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Patent Abstract
A process for producing a water filter material is provided. The
process includes the steps of providing a plurality of mesoporous
activated carbon particles, and treating said plurality of mesoporous
activated carbon particles to produce a plurality of mesoporous
activated carbon particles having a bulk oxygen percentage by weight
of less than about 2.3%.
Patent Claims
What is claimed is:
1. A process for producing a filter material, comprising the steps
of: (a) providing a first material, wherein said first material
comprises a plurality of mesoporous activated carbon filter particles;
and (b) treatment of said first material to produce a second material,
said second material comprising a plurality of mesoporous activated
carbon filter particles, wherein said plurality of mesoporous activated
carbon filter particles of said second material has a bulk oxygen
percentage by weight of less than about 5%.
2. The process of claim 1, wherein said treatment step (b) comprises
exposing said plurality of mesoporous activated carbon filter particles
to a temperature between about 600.degree. C. and about 1,200.degree.
C.
3. The process of claim 1, wherein said plurality of mesoporous
activated carbon filter particles of said second material has a
point of zero charge of greater than about 6.
4. The process of claim 1, wherein said plurality of mesoporous
activated carbon filter particles of said second material has an
ORP of less than about 400 mV.
5. The process of claim 1, wherein said plurality of mesoporous
activated carbon filter particles of said second material has a
bulk oxygen percentage by weight of less than about 2%.
6. The process of claim 1, wherein said process further comprises
an inserting step (c), said inserting step (c) consisting of inserting
said plurality of mesoporous activated carbon filter particles of
said second material into a filter housing having a water inlet
and a water outlet.
7. The process of claim 1, wherein said plurality of mesoporous
activated carbon filter particles of said second material has a
BRI of greater than about 99%.
8. The process of claim 1, wherein said plurality of mesoporous
activated carbon filter particles of said second material has a
VRI of greater than about 90%.
9. A process for producing a filter material, comprising the steps
of: (a) providing a first material, wherein said first material
comprises a plurality of mesoporous activated carbon filter particles;
and (b) treatment of said first material to produce a second material,
said second material comprising a plurality of mesoporous activated
carbon filter particles, wherein said plurality of mesoporous activated
carbon filter particles of said second material has a bulk oxygen
percentage by weight of less than about 2.3%.
10. The process of claim 9, wherein said treatment step (b) comprises
a treatment atmosphere selected from the group consisting of hydrogen,
dissociated ammonia, carbon monoxide, argon, nitrogen, steam, helium
and mixtures thereof.
11. The process of claim 9, wherein said treatment step (b) comprises
a temperature between about 600.degree. C. and about 1,200.degree.
C.
12. The process of claim 9, wherein said treatment step (b) comprises
a temperature between about 100.degree. C. and about 800.degree.
C., and wherein said plurality of mesoporous activated carbon filter
particles comprises noble metal catalysts.
13. The process of claim 9, wherein said plurality of mesoporous
activated carbon filter particles of said second material has a
point of zero charge between about 9 and about 12.
14. The process of claim 9, wherein said plurality of mesoporous
activated carbon filter particles of said second material has an
ORP between about 290 mV and about 175 mV.
15. The process of claim 9, wherein said plurality of mesoporous
activated carbon filter particles of said second material has a
bulk oxygen percentage by weight between about 1.2% and about 0.1%.
16. A process for producing a filter material, comprising the steps
of: (a) Providing a starting material; (b) treatment of said starting
material to produce a first material, said first material comprising
a plurality of mesoporous activated carbon filter particles; and
(c) treatment of said first material to produce a second material,
said second material comprising a plurality of mesoporous activated
carbon filter particles, wherein said plurality of mesoporous activated
carbon filter particles of said second material has a bulk oxygen
percentage by weight of less than about 5%.
17. The process of claim 16, wherein said starting material comprises,
at least in part, wood-based particles, coal-based particles, peat-based
particles, pitch-based particles, tar-based particles, bean-based
particles, other lignocellulosic-based particles, and mixtures thereof,
wherein said treatment step (b) comprises exposing said starting
material to a temperature between about 300.degree. C. to about
600.degree. C., and wherein said treatment step (c) comprises exposing
said plurality of mesoporous activated carbon filter particles of
said first material to a temperature between 600.degree. C. to about
1200.degree. C.
18. The process of claim 17, wherein said process further comprises
washing said plurality of mesoporous activated carbon filter particles
of said first material before said treatment step (c).
19. The process of claim 18, wherein said treatment step (b) comprises
exposing said starting material for a time between about 1 hour
to about 3 hours, and wherein said treatment step (c) comprises
exposing said plurality of mesoporous activated carbon filter particles
of said first material for a time between about 1 hour to about
6 hours.
20. The process of claim 19, wherein said treatment step (b) comprises
the presence of an acid selected from the group consisting of phosphoric
acid, zinc chloride, ammonium phosphate, and mixtures thereof.
21. A process for producing a filter material, comprising the steps
of: (a) providing a first material, wherein said first material
comprises a plurality of mesoporous activated carbon filter particles;
and (b) treatment of said first material to produce a second material,
said second material comprising a plurality of mesoporous and basic
activated carbon filter particles, wherein said plurality of mesoporous
and basic activated carbon filter particles of said second material
has a bulk oxygen percentage by weight of less than about 2.3%,
a sum of mesopore and macropore volumes greater than about 0.6 mL/g,
a point of zero charge of greater than about 8, an ORP of less than
about 325 mV, BRI of greater than about 99.9%, and a VRI of greater
than about 99.99%.
Patent Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] Pursuant to 35 U.S.C. .sctn. 120, this application is a
continuation-in-part of U.S. application Ser. No. 09/935,962, filed
on Aug. 23, 2001 and is also a continuation-in-part of U.S. application
Ser. No. 09/935,810, filed on Aug. 23, 2001, the substances of which
are incorporated herein by reference. Additionally, pursuant to
35 U.S.C. .sctn. 120, this application is a continuation of International
Application No. PCT/US03/05416 designating the U.S., filed Feb.
21, 2003, and is also a continuation of International Application
No. PCT/US03/05409 designating the U.S., filed Feb. 21, 2003, the
substances of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of processes
for manufacturing water filter materials and water filters, and,
more particularly, to the field of processes for manufacturing water
filters containing mesoporous activated carbon particles.
BACKGROUND OF THE INVENTION
[0003] Water may contain many different kinds of contaminants including,
for example, particulates, harmful chemicals, and microbiological
organisms, such as bacteria, parasites, protozoa and viruses. In
a variety of circumstances, these contaminants must be removed before
the water can be used. For example, in many medical applications
and in the manufacture of certain electronic components, extremely
pure water is required. As a more common example, any harmful contaminants
must be removed from the water before it is potable, i.e., fit to
consume. Despite modern water purification means, the general population
is at risk, and in particular infants and persons with compromised
immune systems are at considerable risk.
[0004] In the U.S. and other developed countries, municipally treated
water typically includes one or more of the following impurities:
suspended solids, bacteria, parasites, viruses, organic matter,
heavy metals, and chlorine. Breakdown and other problems with water
treatment systems sometimes lead to incomplete removal of bacteria
and viruses. In other countries, there are deadly consequences associated
with exposure to contaminated water, as some of them have increasing
population densities, increasingly scarce water resources, and no
water treatment utilities. It is common for sources of drinking
water to be in close proximity to human and animal waste, such that
microbiological contamination is a major health concern. As a result
of waterborne microbiological contamination, an estimated six million
people die each year, half of which are children under 5 years of
age.
[0005] In 1987, the U.S. Environmental Protection Agency (EPA)
introduced the "Guide Standard and Protocol for Testing Microbiological
Water Purifiers". The protocol establishes minimum requirements
regarding the performance of drinking water treatment systems that
are designed to reduce specific health related contaminants in public
or private water supplies. The requirements are that the effluent
from a water supply source exhibits 99.99% (or equivalently, 4 log)
removal of viruses and 99.9999% (or equivalently, 6 log) removal
of bacteria against a challenge. Under the EPA protocol, in the
case of viruses, the influent concentration should be 1.times.10.sup.7
viruses per liter, and in the case of bacteria, the influent concentration
should be 1.times.10.sup.8 bacteria per liter. Because of the prevalence
of Escherichia coli (E. coli, bacterium) in water supplies, and
the risks associated with its consumption, this microorganism is
used as the bacterium in the majority of studies. Similarly, the
MS-2 bacteriophage (or simply, MS-2 phage) is typically used as
the representative microorganism for virus removal because its size
and shape (i.e., about 26 nm and icosahedral) are similar to many
viruses. Thus, a filter's ability to remove MS-2 bacteriophage demonstrates
its ability to remove other viruses.
[0006] Due to these requirements and a general interest in improving
the quality of potable water, there is a continuing desire to provide
processes for manufacturing filter materials and filters, which
are capable of removing bacteria and/or viruses from a fluid.
SUMMARY OF THE INVENTION
[0007] A process for producing a water filter material is provided.
The process includes the steps of providing a plurality of mesoporous
activated carbon particles, and treating said plurality of mesoporous
activated carbon particles to produce a plurality of mesoporous
activated carbon particles having a bulk oxygen percentage by weight
of less than about 5%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] While the specification concludes with claims particularly
pointing out and distinctly claiming the invention, it is believed
that the present invention will be better understood from the following
description taken in conjunction with the accompanying drawings
in which:
[0009] FIG. 1a is a BET nitrogen adsorption isotherm of mesoporous
and acidic activated carbon particles CA-10, and mesoporous, basic,
and reduced-oxygen activated carbon particles TA4-CA-10.
[0010] FIG. 1b is a BET nitrogen adsorption isotherm of mesoporous
and basic activated carbon particles RGC, and mesoporous, basic,
and reduced-oxygen activated carbon THe4-RGC.
[0011] FIG. 2a is a mesopore volume distribution of the particles
of FIG. 1a.
[0012] FIG. 2b is a mesopore volume distribution of the particles
of FIG. 1b.
[0013] FIG. 3a is a point-of-zero-charge graph of the particles
of FIG. 1a.
[0014] FIG. 3b is a point-of-zero-charge graph of the particles
of FIG. 1b.
[0015] FIG. 4 is a cross sectional side view of an axial flow filter
made in accordance with the present invention.
[0016] FIG. 5a illustrates the E. coli bath concentration as a
function of time for the activated carbon particles of FIG. 1a.
[0017] FIG. 5b illustrates the E. coli bath concentration as a
function of time for activated carbon particles of FIG. 1b.
[0018] FIG. 6a illustrates the MS-2 bath concentration as a function
of time for the activated carbon particles of FIG. 1a.
[0019] FIG. 6b illustrates the MS-2 bath concentration as a function
of time for the activated carbon particles of FIG. 1b.
[0020] FIG. 7a illustrates the E. coli flow concentration as a
function of the cumulative volume of water through 2 filters; one
containing RGC mesoporous and basic activated carbon, and the other
containing coconut microporous activated carbon particles.
[0021] FIG. 7b illustrates the MS-2 flow concentration as a function
of the cumulative volume of water through of 2 filters; one containing
RGC mesoporous and basic activated carbon, and the other containing
coconut microporous activated carbon particles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] All documents cited are, in relevant part, incorporated
herein by reference. The citation of any document is not to be construed
as an admission that it is prior art with respect to the present
invention.
[0023] I. Definitions
[0024] As used herein, the terms "filters" and "filtration"
refer to structures and mechanisms, respectively, associated with
microorganism removal (and/or other contaminant removal), via primarily
adsorption and/or size exclusion to a lesser extent.
[0025] As used herein, the phrase "filter material" is
intended to refer to an aggregate of filter particles. The aggregate
of the filter particles forming a filter material can be either
homogeneous or heterogeneous. The filter particles can be uniformly
or non-uniformly distributed (e.g., layers of different filter particles)
within the filter material. The filter particles forming a filter
material also need not be identical in shape or size and may be
provided in either a loose or interconnected form. For example,
a filter material might comprise mesoporous and basic activated
carbon particles in combination with activated carbon fibers, and
these filter particles may be either provided in loose association
or partially or wholly bonded by a polymeric binder or other means
to form an integral structure.
[0026] As used herein, the phrase "filter particle" is
intended to refer to an individual member or piece, which is used
to form at least part of a filter material. For example, a fiber,
a granule, a bead, etc. are each considered filter particles herein.
Further, the filter particles can vary in size, from impalpable
filter particles (e.g., a very fine powder) to palpable filter particles.
[0027] As used herein, the phrase "filter material pore volume"
refers to the total volume of the inter-particle pores in the filter
material with sizes larger than 0.1 .mu.m.
[0028] As used herein, the phrase "filter material total volume"
refers to the sum of the inter-particle pore volume and the volume
occupied by the filter particles.
[0029] As used herein, the terms "microorganism", "microbiological
organism" and "pathogen" are used interchangeably.
These terms refer to various types of microorganisms that can be
characterized as bacteria, viruses, parasites, protozoa, and germs.
[0030] As used herein, the phrase "Bacteria Removal Index"
(BRI) of filter particles is defined as:
BRI=100.times.[1-(bath concentration of E. coli bacteria at equilibrium/control
concentration of E. coli bacteria)],
[0031] wherein "bath concentration of E. coli bacteria at
equilibrium" refers to the concentration of bacteria at equilibrium
in a bath that contains a mass of filter particles having a total
external surface area of 1400 cm.sup.2 and Sauter mean diameter
less than 55 .mu.m, as discussed more fully hereafter. Equilibrium
is reached when the E. coli concentration, as measured at two time
points 2 hours apart, remains unchanged to within half order of
magnitude. The phrase "control concentration of E. coli bacteria"
refers to the concentration of E. coli bacteria in the control bath,
and is equal to about 3.7.times.10.sup.9 CFU/L. The Sauter mean
diameter is the diameter of a particle whose surface-to-volume ratio
is equal to that of the entire particle distribution. Note that
the term "CFU/L" denotes "colony-forming units per
liter", which is a typical term used in E. coli counting. The
BRI index is measured without application of chemical agents that
provide bactericidal effects. An equivalent way to report the removal
capability of filter particles is with the "Bacteria Log Removal
Index" (BLRI), which is defined as:
BLRI=-log[1-(BRI/100)].
[0032] The BLRI has units of "log" (where "log"
stands for logarithm). For example, filter particles that have a
BRI equal to 99.99% have a BLRI equal to 4 log. A test procedure
for determining BRI and BLRI values is provided hereafter.
[0033] As used herein, the phrase "Virus Removal Index"
(VRI) for filter particles is defined as:
VRI=100.times.[1-(bath concentration of MS-2 phages at equilibrium/control
concentration of MS-2 phages)],
[0034] wherein "bath concentration of MS-2 phages at equilibrium"
refers to the concentration of phages at equilibrium in a bath that
contains a mass of filter particles having a total external surface
area of 1400 cm.sup.2 and Sauter mean diameter less than 55 .mu.m,
as discussed more fully hereafter. Equilibrium is reached when the
MS-2 concentration, as measured at two time points 2 hours apart,
remains unchanged to within half order of magnitude. The phrase
"control concentration of MS-2 phages" refers to the concentration
of MS-2 phages in the control bath, and is equal to about 6.7.times.10.sup.7
PFU/L. Note that the term "PFU/L" denotes "plaque-forming
units per liter", which is a typical term used in MS-2 counting.
The VRI index is measured without application of chemical agents
that provide virucidal effects. An equivalent way to report the
removal capability of filter particles is with the "Viruses
Log Removal Index" (VLRI), which is defined as:
VLRI=-log[1-(VRI/100)].
[0035] The VLRI has units of "log" ( where "log"
is the logarithm). For example, filter particles that have a VRI
equal to 99.9% have a VLRI equal to 3 log. A test procedure for
determining VRI and VLRI values is provided hereafter.
[0036] As used herein, the phrase "Filter Bacteria Log Removal
(F-BLR)" refers to the bacteria removal capability of the filter
after the flow of the first 2,000 filter material pore volumes.
The F-BLR is defined and calculated as:
F-BLR=-log[(effluent concentration of E. coli)/(influent concentration
of E. coli)],
[0037] where the "influent concentration of E. coli"
is set to about 1.times.10.sup.8 CFU/L continuously throughout the
test and the "effluent concentration of E. coli" is measured
after about 2,000 filter material pore volumes flow through the
filter. F-BLR has units of "log" (where "log"
is the logarithm). Note that if the effluent concentration is below
the limit of detection of the technique used to assay, then the
effluent concentration for the calculation of the F-BLR is considered
to be the limit of detection. Also, note that the F-BLR is measured
without application of chemical agents that provide bactericidal
effects.
[0038] As used herein, the phrase "Filter Viruses Log Removal
(F-VLR)" refers to the virus removal capability of the filter
after the flow of the first 2,000 filter material pore volumes.
The F-VLR is defined and calculated as:
F-VLR=-log [(effluent concentration of MS-2)/(influent concentration
of MS-2)],
[0039] where the "influent concentration of MS-2" is
set to about 1.times.10.sup.7 PFU/L continuously throughout the
test and the "effluent concentration of MS-2" is measured
after about 2,000 filter material pore volumes flow through the
filter. F-VLR has units of "log" (where "log"
is the logarithm). Note that if the effluent concentration is below
the limit of detection of the technique used to assay, then the
effluent concentration for the calculation of the F-VLR is considered
to be the limit of detection. Also, note that the F-VLR is measured
without application of chemical agents that provide virucidal effects.
[0040] As used herein, the phrase "total external surface
area" is intended to refer to the total geometric external
surface area of one or more of the filter particles, as discussed
more fully hereafter.
[0041] As used herein, the phrase "specific external surface
area" is intended to refer to the total external surface area
per unit mass of the filter particles, as discussed more fully hereafter.
[0042] As used herein, the term "micropore" is intended
to refer to an intra-particle pore having a width or diameter less
than 2 nm (or equivalently, 20 .ANG.).
[0043] As used herein, the term "mesopore" is intended
to refer to an intra-particle pore having a width or diameter between
2 nm and 50 nm (or equivalently, between 20 .ANG. and 500 .ANG.)
[0044] As used herein, the term "macropore" is intended
to refer to an intra-particle pore having a width or diameter greater
than 50 nm (or equivalently, 500 .ANG.).
[0045] As used herein, the phrase "total pore volume"
and its derivatives are intended to refer to the volume of all the
intra-particle pores, i.e., micropores, mesopores, and macropores.
The total pore volume is calculated as the volume of nitrogen adsorbed
at a relative pressure of 0.9814 using the BET process (ASTM D 4820-99
standard), a process well known in the art.
[0046] As used herein, the phrase "micropore volume"
and its derivatives are intended to refer to the volume of all micropores.
The micropore volume is calculated from the volume of nitrogen adsorbed
at a relative pressure of 0.15 using the BET process (ASTM D 4820-99
standard), a process well known in the art.
[0047] As used herein, the phrase "sum of the mesopore and
macropore volumes" and its derivatives are intended to refer
to the volume of all mesopores and macropores. The sum of the mesopore
and macropore volumes is equal to the difference between the total
pore volume and micropore volume, or equivalently, is calculated
from the difference between the volumes of nitrogen adsorbed at
relative pressures of 0.9814 and 0.15 using the BET process (ASTM
D 4820-99 standard), a process well known in the art.
[0048] As used herein, the phrase "pore size distribution
in the mesopore range" is intended to refer to the distribution
of the pore size as calculated by the Barrett, Joyner, and Halenda
(BJH) process, a process well known in the art.
[0049] As used herein, the term "carbonization" and its
derivatives are intended to refer to a process in which the non-carbon
atoms in a carbonaceous substance are reduced.
[0050] As used herein, the term "activation" and its
derivatives are intended to refer to a process in which a carbonized
substance is rendered more porous.
[0051] As used herein, the term "activated carbon particles"
or "activated carbon filter particles" and their derivatives
are intended to refer to carbon particles that have been subjected
to an activation process.
[0052] As used herein, the phrase "point of zero charge"
is intended to refer to the pH above which the total surface of
the carbon particles is negatively charged. A well known test procedure
for determining the point of zero charge is set forth hereafter.
[0053] As used herein, the term "basic" is intended to
refer to filter particles with a point of zero charge greater than
7.
[0054] As used herein, the term "acidic" is intended
to refer to filter particles with a point of zero charge less than
7.
[0055] As used herein, the phrase "mesoporous activated carbon
filter particle" refers to an activated carbon filter particle
wherein the sum of the mesopore and macropore volumes may be greater
than 0.12 mL/g.
[0056] As used herein, the phrase "microporous activated carbon
filter particle" refers to an activated carbon filter particle
wherein the sum of the mesopore and macropore volumes may be less
than 0.12 mL/g.
[0057] As used herein, the phrase "mesoporous and basic activated
carbon filter particle" is intended to refer to an activated
carbon filter particle wherein the sum of the mesopore and macropore
volumes may be greater than 0.12 mL/g and has a point of zero charge
greater than 7.
[0058] As used herein, the phrase "mesoporous, basic, and
reduced-oxygen activated carbon filter particle" is intended
to refer to an activated carbon filter particle wherein the sum
of the mesopore and macropore volumes may be greater than 0.12 mL/g,
has a point of zero charge greater than 7, and has a bulk oxygen
percentage by weight of 1.5% or less.
[0059] As used herein, the phrase "mesoporous and acidic activated
carbon filter particle" is intended to refer to an activated
carbon filter particle wherein the sum of the mesopore and macropore
volumes may be greater than 0.12 mL/g and has a point of zero charge
less than 7.
[0060] As used herein, the phrase "starting material"
refers to any precursor containing mesopores and macropores or capable
of yielding mesopores and macropores during carbonization and/or
activation.
[0061] As used herein, the phrase "axial flow" refers
to flow through a planar surface and perpendicularly to that surface.
[0062] As used herein, the phrase "radial flow" typically
refers to flow through essentially cylindrical or essentially conical
surfaces and perpendicularly to those surfaces.
[0063] As used herein, the phrase "face area" refers
to the area of the filter material initially exposed to the influent
water. For example, in the case of axial flow filters, the face
area is the cross sectional area of the filter material at the entrance
of the fluid, and in the case of the radial flow filter, the face
area is the outside area of the filter material.
[0064] As used herein, the phrase "filter depth" refers
to the linear distance that the influent water travels from the
entrance to the exit of the filter material. For example, in the
case of axial flow filters, the filter depth is the thickness of
the filter material, and in the case of the radial flow filter,
the filter depth is half of the difference between the outside and
inside diameters of the filter material.
[0065] As used herein, the phrases "average fluid residence
time" and/or "average fluid contact time" refer to
the average time that the fluid is in contact with the filter particles
inside the filter as it travels through the filter material, and
are calculated as the ratio of the filter material pore volume to
the fluid flow rate.
[0066] As used herein, the phrases "filter porosity"
and/or "filter bed porosity" refer to the ratio of the
filter material pore volume to the filter material total volume.
[0067] As used herein, the phrase "inlet" refers to the
means in which a fluid is able to enter the filter or filter material.
For example, the inlet can be a structure that is part of the filter,
or the filter material face area.
[0068] As used herein, an "outlet" refers to the means
in which a fluid is able to exit the filter or filter material.
For example, the outlet can be a structure that is part of the filter,
or the cross sectional area of the filter material at the exit of
the fluid.
[0069] II. Mesoporous Activated Carbon Filter Particles
[0070] Unexpectedly it has been found that mesoporous activated
carbon filter particles adsorb a larger number of microorganisms
compared to microporous activated carbon filter particles. Also,
unexpectedly it has been found that mesoporous and basic activated
carbon filter particles adsorb a larger number of microorganisms
compared to that adsorbed by mesoporous and acidic activated carbon
filter particles. Furthermore, it has been found unexpectedly that
mesoporous, basic, and reduced-oxygen activated carbon filter particles
adsorb a larger number of microorganisms compared to that adsorbed
by mesoporous and basic activated carbon filter particles without
reduced bulk oxygen percentage by weight.
[0071] Although not wishing to be bound by any theory, applicants
hypothesize that, with regard to porosity, a large number of mesopores
and/or macropores provides more convenient adsorption sites (openings
or entrances of the mesopores/macropores) for the pathogens, their
fimbriae, and surface polymers (e.g. proteins, lipopolysaccharides,
oligosaccharides and polysaccharides) that constitute the outer
membranes, capsids and envelopes of the pathogens because the typical
size of such is similar to that of the entrances of the mesopores
and macropores. Also, mesoporosity and macroporosity may correlate
with one or more surface properties of the carbon, such as surface
roughness.
[0072] Also, not wishing to be bound by theory, applicants hypothesize
that basic activated carbon surfaces contain the types of functionality
that are necessary to attract a larger number of microorganisms
compared to those attracted by an acidic carbon surface. This enhanced
adsorption onto the basic carbon surfaces might be attributed to
the fact that the basic carbon surfaces attract the typically negatively-charged
microorganisms and functional groups on their surface. Applicants
further hypothesize that basic carbon is capable of producing disinfectants
when placed in water by reducing molecular oxygen. Although the
final product of the reduction is hydroxide, applicants believe
that reactive oxygen intermediates, such as superoxide, hydroperoxide,
and/or hydroxy radicals, are formed and maybe sufficiently long-lived
to diffuse from carbon into bulk solution.
[0073] Furthermore, applicants believe that carbon becomes more
basic as the bulk oxygen percentage by weight is reduced. A low
bulk oxygen percentage by weight may lead to improved bacteria/viruses
adsorption because there will be: (1) less carboxylic acids and
hence a less negative surface to repel bacteria/viruses; and (2)
a less hydrated surface so that water is more easily displaced by
bacteria/viruses as they attempt to adsorb to the surface (i.e.,
less of an energy penalty for the bacteria/virus to displace other
species already occupying sites on the surface). This latter reason
(i.e., a less hydrated surface) also ties in with the idea that
the ideal surface, discussed hereafter, should be somewhat hydrophobic
(that is, it should have just enough oxygen substitution on the
edge carbon atoms to allow it to wet out, but not so much as to
make it excessively hydrophilic).
[0074] The filter particles can be provided in a variety of shapes
and sizes. For example, the filter particles can be provided in
simple forms such as powder, granules, fibers, and beads. The filter
particles can be provided in the shape of a sphere, polyhedron,
cylinder, as well as other symmetrical, asymmetrical, and irregular
shapes. Further, the filter particles can also be formed into complex
forms such as webs, screens, meshes, non-wovens, wovens, and bonded
blocks, which may or may not be formed from the simple forms described
above. Like shape, the size of the filter particle can also vary,
and the size need not be uniform among filter particles used in
any single filter. In fact, it can be desirable to provide filter
particles having different sizes in a single filter. Generally,
the size of the filter particles may be between about 0.1 .mu.m
and about 10 mm, preferably between about 0.2 .mu.m and about 5
mm, more preferably between about 0.4 .mu.m and about 1 mm, and
most preferably between about 1 .mu.m and about 500 .mu.m. For spherical
and cylindrical particles (e.g., fibers, beads, etc.), the above-described
dimensions refer to the diameter of the filter particles. For filter
particles having substantially different shapes, the above-described
dimensions refer to the largest dimension (e.g. length, width, or
height).
[0075] The filter particles may be the product of any precursor
that contains mesopores and macropores or generates mesopores and
macropores during carbonization and/or activation. For example,
and not by way of limitation, the filter particles can be wood-based
activated carbon particles, coal-based activated carbon particles,
peat-based activated carbon particles, pitch-based activated carbon
particles, tar-based activated carbon particles, bean-based activated
carbon particles, other lignocellulosic-based activated carbon particles,
and mixtures thereof.
[0076] Activated carbon can display acidic, neutral, or basic properties.
The acidic properties are associated with oxygen-containing functionalities
or functional groups, such as, and not by way of limitation, phenols,
carboxyls, lactones, hydroquinones, anhydrides, and ketones. The
basic properties have heretofore been associated with functionalities
such as pyrones, chromenes, ethers, carbonyls, as well as the basal
plane .pi. electrons. The acidity or basicity of the activated carbon
particles is determined with the "point of zero charge"
technique (Newcombe, G., et al., Colloids and Surfaces A: Physicochemical
and Engineering Aspects, 78, 65-71 (1993)), the substance of which
is incorporated herein by reference. The technique is further described
in section VI hereafter. Filter particles of the present invention
may have a point of zero charge between 1 and 14, preferably greater
than about 4, preferably greater than about 6, preferably greater
than about 7, preferably greater than about 8, more preferably greater
than about 9, and most preferably between about 9 and about 12.
[0077] The point of zero charge of activated carbons inversely
correlates with their bulk oxygen percentage by weight. Filter particles
of the present invention may have a bulk oxygen percentage by weight
less than about 5%, preferably less than about 2.5%, preferably
less than about 2.3%, preferably less than about 2%, more preferably
less than about 1.2%, and most preferably less than about 1%, and/or
greater than about 0.1%, preferably greater than about 0.2%, more
preferably greater than about 0.25%, and most preferably greater
than about 0.3%. Also, the point of zero charge of activated carbon
particles correlates with the ORP of the water containing the particles
because the point of zero charge is a measure of the ability of
the carbon to reduce oxygen (at least for basic carbons). Filter
particles of the present invention may have an ORP less than about
570 mV, preferably less than about 465 mV, preferably less than
about 400, preferably less than about 360 mV, preferably less than
about 325 mV, and most preferably between about 290 mV and about
175 mV.
[0078] The electric resistance of the activated carbon filter particles
or filter material is one of their important properties as it relates
to their ability to form a filter block. For example, a resistive
heating method can be used to form filter blocks, wherein a filter
material is heated by passing electricity between 2 ends of the
filter material. The electric resistance of the filter material
will control its ability to heat in a short time. The electric resistance
is measured by forming filter blocks using conditions as those mentioned
in Examples 3 and 4, supra, and measuring the electric resistance
between the 2 faces of the block by contacting them with 2 electrodes
from a voltmeter. Exemplary electric resistances of the filters
of Examples 3 and 4 are about 350 .OMEGA. and about 40 .OMEGA.,
respectively. Also, the respective electric resistances of filters
made with CARBOCHEM CA-10 of Example 1, supra, and TA4-CA10 of Example
2, supra, are about 1.3 M.OMEGA., and about 100 .OMEGA..
[0079] Filter particles may be achieved by way of treating a starting
material as described herebelow. The treatment conditions may include
atmosphere composition, pressure, temperature, and/or time. The
atmospheres of the present invention may be reducing or inert. Heating
the filter particles in the presence of reducing atmospheres, steam,
or inert atmospheres yields filter material with reduced surface
oxygen functionality. Examples of suitable reducing atmospheres
may include hydrogen, nitrogen, dissociated ammonia, carbon monoxide,
and/or mixtures. Examples of suitable inert atmospheres may include
argon, helium, and/or mixtures thereof.
[0080] The treatment temperature, when the activated carbon particles
do not contain any noble metal catalysts (e.g., platinum, gold,
palladium) may be between about 600.degree. C. and about 1,200.degree.
C., preferably between about 700.degree. C. and about 1,100.degree.
C., more preferably between about 800.degree. C. and about 1,050.degree.
C., and most preferably between about 900.degree. C. and about 1,000.degree.
C. If the activated carbon particles contain noble metal catalysts,
the treatment temperature may be between about 100.degree. C. and
about 800.degree. C., preferably between about 200.degree. C. and
about 700.degree. C., more preferably between about 300.degree.
C. and about 600.degree. C., and most preferably between about 350.degree.
C. and about 550.degree. C.
[0081] The treatment time may be between about 2 minutes and about
10 hours, preferably between about 5 minutes and about 8 hours,
more preferably between about 10 minutes and about 7 hours, and
most preferably between about 20 minutes and about 6 hours. The
gas flow rate may be between about 0.25 standard L/h.g (i.e., standard
liters per hour and gram of carbon; 0.009 standard ft.sup.3/h.g)
and about 60 standard L/h.g (2.1 standard ft.sup.3/h.g), preferably
between about 0.5 standard L/h.g (0.018 standard ft.sup.3/h.g) and
about 30 standard L/h.g (1.06 standard ft.sup.3/h.g), more preferably
between about 1.0 standard L/h.g (0.035 standard ft.sup.3/h.g) and
about 20 standard L/h.g (0.7 standard ft.sup.3/h.g), and most preferably
between about 5 standard L/h.g (0.18 standard ft.sup.3/h.g) and
about 10 standard L/h.g (0.35 standard ft.sup.3/h.g). The pressure
can be maintained greater than, equal to, or less than atmospheric
during the treatment time. As will be appreciated, other processes
for producing a mesoporous, basic, and reduced-oxygen activated
carbon filter material can be employed. Also, such treatment of
a starting material as described above may be repeated multiple
times, depending on the starting material, in order to obtain a
filter material.
[0082] A starting material may be commercially obtained, or may
be made by the methods which are well known in the art, as described
in, for example, Jagtoyen, M., and F. Derbyshire, Carbon, 36(7-8),
1085-1097 (1998), and Evans, et al., Carbon, 37, 269-274 (1999),
and Ryoo et al., J. Phys. Chem. B, 103(37), 7743-7746 (1999), the
substances of which are herein incorporated by reference. Typical
chemicals used for activation/carbonization include phosphoric acid,
zinc chloride, ammonium phosphate, etc., which may be used in combination
with the methods described in the two immediately cited journals.
[0083] The Brunauer, Emmett and Teller (BET) specific surface area
and the Barrett, Joyner, and Halenda (BJH) pore size distribution
can be used to characterize the pore structure of particles. Preferably,
the BET specific surface area of the filter particles may be between
about 500 m.sup.2/g and about 3,000 m.sup.2/g, preferably between
about 600 m.sup.2/g to about 2,800 m.sup.2/g, more preferably between
about 800 m.sup.2/g and about 2,500 m.sup.2/g, and most preferably
between about 1,000 m.sup.2/g and about 2,000 m.sup.2/g. Referring
to FIG. 1a, typical nitrogen adsorption isotherms, using the BET
process, of a mesoporous, basic, and reduced-oxygen wood-based activated
carbon (TA4-CA-10), and a mesoporous and acidic wood-based activated
carbon (CA-10) are illustrated. Referring to FIG. 1b, typical nitrogen
adsorption isotherms, using the BET process, of a mesoporous and
basic wood-based activated carbon (RGC), and a mesoporous, basic,
and reduced-oxygen wood-based activated carbon (THe4-RGC) are illustrated.
[0084] The total pore volume of the mesoporous and basic activated
carbon particles is measured during the BET nitrogen adsorption
and is calculated as the volume of nitrogen adsorbed at a relative
pressure, P/P.sub.0, of 0.9814. More specifically and as is well
known in the art, the total pore volume is calculated by multiplying
the "volume of nitrogen adsorbed in mL(STP)/g" at a relative
pressure of 0.9814 with the conversion factor 0.00156, that converts
the volume of nitrogen at STP (standard temperature and pressure)
to liquid. The total pore volume of the filter particles may be
greater than about 0.4 mL/g, or greater than about 0.7 mL/g, or
greater than about 1.3 mL/g, or greater than about 2 mL/g, and/or
less than about 3 mL/g, or less than about 2.6 mL/g, or less than
about 2 mL/g, or less than about 1.5 mL/g.
[0085] The sum of the mesopore and macropore volumes is measured
during the BET nitrogen adsorption and calculated as the difference
between the total pore volume and the volume of nitrogen adsorbed
at P/P.sub.0 of 0.15. The sum of the mesopore and macropore volumes
of the filter particles may be greater than about 0.12 mL/g, or
greater than about 0.2 mL/g, or greater than about 0.4 mL/g, or
greater than about 0.6 mL/g, or greater than about 0.75 mL/g, and/or
less than about 2.2 mL/g, or less than about 2 mL/g, or less than
about 1.5 mL/g, or less than about 1.2 mL/g, or less than about
1 mL/g.
[0086] The BJH pore size distribution can be measured using the
Barrett, Joyner, and Halenda (BJH) process, which is described in
J. Amer. Chem. Soc., 73, 373-80 (1951) and Gregg and Sing, ADSORPTION,
SURFACE AREA, AND POROSITY, 2nd edition, Academic Press, New York
(1982), the substances of which are incorporated herein by reference.
In one embodiment, the pore volume may be at least about 0.01 mL/g
for any pore diameter between about 4 nm and about 6 nm. In an alternate
embodiment, the pore volume may be between about 0.01 mL/g and about
0.04 mL/g for any pore diameter between about 4 nm and about 6 nm.
In yet another embodiment, the pore volume may be at least about
0.03 mL/g for pore diameters between about 4 nm and about 6 nm or
is between about 0.03 mL/g and about 0.06 mL/g. In a preferred embodiment,
the pore volume may be between about 0.015 mL/g and about 0.06 mL/g
for pore diameters between about 4 nm and about 6 nm. FIG. 2a illustrates
typical mesopore volume distributions, as calculated by the BJH
process, of a mesoporous, basic, and reduced-oxygen activated carbon
(TA4-CA-10), and a mesoporous and acidic wood-based activated carbon
(CA-10). FIG. 2b illustrates typical mesopore volume distributions,
as calculated by the BJH process, of a mesoporous and basic wood-based
activated carbon (RGC), and a mesoporous, basic, and reduced-oxygen
wood-based activated carbon (THe4-RGC).
[0087] The ratio of the sum of the mesopore and macropore volumes
to the total pore volume may be greater than about 0.3, preferably
greater than about 0.4, preferably greater than about 0.6, and most
preferably between about 0.7 and about 1.
[0088] The total external surface area is calculated by multiplying
the specific external surface area by the mass of the filter particles,
and is based on the dimensions of the filter particles. For example,
the specific external surface area of mono-dispersed (i.e., with
uniform diameter) fibers is calculated as the ratio of the area
of the fibers (neglecting the 2 cross sectional areas at the ends
of the fibers) to the weight of the fibers. Thus, the specific external
surface area of the fibers is equal to: 4/D.rho., where D is the
fiber diameter and .rho. is the fiber density. For monodispersed
spherical particles, similar calculations yield the specific external
surface area as equal to: 6/D.rho., where D is the particle diameter
and .rho. is the particle density. For poly-dispersed fibers, spherical
or irregular particles, the specific external surface area is calculated
using the same respective formulae as above after substituting {overscore
(D)}.sub.3,2 for D, where {overscore (D)}.sub.3,2 is the Sauter
mean diameter, which is the diameter of a particle whose surface-to-volume
ratio is equal to that of the entire particle distribution. A process,
well known in the art, to measure the Sauter mean diameter is by
laser diffraction, for example using the Malvern equipment (Malvern
Instruments Ltd., Malvern, U.K.). The specific external surface
area of the filter particles may be between about 10 cm.sup.2/g
and about 100,000 cm.sup.2/g, preferably between about 50 cm.sup.2/g
and about 50,000 cm.sup.2/g, more preferably between about 100 cm.sup.2/g
and about 10,000 cm.sup.2/g, and most preferably between about 500
cm.sup.2/g and about 7,000 cm.sup.2/g.
[0089] The BRI of the mesoporous, or mesoporous and basic, or mesoporous,
basic and reduced-oxygen activated carbon particles, when measured
according to the test procedure set forth herein, may be greater
than about 99%, preferably greater than about 99.9%, more preferably
greater than about 99.99%, and most preferably greater than about
99.999%. Equivalently, the BLRI of the mesoporous, or mesoporous
and basic, or mesoporous, basic and reduced-oxygen activated carbon
particles may be greater than about 2 log, preferably greater than
about 3 log, more preferably greater than about 4 log, and most
preferably greater than about 5 log. The VRI of the mesoporous,
or mesoporous and basic, or mesoporous, basic and reduced-oxygen
activated carbon particles, when measured according to the test
procedure set forth herein, may be greater than about 90%, preferably
greater than about 95%, more preferably greater than about 99%,
and most preferably greater than about 99.9%. Equivalently, the
VLRI of the mesoporous, or mesoporous and basic, or mesoporous,
basic and reduced-oxygen activated carbon particles may be greater
than about 1 log, preferably greater than about 1.3 log, more preferably
greater than about 2 log, and most preferably greater than about
3 log.
[0090] The steady state, one-dimensional, "clean" bed
filtration theory (assuming negligible dispersive transport and
desorption of microorganisms) for an axial flow filter (Yao et al.,
Environ. Sci. Technol. 5, 1102-1112 (1971)), the substance of which
is incorporated herein by reference, describes that:
C/C.sub.0=exp(-.lambda.L) (1)
[0091] where C is the effluent concentration, C.sub.0 is the influent
concentration, .lambda. is the filter coefficient with units of
reciprocal length, and L is the depth of the filter. Note that based
on the definitions above, the number of collisions that a non-attaching
microorganism will experience as it travels over a distance L through
the filter will be (.lambda./.alpha.)L, where .alpha. is the "clean"
bed sticking coefficient (also called, collision efficiency), defined
as the ratio of the number of microorganisms that stick to the collector
surface to the number of microorganisms that strike the collector
surface. Equation 1 is also valid for radial flow filters if L is
substituted by R.sub.0-R.sub.i, where R.sub.0 is the outside radius
and R.sub.i is the inside radius, and the filter coefficient is
averaged over the thickness of the filter. The filter coefficient
for a particle-containing bed (not fibers) is as follows:
.lambda.=(3(1-.epsilon.).eta..alpha.)/2d.sub.c (2)
[0092] where .epsilon. is the filter bed porosity, .eta. is the
single-collector efficiency, defined as the ratio of the number
of microorganisms that strike the collector surface to the number
of microorganisms that flow towards the collector surface, and d.sub.c
is the collector particle diameter. The factor (3/2) in the formula
above is valid for spherical or spherical-like particles. For cylindrical
particles (e.g. fibers) the term becomes (4/.pi.), and d.sub.c is
then the diameter of the cylinder. Also, note that the term "clean"
bed means that the collector surfaces have not yet accumulated enough
microorganisms to cause a reduction in the deposition efficiency
of the new microorganisms (i.e., blocking).
[0093] Based on the above "clean" bed filtration model,
the F-BLR and F-VLR can be calculated as follows:
F-BLR or F-VLR=-log(C/C.sub.0)=(.lambda.L/2.3) (3)
[0094] The single-collector efficiency, .eta., is calculated using
the Rajagopalan and Tien model (RT model; AIChE J., 22(3), 523-533
(1976), and AIChE J., 28, 871-872 (1982)) as follows:
.eta.=4A.sub.s.sup.1/3Pe.sup.-2/3+A.sub.sLo.sup.1/8R.sup.15/8+0.00338A.sub-
.sG.sup.6/5R.sup.-2/5 (4)
[0095] where 1 A s = 2 ( 1 - 5 ) 2 - 3 + 3 5 - 2 6 ,
[0096] .gamma.=(1-.epsilon.).sup.1/3, Pe is the dimensionless Peclet
number 2 Pe = 3 Ud c d m k T ,
[0097] Lo is the dimensionless London-van der Waals number 3 Lo
= 4 H 9 d m 2 U ,
[0098] R is the dimensionless interception number 4 R = d m d c
,
[0099] G is the dimensionless sedimentation number 5 G = g ( m
- f ) d m 2 18 U ,
[0100] .mu. is the dynamic fluid viscosity (equal to 1 mPa.multidot.s
for water), U is the superficial fluid velocity (calculated as:
U=4Q/.pi.D.sup.2, for axial flow filters, where Q is the fluid flowrate,
and D is the diameter of the face area of the filter; and U(R)=Q/2.pi.RX
for radial flow filters, where X is the length of the filter, and
R is the radial position between R.sub.i and R.sub.0), d.sub.m is
the microorganism diameter (or diameter of an equivalent sphere,
if the microorganism is non spherical), k is the Boltzmann's constant
(equal to 1.38.times.10.sup.-23 kg.multidot.m.sup.2/s.sup.2.multidot.K),
T is the fluid temperature, H is the Hamaker constant (it is typically
equal to 10.sup.-20 J), g is the gravitational constant (equal to
9.81 m/s.sup.2), .rho..sub.m is the density of the microorganisms,
and .rho..sub..function. is the fluid density (equal to 1 g/mL for
water). For the purposes and the materials of the present invention,
H is equal to 10.sup.-20 J, T is equal to 298 K, .rho..sub.m is
equal to 1.05 g/mL, .mu. is equal to 1 mPa.multidot.s. Also, for
the purposes of the present invention, d.sub.c is the volume median
diameter D.sub.V ,0.5,which is the particle diameter such that 50%
of the total particle volume is in particles of smaller diameter.
Also, the average fluid residence time is calculated as: 6 = D 2
L 4 Q ,
[0101] for axial flow filters, and 7 = ( R 0 2 - R i 2 ) X Q ,
[0102] for radial flow filters. (5)
[0103] The sticking coefficient, .alpha., is typically calculated
experimentally, for example using the "microbe and radiolabel
kinesis" (MARK) technique described in Gross et al. (Water
Res., 29(4), 1151-1158 (1995)). The single-collector efficiency,
.eta., of the filters of the present invention may be greater than
about 0.002, preferably greater than about 0.02, preferably greater
than about 0.2, preferably greater than about 0.4, more preferably
greater than about 0.6, and most preferably between about 0.8 and
about 1. The filter coefficient, .lambda., of the filters of the
present invention may be greater than about 10 m.sup.-1, preferably
greater than about 20 m.sup.-1, more preferably greater than about
30 m.sup.-1, most preferably greater than about 40 m.sup.-1, and/or
less than about 20,000 m.sup.-1, preferably less than about 10,000
m.sup.-1, more preferably less than about 5,000 m.sup.-1, and most
preferably less than about 1,000 m.sup.-1.
[0104] The F-BLR of filters of the present invention containing
mesoporous, or mesoporous and basic, or mesoporous, basic, and reduced-oxygen
activated carbon particles, when measured according to the test
procedure set forth herein, may be greater than about 2 logs, preferably
greater than about 3 logs, more preferably greater than about 4
logs, and most preferably greater than about 6 logs. The F-VLR of
filters of the present invention containing mesoporous, or mesoporous
and basic, or mesoporous, basic, and reduced-oxygen activated carbon
particles , when measured according to the test procedure set forth
herein, may be greater than about 1 log, preferably greater than
about 2 logs, more preferably greater than about 3 logs, and most
preferably greater than about 4 logs.
[0105] In one preferred embodiment of the present invention, the
filter particles comprise mesoporous activated carbon particles
that are wood-based activated carbon particles. These particles
have a BET specific surface area between about 1,000 m.sup.2/g and
about 2,000 m.sup.2/g, total pore volume between about 0.8 mL/g
and about 2 mL/g, and sum of the mesopore and macropore volumes
between about 0.4 mL/g and about 1.5 mL/g.
[0106] In another preferred embodiment of the present invention,
the filter particles comprise mesoporous and basic activated carbon
particles that are wood-based activated carbon particles. These
particles have a BET specific surface area between about 1,000 m.sup.2/g
and about 2,000 m.sup.2/g, total pore volume between about 0.8 mL/g
and about 2 mL/g, and sum of the mesopore and macropore volumes
between about 0.4 mL/g and about 1.5 mL/g.
[0107] In yet another preferred embodiment of the present invention,
the filter particles comprise mesoporous, basic, and reduced-oxygen
activated carbon particles that were initially acidic and rendered
basic and reduced-oxygen with treatment in a dissociated ammonia
atmosphere. These particles are wood-based activated carbon particles.
The treatment temperature is between about 925.degree. C. and about
1,000.degree. C., the ammonia flowrate is between about 1 standard
L/h.g and about 20 standard L/h.g, and the treatment time is between
about 10 minutes and about 7 hours. These particles have a BET specific
surface area between about 800 m.sup.2/g and about 2,500 m.sup.2/g,
total pore volume between about 0.7 mL/g and about 2.5 mL/g, and
sum of the mesopore and macropore volumes between about 0.21 mL/g
and about 1.7 mL/g. A non-limiting example of an acidic activated
carbon that is converted to a basic and reduced-oxygen activated
carbon is set forth below.
[0108] In even yet another preferred embodiment of the present
invention, the filter particles comprise mesoporous, basic, and
reduced-oxygen activated carbon particles, that were initially mesoporous
and basic, with treatment in an inert (i.e., helium) atmosphere.
These particles are wood-based activated carbon particles. The treatment
temperature is between about 800.degree. C. and about 1,000.degree.
C., the helium flowrate is between about 1 standard L/h.g and about
20 standard L/h.g, and the treatment time is between about 10 minutes
and about 7 hours. These particles have a BET specific surface area
between about 800 m.sup.2/g and about 2,500 m.sup.2/g, total pore
volume between about 0.7 mL/g and about 2.5 mL/g, and sum of the
mesopore and macropore volumes between about 0.21 mL/g and about
1.7 mL/g. A non-limiting example of a basic activated carbon that
is converted to a basic and reduced-oxygen activated carbon is set
forth below.
[0109] III. Treatment Examples
EXAMPLE 1
Treatment of a Mesoporous and Acidic Activated Carbon To Produce
a Mesoporous, Basic, and Reduced-Oxygen Activated Carbon
[0110] About 2 kg of the CARBOCHEM.RTM. CA-10 mesoporous and acidic
wood-based activated carbon particles from Carbochem, Inc., of Ardmore,
Pa., are placed on the belt of a furnace Model BAC-M manufactured
by C. I. Hayes, Inc., of Cranston, R.I. The furnace temperature
is set to about 950.degree. C., the treatment time is about 4 hours,
and the atmosphere is dissociated ammonia flowing with a volumetric
flowrate of about 12,800 standard L/h (i.e., about 450 standard
ft.sup.3/h, or equivalently, about 6.4 standard L/h.g). The treated
activated carbon particles are called TA4-CA-10, and their BET isotherm,
mesopore volume distribution, and point of zero charge analyses
are illustrated in FIGS. 1a, 2a, and 3a, respectively. Numerical
values for BET, the sum of mesopore and macropore volumes, point
of zero charge, BRI/BLRI, VRI/VLRI, bulk oxygen percentage by weight,
and ORP are shown in Section VI.
EXAMPLE 2
Treatment of a Mesoporous and Basic Activated Carbon To Produce
a Mesoporous, Basic, and Reduced-Oxygen Activated Carbon
[0111] About 2 kg of the MeadWestvaco Nuchar.RTM. RGC mesoporous
and basic wood-based activated carbon particles from MeadWestvaco
Corp., of Covington, Va., are placed on the belt of a furnace Model
BAC-M manufactured by C. I. Hayes, Inc., of Cranston, R.I. The furnace
temperature is set to about 800.degree. C., the treatment time is
4 hours, and the atmosphere is helium flowing with a volumetric
flowrate of about 12,800 standard L/h (i.e., about 450 standard
ft.sup.3/h, or equivalently, about 6.4 standard L/h.g). The treated
activated carbon particles are called THe4-RGC, and their BET isotherm,
mesopore volume distribution, and point of zero charge analyses
are illustrated in FIGS. 1b, 2b, and 3b, respectively. Numerical
values for BET, the sum of mesopore and macropore volumes, point
of zero charge, BRI/BLRI, VRI/VLRI, bulk oxygen percentage by weight,
and ORP are shown in Section VI.
[0112] IV. Filters of the Present Invention
[0113] Referring to FIG. 4, an exemplary filter made in accordance
with the present invention will now be described. The filter 20
comprises a housing 22 in the form of a cylinder having an inlet
24 and an outlet 26. The housing 22 can be provided in a variety
of forms, shapes, sizes, and arrangements depending upon the intended
use and desired performance of the filter 20, as known in the art.
For example, the filter 20 can be an axial flow filter, wherein
the inlet 24 and outlet 26 are disposed so that the liquid flows
along the axis of the housing 22. Alternatively, the filter 20 can
be a radial flow filter wherein the inlet 24 and outlet 26 are arranged
so that the fluid (e.g., either a liquid, gas, or mixture thereof)
flows along a radial of the housing 22. Either in axial or radial
flow configuration, filter 20 may be preferably configured to accommodate
a face area of at least about 0.5 in..sup.2 (3.2 cm.sup.2), more
preferably at least about 3 in..sup.2 (19.4 cm.sup.2), and most
preferably at least about 5 in..sup.2 (32.2 cm.sup.2), and preferably
a filter depth of at least about 0.125 in. (0.32 cm) of at least
about 0.25 in. (0.64 cm), more preferably at least about 0.5 in.
(1.27 cm), and most preferably at least about 1.5 in. (3.81 cm).
For radial flow filters, the filter length may be at least 0.25
in. (0.64 cm), more preferably at least about 0.5 in. (1.27 cm),
and most preferably at least about 1.5 in. (3.81 cm). Still further,
the filter 20 can include both axial and radial flow sections.
[0114] The housing may also be formed as part of another structure
without departing from the scope of the present invention. While
the filters of the present invention are particularly suited for
use with water, it will be appreciated that other fluids (e.g.,
air, gas, and mixtures of air and liquids) can be used. Thus, the
filter 20 is intended to represent a generic liquid filter or gas
filter. The size, shape, spacing, alignment, and positioning of
the inlet 24 and outlet 26 can be selected, as known in the art,
to accommodate the flow rate and intended use of the filter 20.
Preferably, the filter 20 is configured for use in residential or
commercial potable water applications, including, but not limited
to, whole house filters, refrigerator filters, portable water units
(e.g., camping gear, such as water bottles), faucet-mount filters,
under-sink filters, medical device filters, industrial filters,
air filters, etc. Examples of filter configurations, potable water
devices, consumer appliances, and other water filtration devices
suitable for use with the present invention are disclosed in U.S.
Pat. Nos. 5,527,451, 5,536,394, 5,709,794, 5,882,507, 6,103,114,
4,969,996, 5,431,813, 6,214,224, 5,957,034, 6,145,670, 6,120,685,
and 6,241,899, the substances of which are incorporated herein by
reference. For potable water applications, the filter 20 may be
preferably configured to accommodate a flow rate of less than about
8 L/min, or less than about 6 L/min, or between about 2 L/min and
about 4 L/min, and the filter may contain less than about 2 kg of
filter material, or less than about 1 kg of filter material, or
less than about 0.5 kg of filter material. Further, for potable
water applications, the filter 20 may be preferably configured to
accommodate an average fluid residence time of at least about 3
s, preferably at least about 5 s, preferably at least about 7 s,
more preferably at least about 10 s, and most preferably at least
about 15 s. Still further, for potable water applications, the filter
20 may be preferably configured to accommodate a filter material
pore volume of at least about 0.4 cm.sup.3, preferably at least
about 4 cm.sup.3, more preferably at least about 14 cm.sup.3, and
most preferably at least about 25 cm.sup.3.
[0115] The filter 20 also comprises a filter material 28 which
may be used in combination with other filter systems including reverse
osmosis systems, ultra-violet light systems, ionic exchange systems,
electrolyzed water systems, and other water treatment systems known
to those with skill in the art.
[0116] The filter 20 also comprises a filter material 28, wherein
the filter material 28 includes one or more filter particles (e.g.,
fibers, granules, etc.). One or more of the filter particles can
be mesoporous, more preferably mesoporous and basic, and most preferably
mesoporous, basic and reduced oxygen and possess the characteristics
previously discussed. The mesoporous; or mesoporous and basic; or
mesoporous, basic and reduced oxygen activated carbon filter material
28 can be combined with particles formed from other materials or
combination of materials, such as activated carbon powders, activated
carbon granules, activated carbon fibers, zeolites, inorganics (including
activated alumina, magnesia, diatomaceous earth, silica, mixed oxides,
such as hydrotalcites, glass, etc.), cationic materials (including
polymers such as polyaminoamides, polyethyleneimine, polyvinylamine,
polydiallyldimethylammonium chloride, polydimethylamine-epichlorohydrin,
polyhexamethylenebiguanide, poly-[2-(2-ethoxy)-ethoxyethlyl-guanidinium
chloride which may be bound to fibers (including polyethylene, polypropylene,
ethylene maleic anhydride copolymers, carbon, glass, etc.) and/or
to irregularly shaped materials (including carbon, diatomaceous
earth, sand, glass, clay, etc.), and mixtures thereof. Examples
of filter materials and combinations of filter materials that mesoporous
and basic activated carbon may be combined with are disclosed in
U.S. Pat. Nos. 6,274,041, 5,679,248, which are herein incorporated
by reference, and U.S. patent application Ser. No. 09/628,632, which
is herein incorporated by reference. As previously discussed, the
filter material can be provided in either a loose or interconnected
form (e.g., partially or wholly bonded by a polymeric binder or
other means to form an integral structure).
[0117] The filter material may be used for different applications
(e.g., use as a pre-filter or post-filter) by varying the size,
shape, complex formations, charge, porosity, surface structure,
functional groups, etc. of the filter particles as discussed above.
The filter material may also be mixed with other materials, as just
described, to suit it for a particular use. Regardless of whether
the filter material is mixed with other materials, it may be used
as a loose bed, a block (including a co-extruded block as described
in U.S. Pat. No. 5,679,248, which is herein incorporated by reference),
and mixtures thereof. Preferred methods that might be used with
the filter material include forming a block filter made by ceramic-carbon
mix (wherein the binding comes from the firing of the ceramic),
using powder between non-wovens as described in U.S. Pat. No. 6,077,588,
which is herein incorporated by reference, using the green strength
method as described in U.S. Pat. No. 5,928,588, which is herein
incorporated by reference, activating the resin binder that forms
the block, which is herein incorporated by reference, or by using
a resistive heating method as described in PCT Application Serial
No. WO 98/43796.
[0118] V. Filter Examples
EXAMPLE 3
Filter Containing Mesoporous and Basic Activated Carbon Particles
[0119] About 18.3 g of Nuchar.RTM. RGC mesoporous and basic activated
carbon powder (with D.sub.V ,0.5 equal to about 45 .mu.m) from MeadWestvaco
Corp. of Covington, Va., is mixed with about 7 g of Microthene.RTM.
low-density polyethylene (LDPE) FN510-00 binder of Equistar Chemicals,
Inc. of Cincinnati, Ohio, and about 2 g of Alusil.RTM. 70 aluminosilicate
powder from Selecto, Inc., of Norcross, Ga. The mixed powders are
then poured into a circular aluminum mold with about 3 in. (about
7.62 cm) internal diameter and about 0.5 in. (about 1.27 cm) depth.
The mold is closed and placed in a heated press with platens kept
at about 204.degree. C. for 1 h. Then, the mold is allowed to cool
to room temperature, opened, and the axial flow filter is removed.
The characteristics of the filter are: face area: about 45.6 cm.sup.2;
filter depth: about 1.27 cm; filter total volume: about 58 mL; filter
porosity (for pores greater than about 0.1 .mu.m): about 0.43; and
filter material pore volume (for pores greater than about 0.1 .mu.m):
about 25 mL (as measured by mercury porosimetry). The filter is
placed in the Teflon.RTM. housing described in the test procedures
below. When the flow rate is about 200 mL/min, the pressure drop
of this filter is about 17 psi (about 1.2 bar, 0.12 MPa) for about
the first 2,000 filter pore volumes. Numerical values for F-BLR,
F-VLR, .eta., and .alpha. are shown in Section VI.
EXAMPLE 4
Filter Containing Microporous and Basic Activated Carbon Particles
[0120] About 26.2 g of coconut microporous and basic activated
carbon powder (with D.sub.V ,0.5 equal to about 92 .mu.m) is mixed
with 7 g of Microthene.RTM. low-density polyethylene (LDPE) FN510-00
binder of Equistar Chemicals, Inc. of Cincinnati, Ohio, and about
2 g of Alusil.RTM. 70 aluminosilicate powder from Selecto, Inc.,
of Norcross, Ga. The mixed powders are then poured into a circular
aluminum mold with about 3 in. (about 7.62 cm) internal diameter
and about 0.5 in. (about 1.27 cm) depth. The mold is closed and
placed in a heated press with platens kept at about 204.degree.
C. for 1 h. Then, the mold is allowed to cool to room temperature,
is opened, and the axial flow filter is removed. The characteristics
of the filter are: face area: about 45.6 cm.sup.2; filter depth:
about 1.27 cm; filter total volume: about 58 mL; filter porosity
(for pores greater than about 0.1 .mu.m): about 0.44; and filter
material pore volume (for pores greater than about 0.1 .mu.m): about
25.5 mL (as measured by mercury porosimetry). The filter is placed
in the Teflon.RTM. housing described in the test procedures below.
When the flow rate is about 200 mL/min, the pressure drop of this
filter is about 17 psi (about 1.2 bar, about 0.12 MPa) for about
the first 2,000 filter pore volumes. Numerical values for F-BLR,
F-VLR, .eta., and .alpha. are shown in Section VI.
[0121] VI. Test and Calculation Procedures
[0122] The following test procedures are used to calculate the
BET, point of zero charge, BRI/BLRI, VRI/VLRI, bulk oxygen percentage
by weight, ORP, F-BLR, and F-VLR values discussed herein. Also discussed
herein are calculation procedures for single-collector efficiency,
filter coefficient, average fluid residence time, and F-BLR.
[0123] While measurement of the BRI/BLRI and VRI/VLRI values is
with respect to an aqueous medium, this is not intended to limit
the ultimate use of filter materials of the present invention, but
rather the filter materials can ultimately be used with other fluids
as previously discussed even though the BRI/BLRI and VRI/VLRI values
are calculated with respect to an aqueous medium. Further, the filter
materials chosen below to illustrate use of the test procedures
are not intended to limit the scope of the manufacture and/or composition
of the filter materials of the present invention or to limit which
filter materials of the present invention can be evaluated using
the test procedures.
[0124] BET Test Procedure
[0125] The BET specific surface area and pore volume distribution
are measured using a nitrogen adsorption technique, such as that
described in ASTM D 4820-99, the substance of which is herein incorporated
by reference, by multipoint nitrogen adsorption, at about 77K with
a Coulter SA3100 Series Surface Area and Pore Size Analyzer manufactured
by Coulter Corp., of Miami, Fla. This process can also provide the
micropore, mesopore, and macropore volumes. For the TA4-CA-10 filter
particles of Example 1, the BET area is about 1,038 m.sup.2/g, micropore
volume is about 0.43 mL/g, and the sum of the mesopore and macropore
volumes is about 0.48 mL/g. For the THe4-RGC filter particles of
Example 2, the BET area is about 2,031 m.sup.2/g, micropore volume
is about 0.81 mL/g, and the sum of the mesopore and macropore volumes
is about 0.68 mL/g. Note that the respective values of the starting
materials CA-10 and RGC are: about 1,309 m.sup.2/g; about 0.54 mL/g;
about 0.67 mL/g; and about 1,745 m.sup.2/g; about 0.70 mL/g; about
0.61 mL/g, respectively. Typical BET nitrogen isotherm and the mesopore
volume distribution for the filter material of Examples 1 and 2
are illustrated in FIGS. 1a and 1b, respectively. As will be appreciated,
other instrumentation can be substituted for the BET measurements
as is known in the art.
[0126] Point of Zero Charge Test Procedure
[0127] About 0.010 M aqueous KCl solution is prepared from reagent
grade KCl and water that is freshly distilled under argon gas. The
water used for the distillation is deionized by a sequential reverse
osmosis and ion exchange treatment. About 25.0 mL volume of the
aqueous KCl solution is transferred into six, about 125 mL flasks,
each fitted with a 24/40 ground glass stopper. Microliter quantities
of standardized aqueous HCl or NaOH solutions are added to each
flask so that the initial pH ranges between about 2 and about 12.
The pH of each flask is then recorded using an Orion model 420A
pH meter with an Orion model 9107BN Triode Combination pH/ATC electrode,
manufactured by Thermo Orion Inc., of Beverly, Mass., and is called
"initial pH". About 0.0750.+-.0.0010 g of activated carbon
particles are added to each of the six flasks, and the aqueous suspensions
are stirred (at about 150 rpm) while stoppered for about 24 hours
at room temperature before recording the "final pH". FIG.
3a shows the initial and final pH values for the experiments run
with CA-10, and TA4-CA-10 activated carbon materials, and FIG. 3b
shows the initial and final pH values for the experiments run with
RGC and The4-RGC activated carbon materials. The point of zero charge
for the CA-10, TA4-CA-10, RGC, and THe4-RGC is about 5.0, about
9.7, about 8.8, and about 8.6, respectively. As will be appreciated,
other instrumentation can be substituted for this test procedure
as is known in the art.
[0128] BRI/BLRI Test Procedure
[0129] A PB-900.TM. Programmable JarTester manufactured by Phipps
& Bird, Inc., of Richmomd, Va., with 2 or more Pyrex.RTM. glass
beakers (depending on the numbers of materials tested) is used.
The diameter of the beakers is about 11.4 cm (about 4.5") and
the height is about 15.3 cm (about 6"). Each beaker contains
about 500 mL of dechlorinated, municipally-supplied tap water contaminated
with the E. coli microorganisms and a stirrer that is rotated at
about 60 rpm. The stirrers are stainless steel paddles about 7.6
cm (about 3") in length, about 2.54 cm (about 1") in height,
and about 0.24 cm (about {fraction (3/32)}") in thickness.
The stirrers are placed about 0.5 cm (about {fraction (3/16)}")
from the bottom of the beakers. The first beaker contains no filter
material and is used as a control, and the other beakers contain
sufficient quantity of the filter materials, having a Sauter mean
diameter less than about 55 .mu.m, so that the total external geometric
surface area of the materials in the beakers is about 1400 cm.sup.2.
This Sauter mean diameter is achieved by a) sieving samples with
broad size distribution and higher Sauter mean diameter or b) reducing
the size of the filter particles (e.g., if the filter particles
are larger than about 55 .mu.m or if the filter material is in an
integrated or bonded form) by any size-reducing techniques that
are well known to those skilled in the art. For example, and by
no way of limitation, size-reducing techniques are crushing, grinding,
and milling. Typical equipment that is used for size reduction includes
jaw crushers, gyratory crushers, roll crushers, shredders, heavy-duty
impact mills, media mills, and fluid-energy mills, such as centrifugal
jets, opposed jets or jets with anvils. The size reduction can be
used on loose or bonded filter particles. Any biocidal coating on
the filter particles or the filter material should be removed before
conducting this test. Alternatively, uncoated filter particles can
be substituted for this test.
[0130] Duplicate samples of water, each about 5 mL in volume, are
collected from each beaker for assay at various times after insertion
of the filter particles in the beakers until equilibrium is achieved
in the beakers that contain the filter particles. Typical sample
times are: about 0, about 2, about 4 and about 6 hours. Other equipment
can be substituted as known in the art.
[0131] The E. coli bacteria used are the ATCC # 25922 (American
Type Culture Collection, Rockville, Md.). The target E. coli concentration
in the control beaker is set to be about 3.7.times.10.sup.9 CFU/L.
The E. coli assay can be conducted using the membrane filter technique
according to process # 9222 of the 20.sup.th edition of the "Standard
Processes for the Examination of Water and Wastewater" published
by the American Public Health Association (APHA), Washington, D.C.,
the substance of which is herein incorporated by reference. The
limit of detection (LOD) is about 1.times.10.sup.3 CFU/L.
[0132] Exemplary BRI/BLRI results for the filter materials of Examples
1 and 2 are shown in FIG. 5a and FIG. 5b. The amount of the CA-10
mesoporous and acidic activated carbon material is about 0.75 g,
and that of the TA40-CA-10 mesoporous, basic, and reduced-oxygen
activated carbon material is about 0.89 g. The amount of the RGC
mesoporous and basic activated carbon material is about 0.28 g,
and that of the THe4-RGC mesoporous, basic, and reduced-oxygen activated
carbon material is about 0.33 g. All four amounts correspond to
about 1,400 cm.sup.2 external surface area. The E. coli concentration
in the control beaker in FIG. 5a is about 3.7.times.10.sup.9 CFU/L,
and that in FIG. 5b is about 3.2.times.10.sup.9 CFU/L. The E. coli
concentrations in the beakers containing the CA-10, TA4-CA-10, RGC,
and THe4-RGC samples reach equilibrium in about 6 hours, and their
values are: about 2.1.times.10.sup.6 CFU/L, about 1.5.times.10.sup.4
CFU/L, about 3.4.times.10.sup.6 CFU/L, and about 1.2.times.10.sup.6
CFU/L, respectively. Then, the respective BRIs are calculated as
about 99.94%, about 99.9996%, about 99.91%, and about 99.97%, and
the respective BLRIs are calculated as about 3.2 log, about 5.4
log, about 3.0 log, and about 3.5 log.
[0133] VRI/VLRI Test Procedure
[0134] The testing equipment and the procedure are the same as
in BRI/BLRI procedure. The first beaker contains no filter material
and is used as control, and the other beakers contain a sufficient
quantity of the filter materials, having a Sauter mean diameter
less than about 55 .mu.m, so that there is a total external geometric
surface area of about 1400 cm.sup.2 in the beakers. Any biocidal
coating on the filter particles or the filter material should be
removed before conducting this test. Alternatively, uncoated filter
particles or filter material can be substituted for this test.
[0135] The MS-2 bacteriophages used are the ATCC # 15597B from
the American Type Culture Collection of Rockville, Md. The target
MS-2 concentration in the control beaker is set to be about 2.07.times.10.sup.9
PFU/L. The MS-2 can be assayed according to the procedure by C.
J. Hurst, Appl. Environ. Microbiol., 60(9), 3462(1994), the substance
of which is herein incorporated by reference. Other assays known
in the art can be substituted. The limit of detection (LOD) is about
1.times.10.sup.3 PFU/L.
[0136] Exemplary VRI/VLRI results for the filter materials of Examples
1 and 2 are shown in FIG. 6a and FIG. 6b. The amount of the CA-10
mesoporous and acidic activated carbon material is about 0.75 g,
and that of the TA40-CA-10 mesoporous, basic, and reduced-oxygen
activated carbon material is about 0.89 g. The amount of the RGC
mesoporous and basic activated carbon material is about 0.28 g,
and that of the THe4-RGC mesoporous, basic, and reduced-oxygen activated
carbon material is about 0.33 g. All four amounts correspond to
about 1,400 cm.sup.2 external surface area. The MS-2 concentration
in the control beaker in FIG. 6a is about 6.7.times.10.sup.7 PFU/L,
and that in FIG. 6b is about 8.0.times.10.sup.7 PFU/L. The MS-2
concentrations in the beakers containing the CA-10, TA4-CA-10, RGC,
and THe4-RGC samples reach equilibrium in 6 hours, and their values
are about 4.1.times.10.sup.4 PFU/L, about 1.times.10.sup.3 PFU/L,
about 3.times.10.sup.3 PFU/L, and less than about 1.0.times.10.sup.3
PFU/L (limit of detection), respectively. Then, the respective VRIs
are calculated as about 99.94%, about 99.999%, about 99.996%, and>about
99.999%, and the respective VLRIs are calculated as about 3.2 log,
about 5 log, about 4.4 log, and>about 5 log.
[0137] Bulk Oxygen Percentage by Weight Test Procedure
[0138] The bulk oxygen percentage by weight is measured using the
PerkinElmer Model 240 Elemental Analyzer (Oxygen Modification; PerkinElmer,
Inc.; Wellesley, Mass.). The technique is based on pyrolysis of
the sample in a stream of helium at about 1000.degree. C. over platinized
carbon. The carbon samples are dried overnight in a vacuum oven
at about 100.degree. C. As will be appreciated, other instrumentation
can be substituted for this test procedure as is known in the art.
Exemplary bulk oxygen percentage by weight values for the filter
materials CA-10, TA4-CA-10, RGC and THe4-RGC are about 8.3%, about
1.1%, about 2.3%, and about 0.8%, respectively.
[0139] ORP Test Procedure
[0140] The ORP is measured using the platinum redox electrode Model
96-78-00 from Orion Research, Inc. (Beverly, Mass.), and following
the ASTM standard D 1498-93. The procedure involves the suspension
of about 0.2 g of carbon in about 80 mL of tap water, and reading
the electrode reading, in mV, after about 5 min of gentle stirring.
As will be appreciated, other instrumentation can be substituted
for this test procedure as is known in the art. Exemplary ORP values
for the filter materials CA-10, TA4-CA-10, RGC and THe4-RGC are
about 427 mV, about 285 mV, about 317 mV, and about 310 mV, respectively.
[0141] F-BLR Test Procedure
[0142] The housings for the axial flow filters with mesoporous
carbon are made from Teflon.RTM. and consist of 2 parts, i.e., a
lid and a base. Both parts have an outside diameter of about 12.71
cm (about 5") and inside diameter of about 7.623 cm (about
3"). The lid counter sets in the base with an o-ring (about
3" ID and about 1/8" thickness) compression seal. The
inlet and outlet hose barb connectors are threaded into the lid
and base with about {fraction (1/16)}" NPT pipe threads. About
1/2 thick by about 23/4 OD stainless steel diverter (with about
{fraction (3/16)}" hole on the upstream side and about 6 mesh
screen on the downstream side) is counter set into the lid of the
housing. The function of the diverter is to distribute the inlet
flow over the entire face of the filter. The lid and base of the
housing engage such that a compression seal exists sealing the filter
within the housing. The lid and the base held together using four
about 1/4" fasteners.
[0143] The filter is mounted inside the housing and water contaminated
with about 1.times.10.sup.8 CFU/L E. coli flows through at a flowrate
of about 200 mL/min. The total amount of water flowing in can be
about 2,000 filter material pore volumes or more. The E. coli bacteria
used are the ATCC # 25922 (American Type Culture Collection, Rockville,
Md.). The E. coli assay can be conducted using the membrane filter
technique according to process # 9222 of the 20.sup.th edition of
the "Standard Processes for the Examination of Water and Wastewater"
published by the American Public Health Association (APHA), Washington,
D.C., the substance of which is herein incorporated by reference.
Other assays known in the art can be substituted (e.g. COLILERT.RTM.).
The limit of detection (LOD) is about 1.times.10.sup.2 CFU/L when
measured by the membrane filter technique, and about 10 CFU/L when
measured by the COLILERT.RTM. technique. Effluent water is collected
after the flow of about the first 2,000 filter material pore volumes,
assayed to count the E. coli bacteria present, and the F-BLR is
calculated using the definition.
[0144] Exemplary results used to calculate F-BLR are shown in FIG.
7a for the axial flow filters of Example 3 and Example 4. The flowrate
used in FIG. 7a is about 200 mL/min and the influent concentration
of E. coli varied between about 1.times.10.sup.8 and about 1.times.10.sup.9
CFU/L. The filters are challenged with about 20 L once a week (every
Tuesday) and the effluent water is assayed as described above. The
average fluid residence time for the RGC filter is about 7.5 s,
and that of the coconut filter is about 7.65 s. The F-BLR of the
RGC filter of Example 3 is calculated as about 6.8 log. For the
coconut filter of the Example 4 the collection of the effluent water
is stopped at about 40 L (which is equivalent to about 1,570 filter
material pore volumes) as the filter shows almost complete breakthrough
at that volume of water. The F-BLR is calculated as about 1.9 log
at about 1,570 filter material pore volumes.
[0145] F-VLR Test Procedure
[0146] The housings for the axial flow filters with mesoporous
carbon are the same as those described in the F-BLR procedure above.
Water contaminated with about 1.times.10.sup.7 PFU/L MS-2 flows
through a housing/filter system at a flowrate of about 200 mL/min.
The total amount of water flowing in can be about 2,000 filter material
pore volumes or more. The MS-2 bacteriophages used are the ATCC
# 15597B (American Type Culture Collection, Rockville, Md.). The
MS-2 assay can be conducted according to the procedure by C. J.
Hurst, Appl. Environ. Microbiol., 60(9), 3462 (1994), the substance
of which is herein incorporated by reference. Other assays known
in the art can be substituted. The limit of detection (LOD) is 1.times.10.sup.3
PFU/L. Effluent water is collected after the flow of about the first
2,000 filter material pore volumes, assayed to count the MS-2 bacteriophages
present, and the F-VLR is calculated using the definition.
[0147] Exemplary results used to calculate F-VLR are shown in FIG.
7b for the axial flow filters of Example 3 and Example 4. The flowrate
used in FIG. 7b is about 200 mL/min and the influent concentration
of MS-2 varied around about 1.times.10.sup.7 PFU/L. The filters
are challenged with about 20 L once a week (every Tuesday) and the
effluent water is assayed as described above. The F-VLR of the RGC
filter of Example 3 is calculated as>about 4.2 log. For the coconut
filter of the Example 4 the collection of the effluent water is
stopped at about 40 L (which is equivalent to about 1,570 filter
material pore volumes) as the filter shows almost complete breakthrough
at that volume of water. The F-BLR is calculated as about 0.3 log
at about 1,570 filter material pore volumes.
[0148] Calculation Procedures for Single-Collector Efficiency,
Filter Coefficient, Average Fluid Residence Time, and F-BLR
[0149] The single-collector efficiency calculation for the filters
uses Equation 4 and the dimensionless numbers described after that
equation. Exemplary calculations for the axial flow RGC filter of
Example 3 using the following parameters: .epsilon.=0.43, d.sub.m=1
.mu.m, d.sub.c=45 .mu.m, H=10.sup.-20 J, .rho..sub.m=1.058 g/mL,
.rho..sub..function.=1.0 g/mL, .mu.=1 mPa.multidot.s, T=298 K, water
flowrate Q=200 mL/min, filter diameter D=7.623 cm, and U=0.0007
m/s, give .eta.=0.01864. For the same parameters and for .alpha.=1,
the filter coefficient is calculated according to Equation 2 as:
.lambda.=354.2 m.sup.-1. Furthermore, the F-BLR of the same filter
is calculated according to Equation 3 as about 1.95 log. Similar
exemplary calculations for the coconut filter of Example 4, using
the same parameters as above, give .eta.=0.00717 and .lambda.=65.5
m.sup.-1. Finally, the F-BLR of the same filter is calculated according
to Equation 3 as about 0.36 log.
[0150] The present invention may additionally include information
that will communicate to the consumer, by words and/or by pictures,
that use of carbon filter particles and/or filter material of the
present invention will provide benefits which include removal of
microorganisms, and this information may include the claim of superiority
over other filter products. In a highly desirable variation, the
information may include that use of the invention provides for reduced
levels of nano-sized microorganisms. Accordingly, the use of packages
in association with information that will communicate to the consumer,
by words and or by pictures, that use of the invention will provide
benefits such as potable, or more potable water as discussed herein,
is important. The information can include, e.g., advertising in
all of the usual media, as well as statements and icons on the package,
or the filter itself, to inform the consumer.
[0151] All documents cited in the Detailed Description of the Invention
are, in relevant part, incorporated herein by reference, the citation
of any document is not to be construed as an admission that it is
prior art with respect to the present invention.
[0152] The embodiments described herein were chosen and described
to provide the best illustration of the principles of the invention
and its practical application to thereby enable one of ordinary
skill in the art to utilize the invention in various embodiments
and with various modifications as are suited to the particular use
contemplated. All such modifications and variations are within the
scope of the invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are fairly,
legally and equitably entitled.
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