U.S. patent application number 10/746152 was filed with the patent office on 2004-09-30 for polyvinyl alcohol filter media.
Invention is credited to Ding, Youzhen, Johnston, Jordan M., Lee, Baosheng, Steward, John.
Application Number | 20040192135 10/746152 |
Document ID | / |
Family ID | 32682375 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040192135 |
Kind Code |
A1 |
Lee, Baosheng ; et
al. |
September 30, 2004 |
Polyvinyl alcohol filter media
Abstract
Filters comprising water-soluble polyvinyl alcohol material are
disclosed. Methods of making and using filters formed from
water-soluble polyvinyl alcohol material are also disclosed.
Inventors: |
Lee, Baosheng; (Duluth,
GA) ; Steward, John; (McKinney, TX) ;
Johnston, Jordan M.; (Goodyear, TX) ; Ding,
Youzhen; (Norcross, GA) |
Correspondence
Address: |
James D. Withers
Withers & Keys LLC
P. O. Box 2049
McDonough
GA
30253
US
|
Family ID: |
32682375 |
Appl. No.: |
10/746152 |
Filed: |
December 24, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60436318 |
Dec 24, 2002 |
|
|
|
Current U.S.
Class: |
442/181 ;
442/304; 442/327 |
Current CPC
Class: |
B01D 2239/0407 20130101;
B01D 39/1623 20130101; B01D 2239/1216 20130101; Y10T 442/60
20150401; B01D 39/18 20130101; B01D 2239/0654 20130101; Y10T 442/40
20150401; B01D 39/083 20130101; Y10T 442/30 20150401; B01D
2239/0695 20130101 |
Class at
Publication: |
442/181 ;
442/327; 442/304 |
International
Class: |
D04H 013/00 |
Claims
What is claimed is:
1. A filter comprising polyvinyl alcohol.
2. The filter of claim 1, wherein the filter comprises: (a) a
filtration media of fibrous material formed from polyvinyl alcohol;
and (b) a support for the fibrous material.
3. The filter of claim 2, wherein the filtration media comprises
polyvinyl alcohol yarn or roving, and the support comprises a core;
wherein the yarn or roving is wound onto the core.
4. The filter of claim 3, wherein the core comprises a
water-soluble or water-degradable polymer.
5. The filter of claim 2, wherein the filtration media comprises a
woven, nonwoven or knitted fabric of polyvinyl alcohol fibers, and
the support comprises a structural support in contact with the
fibrous material.
6. The filter of claim 5, wherein the structural support comprises
a water-soluble or water-degradable polymer.
7. The filter of claim 1, wherein the filter has a nominal pore
size ranging from about 0.1 microns (.mu.m) to about 2500
.mu.m.
8. The filter of claim 1, wherein the filter has a nominal pore
size ranging from about 0.1 .mu.m to about 1.0 .mu.m.
9. The filter of claim 1, wherein the filter has a nominal pore
size ranging from about 10.0 .mu.m to about 100 .mu.m.
10. The filter of claim 2, wherein the filtration media consists
essentially of fibrous material formed from polyvinyl alcohol.
11. The filter of claim 2, wherein the filtration media consists of
fibrous material formed from polyvinyl alcohol.
12. The filter of claim 2, wherein the filtration media and the
support comprise polyvinyl alcohol.
13. The filter of claim 2, wherein the filtration media and the
support consists essentially of polyvinyl alcohol.
14. A method of reducing an amount of radioactive waste generated
by a contaminated filter, wherein the method comprises: (a)
disposing of the filter by placing the filter in an aqueous bath
under condition such that at least a portion of the filter becomes
soluble.
15. The method of claim 14, wherein the aqueous bath has a bath
temperature of greater than about 90.degree. C.
16. The method of claim 14, wherein the aqueous bath contains a
polymer degradation-enhancing reactant, a precursor to a polymer
degradation-enhancing reactant, an oxidizer, ozone, or a
combination thereof.
17. The method of claim 14, wherein the filter comprises a fiber, a
fabric, a film, or a combination thereof containing water-soluble
polyvinyl alcohol material.
18. The method of claim 14, wherein the filter comprises a nonwoven
fabric containing water-soluble polyvinyl alcohol material.
19. The method of claim 14, wherein the filter comprises a woven
fabric containing water-soluble polyvinyl alcohol material.
20. The method of claim 14, wherein the filter comprises a knitted
fabric containing water-soluble polyvinyl alcohol material.
21. The method of claim 14, wherein the filter comprises
water-soluble polyvinyl alcohol material.
22. The method of claim 21, wherein the filter further comprises
one or more additional materials selected from the group consisting
of polyacrylic acid; polymethacrylic acid; polyacrylamide;
water-soluble cellulose derivatives comprising methyl celluloses,
ethyl celluloses, hydroxymethyl celluloses, hydroxypropyl methyl
celluloses, and carboxymethyl celluloses; carboxymethylchitin;
polyvinyl pyrrolidone; ester gum; water-soluble derivatives of
starch comprising hydroxypropyl starch and carboxymethyl starch;
water-soluble polyethylene oxides; alkali water-soluble materials
comprising ethylene copolymers of acrylic acid (EAA) and
methacrylic acid (EMAA), and salts thereof; and ionomers containing
acrylic acid and/or methacrylic acid.
23. The method of claim 21, wherein the water-soluble material
comprises polyvinyl alcohol with or without acetyl groups,
cross-linked or uncross-linked.
24. The method of claim 14, wherein the filter is contaminated due
to exposure to radioactive material, wherein the radioactive
material comprises a transuranic element, a fission product, a
natural radioactive element, an activation product from a nuclear
process, a medical isotope, or a combination thereof.
25. The method of claim 14, further comprising one or more of the
following steps: (i) placing the filter into a disposal reactor;
(ii) introducing water into the reactor to form an aqueous
solution; (iii) adding one or more components to the disposal
vessel, wherein the one or more components comprise a polymer
degradation-enhancing reactant, a precursor to a polymer
degradation-enhancing reactant, an oxidizer, ozone, or a
combination thereof; (iv) heating the aqueous solution to (a)
optionally convert the precursor, when present, to a
degradation-enhancing reactant, and (b) reacting the
degradation-enhancing reactant with the water-soluble polymer to
form one or more degradation products; (v) filtering
non-solubilized material from the second aqueous solution; (vi)
optionally, measuring a parameter to indicate a concentration of
polymer material in the aqueous solution; (vii) separating
radioactive material from the aqueous solution by a separation
technique; (viii) collecting the radioactive material for proper
disposal; (ix) optionally, altering or neutralizing a pH of the
aqueous solution substantially free of radioactive material; (x)
biodegrading the one or more degradation products in the aqueous
solution substantially free of radioactive material to form
CO.sub.2, water and biomass; and (xi) removing any insoluble
components from the reactor.
26. A method of reducing an amount of radioactive waste generated
by at least one contaminated product, wherein the method comprises:
disposing of the at least one contaminated product by placing the
at least one contaminated product in an aqueous bath under
condition such that at least a portion of the product becomes
soluble; and filtering any non-solubilized material from the
aqueous bath using at least one filter comprising water-soluble
polyvinyl alcohol material.
27. The method of claim 26, wherein the aqueous bath in the
disposal step contains a polymer degradation-enhancing reactant, a
precursor to a polymer degradation-enhancing reactant, an oxidizer,
ozone, or a combination thereof.
28. The method of claim 26, wherein the at least one contaminated
product comprises at least one garment, protective clothing,
coverall, bootie, face mask, glove, apparel, linen, drape, towel,
fabric, film, laminate containing at least one fabric or film,
sponge, mop head, web, bag, gauze, pad, wipe, pillow, bandage, or
combination thereof.
29. The method of claim 26, wherein the at least one contaminated
product comprises water-soluble material selected from the group
consisting of polyvinyl alcohol; polyacrylic acid; polymethacrylic
acid; polyacrylamide; water-soluble cellulose derivatives
comprising methyl celluloses, ethyl celluloses, hydroxymethyl
celluloses, hydroxypropyl methyl celluloses, and carboxymethyl
celluloses; carboxymethylchitin; polyvinyl pyrrolidone; ester gum;
water-soluble derivatives of starch comprising hydroxypropyl starch
and carboxymethyl starch; water-soluble polyethylene oxides; alkali
water-soluble materials comprising ethylene copolymers of acrylic
acid (EAA) and methacrylic acid (EMAA), and salts thereof; and
ionomers containing acrylic acid and/or methacrylic acid.
30. The method of claim 29, wherein the water-soluble material
comprises polyvinyl alcohol with or without acetyl groups,
cross-linked or uncross-linked.
31. The method of claim 26, wherein the at least one contaminated
product is contaminated due to exposure to radioactive material,
wherein the radioactive material comprises a transuranic element, a
fission product, a natural radioactive element, an activation
product from a nuclear process, a medical isotope, or a combination
thereof.
32. The method of claim 26, further comprising one or more of the
following steps: (i) placing the at least one contaminated product
into a disposal reactor; (ii) introducing water into the reactor to
form an aqueous solution; (iii) adding one or more components to
the disposal vessel, wherein the one or more components comprise a
polymer degradation-enhancing reactant, a precursor to a polymer
degradation-enhancing reactant, an oxidizer, ozone, or a
combination thereof; (iv) heating the aqueous solution to (a)
optionally convert the precursor, when present, to a
degradation-enhancing reactant, and (b) reacting the
degradation-enhancing reactant with the water-soluble polymer to
form one or more degradation products; (v) optionally, measuring a
parameter to indicate a concentration of polymer material in the
aqueous solution; (vi) separating radioactive material from the
aqueous solution by a separation technique; (vii) collecting the
radioactive material for proper disposal; (viii) optionally,
altering or neutralizing a pH of the aqueous solution substantially
free of radioactive material; (ix) biodegrading the one or more
degradation products in the aqueous solution substantially free of
radioactive material to form CO.sub.2, water and biomass; and (x)
removing any insoluble components from the reactor.
33. The method of claim 32, wherein the filtration step comprises
passing the aqueous solution through a particulate filter having a
nominal pore size of about 10 microns to about 100 microns, wherein
the filter comprises water-soluble polyvinyl alcohol material.
34. The method of claim 32, wherein the separation step (vi)
comprises passing the aqueous solution through a second particulate
filter having a nominal pore size of from about 0.1 microns to
about 1.0 microns and then circulating the aqueous solution through
an ion exchange bed, wherein the second particulate filter
comprises water-soluble polyvinyl alcohol material.
35. A process for treating a material comprising at least one
polymer, comprising the steps: introducing at least one oxidizing
agent and a material comprising at least one polymer into an
aqueous environment, wherein said at least one polymer is a polymer
capable of being reacted, degraded or broken down into at least one
degradation product; reacting, degrading or breaking down at least
a portion of the at least one polymer under conditions effective to
provide at least one degradation product; and filtering the aqueous
environment using a filter comprising water-soluble polyvinyl
alcohol material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims the benefit of priority to
U.S. provisional patent application serial No. 60/436,318 entitled
"POLYVINYL ALCOHOL FILTER MEDIA" filed on Dec. 24, 2002, the
subject matter of which is incorporated herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to filter media
produced from polyvinyl alcohol material.
BACKGROUND OF THE INVENTION
[0003] Over the course of the past 60 years, international
treaties, congressional acts, and executive orders have resulted in
a number of regulations and standards controlling all aspects of
environmental protection and health and safety practices in the
workplace. In particular, the disposal of industrial waste has
become heavily regulated and monitored. Landfills nationwide have
been closed and industry has been forced to turn to using
alternatives such as conservation, recycling, fuel blending,
deep-well injection and incineration. Under such conditions,
industry in general has increased efforts to decrease hazardous and
toxic waste emissions in the face of increasing treatment and
disposal costs, while providing increased worker safety and
exposure control. The "cradle to grave responsibility" that
industry must now bear has greatly increased the importance of
waste minimization, just as workplace safety regulations have
created a focus on exposure control to hazardous and toxic wastes
that are generated. It is just such "waste minimization" that has
become the focus of many industries as a means to managing their
hazardous waste disposal issues while maintaining high levels of
workplace safety and exposure control.
[0004] A representative example is the medical industry, which
generates millions of pounds of waste each year. Much of that waste
is related to the use of disposable materials, such as personal
protective clothing, equipment, and accessories necessary for
patient care that become contaminated with body fluids, human
waste, and/or chemicals that render them unsafe for reuse. To
prevent the spread of disease, it is imperative, and required by
law, that these materials be discarded and not reused, without
consideration to the level of contamination of said article.
[0005] In addition, the nuclear industry also generates millions of
pounds of waste each year. In the nuclear industry, much of the
waste is similarly related to the use of disposable materials such
as personal protective clothing, bags, mop heads, rags, and other
accessories that become contaminated by even low levels of
radioactive material, and are therefore unsafe or impractical for
reuse. The waste disposal and landfilling practices of the nuclear
industry are highly regulated, and nuclear burial ground space is
becoming increasingly scarce and more expensive.
[0006] Various other industries also generate waste streams with
similar characteristics. In seeking alternatives to landfilling and
incineration, water-soluble products have been developed. In some
cases, water-soluble products may be disposed of in a conventional
water treatment facility or the like. Accordingly, in some cases,
water-soluble products present a convenient and cost effective
alternative to conventional waste disposal means. Such articles
provide a means to separate the contamination, and conveniently and
cheaply dispose of the larger uncontaminated portion into municipal
or regular waste streams, thus vastly decreasing the total volume
of hazardous waste that must be dealt with by special regulated
(and expensive) disposal methods.
[0007] Polyvinyl alcohol (PVA) is a commonly used material for
making disposable personal equipment, such as garments, apparel,
linens, drapes, towels, sponges, gauze, utensils, rags, mops and
other useful articles commonly used in industrial settings. These
articles are often produced from non-woven, woven, knitted or
otherwise formed thermoplastic polyvinyl alcohol polymer films,
fabrics, and fibers that are water-soluble, giving these articles
the disposal benefits described above.
[0008] Conventional filter media used by industry, particularly in
filtering hazardous or toxic waste, are made of water-insoluble
materials, and do not provide the benefits of water-soluble
products as described above. Due to increased disposal costs and
regulations, many nuclear utilities have implemented filter storage
programs, opting to use long-term onsite storage as an alternative
to burial. While this serves to combat the immediate problem of
filter disposal in the ever-shrinking nuclear burial space, it has
long-term disadvantages. Conventional filter media tends to degrade
over time. After years of storage, these filters will eventually
have to be handled and dealt with. The likelihood of a radioactive
release due to unstable filter media increases with storage
length.
[0009] Another concern related to the use of conventional filter
media is the overhead costs associated with long-term storage of
conventional filter media. Special facilities have to be
constructed, maintained and monitored. Increased insurance premiums
result from such a procedure.
[0010] What is needed in the art is a filter media that (1)
eliminates one or more problems associated with conventional filter
media, and (2) provides one or more possible benefits, such as (a)
decreased hazardous and toxic waste generation, (b) decreased
expense of waste treatment, (c) regulatory compliance for waste
minimization, and (d) increased work place and personnel safety and
exposure control.
SUMMARY OF THE INVENTION
[0011] The present invention addresses some of the difficulties and
problems discussed above by the discovery of a new filter media
comprising polyvinyl alcohol (PVA) material. The filter media of
the present invention provides one or more benefits including, but
not limited to, (a) decreased hazardous and toxic waste generation,
(b) decreased expense of waste treatment, (c) regulatory compliance
for waste minimization, and (d) increased work place and personnel
safety and exposure control. The filter media may have a variety of
filter configurations, and may comprise additional materials other
than PVA. In one desired embodiment of the present invention, the
filter media comprises as much as 90 percent by weight or greater
of water-soluble PVA.
[0012] The present invention is also directed to methods of making
and using the filter media comprising PVA material. In one
exemplary method, the filter media is used in a process for
treating nuclear waste. In this embodiment, the filter media may be
used to perform a particular purpose (i.e., filtering), and then
disposed of by solubilizing the filter media. Radioactive waste may
be separated from the water-soluble components of the filter media,
substantially reducing the amount of radioactive waste and volume
of waste.
[0013] The present invention is further directed to a method of
reducing an amount of radioactive waste generated by a contaminated
filter, wherein the method comprises disposing of the filter by
placing the filter in an aqueous bath under condition such that at
least a portion of the filter becomes soluble. Desirably, the
water-soluble component of the filter comprises PVA. The method may
further comprise one or more additional steps including, but not
limited to, separating radioactive material from the solubilized
portions of the filter in the aqueous bath.
[0014] The present invention is even further directed to a method
of reducing an amount of radioactive waste generated by at least
one contaminated product, wherein the method comprises (i)
disposing of the at least one contaminated product by placing the
at least one contaminated product in an aqueous bath under
condition such that at least a portion of the product becomes
soluble; and (ii) filtering any non-solubilized material from the
aqueous bath using at least one filter comprising water-soluble
polyvinyl alcohol material. In a subsequent operation or method
step, the at least one filter comprising water-soluble polyvinyl
alcohol material may be disposed of by solubilizing the
water-soluble components of the at least one filter, further
reducing the amount of radioactive waste in the process.
[0015] The present invention is further directed to a process for
treating a material comprising at least one polymer, comprising the
steps (i) introducing at least one oxidizing agent and a material
comprising at least one polymer into an aqueous environment,
wherein said at least one polymer is a polymer capable of being
reacted, degraded or broken down into at least one degradation
product; (ii) reacting, degrading or breaking down at least a
portion of the at least one polymer under conditions effective to
provide at least one degradation product; and (iii) filtering the
aqueous environment using a filter comprising water-soluble
polyvinyl alcohol material. In a subsequent operation or method
step, the filter comprising water-soluble polyvinyl alcohol
material may be disposed of by solubilizing the water-soluble
components of the filter, further reducing the amount of
radioactive waste generated in the process.
[0016] These and other features and advantages of the present
invention will become apparent after a review of the following
detailed description of the disclosed embodiments and the appended
claims.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 depicts an exemplary filter media of the present
invention having a wound-type cartridge design;
[0018] FIG. 2 depicts an end view of the exemplary filter media of
FIG. 1 as viewed along line A-A;
[0019] FIG. 3 depicts a cut-away view of the exemplary filter media
of FIG. 1, wherein a portion of the wound fibrous material has been
removed from the core;
[0020] FIG. 4 depicts an exemplary filter media of the present
invention having a pleated filter design; and
[0021] FIG. 5 is a schematic of an exemplary processing system for
treating waste streams using one or more filter media of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention is directed to filter media comprising
polyvinyl alcohol (PVA) material. The present invention is also
directed to methods of making and using the filter media comprising
PVA material. Polyvinyl alcohol exhibits several unique and
positive physical and chemical characteristics for making filter
media. The excellent resistance of polyvinyl alcohol to chemicals,
acid and base, solvent and oil and grease makes PVA an excellent
material for applications in nuclear, industrial and other
environments.
[0023] For example, the following table compares the impact of
common oils and solvents on fully hydrolyzed PVA resin. As the
table describes, PVA resins are substantially unaffected by most
ester, ethers, ketones, aliphatic, aromatic hydrocarbons and the
higher monohydric alcohols. The lower monohydric alcohols have
cause some swelling action on the resin, but the effect is
negligible. Conventional grades of PVA are unaffected by animal and
vegetable oils, greases, and petroleum hydrocarbons. In the table
below, the percent gain in weight of molded and un-plasticized PVA
resin was measured when they were immersed in a solvent for 10 days
at 25-35.degree. C. The lower the number, the better the resistance
of PVA resin to the chemicals.
1 PVA Resin, Category Solvents Fully Hydrolyzed Alcohols Methanol
0.4 Ethanol 95% <0.1 N-Butanol <0.1 Esters Ethyl acetate
<0.1 Amyl acetate <0.1 Ethers Ethyl ether <0.1 Ketones
Acetone <0.1 Hydrocarbons Heptane <0.1 Kerosene <0.1
Toluene <0.1 Turpentine <0.1 Chlorinated Carbon tetrachloride
<0.1 Hydrocarbons Tetrachloroethane <0.1 Ethylene dichloride
<0.1 Trichloroethylene <0.1 Oil Sea #10 oil <0.1 Lard oil
<0.1 Cottonseed oil <0.1 Raw linseed oil <0.1
Miscellaneous Oleic acid 0.9
[0024] Resources: DuPont ELVANOL.TM. brochure, * Percent gain in
weight of molded unplasticized PVA immersed for 10 days at
25-35.degree. C.
[0025] PVA fiber for use in the present invention is desirably
produced from fully hydrolyzed PVA resin. In addition to chemical
resistance of the PVA resin, the properties of the resulting fiber
may be further enhanced by physical treatments such as heat and
fiber orientation. The chemical resistance of PVA fiber is even
better that the PVA resin.
[0026] PVA fiber is unaffected by the levels of ionizing radiation
normally seen in nuclear filtering operations, making it useful in
both highly radioactive and low level nuclear filtering
operations.
[0027] I. PVA Filter--Manufacturing and Application
[0028] A PVA-based filter may be produced, used, and disposed of in
the same manner as current filters. However, PVA filter media has
the distinct advantage of being able to change its form and be
volume reduced using a chemical oxidation process or simply
dissolving it. In both cases, the components would cease to exist
in filter form; rather the filter media would be liquefied and
discharged or filtered to remove the radioactivity or other
contaminants. In nuclear and other industrial applications, this
puts the filtered radioactive or hazardous contamination into a
much more stable and desired waste form. The user would realize
significant economic advantages since regulations governing the
disposal of highly radioactive or filters containing hazardous
materials would no longer apply. Facilities would no longer pay for
the disposal of these filters in conventional form, saving a
substantial amount of money in handling, packaging, shipping and
disposal.
[0029] PVA filters may be produced to cover a wide range of
filtering capabilities, for example, from about 0.1 to about 2500
microns. PVA exhibits great efficiency in particle removal and
retention. For example, when PVA yarn is used on cord wound filters
in lieu of conventional media (e.g., polypropylene, cotton, and/or
polyester) and wound to the same specifications for a particular
micron rating; PVA typically exceeds the design performance
parameters that would be expected of the original media. This is
due to the slight expansion of the PVA media when exposed to water,
creating a tighter, more tortuous path for filterable particles,
and therefore improved filtration efficiency.
[0030] The strength of PVA fiber makes it very resistant to failure
from pressure surges or high differential pressure under high flow
conditions. The dissolution temperature of PVA may also be
configured during the manufacturing process to ensure media
integrity throughout the range of temperatures seen during filter
operations. Capacity and throughput of PVA filters of the present
invention may be identical to or very consistent with conventional
filter media.
[0031] PVA filters of the present invention may be used in any
water or air filtration application, including nuclear
applications. Other applications for the water filters of the
present invention include, but are not limited to, electronic
component production, medical, wastewater treatment, drinking
water, industrial cooling water systems, and home use. Air filters
of the present invention include fibers used in applications
including, but are not limited to, industrial gas filtration,
respirators, building/home ventilation, and automotive. Other
applications of industrial use include the water or air filtration
of asbestos or fiberglass.
[0032] PVA-containing filters of the present invention may be
manufactured in an array of configurations and designs, suitable
for both liquid and gas applications. In one embodiment of the
present invention, the filter has a wound-type cartridge design.
Such a design is shown in FIGS. 1-3. In this filter media 10, PVA
fiber is spun into roving/yarn 11, which is then wound around a
central support core 12. The core 12 can be metal, plastic, or
another material. As shown in FIG. 3, core 12 has perforations 13
therein to provide flow channels through filter 10. This filter
type is common to many types of existing water filter designs, such
as home use. These same filters are used extensively in
low-activity filtering applications at Boiling Water Reactors (BWR)
throughout the nuclear industry. Cord wound filters can be made in
any length to accommodate any existing filter housing. The
filtering capability (micron rating) can be varied over a very wide
range depending on manufacturing settings, such as yarn density and
winding tension and winding pattern. Filtration ratings of about
0.1 microns and lower are achievable. When dissolved, only the
central support core will remain from the original filter
assembly.
[0033] In some embodiments of the present invention, the central
support core 12 may be prepared from a water-soluble,
water-degradable or water-dispersible material. Suitable
water-soluble materials include, but are not limited to, polyvinyl
alcohols used to make the filtration component (e.g., roving/yarn
11 of filter media 10 shown in FIGS. 1-3) of the filters of the
present invention. In such an embodiment, the central support core
12 may be injection molded using a PVA material alone or in
combination with one or more water-degradable or water-dispersible
materials. Suitable water-degradable or water-dispersible materials
include, but are not limited to, polymers disclosed in U.S. Pat.
No. 6,162,852 assigned to Microtek Medical Holdings, Inc., the
entirety of which is hereby incorporated by reference. In this
embodiment, the central support core 12 also solubilizes and/or
disperses when exposed to alkaline having a water temperature above
about 37.degree. C. further reducing the amount of waste resulting
from the filter media.
[0034] It should be noted that although filter 10 of FIGS. 1-3 has
a cylindrical wound-type cartridge design, filter 10 may have any
volumetric shape other than a cylindrical shape (e.g., a circular
cross-sectional configuration). Suitable cross-sectional
configurations other than a circular cross-sectional configuration
for the wound-type cartridge design include, but are not limited
to, triangular, square, rectangular, oblong, oval, star,
parallelogram, rhombus, hexagonal, and octagonal cross-sectional
configurations. Further, the cross-sectional area through the
wound-type cartridge design filter may be substantially constant
along a length of the filter or may vary along a length of the
filter.
[0035] In a further embodiment of the present invention, the filter
comprising PVA material is a pleated filter for use in both air and
water applications. Such a design is shown in FIG. 4. Pleated
filter 40 comprises a filter media 41 within housing 42. These
filters 40 may have a cage-type housing 42, wherein the filter
media 41 is fully supported from all sides (or combinations of more
than one side) to ensure filter integrity. The housing 42 may be
metal, plastic or another material. The filter media 41 exists as a
woven, knitted or nonwoven sheet, either single or multi-layered,
which is pleated to enhance support and maximize filtering surface
area. The filter media 41 may also exist as an extruded,
monofilament design. Variations of this filter are used in High
Efficiency Particulate Air (HEPA) filters when venting radioactive
systems, use in radioactive vacuum cleaners, or other applications
where radioactive airborne contamination is a concern. Another
variation of the pleated filter is used in water applications, such
as purification systems in reactors, spent fuel pool clean up, and
make-up water filtering. Pleated filters are commonly used in home
and industrial applications as listed above.
[0036] In some embodiments of the present invention, the housing 42
may be prepared from a water-soluble, water-degradable or
water-dispersible material similar to the central support core 12
described above. As discussed above, suitable water-soluble
materials include, but are not limited to, polyvinyl alcohols used
to make the filtration component (e.g., filter media 41 of pleated
filter 40 shown in FIG. 4) of the filters of the present invention.
Suitable water-degradable or water-dispersible materials include,
but are not limited to, polymers disclosed in U.S. Pat. No.
6,162,852 assigned to Microtek Medical Holdings, Inc., the entirety
of which is hereby incorporated by reference.
[0037] In this embodiment, the housing 42 also solubilizes and/or
disperses when exposed to alkaline having a water temperature above
about 37.degree. C. further reducing the amount of waste resulting
from the filter media.
[0038] It should be noted that although filter 40 of FIG. 4 has a
cylindrical housing design, filter 40 may have any volumetric shape
other than a cylindrical shape (e.g., a circular cross-sectional
configuration). Suitable cross-sectional configurations other than
a circular cross-sectional configuration for the pleated design
include, but are not limited to, triangular, square, rectangular,
oblong, oval, star, parallelogram, rhombus, hexagonal, and
octagonal cross-sectional configurations. Further, the
cross-sectional area through the pleated design filter may be
substantially constant along a length of the filter or may vary
along a length of the filter.
[0039] In a further embodiment, the filter may be a flat or pleated
filter having any of the above-mentioned areal configurations. In
other words, the filter may have a circular, triangular, square,
rectangular, oblong, oval, star, parallelogram, rhombus, hexagonal,
or octagonal shape. The filter may have a structural support in
contact with the filter or may be self-supporting (i.e., the filter
does not require a supporting structure). Such filters are
particularly useful for air filtration, wherein air passes through
the filter by entering a first major surface and exiting a second
major surface. A non-limiting example of such a filter is a
rectangular, pleated filter having a length of 60 cm, a height of
30 cm, and a thickness of about 3 cm.
[0040] Other configurations might be made as well using techniques
common to one skilled in the art of filter manufacturing.
Monolithic filter structures, membrane filters, and various other
common forms of filters may be constructed using PVA as the filter
material instead of conventional, water-insoluble materials.
[0041] In any of the above-described filters, the filter may
comprise as much as 90 percent by weight (pbw) or more of
water-soluble material, such as PVA. In one embodiment of the
present invention, the filter comprises at least about 50 pbw of
water-soluble material, such as PVA, based on a total weight of the
filter. In other embodiments of the present invention, the filter
comprises more than 60 pbw (desirably, at least about 70 pbw; more
desirably, at least about 80 pbw; even more desirably, at least
about 90 pbw; even more desirably, at least about 95 pbw; and even
more desirably, 100 pbw) of water-soluble material, such as PVA,
based on a total weight of the filter.
[0042] The PVA filters of the present invention may comprise PVA
alone or in combination with other water-soluble, water-degradable
or water-dispersible materials as described above. Suitable
materials that may be used in combination with PVA include, but are
not limited to, polyacrylic acid; polymethacrylic acid;
polyacrylamide; water-soluble cellulose derivatives comprising
methyl celluloses, ethyl celluloses, hydroxymethyl celluloses,
hydroxypropyl methyl celluloses, and carboxymethyl celluloses;
carboxymethylchitin; polyvinyl pyrrolidone; ester gum;
water-soluble derivatives of starch comprising hydroxypropyl starch
and carboxymethyl starch; water-soluble polyethylene oxides; alkali
water-soluble materials comprising ethylene copolymers of acrylic
acid (EAA) and methacrylic acid (EMAA), and salts thereof; and
ionomers containing acrylic acid and/or methacrylic acid.
[0043] In one embodiment of the present invention, the filter media
of the filters comprises PVA material. Desirably, the PVA material
comprises polyvinyl alcohol with or without acetyl groups,
cross-linked or uncross-linked. In other embodiments of the present
invention, the filter media of the filters consists essentially of
or consists of PVA material. In yet other embodiments of the
present invention, all of the components of the filter, including
the filter media, consist essentially of or consist of PVA
material.
[0044] II. Disposal of Filter Media Containing PVA
[0045] The hot water solubility and chemical degradability of PVA
enable the filters of the present invention to degrade under
desired conditions, minimizing the total waste volume and weight.
Exemplary disposal methods for the filters of the present invention
and exemplary uses for the filters of the present invention are
described in U.S. Pat. No. 6,623,643; International Publication No.
WO03/074432 A1; U.S. Pat. Nos. 5,181,967; 5,207,837; 5,650,219; and
5,885,907, the subject matter of all of which is hereby
incorporated in its entirety by reference.
[0046] Processors for disposing of the filter media can be any
desired size. As described below, some methods of disposal may
include an oxidation step, wherein an oxidizer is used to degrade
polymers within a treated waste stream. In the process steps
describe below, oxidizer concentration may vary, effluents may be
filtered or not, etc. Processing can be done at a users facility or
taken to a remote location. Effluents may also be ion exchanged or
not.
[0047] Hot Water Solubility:
[0048] In this exemplary scenario, the filter of the present
invention is placed into a small processor (60 gallon, nominal).
The processor may be located on top of a container housing used
radioactive ion exchange resin that is being prepared for disposal.
The filter processor is filled with water and heated to a
solubilizing temperature for the filter. The solubilizing
temperature may be (i) greater than about 37.degree. C., (ii)
greater than about 50.degree. C., (iii) greater than about
75.degree. C., (iv) greater than about 90.degree. C., or (v) near
boiling conditions depending on the water-solubility of the
materials used. The filter media will completely dissolve, leaving
at most only the filter housing and/or support structures, although
in some embodiments of the present invention, the filter housing
and/or support structures may also dissolve. The liquid mixture
containing the dilute liquid PVA will be allowed to cool as
appropriate then discharged. In one application, the effluent may
be directed to a vessel containing ion exchange resin. The PVA and
radioactive isotopes will be deposited in the resin matrix,
attaching itself mechanically throughout the torturous path as well
as adhering to ion exchange sites. The filter housing and support
structure will then be removed and disposed of as low-level
radioactive, compactable waste.
[0049] Chemical Degradation:
[0050] In this exemplary scenario, the filter of the present
invention is placed into a small processor (60 gallon, nominal).
The processor may be located on top of a container housing used
radioactive resin that is being prepared for disposal. The filter
processor is filled with water, and any of the following components
are added to the processor: a polymer degradation-enhancing
reactant, a precursor to a polymer degradation-enhancing reactant,
an oxidizer, ozone, or a combination thereof. Desirably, a chemical
oxidizer (e.g., hydrogen peroxide), and an optional catalyst (e.g.,
ferrous sulfate or a Fenton reagent) are added to the filter
processor. The aqueous bath may be heated to near boiling
conditions as described above.
[0051] The filter media completely dissolves, and its chemical form
altered into a dilute aqueous mixture of organic acids, leaving at
most only the filter housing and support structures, although in
some embodiments of the present invention, the filter housing
and/or support structures may also dissolve. The resulting liquid
mixture containing organic acids will be allowed to cool as
appropriate, then drained to the resin container. The organic acids
will be deposited in the resin matrix, where the radioactivity and
the acids will attach to the ion exchange sites. The filter housing
and support structure will then be removed, when applicable, and
disposed of as low-level radioactive, compactable waste.
[0052] In both of the above-described scenarios, it should be noted
that the filter housing and/or core component may also comprise
water-soluble and/or water-degradable polymeric material as
described above. In this case, there may not be a filter housing
and/or support structure remaining for disposal.
[0053] Pleated cartridge filters are commonly used in nuclear
utilities to maintain water purity in Refueling Pools and Spent
Fuel Pools. These filters are housed in a filter housing and
submersed in the appropriate pool. Water is pumped through the
filter (by an integrally attached pump) to maintain the
radioactivity concentration at an acceptable level. When the filter
is taken out of service, it is moved out of the housing remotely
and placed in an underwater disposal container. This container is
removed from the pool and the filter transferred to a High
Integrity Container (HIC) for storage until it can be processed for
its final disposition. Due to stringent regulations, only a small
number of filters can be packaged in a HIC, a number based on total
radioactivity, radioactive dose rates and physical geometry. This
leaves large amounts of unused space in a filter disposal vessel,
space that the utility will pay for regardless. Because of these
stringent regulations, filters are taken out of service based on
radioactive dose rates, not useful life, with the burial of the
filters being the ultimate consideration. The filter media of the
present invention eliminate many of the problems associated with
conventional filters and methods of handling conventional
filters.
[0054] The filter media of the present invention possess other
advantages in that the filters may be utilized to take much higher
dose rates. Since the filter media of the present invention do not
need to be buried in filter form, a cap on dose rate is not
necessary. This allows the utility to use less filters to do the
same job, saving the cost of extra filters and more importantly,
saving the downtime and labor of changing, handling and disposing
of more filters.
[0055] III. Specific Use in the Nuclear Industry
[0056] The filter media of the present invention may be used in a
number of applications including, but not limited to, the treatment
of polymer(s), as well as, degradation-enhancing reactant(s) or
precursors thereof, which may be present in an aqueous environment.
This type of process is described in U.S. Pat. No. 6,623,643 and
International Publication No. WO03/074432 A1, the subject matter of
both of which is hereby incorporated in its entirety by
reference.
[0057] In U.S. Pat. No. 6,623,643 and WO03/074432 A1, processes are
described, wherein a polymer is not completely solubilized in the
aqueous environment. The unsolubilized polymer can optionally be
removed from the environment by a suitable means, such as
filtration and then recycled or reused. The filter media of the
present invention may be used in this filtration step. Further,
U.S. Pat. No. 6,623,643 and WO03/074432 A1 disclose embodiments,
wherein polymer is solubilized prior to the introduction of a
degradation-enhancing reactant or precursor thereof. In these
embodiments, it may be desirable to filter non-solubilized material
from the aqueous solution prior to introduction of the
degradation-enhancing reactant or a precursor thereof using the
filter media of the present invention.
[0058] Similarly, the processes disclosed in U.S. Pat. No.
6,623,643 and WO03/074432 A1 may also include "post-treatment" of
the aqueous environment. The precise type of post-treatment can
depend on the nature of the aqueous environment. In general, where
the polymer is degraded to a product including one or more organic
acids, the acids can then be depleted through biodegrading the
organic acids.
[0059] If the aqueous environment is to be biodegraded, the pH
should be adjusted to a value within the approximate range of about
3.0 to about 10.0 or, more preferably, within the approximate range
of about 5.0 to about 8.0 or, even most preferably, within the
approximate range of about 6.0 to about 7.0 It is desired to pass
the aqueous waste stream through a reverse osmosis unit after the
biodegradation.
[0060] Biodegradation may include inoculating the aqueous waste
stream with microorganisms such as aerobic, heterotrophic bacteria
or anaerobic bacteria. The inoculated aqueous environment or waste
stream may be exposed to an aerated, fluidized bed in a bioreactor
which contains support materials such as pulverized, activated
carbon or plastic bio beads. The inoculated aqueous waste stream
may also be exposed to a fixed media reactor or an activated sludge
process. Conventional extended aeration, step aeration, sequential
batch reactions and contact stabilization may also be used to
reduce the organic carbon content of the inoculated aqueous waste
stream.
[0061] The biological activity of the microorganisms may be
enhanced by injecting a nutrient containing nitrogen, phosphorus,
potassium or a trace mineral, into the bioreactor. The final
resultant waste stream includes neutralized water depleted of
organic carbon, which is suitable for delivery to a waste treatment
facility or for reuse or recycling.
[0062] In an alternative embodiment disclosed in U.S. Pat. No.
6,623,643 and WO03/074432 A1 involving treatment of waste generated
from nuclear facilities, a filtration and/or ion exchange process
may be used to remove radioactive material from the solution. For
example, the step of removing radioactive material may be
accomplished by filtering the solution through a micron filter,
which has a nominal pore size ranging between about 10 and about
100 microns to remove radioactive elements. Optionally, a second
particulate filter having a nominal pore size between about 0.1
micron and about 1.0 micron, a reverse osmosis unit or an ion
exchange unit consisting of an anion bed, a cation bed or an
anion/cation combination bed that reduces depleted radioisotopes at
an elemental level may also be used. In either of these filtration
steps, the filter media of the present invention may be used.
[0063] Desirably, the waste stream may also be adjusted to a higher
pH. More desirably, the pH adjusted waste stream can also be
biodegraded to eliminate the organic acids. If the waste stream is
to be biodegraded, it is desirable to neutralize the waste stream
by adding sodium hydroxide until the pH is adjusted to within the
approximate range of about 3.0 to about 10.0, preferably from about
5.0 to about 8.0 or, even more preferably from about 6.0 to about
7.0.
[0064] In an embodiment disclosed in U.S. Pat. No. 6,623,643 and
WO03/074432 A1 for treating materials that come from a source that
may have been exposed to radioactivity, the potentially radioactive
materials may be filtered using the filter media of the present
invention. The filtering step may occur at any point in the
process, e.g., prior to adding the degradation-enhancing reactant
(e.g., an oxidizing agent) to the aqueous waste stream, after
producing the degradation products (e.g., organic acids) from the
polymer, or after treatment of the degradation products, e.g.,
biodegrading the organic acids. Contaminated products (i.e.,
products exposed to radioactivity) may include, but are not limited
to, at least one garment, protective clothing, coveralls, booties,
face masks, gloves, apparel, linens, drapes, towels, fabrics,
films, laminates containing at least one fabric or film, sponges,
mop heads, webs, bags, gauze, pads, wipes, pillows, bandages,
filters of the present invention, or combinations thereof.
[0065] Filters for removing potentially radioactive material (e.g.,
a transuranic element, a fission product, a natural radioactive
element, an activation product from a nuclear process, a medical
isotope, or a combination thereof) include particulate filters of
the present invention having a nominal pore size of about 10
microns to about 100 microns and optionally a second particulate
filter of the present invention having a nominal pore size of from
about 0.1 micron to about 1.0 micron through which the waste stream
is circulated. Filtering may also comprise circulating the aqueous
waste stream through an ion exchange bed. For example, in one
embodiment, the process includes: (a) filtering potentially
radioactive material from the aqueous waste stream; (b)
neutralizing the pH of the aqueous waste stream after producing
organic acids; and (c) depleting organic acids from the aqueous
waste stream after neutralizing the pH. In any of the
above-described process steps requiring filtration, the filter
media of the present invention may be used.
[0066] One exemplary process disclosed in U.S. Pat. No. 6,623,643
and WO03/074432 A1 comprises the steps of:
[0067] (1) if required, introducing a polymer or polymer-containing
material into an aqueous solution;
[0068] (2) if required, adding a degradation-enhancing reactant, or
a precursor thereof, to the solution;
[0069] (3) heating the aqueous environment so as to react the
precursor to form the degradation-enhancing reactant, if necessary,
and reacting the polymer to form degradation products;
[0070] (4) optionally, filtering non-solubilized material from the
aqueous environment;
[0071] (5) optionally, measuring a parameter indicator of the
concentration of polymer material in the aqueous environment;
[0072] (6) optionally, filtering material, e.g., radioactive
material from the aqueous environment;
[0073] (7) optionally, altering, e.g., neutralizing, the pH of the
aqueous environment;
[0074] (8) optionally, biodegrading the resulting degradation
products in the aqueous environment, e.g., organic acids form
CO.sub.2, H.sub.2O and biomass; and
[0075] (9) removing any insoluble components from the reactor.
[0076] In step (4), the aqueous environment is desirably filtered
through strainers to remove any undissolved polymer material and
non-water-soluble polymer constituents in the solution.
Alternatively, the strainer may be prepared using the
above-described PVA material for forming filter media of the
present invention. In a desired embodiment, the strainers will have
a mesh size in an approximate range of between about 20 and about
50 mesh. In a more desired embodiment, the strainers will have a
mesh size of approximately about 30 mesh. Undissolved polymer
material trapped in the strainers can be recirculated for final
solubilization. In a desired embodiment, polymer material will
constitute an approximate range of greater than 0% to about 10.0%
by weight in the solution. In a more desired embodiment, polymer
material will constitute an approximate range of between about 4.0%
to about 6.0% by weight in the solution. In still a more desired
embodiment, polymer material will be present in an amount of about
5.0% by weight in the solution. Additionally, in a more desired
embodiment, the temperature of the solution during the filtration
process step is maintained at or above about 150.degree. F. to
prevent precipitation of the PVA out of solution prior to its
destruction.
[0077] In step (6), a filter media of the present invention may be
used to filter and deplete radioactivity in solution. This process
step is optional and only applicable when the water-soluble polymer
material contains potentially radioactive waste. This step may or
may not be required, for example, at a nuclear facility. If the
polymer material was exposed to radioactivity that affects the
disposability of the solution, then this process step should be
added. With the addition of this process step, a low-level
radioactive waste management system is created. This waste
management system can be used as an alternative approach to current
dry active radioactive waste treatment methods. The process step of
removal of radioactivity typically occurs prior to biological
degradation. A more detailed desired embodiment of this process
step includes the basic steps of:
[0078] (a) filtration of the solution, and
[0079] (b) ion exchange of the solution.
[0080] At nuclear facilities, radioactivity may be present in
process fluids in both elemental and particulate form. Filtration
of the solution removes radioactive particulates. In a desired
embodiment, the solution is passed through a particulate filter
having a nominal pore size ranging approximately between about 10
and about 100 microns. In a more desired embodiment, the solution
is then passed through a second particulate filter having a nominal
pore size ranging approximately between about 0.1 micron and about
1.0 micron. As described above, a filter media of the present
invention may be used in these filtration steps.
[0081] In another exemplary process disclosed in U.S. Pat. No.
6,623,643 and WO03/074432 A1, the process comprises the steps
of:
[0082] (1) if required, solubilizing water-soluble polymer material
in an aqueous environment;
[0083] (2) filtering non-solubilized material from the aqueous
environment;
[0084] (3) adding a degradation-enhancing reactant, or a precursor
thereof, to the filtered environment;
[0085] (4) where a precursor of the degradation-enhancing reactant
is employed, reacting the precursor to form the
degradation-enhancing reactant, and reacting the polymer;
[0086] (5) optionally, measuring a parameter indicator of the
concentration of polymer material in the aqueous environment;
[0087] (6) optionally, filtering material, e.g., radioactive
material, from the aqueous environment;
[0088] (7) optionally, altering, e.g., neutralizing, the pH of the
solution;
[0089] (8) optionally, biodegrading the degradation products, e.g.,
organic acids in the solution to form CO.sub.2, H.sub.2O and
biomass; and
[0090] (9) removing any insoluble components from the reactor.
[0091] This process differs from the previously discussed process
in connection with steps (1)-(5), which involve solubilization of
the polymer prior to introduction of the degradation-enhancing
reactant/precursor and formation of the degradation-enhancing
reactant from the precursor. Formation of the degradation-enhancing
reactant from the precursor may comprise irradiation of the
solution with electromagnetic radiation, heat, or a combination
thereof as explained in U.S. Pat. No. 6,623,643 and WO03/074432 A1.
As with the above-described process, filter media of the present
invention may be used in steps (2) and (6) of this particular
process.
[0092] A suitable system for performing the second process
discussed above is illustrated by FIG. 5, where the reference
numeral 100 refers generally to a solution vessel. In a desired
embodiment, solution vessel 100 is an autoclave. Solution vessel
100 is desirably made of stainless steel or similarly corrosively
resistant material. Solution vessel 100 is connected by a plumbing
line 102 to a filter system 104. Filter system 104 is connected by
plumbing line 106 to a pump 108. In a desired embodiment, a
plumbing line 112 intersects and connects plumbing line 110 to a
heat exchanger 114. Heat exchanger 114 is connected by a plumbing
line 116 back to solution vessel 100 to form a recirculating
communication.
[0093] Pump 108 is connected by a plumbing line 110 to a
photochemical reaction vessel 200. Reaction vessel 200 is desirably
made of stainless steel or similarly corrosively resistant
material. In one embodiment, photochemical reaction vessel 200 is
comprised of a bank of individual photochemical reactors (not
shown) arranged in an array within the reaction vessel. In this
embodiment, a mechanical mixer (not shown) is located within
reaction vessel 200 to provide circulation of the contents. Each of
the reactors comprising at least one high-intensity ultraviolet
lighting element. In a more desired embodiment, the photochemical
reactors within reaction vessel 200 generate ultraviolet radiation
in the wavelengths between about 185 and about 250 nanometers.
[0094] An oxidative agent injection system 300 is connected by a
plumbing line 302 to reaction vessel 200. In a desired embodiment,
oxidative agent injection system 300 comprising a programmable
logic controller, sensor, recorder, and dispensing mechanism, such
as is well known in industrial chemistry. Photochemical reaction
vessel 200 is connected by a plumbing line 202 to a pump 204. Pump
204 is connected by a plumbing line 206 to a neutralization vessel
400. In an optional embodiment, a plumbing line 208 intersects
plumbing line 206 and is connected to reaction vessel 200 to permit
pump operated re-circulating photochemical treatment of the
solution.
[0095] A pH neutralizing system 402 is connected by a plumbing line
404 to neutralization vessel 400. In a more desired embodiment, pH
neutralizing system 402 comprising an automatic pH controller.
Neutralization vessel 400 is connected by a plumbing line 406 to a
pump 408. Pump 408 is connected by a plumbing line 410 back to
neutralization vessel 400 to form a recirculating communication.
Neutralization vessel 400 is connected by a plumbing line 412 to
bio cells 500. Bio cells 500 are desirably of the fixed media
aerobic type or activated sludge processes. Entrance accommodations
are made for administration of air, microbes and nutrients to the
bio cells by any means well known in the industry. Bio cells 500
are connected by a plumbing line 502 to a pump 504. Pump 504 is
connected by a plumbing line 506 back to bio cells 500 to form a
recirculating communication. Bio cells 500 are connected by a
plumbing line 508 for discharge.
[0096] In an alternative desired embodiment, a plumbing line 602
intersects and connects plumbing line 206 to a radioactive material
filtration system 600. Radioactive material filtration system 600
is connected by a plumbing line 604 back to plumbing line 206 to
form a circulating communication. Optionally, radioactive material
filtration system 600 is connected by a plumbing line 606 back to
reaction vessel 200 to form a recirculating communication by which
depletion of radioactivity in solution can be performed coincident
with oxidation-reduction of the solution. Radioactive material
filtration system 600 may alternatively be connected within the
disclosed system at any position between solution vessel 100 and
neutralization vessel 400.
[0097] While the specification has been described in detail with
respect to specific embodiments thereof, it will be appreciated
that those skilled in the art, upon attaining an understanding of
the foregoing, may readily conceive of alterations to, variations
of, and equivalents to these embodiments. Accordingly, the scope of
the present invention should be assessed as that of the appended
claims and any equivalents thereto.
* * * * *