aspect, the invention relates to a system for concentrating a feed stream and recovering draw solution solutes from an osmotically driven membrane system. The system includes one or more forward osmosis module(s), each comprising one or more membranes having first sides and second sides, the first side(s) of the membrane(s) fluidly coupled to a source of a first solution and the second side(s) of the membrane(s) fluidly coupled to a source of a concentrated draw solution, wherein the membrane(s) is configured for osmotically separating a solvent from the first solution, thereby forming a more concentrated first solution on the first side(s) of the membrane(s) and a dilute draw solution on the second side(s) of the membrane(s) and a separation system in fluid communication with the forward osmosis module(s) and configured for receiving the concentrated first solution and the dilute draw solution from the forward osmosis modules(s). The separation system includes a first separation apparatus and a second separation apparatus. The first separation apparatus is in fluid communication with the osmotically driven membrane system and includes a first thermal recovery device, a first heat transfer means in fluid communication with the forward osmosis module(s) for receiving the dilute draw solution and a first source of thermal energy for preheating the dilute draw solution, the first heat transfer means coupled to a first inlet of the first thermal recovery device for introducing the preheated dilute draw solution into the first thermal recovery device, a second heat transfer means coupled to the first thermal recovery device and having an inlet coupled to a second source of thermal energy and an outlet coupled to the first thermal recovery device for directing the second source of thermal energy to the first thermal recovery device to cause solutes within the dilute draw solution in the first thermal recovery device to vaporize, a first outlet for removing the vaporized dilute draw solution solutes from the first thermal recovery device, and a second outlet for removing a bottoms product from the first thermal recovery device, wherein the second outlet is in fluid communication with the first heat transfer means for providing the bottoms product as the first source of thermal energy thereto for preheating the dilute draw solution. 
     The second separation apparatus is in fluid communication with the osmotically driven membrane system and includes a second thermal recovery device, a heat transfer means in fluid communication with the forward osmosis module(s) for receiving the concentrated first solution and a source of thermal energy for heating the concentrated first solution, the heat transfer means coupled to a first inlet of the second thermal recovery device for introducing the heated concentrated first solution into the second thermal recovery device, where solutes within the concentrated first solution in the second thermal recovery device are vaporized, a first outlet for removing the vaporized solutes from the second thermal recovery device, and a second outlet for removing a concentrated brine from the second thermal recovery device. 
     In various embodiments of the foregoing aspects, the first and second thermal recovery devices can be distillation apparatus (e.g., column- or membrane-based). In some embodiments, the second thermal recovery device can be a crystallizer. In one or more embodiments, the systems can include one or more compressors in fluid communication with the first outlet of the first thermal recovery device and at least one of the heat transfer means of the first and/or second separation apparatus and/or one or more compressors in fluid communication with the first outlet of the second thermal recovery device and at least one of the heat transfer means of the first and/or second thermal recovery devices for providing at least a portion of the source of thermal energy thereto. Additionally, the systems can include at least one condenser having an inlet in fluid communication with at least one of the first outlet of the first thermal recovery device and/or the first outlet of the second thermal recovery device for receiving the bottoms product of the first and/or second thermal recovery device and an outlet in fluid communication with the forward osmosis module(s) for providing the concentrated draw solution thereto. The first and second separation apparatus can be configured for essentially parallel operation and the apparatus can themselves include one or more thermal recovery devices (e.g., distillation apparatus) configured in series, parallel, or combinations thereof. 
     In another aspect, the invention relates to a method of enhancing brine concentration and recovering draw solutes from an osmotically driven membrane system. The method can include the steps of providing a source of dilute draw solution from the osmotically driven membrane system, wherein the dilute draw solution comprises thermally removable draw solutes; providing a source of a concentrated feed solution from the osmotically driven membrane system, wherein the concentrated feed comprises a brine and thermally removable draw solutes that reverse fluxed through the membrane system; introducing at least a portion of the dilute draw solution to a first separation system; introducing a first source thermal energy to the first separation system; vaporizing dilute draw solution solutes out of the dilute draw solution; recovering the vaporized dilute draw solution solutes from the first separation system; recycling the draw solution solutes from the first separation system to the osmotically driven membrane system; introducing at least a portion of the concentrated feed solution to a second separation system; introducing a second source of thermal energy to the second separation system; vaporizing draw solutes and solvent out of the concentrated feed solution; recovering the vaporized draw solutes and solvent from the second separation system and discharging a further concentrated feed solution therefrom; and recycling the draw solutes and solvent from the second separation system to the osmotically driven membrane system. 
     In various embodiments, the method further includes directing the further concentrated feed solution to at least one of a filter press or a centrifuge. In addition, the further concentrated feed solution can be reintroduced from the at least one of a filter press or a centrifuge to the second separation apparatus. In some embodiments, the step of vaporizing the dilute draw solution solutes out of the first separation system can include exposing the dilute draw solution to the first source of thermal energy via a distillation apparatus and the step of vaporizing the draw solutes and solvent out of the second separation system can include exposing the concentrated feed solution to the second source of thermal energy via a crystallizer. In addition, the steps of recycling the dilute draw solution solutes from the first separation apparatus and recycling the draw solutes from the concentrated feed solution includes condensing the vapors prior to re-introduction of the solutes to the osmotically driven membrane system as a source of concentrated draw solution. 
     In another aspect, the invention relates to a system for concentrating a feed stream and recovering draw solution solutes from an osmotically driven membrane system. The system includes one or more forward osmosis modules, each having one or more membranes having first side(s) and second side(s), the first side(s) of the membrane(s) fluidly coupled to a source of a first solution and the second side(s) of the membrane(s) fluidly coupled to a source of a concentrated draw solution, wherein the membrane(s) is configured for osmotically separating a solvent from the first solution, thereby forming a more concentrated first solution on the first side(s) of the membrane(s) and a dilute draw solution on the second side(s) of the membrane(s), and a separation system in fluid communication with the forward osmosis module(s) and configured for receiving the concentrated first solution and the dilute draw solution from the forward osmosis module(s). The separation system includes a first separation apparatus in fluid communication with the osmotically driven membrane system and a second separation apparatus in fluid communication with the osmotically driven membrane system. The first separation apparatus includes a first thermal recovery device, a first heat transfer means in fluid communication with the forward osmosis unit and configured for receiving the dilute draw solution and coupled to a first inlet of the first thermal recovery device for preheating and introducing the dilute draw solution into the first thermal recovery device, a second heat transfer means coupled to the first thermal recovery device and having an inlet coupled to a first source of thermal energy and an outlet coupled to the first thermal recovery device for directing the first source of thermal energy to the first thermal recovery device to cause solutes within the dilute draw solution in the first thermal recovery device to vaporize, a first outlet for removing the vaporized draw solution solutes from the first thermal recovery device, and a second outlet for removing a heated bottoms product from the first thermal recovery device, wherein the second outlet is in fluid communication with the first heat transfer means for providing the heated bottoms product as a source of thermal energy thereto for preheating the dilute draw solution. 
     The second separation apparatus includes a second thermal recovery device, a first heat transfer means in fluid communication with the forward osmosis unit and configured for receiving the concentrated first solution and coupled to a first inlet of the second thermal recovery device for preheating and introducing the concentrated first solution into the second thermal recovery device, wherein the first outlet of the first separation apparatus is in fluid communication with the first heat transfer means of the second separation apparatus for providing the vaporized draw solution solutes as a source of thermal energy thereto for preheating the concentrated first solution, a second heat transfer means coupled to the second thermal recovery device and having an inlet coupled to a second source of thermal energy and an outlet coupled to the second thermal recovery device for directing the second source of thermal energy to the second thermal recovery device to cause solutes within the concentrated first solution in the second thermal recovery device to vaporize, a first outlet for removing the vaporized solutes from the second thermal recovery device, wherein the first outlet is in fluid communication with the first thermal recovery device for providing the vaporized solutes as an additional source of thermal energy thereto, and a second outlet for removing a bottoms product from the second thermal recovery device. 
     In various embodiments of the foregoing aspect, at least one of the first thermal recovery device or the second thermal recovery device can be a distillation apparatus, such as a distillation column or membrane distillation device. In some embodiments, the second thermal recovery device can be a crystallizer. Additionally, the system can further include at least one condenser having an inlet in fluid communication with at least one of the first outlet of the first thermal recovery device or the first outlet of the second thermal recovery device for receiving the tops product (i.e., vaporized draw solutes) of the first and/or second thermal recovery device (either directly or after exiting one of the heat transfer means) and an outlet in fluid communication with the forward osmosis module(s) for providing the concentrated draw solution thereto. 
     In another aspect, the invention relates to a system for concentrating a feed stream and recovering draw solution solutes from an osmotically driven membrane system. The system includes one or more forward osmosis modules, each having one or more membranes having first side(s) and second side(s), the first side(s) of the membrane(s) fluidly coupled to a source of a first solution and the second side(s) of the membrane(s) fluidly coupled to a source of a concentrated draw solution, wherein the membrane(s) is configured for osmotically separating a solvent from the first solution, thereby forming a more concentrated first solution on the first side(s) of the membrane(s) and a dilute draw solution on the second side(s) of the membrane(s), and a separation system in fluid communication with the forward osmosis module(s) and configured for receiving the concentrated first solution and the dilute draw solution from the forward osmosis module(s). The separation system includes a first separation apparatus in fluid communication with the osmotically driven membrane system for receiving the dilute draw solution and a second separation apparatus in fluid communication with the osmotically driven membrane system for receiving the concentrated first solution. The first separation apparatus includes a first thermal recovery device in fluid communication with the forward osmosis module(s) and configured for receiving the dilute draw solution, a first heat transfer means coupled to the first thermal recovery device and having an inlet coupled to a first source of thermal energy and an outlet coupled to the first thermal recovery device for directing the first source of thermal energy to the first thermal recovery device to cause solutes within the dilute draw solution in the first thermal recovery device to vaporize, a first outlet for removing the vaporized dilute draw solution solutes from the first thermal recovery device, a second outlet for removing a bottoms product from the first thermal recovery device, and a compressor in fluid communication with the first outlet of the thermal recovery device and the inlet of the first heat transfer means for providing at least a portion of the first source of thermal energy. The second separation apparatus includes a second thermal recovery device in fluid communication with the forward osmosis module(s) and configured for receiving the concentrated first solution, a heat transfer means coupled to a first inlet of the second thermal recovery device for introducing a second source of thermal energy to the second thermal recovery device to cause solutes within the second thermal recovery device to vaporize, a first outlet for removing the vaporized solutes from the second thermal recovery device and in fluid communication with an inlet on the first thermal recovery device to transfer the vaporized solutes thereto and provide an additional source of thermal energy to the first thermal recovery device, and a second outlet for removing a concentrated brine from the second thermal recovery device. In various embodiments, the second source of thermal energy is process or direct steam. 
     In another aspect, the invention relates to a method of enhancing brine concentration and recovering draw solutes from an osmotically driven membrane system, such as those previously described. The method includes the steps of providing a source of dilute draw solution from the osmotically driven membrane system, wherein the dilute draw solution comprises thermally removable draw solutes; providing a source of a concentrated feed solution from the osmotically driven membrane system, wherein the concentrated feed comprises a brine and thermally removable draw solutes that reverse fluxed through the membrane system; introducing at least a portion of the dilute draw solution to a first separation system; introducing a first source of thermal energy to the first separation system; vaporizing draw solution solutes out of the dilute draw solution; directing the vaporized draw solution solutes from the first separation system to a compressor; introducing the compressed vaporized draw solution solutes to the first separation system as at least a portion of the first source of thermal energy; introducing at least a portion of the concentrated feed solution to a second separation system; introducing a second source of thermal energy to the second separation system; vaporizing draw solutes and solvent out of the concentrated feed solution; directing the vaporized draw solutes and solvent from the second separation system to the first separation system to provide an additional source of thermal energy to the first separation system; and discharging a further concentrated feed solution from the second separation system. 
     In various embodiments of the foregoing aspect, the second source of thermal energy is process or direct steam. The method can also include the step of recycling the draw solution solutes from the first separation system to the osmotically driven membrane system. In various embodiments, the step of vaporizing the dilute draw solution solutes out of the first separation system can include exposing the dilute draw solution to the first source of thermal energy via a distillation apparatus, the step of vaporizing the draw solutes and solvent out of the second separation system can include exposing the concentrated feed solution to the second source of thermal energy via a distillation apparatus, and/or the step of vaporizing the draw solutes and solvent out of the second separation system can include exposing the concentrated feed solution to the second source of thermal energy via a crystallizer. 
     These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention and are not intended as a definition of the limits of the invention. For purposes of clarity, not every component may be labeled in every drawing. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  is a schematic representation of an exemplary osmotically driven membrane system/process using a solute recovery system in accordance with one or more embodiments of the invention; 
         FIG. 2  is a schematic representation of one embodiment of a draw solution recovery system in accordance with one or more embodiments of the invention; 
         FIGS. 3A-3D  are a schematic representation of osmotically driven membrane systems and alternative draw solution recovery systems in accordance with one or more embodiments of the invention; 
         FIG. 4  is a schematic representation of an alternative osmotically driven membrane system for enhanced brine concentration and draw solute recovery in accordance with one or more embodiments of the invention; 
         FIG. 5  is a schematic representation of another alternative osmotically driven membrane system for enhanced brine concentration and draw solute recovery in accordance with one or more embodiments of the invention; 
         FIG. 6  is a schematic representation of yet another alternative osmotically driven membrane system for enhanced brine concentration and draw solute recovery in accordance with one or more embodiments of the invention; and 
         FIG. 7  is a schematic representation of an osmotically driven membrane system and another alternative system for enhanced draw solute recovery in accordance with one or more embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the invention may be used in any osmotically driven membrane process, such as FO, PRO, OD, DOC, etc. An osmotically driven membrane process for extracting a solvent from a solution generally involves exposing the solution to a first surface of a forward osmosis membrane. In some embodiments, the first solution (known as a process or feed solution) may be seawater, brackish water, wastewater, contaminated water, a process stream, or other aqueous solution. In at least one embodiment, the solvent is water; however, other embodiments may use non-aqueous solvents. A second solution (known as a draw solution) with an increased concentration of solute(s) relative to that of the first solution is exposed to a second, opposed surface of the forward osmosis membrane. Solvent, for example water, may then be drawn from the first solution through the forward osmosis membrane and into the second solution generating a solvent-enriched solution via forward osmosis. The solvent-enriched solution, also referred to as a dilute draw solution, may be collected at a first outlet and undergo a further separation process. In some embodiments, purified water may be produced as a product from the solvent-enriched solution. A second product stream, i.e., the depleted or concentrated first solution, may be collected at a second outlet for discharge or further treatment. The concentrated first solution may contain one or more target compounds that it may be desirable to concentrate or otherwise isolate for downstream use. 
       FIG. 1  depicts one exemplary osmotically driven membrane system/process  10  utilizing a draw solute recovery system  22  in accordance with one or more embodiments of the invention. As shown in  FIG. 1 , the system/process  10  includes a forward osmosis module  12 , such as those incorporated by reference herein, in fluid communication with a feed solution source or stream  14  and a draw solution source or stream  16 . The draw solution source  16  can include, for example, a saline stream, such as sea water, or another solution as described herein that can act as an osmotic agent to dewater the feed source  14  by osmosis through a forward osmosis membrane within the module  12 . The module  12  outputs a stream of concentrated solution  18  from the feed stream  14  that can be further processed. The module  12  also outputs a dilute draw solution  20  that can be further processed via the recovery system  22 , as described herein, where draw solutes and a target solvent can be recovered. In accordance with one or more embodiments of the invention, the draw solutes are recovered for reuse. 
     The forward osmosis membranes may generally be semi-permeable, for example, allowing the passage of a solvent such as water, but excluding dissolved solutes therein, such as those disclosed herein. Many types of semi-permeable membranes are suitable for this purpose provided that they are capable of allowing the passage of the solvent, while blocking the passage of the solutes and not reacting with the solutes in the solution. The membrane can have a variety of configurations, including thin films, hollow fiber, spiral wound, monofilaments, and disk tubes. There are numerous well-known, commercially available semi-permeable membranes that are characterized by having pores small enough to allow water to pass while screening out solute molecules, such as, for example, sodium chloride and their ionic molecular species such as chloride. Such semi-permeable membranes can be made of organic or inorganic materials, as long as the material selected is compatible with the particular draw solution used. 
     Generally, the material selected for use as the semi-permeable membrane should be able to withstand various process conditions to which the membrane may be subjected. For example, it may be desirable that the membrane be able to withstand elevated temperatures, such as those associated with sterilization or other high temperature processes. In some embodiments, a forward osmosis membrane module may be operated at a temperature in the range of about 0 degrees Celsius to about 100 degrees Celsius. In some embodiments, process temperatures may range from about 40 degrees Celsius to about 50 degrees Celsius. Likewise, it may be desirable for the membrane to be able to maintain integrity under various pH conditions. For example, one or more solutions in the membrane environment, such as the draw solution, may be more or less acidic or basic. In some embodiments, a forward osmosis membrane module may be operated at a pH level of between about 2 and about 11. In certain embodiments, the pH level may be about 7 to about 10. In at least one embodiment, the membrane may be an asymmetric membrane, such as with an active layer on a first surface, and a supporting layer on a second surface. One example of a suitable membrane is disclosed in U.S. Pat. No. 8,181,794, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     Generally, the various draw solutions discussed herein can be regenerated by recovering and recycling the draw solutes using various combinations of distillation apparatus, filters, condensers, crystallizers, compressors, and related components, as shown in  FIGS. 2-7 .  FIG. 2  depicts one embodiment of a draw solute recovery/separation system  422  as can be part of, for example, a membrane brine concentrator. As shown, the system  422  incorporates two separation apparatus; the dilute draw solution (DDS) stripping column  460  and the concentrate or brine stripping column  462 . The DDS column feed includes the dilute draw solution  420 , which includes the water recovered from an osmotically driven membrane system. The DDS column  460  eventually outputs the product solvent. The concentrate column feed includes at least the concentrated brine  418  from the osmotically driven membrane system. These columns are in fluid communication with one or more compressors  470 ,  475 . Mechanical vapor compression (MVC) is incorporated with the distillation columns to recover and re-use heat. Membrane distillation devices are also contemplated and considered within the scope of the invention. 
     The vapor  464  exiting the top of the concentrate column  462  is fed to the DDS column  460  in order to reduce the overall energy requirements of the DDS column  460 . In some embodiments, the vapor  464  is first compressed (via compressor  475 ) to the pressure of the DDS column  460  so that the two columns  460 ,  462  can be operated at different pressures. In some embodiments, this vapor  464  includes additional draw solutes that may have reverse fluxed through the membrane of the osmotically driven membrane system and additional product solvent that did not pass through the membrane. The vapor  466  exiting the top of the DDS column  460  is compressed and exchanged with the DDS column reboiler  468 . By compressing the DDS column vapor  466 , the vapor condensing temperature is raised to a temperature that is higher than the DDS column reboiler  468  and, therefore, the latent heat of the vapor can be utilized as the supply heat to the column reboiler  468 . Typically this vapor  466  will include the draw solutes in gaseous form. The pressure of the DDS column vapor  466  is controlled by a pressure control valve  477  and compressed to the appropriate pressure using a 3 stage rotary lobe blower system or a screw compressor  470 . Different compressors/blowers and various numbers of stages may be used to suit a particular application. In one embodiment, with approximately 650 kW of blower input power, the system is able to transfer approximately 6,600 kW of thermal energy. In an alternative embodiment, the heat from each stage is transferred to the column reboiler. 
     Leaving the DDS column reboiler heat exchanger  469 , the compressed partially condensed DDS column vapor  466 ′ is exchanged with the concentrate column reboiler  472 . In this exemplary embodiment, the concentrate column  462  is run under a vacuum (approximately 0.1-0.9 atm absolute pressure) in order to reduce the boiling temperature of the reboiler loop water supplying steam to the column in order to exchange the remaining latent heat of the DDS column vapor  466 ′ with the concentrate column reboiler  472 . Leaving the concentrate column reboiler heat exchanger  473 , the mostly condensed DDS column vapor  466 ″ is fully condensed in a final condenser  474  utilizing cooling water  476 , thereby forming the concentrated draw solution  416 . Alternatively, the columns  460 ,  462  can be operated at the same or substantially equivalent pressures and the vapor stream  466  split and sent to each reboiler separately, typically without the use of a compressor. In this embodiment, the partially/mostly condensed DDS columns vapors  466 ′,  466 ″ exiting the reboilers  469 ,  473  can be combined and sent to the final condenser  474  to form the concentrated draw solution  416 . 
     In some embodiments, for example where the vapor exiting the column contains essentially no liquid portion, there is nothing for the draw solutes (e.g., ammonia and carbon dioxide in gaseous form) to be compressed into. The solutes could transition from the gaseous phase directly to the solid phase (e.g., deposition or desublimation), which could potentially render the recovery system  422  inoperable. Where that may be the case, the system  422  can include a by-pass line  461  for directing a portion of the dilute draw solution  420  to the compression operation, thereby providing a liquid for absorbing the gaseous solutes. In some embodiments, the introduction of the dilute draw solution may expedite the absorption of CO 2  (e.g., as may be present when using a NH 3 —CO 2  draw solution). As shown, the dilute draw solution  420  can be combined with the vapor  466  before or after any particular compressor to suit a particular application (e.g., a single compressor or series of compressors, the nature of the draw solutes, etc.). Additionally, the dilute draw solution  420 , or other suitable liquid, can also be used to provide the liquid injection at the identified points  441   a ,  441   b  to reduce heat. The by-pass line  461  can include any number and combination of valves and sensors as necessary to suit a particular application. 
       FIG. 3A  depicts an osmotically driven membrane system  500  including an alternative arrangement for recovering draw solutes. As shown in  FIG. 3 , the system  500  includes one or more forward osmosis membrane modules  512  (similar to those described above) in fluid communication with a draw solute recovery/separation system  522 . Each forward osmosis module can include one or more forward osmosis membranes  513  at least partially creating first and second chambers  512   a ,  512   b  for receiving the various streams. In an embodiment with a plurality of forward osmosis membrane modules  512 , the modules can be arranged in series, parallel, or a combination of both. The module(s)  512  is also in fluid communication with a feed source or stream  514  and a concentrated draw solution source or stream  516  and outputs a concentrated feed stream  518  (e.g., brine) and a dilute draw solution  520 . All or a portion of the concentrated feed stream  518  and the dilute draw solution  520  are directed to the separation system  522 . 
     Generally, the dilute draw solution  520  is directed to a first separation apparatus  560 , such as a thermal recovery device (e.g., a distillation column or membrane distillation apparatus); however, other mechanical separation means (e.g., filtration or chemical manipulation) can be used in combination with or in place of the thermal recovery device. The concentrated feed  518  is directed to a second separation apparatus  562 , similar to  560 , for further concentration. The two separation apparatus  560 ,  562  and related componentry (e.g., valves, sensors, controls, plumbing etc.) make up the basic draw solute recovery/separation system  522 . 
     The separation system  522  is similar to that described in  FIG. 2 , but is modified for alternative thermal integration and direct heat application, for example, via steam or a hot fluid. In some cases, this arrangement may actually have an increased cost associated with the use of direct steam; however, the use of direct steam, as opposed to electricity, can result in an overall energy savings. Generally, earlier designs required a large amount of cooling water at a final condenser for recycling the concentrated draw solution, as the draw solute vapors going to the final condenser are coming from the tops of both separation apparatus  560 ,  562  in the case of thermal recovery (e.g., distillation columns). In the depicted embodiment, the vapors  564 ,  566  from the column tops are used to preheat the associated dilute draw solution  520  and brine  518  that are being introduced to the separation apparatus  560 ,  562 , as described in greater detail below. 
     This arrangement has at least two advantages: As the vapors  564 ,  566  exchange with pre-heaters  543   a ,  543   b , the draw solution vapors  564 ,  566  are at least partially condensed, thereby reducing the load on the final condenser  574 ; which also reduces the overall steam requirements for the separation apparatus  560 ,  562 . For example, at the brine separation apparatus  562 , when exchanging with the high energy brine vapor stream  564 , the preheating partially vaporizes the brine feed  518 ′ reducing the load on the apparatus reboiler  573  and reducing steam requirements. The brine  544  being discharged is typically not separately cooled, which is an advantage for further concentrating the brine  544  (e.g., a higher temperature brine is more favorable for a crystallizer process or other ZLD process). With respect to the product water  552  exiting the apparatus  560 , this water is typically not cooled, unless there is a specific product water discharge temperature required, thereby providing additional savings. If there is a need for cooling the product water, the savings achieved on the duty of the condenser  574  exceeds any additional cooling requirements for the product water  552  by, for example, a minimum of 20% on the overall cooling load in a particular embodiment. In embodiments where the product water  552  requires cooling or other processing, the product water  552  can be directed to an optional, secondary apparatus/process  558  that can include cooling and/or filtration (e.g., RO polishing) as needed. In the case of RO polishing or similar process, the retentate can be directed back to the feed  518 . 
     Referring back to  FIG. 3A , the overall system  500  includes one or more means  545  for introducing an additive (e.g., anti-scalants, acid, catalyst, etc.) to one or more streams (e.g., the feed stream  514 ) and/or system operations. Typically, the means  545  will include a valve and porting arrangement and may also include any necessary reservoirs, sensors, and/or controls for manual or automatic operation thereof.  FIG. 3A  also depicts an optional valve  577  for by-passing all or a portion of the dilute draw solution  520  from the membrane module(s)  512 . Generally, a portion of the dilute draw solution  520  may by-pass the separation apparatus  560  as necessary to maintain a particular concentration level of draw solutes in the concentrated draw solution  516  being returned to the membrane module(s)  512 . Additionally, where the afore-mentioned portion of the dilute draw solution  520  by-passes the preheater  543   a , this cooler dilute draw solution  520  may assist in further lowering the cooling load on the final condenser  574 . Generally, the cooling fluid  576  provided to the final condenser  574  may be an independent source of cooling water or could be another stream within the system  500  that requires heating. In some embodiments, the feed stream  514  may be used as the cooling fluid to provide preheating to the feed  514 , in which case, the exiting cooling fluid  576 ′ is directed to the membrane module(s)  512  for introduction thereto. 
     During operation, the preheated dilute draw solution  520 ′ exiting the preheater  543   a  is introduced to the separation apparatus  560  while thermal energy (e.g., steam)  528   a  is introduced to the apparatus  560  via its reboiler  568 . The exiting thermal energy (e.g., the condensed steam)  528   a ′ can be discarded or recycled elsewhere in the system. The volatilized draw solutes (and some solvent)  566  form the tops product of the apparatus  560  and are directed through the preheater  543   a  to preheat the dilute draw solution  520  and at least partially condense the draw solutes  566 ′, which in turn are directed to the final condenser  574  before reintroduction to the membrane module(s)  512  as concentrated draw solution  516 . In one or more embodiments, the partially condensed draw solutes  566 ′ are combined with a portion of the dilute draw solution  520  and/or an additive (e.g., make-up draw solutes, anti-scalants, pH adjusters, etc.) as necessary to maintain a desired draw solute concentration and/or draw solution  516  composition. The bottoms product of the apparatus  560  is the previously described product solvent (e.g., water)  552 , which may be further processed and output as a final product solvent  552 ′. 
     Similarly, the concentrated feed  518  is directed to the second separation apparatus  562  and its associated preheater  543   b . The preheated brine  518 ′ enters the apparatus  562 , while thermal energy  528   b  is introduced to the apparatus  562  via its reboiler  573 . The exiting thermal energy  528   b ′ can be discarded or recycled elsewhere in the system  500 . Any draw solutes that reverse fluxed through the membrane(s) will be volatilized, along with additional solvent within the concentrated feed  518 ′, to form the tops product  564  of the apparatus  562 , which is directed through the preheater  543   b  to preheat the concentrated feed  518  and at least partially condense any draw solutes  564 ′ contained therein. These draw solutes and solvent are in turn directed to the final condenser  574  before reintroduction to the membrane module(s)  512  as concentrated draw solution  516 . In one or more embodiments, the partially condensed draw solutes  564 ′ are combined with one or more of the partially condensed draw solutes  566 ′ from separation apparatus  560 , a portion of the by-passed dilute draw solution  520 , or an additive (e.g., make-up draw solutes). The bottoms product  544  of the apparatus  560  is a further concentrated version of the concentrated feed  518 ′, which can be discarded or sent for further processing, such as to a crystallizer. 
       FIG. 3B  depicts an alternative embodiment of the system of  FIG. 3A . Generally, the system of  FIG. 3B  is configured to use different streams for preheating the various streams to be processed. This arrangement, as discussed in greater detail below, provides a cooled product water for further processing and reduces the thermal load on the reboilers and final condenser. Generally, this alternative arrangement reduces the utility consumption of both steam and cooling water for the direct heat application for draw solute recovery. As shown in  FIG. 3B , the vaporized draw solutes and solvent  564  from the second separation apparatus  562  are directed to the first separation apparatus  560  for use as a source of thermal energy therein to vaporize the draw solutes out of the dilute draw solution  520 . These vaporized draw solutes  566  are now directed to the preheater  543   b  for preheating the concentrated first solution  518  prior to it being introduced to the second separation apparatus  562 . The partially condensed draw solutes  566 ′ are then directed to the final condenser  574 , as previously described with respect to  FIG. 3A , and then returned to the osmotically driven membrane system  512  for use as the concentrated draw solution  516 . The now heated bottoms product  552  (e.g., the product solvent) of the first separation apparatus  560  is directed to preheater  543   a  to preheat the dilute draw solution  520  prior to it being introduced to the first separation apparatus  560 . The cooled product  552 ′ can be directed to a further process  558  as described above with respect to  FIG. 3A  and then collected as a final product  552 ″ 
       FIG. 3C  depicts an alternative embodiment of the systems of  FIGS. 3A and 3B . Generally, the system  500  is similar to those described with respect to  FIGS. 3A and 3B , except the heated brine (i.e., bottoms product)  544  from the second separation apparatus  562  is used to preheat the incoming concentrated feed  518 . The cooled brine  544 ′ can be discarded or sent for further processing as described herein. Tops product (i.e., vaporized draw solutes)  566  of the first separation apparatus  560  can be directed to the final condenser  574  as shown and/or a portion of the product  566  can be used for preheating the dilute draw solution, for example with a second preheater in series with the first preheater  543   a  or in place of the product  552  as the heating medium. 
       FIG. 3D  depicts yet another alternative embodiment of the systems of  FIGS. 3A-3C . Generally, the system  500  is similar to those described with respect to  FIGS. 3A-5C , with a portion of the heated brine (i.e., bottoms product)  544  from the second separation apparatus  562  is used to preheat the incoming concentrated feed  518  and a portion recirculated within the second separation apparatus  562 . The apportionment of the heated brine  544  can be accomplished with a metering/multi-directional valve as necessary. The cooled brine  544 ′ can be discarded or sent for further processing as described herein. As shown in  FIG. 3D , the tops product (i.e., vaporized draw solutes)  564  of the second separation apparatus  562  are directed to a compressor  575  to create a vacuum on the second separation apparatus  562  and lower the temperature for vaporizing the solutes out of the brine  518 . The compressed vapors  564 ′ are directed to the first separation apparatus  560  as previously described with respect to other embodiments of the separation system  522 . The first separation apparatus  560  generally operates as previously described, with the tops product (i.e., vaporized draw solutes)  566  being directed to the final condenser  574  as shown and/or a portion of the product  566  can be used for preheating the dilute draw solution. The heated bottoms product (i.e., product water)  552  can also be apportioned with one portion being used for preheating the dilute draw solution  520  and another portion being recirculated through the apparatus  560  via a metering valve  577   a . In one embodiment, the thermal energy  528   a  used for heating the first separation apparatus is direct steam with the condensate (i.e., only partially condensed steam) being directed to the reboiler  573  of the second separation apparatus  562 . 
       FIG. 4  depicts an alternative osmotically driven membrane system  600  configured for enhancing brine concentration in addition to recovering draw solutes. As shown in  FIG. 4 , the system  600  includes one or more forward osmosis membrane modules  612  (similar to those described above) in fluid communication with a draw solute recovery/separation system  622 . In an embodiment with a plurality of forward osmosis membrane modules  612 , the modules can be arranged in series, parallel, or a combination of both. The module(s)  612  is also in fluid communication with a feed source or stream  614  and a concentrated draw solution source or stream  616  and outputs a concentrated feed stream  618  (e.g., brine) and a dilute draw solution  620 . The draw solute recovery system  622  generally includes one or more separation apparatus in fluid communication with the concentrated feed stream  618  and the dilute draw solution  620  and further includes any necessary valves, heat exchangers, sensors, controls, plumbing, etc. 
     Generally, the dilute draw solution  620  is directed to a first separation apparatus  660 , such as a thermal recovery device (e.g., one or more distillation columns and/or membrane distillation apparatus). In some embodiments, mechanical separation means (e.g., filtration or chemical manipulation) can be used in place of or in addition to the thermal recovery device. The concentrated feed  618  is directed to a second separation apparatus  662 , such as a crystallizer or other thermal separation device for further concentration. In addition, the system  600  can include one or more means  645  for introducing an additive (e.g., anti-scalants, acid, catalyst, seeds, etc.) to one or more streams (e.g., the feed stream  614 ) and/or system operations. Similar to those described above, the means  645  can include a valve and porting arrangement and any necessary reservoirs, sensors, and/or controls for manual or automatic operation thereof. 
     As shown in  FIG. 4 , the first separation apparatus  660  receives the dilute draw solution  620  and includes a reboiler  668 , as commonly known in the art, configured for receiving a source of thermal energy  628   a  (e.g., steam) and outputting a depleted thermal energy stream  628   a ′ (e.g., condensed steam) that can be discarded or otherwise recycled within the system  600  (e.g., added to the feed stream  614  for purification or used for additional heating). As also shown, the dilute draw solution  620  passes through a first preheater  643   a  before entering the first separation apparatus  660 , which outputs a tops product (typically vaporized draw solutes and a portion of solvent)  666  that can be recycled as re-concentrated draw solution  616  (described below) and a bottoms product (typically heated solvent)  652 . In some cases, the bottoms product  652  can be recovered as the product solvent or sent for further processing (described below). In one or more embodiments, all or a portion of the product solvent  652  can be used to preheat the incoming dilute draw solution  620  via the preheater  643   a . The cooled product solvent  652 ′ can be used as is, discarded, or sent for further processing. For example, all or a portion of the product solvent  652 ,  652 ′ can be directed to an additional system/process  658 , such as filtration (e.g., reverse osmosis or nanofiltration) or additional thermal separation. In one or more embodiments, the additional system  658  is a polishing RO unit that produces a more purified product solvent  654  and a retentate  656  that can be recycled to the feed stream  618  for further processing. In some embodiments, the tops product  666  can be used for preheating the dilute draw solution  620 , similar to what is described with respect to  FIG. 3A . 
     As shown in  FIG. 4 , all or a portion of the concentrated feed  618  can be directed to the crystallizer (e.g., a forced circulation crystallizer)  662 . Typically, the concentrated feed  618  is going to include a brine having a concentration of about 75,000 to 300,000 total dissolved solids (TDS), preferably about 200,000 TDS or greater. Generally, the greater the concentration, the more efficient the brine concentration process. Typical osmotically driven membrane systems cannot produce a concentrated feed high enough and will require additional thermal separation/concentration process to be performed on the concentrated feed before it can be sent to a crystallizer or other ZLD process. The second separation apparatus operating on a more concentrated brine eliminates the need for additional equipment to bring the concentrated output of the osmotically driven membrane system to saturation, while also recovering additional draw solutes. 
     Generally, the concentrated feed  618  passes through a second preheater  643   b  prior to entering the second separation apparatus  662 , in this case one or more crystallizers. Similar to that described above, the second preheater  643   b  receives a source of thermal energy  628   b  and outputs a depleted thermal energy source  628   b ′ that can be discarded or recycled within the system  600 . Typically, certain draw solutes will have reverse fluxed through the membrane module  612  and will be contained within the concentrated feed  618 . These draw solutes and additional solvent (collectively product  664 ) are vaporized within the crystallizer  662  and outputted therefrom, where they can be combined with the product  666  from the first separation apparatus  660  and recovered. 
     The combined products  664 ,  666  are directed to a final condenser  674  to fully absorb the draw solutes into the concentrated draw solution  616  and lower the temperature of the re-concentrated draw solution  616  as necessary for reintroduction into the membrane module(s)  612 . Generally, the cooling fluid  676  provided to the final condenser  674  may be an independent source of cooling water or could be another stream within the system  600  that requires heating, such as the feed stream  614 . Where the feed stream  614  is preheated via the condenser  674 , the exiting cooling fluid (i.e., preheated feed stream)  676 ′ will be directed back to the membrane module(s)  612  for introduction thereto. 
     The crystallizer  662  also outputs a further concentrated brine slurry  644  that can be discarded or sent for further processing. Typically, the brine  644  is directed to additional dewatering equipment (not shown), such as that described in PCT Publication No. WO2015/157031, the entire disclosure of which is hereby incorporated by reference herein. In one or more embodiments, the brine  644  is sent to a filter press or centrifuge with the resulting mother liquor  644 ′ being directed back to the crystallizer  662  for further processing. In some embodiments, all or a portion of the brine slurry  644  can be recirculated back into the crystallizer  662  (e.g., small portion of the slurry  644  is recirculated while a larger portion is directed to the filter press or centrifuge). In some embodiments, the crystallizer circuit also includes introduction means  645   b  for introducing seeds or other additives to the concentrated feed  618  and/or brine  644 ′ being directed to the crystallizer  662  to, for example, promote crystallization. 
       FIG. 4  depicted a draw solute recovery and brine concentration system/process  622  using direct steam introduction. The system  700  depicted in  FIG. 5  is similar to the system  600  of  FIG. 4 , but incorporates mechanical vapor recompression similar to that described above with respect to  FIG. 2 , which also includes the use of boiler start-up steam similar to that shown in  FIG. 2 . As shown in  FIG. 5 , the system  700  includes one or more forward osmosis membrane modules  712  in fluid communication with a draw solute recovery/separation system  722  that includes first and second separation apparatus  760 ,  762  similar to those described above. The membrane modules  712  are also in fluid communication with a feed source or stream  714  and a concentrated draw solution source or stream  716  and output a concentrated feed stream  718  and a dilute draw solution  720 , where the dilute draw solution  720  and the concentrated feed stream  718  are introduced to the first and second separation apparatus  760 ,  762  as described above with respect to  FIG. 4 . 
     As shown in  FIG. 5 , the separation apparatus  760 ,  762  of the draw solute recovery system  722  each include one or more compressors  770 ,  775 , respectively, for recovering and reusing the heat of the thermal energy introduced to the respective apparatus  760 ,  762 . The vapor  766  exiting the first separation apparatus  760  is directed to the compressor(s)  770 , with the compressed vapors  766 ′ exiting the compressor  770  and being directed to the reboiler  768  to reduce the overall thermal energy requirement of the first separation apparatus  760 . As described with respect to  FIG. 2 , by compressing the vapor  766 , the vapor condensing temperature is raised to a temperature higher than the reboiler  768  such that the latent heat of the compressed vapor  766 ′ can be used as the thermal energy supply to the separation apparatus  760 . The number and capacity of the compressor(s) will be selected to suit a particular application (e.g., the required differential temperature at the reboiler, the separation apparatus operating pressure, the compressor&#39;s compression ratio, flow rate, and ambient conditions). The partially condensed vapor  766 ″ leaving the reboiler  768  can be directed to a final condenser  774 , similar to that described with respect to  FIG. 4 . 
     Further, the vapor  764  exiting the crystallizer/second separation apparatus  762  is also directed to one or more compressors  775 , with the compressed vapors  764 ′ exiting the compressor(s)  775  and being directed to the second preheater  743   b  to reduce the overall thermal energy requirement of the second separation apparatus  762 . As described above, the increased vapor condensing temperature allows the latent heat of the compressed vapor  764 ′ to be used as the thermal energy supply to the separation apparatus  762 . The number and capacity of the compressor(s) for the second separation apparatus  762  will also be selected to suit a particular application. The partially condensed vapor  764 ″ leaving the preheater  743   b  can be discarded or combined with vapor  766 ″ and directed to the final condenser  774 , similar to that described with respect to  FIG. 4 . The rest of the system  700  operates similar to that described with respect to  FIG. 4 . 
       FIG. 6  depicts an alternative system  800  to the system  700  of  FIG. 5 , but with an integrated mechanical vapor recompression subsystem, as opposed to the two separate subsystems depicted in  FIG. 5 . Generally, the system  800  and various components are the same as those described with respect to  FIGS. 6 and 7 , except as follows. As shown in  FIG. 6 , the heated vapor  864  exiting the second separation apparatus  862  (also a crystallizer in this embodiment) is directed to one or more compressors  875  and then to the first separation apparatus  860  as its thermal energy input. Similar to that described above, the tops product  866  of the first separation apparatus  860  is directed to one or more compressors  870  and then directed to the first separation apparatus&#39; reboiler  868 , further reducing the overall thermal energy requirement of the first separation apparatus  860 . 
     In contrast to the system  700  of  FIG. 5 , the partially condensed vapor  866 ″ is not directed to the final condenser  874 , but instead first directed to the second preheater  843   b  to preheat the concentrated feed  818  directed to the second separation apparatus  862 . The further condensed vapor  866 ′″ is then directed to the final condenser  874  for completing the recovery and recycling of the concentrated draw solution  816 . The rest of the system  800  operates similar to that described with respect to  FIGS. 4 and 5 . 
     In some of the previously described embodiments, the draw solute recovery process, and in some cases the additional brine concentration process, is supplied with thermal energy via either direct steam or through the use of MVC. In some cases, the use of MVC has a high capital cost (CapEx) and process complexity associated, at least in part, to the need for large and/or multiple compressors and multiple points of partial condensation in the system. Additionally, the second separation apparatus (typically the distillation apparatus for further brine concentration) is required to run under vacuum to utilize any partially condensed draw solute vapor stream to power the reboiler. A direct steam system tends to have lower capital cost and be a simpler process; however, direct steam has a high operation cost (OpEx). For example, in some facilities (e.g., the power sector), process steam is nearly twice as expensive as electricity and in those cases the latent heat of the draw solute vapors is not integrated back into the system. Another advantage of steam over MVC is that when concentrating the brine from the osmotically driven membrane system in the brine concentration apparatus (i.e., second separation apparatus), the use of steam eliminates the need to go to the high compression ratios necessary in MVC systems to overcome any boiling point elevation issues in the brine concentration apparatus, which can be more expensive and complex, and in some cases it is just not possible to achieve the necessary boiling points. As such, there is a need for a hybrid system that utilizes both direct process steam and electricity/MVC to minimize overall CapEx and OpEx expenses for recovering draw solutes and concentrating the brine output from the osmotically driven membrane system, while providing flexibility in utilizing the best available resources. 
       FIG. 7  depicts an example of the afore-mentioned hybrid system  900  discussed above, with or without the use of preheating. Generally, the system  900  for recovering draw solutes and further concentrating the brine can be a hybrid approach incorporating any of the various features of the foregoing systems described herein. In various embodiments, the second separation apparatus  962  is operated using direct steam for the thermal energy input  928 , while utilizing MVC and the tops vapors from the second apparatus  962  as the thermal energy for the first separation apparatus  960 . This arrangement of combining process steam and electricity to separate the various streams results in about half of the energy used and a reduction in CapEx where a single compressor can be used. This arrangement also lowers the discharge pressure required on the compressor(s), which gives greater flexibility in the selection of compressors. 
     More specifically, the system  900  as shown in  FIG. 7  includes an osmotically driven membrane system  912 , similar to those previously described, in fluid communication with a source of feed solution  914  and concentrated draw solution  916  and configured for receiving same. The osmotically driven membrane system  912  is also in fluid communication with a draw solute recovery system  922  that includes two or more separation apparatus  960 ,  962  configured for receiving a dilute draw solution  920  and a concentrated feed solution  918  outputted from the membrane system  912 . 
     As shown, all or at least a portion of the concentrated feed solution  918  is directed to the second separation apparatus  962 , similar to those previously described, while a source of thermal energy  928  is directed to a heat transfer means  973  (e.g., reboiler) associated with the second separation apparatus  962 . The thermal energy  928  heats the concentrated first solution within the second separation apparatus causing draw solute vapors and solvent within the solution  918  to vaporize. Direct steam is used as the thermal energy  928  for the second separation apparatus  962  with vaporized draw solutes and solvent  964  exiting the apparatus  962  then entering the first separation apparatus  960  at a specified stage 
     As further shown in  FIG. 7 , at least a portion of the dilute draw solution  920  is directed to the first separation apparatus  960  along with the vaporized draw solutes and solvent  964  that are used to supplement the thermal requirements of the first separation apparatus reboiler  968 . The thermal energy introduced to the first separation apparatus  960  vaporizes the draw solutes within the apparatus. The draw solute vapors  966  exiting the first separation apparatus  960  are directed to one or more compressors  970 , where they are mechanically compressed and then directed to the reboiler  968  to provide additional thermal energy to the first separation apparatus  960 . The vapors that condense within the reboiler are essentially re-concentrated draw solution  916  that can be directed back to the osmotically driven membrane system  912  or further processed (e.g., additional condensing and/or concentration) before being used as the concentrated draw solution  916 . 
     In accordance with one or more embodiments, the devices, systems and methods described herein may generally include a controller for adjusting or regulating at least one operating parameter of the device or a component of the systems, such as, but not limited to, actuating valves and pumps, as well as adjusting a property or characteristic of one or more fluid flow streams through an osmotically driven membrane module, or other module in a particular system. A controller may be in electronic communication with at least one sensor configured to detect at least one operational parameter of the system, such as a concentration, flow rate, pH level, or temperature. The controller may be generally configured to generate a control signal to adjust one or more operational parameters in response to a signal generated by a sensor. For example, the controller can be configured to receive a representation of a condition, property, or state of any stream, component, or subsystem of the osmotically driven membrane systems and associated pre- and post-treatment systems. The controller typically includes an algorithm that facilitates generation of at least one output signal that is typically based on one or more of any of the representation and a target or desired value, such as a set point. In accordance with one or more particular aspects, the controller can be configured to receive a representation of any measured property of any stream, and generate a control, drive or output signal to any of the system components, to reduce any deviation of the measured property from a target value. 
     In accordance with one or more embodiments, process control systems and methods may monitor various concentration levels, such as may be based on detected parameters including pH and conductivity. Process stream flow rates and tank levels may also be controlled. Temperature and pressure may be monitored. Membrane leaks may be detected using ion selective probes, pH meters, tank levels, and stream flow rates. Leaks may also be detected by pressurizing a draw solution side of a membrane with gas and using ultrasonic detectors and/or visual observation of leaks at a feed water side. Other operational parameters and maintenance issues may be monitored. Various process efficiencies may be monitored, such as by measuring product water flow rate and quality, heat flow and electrical energy consumption. Cleaning protocols for biological fouling mitigation may be controlled such as by measuring flux decline as determined by flow rates of feed and draw solutions at specific points in a membrane system. A sensor on a brine stream may indicate when treatment is needed, such as with distillation, ion exchange, breakpoint chlorination or like protocols. This may be done with pH, ion selective probes, Fourier Transform Infrared Spectrometry (FTIR), or other means of sensing draw solute concentrations. A draw solution condition may be monitored and tracked for makeup addition and/or replacement of solutes. Likewise, product water quality may be monitored by conventional means or with a probe such as an ammonium or ammonia probe. FTIR may be implemented to detect species present providing information which may be useful to, for example, ensure proper plant operation, and for identifying behavior such as membrane ion exchange effects. 
     Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the systems and techniques of the invention are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments of the invention. It is, therefore, to be understood that the embodiments described herein are presented by way of example only and that, within the scope of the appended claims and equivalents thereto; the invention may be practiced otherwise than as specifically described. 
     Moreover, it should also be appreciated that the invention is directed to each feature, system, subsystem, or technique described herein and any combination of two or more features, systems, subsystems, or techniques described herein and any combination of two or more features, systems, subsystems, and/or methods, if such features, systems, subsystems, and techniques are not mutually inconsistent, is considered to be within the scope of the invention as embodied in the claims. Further, acts, elements, and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.