U.S. patent application number 12/018047 was filed with the patent office on 2008-07-31 for method for treatment of feedwaters by membrane separation under acidic conditions.
Invention is credited to Debasish Mukhopadhyay.
Application Number | 20080179242 12/018047 |
Document ID | / |
Family ID | 29418386 |
Filed Date | 2008-07-31 |
United States Patent
Application |
20080179242 |
Kind Code |
A1 |
Mukhopadhyay; Debasish |
July 31, 2008 |
METHOD FOR TREATMENT OF FEEDWATERS BY MEMBRANE SEPARATION UNDER
ACIDIC CONDITIONS
Abstract
A process for treatment of acidic waters via membrane separation
equipment. A feedwater is maintained or adjusted to a pH of 4.3 or
lower, and fed to a membrane separation system. In this manner,
species such as total organic carbon (TOC) become more ionized, and
(a) their rejection by the membrane separation process is
significantly increased, and (b) their solubility in the reject
stream from the membrane process is significantly increased.
Passage of total organic carbon (TOC) through the membrane is
significantly reduced. A recovery ratio at or exceeding eighty
percent (80%) is achievable with most feedwaters, while
simultaneously achieving a substantial reduction in cleaning
frequency of the membrane separation equipment. The method is
particularly useful for the preparation of high purity water.
Inventors: |
Mukhopadhyay; Debasish;
(Palo Alto, CA) |
Correspondence
Address: |
R REAMS GOODLOE, JR. & R. REAMS GOODLOE, P.S.
24722 104TH. AVENUE S.E., SUITE 102
KENT
WA
98030-5322
US
|
Family ID: |
29418386 |
Appl. No.: |
12/018047 |
Filed: |
January 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10140445 |
May 6, 2002 |
7320756 |
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12018047 |
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60288861 |
May 5, 2001 |
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Current U.S.
Class: |
210/627 ;
210/652 |
Current CPC
Class: |
C02F 1/441 20130101;
B01D 2311/18 20130101; B01D 2311/2649 20130101; B01D 61/04
20130101; B01D 2311/04 20130101; Y10S 210/90 20130101; B01D 61/022
20130101; B01D 2311/04 20130101 |
Class at
Publication: |
210/627 ;
210/652 |
International
Class: |
C02F 3/02 20060101
C02F003/02; B01D 61/04 20060101 B01D061/04 |
Claims
1. A process for treatment of a feedwater stream using reverse
osmosis membrane separation equipment, said reverse osmosis
membrane separation equipment comprising at least one reverse
osmosis membrane separator, to produce a low solute containing
product stream and a high solute containing reject stream, said
process comprising: (a) providing a feedwater stream containing
solutes, said solutes comprising at least one constituent that can
contribute to fouling of said reverse osmosis membrane separator in
the absence of free mineral acidity; (b) pretreating said feedwater
stream by controlling the pH of said feedwater stream to about 4.3
or lower by the time said feedwater stream enters said reverse
osmosis membrane separator, to assure at least some free mineral
acidity in the pretreated feedwater; (c) passing the resultant
pretreated feedwater stream through said reverse osmosis membrane
separation equipment, said reverse osmosis membrane separation
equipment substantially resisting passage of at least some
dissolved species therethrough, to concentrate said pretreated
feedwater to said preselected concentration factor, to produce (i)
a high solute containing reject stream, and (ii) a low solute
containing product stream; (d) wherein feedwater stream comprises
one or more total organic carbon (TOC) constituents, and wherein
said one or more total organic carbon (TOC) constituents are
substantially prevented from passing through said reverse osmosis
membrane separator to said product stream; and (e) wherein said one
or more total organic carbon (TOC) constituents comprise one or
more non-ionizable species, said one or more non-ionizable species
comprising isopropyl alcohol, or acetone.
2. The process as set forth in claim 1, wherein said total organic
carbon (TOC) constituents in said product stream is approximately
ten percent (10%) or less of the concentration of such total
organic carbon (TOC) constituents in said feedwater stream.
3. The process as set forth in claim 1, or in claim 2, wherein said
feedwater stream comprises ammonium ions, and wherein said product
stream contains approximately eight percent (8%) or less of the
ammonium ion concentration present in said feedwater stream.
4. The process as set forth in claim 1, or in claim 2, further
comprising (i) adding either ferrous or ferric ions to said
feedwater stream before entry of said feedwater stream to said
reverse osmosis membrane separation equipment, as reactants to
facilitate removal of total organic carbon (TOC) constituents, and
(ii) adding hydrogen peroxide to said feedwater stream at any point
before feed to said reverse osmosis membrane separation
equipment.
5. The process as set forth in claim 1, or in claim 2, further
comprising ozonation of said feedwater stream with an ozone
containing gas, and wherein said total organic carbon (TOC)
constituents are effectively prevented from entering said product
stream.
6. The process as set forth in claim 1, or in claim 2, further
comprising ozonation of said product water stream with an ozone
containing gas, and wherein said total organic carbon (TOC)
constituents are effectively eliminated from said product
stream.
7. The process as set forth in claim 1, or in claim 2, further
comprising removal of oxidants from said feedwater stream, and
wherein said pretreatment process of oxidant removal comprises the
addition of sodium meta-bisulfite to said feedwater stream.
8. The process as set forth in claim 7, further comprising one or
more additional pretreatment processes, said additional
pretreatment processes comprising (i) media filtration, (ii)
cartridge filtration, (iii) ultrafiltration, (iv) nanofiltration,
or (v) degasification.
9. The process as set forth in claim 1, further comprising one or
more additional pretreatment processes, said additional
pretreatment processes comprising (i) media filtration, (ii)
cartridge filtration, (iii) ultrafiltration, (iv) nanofiltration,
(v) degasification, or (vi) oxygen removal.
10. The process as set forth in claim 1, wherein said membrane
separator comprises a loose reverse osmosis membrane.
11. A process for treatment of a feedwater stream using reverse
osmosis membrane separation equipment, said reverse osmosis
membrane separation equipment comprising at least one reverse
osmosis membrane separator, to produce a low solute containing
product stream and a high solute containing reject stream, said
process comprising: (a) providing a feedwater stream containing
solutes, said solutes comprising at least one constituent that can
contribute to fouling of said reverse osmosis membrane separator in
the absence of free mineral acidity; (b) pretreating said feedwater
stream to reduce the pH of said feedwater stream to about 4.3 or
lower by the time said feedwater stream enters said reverse osmosis
membrane separator, to assure at least some free mineral acidity in
the pretreated feedwater; (c) passing the resultant pretreated
feedwater stream through said reverse osmosis membrane separation
equipment, said reverse osmosis membrane separation equipment
substantially resisting passage of at least some dissolved species
therethrough, to concentrate said pretreated feedwater to said
preselected concentration factor, to produce (i) a high solute
containing reject stream, and (ii) a low solute containing product
stream; (d) wherein feedwater stream comprises one or more total
organic carbon (TOC) constituents, and wherein said one or more
total organic carbon (TOC) constituents are substantially prevented
from passing through said reverse osmosis membrane separator to
said product stream; and (e) wherein the ratio of the quantity of
said product stream produced to the quantity of said feedwater
stream provided is about eighty percent (80%) or more.
12. The process as set forth in claim 11, wherein the ratio of the
quantity of said product stream produced to the quantity of said
feedwater stream provided is about eighty-five percent (85%) or
more.
13. The process as set forth in claim 11, wherein the ratio of the
quantity of said product stream produced to the quantity of said
feedwater stream provided is about ninety percent (90%) or
more.
14. The process as set forth in claim 11, or in claim 12, or in
claim 13, wherein said total organic carbon (TOC) constituents in
said product stream is approximately ten percent (10%) or less of
the concentration of such total organic carbon (TOC) constituents
in said feedwater stream.
15. The process as set forth in claim 14, wherein said feedwater
stream comprises ammonium ions, and wherein said product stream
contains approximately eight percent (8%) or less of the ammonium
ion concentration present in said feedwater stream.
16. The process as set forth in claim 11, or in claim 12, or in
claim 13, wherein said feedwater stream comprises ammonium ions,
and wherein said product stream contains approximately eight
percent (8%) or less of the ammonium ion concentration present in
said feedwater stream.
17. The process as set forth in claim 14, further comprising (i)
adding either ferrous or ferric ions to said feedwater stream
before entry of said feedwater stream to said reverse osmosis
membrane separation equipment, as reactants to facilitate removal
of total organic carbon (TOC) constituents, and (ii) adding
hydrogen peroxide to said feedwater stream at any point before feed
to said reverse osmosis membrane separation equipment.
18. The process as set forth in claim 11, further comprising
ozonation of said feedwater stream with an ozone containing gas,
and wherein said total organic carbon (TOC) constituents are
effectively prevented from entering said product stream.
19. The process as set forth in claim 11, further comprising
ozonation of said product water stream with an ozone containing
gas, and wherein said total organic carbon (TOC) constituents are
effectively eliminated from said product stream.
20. The process as set forth in claim 11, further comprising
pretreatment for removal of oxidants from said feedwater stream,
and wherein said pretreatment process of oxidant removal comprises
the addition of sodium meta-bisulfite to said feedwater stream.
21. The process as set forth in claim 20, further comprising one or
more additional pretreatment processes, said additional
pretreatment processes comprising (i) media filtration, (ii)
cartridge filtration, (iii) ultrafiltration, (iv) nanofiltration,
or (v) degasification.
22. The process as set forth in claim 11, further comprising one or
more additional pretreatment processes, said additional
pretreatment processes comprising (i) media filtration, (ii)
cartridge filtration, (iii) ultrafiltration, (iv) nanofiltration,
(v) degasification, or (vi) oxygen removal.
23. The process as set forth in claim 11, wherein said membrane
separator comprises a loose reverse osmosis membrane.
24. A process for treatment of a feedwater stream using membrane
separation equipment, said membrane separation equipment comprising
at least one membrane separator, to produce a low solute containing
product stream and a high solute containing reject stream, said
process comprising: (a) providing an acidic feedwater stream
containing solutes, said acidic feedwater stream having a pH that
assures the presence of free mineral acidity therein; (b)
pretreating said acidic feedwater stream, if necessary, to maintain
the acidity of said feedwater stream to a pH of between about 4.3
and about 2.0 at the time said feedwater stream enters said
membrane separator, to assure at least some free mineral acidity
remains in the pretreated feedwater; (c) passing the resultant
pretreated feedwater stream through said reverse osmosis membrane
separation equipment, said membrane separation equipment
substantially resisting passage of at least some dissolved species
therethrough, to concentrate said pretreated feedwater to said
preselected concentration factor, to produce (i) a high solute
containing reject stream, and (ii) a low solute containing product
stream;
25. The process as set forth in claim 24, wherein said membrane
separator comprises a reverse osmosis membrane separator.
26. The process as set forth in claim 24, wherein said membrane
separator comprises a loose reverse osmosis separator.
27. The process as set forth in claim 24, wherein said membrane
separator comprises a nanofiltration separator.
28. The process as set forth in claim 24, wherein in the pH of said
acidic feedwater stream is adjusted to a pH of about 2.6 or
lower.
29. The process as set forth in claim 24, wherein said acidic
feedwater stream comprises total organic carbon (TOC) constituents,
and wherein said total organic carbon (TOC) constituents are
substantially prevented from entering said product stream.
30. The process as set forth in claim 29, wherein said total
organic carbon (TOC) constituents in said product stream are
approximately ten percent (10%) or less of the concentration of
such constituents in said acidic feedwater stream.
31. The process as set forth in claim 24, wherein said acidic
feedwater stream comprises sodium ions, and wherein said product
stream contains approximately two percent (2%) or less of the
sodium ion concentration present in said feedwater stream.
32. The process as set forth in claim 24, wherein said acidic
feedwater stream comprises ammonium ions, and wherein said product
stream contains approximately eight percent (8%) or less of the
ammonium ion concentration present in said acidic feedwater
stream.
33. The process as set forth in claim 24, wherein said acidic
feedwater stream comprises chloride ions, and wherein said product
stream contains approximately twenty five percent (25%) or less of
the chloride ion concentration present in said acidic feedwater
stream.
34. The process as set forth in claim 1, or in claim 11, or in
claim 24, further comprising treating said product stream in an
anion exchange system, said anion exchange system removing free
mineral acidity from said product stream.
35. The process as set forth in claim 34, wherein said anion
exchange system is selected as one or more system from the group
consisting of (a) a weak base anion exchange system, (b) an
intermediate base anion exchange system, and (c) a strong base
anion exchange system.
36. The process as set forth in claim 34, wherein said anion
exchange system effectively removes all anions contained in said
product stream.
37. The process as set forth in claim 24, wherein said pretreatment
comprises adding ferric or ferrous ions to said acidic feedwater
stream.
38. The process as set forth in claim 37, further comprising adding
hydrogen peroxide to said acidic feedwater stream.
39. The process as set forth in claim 24, wherein said pretreatment
comprises use of cation exchange.
40. The process as set forth in claim 39, wherein said pretreatment
using cation exchange comprises use of weak acid cation
exchange.
41. The process as set forth in claim 39, wherein said pretreatment
using cation exchange comprises use of strong acid cation
exchange.
42. The process as set forth in claim 27, wherein said pretreatment
comprises irradiation of said acidic feedwater stream with a UV
light source, and wherein said total organic carbon constituents
are effectively eliminated from said product stream.
43. The process as set forth in claim 29, further comprising
irradiation of said product stream with a UV light source, and
wherein said total organic carbon constituents are effectively
eliminated from said product stream.
44. The process as set forth in claim 24, wherein said pretreatment
process comprises oxidant removal, said oxidant removal comprising
the addition of sodium meta-bisulfite to said feedwater stream.
45. The process as set forth in claim 24, further comprising one or
more additional pretreatment processes, said additional
pretreatment processes comprising (i) media filtration, (ii)
cartridge filtration, (iii) ultrafiltration, (iv) nanofiltration,
or (v) degasification.
46. The process as set forth in claim 24, further comprising one or
more additional pretreatment processes, said additional
pretreatment processes comprising (i) media filtration, (ii)
cartridge filtration, (iii) ultrafiltration, (iv) nanofiltration,
(v) degasification, or (vi) oxygen removal.
47. The process as set forth in claim 24, wherein said acidic
feedwater stream comprises hydrogen peroxide, and wherein said
process further comprises treatment of said acidic feedwater stream
in an activated carbon system, so as to effective remove hydrogen
peroxide from said acidic feedwater stream.
48. The process as set forth in claim 24, further comprising
ozonation of said feedwater stream with an ozone containing gas,
and wherein said total organic carbon (TOC) constituents are
effectively prevented from entering said product stream.
49. The process as set forth in claim 24, further comprising
ozonation of said product water stream with an ozone containing
gas, and wherein said total organic carbon (TOC) constituents are
effectively eliminated from said product stream.
Description
RELATED PATENT APPLICATIONS
[0001] This patent application claims priority from and is a
continuation of co-pending U.S. patent application Ser. No.
10/140,445, issued as U.S. Pat. No. 7,320,756, on Jan. 22, 2008;
that application claimed priority from U.S. Provisional Patent
Application Ser. No. 60/288,861, filed on May 5, 2001; each of
those patent applications are incorporated herein by this reference
in their entirety, including the specification, drawing figures,
and claims.
TECHNICAL FIELD
[0002] This invention relates to a method for the treatment of
acidic waters and wastewaters in membrane based water treatment,
purification, and concentration systems, and to apparatus for
carrying out the method. More particularly, the invention relates
to methods for feedwater pretreatment and for operation of membrane
based treatment systems such as reverse osmosis ("RO") and
nanofiltration ("NF"), which achieve increased solute rejection,
thereby producing very high purity (low solute containing) product
water, while significantly increasing on the on-stream availability
of the water treatment equipment.
BACKGROUND
[0003] Naturally occurring acidic waters and acidic wastewaters
from industrial processes are found in many geographical areas of
the world. Conventional treatment methods commonly employed for
treatment of such waters involve neutralization with alkali, to
raise the pH, so that the water can be discharged or beneficially
utilized. However, such methods are not always desirable, or even
feasible in some instances, since such methods can add significant
amounts of dissolved solids to the water. And, the cost of the
necessary chemicals, and particularly the alkali, can be quite
high.
[0004] If the treated water is to be utilized for potable
applications, one commonly encountered standard which must be met
is a World Health Organization criterion that potable water contain
no more than 500 milligrams per liter of dissolved solids, and no
more than 250 mg/l each of sulfate ion or chloride ion. However,
criteria for reuse of water in most industrial applications are far
stricter. Consequently, the common "straight neutralization"
treatment process is not an acceptable option in a large number of
water treatment applications.
[0005] In industrial applications, treatment/reclamation of acidic
waters is most often presently based on ion-exchange or on reverse
osmosis (RO) systems. Depending upon factors such as the level of
hardness (polyvalent cations), total organic carbon (TOC), and
other contaminants present in the water, anion-exchange can be used
for treatment of such acidic feedwaters for the reduction/removal
of acidity. Further, the addition of a cation exchange process
before or after the anion exchange can indeed produce water that is
almost completely demineralized. For this process, a weak base, an
intermediate base, or a strong base anion exchange resin is
employed, either singularly or in combination.
[0006] The major advantages of such prior art ion exchange
treatment methods include the following:
[0007] (1) In industry, the method is considered "passive", meaning
that the process is not sensitive to changes in the influent
characteristics.
[0008] (2) Compared to conventional reverse osmosis, the method has
lower capital cost.
[0009] The major disadvantages of such prior art ion exchange
treatment methods include the following:
[0010] (1) The quality, type (e.g., sodium based), and quantity of
alkali needed (for regeneration of the IX resin) are actually
higher and/or more restrictive than that required for straight
neutralization, so the cost of the necessary chemicals is quite
high.
[0011] (2) A very substantial volume of anion exchange resin is
necessary; such resin is generally quite expensive. Thus, the
initial and replacement cost of ion exchange resin in such systems
is quite high compared to a membrane based treatment system.
[0012] (3) Depending upon the specific variety of ion exchange
resin utilized, fouling by total organic carbon (TOC) can be quite
high. Unfortunately, fouled anion resin can be difficult and
expensive to clean. And, non-ionizable TOC components, such as IPA
(iso-propyl alcohol) are not removed. Further, TOC components that
are cationic in nature are not removed, either. Typically, removal
of TOC, or at least significant reduction of TOC, is often an
important requirement in a number of industrial applications where
reuse of treated waters is desired.
[0013] In conventional membrane based systems that are used for
treatment of acidic waste waters or of naturally acidic waters, the
pH of the RO/NF feed is commonly adjusted by addition of alkali.
Thus, such conventional RO/NF systems operate at, or reasonably
close to, neutral pH conditions. With certain exceptions,
conventional RO/NF systems are operated under such pH conditions in
order to ensure that the RO/NF membranes are not damaged due to
very high or to very low pH conditions. More fundamentally, for
many commonly encountered membrane materials, the overall solute
rejection across the membrane is typically highest at a pH of
approximately 8. Thus, the conventional wisdom in the water
treatment industry is to avoid operation of RO/NF membranes at low
pH conditions.
[0014] Yet, some of the basic RO/NF process characteristics point
to some particular potential advantages, when compared to ion
exchange systems.
For example:
[0015] (1) RO/NF will simultaneously remove cationic as well as
anionic species.
[0016] (2) RO/NF will, in general, remove a larger percentage of
the TOC present before fouling of the media or membrane becomes a
major concern. For instance, RO is capable of removing about eighty
percent 80%, or sometimes more, of non-ionizable species, such as
IPA.
[0017] (3) The capital, as well as the operating costs of RO/NF
systems, unlike those of ion-exchange systems, are not particularly
sensitive to the influent water chemistry characteristics.
[0018] Nonetheless, the conventional RO/NF systems known to me for
treatment of such acidic waters, whether for wastewaters or for
naturally occurring waters, still exhibit major shortcomings. Such
deficiencies include:
[0019] (1) The quantity and cost of alkali needed to neutralize the
RO feed remain comparable to mere neutralization, alone.
Consequently, overall treatment costs are high, since RO system
capital and operating costs must be added to the costs of
neutralization.
[0020] (2) The combination of pH neutralization followed by RO is
fundamentally inefficient, since the total dissolved solids content
is first increased by the pH neutralization, but then the total
dissolved solids content is decreased by the RO/NF process.
[0021] (3) RO/NF systems are quite susceptible to biofouling and/or
particulate and/or organic fouling when they are operated at
neutral or near neutral pH conditions. Unfortunately, however, the
commonly utilized thin film composite membranes do not tolerate
oxidizing biocides, such as chlorine. Consequently, control of
biofouling is problematic, especially for treating waters
containing organic contaminants.
[0022] Thus, a continuing demand exists for a simple, efficient and
inexpensive process which can reliably treat acidic waters, whether
naturally occurring or a wastewater from another process. It would
be desirable to provide water of a desired purity, in equipment
that requires a minimum of maintenance. In particular, it would be
desirable to improve efficiency of feed water usage, and lower both
operating costs and capital costs for water treatment systems, as
is required in various industries, such as semiconductors, chemical
production, mining, pharmaceuticals, biotechnology, and electric
power plants.
[0023] Clearly, if a new water treatment process were developed and
made available that combines the benefits of both conventional
RO/NF membrane treatment and of ion exchange processes,
particularly for the treatment of naturally occurring acidic waters
as well as industrial waste waters, it would be of significant
benefit. Additionally, such a process would be even more attractive
if it were immune to the most vexing problems associated with
either of reverse osmosis/nanofiltration or of ion exchange. In
summary, an economically important new acidic water treatment
process would necessarily offer some (if not most) of the benefits
of both reverse osmosis and of ion exchange. At the same time, any
such new process must be capable of effectively coping with the
problems which beset the reverse osmosis/nanofiltration process or
the ion exchange process.
OBJECTS, ADVANTAGES, AND NOVEL FEATURES
[0024] From the foregoing, it will be apparent that one important
and primary object of the present invention resides in the
provision of a novel method for treatment of water to reliably and
continuously produce consistently pure water from acidic waters and
wastewaters. More specifically, an important object of my invention
is to provide a membrane based water treatment method which is
capable of avoiding common pre-treatment costs and the operational
fouling problems, so as to reliably provide a method of producing
pure water while operating at high efficiency. Other important but
more specific objects of the invention reside in the provision of a
method for water treatment as described in the preceding paragraph
which has the following attributes:
[0025] (1) on an overall "ownership and operating cost" basis, a
process is provided which is cheaper to own and operate than
conventional reverse osmosis/nanofiltration or ion exchange
systems;
[0026] (2) it does not require "close control", and accordingly it
is easily able to cope with variability of feedwater;
[0027] (3) it is reliably capable of producing a consistently high
quality product;
[0028] (4) the reverse osmosis or nanofiltration membranes may be
arranged so as to render them unsusceptible to biological or
organic fouling;
[0029] (5) that simultaneous removal of cationic, anionic, and
non-ionic contaminants is achieved;
[0030] (6) that a very substantial portion of the TOC present be
rejected or removed, independent of the ionic characteristics of
the TOC components;
[0031] (7) that the addition of chemicals be minimized, not only as
a matter of cost, but also as a matter of good environmental
stewardship;
[0032] (8) that it can be practiced utilizing easily available
components that are routinely manufactured by various
companies;
[0033] (9) that available components are integrated
synergistically, rather than in a contradictory manner, in order to
provide the fullest possible benefit of available process
equipment;
[0034] (10) that a high recovery rate, or volumetric efficiency,
can be achieved when treating acidic waters and wastewaters;
[0035] (11) that a membrane can achieve a much higher productivity
(flux) compared to conventional systems, and can do so while
minimizing or eliminating membrane fouling; importantly, this also
reduces capital and operating costs; and
[0036] (12) simplification and cost reduction in reverse osmosis or
nanofiltration pre-treatment operations is attainable.
[0037] Other important objects, features, and additional advantages
of my invention will become apparent to those skilled in the art
from the foregoing, and from the detailed description which
follows, and from the appended claims, in conjunction with the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0038] In order to enable the reader to attain a more complete
appreciation of the invention, and of the novel features and the
advantages thereof, attention is directed to the following detailed
description when considered in connection with the accompanying
drawings, wherein:
[0039] FIG. 1 illustrates a process flow diagram of the equipment
utilized in a field test of my novel process for treating acid
waters and wastewaters.
[0040] FIG. 2 illustrates a generalized process flow diagram for
employing my novel water treatment process in a variety of
applications and with a variety of feedwaters.
[0041] The foregoing figures, being merely exemplary, contain
various unit processes or treatment elements that may be present or
omitted from actual implementations depending upon the
circumstances. An attempt has been made to draw the figures in a
way that illustrates at least those elements that are significant
for an understanding of the various embodiments and aspects of the
invention. However, various other unit processes or treatment
elements of an exemplary low pH membrane treatment process,
especially as applied for different variations of the functional
components illustrated, may be utilized in order to provide a
complete water or wastewater treatment system suitable for use in a
particular set of circumstances.
DETAILED DESCRIPTION
[0042] By means of extensive studies and the evaluation of the
weaknesses of the existing processes, I have now developed a new
water treatment process for the processing of acidic waters.
Importantly, I have now confirmed that certain reverse
osmosis/nanofiltration systems can be successfully operated at pH
values as low as 2, often without any, or with minimal chemical or
physical pretreatment. Currently, the lowest allowable pH limit is
determined by the characteristics of commercially available reverse
osmosis membranes, which is about a pH of 2.0, for continuous
operation. In the future, if better (i.e., lower pH tolerant)
membranes become available, my novel process will operate at even
lower pH than the current limit of pH 2.0.
[0043] In spite of low pH operations, and contrary to conventional
industry guidelines, extremely good rejection of cationic solutes,
and of multivalent anionic solutes, is achieved. The rejection of
sodium and ammonium ions is extraordinarily high, and this is a
very significant and unexpected benefit from my new acidic water
treatment process. The rejection of TOC is also very high under the
process conditions of this new acidic water treatment process.
[0044] Also, I have found that the addition of a TOC removal
process prior to feed of water to a low pH reverse osmosis membrane
(or even after it, or even later after the anion exchange) can
produce desired low TOC levels in the final product water.
Acceptable TOC removal methods include:
[0045] (1) bubbling, including the use of microbubbles of air or an
inert gas, in a storage tank or any other suitable column of
water;
[0046] (2) mechanical or membrane treatment based
degasification;
[0047] (3) ultraviolet radiation with 185 nm wavelength UV light,
with or without the addition of oxidants such as hydrogen peroxide
and/or ozone;
[0048] (4) addition of ferrous or ferric iron, along with hydrogen
peroxide, if needed, for in-site formation of Fenton's reagent,
which is known to be an effective oxidant for removing TOC
compounds; or
[0049] (5) addition of ozone to feedwater, or to product water.
[0050] An especially important application is possible when the
hydrogen peroxide present from semiconductor manufacturing
wastewaters is augmented with ferrous or ferric salts. In such a
case, the oxidation products are typically organic acids, and or
carbon dioxide, which can be effectively removed by an anion
exchange process. In contrast, IPA cannot be removed by the anion
exchange, without prior oxidation, since it does not ionize.
[0051] Turning now to FIG. 1, the test setup for one evaluation of
my treatment process for acidic wastewaters is shown. A three-stage
reverse osmosis system was utilized. Feedwater having a
conductivity of 2700 uS/cm was fed under pressure at 1.45 MPa at
the rate of 2 m.sup.3/hr and at the pH of 2.6 and a temperature of
28 degrees C. to the first stage of the system. Subsequently, first
stage reject was sent to the second stage at 1.4 MPa. Reject from
the second stage was sent to the third stage at 1.35 MPa. Finally,
rejected concentrate from the third stage was discharged at the
pressure of 1.25 MPa and a pH of 2.4 at the rate of 0.5 m.sup.3/hr.
The permeate from all three stages together was produced at the
rate of 1.5 m.sup.3/h, a pressure of 0.3 MPa, and a conductivity of
28.5 uS/cm.
[0052] Overall, considering all three product stages, the product
was produced at an average flux of 22.1 gallons per square foot per
day (0.9 9089 m.sup.3/m2/day). This provided an overall recovery
ratio of about 75%. The RO permeate was then sent to an anion
exchanger at a pressure of 0.02 MPa, and produced a final effluent,
after anion exchange, having a conductivity of 6.7 uS/cm.
[0053] The exemplary results of such testing, and in particular the
very high purity of the RO product, as well as the quality of the
final effluent from the anion exchange unit, demonstrate the
efficacy of this novel process.
[0054] In FIG. 2, a generalized flow schematic is illustrated for
use of my novel acidic wastewater treatment process in industry.
Raw acidic water 10 is provided, either directly, as shown, to a
low pH RO unit 12, or alternately, is routed through one or more
pretreatment system components, as indicated in broken lines.
First, the raw water 10 can be sent to a UV unit 20, in which
preferably hydrogen peroxide 22 and/or a source of ferrous or
ferric iron 24 is provided. Then, the partially treated water is
routed to a degas 30 or other liquid-gas contactor, for further
removal of total organic carbon (TOC) constituents. Reject from the
RO is sent for further treatment or discharge as appropriate.
Permeate as indicated by line 32 is sent to an anion ion exchange
("I-X") unit 34. Then, the product from the ion exchange treatment
is ready for use as makeup to an ultrapure water system 40, or
alternately, can be sent to primary mixed bed I-X units 42 and/or
secondary mixed bed I-X units 44. Then, the high purity water can
be used, or further treated as appropriate, such as in a filter
unit 50 or a second UV treatment apparatus 52, before being sent to
an ultrapure water (UPW) system 54.
[0055] The process described herein can be practiced in membrane
separation equipment which includes at least one separation unit
having a membrane separator, to produce a low solute containing
product stream and a high solute containing reject stream. In the
process, a feedwater stream containing solutes therein is provided
for processing. In some cases, the solutes may include at least one
constituent that contributes to membrane fouling when the feedwater
does not contain free mineral acidity. Before processing the
feedwater in a membrane separator, the pH of the feedwater is
adjusted, if necessary, to assure that at least some free mineral
acidity is present in the feedwater as input to the membrane
separator. The pH adjusted feedwater is fed through the membrane
separation equipment, in which the membrane substantially resists
passage of at least some dissolved species therethrough, to
concentrate the feedwater to a preselected concentration factor, to
produce (i) a high solute containing reject stream, and (ii) a low
solute containing product stream. Often, in this process, the pH of
the feedwater is adjusted to a pH of about 4.3 or lower.
Importantly, the process can be applied in applications where the
membrane separator is a reverse osmosis membrane, or a
nanofiltration membrane, or a loose reverse osmosis membrane.
[0056] For many important applications, the feedwater includes one
or more total organic carbon (TOC) constituent(s), and the total
organic carbon (TOC) constituent(s) are effectively removed from
the product stream. For many applications, treatment objectives
include removal of the TOC so that the TOC present in the product
stream is approximately ten percent (10%) or less of the
concentration of such constituent(s) in the feedwater. The process
can be advantageously utilized when the TOC components include one
or more substantially non-ionizable species, such as isopropyl
alcohol, and acetone.
[0057] Other constituent removals are also of importance. For
example, when the feedwater includes sodium ions, treatment in some
applications be can be achieved to the degree where the product
stream contains approximately two percent (2%) or less of the
sodium ion concentration present in the feedwater. And, when the
feedwater includes ammonium ions, treatment in some applications
can be achieved to the degree where the product stream contains
approximately eight percent (8%) or less of the ammonium ion
concentration present in the feedwater. Where the feedwater
includes chloride ions, treatment in some applications can be
achieved to the degree that the product stream contains
approximately twenty-five percent (25%) or less of the chloride ion
concentration present in the feedwater. Where sulfate ions are
present in the feedwater, treatment can be achieved to the degree
that the product stream contains approximately one-half of one
percent (0.5%) or less of the sulfate ion concentration present in
the feedwater. However, with fluoride ions, it is common that the
concentration of fluoride ions present in the product stream is
approximately the same as the concentration of fluoride ions
present in the feedwater stream.
[0058] As an additional pretreatment process in the treatment of a
feedwater at low pH in a membrane separation system, the free
mineral acidity present in the product stream can be removed, at
least to some desirable degree, if not substantially completely, by
treatment in an anion exchange system. An appropriate anion
exchange system could be (a) a weak base anion exchange system, (b)
an intermediate base anion exchange system, or (c) a strong base
anion exchange system. If desired, the anion exchange system can be
set up to process the product stream to effectively removes all
anions contained therein.
[0059] For further treatment effectiveness, particularly for
removal of TOC, an additional feedwater treatment, prior to
treatment in the membrane separation unit, can be added. On
suitable such additional treatment process includes the addition of
either ferrous or ferric ions to the feedwater. In addition, in
such a process, hydrogen peroxide could be further added, for
example to create a Fenton's reagent for treatment of total organic
carbon (TOC). In this manner, total organic carbon constituents can
be effectively eliminated in the product stream. Alternately, or
additionally, the feedwater stream can be further treated prior to
membrane separation by adding of irradiation of the feedwater
stream with a UV light source, and in such a manner, the total
organic carbon constituents can be effectively eliminated from the
product stream. For yet further treatment to achieve high purity
water effluent from the overall treatment process, the additional
process of irradiation of the product water stream with a UV light
source, so that the total organic carbon constituent(s) is
effectively eliminated from the product stream.
[0060] In yet another embodiment, the process further includes
ozonation of the feedwater stream with an ozone containing gas, and
wherein the total organic carbon constituents are effectively
eliminated from the product stream. Alternately, or additionally,
the process can further include ozonation of the product water
stream with an ozone containing gas, so that the total organic
carbon constituent(s) is effectively eliminated from the product
stream.
[0061] In yet another embodiment of the process of treating a
feedwater in low pH membrane separation operation, in those cases
where the feedwater contains hydrogen peroxide, either from an
industrial process or via a prior treatment, the process can be set
up to further include pretreatment of the feedwater stream in an
activated carbon system, so that the hydrogen peroxide is
effectively eliminated from the product stream.
[0062] Production of permeate product water at a production rate
(flux) of at least 15 gallons per square foot per day is normally
easily achievable. Importantly, the recovery is normally at least
sufficient so that the ratio of the quantity of the product stream
produced to the quantity of the feedwater stream provided is about
seventy-five percent (75%) or more. In other embodiments, the
recovery is sufficient so that the ratio of the quantity of the
product stream produced to the quantity of the feedwater stream
provided is about eighty percent (80%) or more. In yet other
embodiments, the recovery is sufficient so that the ratio of the
quantity of the product stream produced to the quantity of the
feedwater stream provided is about eighty-five percent (85%) or
more. In still further embodiments, the recovery is sufficient so
that the ratio of the quantity of the product stream produced to
the quantity of the feedwater stream provided is about ninety
percent (90%) or more. In certain applications, it is anticipated
that the recovery will be sufficient so that the ratio of the
quantity of the product stream produced to the quantity of the
feedwater stream provided is about ninety five percent (95%) or
more.
[0063] For still more treatment in combination with the basic low
pH membrane separation process described herein, other pretreatment
processes may be provided prior to acidification of the feedwater.
Such pretreatment processes can include (a) media filtration, (b)
cartridge filtration, (c) ultrafiltration, (d) nanofiltration, (e)
oxidant removal, (f) softening, (g) cation exchange, (h)
degasification, or (i) oxygen removal. In some embodiments,
pretreatment using cation exchange is accomplished by weak acid
cation exchange. In other embodiments, the pretreatment using
cation exchange is accomplished by the use of strong acid cation
exchange. Also, the pretreatment process of oxidant removal can
include the addition of sodium meta-bisulfite to the feedwater.
[0064] More generally, the process provided herein can be
fundamentally described as the treatment of a feedwater stream in
membrane separation equipment, wherein the membrane separation
equipment has at least one unit having a membrane separator, to
produce a low solute containing product stream and a high solute
containing reject stream. In the process, a feedwater stream
containing solutes therein is provided, and the pH of the feedwater
stream is adjusted, if necessary, to assure at least some free
mineral acidity presence, to produce a pretreated feedwater stream.
The pretreated feedwater stream, having a preselected pH, is passed
through the membrane separation equipment, wherein the membrane
substantially resists the passage of at least some dissolved
species therethrough, to concentrate the pretreated feedwater to a
preselected concentration factor. A high solute containing reject
stream having a pH lower than the pretreated feedwater stream is
produced. Also, a low solute containing product stream having a pH
higher than the pretreated feedwater stream is produced.
[0065] The unique process disclosed herein can also be
advantageously practiced by further including the process of
utilizing the reject stream from the membrane separation process in
the regeneration of a cation exchange system. For example, such a
process could include utilizing the reject stream as an acid source
for regeneration of a weak acid cation exchange system. Or, such a
process could include utilization of the reject stream as an acid
source for regeneration of the strong acid cation exchange
system.
[0066] The method and apparatus for processing acidic waters via
membrane separation equipment, and in particular, via the
combination of reverse osmosis/nanofiltration and ion exchange
equipment, by the process design as described herein, provides a
revolutionary, paradoxical result, namely, simultaneous decrease in
total dissolved solids in the water to be treated, and reliable,
high purity in the purified RO permeate. This method of operating
membrane separation systems, and in particular, for operating
reverse osmosis systems, represents a significant option for
treating acidic waters, while simultaneously reducing capital and
operating costs of the water treatment system. Further, given the
efficiencies, dramatically less usage of chemical reagents, whether
for neutralization, or for ion exchange regenerant or for RO
cleaning, will be achieved per gallon of product water
produced.
[0067] It will thus be seen that the objects set forth above,
including those made apparent from the proceeding description, are
efficiently attained, and, since certain changes may be made in
carrying out the above method and in construction of a suitable
apparatus in which to practice the method and in which to produce
the desired product as set forth herein, it is to be understood
that the invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. For
example, while I have set forth an exemplary design for treatment
of acidic waters, other embodiments are also feasible to attain the
result of the principles of the method disclosed herein. Therefore,
it will be understood that the foregoing description of
representative embodiments of the invention have been presented
only for purposes of illustration and for providing an
understanding of the invention, and it is not intended to be
exhaustive or restrictive, or to limit the invention to the precise
forms disclosed. On the contrary, the intention is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as expressed in the appended
claims. As such, the claims are intended to cover the methods and
structures described therein, and not only the equivalents or
structural equivalents thereof, but also equivalent structures or
methods. Thus, the scope of the invention, as indicated by the
appended claims, is intended to include variations from the
embodiments provided which are nevertheless described by the broad
meaning and range properly afforded to the language of the claims,
or to the equivalents thereof.
* * * * *