U.S. patent application number 09/976498 was filed with the patent office on 2003-04-17 for air diffuser membrane treated with biocide.
Invention is credited to Tharp, Charles E..
Application Number | 20030071377 09/976498 |
Document ID | / |
Family ID | 25524161 |
Filed Date | 2003-04-17 |
United States Patent
Application |
20030071377 |
Kind Code |
A1 |
Tharp, Charles E. |
April 17, 2003 |
AIR DIFFUSER MEMBRANE TREATED WITH BIOCIDE
Abstract
A fine bubble diffuser membrane used in the aeration of
wastewater is treated with biocide to inhibit growth and
accumulation of biological materials on the membrane. The membrane
may be constructed of EPDM rubber or urethane. The biocide may be
carbolic acid either dispersed throughout the membrane or applied
as a coating on the surface of the membrane exposed to the
wastewater. The membrane is a flexible and elastic structure
impervious to liquid and provided with slits that close to prevent
wastewater inflow in the absence of aeration and open in response
to aeration pressure to discharge air into the wastewater.
Inventors: |
Tharp, Charles E.;
(Columbia, MO) |
Correspondence
Address: |
Richard R. Johnson
SHOOK, HARDY & BACON L.L.P.
1200 Main Street
Kansas City
MO
64105-2118
US
|
Family ID: |
25524161 |
Appl. No.: |
09/976498 |
Filed: |
October 12, 2001 |
Current U.S.
Class: |
261/122.2 ;
210/501; 210/755 |
Current CPC
Class: |
B01F 23/23124 20220101;
C02F 3/201 20130101; C02F 1/50 20130101; B01F 23/231232 20220101;
Y10S 261/70 20130101; A01N 31/08 20130101; B01F 23/231244 20220101;
B01F 23/231265 20220101; Y02W 10/10 20150501; B01F 23/231281
20220101; A01N 25/34 20130101; A01N 31/08 20130101; A01N 25/34
20130101; A01N 31/08 20130101; A01N 2300/00 20130101 |
Class at
Publication: |
261/122.2 ;
210/501; 210/755 |
International
Class: |
B01F 003/04 |
Claims
Having thus described the invention, what is claimed is:
1. A diffuser membrane for applying air to wastewater for aeration
of the wastewater, said membrane comprising: a flexible and elastic
membrane wall which is impervious to the passage of liquid
therethrough; a plurality of aeration slits in said membrane wall
which are normally closed to prevent passage of the wastewater
therethrough but which open when air under pressure is applied to
said membrane wall so that air can pass through said slits into the
wastewater; and a biocide applied to said membrane wall to resist
biological growth thereon.
2. A membrane as set forth in claim 1, wherein said membrane wall
comprises EPDM.
3. A membrane as set forth in claim 2, wherein said biocide
comprises carbolic acid.
4. A membrane as set forth in claim 3, wherein said carbolic acid
is dispersed throughout said EPDM.
5. A membrane as set forth in claim 3, wherein said carbolic acid
is coated on said EPDM on a surface thereof exposed to the
wastewater.
6. A membrane as set forth in claim 1, wherein said membrane wall
comprises urethane.
7. A membrane as set forth in claim 6, wherein said biocide
comprises carbolic acid.
8. A membrane as set forth in claim 7, wherein said carbolic acid
is dispersed throughout said urethane.
9. A membrane as set forth in claim 7, wherein said carbolic acid
is coated on said urethane on a surface thereof exposed to the
wastewater.
10. A membrane as set forth in claim 1, wherein said biocide
comprises carbolic acid.
11. A membrane as set forth in claim 10, wherein said carbolic acid
is dispersed throughout said membrane wall.
12. A membrane as set forth in claim 10, wherein said carbolic acid
is coated on said membrane wall on a surface thereof exposed to the
wastewater.
13. A membrane as set forth in claim 1, wherein said biocide is
dispersed throughout said membrane wall.
14. A membrane as set forth in claim 1, wherein said biocide is
coated on said membrane wall on a surface thereof exposed to the
wastewater.
15. A membrane construction for use in the application of air to
wastewater, comprising: a tubular membrane impervious to the
passage of the wastewater therethrough and constructed of a
flexible and elastic material to allow the membrane to be sleeved
closely on a diffuser body ported to apply air to the inside of the
membrane; a plurality of slits through said membrane normally
closed to prevent passage of wastewater into the membrane, said
slits opening upon application of air under pressure to the inside
of the membrane to allow the air to discharge into the wastewater;
and a biocide on said membrane for resisting biological growth
thereon.
16. An air diffuser for submergence in wastewater to apply air for
treatment of the wastewater, said diffuser comprising: a rigid
diffuser body having a tubular shape and a hollow interior for
receiving air to be applied to the wastewater, said diffuser body
having a port for discharging air from said interior; a tubular
membrane constructed of a flexible and elastic material impervious
to passage of wastewater therethrough, said membrane being sleeved
on said diffuser body and being normally collapsed thereon but
expanded when air under pressure is supplied to the membrane
through said port; a plurality of aeration slits in said membrane,
said slits being closed when said membrane is collapsed on said
diffuser body and opened to discharge air when said membrane is
expanded by air supplied thereto through said port; and said
membrane being treated with biocide for resisting biological growth
thereon.
17. A method of constructing an air diffuser membrane of the type
used to apply air to wastewater at a submerged location for
aeration of the wastewater, said method comprising the steps of:
(a) mixing together structural materials of which the membrane is
to be constructed with a biocide resistant to biological growth,
said structural materials being selected to provide the membrane
with flexibility and elasticity; (b) forming the membrane into a
selected shape; and (c) cutting aeration slits in the membrane in a
manner wherein the slits are normally closed but open when the
membrane is expanded by the application of air thereto under
pressure.
18. A method as set forth in claim 17, wherein said biocide
comprises carbolic acid.
19. A method as set forth in claim 17, wherein said structural
materials are selected from the group comprising EPDM and
urethane.
20. A method as set forth in claim 19, wherein said biocide
comprises carbolic acid.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to the aeration of
wastewater and more particularly to an air diffuser membrane that
is treated with a biocidal agent which inhibits biological growth
on the membrane surface.
BACKGROUND OF THE INVENTION
[0002] Flexible membrane diffusers are in widespread use for the
aeration and mixing of wastewater. By way of example, U.S. Pat. No.
4,960,546 to Tharp discloses a flexible membrane diffuser that is
sleeved onto a rigid tubular diffuser body to provide a
construction that has achieved considerable popularity. The
membrane collapses on the diffuser body and fits closely around it
when no air is being supplied by the blower to the piping of the
aeration system. When the aeration is active, air is supplied
through the piping to the diffuser body and enters the inside of
the membrane through ports in the diffuser body. The air pressure
causes the membrane to expand as it receives the air.
[0003] This type of diffuser membrane is provided with a large
number of aeration slits which are closed when the membrane is
collapsed on the diffuser tube in the absence of air pressure. The
wastewater cannot seep into the aeration piping because the closed
slits do not provide access and the membrane is impervious to
liquid. However, when the air is turned on and the membrane
expands, the slits open and allow the air to discharge into the
wastewater in the form of fine bubbles. Such small bubbles are
advantageous from an efficiency standpoint because their relatively
small volume to surface area ratio results in more efficient
aeration. The slits are controlled apertures because the extent to
which they open varies with varying air pressure.
[0004] In addition to use in tubular diffuser systems, flexible
membranes have been used in other diffuser configurations,
including disk type diffusers. The membrane is used in this
application as a flat disk member which covers the diffuser plenum
in the body of the diffuser and discharges air in fine bubbles in
much the same manner as in the case of tubular diffusers.
[0005] Flexible membrane diffusers are typically constructed of
EPDM rubber or urethane. These materials exhibit the necessary
structural characteristics. They are also flexible and elastic and
thus able to meet the operational requirements for the membrane in
these aspects.
[0006] Although flexible membrane diffusers have been satisfactory
for the most part, they can be susceptible to biological fouling,
especially when used in relatively severe applications where
biological growth is promoted due to the conditions of the
wastewater. In harsh wastewater environments, it is not uncommon
for algae and other biological material to build up on the surface
of the membrane, often quickly and to a significant extent. When
biological growth accumulates on the membrane, there is a marked
increase in the size of the bubbles that are released into the
wastewater, as the fine bubbles tend to merge in the biological
growth and create larger bubbles which are finally released into
the liquid. As a result, the efficiency of the oxygen transfer to
the wastewater suffers a significant reduction.
[0007] Although there have been proposals made to apply biocides to
other types of membranes, such as filtration membranes which are
permeable, impermeable flexible membrane diffusers have not been
treated with biocidal agents. U.S. Pat. No. 5,102,547 to Waite et
al. discloses a filter membrane that is treated with biostatic or
biocidal agents. Because the membrane serves as a filter, it is
necessarily permeable to liquids in order to allow liquids to pass
through it for filtration of the liquid. This type of filter
membrane is clearly of no use in treating wastewater and can only
be used in clean water environments because it would quickly become
fouled by solids in wastewater or other liquids having suspended
solids. Similarly, U.S. Pat. No. 5,106,267 to Vaughn et al. is
directed only to the biocidal treatment of porous or permeable
membranes that have no applicability for aeration and are not
useful in wastewater applications.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to a flexible and elastic
diffuser membrane which is used in the aeration of wastewater and
which is impregnated or otherwise treated with biocide in order to
resist biological accumulations on the membrane surface.
[0009] In accordance with the invention, a diffuser membrane is
preferably constructed of a material such as EPDM rubber or
urethane. The structural materials of the membrane are preferably
mixed with a biocide such as carbolic acid which is thereby
dispersed throughout the membrane structure. Alternatively, the
membrane can be coated with biocide on the surface which is exposed
to wastewater when the membrane is in service submerged in the
wastewater.
[0010] In either case, the membrane is a flexible and elastic
structure which is slitted to provide controlled apertures for the
release of fine bubbles of air into the wastewater for aeration and
mixing of the wastewater. The membrane may be closely sleeved on a
rigid tubular diffuser body which is ported in order to apply air
to the inside of the membrane. In the absence of air pressure, the
membrane collapses tightly on the diffuser body and the slits are
closed to prevent entry of wastewater into the piping of the
aeration system. When air is applied, it expands the membrane and
opens the slits to allow the discharge of air into the wastewater
in the form of fine bubbles.
[0011] The membrane may take other forms, including the form of a
disk diffuser in which a plenum is covered by a flat membrane. When
air is supplied to the plenum, the membrane expands and the slits
open for discharge of the air into the wastewater.
[0012] The treatment of the diffuser membrane with biocide inhibits
the growth and accumulation of algae and other biological
substances on the membrane. This has the beneficial effect of
preventing biological growth from causing the air bubbles to
increase in size, often dramatically, as can occur in wastewaters
that have severe conditions conducive to biological growth.
Consequently, the biocidally treated membrane of the present
invention retains its ability to produce fine bubbles and thus
continues to operate near peak efficiency even in harsh or severe
wastewater conditions.
[0013] Other and further objects of the invention, together with
the features of novelty appurtenant thereto, will appear in the
course of the following description.
DESCRIPTION OF THE DRAWING
[0014] In the accompanying drawing which forms a part of the
specification and is to be read in conjunction therewith and in
which like reference numerals are used to indicate like parts in
the various views:
[0015] FIG. 1 is an exploded perspective view of a tubular air
diffuser arrangement of a type that may incorporate a biocidally
treated diffuser membrane constructed according to a preferred
embodiment of the present invention, with the break lines
indicating continuous length.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention is directed to a flexible and elastic
diffuser impermeable membrane which is biocidally treated in order
to inhibit biological growth and which is used in an aeration
system that operates to aerate and mix wastewater. One type of
aeration system with which the biocidally treated membrane of the
present invention may be used is disclosed in U.S. Pat. No.
4,960,546 which issued on Oct. 2, 1990 to Charles E. Tharp, which
patent is incorporated by reference.
[0017] As disclosed in the aforementioned Tharp patent and shown in
FIG. 1 of this application, air is supplied by the aeration system
to a tee fitting 10 having a vertically oriented inlet 11 which
receives the air and a pair of oppositely directed outlets 12 which
discharge the air in a horizontal direction. Secured in each of the
outlets 12 is an elongated tubular diffuser body 14 which is
preferably constructed of a rigid plastic and has a hollow interior
16. A plug 18 may plug the outer end of each diffuser body 14 or
may be secured at an intermediate location along the length of each
diffuser body, as desired. Each diffuser body 14 preferably has a
cylindrical shape and is provided with a plurality of ports such as
the port 20 through which air passes from the interior 16 of the
diffuser body to its exterior.
[0018] In accordance with the present invention, each diffuser body
14 is provided with a flexible membrane diffuser 22 which is
sleeved over the diffuser body 14 and suitably secured to it, as by
hose clamps 24 equipped with conventional fasteners 26. Each
membrane 22 has a wall which is a cylindrical structure that is
flexible and elastic. The membrane 22 fits closely on the diffuser
body 14 and is collapsed tightly on the exterior surface of the
diffuser body when air is not being applied to the diffuser body 14
by the aeration system.
[0019] The membrane 22 is preferably constructed of a material such
as EPDM rubber or urethane. In accordance with the present
invention, the structural components of the membrane 22, which may
constitute a suitable polymer, carbon black and calcium carbonate,
may be mixed with a biocide that, due to the mixing process, is
dispersed throughout the wall of membrane 22 in a relatively
uniform manner. The biocide is preferably carbolic acid or phenol.
By way of example, the biocide may be a compound that is
commercially available from Clariant Corporation of Charlotte, N.C.
under the trademark NIPACIDE which is an antimicrobial agent. Other
suitable biocidal agents are also contemplated.
[0020] By mixing the biocide with the other components of the
membrane, the biocide is dispersed throughout the EPDM rubber
matrix. The EPDM rubber, in which the biocide is dispersed, is
preferably molded or otherwise suitably formed into the shape
desired for the membrane 22. The membrane material is impervious to
liquid.
[0021] Alternatively, the membrane 22 can be molded or otherwise
formed, and the biocide can then be applied as a coating on the
exterior surface of the membrane 22 which is the surface exposed to
the wastewater when the membrane is in service submerged in the
wastewater.
[0022] After the biocide has been applied to the membrane 22,
either by dispersing it throughout the membrane or applying it as a
coating on the surface of the membrane, and the membrane has been
molded or otherwise formed, a plurality of small aeration slits 28
are formed through the membrane wall. The slits 28 serve as
controlled aeration apertures which are closed when the membrane 22
is sealed against the outer surface of the diffuser body 14 in the
absence of air pressure. However, when air is supplied to the
interior of the membrane through the ports 20 of the diffuser body
14, the membrane 22 expands outwardly away from the diffuser body,
as permitted by its flexibility. Then, the aeration slits 28 open
and allow the air to pass through them and discharge into the
wastewater in the form of a fine bubbles resulting from the small
size of the slits 28. When the aeration system is deactivated and
the air pressure is withdrawn, the elasticity of the membrane 22
causes it to collapse again tightly on the diffuser body 14,
thereby again closing the slits 28 and sealing the diffuser against
the outside surface of the diffuser body. Consequently, the
wastewater is unable to enter the diffuser body 14 and the
distribution piping of the aeration system because the openings 28
do not provide access for the wastewater and the membrane 22 is
impervious to liquid.
[0023] The treatment of the membrane 22 with biocide, whether it is
dispersed throughout the membrane or coated on its surface,
inhibits the growth and buildup of algae and other biological
material on the membrane surface. A membrane that is not treated
with biocide can be subject to accumulation of biological growth
which traps the fine bubbles discharged through the slits 28 and
causes them to merge and form larger bubbles before they are
released from the biological growth into the wastewater. Large
bubbles result in less efficient aeration because the bubble volume
to surface area ratio is larger with larger bubbles, and the oxygen
transfer to the wastewater suffers accordingly. Thus, by using the
biocidally treated membrane 22 of the present invention, the
efficiency of the oxygen transfer remains intact because the growth
and buildup of biological materials is inhibited by the
biocide.
[0024] In the case of a biocidal agent that is dispersed throughout
the cylindrical wall of the membrane 22, when the membrane has been
in service for an extended time period, the biocidal within the
membrane tends to migrate toward the surface and thus remains
effective in inhibiting biological growth for a prolonged period of
time. In the case of the biocide that is coated on the surface of
the membrane, the biocide may remain effective for a prolonged
period depending upon a number of factors that vary with the
construction and configuration of the diffuser and the conditions
of the wastewater.
[0025] The present invention contemplates biocially treated
membranes having configurations other than the tubular or
cylindrical configuration of the membrane 22. By way of example,
disk type diffusers having a diffuser body presenting a plenum that
is covered by a disk-shaped membrane can make use of a biocidally
treated membrane in accordance with the present invention. With
this type of diffuser, the membrane collapses to a flat condition
covering the plenum in the absence of air pressure, with the
aeration slits closing to prevent seepage of wastewater into the
plenum and the aeration piping of the system. When air pressure is
applied, the air flows to the plenum and causes the membrane to
expand or bulge outwardly, thereby opening the aeration slits and
allowing the air to discharge into the wastewater in the form of
fine bubbles which are efficient for the aeration and mixing
function of the aeration system. The effect of the biocidal agent
in connection with a membrane of a disk type diffuser is
substantially the same as in the case with a tubular membrane such
as a membrane 22. References to elasticity herein means the
tendency of the material to revert to its original shape after
having been deformed.
[0026] From the foregoing it will be seen that this invention is
one well adapted to attain all ends and objects hereinabove set
forth together with the other advantages which are obvious and
which are inherent to the structure.
[0027] It will be understood that certain features and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. This is
contemplated by and is within the scope of the claims.
[0028] Since many possible embodiments may be made of the invention
without departing from the scope thereof, it is to be understood
that all matter herein set forth or shown in the accompanying
drawings is to be interpreted as illustrative, and not in a
limiting sense.
* * * * *