Return Flow System for Ion Concentration Polarization (ICP)

Abstract

A device for purifying and/or concentrating a first water stream containing ionic impurities includes a first and second ion exchange membrane and a first porous membrane. The ion exchange membranes have the same charge, and a channel into which the first water stream can be directed is defined between the first and second ion exchange membranes. The channel has an inlet end and a return flow end and comprises a first and second outlet. The inlet and at least the first outlet are located on the inlet end of the channel and are separated by the first porous membrane that traverses the length of the channel between the ion exchange membranes and terminates at a return flow zone that is at least partially closed. At least part of the first water stream flows through the first porous membrane, joining a first return flow stream.

What is claimed is: 
     
         1 . A device for purifying and/or concentrating a first water stream containing charged contaminants, comprising:
 a first ion exchange membrane;   a second ion exchange membrane, wherein the ion exchange membranes are characterized by the same charge, wherein a channel into which the first water stream can be directed is defined between the first ion exchange membrane and the second ion exchange membrane, wherein the channel is further characterized as having an inlet end and a return flow end, wherein the inlet end is where an inlet is located, and wherein the return flow end is downstream from the inlet end when the first water stream is directed into the channel through the inlet; and   a first porous membrane, wherein the channel further comprises a first outlet and a second outlet, wherein the inlet and at least the first outlet are located on the inlet end of the channel and are separated by the first porous membrane that traverses the length of the channel between the ion exchange membranes and terminates at a return flow zone, wherein the return flow zone is a section of the channel at the return flow end, and wherein the return flow end is at least partially closed,   wherein the ion exchange membranes and the first porous membrane are configured such that directing the first water stream into the inlet of the channel and applying an electric field across the channel forms an ion depletion zone comprising a purified water stream and an ion enrichment zone comprising a concentrated ion aqueous stream, wherein at least part of the first water stream enters the return flow zone and forms a first return flow stream that flows to the opposing side of the first porous membrane and the first return flow stream flows in the direction of the first outlet, and at least part of the first water stream, including the water and the charged contaminants, adjacent to the first porous membrane flows through the first porous membrane joining the first return flow stream, and wherein the purified water stream is the stream directed to the first or the second outlet, and the concentrated-charged-contaminant aqueous stream is the stream directed to the other of the first and the second outlet.   
     
     
         2 . The device of  claim 1 , wherein the ion exchange membranes are cation exchange membranes. 
     
     
         3 . The device of  claim 1 , wherein the ion exchange membranes are anion exchange membranes. 
     
     
         4 . The device of  claim 1 , wherein the first porous membrane is a non-ionic porous membrane. 
     
     
         5 . The device of  claim 1 , further comprising a second porous membrane that traverses the length of the channel between the ion exchange membranes and terminates at the return flow zone, wherein the second outlet is located on the inlet end of the channel, wherein the inlet is located between the first outlet and the second outlet, wherein the inlet and the second outlet are separated by the second porous membrane, wherein the return flow end is fully closed, wherein each porous membrane has a cathodic side and an anodic side, wherein the first outlet is located on the cathodic side of the first porous membrane, wherein the second outlet is located on the anodic side of the second porous membrane, wherein the ion exchange membranes and the porous membranes are configured, when the first water stream is directed into the inlet of the channel and an electric field is applied across the channel, to direct the purified water stream to the first outlet, to direct the concentrated ion aqueous stream to the second outlet, to direct at least part of the first water stream into the return flow zone, to form a second return flow stream that flows to the opposing side of the second porous membrane and flows in the direction of the second outlet, and to direct at least part of the first water stream adjacent to the second porous membrane through the second porous membrane joining the second return flow stream. 
     
     
         6 . The device of  claim 5 , wherein the second porous membrane is a non-ionic porous membrane. 
     
     
         7 . The device of  claim 1 , wherein the device comprises a plurality of the channels. 
     
     
         8 . The device of  claim 1 , further comprising an electrode and a ground, each located external and parallel to the channel and configured to create the electric field across the channel. 
     
     
         9 . The device of  claim 8 , wherein the electrode forms a second channel with the first ion exchange membrane and the ground forms a third channel with the second ion exchange membrane. 
     
     
         10 . The device of  claim 9 , wherein the second and third channels are filled with an electrolyte solution. 
     
     
         11 . The device of  claim 10 , wherein the electrolyte solution is the first water stream. 
     
     
         12 . The device of  claim 1 , wherein the ion exchange membranes are cation exchange membranes, wherein the first porous membrane has a cathodic side and an anodic side, and wherein the first outlet is located on the cathodic side of the first porous membrane, the inlet is located on the anodic side of the first porous membrane, and the cation exchange membranes and the first porous membrane are configured to direct the purified water stream to the first outlet. 
     
     
         13 . The device of  claim 12 , wherein the second outlet is located at the return flow end. 
     
     
         14 . The device of  claim 13 , wherein the second outlet is located on the anodic side of the first porous membrane. 
     
     
         15 . The device of  claim 1 , wherein the ion exchange membranes are cation exchange membranes, wherein the first porous membrane has a cathodic side and an anodic side, and wherein the first outlet is located on the anodic side of the first porous membrane, the inlet is located on the cathodic side of the first porous membrane, and the cation exchange membranes and the first porous membrane are configured to direct the purified water stream is directed to the first outlet. 
     
     
         16 . The device of  claim 15 , wherein the second outlet is located at the return flow end. 
     
     
         17 . The device of  claim 16 , wherein the second outlet is located on the cathodic side of the first porous membrane. 
     
     
         18 . The device of  claim 1 , wherein the second outlet is located at the inlet end of the channel, wherein the inlet is located between the first outlet and the second outlet, and wherein the inlet and the second outlet are separated by a second porous membrane that traverses the length of the channel between the ion exchange membranes and terminates at the return flow zone, and wherein the return flow end is fully closed. 
     
     
         19 . The device of  claim 18 , wherein the ion exchange membranes are cation exchange membranes. 
     
     
         20 . The device of  claim 18 , wherein the ion exchange membranes are anion exchange membranes. 
     
     
         21 . A method of purifying and/or concentrating a first water stream containing impurities by electrodialysis, comprising the steps of:
 directing the first water stream into a first inlet of a first channel and into a second inlet of a second channel of an electrodialysis unit as a first feed stream and a second feed stream, respectively, wherein each feed stream comprises water and charged contaminants,   wherein the electrodialysis unit has an anodic side and a cathodic side and comprises at least three stacked ion exchange membranes (IEMs), wherein a first IEM and a third IEM have the same charge polarity, and a second IEM has a charge polarity opposite to that of the first and third IEMs, and further wherein the second IEM is arranged between the first and the third IEMs,   wherein the first channel is defined, at least in part, by the first and the second IEMs, wherein the second channel is defined, at least in part, by the second and third IEMs, and wherein the first channel is on the anodic side of the electrodialysis unit, and wherein the second channel is on the cathodic side of the electrodialysis unit, wherein the first channel and the second channel are each further characterized as having an inlet end and a return flow end, wherein the inlet end of the first channel and of the second channel is where the first inlet and the second inlet, respectively, are located, and wherein the return flow end of the first channel and of the second channel is downstream from the respective inlet end when the first water stream is directed into the first and second channels through the first and second inlets, respectively,   wherein the first channel and the second channel each further comprise two outlets on the inlet end of the channels, wherein the first inlet is located between the two outlets of the first channel and the second inlet is located between the outlets of the second channel,   wherein the first inlet is separated from the two outlets of the first channel by two porous membranes, respectively, that traverse the length of the first channel between the first and second IEMs, and terminate at a return flow zone of the first channel, wherein the return flow zone is a section of the channel at the return flow end, and wherein each return flow end is fully closed, and   wherein the second inlet is separated from the two outlets of the second channel by two porous membranes, respectively, that traverse the length of the second channel between the second and third IEMs, and terminates at the return flow zone of the second channel, wherein the return flow zone is a section of the channel at the return flow end, and wherein each return flow end is fully closed; and   applying an electric field across the first and the second channels, wherein the electric field causes formation of two purified water streams in the first or the second channel and formation of two concentrated-charged-contaminant aqueous streams in the other of the first and the second channels;   entering at least part of the first feed stream into the return flow zone of the first channel and forming two return flow streams that flow to opposing sides of the porous membranes; flowing the return flow streams in the direction of the outlets; and flowing at least part of the first feed stream, including the water and the charged contaminants, adjacent to the porous membranes through the porous membranes, joining the return flow streams;   entering at least part of the second feed stream into the return flow zone of the second channel and forming two return flow streams that flow to the opposing sides of the porous membranes; flowing the return flow streams in the direction of the outlets, and flowing at least part of the second feed stream adjacent to the porous membranes through the porous membranes, joining the return flow streams,   wherein the purified water stream is the stream directed to the outlets of the first or the second channel, and wherein the concentrated-charged-contaminant aqueous stream is the stream directed to the outlets of the other of the first and the second channel; and   collecting at least one of the purified water stream and the concentrated-charged-contaminant aqueous stream from the outlets of at least one of the first and second channels.