U.S. patent application number 15/918658 was filed with the patent office on 2018-07-19 for membraneless seawater desalination.
The applicant listed for this patent is Board of Regents, The University of Texas System. Invention is credited to Richard A. Crooks, Kyle N. Knust, Robbyn K. Perdue.
Application Number | 20180201525 15/918658 |
Document ID | / |
Family ID | 50979248 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180201525 |
Kind Code |
A1 |
Crooks; Richard A. ; et
al. |
July 19, 2018 |
MEMBRANELESS SEAWATER DESALINATION
Abstract
Disclosed are microfluidic devices and systems for the
desalination of water. The devices and systems can include an
electrode configured to generate an electric field gradient in
proximity to an intersection formed by the divergence of two
microfluidic channels from an inlet channel. Under an applied bias
and in the presence of a pressure driven flow of saltwater, the
electric field gradient can preferentially direct ions in saltwater
into one of the diverging microfluidic channels, while desalted
water flows into second diverging channel. Also provided are
methods of using the devices and systems described herein to
decrease the salinity of water.
Inventors: |
Crooks; Richard A.; (Austin,
TX) ; Knust; Kyle N.; (Austin, TX) ; Perdue;
Robbyn K.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Board of Regents, The University of Texas System |
Austin |
TX |
US |
|
|
Family ID: |
50979248 |
Appl. No.: |
15/918658 |
Filed: |
March 12, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14136541 |
Dec 20, 2013 |
9932251 |
|
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15918658 |
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61740780 |
Dec 21, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F 2103/08 20130101;
C02F 1/4604 20130101; C02F 2001/46128 20130101; C02F 1/4696
20130101 |
International
Class: |
C02F 1/46 20060101
C02F001/46 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with Government Support under
Agreement DE-FG02-06ER15758 awarded by the U.S. Department of
Energy, and Contract EP-D-12-026 awarded by the U.S. Environmental
Protection Agency. The Government has certain rights in the
invention.
Claims
1. A microfluidic device comprising (a) a desalination unit
comprising an inlet channel fluidly connected to a dilute outlet
channel and a concentrated outlet channel, wherein the dilute
outlet channel and the concentrated outlet channel diverge from the
inlet channel at an intersection; and (b) an electrode in
electrochemical contact with the desalination unit; wherein the
electrode is configured to generate an electric field gradient in
proximity to the intersection where the dilute outlet channel and
the concentrated outlet channel diverge from the inlet channel.
2. The device of claim 1, wherein the electrode comprises an
anode.
3. The device of claim 1, wherein the inlet channel has a width of
from about 150 microns to about 25 microns.
4. The device of claim 1, wherein the dilute outlet channel, the
concentrated outlet channel, or both the dilute outlet channel and
the concentrated outlet channel have a width of from about 80
microns to about 10 microns.
5. The device of claim 1, wherein the sum of the area of a
cross-section of dilute outlet channel and the area of a
cross-section of the concentrated outlet channel is substantially
equal to the area of a cross-section of the inlet channel.
6. The device of claim 1, wherein the angle formed between the
dilute outlet channel and the concentrated outlet channel at the
intersection is 60 degrees or less.
7. The device of claim 1, further comprising an auxiliary channel
fluidly isolated from the desalination unit.
8. The device of claim 7, wherein the electrode comprises a bipolar
electrode electrochemically connecting the desalination unit and
the auxiliary channel.
9. The device of claim 8, wherein the bipolar electrode comprises
an anode in electrochemical contact with the desalination unit and
a cathode in electrochemical contact with the auxiliary
channel.
10. The device of claim 7, wherein the auxiliary channel comprises
a second desalination unit comprising an inlet channel fluidly
connected to a dilute outlet channel and a concentrated outlet
channel, wherein the dilute outlet channel and the concentrated
outlet channel diverge from the inlet channel at an intersection;
and an electrode in electrochemical contact with the second
desalination unit; wherein the electrode is configured to generate
an electric field gradient in proximity to the intersection where
the dilute outlet channel and the concentrated outlet channel
diverge from the inlet channel.
11. A water purification system comprising a plurality of devices
defined by claim 1, wherein the inlet channels of the plurality of
devices are fluidly connected to a water inlet, and the dilute
outlet channels of the plurality of devices are fluidly connected
to a water outlet.
12. A method of decreasing the salinity of water comprising (a)
providing a flow of saltwater through the inlet channel of the
device defined by claim 1; (b) applying a potential bias to
generate an electric field gradient that influences the flow of
ions through the desalination unit of the device defined by claim
1; and (c) collecting water from the dilute outlet channel of the
device defined by claim 1; wherein the water collected from the
dilute outlet channel of the device defined by claim 1 has a lower
electrical conductivity than the saltwater.
13. The method of claim 14, wherein the saltwater comprises
seawater.
14. The method of claim 14, wherein the saltwater comprises
brackish water.
15. The method of claim 14, wherein the conductivity of the water
collected does not exceed about 80% of the conductivity of the
saltwater.
16. The method of claim 14, wherein the water collected has a
conductivity of less than about 0.1 S/m.
17. The method of claim 14, wherein the water collected has a
conductivity of from about 0.05 S/m to about 0.005 S/m
18. The method of claim 14, wherein the water collected has a
conductivity of from about 0.005 S/m to about 5.5.times.10.sup.-6
S/m.
19. The method of claim 14, wherein potential bias applied ranges
from about 1 volt to about 10 volts.
20. The method of claim 14, wherein the rate of flow of the
saltwater through the desalination unit of the device defined by
claim 1 ranges from about 0.01 to about 1 microliter per
minute.
21. A method of decreasing the salinity of water comprising (a)
flowing saltwater through a desalination unit comprising an inlet
channel fluidly connected to a dilute outlet channel and a
concentrated outlet channel, wherein the dilute outlet channel and
concentrated outlet channel diverge from the inlet channel at an
intersection; and (b) performing a faradaic reaction at an
electrode positioned in proximity to the intersection to generate
an electric field gradient; wherein the electric field gradient
directs ions in the saltwater away from the dilute outlet channel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional
Application No. 61/740,780, filed Dec. 21, 2012, which is hereby
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0003] This application relates generally to devices, systems, and
methods for the desalination of water.
BACKGROUND
[0004] The global demand for freshwater is growing rapidly. Many
conventional sources of freshwater, including lakes, rivers, and
aquifers, are rapidly becoming depleted. As a consequence,
freshwater is becoming a limited resource in many regions. In fact,
the United Nations estimates two-thirds of the world's population
could be living in water stressed regions by 2025.
[0005] Currently, approximately 97% of the world's water supply is
present as seawater. Desalination--the process by which salinated
water (e.g., seawater) is converted to fresh water--offers the
potential to provide dependable supplies of freshwater suitable for
human consumption or irrigation. Unfortunately, existing
desalination processes, including distillation and reverse osmosis,
require both large amounts of energy and specialized, expensive
infrastructure. As a consequence, desalination is currently
expensive compared to most conventional sources of water, and often
prohibitively expensive in developing regions of the world.
Therefore, only a small fraction of total human water use is
currently satisfied by desalination. More energy efficient methods
for water desalination offer the potential to address the
increasing demands for freshwater, particularly in water stressed
regions.
SUMMARY
[0006] Disclosed are microfluidic devices and systems for the
desalination of water.
[0007] Microfluidic devices for the desalination of water can
comprise a desalination unit. The desalination unit can comprise an
inlet channel fluidly connected to a dilute outlet channel and a
concentrated outlet channel. The dilute outlet channel and the
concentrated outlet channel can diverge from the inlet channel at
an intersection. The desalination unit can further comprise an
electrode in electrochemical contact with the desalination unit.
The electrode can be configured to generate an electric field
gradient in proximity to the intersection where dilute outlet
channel and concentrated outlet channel diverge from the inlet
channel. Under an applied bias and in the presence of a flow of
saltwater, the electric field gradient can preferentially direct
ions in the saltwater into concentrated outlet channel, while
desalted water flows into the dilute outlet channel.
[0008] In some embodiments, the microfluidic device can further
include an auxiliary channel fluidly isolated from the desalination
unit. The auxiliary channel can be electrochemically connected to
the desalination unit via a bipolar electrode. In these cases, the
bipolar electrode can be configured to be in electrochemical
contact with both the desalination unit and the auxiliary channel.
Under an applied bias across the auxiliary channel and the
desalination unit and in the presence of a flow of saltwater, the
electric field gradient can preferentially direct ions in the
saltwater into concentrated outlet channel of the desalination
unit, while desalted water flows into the dilute outlet
channel.
[0009] In some embodiments, the auxiliary channel comprises a
desalination unit. In these embodiments, the microfluidic device
can comprise two desalination units, which can be of identical or
different structure. The first desalination unit can be
electrochemically connected to the second desalination unit by a
bipolar electrode. Under an applied bias across the first
desalination unit and the second desalination unit and in the
presence of a pressure driven flow of saltwater, the electric field
gradient can preferentially direct ions in the saltwater into
concentrated outlet channels of the first and second desalination
units, while desalted water flows into the dilute outlet channels
of the first and second desalination units.
[0010] A plurality of the microfluidic devices described herein can
be combined to form a water purification system. The system can
comprise a plurality of the devices described herein arranged in
parallel or fluidly connected in series. The systems can also
comprise a plurality of devices both arranged in parallel and
fluidly connected in series. For example, the device can include a
first pair of devices fluidly connected in series which are
arranged in parallel with a second pair of devices fluidly
connected in series. In such systems, the plurality of devices can
be fabricated in a single plane (i.e., as a 2-dimensional system)
or in three dimensions.
[0011] Also provided are methods of using the devices and systems
described herein to decrease the salinity of water.
DESCRIPTION OF DRAWINGS
[0012] FIG. 1A is a schematic drawing illustrating a microfluidic
device for the desalination of water.
[0013] FIG. 1B is a schematic drawing illustrating an enlarged
portion of the microfluidic device shown in FIG. 1A.
[0014] FIG. 1C is a schematic drawing illustrating a microfluidic
device for the desalination of water in combination with a power
supply configured to apply a potential bias across the desalination
unit.
[0015] FIG. 2 is a schematic drawing illustrating a microfluidic
device for the desalination of water. The device includes a
desalination unit and an auxiliary channel electrochemically
connected by a bipolar electrode.
[0016] FIG. 3 is a schematic drawing illustrating a microfluidic
device for the desalination of water. The device includes two
desalination units electrochemically connected by a bipolar
electrode.
[0017] FIG. 4 is a schematic drawing of a water purification system
for the desalination of water. The system includes multiple
desalination units configured to operate in parallel.
[0018] FIG. 5 is a schematic drawing of a water purification system
for the desalination of water. The system includes multiple
desalination units configured to operate in parallel.
[0019] FIG. 6 is a schematic drawing of a water purification system
for the desalination of water. The device includes multiple
desalination units configured to operate in series.
[0020] FIGS. 7A-7B are fluorescence micrographs illustrating the
flow of a solution of Ru(bpy).sup.2+ (a fluorescent cationic
tracer) in saltwater through the device illustrated in FIG. 2. FIG.
7A is a fluorescence micrograph of the device taken before
application of a potential bias. FIG. 7B is a fluorescence
micrograph of the device taken upon application of a potential
bias.
[0021] FIG. 8 is a fluorescence micrograph illustrating the flow of
a solution of Ru(bpy).sup.2+ (a fluorescent cationic tracer) in
Na.sub.2SO.sub.4 through the device illustrated in FIG. 2 upon
application of a potential bias.
[0022] FIG. 9 is a graph of total current flowing through the
device illustrated in FIG. 2 (i.sub.tot, plotted in nanoamperes) as
a function of time (in seconds) during operation.
DETAILED DESCRIPTION
[0023] Disclosed are microfluidic devices and systems for the
desalination of water.
[0024] Microfluidic devices for the desalination of water can
comprise a desalination unit. The desalination unit can comprise an
inlet channel fluidly connected to a dilute outlet channel and a
concentrated outlet channel. The dilute outlet channel and the
concentrated outlet channel can diverge from the inlet channel at
an intersection. The desalination unit can also comprise an
electrode in electrochemical contact with the desalination unit.
The electrode can be configured to generate an electric field
gradient in proximity to the intersection where dilute outlet
channel and concentrated outlet channel diverge from the inlet
channel.
[0025] An example device comprising a desalination unit (100) is
schematically illustrated in FIG. 1A. The desalination unit
includes an inlet channel (102) fluidly connected to a dilute
outlet channel (104) and a concentrated outlet channel (106). The
dilute outlet channel (104) and the concentrated outlet channel
(106) diverge from the inlet channel (102) at an intersection
(107). An electrode (108) is positioned in proximity to the
intersection (107). The electrode (108) is configured to form an
ion depletion zone (109) at and downstream of the electrode during
device operation, resulting in the formation of an electric field
gradient in proximity to the intersection. The example device
further includes a fluid reservoir (110) fluidly connected to the
upstream terminus of the inlet channel (102), a fluid reservoir
(114) fluidly connected to the downstream terminus of the dilute
outlet channel (104), and a fluid reservoir (112) fluidly connected
to the downstream terminus of the concentrated outlet channel
(106).
[0026] The dimensions of the microfluidic channels in the
desalination unit (100) (e.g., the inlet channel (102), the dilute
outlet channel (104), and the concentrated outlet channel (106))
can individually and/or in combination be selected in view of a
number of factors, including the size and position of the electrode
relative to the microfluidic channels in the desalination unit, the
desired device flow rate, salinity of the saltwater being treated
using the device, and the desired degree of salinity reduction.
[0027] In some instances, the dimensions of the inlet channel
(102), the dilute outlet channel (104), and the concentrated outlet
channel (106) are selected such that the sum of the area of a
cross-section of dilute outlet channel and the area of a
cross-section of the concentrated outlet channel is substantially
equal to the area of a cross-section of the inlet channel. In this
context, substantially equal can mean that the sum of the area of a
cross-section of dilute outlet channel and the area of a
cross-section of the concentrated outlet channel is with for
example, 15%, of the area of a cross-section of the inlet channel
(e.g., within 10% of the area of a cross-section of the inlet
channel, or within 5% of the area of a cross-section of the inlet
channel). In some embodiments, the dilute outlet channel, and the
concentrated outlet channel have substantially equivalent
cross-sectional dimensions, meaning that the height and width of
the dilute outlet channel are substantially equivalent (e.g.,
within 15%, within 10%, or within 5%) to the height and width of
the concentrated outlet channel.
[0028] The dimensions of the microfluidic channels in the
desalination unit (100) (e.g., the inlet channel (102), the dilute
outlet channel (104), and the concentrated outlet channel (106))
can be fabricated so as to have a variety of cross-sectional
shapes. In some embodiments, the microfluidic channels in the
desalination unit (e.g., the inlet channel, the dilute outlet
channel, and the concentrated outlet channel) have a substantially
square or rectangular cross-sectional shape.
[0029] In some embodiments, the inlet channel (102) has a width of
about 1000 microns or less (e.g., about 900 microns or less, about
800 microns or less, about 750 microns or less, about 700 microns
or less, about 600 microns or less, about 500 microns or less,
about 400 microns or less, about 300 microns or less, about 250
microns or less, about 200 microns or less, about 150 microns or
less, about 100 microns or less, about 75 microns or less, or about
50 microns or less). In some embodiments, the inlet channel (102)
has a width of at least about 1 micron (e.g., at least about 5
microns, at least about 10 microns, at least about 15 microns, at
least about 20 microns, at least about 25 microns, at least about
50 microns, at least about 75 microns, at least about 100 microns,
at least about 150 microns, at least about 200 microns, at least
about 250 microns, at least about 300 microns, at least about 400
microns, at least about 500 microns, at least about 600 microns, at
least about 700 microns, at least about 750 microns, at least about
800 microns, at least about 900 microns, or at least about 1000
microns).
[0030] The inlet channel (102) can have a width that ranges from
any of the minimum dimensions to any of the maximum dimensions
described above. For example, the inlet channel (102) can have a
width that ranges from about 1000 microns to about 1 micron (e.g.,
from about 750 microns to about 5 microns, from about 500 microns
to about 10 microns, from about 250 microns to about 20 microns, or
from about 150 microns to about 25 microns).
[0031] In some embodiments, the inlet channel (102) has a height of
about 50 microns or less (e.g., about 45 microns or less, about 40
microns or less, about 35 microns or less, about 30 microns or
less, about 25 microns or less, about 20 microns or less, about 15
microns or less, about 10 microns or less, about 9 microns or less,
about 8 microns or less, about 7.5 microns or less, about 7 microns
or less, about 6 microns or less, about 5 microns or less, about 4
microns or less, about 3 microns or less, about 2.5 microns or
less, or about 2 microns or less). In some embodiments, the inlet
channel (102) has a height of at least about 1 micron (e.g., at
least about 2 microns, at least about 2.5 microns, at least about 3
microns, at least about 4 microns, at least about 5 microns, at
least about 6 microns, at least about 7 microns, at least about 7.5
microns, at least about 8 microns, at least about 9 microns, at
least about 10 microns, at least about 15 microns, at least about
20 microns, at least about 25 microns, at least about 30 microns,
at least about 35 microns, at least about 40 microns, or at least
about 45 microns).
[0032] The inlet channel (102) can have a height that ranges from
any of the minimum dimensions to any of the maximum dimensions
described above. For example, the inlet channel (102) can have a
height that ranges from about 50 microns to about 1 micron (e.g.,
from about 45 microns to about 1 micron, from about 40 microns to
about 1 micron, from about 35 microns to about 1 micron, from about
30 microns to about 1 micron, from about 25 microns to about 1
micron, or from about 20 microns to about 1 micron).
[0033] In some embodiments, the dilute outlet channel (104) has a
width of about 500 microns or less (e.g., about 450 microns or
less, about 400 microns or less, about 350 microns or less, about
300 microns or less, about 250 microns or less, about 200 microns
or less, about 150 microns or less, about 125 microns or less,
about 100 microns or less, about 75 microns or less, about 50
microns or less, about 25 microns or less, about 20 microns or
less, about 15 microns or less, about 10 microns or less, about 5
microns or less, or about 1 micron or less). In some embodiments,
the dilute outlet channel (104) has a width of at least about 0.5
microns (e.g., at least about 1 micron, at least about 2.5 microns,
at least about 5 microns, at least about 10 microns, at least about
15 microns, at least about 20 microns, at least about 25 microns,
at least about 50 microns, at least about 75 microns, at least
about 100 microns, at least about 150 microns, at least about 200
microns, at least about 250 microns, at least about 300 microns, at
least about 400 microns, or at least about 450 microns).
[0034] The dilute outlet channel (104) can have a width that ranges
from any of the minimum dimensions to any of the maximum dimensions
described above. For example, the dilute outlet channel (104) can
have a width that ranges from about 500 microns to about 0.5
microns (e.g., from about 400 microns to about 1 micron, from about
250 microns to about 1 micron, from about 150 microns to about 5
microns, or from about 80 microns to about 10 microns).
[0035] In some embodiments, the dilute outlet channel (104) has a
height of about 50 microns or less (e.g., about 45 microns or less,
about 40 microns or less, about 35 microns or less, about 30
microns or less, about 25 microns or less, about 20 microns or
less, about 15 microns or less, about 10 microns or less, about 9
microns or less, about 8 microns or less, about 7.5 microns or
less, about 7 microns or less, about 6 microns or less, about 5
microns or less, about 4 microns or less, about 3 microns or less,
about 2.5 microns or less, or about 2 microns or less). In some
embodiments, the dilute outlet channel (104) has a height of at
least about 1 micron (e.g., at least about 2 microns, at least
about 2.5 microns, at least about 3 microns, at least about 4
microns, at least about 5 microns, at least about 6 microns, at
least about 7 microns, at least about 7.5 microns, at least about 8
microns, at least about 9 microns, at least about 10 microns, at
least about 15 microns, at least about 20 microns, at least about
25 microns, at least about 30 microns, at least about 35 microns,
at least about 40 microns, or at least about 45 microns).
[0036] The dilute outlet channel (104) can have a height that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the dilute outlet channel
(104) can have a height that ranges from about 50 microns to about
1 micron (e.g., from about 45 microns to about 1 micron, from about
40 microns to about 1 micron, from about 35 microns to about 1
micron, from about 30 microns to about 1 micron, from about 25
microns to about 1 micron, or from about 20 microns to about 1
micron).
[0037] In some embodiments, the concentrated outlet channel (106)
has a width of about 500 microns or less (e.g., about 450 microns
or less, about 400 microns or less, about 350 microns or less,
about 300 microns or less, about 250 microns or less, about 200
microns or less, about 150 microns or less, about 125 microns or
less, about 100 microns or less, about 75 microns or less, about 50
microns or less, about 25 microns or less, about 20 microns or
less, about 15 microns or less, about 10 microns or less, about 5
microns or less, or about 1 micron or less). In some embodiments,
the concentrated outlet channel (106) has a width of at least about
0.5 microns (e.g., at least about 1 micron, at least about 2.5
microns, at least about 5 microns, at least about 10 microns, at
least about 15 microns, at least about 20 microns, at least about
25 microns, at least about 50 microns, at least about 75 microns,
at least about 100 microns, at least about 150 microns, at least
about 200 microns, at least about 250 microns, at least about 300
microns, at least about 400 microns, or at least about 450
microns).
[0038] The concentrated outlet channel (106) can have a width that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the concentrated outlet
channel (106) can have a width that ranges from about 500 microns
to about 0.5 microns (e.g., from about 400 microns to about 1
micron, from about 250 microns to about 1 micron, from about 150
microns to about 5 microns, or from about 80 microns to about 10
microns).
[0039] In some embodiments, the concentrated outlet channel (106)
has a height of about 50 microns or less (e.g., about 45 microns or
less, about 40 microns or less, about 35 microns or less, about 30
microns or less, about 25 microns or less, about 20 microns or
less, about 15 microns or less, about 10 microns or less, about 9
microns or less, about 8 microns or less, about 7.5 microns or
less, about 7 microns or less, about 6 microns or less, about 5
microns or less, about 4 microns or less, about 3 microns or less,
about 2.5 microns or less, or about 2 microns or less). In some
embodiments, the concentrated outlet channel (106) has a height of
at least about 1 micron (e.g., at least about 2 microns, at least
about 2.5 microns, at least about 3 microns, at least about 4
microns, at least about 5 microns, at least about 6 microns, at
least about 7 microns, at least about 7.5 microns, at least about 8
microns, at least about 9 microns, at least about 10 microns, at
least about 15 microns, at least about 20 microns, at least about
25 microns, at least about 30 microns, at least about 35 microns,
at least about 40 microns, or at least about 45 microns).
[0040] The concentrated outlet channel (106) can have a height that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the concentrated outlet
channel (106) can have a height that ranges from about 50 microns
to about 1 micron (e.g., from about 45 microns to about 1 micron,
from about 40 microns to about 1 micron, from about 35 microns to
about 1 micron, from about 30 microns to about 1 micron, from about
25 microns to about 1 micron, or from about 20 microns to about 1
micron).
[0041] The length of the microfluidic channels in the desalination
unit (100) (e.g., the inlet channel (102), the dilute outlet
channel (104), and the concentrated outlet channel (106)) can vary.
The length of the microfluidic channels in the desalination unit
can individually be selected in view of a number of the overall
device design and other operational considerations. In some
embodiments, the inlet channel (102), the dilute outlet channel
(104), and the concentrated outlet channel (106) each have a length
of at least about 0.1 cm (e.g., at least about 0.2 cm, at least
about 0.3 cm, at least about 0.4 cm, at least about 0.5 cm, at
least about 0.6 cm, at least about 0.7 cm, at least about 0.8 cm,
at least about 0.9 cm, at least about 1 cm, at least about 2 cm, at
least about 2.5 cm, at least about 3 cm, at least about 4 cm, at
least about 5 cm, or longer). The microfluidic channels in the
desalination unit can be substantially linear in shape, or they can
possess one or more non-linear regions (e.g., a curved region, a
spiral region, an angular region, or combinations thereof) along
the length of their fluid flow path.
[0042] With reference again to FIG. 1A, the dilute outlet channel
(104) and the concentrated outlet channel (106) diverge from the
inlet channel (102) at an intersection (107). The orientation of
the dilute outlet channel (104) and the concentrated outlet channel
(106) with respect to one another at the intersection can be
varied. The angle formed between the dilute outlet channel (104)
and the concentrated outlet channel (106) in a device can be
selected in view of a number of parameters, including the size and
position of the electrode relative to the microfluidic channels in
the desalination unit, the desired device flow rate, salinity of
the saltwater being treated using the device, and the desired
degree of salinity reduction.
[0043] In some cases, the angle formed between the dilute outlet
channel (104) and the concentrated outlet channel (106) at the
intersection (107) is about 60 degrees or less (e.g., about 55
degrees or less, about 50 degrees or less, about 45 degrees or
less, about 40 degrees or less, about 35 degrees or less, about 30
degrees or less, about 25 degrees or less, about 20 degrees or
less, about 15 degrees or less, or less).
[0044] The electrode (108) can be fabricated from any suitable
conductive material, such as a metal (e.g., gold), metal alloy,
metal oxide, or conductive carbon. The electrode (108) is
configured so as to be in electrochemical contact with the
desalination unit (100), meaning that the electrode (108) can
participate in a faradaic reaction with one or more components of a
solution present in a microfluidic channel of the desalination
unit. For example, the electrode (108) can be configured such that
a surface of the electrode is in direct contact with fluid present
in a microfluidic channel of the desalination unit. The device can
be configured such that the electrode (108) can function as either
an anode, cathode, or anode and cathode during device
operation.
[0045] The position and dimensions of the electrode (108) relative
to the desalination unit can be selected in view of a number of
factors, including the size and configuration of the microfluidic
channels in the desalination unit, the desired device flow rate,
salinity of the saltwater being treated using the device, and the
desired degree of salinity reduction. The electrode (108) can have
a variety of 2-dimensional or 3-dimensional shapes, provided that
the electrode (108) can be integrated into the device, and is
compatible with the formation of an electric field gradient
suitable to direct ions flowing through the inlet channel (102)
preferentially into the concentrated outlet channel (106). In
certain embodiments, the electrode (108) is a conductive surface
(e.g., a line, a rectangular pad, or a square pad) substantially
co-planar with the floor of the inlet channel (102), and integrated
into the floor of the inlet channel in proximity to the
intersection (107). In other embodiments, the electrode (108) is a
conductive surface (e.g., a line, a rectangular pad, or a square
pad) that is fabricated onto/into the floor of the inlet channel in
proximity to the intersection (107), and which extends from the
floor of the inlet channel into the inlet channel. In these
embodiments, the electrode can be said to have a height, measured
as the distance from the floor of the inlet channel to the surface
or edge of the electrode within the inlet channel positioned at
greatest distance from the floor of the inlet channel.
[0046] With reference again to FIG. 1A, the electrode (108) can be
positioned in proximity to the intersection (107) so as to form an
ion depletion zone (109) at and downstream of the electrode (108),
and extending into the dilute outlet channel (104) during device
operation. The ion depletion zone (109) can optionally extend into
a portion of the concentrated inlet channel (106). In some
embodiments, the electrode (108) is positioned within the floor of
the inlet channel (102) upstream of the opening of the dilute
outlet channel (104).
[0047] By way of exemplification, FIG. 1B illustrates an enlarged
view of the intersection (107) of the device shown in FIG. 1A. The
electrode (108) is positioned within the floor of the inlet channel
(102). The surface of the electrode (108) in electrochemical
contact with the desalination unit is positioned approximately
.+-.50 microns (measured as the distance from the opening of the
dilute outlet channel to the downstream edge of the electrode, 130)
upstream or downstream of the opening of the dilute outlet channel
(104).
[0048] In certain embodiments, the surface of the electrode (108)
in electrochemical contact with the desalination unit is positioned
upstream of the opening of the dilute outlet channel (104), and
within about 500 microns of the opening of the dilute outlet
channel (e.g., within about 400 microns, within about 300 microns,
within about 250 microns, within about 200 microns, within about
150 microns, within about 100 microns, within about 90 microns,
within about 80 microns, within about 75 microns, within about 70
microns, within about 60 microns, within about 50 microns, within
about 40 microns, within about 30 microns, within about 25 microns,
within about 20 microns, or within about 10 microns).
[0049] In some embodiments, the surface of the electrode (108) in
electrochemical contact with the desalination unit is positioned
downstream of the opening of the dilute outlet channel (104), and
within about 100 microns of the opening of the dilute outlet
channel (e.g., within about 90 microns, within about 80 microns,
within about 75 microns, within about 70 microns, within about 60
microns, within about 50 microns, within about 40 microns, within
about 30 microns, within about 25 microns, within about 20 microns,
within about 10 microns, or within about 5 microns). When the
surface of the electrode (108) in electrochemical contact with the
desalination unit is positioned downstream of the opening of the
dilute outlet channel (104), the length of the electrode (as
discussed below) must be sufficient such that at least a portion of
the electrode (108) in electrochemical contact with the
desalination unit extends beyond the opening of the dilute outlet
channel (104), and into the inlet channel (i.e., a portion of the
electrode must be located upstream of the dilute outlet
channel)
[0050] Again referring to FIG. 1B, the surface of the electrode
(108) in electrochemical contact with the desalination unit can
have a width (132, measured as the distance from one side of the
surface of the electrode to the other side of the surface of the
electrode along an axis perpendicular to the direction of fluid
flow through the inlet channel) and a length (134, measured as the
distance from one side of the surface of the electrode to the other
side of the surface of the electrode along an axis parallel to the
direction of fluid flow through the inlet channel). By way of
exemplification, in the example device to FIG. 1B, the surface of
the electrode (108) in electrochemical contact with the
desalination unit has a width (132) that is about equal to the
width of the dilute outlet channel (104) (50 microns), and a length
(134) of about 100 microns.
[0051] In some embodiments, the surface of the electrode (108) in
electrochemical contact with the desalination unit has a width
(132) of at least about 50% of the width of the dilute outlet
channel (104) (e.g., at least about 60% of the width of the dilute
outlet channel, at least about 70% of the width of the dilute
outlet channel, at least about 75% of the width of the dilute
outlet channel, at least about 80% of the width of the dilute
outlet channel, at least about 90% of the width of the dilute
outlet channel, at least about 90% of the width of the dilute
outlet channel, at least the width of the dilute outlet channel, at
least about 105% of the width of the dilute outlet channel, or at
least about 110% of the width of the dilute outlet channel). In
some embodiments, the surface of the electrode (108) in
electrochemical contact with the desalination unit has a width
(132) that is less than about 150% of the width of the dilute
outlet channel (104) (e.g., less than about 140% of the width of
the dilute outlet channel, less than about 130% of the width of the
dilute outlet channel, less than about 125% of the width of the
dilute outlet channel, less than about 120% of the width of the
dilute outlet channel, less than about 110% of the width of the
dilute outlet channel, less than about 105% of the width of the
dilute outlet channel, or less than the width of the dilute outlet
channel).
[0052] The surface of the electrode (108) in electrochemical
contact with the desalination unit can have a width (132) that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the surface of the
electrode (108) in electrochemical contact with the desalination
unit can have a width (132) that ranges from about 50% of the width
of the dilute outlet channel (104) to about 150% of the width of
the dilute outlet channel (e.g., from about 75% of the width of the
dilute outlet channel to about 125% of the width of the dilute
outlet channel, from about 90% of the width of the dilute outlet
channel to about 110% of the width of the dilute outlet channel, or
from about 95% of the width of the dilute outlet channel to about
105% of the width of the dilute outlet channel). In certain
embodiments, the surface of the electrode (108) in electrochemical
contact with the desalination unit has a width (132) that is about
equal to the width of the dilute outlet channel (104).
[0053] In some embodiments, the surface of the electrode (108) in
electrochemical contact with the desalination unit has a width
(132) that is at least about 25% of the width of the inlet channel
(102) (e.g., at least about 30% of the width of the inlet channel,
at least about 40% of the width of the inlet channel, at least
about 45% of the width of the inlet channel, at least about 50% of
the width of the inlet channel, at least about 55% of the width of
the inlet channel, or at least about 60% of the width of the inlet
channel). In some embodiments, the surface of the electrode (108)
in electrochemical contact with the desalination unit has a width
(132) that is less than about 75% of the width of the inlet channel
(102) (e.g., less than about 60% of the width of the inlet channel,
less than about 55% of the width of the inlet channel, less than
about 50% of the width of the inlet channel, less than about 45% of
the width of the inlet channel, or less than about 40% of the width
of the inlet channel).
[0054] The surface of the electrode (108) in electrochemical
contact with the desalination unit can have a width (132) that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the surface of the
electrode (108) in electrochemical contact with the desalination
unit can have a width (132) that ranges from about 25% of the width
of the inlet channel (102) to about 75% of the width of the inlet
channel (e.g., from about 30% of the width of the dilute outlet
channel to about 70% of the width of the dilute outlet channel,
from about 40% of the width of the dilute outlet channel to about
60% of the width of the dilute outlet channel, or from about 45% of
the width of the dilute outlet channel to about 55% of the width of
the dilute outlet channel). In certain embodiments, the surface of
the electrode (108) in electrochemical contact with the
desalination unit has a width (132) that is about 50% of the width
of the inlet channel (102).
[0055] In some embodiments, the surface of the electrode (108) in
electrochemical contact with the desalination unit has a width
(132) of about 600 microns or less (e.g., about 500 microns or
less, about 450 microns or less, about 400 microns or less, about
350 microns or less, about 300 microns or less, about 250 microns
or less, about 200 microns or less, about 150 microns or less,
about 125 microns or less, about 100 microns or less, about 75
microns or less, about 50 microns or less, about 25 microns or
less, about 20 microns or less, about 15 microns or less, about 10
microns or less, about 5 microns or less, or about 1 micron or
less). In some embodiments, the surface of the electrode (108) in
electrochemical contact with the desalination unit has a width
(132) of at least about 0.5 microns (e.g., at least about 1 micron,
at least about 2.5 microns, at least about 5 microns, at least
about 10 microns, at least about 15 microns, at least about 20
microns, at least about 25 microns, at least about 50 microns, at
least about 75 microns, at least about 100 microns, at least about
150 microns, at least about 200 microns, at least about 250
microns, at least about 300 microns, at least about 400 microns, at
least about 450 microns, or at least about 500 microns).
[0056] The surface of the electrode (108) in electrochemical
contact with the desalination unit can have a width (132) that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the surface of the
electrode (108) in electrochemical contact with the desalination
unit can have a width (132) that ranges from about 600 microns to
about 0.5 microns (e.g., from about 400 microns to about 1 micron,
from about 250 microns to about 1 micron, from about 150 microns to
about 5 microns, or from about 80 microns to about 10 microns).
[0057] The length (134) of the surface of the electrode (108) in
electrochemical contact with the desalination unit can be varied.
In some embodiments the surface of the electrode (108) has a length
(134) of at least about 10 microns (e.g., at least about 15
microns, at least about 20 microns, at least about 25 microns, at
least about 50 microns, at least about 75 microns, at least about
100 microns, at least about 150 microns, at least about 200
microns, at least about 250 microns, at least about 300 microns, at
least about 400 microns, at least about 450 microns, or at least
about 450 microns). In some embodiments, the surface of the
electrode (108) has a length (134) of less than about 500 microns
(e.g., less than about 400 microns, less than about 300 microns,
less than about 250 microns, less than about 200 microns, or less
than about 100 microns).
[0058] The surface of the electrode (108) in electrochemical
contact with the desalination unit can have a length (134) that
ranges from any of the minimum dimensions to any of the maximum
dimensions described above. For example, the surface of the
electrode (108) can have a length (134) that ranges from about 10
microns to about 500 microns (e.g., from about 25 microns to about
250 microns, or from about 50 microns to about 150 microns).
[0059] The height of the electrode (108) in electrochemical contact
with the desalination unit can also be varied. The height of the
electrode (108) can be selected in view of a number of factors,
including the height of the microfluidic channels in the
desalination unit. In some cases, the height of the electrode (108)
is approximately zero (i.e., the electrode is substantially
co-planar with the floor of the inlet channel). In some
embodiments, the height of the electrode (108) is less than about 1
micron (e.g., less than about 900 nm, less than about 800 nm, less
than about 750 nm, less than about 700 nm, less than about 600 nm,
less than about 500 nm, less than about 400 nm, less than about 300
nm, less than about 250 nm, less than about 200 nm, or less than
about 100 nm).
[0060] As shown in FIG. 1C, a power supply (140) can be configured
to apply a potential bias across the desalination unit. A flow of
saltwater (120) can be initiated from the inlet channel (102) to
the dilute outlet channel (104) and the concentrated outlet channel
(106). Upon application of a potential bias, an ion depletion zone
(109) and subsequent electric field gradient are formed near the
electrode (108) in proximity to the intersection (107). As a
consequence, ions in the saltwater are preferentially directed into
the concentrated outlet channel (106), resulting in a brine (122)
flowing through the concentrated outlet channel. Desalted water
(i.e., water containing less salt that the saltwater introduced
into the inlet channel; 124) flows into the dilute outlet channel
(104).
[0061] In some embodiments, the microfluidic device can further
include an auxiliary channel fluidly isolated from the desalination
unit. An example device comprising a desalination unit (100) and an
auxiliary channel (202) is schematically illustrated in FIG. 2. The
desalination unit includes an inlet channel (102) fluidly connected
to a dilute outlet channel (104) and a concentrated outlet channel
(106). The dilute outlet channel (104) and the concentrated outlet
channel (106) diverge from the inlet channel (102) at an
intersection (107). The device also includes and an auxiliary
channel (202) which is fluidly isolated from the desalination unit
(100).
[0062] The auxiliary channel (202) can comprise, for example, a
single microfluidic channel. In these embodiments, dimensions of
the auxiliary channel (e.g., height, width, and length) can vary.
The dimensions of the auxiliary channel (202) can individually be
selected in view of a number of the overall device design and other
operational considerations. The auxiliary channel (202) can be
substantially linear in shape, or it can possess one or more
non-linear regions (e.g., a curved region, a spiral region, an
angular region, or combinations thereof) along the length of their
fluid flow path. The auxiliary channel (202) can optionally possess
one or more branch points. The auxiliary channel (202) can further
include additional elements, such as electrodes, fluid inlets,
fluid outlets, fluid reservoirs, valves, pumps, and combinations
thereof, connected to the auxiliary channel to facilitate device
operation.
[0063] The auxiliary channel (202) can be electrochemically
connected to the desalination unit (100) via a bipolar electrode.
In these embodiments, the bipolar electrode is configured so as to
be in electrochemical contact with both the desalination unit (100)
and the auxiliary channel (202), meaning that a first surface of
the bipolar electrode can participate in a faradaic reaction with
one or more components of a solution present in a microfluidic
channel of the desalination unit, and a second surface of the
bipolar electrode can participate in a faradaic reaction with one
or more components of a solution present in the auxiliary channel.
The device can be configured such that the bipolar electrode
comprises an anode in electrochemical contact with the desalination
unit and a cathode in electrochemical contact with the auxiliary
channel during device operation. Alternatively, the device can be
configured such that the bipolar electrode comprises a cathode in
electrochemical contact with the desalination unit and an anode in
electrochemical contact with the auxiliary channel during device
operation.
[0064] By way of exemplification, referring again to the example
device illustrated in FIG. 2, a bipolar electrode (204)
electrochemically connects the auxiliary channel (202) and the
desalination unit (100). A first surface of the bipolar electrode
(206) is in electrochemical contact with the desalination unit
(100), and is positioned in proximity to the intersection (107).
The first surface of the bipolar electrode (206) is configured to
form an ion depletion zone (109) at and downstream of the surface
of the bipolar electrode during device operation, resulting in the
formation of an electric field gradient in proximity to the
intersection. A second surface of the bipolar electrode (208) is in
electrochemical contact with the auxiliary channel (202).
[0065] The first surface of the bipolar electrode (206) can occupy
the same position within the desalination unit, and have the same
dimensions as the surface of electrode (108) described above with
respect to the first desalination unit.
[0066] Referring again to FIG. 2, the example device further
includes a fluid reservoir (110) fluidly connected to the upstream
terminus of the inlet channel (102), a fluid reservoir (114)
fluidly connected to the downstream terminus of the dilute outlet
channel (104), a fluid reservoir (112) fluidly connected to the
downstream terminus of the concentrated outlet channel (106), and
fluid reservoirs (210 and 212) fluidly connected to the termini of
the auxiliary channel (202).
[0067] A power supply can be configured to apply a potential bias
across the auxiliary channel (202) and the desalination unit (100).
A flow of saltwater (120) can be initiated from the inlet channel
(102) to the dilute outlet channel (104) and the concentrated
outlet channel (106). Upon application of a potential bias, an ion
depletion zone (109) and subsequent electric field gradient are
formed near the first surface of the bipolar electrode (206) in
proximity to the intersection (107). As a consequence, ions in the
saltwater are preferentially directed into the concentrated outlet
channel (106), resulting in a brine (122) flowing through the
concentrated outlet channel. Desalted water (124) flows into the
dilute outlet channel (104).
[0068] In some embodiments, the auxiliary channel can comprise a
desalination unit. In these embodiments, the microfluidic device
can comprise two desalination units, which can be of identical or
different structure. An example device comprising two desalination
units is illustrated in FIG. 3. The device includes a first
desalination unit (100) electrochemically connected to a second
desalination unit (302) by a bipolar electrode (310). The first
desalination unit (100) is fluidly isolated from the second
desalination unit (302).
[0069] The first desalination unit (100) includes an inlet channel
(102) fluidly connected to a dilute outlet channel (104) and a
concentrated outlet channel (106). The dilute outlet channel (104)
and the concentrated outlet channel (106) diverge from the inlet
channel (102) at an intersection (107). The second desalination
unit (302) includes an inlet channel (304) fluidly connected to a
dilute outlet channel (306) and a concentrated outlet channel
(308). The dilute outlet channel (306) and the concentrated outlet
channel (308) diverge from the inlet channel (304) at an
intersection (307).
[0070] A bipolar electrode (310) electrochemically connects the
first desalination unit (100) and the second desalination unit
(302). A first surface of the bipolar electrode (312) is in
electrochemical contact with the first desalination unit (100), and
is positioned in proximity to the intersection (107). The first
surface of the bipolar electrode (312) is configured to form an ion
depletion zone (109) downstream of the surface of the bipolar
electrode during device operation, resulting in the formation of an
electric field gradient in proximity to the intersection of the
first desalination unit. A second surface of the bipolar electrode
(314) is in electrochemical contact with the second desalination
unit (302), and is positioned in proximity to the intersection of
the second desalination unit (307). The second surface of the
bipolar electrode (314) is configured to form an ion depletion zone
(309) downstream of the surface of the bipolar electrode during
device operation, resulting in the formation of an electric field
gradient in proximity to the intersection of the second
desalination unit. The example device further includes fluid
reservoirs (110 and 320) fluidly connected to the upstream termini
of the inlet channels of the first and second desalination units,
fluid reservoirs (114 and 322) fluidly connected to the downstream
termini of the dilute outlet channels of the first and second
desalination units, and fluid reservoirs (112 and 324) fluidly
connected to the downstream termini of the concentrated outlet
channels of the first and second desalination units.
[0071] The second desalination unit (302), as well as all of the
elements making up the second desalination unit (e.g., the inlet
channel (304), the dilute outlet channel (306), and the
concentrated outlet channel (308)) can have the same dimensions and
relative configurations as those described above with respect to
the first desalination unit. The first surface of the bipolar
electrode (312) and the second surface of the bipolar electrode
(314) can occupy the same positions within their respective
desalination units, and have the same dimensions as the surface of
electrode (108) described above with respect to the first
desalination unit.
[0072] A power supply can be configured to apply a potential bias
across the first desalination unit (100) and the second
desalination unit (302). A flow of saltwater (120 and 330) can be
initiated from the inlet channels of the first and second
desalination units to the dilute outlet channels and the
concentrated outlet channels of the first and second desalination
units. Upon application of a potential bias, ion depletion zones
(109 and 309) and subsequent electric field gradients are formed
near the first surface of the bipolar electrode (312) in proximity
to the intersection (107) of the first desalination unit, and near
the second surface of the bipolar electrode (314) in proximity to
the intersection (307) of the second desalination unit. As a
consequence, ions in the saltwater are preferentially directed into
the concentrated outlet channels of the first and second
desalination units (106 and 308), resulting in a brine (122 and
334) flowing through the concentrated outlet channels of the first
and second desalination units. Desalted water (124 and 332) flows
into the dilute outlet channels (104 and 306) of the first and
second desalination units.
[0073] The microfluidic devices described herein can further
include one or more additional components (e.g., pressure gauges,
valves, pressure inlets, pumps, fluid reservoirs, sensors,
electrodes, power supplies, and combinations thereof) to facilitate
device function. In some embodiments, the devices include a pump,
valve, fluid reservoir, or combination thereof configured to
regulate fluid flow into the inlet channel of the device.
[0074] The devices can include a salinometer configured to measure
the salinity of fluid flowing through one or more of the
microfluidic channels of the device. For example, in some cases,
the devices can include a salinometer configured to measure the
salinity of fluid flowing through the dilute outlet channel. The
salinometer can measure the salinity of the fluid via any suitable
means. For example, the salinometer can measure the fluid's
electrical conductivity, specific gravity, index of refraction, or
combinations thereof.
[0075] In certain embodiments, the devices include a salinometer
configured to measure the salinity of fluid flowing through the
dilute outlet channel, and a pump, valve, fluid reservoir, or
combination thereof configured to regulate fluid flow into the
inlet channel of the device. The devices can further include signal
processing circuitry or a processor configured to operate the pump
and/or valve connected to the inlet channel so as to adjust fluid
flow into the inlet channel of the device in response to the
salinity of fluid flowing through the dilute outlet channel.
[0076] Systems
[0077] A plurality of the microfluidic devices described herein can
be combined to form a water purification system.
[0078] Water purification systems can comprise any number of the
devices described herein. The number of devices incorporated within
the water purification system can be selected in view of a number
of factors, including the overall system design, the desired
throughput of the system, salinity of the saltwater being treated
using the system, and the desired degree of salinity reduction.
[0079] In some cases, the inlet channels of two or more of the
devices in the system are fluidly connected to a common water
inlet, so as to facilitate the flow of saltwater into the inlet
channels of multiple devices in the system. Similarly, the dilute
outlet channels of two or more of the devices in the system can be
fluidly connected to a common water outlet, so as to facilitate the
collection of desalted water from the dilute outlet channels of
multiple devices in the system.
[0080] The system can comprise a plurality of the devices described
herein arranged in parallel. Within the context of the systems
described herein, two devices can be described as being arranged in
parallel within a system when fluid flowing from either the dilute
outlet channel or the concentrated outlet channel of the first
device in the system does not subsequently flow into the inlet
channel of the second device in the system.
[0081] By way of example, FIG. 4 is a schematic drawing of a water
purification system (400) that includes a first desalination unit
(402) and a second desalination unit (404) arranged in parallel.
The example device further includes an auxiliary channel (406)
which is fluidly isolated from both the first and second
desalination unit. A first bipolar electrode (408)
electrochemically connects the auxiliary channel (406) and the
first desalination unit (402). A second bipolar electrode (410)
electrochemically connects the auxiliary channel (406) and the
second desalination unit (404). The example system can be operated
by applying a potential bias between the auxiliary channel and the
first and second desalination units.
[0082] FIG. 5 illustrates a second example water purification
system (500) that includes two devices arranged in parallel. The
system (500) comprises a first device which includes a first
desalination unit (502) electrochemically connected to a first
auxiliary channel (504) by a first bipolar electrode (506). The
system (500) further comprises a second device which is arranged in
parallel with respect to the first device, and which includes a
second desalination unit (508) electrochemically connected to a
second auxiliary channel (510) by a second bipolar electrode (512).
As illustrated in FIG. 5, a power supply can be configured to apply
a potential bias across both the first auxiliary channel (504) and
desalination unit (502) and the second auxiliary channel (510) and
desalination unit (508).
[0083] The system can comprise a plurality of the devices described
herein fluidly connected in series. Within the context of the
systems described herein, two devices can be described as being
fluidly connected in series within a system when fluid flowing from
either the dilute outlet channel or the concentrated outlet channel
of the first device in the system subsequently flows into the inlet
channel of the second device in the system.
[0084] By way of example, FIG. 6 is a schematic drawing of a water
purification system (600) that includes two devices fluidly
connected in series. The system (600) includes a first desalination
unit (602) and a second desalination unit (604) fluidly connected
in series, such that the dilute outlet channel of the first
desalination unit is fluidly connected to the inlet channel of the
second desalination unit. The example device further includes an
auxiliary channel (606) which is fluidly isolated from both the
first and second desalination unit. A first bipolar electrode (608)
electrochemically connects the auxiliary channel (606) and the
first desalination unit (602). A second bipolar electrode (610)
electrochemically connects the auxiliary channel (606) and the
second desalination unit (604). The example system can be operated
by applying a potential bias between the auxiliary channel and the
first and second desalination units.
[0085] If desired, the systems can contain a plurality of devices
both arranged in parallel and fluidly connected in series. For
example, the device can include a first pair devices fluidly
connected in series which are arranged in parallel with a second
pair of devices fluidly connected in series.
[0086] Methods of Making
[0087] The microfluidic devices and systems described herein can be
fabricated from any substrate material which is non-conductive, and
suitable for the flow of aqueous solutions through the microfluidic
channels of the device or system. For example, the device or system
can be fabricated, in whole or in part, from glass, silicon, or
combinations thereof. The device or system can also be fabricated,
in whole or in part, from a polymer and/or plastic, such as a
polyester (e.g., polyethylene terephthalate; PET) polyurethane,
polycarbonate, halogenated polymer (e.g., polyvinyl chloride and/or
fluorinated polymer such as polytetrafluoroethylene (PTFE)),
polyacrylate and/or poly methacrylate (e.g., polymethyl
methacrylate; PMMA), silicone (e.g., polydimethylsiloxane; PDMS), a
thermosetting resin (e.g., Bakelite), or a copolymer, blend, and/or
combination thereof. The device or system can also be fabricated,
in whole or in part, from a ceramic (e.g., silicon nitride, silicon
carbide, titania, alumina, silica, etc.).
[0088] In certain embodiments, the device or system is fabricated,
in whole or in part, from a photocurable epoxy. In certain
embodiments, the device or system is fabricated, in whole or in
part, from PDMS.
[0089] The microfluidic devices and systems described herein can be
fabricated using a variety of microfabrication techniques known in
the art. Suitable methods for the microfabrication of microfluidic
devices include, for example, lithography, etching, embossing,
roll-to-roll manufacturing, lamination, printing, and molding of
polymeric substrates. The microfabrication process can involve one
or more of the processes described below (or similar processes).
Different portions of the device or system can be fabricated using
different methods, and subsequently assembled or bonded together to
form the final microfluidic device or system. Suitable fabrication
methods can be selected in view of a number of factors, including
the nature of the substrate(s) used to form the device or system,
performance requirements, and the dimensions of the microfluidic
features making up the device or system.
[0090] Lithography involves use of light or other form of energy
such as electron beam to selectively alter a substrate material.
Typically, a polymeric material or precursor (e.g., photoresist, a
light-resistant material) is coated on a substrate and is
selectively exposed to light or other form of energy. Depending on
the photoresist, exposed regions of the photoresist either remain
or are dissolved in subsequent processing steps known generally as
"developing." This process results in a pattern of the photoresist
on the substrate. In some embodiments, the photoresist is used as a
master in a molding process. In some embodiments, a polymeric
precursor is poured on the substrate with photoresist, polymerized
(i.e., cured) and peeled off. The resulting polymer is bonded or
glued to another flat substrate after drilling holes for inlets and
outlets.
[0091] In some embodiments, the photoresist is used as a mask for
an etching process. For example, after patterning photoresist on a
silicon substrate, channels can be etched into the substrate using
a deep reactive ion etch (DRIE) process or other chemical etching
process known in the art (e.g., plasma etch, KOH etch, HF etch,
etc.). The photoresist can then be removed, and the substrate can
be bonded to another substrate using one of any bonding procedures
known in the art (e.g., anodic bonding, adhesive bonding, direct
bonding, eutectic bonding, etc.). Multiple lithographic and etching
steps and machining steps such as drilling can be included. Carbon
electrodes may be fabricated in place by means of photoresist
pyrolysis.
[0092] In some embodiments, a polymeric substrate, such as PMMA,
can be heated and pressed against a master mold for an embossing
process. The master mold can be formed by a variety of processes,
including lithography and machining. The polymeric substrate can
then be bonded with another substrate to form a microfluidic device
or system. Machining processes can be included if necessary.
[0093] Devices and systems can also be fabricated using an
injection molding process. In an injection molding process, a
molten polymer or metal or alloy is injected into a suitable mold
and allowed to cool and solidify. The mold typically consists of
two parts that allow the molded component to be removed. Parts thus
manufactured can be bonded to result in the device or system.
[0094] In some embodiments, sacrificial etch can be used to form
the device or system. Lithographic techniques can be used to
pattern a material on a substrate. This material can then be
covered by another material of different chemical nature. This
material can undergo lithography and etch processes, or another
suitable machining process. The substrate can then be exposed to a
chemical agent that selectively removes the first material. In this
way, channels can be formed in the second material, leaving voids
where the first material was present before the etch process.
[0095] In some embodiments, microchannels can be directly machined
into a substrate by laser machining or CNC machining. If desired,
several layers can be machined, and subsequently bonded together to
obtain the final device or system.
[0096] Electrodes as well as other electrical device components can
be fabricated within the devices and systems by patterning suitable
conductive materials on and/or within substrate materials using a
number of suitable methods known in the art.
[0097] In one or more embodiments, the conductive material includes
one or more metals. Non-limiting examples of suitable metals
include Sn, Zn, Au, Ag, Ni, Pt, Pd, Al, In, Cu, or a combination
thereof. Other suitable conductive materials include metal oxides
and conductive non-metals (e.g., carbon derivatives such as
graphite). Conductive materials can be deposited using a vacuum
deposition process (e.g., cathodic arc deposition, electron beam
physical vapor deposition, evaporative deposition, pulsed laser
deposition, or sputter deposition). Conductive material can also be
provided in the form of a conductive ink which can be screen
printed, ink-jet printed, or otherwise deposited onto the surface
of the substrate material to form an electrical device component.
Conductive inks are typically formed by blending resins or
adhesives with one or more powdered conductive materials such as
Sn, Zn, Au, Ag, Ni, Pt, Pd, Al, In, Cu, graphite powder, carbon
black, or other conductive metals or metal alloys. Examples include
carbon-based inks, silver inks, and aluminum inks.
[0098] When forming an electrical device component, such as an
electrode, in the devices or systems described herein, one or more
conductive materials will preferably be deposited or applied as a
thin film. In certain embodiments, the conductive layers are thin
metallic or carbon films which are about 50 microns in thickness or
less (e.g., about 40 microns in thickness or less, about 30 microns
in thickness or less, about 25 microns in thickness or less, about
20 microns in thickness or less, about 15 microns in thickness or
less, about 10 microns in thickness or less, about 5 microns in
thickness or less, about 1 micron in thickness or less, about 900
nm in thickness or less, about 800 nm in thickness or less, about
750 nm in thickness or less, about 700 nm in thickness or less,
about 600 nm in thickness or less, about 500 nm in thickness or
less, about 400 nm in thickness or less, about 300 nm in thickness
or less, or about 250 nm in thickness or less).
[0099] Methods of Using
[0100] The microfluidic devices and systems described herein can be
used to decrease the salinity of water. The salinity of water can
be decreased by flowing saltwater through the desalination unit of
a device or system described herein, and performing a faradaic
reaction at the electrode positioned in proximity to the
intersection of the desalination unit. The faradaic reaction
generates an electric field gradient that directs ions in the
saltwater away from the dilute outlet channel of the desalination
unit, and towards the concentrated outlet channel of the
desalination unit. As a result, the salinity of water which flows
into the dilute outlet channel is lower than the salinity of the
saltwater flowing into the inlet channel.
[0101] In some embodiments, methods of decreasing the salinity of
water include providing a flow of saltwater through the inlet
channel of a device described herein or the water inlet of a system
described herein, applying a potential bias to generate an electric
field gradient that influences the flow of ions in the saltwater
through the desalination unit of the device or the desalination
units of the system, and collecting water from the dilute outlet
channel of the device or the water outlet of the system. In these
methods, the water collected from the dilute outlet channel of the
device or the water outlet of the system can have a lower
electrical conductivity than the saltwater flowed through the inlet
channel of the device or the water inlet of the system.
[0102] In some embodiments, the potential bias applied to generate
an electric field gradient is greater than about 1 volt (e.g.,
greater than about 2 volts, greater than about 2.5 volts, greater
than about 3 volts, greater than about 4 volts, greater than about
5 volts, greater than about 6 volts, greater than about 7 volts,
greater than about 8 volts, or greater than about 9 volts). In some
embodiments, the potential bias applied to generate an electric
field gradient is less than about 10 volts (e.g., less than about 9
volts, less than about 9 volts, less than about 8 volts, less than
about 7 volts, less than about 6 volts, less than about 5 volts,
less than about 4 volts, less than about 3 volts, less than about
2.5 volts, or less than about 2 volts).
[0103] The potential bias applied to generate an electric field
gradient can range from any of the minimum voltages to any of the
maximum voltages described above. In some embodiments, the
potential bias applied to generate an electric field gradient
ranges from about 1 volt to about 10 volts (e.g., from about 1 volt
to about 7 volts, from about 2 volts to about 7 volts, or from
about 2.5 to about 5 volts).
[0104] In some embodiments, the flow rate of the saltwater through
the desalination unit of the device or the flow rate of the
saltwater through each desalination unit of the system ranges from
about 0.01 to about 1 microliter per minute (e.g., from about 0.05
to about 0.5 microliters per minute, or from about 0.1 to about 0.5
microliters per minute). Suitable flow rates can be selected in
view of a variety of factors including the architecture of the
device or system, the salinity of the saltwater being treated using
the device or system, and the desired degree of salinity
reduction.
[0105] The devices, systems, and methods described herein can be
used to decrease the salinity of saltwater having any measurable
concentration of dissolved sodium chloride. The saltwater can be
seawater (e.g., saltwater having a conductivity of between about 4
S/m and about 6 S/m). The saltwater can be brackish water (e.g.,
saltwater having a conductivity of between about 0.05 S/m and about
4 S/m). In certain embodiments, the saltwater has a conductivity of
greater than about 0.05 S/m (e.g., greater than about 0.1 S/m,
greater than about 0.5 S/m, greater than about 1.0 S/m, greater
than about 2.0 S/m, greater than about 2.5 S/m, greater than about
3.0 S/m, greater than about 3.5 S/m, greater than about 4.0 S/m,
greater than about 4.5 S/m, greater than about 5.0 S/m, or greater
than about 5.5 S/m).
[0106] The devices, systems, and methods described herein can be
used to decrease the salinity of saltwater by varying degrees. The
degree of salinity reduction can depend on a number of factors,
including the architecture of the device or system, and the
salinity of the saltwater being treated using the device or
system.
[0107] In some embodiments, the conductivity of the water
desalinated using the devices, systems, and methods described
herein (e.g., the water collected from the dilute outlet channel of
the device or the water outlet of the system) does not exceed about
90% of the conductivity of the saltwater flowed into the device or
system (e.g., it does not exceed about 80% of the conductivity of
the saltwater flowed into the device or system, it does not exceed
about 75% of the conductivity of the saltwater flowed into the
device or system, it does not exceed about 70% of the conductivity
of the saltwater flowed into the device or system, it does not
exceed about 60% of the conductivity of the saltwater flowed into
the device or system, it does not exceed about 50% of the
conductivity of the saltwater flowed into the device or system, it
does not exceed about 40% of the conductivity of the saltwater
flowed into the device or system, it does not exceed about 30% of
the conductivity of the saltwater flowed into the device or system,
it does not exceed about 25% of the conductivity of the saltwater
flowed into the device or system, it does not exceed about 20% of
the conductivity of the saltwater flowed into the device or system,
it does not exceed about 10% of the conductivity of the saltwater
flowed into the device or system, it does not exceed about 5% of
the conductivity of the saltwater flowed into the device or system,
it does not exceed about 1% of the conductivity of the saltwater
flowed into the device or system, it does not exceed about 0.5% of
the conductivity of the saltwater flowed into the device or system,
it does not exceed about 0.1% of the conductivity of the saltwater
flowed into the device or system, it does not exceed about 0.05% of
the conductivity of the saltwater flowed into the device or system,
it does not exceed about 0.01% of the conductivity of the saltwater
flowed into the device or system, or less).
[0108] In some cases, water desalinated using the devices, systems,
and methods described herein (e.g., water collected from the dilute
outlet channel of the device or the water outlet of the system) has
a conductivity of less than about 2.0 S/m (e.g., less than about
1.75 S/m, less than about 1.5 S/m, less than about 1.25 S/m, less
than about 1.0 S/m, less than about 0.75 S/m, less than about 0.5
S/m, less than about 0.25 S/m, less than about 0.1 S/m, less than
about 0.05 S/m, less than about 0.01 S/m, less than about 0.005
S/m, less than about 0.001 S/m, less than about 5.0.times.10.sup.-4
S/m, less than about 1.0.times.10.sup.-4 S/m, less than about
5.0.times.10.sup.-5 S/m, less than about 1.0.times.10.sup.-5 S/m,
or less).
[0109] In some embodiments, the water desalinated using the
devices, systems, and methods described herein (e.g., water
collected from the dilute outlet channel of the device or the water
outlet of the system) is drinking water (e.g., the water has a
conductivity of from about 0.05 S/m to about 0.005 S/m). In some
embodiments, the water desalinated using the devices, systems, and
methods described herein (e.g., water collected from the dilute
outlet channel of the device or the water outlet of the system) is
ultrapure water (e.g., the water has a conductivity of from about
0.005 S/m to about 5.5.times.10.sup.-6 S/m).
[0110] If desired, water can be treated multiple times using the
devices, systems, and methods described herein to achieve a desired
decrease in the salinity of the saltwater.
[0111] The devices and systems described herein can be used to
desalinate water with greater energy efficiency than conventional
desalination methods. In some cases, the devices and systems
described herein can be used to desalinate water with at an energy
efficiency of less than about 1000 mWh/L (e.g., at least about 900
mWh/L, at least about 800 mWh/L, at least about 750 mWh/L, at least
about 700 mWh/L, at least about 600 mWh/L, at least about 500
mWh/L, at least about 400 mWh/L, at least about 300 mWh/L, at least
about 250 mWh/L, at least about 200 mWh/L, at least about 100
mWh/L, at least about 90 mWh/L, at least about 80 mWh/L, at least
about 75 mWh/L, at least about 70 mWh/L, at least about 60 mWh/L,
at least about 50 mWh/L, at least about 40 mWh/L, at least about 30
mWh/L, at least about 25 mWh/L, at least about 20 mWh/L, at least
about 15 mWh/L, or at least about 10 mWh/L, or at least about 5
mWh/L). In some embodiments, the devices and systems described
herein can be used to desalinate water with at an energy efficiency
ranging from any of the minimum values above to about 1 mWh/L
(e.g., from at least about 1000 mWh/L to about 1 mWh/L, from at
least about 500 mWh/L to about 1 mWh/L, from at least about 100
mWh/L to about 1 mWh/L, from at least about 75 mWh/L to about 1
mWh/L, or from at least about 50 mWh/L to about 1 mWh/L).
[0112] In some cases, the saltwater is not pre-treated prior to
desalination with the devices and systems described herein. In
other embodiments, the saltwater can be treated prior to
desalination. For example, the removal of multivalent cations
(e.g., Ca.sup.2+, Mg.sup.2+, or combinations thereof) from
saltwater prior to desalination could reduce precipitate formation
within the device or system over long operation times. Accordingly,
in some embodiments, the saltwater can be pre-treated to reduce the
level of dissolved multivalent cations in solution, for example, by
contacting the saltwater with a suitable ion exchange resin. If
necessary, saltwater can also be pre-treated to remove debris, for
example, by sedimentation and/or filtration. If desired, saltwater
can also be disinfected prior to desalination.
[0113] If desired for a particular end use, water can be further
treated following desalination with the devices and systems
described herein. For example, water can be fluoridated by addition
of a suitable fluoride salt, such as sodium fluoride, fluorosilicic
acid, or sodium fluorosilicate. Water can also be passed through an
ion exchange resin and/or treated to adjust pH following
desalination with the devices and systems described herein.
EXAMPLES
Example 1: Desalination Using a Microfluidic Device
[0114] A microelectrochemical cell comprising a desalination unit
and an auxiliary channel spanned by a single bipolar electrode
(BPE) was used to desalinate seawater along a locally generated
electric field gradient in the presence of pressure driven flow
(PDF). Seawater desalination was achieved by applying a potential
bias between a parallel desalination unit and auxiliary channel to
drive the oxidation of chloride at the anodic pole of the bipolar
electrode. At the cathodic pole, water reduction occurs to support
current flow.
[0115] The oxidation of chloride at the anodic pole of the BPE
results in an ion depletion zone and subsequent electric field
gradient. The electric field gradient directed ions flowing through
the desalination unit into a branching microchannel, creating a
brine stream, while desalted water continued to flow forward when
the rate of pressure driven flow was controlled. Seawater
desalination could thus be achieved by controlling the rate of
pressure driven flow to create both a salted and desalted
stream.
[0116] Materials and Methods
[0117] Fabrication of Microfluidic Device
[0118] A PDMS/quartz hybrid microfluidic device was prepared using
microfabrication methods known in the art. The structure of the
microfluidic device is schematically illustrated in FIG. 2. The
device comprises a desalination unit and an auxiliary channel
spanned by a single bipolar electrode.
[0119] A pyrolyzed photoresist carbon electrode was fabricated on a
quartz slide (1 in.times.1 in). Photoresist was spin coated onto
the slide at 3500 rpm for 45 seconds, and then soft baked on a hot
plate at 100.degree. C. for 1 minute to remove excess solvent. The
device was then exposed to a UV lamp with patterned mask above to
reveal the electrode (100 .mu.m wide by 6.3 mm long) design. The
excess photoresist was then removed by development. The devices
were then placed in a quartz tube furnace with a forming gas of 5%
H.sub.2 and 95% N.sub.2 continuously flowing at 100 standard cubic
centimeters per minute to allow the photoresist to pyrolyze. After
pyrolysis, the device was cooled to room temperate.
[0120] A PDMS desalination unit (5.0 mm long and 22 .mu.m tall)
with a 100 .mu.m wide inlet channel and 50 .mu.m wide dilute outlet
channel and concentrated outlet channel was fabricated parallel to
an auxiliary channel (5.0 mm long, 22 .mu.m tall, 100 .mu.m wide)
using a SU-8 photoresist mold patterned on a silicon wafer. The
separation between the desalination unit and the auxiliary channel
was 6.0 mm (center-to-center). The PDMS channels were rinsed with
ethanol and dried under N.sub.2, then the PDMS and quartz/electrode
surfaces were exposed to an air plasma for 15 seconds, and finally
the two parts were bound together with the BPE aligned at the
intersection where the dilute outlet channel and concentrated
outlet channel diverge from the inlet channel. The PDMS/quartz
microfluidic device was then placed in an oven at 65.degree. C. for
5 min to promote irreversible bonding.
[0121] Evaluation of Desalination
[0122] Seawater collected from Port Aransas, Tex. was used to
evaluate desalination. To prevent obstruction of the microfluidic
channel, the seawater samples were allowed to undergo a simple
sedimentation process before sample collection. The seawater was
spiked with a cationic (20 .mu.M Ru(bpy).sup.2+) tracer to
fluorescently monitor the movement of ions through the desalination
unit during desalination.
[0123] A solution height differential was created between the fluid
reservoir fluidly connected to the inlet channel (110; V.sub.1) and
the fluid reservoirs fluidly connected to the concentrated outlet
channel (112; V.sub.2) and fluidly connected to the dilute outlet
channel (114, V.sub.3). In this way, a pressure driven flow (PDF)
from right to left was initiated.
[0124] Results
[0125] Using Au driving electrodes, E.sub.tot=2.5 V was applied to
reservoirs 212 and 210 while fluid reservoirs 110, 112, and 114
were grounded. The potential bias created a sufficiently large
potential difference between the poles of the BPE (204) to drive
water oxidation and reduction at the BPE anode (206) and cathode
(208). See Eqn. 1 and 2, respectively. Moreover, chloride oxidation
occurred at the BPE anode (206; Eqn. 3) directly resulting in an
ion depletion zone near the BPE as chlorine was generated.
2H.sub.2O-4e.sup.-O.sub.2+4H.sup.+ (Eqn. 1)
2H.sub.2O+2e.sup.-H.sub.2+2OH.sup.- (Eqn. 2)
2Cl.sup.--2e.sup.-Cl.sub.2(2) (Eqn. 3)
In addition, H.sup.+ electrogenerated by water oxidation (Eqn. 1)
can neutralize bicarbonate and borate that can be present in
seawater, further contributing to the strength of the ion depletion
zone (109) and subsequently formed electric field gradient. With
PDF from right to left, seawater, and thus the ions present is
seawater, were transported toward the electric field gradient
formed at intersection where the dilute outlet channel (104) and
concentrated outlet channel (106) diverge from the inlet channel
(102).
[0126] The electrophoretic velocity (u.sub.ep) of a charged analyte
is governed by Eqn. 4, where .mu..sub.ep is the analyte's
electrophoretic mobility and V.sub.1 is the local electric field
strength.
u.sub.ep=.mu..sub.epV.sub.1 (Eqn. 4)
In all regions of the device depicted in FIG. 2, except near the
ion depletion zone formed by the anode of the bipolar electrode in
proximity to the intersection where dilute outlet channel and
concentrated outlet channel diverge from the inlet channel, the
transport of water and all dissolved species is controlled by PDF.
As a consequence, all neutrals and ions to move generally in the
direction of fluid flow (i.e., from right to left) throughout the
device. However, as ions approach the local electric field gradient
formed by the electrode in proximity to the intersection, they
experience an increasing u.sub.ep as the electric field strength
increases. In the case of cations, this gradient causes them to
redirect toward the grounded reservoir in the brine stream as a
result of the local electrophoretic velocity of the ions (u.sub.ep)
exceeding the mean convective velocity of the fluid (PDF). To
maintain electroneutrality with the microchannel, anions are also
redirected into the brine stream.
[0127] The flow of ionic species through the microchannels of the
device was monitored by observing the flow of Ru(bpy).sup.2+ (a
fluorescent cationic tracer) through the device. FIGS. 7A and 7B
are fluorescence micrographs of the device taken before (FIG. 7A)
and after (FIG. 7B) application of a potential bias. As shown in
FIG. 7A, when no potential bias was applied, ions flowed through
the inlet channel (702), and into both the dilute outlet channel
(704) and the concentrated outlet channel (706). Upon application
of a potential bias, an ion depletion zone and subsequent electric
field gradient are formed near the BPE anode (708) in proximity to
the intersection (710) of the dilute outlet channel (704) and the
concentrated outlet channel (706; FIG. 7B). As a consequence, ions,
including the fluorescent cationic tracer Ru(bpy).sup.2+, are
directed into the concentrated outlet channel (706). Desalted water
(which is non-fluorescent in the micrograph due to the absence of
fluorescent cationic tracer Ru(bpy).sup.2+) flows into the dilute
outlet channel (704). These results demonstrate that both cations
and anions flow into the concentrated outlet channel (706). The
initial application of 2.5 V creates an oxidizing environment near
the BPE anode which causes partial dissolution of the Au anode.
[0128] To confirm that the formation of an ion depletion zone
resulted in the deionization of the fluid flowing into the device,
a similar experiment was conducted using a solution lacking
chloride ions. If all chloride ions are eliminated from solution,
one would not expect the BPE anode to induce formation of an ion
depletion zone and local electric field gradient (as in the case of
saltwater containing chloride ions). In the control experiment, a
solution of Na.sub.2SO.sub.4 was flowed through the device. As
shown in FIG. 8, upon application of 2.5 V, no decrease in
fluorescence intensity near the BPE anode was observed. This
finding was consistent with the seawater desalination being the
result of an ion depletion zone formed near the BPE anode.
[0129] FIG. 9 shows a representative plot of total current flowing
through the device (i.sub.tot) vs. time. The steady-state operating
current of the device was 65 nA. With a 2.5 V potential bias
driving the desalination process, the device operated at a power
consumption of only 162.5 nW.
[0130] Fluid flow rates through the dilute outlet channel could be
measured using non-charged beads. Fluid flow rates through the
dilute outlet channel could also be measured by tracking the
movement of fluorescent tracer after the 2.5 V driving potential
was turned off, in which case all mass transport was due to
PDF.
[0131] The average operating fluid flow rate of the devices was
.about.400 .mu.m/s. At higher fluid flow rates, the ion depletion
zone does not extend as far into the dilute outlet channel.
Consequently, the desalination process becomes less efficient, and
ions begin to flow into the dilute outlet channel during device
operation.
[0132] Using the device operating at 162.5 nW, 34 mWh/L energy
efficiencies were achieved. This energy efficiency is orders of
magnitude higher than the current state-of-the-art seawater
desalination technologies. For example, reverse osmosis is
typically performed at energy efficiencies of approximately 5 Wh/L,
and has only achieved maximum energy efficiencies of approximately
1.8 Wh/L. This superior efficiency of the microfluidic device
relative to reverse osmosis is particularly notable when
considering that these reverse osmosis energy efficiencies
correspond to the efficiencies of industrial desalination
facilities (which are often higher than efficiencies observed for
the same process conducted on a smaller scale).
[0133] A reduction in device scale typically results in a decrease
in energy efficiency. As a consequence, these devices appear to be
extremely competitive for small-scale desalination use. Moreover,
because little equipment is required, and device operation only
requires a 2.5 V power supply, these devices can be used in water
stresses regions. In addition, because BPEs do not require a direct
electrical connection, it is possible to simultaneously operate
numerous devices in parallel using a simple power supply.
[0134] The devices, systems, and methods of the appended claims are
not limited in scope by the specific devices, systems, and methods
described herein, which are intended as illustrations of a few
aspects of the claims. Any devices, systems, and methods that are
functionally equivalent are intended to fall within the scope of
the claims. Various modifications of the devices, systems, and
methods in addition to those shown and described herein are
intended to fall within the scope of the appended claims. Further,
while only certain representative devices, systems, and method
steps disclosed herein are specifically described, other
combinations of the devices, systems, and method steps also are
intended to fall within the scope of the appended claims, even if
not specifically recited. Thus, a combination of steps, elements,
components, or constituents may be explicitly mentioned herein or
less, however, other combinations of steps, elements, components,
and constituents are included, even though not explicitly
stated.
[0135] The term "comprising" and variations thereof as used herein
is used synonymously with the term "including" and variations
thereof and are open, non-limiting terms. Although the terms
"comprising" and "including" have been used herein to describe
various embodiments, the terms "consisting essentially of" and
"consisting of" can be used in place of "comprising" and
"including" to provide for more specific embodiments of the
invention and are also disclosed. Other than where noted, all
numbers expressing geometries, dimensions, and so forth used in the
specification and claims are to be understood at the very least,
and not as an attempt to limit the application of the doctrine of
equivalents to the scope of the claims, to be construed in light of
the number of significant digits and ordinary rounding
approaches.
[0136] Unless defined otherwise, all technical and scientific terms
used herein have the same meanings as commonly understood by one of
skill in the art to which the disclosed invention belongs.
Publications cited herein and the materials for which they are
cited are specifically incorporated by reference.
* * * * *