DRAW SOLUTIONS AND DRAW SOLUTE RECOVERY FOR OSMOTICALLY DRIVEN MEMBRANE PROCESSES

1 . A draw solution for an osmotically driven membrane system, the draw solution comprising:

an aqueous solvent having a pH in the range of 2-11; and

a draw solute comprising a cation source including at least one volatile gas-based cation and an anion source including at least one volatile gas-based anion, wherein the anion source further comprises a viscosity modifier.

2 . The draw solution of claim 1 , wherein the cation source comprises an alkyl amine having a boiling point less than water and the viscosity modifier comprises hydrogen sulfide.

3 . The draw solution of claim 1 , wherein the cation source comprises a blend of cations.

4 . The draw solution of claim 3 , wherein the blend of cations comprises one or more of an alkyl amine, ammonia, and sodium hydroxide.

5 . The draw solution of claim 1 , wherein the anion source comprises a blend of anions.

6 . The draw solution of claim 5 , wherein the blend of anions comprises one or more of hydrogen sulfide, carbon dioxide, hydrogen chloride, sulfur dioxide, and sulfur trioxide.

7 . The draw solution of claim 1 , wherein the viscosity modifier comprises at least one of ethanol, polyoxyalkylene, sodium xylene sulfonate, polyacrylics, sodium lauryl sulfonate, ethers, sulfides, and combinations thereof.

8 . A draw solution recovery method for a draw solution comprising one or more thiol based draw solutes, the method comprising the steps of:

introducing a dilute draw solution comprising a solvent and at least one thiol based draw solute to an oxidizing environment;

stripping hydrogen ions from the draw solute;

passing the hydrogen ions across a barrier;

bonding the remaining solute via disulfide polymerization;

directing the solvent and polymerized solutes to a filtration module;

separating at least a portion of the solvent from the polymerized solute to produce a product solvent;

directing the polymerized solute and any remaining solvent to a reducing environment;

depolymerizing the polymerized solute; and

reintroducing the hydrogen ions to the depolymerized draw solute to reform the at least one thiol based draw solute and create a concentrated draw solution.

9 . The method of claim 8 , further comprising the step of directing the concentrated draw solution to an osmotically driven membrane system.

10 . The method of claim 8 , wherein the dilute draw solution is introduced from an osmotically driven membrane system.

11 . The method of claim 8 , wherein the filtration module comprises a reverse osmosis module.

12 . The method of claim 8 , wherein the oxidizing environment and the reducing environment are part of a redox cell separated by a hydrogen permeable barrier.

13 . An osmotically driven membrane system comprising:

a forward osmosis membrane module comprising one or more membranes;

a source of a 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, wherein the draw solution comprises an aqueous solvent having a pH in the range of 2-11 and a draw solute comprising a cation source including at least one volatile gas-based cation and an anion source including at least one volatile gas-based anion, wherein the anion source further comprises a viscosity modifier; and

a draw solution recovery system in fluid communication with the forward osmosis membrane module.

14 . The system of claim 13 , wherein the draw solution recovery system comprises:

at least one redox cell in fluid communication with the opposite side of the one or more membranes and configured for receiving a dilute draw solution from the forward osmosis membrane module, the at least one redox cell comprising an oxidizing environment and a reducing environment separated by a hydrogen permeable barrier; and

a filtration module in fluid communication with the at least one redox cell.

15 . The system of claim 14 further comprising an energy source in communication with the at least one redox cell.