Osmotic separation systems and methods

Abstract

Separation processes using osmotically driven membrane systems are disclosed generally involving the extraction of solvent from a first solution to concentrate solute by using a second concentrated solution to draw the solvent from the first solution across a semi-permeable membrane.

What is claimed is: 
     
         1 . A system for osmotic extraction of a solvent from a first solution, comprising:
 a forward osmosis unit comprising:
 a first chamber having an inlet fluidly coupled to a source of the first solution; 
 a second chamber having an inlet fluidly coupled to a source of a concentrated draw solution; and 
 a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating the solvent from the first solution, thereby forming a second solution in the first chamber and a dilute draw solution in the second chamber; 
   a reverse osmosis unit fluidly coupled to an outlet of the second chamber of the forward osmosis unit and comprising:
 a first chamber in fluid communication with the second chamber of the forward osmosis unit and configured for receiving the dilute draw solution under pressure; 
 a semi-permeable membrane coupled to the first chamber; and 
 a second chamber coupled to the semi-permeable membrane and configured for receiving a solvent fluxed through the membrane, thereby leaving a less dilute draw solution in the first chamber of the reverse osmosis unit; and 
   a separation system in fluid communication with the forward osmosis unit and the reverse osmosis unit and configured to separate the dilute or less dilute draw solution into the concentrated draw solution and a solvent stream, the separation system comprising:
 an inlet fluidly coupled to an outlet of the first chamber of the reverse osmosis unit for receiving the less dilute draw solution therefrom; and 
 an outlet fluidly coupled to the second chamber of the forward osmosis unit for introducing the concentrated draw solution to the forward osmosis unit. 
   
     
     
         2 . The system of  claim 1  further comprising a pressure exchanger disposed between and in fluid communication with the second chamber of the forward osmosis unit and the first chamber of the reverse osmosis unit, where the pressure exchanger is configured to increase the pressure of the dilute draw solution introduced to the first chamber of the reverse osmosis unit. 
     
     
         3 . The system of  claim 1  further comprising a by-pass system in fluid communication with the first chamber of the reverse osmosis unit and the second chamber of the forward osmosis unit for directing the less dilute draw solution back to the forward osmosis unit. 
     
     
         4 . The system of  claim 1  further comprising means for reducing an osmotic pressure of the dilute draw solution. 
     
     
         5 . The system of  claim 4 , wherein the means for reducing the osmotic pressure of the dilute draw solution comprises at least one of chemical addition, chemical subtraction, reduction-oxidation, reactive extraction, filtration, precipitation, or exposure to an energy signal. 
     
     
         6 . The system of  claim 4  further comprising at least one treatment system in fluid communication with at least one of the forward osmosis unit, the reverse osmosis unit, or the separation system to reverse the osmotic pressure reduction of the dilute draw solution. 
     
     
         7 . The system of  claim 4 , wherein the means for reducing the osmotic pressure of the dilute draw solution is in fluid communication with the first chamber of the reverse osmosis unit. 
     
     
         8 . A system for osmotic extraction of a solvent from a first solution, comprising:
 a first forward osmosis unit comprising:
 a first chamber having an inlet fluidly coupled to a source of the first solution; 
 a second chamber having an inlet fluidly coupled to a source of a concentrated first draw solution; and 
 a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating the solvent from the first solution, thereby forming a second solution in the first chamber and a dilute first draw solution in the second chamber; 
   a second forward osmosis unit in fluid communication with the first forward osmosis unit and comprising:
 a first chamber having an inlet fluidly coupled to an outlet of the second chamber of the first forward osmosis unit and configured for receiving the dilute first draw solution from the first forward osmosis unit; 
 a second chamber having an inlet fluidly coupled to a source of a concentrated second draw solution; and 
 a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating the solvent from the dilute first draw solution, thereby forming the concentrated first draw solution in the first chamber and a dilute second draw solution in the second chamber; and 
   a separation system in fluid communication with the second forward osmosis unit and configured to separate the dilute second draw solution into the concentrated second draw solution and a solvent stream, the separation system comprising:
 an inlet fluidly coupled to an outlet of the second chamber of the second forward osmosis unit for receiving the dilute second draw solution therefrom; and 
 an outlet fluidly coupled to the second chamber of the forward osmosis unit for introducing the concentrated second draw solution to the second forward osmosis unit. 
   
     
     
         9 . The system of  claim 8 , wherein at least one of the first or second forward osmosis units is submerged. 
     
     
         10 . The system of  claim 8  further comprising a stripper in fluid communication with the second chamber of the first forward osmosis unit and the first chamber of the second forward osmosis unit and configured to further concentrate the first draw solution. 
     
     
         11 . The system of  claim 8  further comprising a reverse osmosis unit in fluid communication with the second chamber of the first forward osmosis unit and the first chamber of the second forward osmosis unit and configured to remove solvent from the dilute first draw solution. 
     
     
         12 . A system for osmotic extraction of a solvent from a first solution, comprising:
 a reverse osmosis unit comprising:
 a first chamber in fluid communication with a source of the first solution; 
 a semi-permeable membrane coupled to the first chamber; and 
 a second chamber coupled to the semi-permeable membrane and configured for receiving a first portion of the solvent fluxed through the membrane, thereby leaving a concentrated first solution in the first chamber of the reverse osmosis unit; and 
   a first forward osmosis unit fluidly coupled to the reverse osmosis unit and comprising:
 a first chamber having an inlet in fluid communication with the first chamber of the reverse osmosis unit and configured for receiving the concentrated first solution; 
 a second chamber having an inlet fluidly coupled to a source of a concentrated draw solution; and 
 a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating a second portion of the solvent from the concentrated first solution, thereby forming a further concentrated first solution in the first chamber and a dilute draw solution in the second chamber; 
   a separation system in fluid communication with the first forward osmosis unit and configured to separate the dilute draw solution into the concentrated draw solution and a solvent stream, the separation system comprising:
 an inlet fluidly coupled to an outlet of the second chamber of the first forward osmosis unit for receiving the dilute draw solution therefrom; and 
 an outlet fluidly coupled to the second chamber of the first forward osmosis unit for introducing the concentrated draw solution to the first forward osmosis unit; and 
   a second forward osmosis unit in fluid communication with the first forward osmosis unit and comprising:
 a first chamber having an inlet fluidly coupled to an outlet of the first chamber of the first forward osmosis unit and configured for receiving the further concentrated first solution from the first forward osmosis unit; 
 a second chamber having an inlet fluidly connected to a source of a feed solution; and 
 a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating a solvent from the feed solution, thereby diluting the concentrated first solution in the first chamber and concentrating the feed solution in the second chamber. 
   
     
     
         13 . The system of  claim 12 , wherein the second forward osmosis unit is a pressure retarded osmosis unit. 
     
     
         14 . The system of  claim 13  further comprising a turbine in fluid communication with the first chamber of the second forward osmosis unit and configured for receiving the diluted first solution. 
     
     
         15 . The system of  claim 12  further comprising a by-pass system in fluid communication with the reverse osmosis unit and the second forward osmosis unit and configured to return the diluted first solution from the outlet of the first chamber of the second forward osmosis unit to the inlet of the first chamber of the reverse osmosis unit. 
     
     
         16 . The system of  claim 12 , wherein the feed solution comprises a wastewater effluent stream. 
     
     
         17 . A system for osmotic extraction of a solvent from a first solution, comprising:
 a selective membrane unit for conditioning the first solution, the unit comprising:
 a first chamber having an inlet fluidly coupled to a source of the first solution; 
 a second chamber having an inlet fluidly coupled to a source of a second solution; and 
 a selective membrane separating the first chamber from the second chamber and configured to selectively allow certain ions within at least the first solution to pass from the first solution to the second solution; 
   a forward osmosis unit in fluid communication with the selective membrane unit and comprising:
 a first chamber having an inlet fluidly coupled to at least one of the source of the first solution or an outlet of the first chamber of the selective membrane unit for receiving the conditioned first solution; 
 a second chamber having an inlet fluidly coupled to a source of a concentrated draw solution; and 
 a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating the solvent from the first solution, thereby forming the source of the second solution in the first chamber and a dilute draw solution in the second chamber; 
   a separation system in fluid communication with the forward osmosis unit and configured to separate the dilute draw solution into the concentrated draw solution and a solvent stream, the separation system comprising:
 an inlet fluidly coupled to an outlet of the second chamber of the forward osmosis unit for receiving the dilute draw solution therefrom; and 
 an outlet fluidly coupled to the second chamber of the forward osmosis unit for introducing the concentrated draw solution to the forward osmosis unit; and 
   a valve arrangement in fluid communication with the first chamber of the forward osmosis unit, the second chamber of the selective membrane unit, and an alternative source of the second solution, the valve arrangement configured to direct the second solution from either the first chamber of the forward osmosis unit or the alternative source to the second chamber of the selective membrane unit.   
     
     
         18 . The system of  claim 17  further comprising a second valve arrangement in fluid communication with the source of the first solution, the selective membrane unit, and the forward osmosis unit, the second valve arrangement configured for directing the first solution to either the selective membrane unit or the forward osmosis unit or directing the conditioned first solution to the forward osmosis unit. 
     
     
         19 . The system of  claim 17  further comprising at least one treatment system in fluid communication with at least one of the selective membrane unit, the forward osmosis unit, or the separation system. 
     
     
         20 . The system of  claim 17 , where in the selective membrane is a cation selective membrane.