U.S. patent application number 13/163055 was filed with the patent office on 2018-01-11 for systems and methods for performing the bacterial disinfection of a fluid using point radiation sources.
The applicant listed for this patent is Jennifer Godwin PAGAN, Thomas Andrew SCHMEDAKE, Edward Brittain STOKES. Invention is credited to Jennifer Godwin PAGAN, Thomas Andrew SCHMEDAKE, Edward Brittain STOKES.
Application Number | 20180008741 13/163055 |
Document ID | / |
Family ID | 42269126 |
Filed Date | 2018-01-11 |
United States Patent
Application |
20180008741 |
Kind Code |
A9 |
STOKES; Edward Brittain ; et
al. |
January 11, 2018 |
SYSTEMS AND METHODS FOR PERFORMING THE BACTERIAL DISINFECTION OF A
FLUID USING POINT RADIATION SOURCES
Abstract
A system for disinfecting a fluid, including: a flow cell
including one or more inlet ports and one or more outlet ports,
wherein the flow cell is configured to communicate a fluid
containing a biological contaminant from the one or more inlet
ports to the one or more outlet portions through an interior
portion thereof; and one or more point radiation sources disposed
about the flow cell, wherein the one or more point radiation
sources are operable for delivering radiation to the biological
contaminant; wherein an interior surface of the flow cell is
operable for reflecting the radiation delivered to the biological
contaminant by the one or more point radiation sources; and wherein
the interior surface of the flow cell is operable for reflecting
the radiation delivered to the biological contaminant by the one or
more point radiation sources such that a radiation intensity is
uniform throughout the interior portion of the flow cell. In one
exemplary embodiment, the flow cell is an integrating sphere.
Optionally, the system also includes a photocatalyzing material
disposed on at least a portion of the interior surface of the flow
cell.
Inventors: |
STOKES; Edward Brittain;
(Charlotte, NC) ; PAGAN; Jennifer Godwin;
(Charlotte, NC) ; SCHMEDAKE; Thomas Andrew;
(Charlotte, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STOKES; Edward Brittain
PAGAN; Jennifer Godwin
SCHMEDAKE; Thomas Andrew |
Charlotte
Charlotte
Charlotte |
NC
NC
NC |
US
US
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20120318749 A1 |
December 20, 2012 |
|
|
Family ID: |
42269126 |
Appl. No.: |
13/163055 |
Filed: |
June 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2009/068765 |
Dec 18, 2009 |
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13163055 |
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61139022 |
Dec 19, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F 2305/10 20130101;
G01N 21/031 20130101; G01N 21/33 20130101; C02F 2201/3225 20130101;
C02F 1/32 20130101; A61L 2/10 20130101; A61L 9/205 20130101; C02F
2201/3227 20130101; C02F 2303/04 20130101; C02F 2201/3222 20130101;
A61L 2209/11 20130101; C02F 2201/3228 20130101; C02F 2201/328
20130101; G01N 21/5907 20130101; G01N 2201/065 20130101; C02F
2201/326 20130101; C02F 1/325 20130101; C02F 2209/11 20130101 |
International
Class: |
A61L 9/20 20060101
A61L009/20; G01N 21/33 20060101 G01N021/33; C02F 1/32 20060101
C02F001/32 |
Goverment Interests
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
[0002] The U.S. Government has a paid-up license in the present
invention and the right, in limited circumstances, to require the
patent owner to license to others on reasonable terms as provided
for by the terms of Award Nos. 0740524 and 0848759 awarded by the
National Science Foundation (NSF).
Claims
1. A system for disinfecting a fluid, comprising: a flow cell
comprising one or more inlet ports and one or more outlet ports,
wherein the flow cell is configured to communicate a fluid from the
one or more inlet ports to the one or more outlet portions through
an interior portion thereof; and one or more point radiation
sources disposed about the flow cell, wherein the one or more point
radiation sources are operable for delivering radiation to the
fluid; wherein an interior surface of the flow cell is operable for
reflecting the radiation delivered to the fluid by the one or more
point radiation sources.
2. The system of claim 1, wherein the flow cell comprises one or
more of an integrating cavity, an integrating ellipsoid, and an
integrating sphere.
3. The system of claim 1, wherein the one or more point radiation
sources comprise one or more of one or more semiconductor optical
sources, one or more light-emitting diode optical sources, one or
more ultraviolet optical sources, and one or more deep-ultraviolet
optical sources.
4. The system of claim 1, wherein the interior surface of the flow
cell is operable for reflecting the radiation delivered to the
fluid by the one or more point radiation sources such that a
radiation intensity is uniform throughout the interior portion of
the flow cell.
5. The system of claim 1, further comprising one or more mechanical
baffles or stirring mechanisms disposed within the interior portion
of the flow cell for selectively modifying a flow of the fluid
therethrough.
6. The system of claim 1, further comprising a photocatalyzing
material disposed on at least a portion of the interior surface of
the flow cell.
7. The system of claim 5, further comprising a photocatalyzing
material disposed on at least a portion of a surface of the one or
more mechanical baffles or stirring mechanisms.
8. The system of claim 1, further comprising a controller operable
for selectively activating/deactivating the one or more point
radiation sources.
9. The system of claim 1, further comprising a controller operable
for selectively controlling the residence time of the fluid in the
interior portion of the flow cell.
10. A method for disinfecting a fluid, comprising: providing a flow
cell comprising one or more inlet ports and one or more outlet
ports, wherein the flow cell is configured to communicate a fluid
from the one or more inlet ports to the one or more outlet portions
through an interior portion thereof; and providing one or more
point radiation sources disposed about the flow cell, wherein the
one or more point radiation sources are operable for delivering
radiation to the fluid; wherein an interior surface of the flow
cell is operable for reflecting the radiation delivered to the
fluid by the one or more point radiation sources.
11. The method of claim 10, wherein the flow cell comprises one or
more of an integrating cavity, an integrating ellipsoid, and an
integrating sphere.
12. The method of claim 10, wherein the one or more point radiation
sources comprise one or more of one or more semiconductor optical
sources, one or more light-emitting diode optical sources, one or
more ultraviolet optical sources, and one or more deep-ultraviolet
optical sources.
13. The method of claim 10, wherein the interior surface of the
flow cell is operable for reflecting the radiation delivered to the
fluid by the one or more point radiation sources such that a
radiation intensity is uniform throughout the interior portion of
the flow cell.
14. The method of claim 10, further comprising providing one or
more mechanical baffles or stirring mechanisms disposed within the
interior portion of the flow cell for selectively modifying a flow
of the fluid therethrough.
15. The method of claim 10, further comprising providing a
photocatalyzing material disposed on at least a portion of the
interior surface of the flow cell.
16. The method of claim 14, further comprising providing a
photocatalyzing material disposed on at least a portion of a
surface of the one or more mechanical baffles or stirring
mechanisms.
17. The method of claim 10, further comprising providing a
controller operable for selectively activating/deactivating the one
or more point radiation sources.
18. The method of claim 10, further comprising providing a
controller operable for selectively controlling the residence time
of the fluid in the interior portion of the flow cell.
19. A system for disinfecting a fluid, comprising: a flow cell
comprising one or more inlet ports and one or more outlet ports,
wherein the flow cell is configured to communicate a fluid
comprising a biological contaminant from the one or more inlet
ports to the one or more outlet portions through an interior
portion thereof; and one or more point radiation sources disposed
about the flow cell, wherein the one or more point radiation
sources are operable for delivering radiation to the biological
contaminant; wherein an interior surface of the flow cell is
operable for reflecting the radiation delivered to the biological
contaminant by the one or more point radiation sources; and wherein
the interior surface of the flow cell is operable for reflecting
the radiation delivered to the biological contaminant by the one or
more point radiation sources such that a radiation intensity is
uniform throughout the interior portion of the flow cell.
20. The system of claim 19, wherein the flow cell comprises one or
more of an integrating cavity, an integrating ellipsoid, and an
integrating sphere.
21. The system of claim 19, wherein the one or more point radiation
sources comprise one or more of one or more semiconductor optical
sources, one or more light-emitting diode optical sources, one or
more ultraviolet optical sources, and one or more deep-ultraviolet
optical sources.
22. The system of claim 19, further comprising a photocatalyzing
material disposed on at least a portion of the interior surface of
the flow cell.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present non-provisional patent application/patent claims
the benefit of priority of U.S. Provisional Patent Application No.
61/139,022, filed on Dec. 19, 2008, and entitled "BACTERIAL
DISINFECTION UNIT," the contents of which are incorporated in full
by reference herein.
FIELD OF THE INVENTION
[0003] The present invention relates to systems and methods for
performing the bacterial disinfection of a fluid using point
radiation sources and encompasses the fields of optical
engineering, fluid engineering, materials engineering, and the
biological sciences.
BACKGROUND OF THE INVENTION
[0004] Conventionally, the bacterial disinfection of fluids, such
as water, air, fuel, other liquids and gases, and the like, is
performed using ultraviolet (UV) lamps (or deep-UV lamps), such as
low to medium pressure mercury lamps. For example, water may be
disinfected using such lamps, for a germicidal effect, in a
conventional point-of-use (POU) water filtration system. The
deoxyribonucleic acid (DNA) of bacteria, viruses, cysts, and the
like absorbs the UV radiation and the reproductive capabilities of
the biological entities are thereby deactivated. Unlike chlorinated
methods of water disinfection, the UV radiation does not impact the
biological stability of the water. Thus, UV assisted water
filtration has become a standard practice for germicidal benefit in
water filtration systems, including the large reactors used in
public water systems (PWSs), as well as the small POU water
filtration systems. Comparable bacterial disinfection systems are
used in conjunction with other fluids.
[0005] These bacterial disinfection systems, however, suffer from a
number of significant shortcomings. First, the bacterial
disinfection systems, because they use tubular UV lamps or the
like, typically have high power requirements and large form
factors, requiring that they utilize line voltage, represent
separate components from associated fluid filtration systems, are
not compatible with smaller form factor POU fluid filtration
systems, and/or are not arbitrarily scalable. Second, the bacterial
disinfection systems are inherently inefficient. The tubular UV
lamps used emit photons that pass through the fluid and are
absorbed by another surface or reflected once or twice and lost.
The result is that photons must continually be generated and
replaced. Further, the radiation field present is not uniform. High
intensity is typically used in lamp based systems to compensate for
losses and non-uniform radiation fields. Thus, what is still needed
in the art is an improved bacterial disinfection system that
addresses these shortcomings and provides other advantages.
BRIEF SUMMARY OF THE INVENTION
[0006] Again, the present invention relates to systems and methods
for performing the bacterial disinfection of a fluid using point
radiation sources. Generally, these systems and methods utilize one
or more point radiation sources that are arranged around the
interior of an integrating sphere flow-through cell, also referred
to herein as a flow-through integrating sphere (FIS), or the like.
Preferably, the one or more point radiation sources are UV optical
sources, and optionally the one or more point radiation sources are
deep-UV optical sources, such as semiconductor or light-emitting
diode (LED) optical sources. The one or more point radiation
sources are operable to disinfect a fluid selectively exposed to
them as the DNA of bacteria, viruses, cysts, and the like in the
fluid absorbs the radiation generated and reflected in the
integrating sphere flow-through cell or the like and the biological
entities are thereby deactivated. Optionally, the interior of the
integrating sphere flow-through cell or the like is coated with a
Lambertian scattering material, and/or with a photocatalytic
material capable of destroying adsorbed biological materials in the
presence of the generated and reflected radiation, and/or with a
photocatalytic capable of generating a disinfecting agent in the
presence of the generated and reflected radiation.
[0007] In one exemplary embodiment, the present invention provides
a system for disinfecting a fluid, including: a flow cell including
one or more inlet ports and one or more outlet ports, wherein the
flow cell is configured to communicate a fluid from the one or more
inlet ports to the one or more outlet portions through an interior
portion thereof; and one or more point radiation sources disposed
about the flow cell, wherein the one or more point radiation
sources are operable for delivering radiation to the fluid; wherein
an interior surface of the flow cell is operable for reflecting the
radiation delivered to the fluid by the one or more point radiation
sources. In one exemplary embodiment, the flow cell is an
integrating sphere. Optionally, the one or more point radiation
sources include one or more of one or more semiconductor optical
sources, one or more light-emitting diode optical sources, one or
more ultraviolet optical sources, and one or more deep-ultraviolet
optical sources. The interior surface of the flow cell is operable
for reflecting the radiation delivered to the fluid by the one or
more point radiation sources such that a radiation intensity is
uniform throughout the interior portion of the flow cell.
Optionally, the system also includes one or more mechanical baffles
or stirring mechanisms disposed within the interior portion of the
flow cell for selectively modifying a flow of the fluid
therethrough. Optionally, the system further includes a
photocatalyzing material disposed on at least a portion of the
interior surface of the flow cell. Optionally, the system still
further includes a photocatalyzing material disposed on at least a
portion of a surface of the one or more mechanical baffles or
stirring mechanisms. Preferably, the system includes a controller
operable for selectively activating/deactivating the one or more
point radiation sources and a controller operable for selectively
controlling the residence time of the fluid in the interior portion
of the flow cell.
[0008] In another exemplary embodiment, the present invention
provides a method for disinfecting a fluid, including: providing a
flow cell including one or more inlet ports and one or more outlet
ports, wherein the flow cell is configured to communicate a fluid
from the one or more inlet ports to the one or more outlet portions
through an interior portion thereof; and providing one or more
point radiation sources disposed about the flow cell, wherein the
one or more point radiation sources are operable for delivering
radiation to the fluid; wherein an interior surface of the flow
cell is operable for reflecting the radiation delivered to the
fluid by the one or more point radiation sources. In one exemplary
embodiment, the flow cell is an integrating sphere. Optionally, the
one or more point radiation sources include one or more of one or
more semiconductor optical sources, one or more light-emitting
diode optical sources, one or more ultraviolet optical sources, and
one or more deep-ultraviolet optical sources. The interior surface
of the flow cell is operable for reflecting the radiation delivered
to the fluid by the one or more point radiation sources such that a
radiation intensity is uniform throughout the interior portion of
the flow cell. Optionally, the method also includes providing one
or more mechanical baffles or stirring mechanisms disposed within
the interior portion of the flow cell for selectively modifying a
flow of the fluid therethrough. Optionally, the method further
includes providing a photocatalyzing material disposed on at least
a portion of the interior surface of the flow cell. Optionally, the
method still further includes providing a photocatalyzing material
disposed on at least a portion of a surface of the one or more
mechanical baffles or stirring mechanisms. Preferably, the method
includes providing a controller operable for selectively
activating/deactivating the one or more point radiation sources and
a controller operable for selectively controlling the residence
time of the fluid in the interior portion of the flow cell.
[0009] In a further exemplary embodiment, the present invention
provides a system for disinfecting a fluid, including: a flow cell
including one or more inlet ports and one or more outlet ports,
wherein the flow cell is configured to communicate a fluid
comprising a biological contaminant from the one or more inlet
ports to the one or more outlet portions through an interior
portion thereof; and one or more point radiation sources disposed
about the flow cell, wherein the one or more point radiation
sources are operable for delivering radiation to the biological
contaminant; wherein an interior surface of the flow cell is
operable for reflecting the radiation delivered to the biological
contaminant by the one or more point radiation sources; and wherein
the interior surface of the flow cell is operable for reflecting
the radiation delivered to the biological contaminant by the one or
more point radiation sources such that a radiation intensity is
uniform throughout the interior portion of the flow cell. In one
exemplary embodiment, the flow cell is an integrating sphere.
Optionally, the one or more point radiation sources include one or
more of one or more semiconductor optical sources, one or more
light-emitting diode optical sources, one or more ultraviolet
optical sources, and one or more deep-ultraviolet optical sources.
Optionally, the system also includes a photocatalyzing material
disposed on at least a portion of the interior surface of the flow
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention is illustrated and described herein
with reference to the various drawings, in which like reference
numbers are used to denote like system components/method steps, as
appropriate, and in which:
[0011] FIG. 1 is a schematic diagram illustrating one exemplary
embodiment of the integrating sphere point radiation source fluid
disinfection system of the present invention; and
[0012] FIG. 2 is a schematic diagram illustrating another exemplary
embodiment of the integrating sphere point radiation source fluid
disinfection system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Again, the present invention relates to systems and methods
for performing the bacterial disinfection of a fluid using point
radiation sources. Generally, these systems and methods utilize one
or more point radiation sources that are arranged around the
interior of an integrating sphere flow-through cell, also referred
to herein as a FIS, or the like. Preferably, the one or more point
radiation sources are UV optical sources, and optionally the one or
more point radiation sources are deep-UV optical sources, such as
semiconductor or LED optical sources. The one or more point
radiation sources are operable to disinfect a fluid selectively
exposed to them as the DNA of bacteria, viruses, cysts, and the
like in the fluid absorbs the radiation generated and reflected in
the integrating sphere flow-through cell or the like and the
biological entities are thereby deactivated. Optionally, the
interior of the integrating sphere flow-through cell or the like is
coated with a Lambertian scattering material, and/or with a
material that undergoes photocatalysis, thereby locally generating
a disinfecting agent in the presence of the generated and reflected
radiation.
[0014] As a preliminary matter, it should be noted that the
bacterial disinfection systems and methods of the present invention
are illustrated and described herein largely in connection with an
application involving the disinfection of polished water in a
commercial under-sink water filtration unit. This specific
application is exemplary only and should not be construed to be
limiting in any manner. The bacterial disinfection systems and
methods of the present invention may be generalized and utilized in
any fluid disinfection application, including, but not limited to,
the bacterial disinfection of water, air, fuel, other fluids and
gases, and the like. Thus, the bacterial disinfection systems of
the present invention are robust and encompass a wide variety of
applications and industries. They are also scalable in size and
scope.
[0015] Referring to FIG. 1, in one exemplary embodiment, the
disinfection system 10 of the present invention includes a flow
cell 12 that takes the form of an integrating sphere or the like.
Although the integrating sphere configuration is discussed at
length herein, other configurations may also be utilized. The key
consideration is that photons are repeatedly reflected within the
flow cell 12 and that a uniform radiation field is formed for
optimal disinfection with low intensity sources. Along these lines,
the flow cell 12 should have substantially curved and concave
opposed interior surfaces. To restate, the flow cell 12 must not
have internal "corners," and every point on the interior surface
should be visible from every other point on the interior surface.
Ovoids, ellipsoids, cubes with rounded corners, etc. all fit these
criteria. The flow cell 12 is made of plastic or the like for ease
of manufacturing, and, in such cases where the material is not a
good Lambertian scatterer, the interior surfaces thereof are coated
with a Lambertian scattering material 14. Alternatively, the flow
cell 12 is made of a metallic or other reflective or coated
reflective material, such as aluminum, stainless steel, copper,
etc., which may be anodized or otherwise coated with organic
polymer, silicone, inorganic oxide, etc. The flow cell 12 is
scalable and may have any suitable dimensions, on the order of
millimeters to meters, for example.
[0016] The flow cell 12 includes at least an inlet port 16 and an
outlet port 18 manufactured into it that provides for the flow of a
fluid 19 (i.e. a liquid or gas) from the inlet port 16 to the
outlet port 18. It will be readily apparent to those of ordinary
skill in the art that multiple inlet ports 16 and/or multiple
outlet ports 18 may also be utilized. Preferably, the fluid 19 is
not allowed to stagnate in any portion of the interior of the flow
cell 12 for an appreciable period of time, as described in greater
detail herein below, and the flow cell 12 is kept 100% full at all
times. Likewise, it may be desirable that the fluid 19 be directed
towards one or more interior surfaces of the flow cell 12, such
that a disinfecting agent generated by a photocatalyzing material
may be encountered, as also described in greater detail herein
below.
[0017] In the nominal design, one or more point radiation sources
20, such as one or more UV optical sources, one or more deep-UV
optical sources, one or more semiconductor optical sources, and/or
one or more LED optical sources, are disposed within or partially
or wholly through one or more ports (not illustrated) manufactured
through the flow cell 12, preferably at symmetric positions. The
one or more point radiation sources 20 are operable to disinfect
the fluid 19 that is selectively exposed to them as the DNA of
bacteria, viruses, cysts, and the like 22 in the fluid 19 absorbs
the radiation generated and reflected in the flow cell 12 and the
biological entities are thereby deactivated. "Point radiation
sources" as used herein refer to small, roughly symmetrical
radiation sources as compared to the other dimensions of the
system.
[0018] Referring to FIG. 2, in another exemplary embodiment, the
disinfection system 10 of the present invention includes one or
more mechanical baffles 24, mechanical stirring mechanisms, or the
like, also optionally coated with Lambertian scattering material 14
and/or photocatalyzing material. This configuration is used to
equilibrate and maximize the residence time of the fluid 19 in the
interior volume of the flow cell 12. When a bacterium or the like
22 is in the interior volume of the flow cell 12, the goal is to
optimize the design parameters (i.e. size of the flow cell 12,
reflectance of Lambertian scattering material 14, residence time,
and the radiant power of the one or more point radiation sources
20) to ensure that the bacterium or the like 22 receives a lethal
dose of UV radiation while it is in the flow cell 12.
[0019] Optionally, a photocatalytic material 14, such as titanium
dioxide (TiO.sub.2), zinc oxide, zirconium dioxide, iron oxide,
aluminum oxide, Fe(III)/Al.sub.2O.sub.3, cerium oxide, manganese
oxide, titanium silicates, metal substituted silicates or
aluminosilicates, and any other metal oxide, mixed metal oxide,
and/or metal doped/supported metal oxide substrates (e.g. gold
nanoparticles supported on silicon dioxide or titanium dioxide), or
the like, may be disposed on the inner surface(s) of the flow cell
12 or otherwise integrated with these surfaces to enhance the
photo-oxidation, photo-reduction, and decontamination of
contaminants on a near-field basis, including bacteria, pathogens,
organic materials, halogenated compounds, biogenic compounds, metal
ions, and/or biological agents. Alternatively, the photocatalyst
material 14 could be suspended on a non-absorbing substrate (such
as a fiber or a mesoporous or macroporous sol-gel, ormisil,
polymer, or aeorogel) which occupies some of the interior region of
the flow cell 12. This would provide uniform illumination of the
catalyst from all directions for optimal photocatalytic rates due
to the unique highly reflective and randomizing nature of the
integrating sphere surface. A flow detector (not illustrated) or
the like may be used before or after the flow cell 12 to turn off
the one or more point radiation sources 20 during periods of no
flow to maximize the life of the one or more point radiation
sources 20, and the entire system may be coupled to an appropriate
computer controller/processor (not illustrated) or the like that
controls the overall function of the disinfection system 10.
[0020] As a preliminary matter, DNA has peak absorption at about
260 nm, but the absorption curve is broad, with the majority of UV
absorption occurring between about 240 nm and about 280 nm. Low and
medium pressure mercury lamps have emission peaks at about 253.7
nm, with medium pressure lamps having emission peaks which are
narrow and sporadic across the peak microbicidal region of DNA. In
comparison, UV LEDs have broadband deep-UV emission and may be
tailored for peak emission at about 260 nm to provide the maximum
dose more effectively than mercury lamps. The LED wavelength may be
shifted by varying the percent composition of aluminum within the
Al.sub.xGa.sub.(1-x)N active layer of the LED. LEDs with
wavelengths centered at the peak of DNA absorption are recently
commercially available. In addition, UV LEDs contain no mercury,
which is extremely toxic such that discharge lamps containing
mercury must be treated as hazardous waste and sent to an approved
recycling facility when spent. Also, mercury based sources produce
emission lines at about 185 nm, which results in ozone production;
ozone is corrosive and absorbs UV light, as well as being toxic. UV
LEDs are mercury free solid state sources and may be manufactured
to have no emission shorter than about 200 nm. In addition to being
mercury free, UV LEDs have some distinct advantages over lamp
sources. Lamps are bulky and require line voltage which is
undesirable in POU systems, where line voltage is not always
available where the unit would be positioned. Also, mercury lamps
have a start-up delay time associated with the creation of the
plasma in the lamp envelop, which in turn heats the inert gas,
which then vaporizes the mercury allowing the mercury and plasma
ions to collide and excite the Hg to emission. In contrast, UV LEDs
may be turned on instantly and operated at a very fast on/off duty
cycle to increase their lifetime.
[0021] With regard to the exemplary integrating sphere embodiment
of the present invention, integrating spheres are typically used by
optical scientists and spectroscopists to (1) efficiently collect
light from a light source with a random radiation pattern and (2)
create a diffuse source from the light so collected. This is
accomplished through multiple reflections from the highly
scattering interior walls of the integrating sphere, which are
inherently reflective or coated with a Lambertian scattering
material. In some cases, the collection is important, such as in
the characterization of light bulbs. In other cases, the goal is to
create a diffuse light source, such as for spectroscopy or
photochemistry applications. In these applications, the inside
volume of the integrating sphere is kept as empty as possible,
usually containing only air. Because of the highly scattering
interior walls, and the resulting path length enhancement, several
individuals have recently proposed using the integrating sphere as
an enhanced sample holder for absorption spectroscopy, and as a
product for characterizing samples, e.g. ocean or lake water has
been characterized using this principle. During operation, while
filled with a substantially or partially transparent medium, such
as air (or water), the light intensity inside the integrating
sphere is everywhere the same, independent of direction. This is a
unique feature of the integrating sphere, provided that the optical
source (or sources) are small in area as compared to the interior
surface area of the integrating sphere.
[0022] In conjunction with the systems and methods of the present
invention, a fluid containing a very small population of bacteria
or the like is allowed to flow through the radiation filled
integrating sphere. The following series of simple calculations
demonstrates that, if the residence time of the fluid (e.g. water)
is controlled, then the water may be disinfected using a relatively
small number of commercially available UV LEDs or the like in
conjunction with a properly designed integrating sphere flow
cell.
[0023] UV LEDs are a relatively recent emerging technology, and are
ideally suited for optimization using an integrating sphere, since
they are small (e.g. microns square) as compared to the inner
surface of a sphere of nominal size (e.g. 2-inch radius). Earlier
UV light sources, such as mercury discharge lamps and the like, may
not effectively be integrated with an integrating sphere flow cell
in this manner due to their large form factor, among other
considerations.
[0024] The nominal maximum flow rate of a kitchen sink, for
example, is:
Q = 2.5 gal min = 10.0 qt min = 9460 ml min = 158 ml sec . ( 1 )
##EQU00001##
A proposed FIS UV LED flow cell with radius R has a volume of:
V = 4 3 .pi. R 3 . ( 2 ) ##EQU00002##
So, if a particular flow of water Q is passing through the volume
V, the average residence time of a particulate, such as a
bacterium, is:
.tau. = V Q . ( 3 ) ##EQU00003##
[0025] It is assumed that otherwise potable water is contaminated
with a very small population of bacteria, at a concentration of
less than about one bacterium per volume of the sphere. In the
exemplary embodiment of FIGS. 1 and 2, the water flows upwards
through the flow cell, from a round port in the bottom of the
sphere to a round port in the top of the sphere. In order to
achieve a residence time for every bacterium of order .tau., it is
anticipated that the flow should be disrupted somewhere near mid
sphere, to slow down the relatively fast moving polar axial jet,
and to sweep clean the relatively stagnant equatorial volume. This
is illustrated in FIG. 2, by using a mechanical baffle or the like.
Other methods for increasing residence time include: (1) the use of
mechanical stirring; (2) the use of mechanical stirring in
conjunction with non-spherical "dimples" or the like strategically
located in the equatorial areas of the integrating sphere, for
example; (3) utilizing directional flow via a perforated nozzle
(i.e. showerhead) or the like at the water inlet; and (4) otherwise
forcing the water to follow a circuitous path inside the sphere, by
using a randomly bent tube, for example--the tube should be made
from a UV transparent material, such as quartz or the like. The
preferred way to maximize residence time may be to inject the
incoming fluid into the flow cell in a direction parallel to a
latitude in the southern hemisphere, for example, with the outlet
perpendicular to the flow cell at the north pole, for example; this
way the swirling fluid fills up the flow cell evenly from bottom to
top. Optimum placement of inlet, outlet, baffles, etc. may be
modeled using computational fluid dynamics (CFD). It should be
noted that any non-uniformities in the integrating sphere, such as
holes, dimples, baffles, etc. may degrade its optical performance.
Thus, successful development of the systems and methods of the
present invention requires the optimization of the trade-offs
between residence time and ideal integrating sphere
functionality.
[0026] If point radiation sources (e.g. UV LEDs) and receivers
(i.e. bacteria, e.g E. coli bacteria) have areas that are small
compared to the inside surface area of the sphere, and if the LED
power is .phi..sub.s (typically mW), radius of the sphere is R,
flow rate is Q (typically cc per second), inner-surface reflectance
of the sphere is k (%), reflectance is Lambertian, and f is the
port fraction of the holes for sources, etc. in the sphere, then
the dose per unit area delivered to a receiver (such as a
bacterium) inside the sphere for each UV LED is:
dose = .tau. ( .phi. A ) = ( 4 .pi. R 3 3 Q ) ( k 1 - k ( 1 - f ) )
( .phi. s 4 .pi. R 2 ) = R .phi. s 3 Q ( k 1 - k ( 1 - f ) ) . ( 4
) ##EQU00004##
[0027] Assume that a dose of D=5 mJ/cm.sup.2 is required for
bacterial disinfection. Then the number of LEDs (N) required for a
sphere of reflectance k, radius R, and negligible port fraction
is:
N = 3 DQ R .phi. s ( 1 - k k ) = 98.2 R ( inches ) . ( 5 )
##EQU00005##
[0028] Assuming a SET UV LEDs with radiant power .phi..sub.s=0.5 mW
at a forward current of 20 mA, k=95% for Spectralon coating the
inner surface of the sphere, and Q=158 cm.sup.3/sec as above. Then
the number of LEDs to achieve the required dose is:
TABLE-US-00001 Radius of integrating sphere Number UV LEDs required
(inches) (@ 0.5 mW) 2 49 3 33 4 25 5 20
[0029] It should be noted that the number of required LEDs scales
with 1/R and also with 1/.phi..sub.s. The radiant power of
available LEDs is expected to increase over the time through
continuous UV materials technological developments. Likewise, the
lifetime of UV LEDs is currently relatively short, on the order of
about 300 hours. But LED operation may be optimized utilizing a
pulsing algorithm or the like, and this lifetime is expected to
continue to increase through continuous UV materials technological
developments. The current generation of 0.5 mW UV LEDs consume
about 100 mW of power each, so the total required system power for
kitchen faucet UV water disinfection unit with a sphere of 2.5-inch
radius is 2.5 watts. The power consumed by UV LEDs is also expected
to continue to decrease through technological developments. By
comparison, a commercially available water disinfection unit with a
conventional UV mercury lamp uses 14 watts for 3 gallons per minute
of flow and a 10,000 hour lamp life.
[0030] The Lambertian reflectance material must be non-toxic and
highly reflecting. The sphere may be made of metal or plastic, and
coated with metal, organic polymer, silicone, inorganic oxide, or
anodized. Other materials are available with reasonably Lambertian
characteristics, and reflectances on the order of k.about.90% or
more (e.g. certain aluminum coatings).
[0031] As an enhancement to the systems and methods of the present
invention, photocatalytic materials, such as titanium dioxide
(TiO.sub.2), zinc oxide, zirconium dioxide, iron oxide, aluminum
oxide, Fe(III)/Al.sub.2O.sub.3, cerium oxide, manganese oxide,
titanium silicates, metal substituted silicates or
aluminosilicates, and any other metal oxide, mixed metal oxide,
and/or metal doped/supported metal oxide substrates (e.g. gold
nanoparticles supported on silicon dioxide or titanium dioxide), or
the like, may also be included inside the sphere or as part of the
internal surface of the sphere to enhance photo-oxidation,
photo-reduction, and the decontamination of water contaminants,
including bacteria, pathogens, organic materials, halogenated
compounds, biogenic compounds, metal ions, and/or biological
agents. For any of these contaminants in which the direct
absorbance of ultraviolet light is not possible or does not result
in a decontamination, detoxification, or destruction of the
contaminant, the photocatalyst inside the sphere would act as the
"UV-receiver" instead of or in addition to the contaminant. Upon UV
exposure, the excited photocatalyst would interact with
contaminants in the water stream to purify the water. It should be
noted that this process may be staged with the radiation exposure
process.
[0032] Because certain UV LEDs may operate in the near-UV region of
the emission spectrum, germicidal effect of the titanium dioxide
(TiO.sub.2) or the like may be exploited. Titanium dioxide, for
example, absorbs the near-UV effectively, having a wide bandgap of
3.2 eV; this absorption resulting in a photocatalytic reaction.
Absorption of UV light leads to photoexcited electrons and holes,
which are powerful reducing and oxidizing agents respectively (see
eq. 6). The photoexcited holes react with adsorbed water to
generate highly reactive hydroxy radicals (.OH, see eq. 7).
Simultaneously, the photoexcited electrons readily reduce adsorbed
O.sub.2 to generate superoxide radicals (.O2-, see eq. 8). These
reactive oxygen species (ROS), along with various side products,
such as hydrogen peroxide, are believed to contribute to cell death
in photocatalytic decontamination schemes.
TiO.sub.2+hv.fwdarw.TiO.sub.2(e.sup.-+h.sup.+). (6)
TiO.sub.2(h.sup.+)+H.sub.2O.sub.adsorbed.fwdarw.TiO.sub.2+.OH.sub.adsorb-
ed+H.sup.+. (7)
TiO.sub.2(e.sup.-)+O.sub.2 adsorbed.fwdarw.O.sub.2..sup.-. (8)
[0033] In accordance with the systems and methods of the present
invention, the titanium dioxide or the like is immobilized along
the walls of the highly reflecting integrating sphere.
Fluoropolymer represents a potential matrix for coating the inside
of the sphere due to its high reflectivity in the UV, its chemical
inertness, and its ability to immobilize titanium dioxide. Titanium
dioxide may also be immobilized into other organic and inorganic
coatings, or deposited by sputtering or electron beam deposition.
However, the continuous generation of reactive oxygen species has a
long-term negative effect on most immobilization substrates. In one
study, the photocatalytic oxidation via titanium dioxide of a
variety of polymer films and metal surfaces showed that
fluoropolymer was the only substrate that was resistant to
oxidation from the reactive oxygen species produced upon
photoexcitation of titanium dioxide. Titanium dioxide immobilized
on metal supports via a fluoropolymer binder has been shown to
maintain much of its photocatalytic activity, as demonstrated via
photodecomposition of 4-chlorophenol.
Experimental Discussion
[0034] Bacterial DNA is known to have peak absorption at a
wavelength of 260 nm and initial bacterial log reduction rates were
determined using a planar array of 5 LEDs. The LEDs were used to
irradiate a Petri dish with 20 mL of water infused with an e-coli
strain. This set up was used to base line the dose received from UV
LEDs to the standard mercury lamp sources currently used in water
disinfection. A prototype FIS was also designed, built, and tested
to validate the UV dose enhancement. The FIS design could hold
about 230 mL of liquid and was fitted with 5 LEDs (Sphere 1) and 32
LEDs (Sphere 2). Mercury lamp source (.lamda.=254 nm) dose
requirements for 6 log reduction was found to be 30 mJ/cm.sup.2.
However, the NSF/ANSI 55-20072 standard requires a minimum dose of
40 mJ/cm.sup.2 at 254 nm for Class A point of entry (POE) or point
of use (POU) UV systems. The 5-260 nm LEDs Petri dish setup
resulted in a greater than 6 log reduction in bacteria at a
calculated dose of 61 mJ/cm.sup.2, and a greater than 5 log
reduction at 36 mJ/cm.sup.2. When comparing the Petri dish
configuration with 5 LEDs exposing 20 mL of bacteria laden water
versus prototype Sphere 1 also with 5 LEDs exposing 230 mL of
bacteria laden water, it was observed that the sphere prototype is
capable of disinfecting 10 times the liquid volume of water than
the Petri dish apparatus.
[0035] This comparison, along with the theoretical results,
indicated that the integrating sphere prototype configuration
offers an enhancement in dose over a planar array of LEDs. It
should be noted that both tests started with a bacterial (E. coli)
concentration of approximately 1E7 CFU/mL.
[0036] A 6 log reduction in E. coli within 3 minutes was observed
using sphere 2 with 32 LEDs. The theoretical equations proposed
predicted the number of required LEDs to be N=33 for a certain
reflectance value k, LED power .PHI., and sphere radius R. This
calculation is comparable to the experimental value of N=32 used in
the prototype testing.
[0037] During testing, the sphere flow cell was mechanically mixed
on a slow moving orbital shaker while irradiating the bacteria
infested water. Fluid dynamics modeling was performed to simulate
water flow in the sphere for analysis of particle residence time.
Two different models were used to investigate particle residence
time and fluid flow in the sphere. Design A, the built prototype,
had inlet and outlet ports horizontally aligned, while Design B had
the inlet and outlet ports skewed horizontally with respect to each
other. Both models had inlet and outlet pipes of 0.5-inch diameter
and were modeled with a volumetric flow rate of 23.2 cm.sup.3/s,
giving an inflow velocity of 0.183 m/s.
[0038] Increasing the pathlength of the fluid increased the
residence time of any microorganisms in the fluid. To determine the
particle residence time, 12 zero mass particles were released
through the inlet pipe of the sphere and tracked over time in order
to replicate the particle residence time (PRT) of microorganisms in
the sphere. These simulations demonstrated Design A having a
minimum PRT of 0.9 s while Design B had a minimum PRT of 1.4 s. In
Design A, half of the particles were caught in an eddy current and
hence not released within the first 2000 inches of travel in the
sphere. Design B on the other hand, exhibited a more evenly
distributed PRT with some particles revolving in eddy currents but
not for longer than 50 seconds before exiting the sphere.
[0039] These results served to prove that the concept of using deep
UV LEDs in an integrating sphere for water disinfection is
feasible. Certification level 6 log reduction of E. coli bacteria
in water was demonstrated in the integrating sphere flow cell
prototype.
[0040] The ideal material set for the spherical flow through
integrating sphere would be non-toxic, easily machine-able (so that
portals may be made for fluid flow and optical sources), of
sufficient mechanical integrity and strength, inexpensive,
leak-proof, and mass manufacturable. Additionally, the inner
surface coating of the sphere should have appropriate optical
scattering properties, ideally Lambertian, and with a reflectivity
of 1.0 in the deep ultraviolet. A reflectivity of 1.0 is not
achievable in practice, but certain materials are close.
[0041] The standard scattering material currently used for coating
surfaces in most deep UV applications is low density
polytetrafluoroethylene (PTFE) inside a high reflectivity metal
outer shell; PTFE acts somewhat as a diffuser, so high system
reflectivity cannot be fully attained without a reflective outer
layer. For a 260 nm water disinfection flow cell application,
aluminum or the like provides an appropriate outer shell. Low
density PTFE objects are formed by a labor intensive multistep
process of (1) pressing PTFE powder into a solid form (e.g. a cube
or a cylinder), (2) sintering at high temperature e.g. 500-600
degrees F., (3) machining parts with oil-free cutting tools in a
clean room environment, and (4) encapsulating in a hard mechanical
metal or polymer shell. An integrating sphere is typically made by
hollowing out a cube of pressed and sintered PTFE. Since low
density PTFE so prepared for deep-UV scattering has a porous
structure, in the proposed application it may act as an "organic
sponge", picking up any contaminants (e.g. minerals, trace
organics) in the flowing water, and thus the optical properties of
the sphere may be adversely affected. Nevertheless, a virgin
integrating sphere flow cell made from low density PTFE provides an
acceptable option in terms of optical properties, and therefore
initial measurements made with such a device represent the
entitlement of the system for a particular set of source power,
source geometry, and inlet/outlet geometry. It should be noted that
PTFE is also available in paint-on solutions with organic binders
such as polyvinyl alcohol, however, these material are not as good
of reflectors at wavelengths shorter than 300 nm due to absorption
and degradation of the organic binder materials. The organic
binders also present toxicity concerns.
[0042] Barium sulfate (BaSO4) is also an exemplary option and is
commonly available in paint-on coatings which contain organic
binder and solvent. Coatings from this type of material are
specified to have reflectivity of 0.92 to 0.98 over the spectral
range 300 nm to 1200 nm. However, for deep-UV (i.e. 260 nm), the
decreasing reflectivity of the BaSO4 and the UV absorption of the
organic binder combine to make BaSO4 less suitable for the current
application.
[0043] Aluminum is a good candidate material for the entire
integrating sphere, being a good reflector in the UV, i.e. better
then e.g. silver or gold. Aluminum has been extensively used as a
reflective material in the extreme UV (EUV, i.e. shorter than 200
nm) in satellite mirror applications, and after performance has
degraded due to oxidation during use, the reflectance may be
regenerated by over-coating with more aluminum. With a thin
protective layer of e.g. magnesium fluoride (MgF.sub.2),
regeneration is not required, and aluminum can sustain a
reflectance of around 85% at 260 nm. This is typically accomplished
by sputtering a thin (e.g. half wavelength) film of MgF.sub.2 onto
a microns thick aluminum film that is deposited onto a surface like
the inside of a spherical shell. The spherical shell might be made
of aluminum, and if so the scattering can be rendered more
Lambertian by roughening through e.g. "bead blasting", essentially
sandblasting with glass beads before the aluminum and MgF.sub.2
thin films are deposited. Aluminum and MgF.sub.2 could also be
deposited in a similar way onto the inner surface of a plastic
sphere. Magnesium fluoride raises concerns with respect to its
toxicity, though it is approved in certain small quantities by the
FDA as e.g. a bonding agent for aluminum foil. It is only slightly
soluble in water. Its use as a thin solid reflector coating in this
water disinfection application would possibly require an extra
layer of water impervious encapsulation over the exposed MgF.sub.2.
Another possibility would be to coat the inner Lambertian surface
of an aluminum sphere with a high temperature (e.g. 600 degree F.)
primer/topcoat PTFE process. Another possibility is a
UV-transparent silicone hard coat on aluminum. Another possibility
is anodized aluminum.
[0044] Polymers are attractive materials for flexible spherical
shell prototype geometries and manufacturability, though their UV
absorbance is high, and thus some kind of coating is required (e.g.
aluminum, Al+MgF.sub.2, PTFE, etc.) to achieve a Lambertian inner
scattering surface. Rapid prototyping technology such as solid
state stereolithography (SLA) and selective laser sintering (SLS)
can be used to quickly and cheaply construct hollow spherical
prototypes with complex geometric features using engineering
thermoplastics such as Accura and Duraform (nylon), respectively.
The benefit is that a large number of computer aided designs (CADs)
incorporating various flow cell geometries, baffles, etc., can be
first simulated using fluid dynamics software to optimize flow cell
residence time. Only the best performers are thus be prototyped and
evaluated. These prototypes can then be used as models to set up
inexpensive injection molding processed for mass manufacturing from
other thermoplastic materials and coatings, optimized for
Lambertian scattering at 260 nm.
[0045] Although the present invention has been illustrated and
described herein with reference to preferred embodiments and
specific examples thereof, it will be readily apparent to those of
ordinary skill in the art that other embodiments and examples may
perform similar functions and/or achieve like results. All such
equivalent embodiments and examples are within the spirit and scope
of the present invention, are contemplated thereby, and are
intended to be covered by the following claims.
* * * * *