ELECTRODEIONIZATION DEVICE AND METHOD WITH IMPROVED
SCALING RESISTANCE
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The invention relates to apparatus and methods for carrying out
electrodeionization to purify water, and more particularly to an electrodeionization
device and method with improved scaling resistance.
Description of Related Art
[0002] Electrodeionization (EDI) is a membrane separation deionization
technique that combines the techniques of electodialysis and ion exchange. EDI
purification apparatus has many advantages, such as, producing water continuously,
regenerating ion exchange resins without using alkalis and acids, automatically
operating, etc. It has become a standard alternative to mixed bed as the final water
treatment apparatus used in pure water preparation systems. A plate and frame type
EDI apparatus includes an anode, a cathode, anion-permeable membranes and cationpermeable
membranes. The membranes are arranged alternately in such a manner as to
alternately form concentrating compartments and desalting compartments (dilution
compartments) in a stack between the anode and the cathode. The desalting
compartments are filled with an ion exchanger such as an ion exchange resin beads. The
liquid being treated in the diluting compartments is depleted of ions while the liquid in
the concentrating compartments becomes enriched with the transferred ions through
their respective membrane and carries them in concentrated form.
[0003] The cations and anions ions in the feed water to the EDI apparatus can
perform ion exchange with the H+ and OH in the cation and anion exchange resins
respectively, and therefore are ionically attach to the resin particles. The ions migrate
under the influence of electric field through the ion-flow passage formed by resin
particles. This is because that in the application systems of EDI, the electric
conductivity of the resin is several magnitudes higher than that of the water solution.
The ions migrate into the concentrate chamber through the ion exchange membranes,
and hence complete the process of water deionization. Under a certain potential drop,
the water is decomposed into H+ and OH due to the assisted water dissociation at the
interface of the two different types of resins and membranes and the resin is therefore
regenerated.
[0004] The diluting compartments are filled with porous ion exchanging solid
materials producing voids between the particles through which the water to be
deionized flows. The ion exchanging materials are commonly mixtures of cation
exchanging resins and anion exchanging resins or woven and non-woven fibers. An
assembly of one or more pairs of diluting and concentrating compartments, referred to
as a "cell pair", is bounded on either side by an anode and a cathode which typically
apply an electric field perpendicular to the general direction of liquid flow. However, in
other configurations, the current and liquid flow in the same or opposite directions. The
applied electric field causes anions to move from the diluting compartment across the
anion exchange membrane into the concentrating compartment nearer the anode and
cations to move from the diluting compartment across the cation exchange membrane
into the concentrating compartment nearer the cathode. The anions and cations become
trapped in the concentrating compartments because the movement of anions toward the
anode is blocked by a cation exchange membrane, and the movement of cations toward
the cathode is blocked by an anion exchange membrane. A flow of water is set up to
remove the ions from the concentrating compartments. The net result of the process is
the removal of ions from the water stream flowing through the diluting compartments
and their concentration in the water flowing through the concentrating compartments.
[0005] Typically, the EDI feed water is initially pretreated in a reverse osmosis
step to reduce the ionic load and colloidal contaminants therein, prior to being directed
towards electrodeionization. This practice extends the useful life of the resin beads
used in electrodeionization. However, even when using a reverse osmosis pretreating
step, the concentration of calcium and/or magnesium cations and sulfate and/or
carbonate anions can cause so-called "scaling" in the concentration compartments due
to precipitation. The consequence of this scaling is restricted concentrate flow, an
increase in stack electrical resistance, a drop in current density and eventually a sharp
decrease in the purity of the product water. This negatively affects performance
characteristics by increasing operating cost, decreasing product water quality, or making
the EDI stack inoperable.
[0006] It is desired to have an electrodeionization device and method with
improved scaling resistance.
SUMMARY OF THE INVENTION
[0007] In one aspect, the invention is directed to an electrodeionization
apparatus. The electrodeionization apparatus includes an anode compartment provided
with an anode and a cathode compartment spaced from the anode compartment and
provided with a cathode, wherein the anode and cathode are configured for coupling to
a DC power source to effect an electric potential difference between the anode and the
cathode and thereby influence transport of ionic material in liquid media and ion
exchange media by the influence of the electric potential difference. The
electrodeionization apparatus also includes a feed inlet receiving a feed solution, a
product water outlet and a plurality of anion exchange membranes and a plurality of
cation exchange membranes alternately arranged between the anode compartment and
the cathode compartment. The electrodeionization apparatus also includes a plurality of
spacers, wherein the spacers and the anion and cation exchange membranes are
arranged to form a first diluting compartment receiving feed solution from the feed
inlet, a second diluting compartment in series with the first diluting compartment and
delivering product water to the product water outlet, a first concentrating compartment
and a second concentrating compartment. The first and second diluting compartments
are bounded by an anion exchange membrane on the side closest to the anode and by a
cation exchange membrane on the side closest to the cathode. The first and second
concentrating compartments are bounded by a cation exchange membrane on the side
closest to the anode and by an anion exchange membrane on the side closest to the
cathode.
[0008] In another aspect, the spacers and the anion and cation exchange
membranes together form an electrodeionization group. The electrodeionization
apparatus includes a plurality of repeating electrodeionization groups assembled
together as a stack.
[0009] The present invention and its advantages over the prior art will become
apparent upon reading the following detailed description and the appended claims with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above mentioned and other features of this invention will become
more apparent and the invention itself will be better understood by reference to the
following description of embodiments of the invention taken in conjunction with the
accompanying drawings, wherein:
[0011] FIG. 1 illustrates a schematic view of a system for reducing recalcitrant
organic pollutants according to an embodiment of the invention;
[0012] FIG. 2 illustrates a schematic view of a system for reducing recalcitrant
organic pollutants according to an embodiment of the invention; and
[0013] FIG. 3 illustrates a schematic view of a system for reducing recalcitrant
organic pollutants according to an embodiment of the invention.
[0014] Corresponding reference characters indicate corresponding parts
throughout the views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The invention will now be described in the following detailed description
with reference to the drawings, wherein preferred embodiments are described in detail
to enable practice of the invention. Although the invention is described with reference
to these specific preferred embodiments, it will be understood that the invention is not
limited to these preferred embodiments. But to the contrary, the invention includes
numerous alternatives, modifications, and equivalents as will become apparent from
consideration of the following detailed description.
[0016] Referring to FIG. 1, there is shown an electrodeionization apparatus 10
having a plurality of diluting chambers 1 and a plurality of concentrating chambers 13
as will be further described below which have both anion exchange resin and cation
exchange resin contained therein. According to the invention, each diluting chamber 12
comprises into a first diluting compartment 14 and a second diluting compartment 16.
Each concentrating chamber 13 is divided into a first concentrating compartment 15 and
a second concentrating compartment 17. As seen in FIG. 1, the electrodeionization
apparatus 10 is made of repeating groups G of components comprising first and second
diluting compartments 14, 16 and first and second concentrating compartments 15, 17.
[0017] The electrodeionization apparatus 10 includes an anode compartment 20
provided with an anode 22, and a cathode compartment 24 spaced from the anode
compartment and provided with a cathode 25. Each of the compartments 20, 24 is
configured to receive a flow of electrolytic material 26, such as feed water or an
aqueous solution. The anode 22 and cathode 25 are configured for coupling to a DC
power source to effect an electric potential difference between the anode 22 and the
cathode 25 and thereby influence transport of ionic material in liquid media and ion
exchange media by the influence of the electric potential difference. As the anode
compartment 20 and/or the cathode compartment 24 may, in some embodiments, be
disposed adjacent to a concentrating chamber 13, the compartments 20 and 24 may also
be considered to be diluting chambers 12.
[0018] In an embodiment in which the anode compartment 20 and/or the
cathode compartment 24 is considered a diluting chamber 12, the anode compartment
20 and/or the cathode compartment 24 is configured to receive feed solution 40. In an
embodiment in which the anode compartment 20 and/or the cathode compartment 24 is
considered a concentrating chamber 13, the anode compartment 20 and/or the cathode
compartment 24 is configured to receive first concentrating solution 5 1 or second
concentrating solution 55.
[0019] In Fig. 1, the anode compartment 20 is configured as a diluting chamber
12 and receives feed solution 40. However, cathode compartment 24, which is not
configured as either a diluting chamber 12 or a concentrating chamber 13, receives a
flow of electrolytic material 26.
[0020] A plurality of anion exchange membranes 28 and cation exchange
membranes 30 are alternately arranged between the anode compartment 20 and the
cathode compartment 24 to form the first and second diluting compartments 14, 16 and
the first and second concentrating compartments 15, 17. As used herein, the term
"anion exchange membrane" means a membrane which is configured to preferentially
permit the transport of anions over that of cations from the first and second diluting
compartments 14, 16 to the first and second concentrating compartments 15, 17 and the
term "cation exchange membrane" means a membrane which is configured to
preferentially permit the transport of cations over that of anions from the first and
second diluting compartments 14, 16 to the first and second concentrating
compartments 15, 1 during operation of the electrodeionization apparatus 10. The
illustrated ion fluxes across the membranes 28, 30 in FIG. 1 is limited to Sodium,
Calcium, Hydrogen, Hydroxide, Chloride, and Carbonate ions for the purpose of
simplicity. One skilled in the art will understand that other ions would be transferred in
a similar manner.
[0021] Each of the first and second diluting compartments 14, 16 are bounded
by an anion exchange membrane 28 on the anode side (i.e., the side closest to the anode
22) and by a cation exchange membrane 30 on the cathode side (i.e., the side closest to
the cathode 25). Each of the first and second concentrating compartments 15, 17 are
bounded by a cation exchange membrane 30 on the anode side and by an anion
exchange membrane 28 on the cathode side. The anion exchange membranes 28 are
configured to permit preferential transport of anions into the concentrating
compartments 15, 17. The cation exchange membranes 30 are configured to permit
preferential transport of cations into the concentrating compartments 15, 17. FIG. 1
shows the electrodeionization apparatus 10 with three repeating groups G. One skilled
in the art will understand that the number of repeating groups may be more or less
without departing from the scope of the invention.
[0022] The components shown on FIG. 1 are assembled together as a stack
between pressure plates (not show) held together by bolts or a hydraulic ram or in a
housing that contains the components and provides manifolds to direct the incoming
liquid to and the outgoing liquid from diluting compartments 14, 16 and concentrating
compartments 15, 17. Diluting compartments 14, 16 and concentrating compartments
15, 17 are typically between about 1.0 mm and 10.0 mm thick, and there typically are
about 10 to 300 diluting compartments in apparatus 10. The surface area of each
exchange membrane 28, 30 is typically between about 0.5 (0.0465 m2) and 5.0 square
feet (0.465 m2) .
[0023] A feed solution 40 (typically the product water output of an RO
apparatus) enters inlet 42 of the first diluting compartment 14. The first diluting
compartment is separated by the cation exchange membrane 30 from the first
concentrate compartment 15 and by the anion exchange membrane 28 from the second
concentrate compartment 17. Desirably, a major portion of ionic contaminants present
in the feed solution 40 is transferred to the adjacent first and second concentrating
compartments 15, 17 during the path through the first diluting compartment 14. Thus,
most of cations would be transferred to the first concentrate compartment 15 and most
of the anions would be transported to the second concentrate compartment 17.
[0024] In one embodiment, the thickness of the first diluting compartment 14 is
greater than the thickness of the second diluting compartment 16. In another
embodiment, the thickness of the first diluting compartment 14 is about two to four
times greater than the thickness of the second diluting compartment 16. In an additional
embodiment, the thickness of the first diluting compartment 14 is about four to eight
times greater than the thickness of the second diluting compartment 16.
[0025] Further, in another embodiment, the thickness of the first diluting
compartment 14 is less than the thickness of the second diluting compartment 16. In
another embodiment, the thickness of the first diluting compartment 14 is about two to
four times less than the thickness of the second diluting compartment 16. In an
additional embodiment, the thickness of the first diluting compartment 14 is about four
to eight times less than the thickness of the second diluting compartment 16.
[0026] After passing through the first diluting compartment 14, the feed solution
enters the second diluting compartment 16. During this stage, remaining trace
contaminants are removed. The predominant ions crossing through the adjacent anion
exchange and cation exchange membranes 28, 30 from the second diluting compartment
16 are hydrogen and hydroxide ions produced from water splitting. More particularly,
in the interface between the ion exchange resins and the ion exchange resins and ion
exchange membrane 28, 30, water is actively dissociated to form H+ and OH . In such a
case, part of the H+ ions will permeate through the cation exchange membrane 30 into
the second concentrate chamber 17 and part of OH will permeate through the anion
exchange membrane 28 into the first concentrate chamber 15. The surface of the
concentrate chamber side of the cation exchange membrane 30 exhibits strong acidic,
indicating the existence of local high H+ concentration. As comparison, the surface of
concentrate chamber side of the anion exchange membrane 28 exhibits strong alkaline,
indicating the existence of high OH concentration. As a result, the stream in the first
concentrate compartment 15 carries a majority of cations and has a high pH, and the
stream in the second concentrate compartment 1 carries a majority of anions and has a
low pH. Cation/anion segregation provides reduced contact times between scaling
cations and scaling anions so as to reduce the risk of calcium/magnesium
carbonate/sulfate scale formation within the electrodeionization apparatus.
[0027] The feed solution 40 is purified in first and second diluting
compartments 14, 16 and is discharged as a purified liquid flow through outlet 48. The
first concentrating compartment 15 is configured to receive a first concentrating flow 5 1
of liquid, such as water or an aqueous solution, which accepts the ions that transport
from adjacent first and second diluting compartments 14, 16, out of the first
concentrating compartment 15. A liquid flow 53, which is concentrated in these ions, is
discharged from the first concentrating compartment 17. The second concentrating
compartment 17 is configured to receive a second concentrating flow 55 of liquid, such
as water or an aqueous solution, which accepts the ions that transport from adjacent first
and second diluting compartments 14, 16, out of the second concentrating compartment
17. A liquid flow 59, which is concentrated in these ions, is discharged from the second
concentrating compartment 17. The liquid flowing through the first and second
concentrating compartments 15, 17 can flow in a co-current or counter-current or cross
current direction, or other possible flow configurations, relative to the feed solution 40
liquid flowing through first and second diluting compartments 14, 16.
[0028] In the embodiment illustrated in FIG. 2, one repeating group G consists
of a first diluting compartment spacer 114 and a second diluting compartment spacer
116 for diluting streams, a first concentrating compartment spacer 115 and a second
concentrating compartment spacer 117 for concentrating streams, two cation-exchange
membranes 30 and two anion exchange membranes 28. The spacers 114, 115, 116, 117
and membranes 28, 30 are placed in alternating manner. The anion and cation exchange
membranes 28, 30 are substantially impermeable for liquid flow and separate streams in
adjacent spacers. Each spacer has ports allowing entering and exiting of corresponding
stream or providing isolated connection for other streams as will be described below.
[0029] The group G comprise of (from top to bottom) first diluting compartment
14, cation exchange membrane 30, first concentrate compartment 15, anion exchange
membrane 28, second diluting compartment 16, cation exchange membrane 30, second
concentrate compartment 17, and an anion exchange membrane 28. The feed solution
40 entering the first diluting compartment 14 through port 120 shown in the front-right
corner of the first diluting compartment spacer 114 and exits through two ports 122 on
the far corners of the first diluting compartment spacer. Arrows indicate the stream
direction. The majority of cations present in the incoming feed solution are transferred
through cation exchange membrane 30 to the concentrate stream in the first concentrate
compartment 15. The exiting ports 122 of the first diluting compartment 14 are
hydraulically connected with entrance ports 124 of the second diluting compartment 16.
In the illustrated embodiment, the ports 124 are shown in the far corners of the second
dilute compartment spacer 116 forming the second dilute compartment 16. Arrows
show the flow direction in the second dilute compartment 16. The treated stream is
exiting the second dilute compartment 16 through the port 128 shown in the close-left
corner. First and second concentrating compartments 15, 17 have streams flowing in
parallel through corresponding spacers 115, 117 as shown by flow arrows. The
concentrating streams have common entry port 130 (far side, middle) and common exit
port 132 (close side, middle).
[0030] The ports in the spacers, the spacer relative placement, and other
necessary hydraulic connection allow the first and second dilute compartments 14, 16 to
be connected in series and the first and second concentrated compartments 15, 17 to be
connected in parallel all within each repeating group G of components. Desirably, the
operating parameters of the electrodeionization apparatus 10 are chosen such that a
substantial fraction of scale-forming ions in the feed solution 40 are transferred to the
adjacent first and second concentrate compartments 15, 17 from the first dilute
compartment 14.
[0031] One skilled in the art will understand that the stream in the first diluting
compartment 14 can flow counter current or co-current to the stream in the second
diluting compartment 16, the stream in the first concentrating compartment 15 can flow
counter current or co-current to the stream in the first diluting compartment 14, the
stream in the first concentrating compartment 15 can flow counter current or co-current
to the stream in the second concentrating compartment 17. Additionally, the first
concentrating compartment 14 and the second concentrating compartment 1 can be
recombined at place, where electrically induced water splitting/recombination is absent
or may be kept separately in the stack and evacuated through separate ports. First
concentrate compartment 15 and second concentrate compartment 17 can be fed from
the same source or can be fed from different sources. In one embodiment, concentrate
flow (at least one of the two) is fed by dilute feed. It is also contemplated that
concentrate flow (at least one of the two) is fed by dilute product water, or that
concentrate flow (at least one of the two) is fed by intermediate product water obtained
from between the first and second diluting compartments 14, 16. Alternately,
concentrate flow (at least one of the two) may be fed by an independent source of low
hardness/ low inorganic carbon water.
[0032] Spacers 114, 115, 116, 117 are interposed between the alternating anion
and cation exchange membranes 28, 20 so as to maintain spacing between opposing
anion and cation exchange membranes 28, 20 and thereby provide compartments 14,
15, 16, 17 with respective flowpaths for liquid flow. Spacers 114, 115, 116, 117 may
include a mesh, wherein the mesh is provided to maintain spacing between opposing
membranes, or an opposing membrane and an end frame assembly, of the concentrating
chambers of the electrodeionization apparatus 10, and thereby facilitate provision of a
fluid flowpath within the concentrating compartments. It is understood that
concentrating compartments containing ion exchange material do not necessarily
require spacers with mesh, as the ion exchange material within the concentrating
compartments facilitate the provision of a flowpath in the compartments. One such
concentrate chamber ion exchange resin arrangement can be found in
US20080073215A, herein incorporated by reference. Having said that, concentrating
compartments whose construction includes spacers with mesh are not precluded from
the scope of the invention. Accordingly, suitable spacers include spacers with or
without a mesh.
[0033] FIG 3. illustrates another embodiment of electrodeionization apparatus
10'. FIG. 3 shows a single repeating group G of components; however, one skilled in
the art will understand that more groups may be arranged as a stack in the apparatus
10'. A diluting compartment spacer 212 (top) has an entrance port 220 at close-right
corner and exits though an exit port 222 in the far-left corner. The first half of this
diluting compartment spacer 212 forms a first diluting compartment 214 that operates in
a manner similar to operation of the first diluting compartment 14 described above. The
second half of the diluting compartment spacer 212 forms a second diluting
compartment 216 that is similar to second diluting compartment 16 in previous
example.
[0034] A concentrate spacer 213 adjacent the diluting compartment spacer 212
has a concentrate entrance port 230 in the middle of the spacer 213 and the incoming
concentrate stream splits in two flow directions. The concentrate compartment spacer
213 forms a first concentrating compartment 215 that receives a portion of the stream
directed in a first direction as represented by flow arrows 260 and forms a second
concentrating compartment 217 that receives a second portion of the stream directed in
a second direction as represented by flow arrows 262. The flow 260 directed in the first
direction is similar to the flow in the first concentrating compartment spacer 115 from
FIG. 2. This flow would accept most of cations from dilute stream above it and mostly
hydroxides from dilute flow below. The flow 262 directed in the second direction
would be similar to the flow in the second concentrating compartment spacer 117 from
FIG. 2. It would be collecting anions from dilute stream below and hydrogen ions from
dilute stream above it. The two other spacers 212' and 213' in FIG. 3 accommodate
flows similar to the flows in spacers 212 and 213, but directed in the opposite direction.
The operation conditions desirably allows for transfer of a majority of scale-forming
ions within a first diluting compartment 215.
[0035] Example of suitable ion permeable membranes 28, 30 include
heterogeneous ion exchange membranes and homogeneous ion permeable membranes.
Suitable heterogeneous ion permeable membranes include, for example, Membranes
International CMI-7000S™ (a cation exchange membrane) and Membranes
International AMI-7001S™ (an anion exchange membrane). Suitable homogeneous ion
permeable membrane include, for example, GE Infrastructure Water and Process
Technologies (formerly IONICS) CR67HMP™ (a cation exchange membrane) and GE
Infrastructure Water and Process Technologies (formerly IONICS) A103QDP™ (an
anion exchange membrane). Fixed ion exchange materials can be provided in strands of
combined anion and cation exchange materials in woven fabric, nonwoven fabric
(randomly oriented strands) or extruded netting. Fixed ion exchange materials could
also be provided by open cell foam and by combined exchange particles. The strands
used in the fabrics can also take a variety of forms. The strands can be made in the
form of a bundle of multiple filaments, in the form of braided strands, and in the form
of a combined exchange particle filament, which is made of cation exchange particles
and anion exchange particles that are held together by binder. The open cell foam
includes cation exchange particles, anion exchange particles and binder and has an
interconnected network of flow passages herethrough. The combined ion exchange
particles are made up of cation exchange particles, anion exchange particles and binder
and are sufficiently large so as to cause an acceptably low pressure drop in the flow
channels. In some embodiments the ion exchange materials are not mixed, but instead
include only anion exchange materials or particles or cation exchange materials or
particles in a channel between membranes or region in a channel between membranes.
It is also possible to use packed ion exchange in the diluting and concentrating channels
in which the ion exchange material is fixed in place by compression of the materials so
as to limit the movement of the material in the device, see US 5,961,805, herein
incorporated by reference.
[0036] In one embodiment, ion exchange material is disposed within each of the
diluting compartments 14, 16 and concentrating compartments 15, 17. For example, the
ion exchange material is mixed ion exchange material. Examples of suitable forms of
ion exchange materials include beads, irregular shaped particles, fibers, rods, fabrics, or
porous monoliths. The ion exchange materials may include both natural and synthetic
materials.
[0037] As used herein, the term "anion exchange material" means material
which is preferentially conductive to anionic species. In this respect, such material is
configured to selectively exchange anionic species present in the material for anionic
species from surrounding liquid and facilitate migration of the exchanged anionic
species under an applied electric field. Examples of suitable anion exchange material
include synthetic poly-styrenic beads cross-linked with divinyl benzene, such beads
being functionalized with trimethylammonium or dimethylethanolammonium groups
(e.g., Mitsubishi DIAION SA10A™ or Mitsubishi DIAION SA20A™). As used
herein, the term "cation exchange material" means material which is preferentially
conductive to cationic species. In this respect, such material is configured to selectively
exchange cationic species present in the material for cationic species from surrounding
liquid and facilitate migration of the exchanged cationic species under an applied
electric field. Examples of suitable cation exchange material include synthetic polystyrenic
beads cross-linked with divinyl benzene, such beads being functionalized with
sulphonic acid groups (e.g., Mitsubishi DIAION SK-1B™).
[0038] While the disclosure has been illustrated and described in typical
embodiments, it is not intended to be limited to the details shown, since various
modifications and substitutions can be made without departing in any way from the
spirit of the present disclosure. As such, further modifications and equivalents of the
disclosure herein disclosed may occur to persons skilled in the art using no more than
routine experimentation, and all such modifications and equivalents are believed to be
within the scope of the disclosure as defined by the following claims.
[0039] What is claimed is:
CLAIMS
1. An electrodeionization apparatus comprising:
an anode compartment provided with an anode;
a cathode compartment spaced from the anode compartment and provided with a
cathode, wherein the anode and cathode are configured for coupling to a DC power
source to effect an electric potential difference between the anode and the cathode and
thereby influence transport of ionic material in liquid media and ion exchange media by
the influence of the electric potential difference;
a feed inlet receiving a feed solution;
a product water outlet;
a plurality of anion exchange membranes and a plurality of cation exchange
membranes alternately arranged between the anode compartment and the cathode
compartment; and
a plurality of spacers, wherein said spacers and said anion and cation exchange
membranes are arranged to form a first diluting compartment receiving feed solution
from the feed inlet, a second diluting compartment in series with the first diluting
compartment and delivering product water to the product water outlet, a first
concentrating compartment and a second concentrating compartment, wherein the first
and second diluting compartments are bounded by an anion exchange membrane on the
side closest to the anode and by a cation exchange membrane on the side closest to the
cathode, and the first and second concentrating compartments are bounded by a cation
exchange membrane on the side closest to the anode and by an anion exchange
membrane on the side closest to the cathode.
2. The electrodeionization apparatus of claim 1 wherein said spacers which
form first and second diluting compartments and first and second concentrating
compartments and said anion and cation exchange membranes together form an
electrodeionization group, the electrodeionization apparatus comprising a plurality of
repeating electrodeionization groups assembled together as a stack.
3. The electrodeionization apparatus of claim 2 wherein a majority portion
of ionic contaminants present in the feed solution is transferred to the adjacent first and
second concentrating compartments during a path through the first diluting
compartment such that a majority of cations are transferred to the first concentrate
compartment and a majority of the anions are transported to the second concentrate
compartment.
4. The electrodeionization apparatus of claim 3 wherein the first
concentrate compartment carries a majority of cations and has a high pH, and the
second concentrate compartment carries a majority of anions and has a low pH to
reduce scale formation within the electrodeionization apparatus.
5. The electrodeionization apparatus of claim 2 wherein the
electrodeionization group has first and second cation exchange membranes and first and
second anion exchange membranes and is arranged with the first cation exchange
membrane adjacent the first diluting compartment, the first concentrate compartment
adjacent the first cation exchange membrane, the first anion exchange membrane
adjacent the first concentrate compartment, the second diluting compartment adjacent
the first anion exchange membrane, the second cation exchange membrane adjacent the
second diluting compartment, the second concentrate compartment adjacent the second
cation exchange membrane, and the second anion exchange membrane adjacent the
second concentrate compartment.
6. The electrodeionization apparatus of claim 2 wherein the
electrodeionization group comprises first and second diluting compartment spacers and
first and second concentrating compartment spacers, wherein:
a first of said diluting compartment spacers forms first and second diluting
compartments, said first diluting compartment spacer having an entrance port at one end
and an exit port at an opposite end, where a first portion of the first diluting
compartment spacer forms a first diluting compartment receiving feed solution from its
feed inlet and a second diluting compartment receiving feed solution from said first
diluting compartment,
a second of said diluting compartment spacers configured such that its entrance
and exit ports are on opposite ends from that of the first diluting compartment spacer
such that flow through the second diluting compartment is in the opposite direction
compared to the flow in the first diluting compartment spacer, wherein said second
diluting compartment spacer forms first and second diluting compartments configured
in series; and
each of said concentrating compartment spacers have an entrance port receiving
concentrate stream in the middle of the concentrating spacer, the concentrating spacer
directing incoming concentrate stream in two flow directions, wherein the concentrate
compartment spacer forms the first and second concentrate compartments, wherein the
first concentrating compartment receives a first portion of the concentrate stream
directed in a first direction, and the second concentrating compartment receives a
second portion of the stream directed in a second direction.
7. The electrodeionization apparatus of claim 6 wherein the
electrodeionization group has first and second cation exchange membranes and first and
second anion exchange membranes and is arranged with the first cation exchange
membrane adjacent the first diluting spacer, the first concentrate compartment spacer
adjacent the first cation exchange membrane, the first anion exchange membrane
adjacent the first concentrate compartment spacer, the second diluting compartment
spacer adjacent the first anion exchange membrane, the second cation exchange
membrane adjacent the second diluting compartment spacer, the second concentrate
compartment spacer adjacent the second cation exchange membrane, and the second
anion exchange membrane adjacent the second concentrate compartment spacer.
8. The electrodeionization apparatus of claim 1 wherein the diluting
compartments and concentrating compartments are between about 1.0 mm and 10.0 mm
thick.
9. The electrodeionization apparatus of claim 1 wherein the thickness of
said first diluting compartment is greater than the thickness of said second diluting
compartment.
10. The electrodeionization apparatus of claim 9 wherein the thickness of
said first diluting compartment is about two to four times greater than the thickness of
said second diluting compartment.
11. The electrodeionization apparatus of claim 9 wherein the thickness of
said first diluting compartment is about four to eight times greater than the thickness of
said second diluting compartment.
12. The electrodeionization apparatus of claim 1 wherein the thickness of
said first diluting compartment is less than the thickness of said second diluting
compartment.
13. The electrodeionization apparatus of claim 12 wherein the thickness of
said first diluting compartment is about two to four times less than the thickness of said
second diluting compartment.
14. The electrodeionization apparatus of claim 12 wherein the thickness of
said first diluting compartment is about four to eight times less than the thickness of
said second diluting compartment.