U.S. patent application number 09/756135 was filed with the patent office on 2002-06-13 for system for converting organic waste reservoirs into anaerobic digesters.
Invention is credited to Charbonneau, Robert.
Application Number | 20020070152 09/756135 |
Document ID | / |
Family ID | 4167878 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020070152 |
Kind Code |
A1 |
Charbonneau, Robert |
June 13, 2002 |
System for converting organic waste reservoirs into anaerobic
digesters
Abstract
The system for converting organic waste reservoirs into
anaerobic digester comprises an inflatable roof structure adapted
to be installed on a variety of reservoirs to seal it from the
atmosphere. The roof structure includes an inner gas-impermeable
membrane which is adapted to raise and lower with the level of
organic waste contained in the reservoir. A peripheral fold is
defined in the gas-impermeable membrane adjacent the inner surface
of the surrounding wall of the reservoir to form a downwardly
depending skirt which acts as a gas barrier to prevent gas leakage
along the inner surface of the reservoir. A gas removal unit is
also provided for removing biogas trapped beneath the
gas-impermeable membrane from the reservoir.
Inventors: |
Charbonneau, Robert;
(Longueuil, CA) |
Correspondence
Address: |
OGILVY RENAULT
1981 MCGILL COLLEGE AVENUE
SUITE 1600
MONTREAL
QC
H3A2Y3
CA
|
Family ID: |
4167878 |
Appl. No.: |
09/756135 |
Filed: |
January 9, 2001 |
Current U.S.
Class: |
210/170.08 ;
210/170.09 |
Current CPC
Class: |
C12M 41/40 20130101;
C12M 21/04 20130101; C12M 23/46 20130101; C12M 23/38 20130101; C02F
3/286 20130101; Y10S 210/09 20130101; C12M 23/36 20130101 |
Class at
Publication: |
210/170 |
International
Class: |
C02F 003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2000 |
CA |
2,328,015 |
Claims
1. A system for converting a reservoir into an anaerobic digester
in which organic waste contained in the reservoir can be at least
partly anaerobically decomposed, wherein the reservoir is of the
type having a surrounding containing wall, the system comprising a
roof structure adapted to be installed on the reservoir to seal the
reservoir from the atmosphere, said roof structure including a
gas-impermeable membrane adapted to extend over the organic waste
contained in the reservoir for trapping, beneath said
gas-impermeable membrane, gas generated during decomposition of the
organic waste in the reservoir, said gas-impermeable membrane
having a peripheral depending skirt adapted to extend downwardly
and inwardly of an inner surface of the surrounding containing wall
of the reservoir below a level of organic waste to prevent the gas
from escaping along the inner surface of the reservoir.
2. A system as defined in claim 1, wherein said gas-impermeable
membrane is adapted to be sealingly attached to the inner surface
of the surrounding containing wall of the reservoir.
3. A system as defined in claim 1, wherein said gas-impermeable
membrane is adapted to float on top of the organic waste to raise
and lower with the level of organic waste in the reservoir.
4. A system as defined in claim 1, wherein said gas-impermeable
membrane is adapted to be attached to the reservoir with a wall
overlying portion of said gas-impermeable membrane extending
downwardly along the inner surface of the surrounding containing
wall of the reservoir and a central portion of said gas-impermeable
membrane floating on top of the organic waste contained in the
reservoir, a fold being provided in said gas-impermeable membrane
about said central portion to form said downwardly depending skirt
and allow said central portion to raise and lower with the level of
organic waste, while preventing gas from escaping along the inner
surface of the surrounding containing wall of the reservoir.
5. A system as defined in claim 4, wherein said fold defines a
pocket having an open top end, said pocket being adapted to vary in
depth according to the level of organic waste in the reservoir.
6. A system as defined in claim 5, wherein liquid is provided
within said pocket to prevent the same from collapsing under the
pressure exerted thereon by the organic waste.
7. A system as defined in claim 5, wherein a ballast is provided
within said pocket to ensure that said fold remains settled in the
organic waste.
8. A system as defined in claim 3, wherein said roof structure
further includes an external cover extending over said
gas-impermeable membrane to prevent precipitation from entering
into the reservoir.
9. A system as defined in claim 8, wherein said external cover
comprises a liquid-impermeable membrane adapted to be installed on
the reservoir to form with said gas-impermeable membrane an
enclosed space in which a gas is provided under pressure such that
said liquid-impermeable membrane assumes a dome-shaped
configuration and said gas-impermeable membrane is pressed against
the inner surface of the surrounding containing wall of the
reservoir and the organic waste contained therein.
10. A system as defined in claim 4, wherein a floating structure is
provided at a periphery of said central portion of said
gas-impermeable membrane to preserve a relative position of said
wall overlying portion and said central portion.
11. A system as defined in claim 1, wherein a layer of insulating
material is provided on top of said gas-impermeable membrane to
maintain a desired temperature in the reservoir.
12. A system as defined in claim 11, wherein said layer of
insulating material includes a replaceable insulating foam which is
produced by a foam generator and directed in a cavity defined
between said gas-impermeable membrane and a retention membrane
extending thereabove.
13. A system as defined in claim 12, wherein a fold is defined in
said gas-impermeable membrane adjacent the inner surface of the
surrounding containing wall of the reservoir, said fold forming
said downwardly depending skirt, and wherein said gas-impermeable
membrane is sloped to cause liquid produced from collapsed
insulating foam to drain into said fold for subsequent
regeneration.
14. A system as defined in claim 13, wherein a foam destroying
barrier is provided at an entry end of said fold.
15. A system as defined in claim 12, wherein a plurality of vents
are defined in said retention membrane for releasing gases
generated from a degradation of said insulating foam while
preventing a liquid content of the insulating foam from escaping
therethrough.
16. A system as defined in claim 1, further including a gas removal
unit for removing the gas trapped beneath said gas-impermeable
membrane, said gas removal unit including a conduit connected to a
hole defined in said gas-impermeable membrane.
17. A system as defined in claim 16, wherein said roof structure
includes an inflatable roof, said gas-impermeable membrane forming
part of said inflatable roof such as to cause the gas generated
during decomposition of the organic waste in the reservoir to flow
through said conduit under a pressure exerted by the inflatable
roof.
18. A system as defined in claim 16, wherein said conduit includes
a coupling sleeve and a gas line in fluid communication with said
coupling sleeve, said coupling sleeve being sealingly connected to
said hole in said gas-impermeable membrane and supported thereon by
a floating structure.
19. A system as defined in claim 18, wherein said hole is defined
in a central area of said gas-impermeable membrane.
20. A system as defined in claim 18, wherein said floating
structure extends about said coupling sleeve and is discontinuous
to allow the gas to flow to the coupling sleeve.
21. A system as defined in claim 1, further including a submersible
pump beneath said gas-impermeable membrane for mixing the organic
waste and allowing the same to be discharged from the reservoir
without having to remove said roof structure.
22. An anaerobic digester comprising a surrounding wall forming a
digester vessel for containing an organic waste material, a roof
structure for sealing said digester vessel from the atmosphere,
said roof structure comprising a gas-impermeable membrane adapted
to extend over the organic waste contained in said digester vessel
for trapping, beneath said gas-impermeable membrane, gas generated
from a decomposition of the organic waste, said gas-impermeable
membrane having a peripheral depending skirt adapted to extend
downwardly and inwardly of an inner surface of said surrounding
wall of said digester vessel below a level of organic waste to
prevent the gas from escaping along said inner surface.
23. An anaerobic digester as defined in claim 22, wherein said
gas-impermeable membrane is adapted to float on top of the organic
waste to raise and lower with the level of organic waste in said
digester vessel.
24. An anaerobic digester as defined in claim 22, wherein said
gas-impermeable membrane is adapted to be attached at a peripheral
portion thereof to an upper portion of said digester vessel with a
wall overlying portion of said gas-impermeable membrane extending
downwardly along said inner surface of said surrounding wall of
said digester vessel and a central portion of said gas-impermeable
membrane floating on top of the organic waste contained in said
digester vessel, a fold being provided in said gas-impermeable
membrane about said central portion thereof to form said downwardly
depending skirt and allow said central portion to raise and lower
with the level of organic waste, while preventing gas from escaping
along said inner surface of said surrounding wall of said digester
vessel.
25. An anaerobic digester as defined in claim 24, wherein said fold
defines a pocket having an open top end, said pocket being adapted
to vary in depth according to the level of organic waste in said
digester vessel.
26. An anaerobic digester as defined in claim 25, wherein liquid is
provided within said pocket to prevent the same from collapsing
under the pressure exerted thereon by the organic waste.
27. An anaerobic digester as defined in claim 25, wherein a ballast
is provided within said pocket to ensure that said fold remains
settled in the organic waste.
28. An anaerobic digester as defined in claim 23, further including
an external cover extending over said gas-impermeable membrane to
prevent precipitation from entering into said digester vessel.
29. An anaerobic digester as defined in claim 28, wherein said
external cover comprises a liquid-impermeable membrane adapted to
be installed on said digester vessel to form with said
gas-impermeable membrane an enclosed space in which a gas is
provided under pressure such that said liquid-impermeable membrane
assumes a dome-shaped configuration and said gas-impermeable
membrane is pressed against said inner surface of said surrounding
wall of said digester vessel and the organic waste contained
therein.
30. An anaerobic digester as defined in claim 24, wherein a
floating structure is provided at a periphery of said central
portion of said gas-impermeable membrane to preserve a relative
position of said wall overlying portion and said central
portion.
31. An anaerobic digester as defined in claim 22, wherein a
replaceable layer of insulating material is provided on top of said
gas-impermeable membrane to maintain a desired temperature in said
digester vessel.
32. A system for converting an existing reservoir containing an
organic waste into an anaerobic digester, comprising an inflatable
roof structure adapted to be installed on the existing reservoir
for allowing anaerobic conditions to be reached therein, and a gas
removal unit for removing gas captured beneath said inflatable roof
structure from the existing reservoir.
33. A system as defined in claim 32, wherein said inflatable roof
structure includes an external membrane and an internal membrane
defining an enclosed space, and wherein a replaceable insulating
foam layer is provided within said enclosed space on top of said
internal membrane.
34. A system as defined in claim 32, wherein said gas removal unit
includes a conduit for conducting the gas captured beneath said
inflatable roof structure away from the existing reservoir under a
pressure exerted by said inflatable roof structure on the organic
waste contained in the reservoir.
35. A system for converting a reservoir containing organic waste
into an anaerobic digester, comprising a roof structure adapted to
be installed on the reservoir to seal the same from the atmosphere,
wherein said roof structure includes a gas-impermeable membrane
adapted to float on top of the organic waste to raise and lower
with a level of the organic waste while at the same time trapping
gas generated from the decomposition of the organic waste beneath
said gas-impermeable membrane.
36. A system as defined in claim 35, wherein said gas-impermeable
membrane is adapted to be attached at a peripheral portion thereof
to an upper end portion of the reservoir for extending downwardly
therefrom and inwardly of an inner surface of a surrounding wall of
the reservoir and then over a surface area of the organic waste.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to organic waste treatment
and, more particularly, to a system for converting organic waste
reservoirs into anaerobic digesters.
[0003] 2. Description of the Prior Art
[0004] Throughout the world where there is large hog livestock, the
management of the hog manure is problematic. The hog manure is
often stored and subsequently spread on fields as a fertilizer.
However, raw manure is quite toxic and detrimental to the
environment by polluting the air, the water and the soil. In order
to overcome this problem, the raw hog manure must be treated.
Accordingly, various treatment methods have been developed. One of
these methods consists in promoting the action of certain types of
bacteria contained in the hog manure so that these bacteria digest
the organic matter in transforming the latter into an inert and
deodorized fertilizer. The basic conditions of this digestion
process are the absence of air and the obtention of an appropriate
constant temperature. This process is characterized as anaerobic
digestion and is at the root of the present invention.
[0005] The raw hog manure is typically stored within cylindrical
concrete reservoirs. When such reservoirs are not covered, the
precipitation, e.g. rain, are allowed to fall into the reservoirs,
thereby increasing the volume of the manure and, thus, the cost
associated with the transportation thereof. Furthermore, the
presence of oxygen promotes the proliferation of a particular type
of bacteria that produce carbonic gas (CO.sub.2), which is
associated with nauseating odors. Open reservoirs also permit the
evaporation of the nitrogen contained in the raw manure, which
significantly reduces the fertilizing potential thereof.
[0006] Reservoirs containing other types of organic waste also
suffers from similar drawbacks. Accordingly, there is a need for a
new system which could be adapted to a variety of organic waste
reservoirs to convert the same into anaerobic digesters.
SUMMARY OF THE INVENTION
[0007] It is therefore an aim of the present invention to provide a
new system for converting a reservoir into an anaerobic
digester.
[0008] It is also an aim of the present invention to provide a new
roof structure which is adapted to seal a reservoir from the
atmosphere.
[0009] It is a further aim of the present invention to provide a
new sealing system which is adapted to be installed on a reservoir
to seal it from the atmosphere while allowing the recovery of the
biogas generated during the anaerobic transformation of the organic
waste contained in the reservoir.
[0010] Therefore, in accordance with the present invention, there
is provided a system for converting a reservoir into an anaerobic
digester in which organic waste contained in the reservoir can be
at least partly anaerobically decomposed. The system comprises a
roof structure adapted to be installed on the reservoir to seal the
reservoir from the atmosphere. The roof structure includes a
gas-impermeable membrane adapted to extend over the organic waste
contained in the reservoir for trapping, beneath the
gas-impermeable membrane, gas generated during decomposition of the
organic waste in the reservoir. The gas-impermeable membrane has a
peripheral depending skirt adapted to extend downwardly and
inwardly of an inner surface of a surrounding containing wall of
the reservoir below a level of organic waste to prevent the gas
from escaping along the inner surface of the reservoir.
[0011] In accordance with a further general aspect of the present
invention, there is provided an anaerobic digester comprising a
surrounding wall forming a digester vessel for containing an
organic waste material, and a roof structure for sealing the
digester vessel from the atmosphere. The roof structure comprises a
gas-impermeable membrane adapted to extend over the organic waste
contained in said digester vessel for trapping, beneath said
gas-impermeable membrane, gas generated from a decomposition of the
organic waste. The gas-impermeable membrane has a peripheral
depending skirt adapted to extend downwardly and inwardly of an
inner surface of the surrounding wall of the digester vessel below
a level of organic waste to prevent the gas from escaping along the
inner surface.
[0012] In accordance with a further general aspect of the present
invention, there is provided a system for converting an existing
reservoir containing an organic waste into an anaerobic digester,
comprising an inflatable roof structure adapted to be installed on
the existing reservoir for allowing anaerobic conditions to be
reached therein, and a gas removal unit for removing gas captured
beneath said inflatable roof structure from the existing
reservoir.
[0013] In accordance with a still further general aspect of the
present invention, there is provided a system for converting a
reservoir containing organic waste into an anaerobic digester,
comprising a roof structure adapted to be installed on the
reservoir to seal the same from the atmosphere, wherein said roof
structure includes a gas-impermeable membrane adapted to float on
top of the organic waste to raise and lower with a level of the
organic waste while at the same time trapping gas generated from
the decomposition of the organic waste beneath said gas-impermeable
membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Having thus generally described the nature of the invention,
reference will now be made to the accompanying drawings, showing by
way of illustration a preferred embodiment thereof, and in
which:
[0015] FIG. 1 is a schematic elevational cross-sectional view of a
liquid manure reservoir which has been converted into an anaerobic
digester by installing thereon a system in accordance with a
preferred embodiment of the present invention;
[0016] FIG. 2 is a schematic top plan view of a so formed anaerobic
digester comprising an inflatable roof structure including an outer
membrane and an inner gas-impermeable membrane, the outer membrane
being omitted for clarity;
[0017] FIGS. 3a to 3f are schematic enlarged partial elevational
views of the anaerobic digester illustrating the movement of the
inner gas-impermeable membrane with the level of liquid manure
contained in the reservoir;
[0018] FIG. 4 is a schematic elevational view of a gas removal unit
forming part of the system to remove gas entrapped beneath the
inner gas-impermeable membrane;
[0019] FIG. 5 is a schematic enlarged top plan view of a feed line
arrangement which can be used to direct liquid manure into the
reservoir beneath the inner gas-impermeable membrane;
[0020] FIG. 6 is a schematic enlarged cross-sectional elevational
view of the feed line arrangement of FIG. 5;
[0021] FIG. 7 is a schematic enlarged cross-sectional elevational
view of a detail of the system illustrating how the gas-impermeable
membrane is attached to the reservoir;
[0022] FIG. 8a is a schematic enlarged elevational view of a
portion of a foam generator used for producing a layer of
insulation material on top of the inner gas-impermeable
membrane;
[0023] FIG. 8b is a schematic enlarged elevational view of a
conduit forming part of the foam generator for directing
pressurized air into a liquid reservoir defined into a peripheral
portion of the inner gas-impermeable membrane; and
[0024] FIG. 9 is a schematic enlarged elevational view of a side
wall of a retention membrane extending over the gas-impermeable
membrane to retain the insulation foam material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] FIG. 1 illustrates a system 10 for converting a variety of
reservoirs into anaerobic digesters, wherein organic waste, such as
liquid manure, contained in the reservoirs can be anaerobically
decomposed to produce methane gas which can be collected for
subsequent utilization as a combustible agent, while the manure
remaining after decomposition can be used as a nutrient source.
[0026] As will be seen hereinafter, the present invention allows to
stabilize, deodorize, reduce pollution potential and add value to
organic waste, such as raw animal manure.
[0027] The system 10 generally comprises an inflatable roof
structure 12 adapted to be sealingly installed, for instance, on a
concrete cylindrical reservoir 14 to form therewith an anaerobic
digester. The reservoir 14 includes a surrounding containing wall
16 defining a chamber 18 in which liquid manure M can be introduced
via a feed line 20 (FIGS. 5 and 6) extending through the roof
structure 12 and into the reservoir 14 at a given location along
the circumference thereof. The system 10 may further comprise an
optional submersible pump 22 which can be used to agitate the
liquid manure M in the reservoir 14 and to withdraw the liquid
manure M from the reservoir 14 without having to remove the roof
structure 12 therefrom.
[0028] The inflatable roof structure 12 includes an outer
liquid-impermeable membrane 24 and an inner gas-impermeable
membrane 26. The outer and inner membranes 24 and 26 are adapted to
be attached to the reservoir 14 to form a closed volume 28
thereover into which pressurized air can be directed to inflate the
outer membrane 24 so that it forms a dome-shaped roof over the
reservoir 14 to prevent precipitation, e.g. rain, from entering
into the chamber 18 of the reservoir 14. The outer membrane 24 can
be made of a vinyl material or any other flexible structural fabric
which will resist to the elements. The inner gas-impermeable
membrane 26 is preferably made of a polyethylene material.
[0029] As best seen in FIGS. 1 and 3a to 3f, the inner
gas-impermeable membrane 26 extends across the chamber 18 and over
the liquid manure M to seal the chamber 18 from the atmosphere,
thereby allowing anaerobic conditions to be reached therein. More
particularly, the inner gas-impermeable membrane 26 is sealingly
attached at its peripheral edges to an upper portion of an inner
surface 30 of the surrounding containing wall 16 of the reservoir
14 and extends downwardly therefrom substantially along the inner
surface 30 of the surrounding containing wall 16 and then
horizontally over the liquid manure M contained in the chamber 18.
The inner gas-impermeable membrane 26 has a peripheral adjustable
wall overlying portion 32 and a central portion 34 extending
inwardly thereof and floating on top of the liquid manure M. A fold
36 is formed in the inner gas-impermeable membrane 26 about the
central portion 34 thereof adjacent the inner surface 30 of the
surrounding containing wall 16 of the reservoir 14 to provide a
peripheral depending skirt which extends below the level of liquid
manure M to allow the central portion 36 of the membrane 26 to
displace vertically with the level of the manure M and to act as a
barrier to prevent the biogas generated during the transformation
of the liquid manure M from escaping along the inner surface 30 of
the surrounding containing wall 16 of the reservoir 14. Ballast 38
(FIGS. 3a to 3f) is provided within the fold 36 to ensure that the
same will remain settled in the liquid manure M. The inner
gas-impermeable membrane 26 can be slightly conical to facilitate
the formation of the fold 36.
[0030] As schematically illustrated in FIGS. 3a to 3f, the depth of
the fold 36 will vary according to the level of liquid manure M
contained in the chamber 18, and the central portion 34, which acts
as a floating floor, will be allowed to raise and lower with the
level of liquid manure M, while still preserving the airtightness
of the chamber 18. When the level of the liquid manure M is low
(FIGS. 3a and 3b), the depth of the fold 36 is small and the
portion of the inner membrane 26 which is unfolded to form the wall
overlying portion 26 is great. In contrast, when the level of the
liquid manure M raises, the portion of the gas-impermeable membrane
26 overlying the inner surface 30 decreases and the depth of the
fold 36 increases, as generally shown in FIGS. 3a to 3f.
[0031] The fold 36 defines an open pocket 40 which is filled up
with a liquid 42 to prevent the pocket 40 from collapsing under the
pressure exerted thereon by the liquid manure M. If the pocket 40
was left empty, the opposed inner facing sides 44a and 44b of the
pocket 40 would very likely be pressed against each other,
resulting in frictional forces opposing to the mobility of the
central portion 34 of the inner gas-impermeable membrane 26.
[0032] Peripheral floating members 46 are provided about the
central portion 34 and inwardly of the fold 36 to preserve the
relative lateral position of the central portion 34 and the wall
overlying portion 32 of the gas-impermeable membrane 26. The
peripheral floating members 46 are attached to the inner side 44b
of the pocket 40 to support the ballast 38. The combined effect of
the peripheral floating members 46 and the ballast 38 will create a
tension on the central portion 34 so as to maintain the latter
slightly stretched at all time, which will contribute to push the
biogas generated during the anaerobic transformation of the liquid
manure M towards the center of the central portion 34. i.e. where
the resistance is less.
[0033] As seen in FIGS. 1, 2 and 4, the system 10 further includes
a gas removal unit 48 having a coupling sleeve 50 connected at a
first end thereof in fluid flow communication to a central opening
(not shown) defined through the central portion 34 of the
gas-impermeable membrane 26. The coupling sleeve 50 is connected at
a second opposed end thereof to a flexible hose 52 extending
outwardly of the reservoir 14 to convey the methane, which is
generated during the anaerobic transformation of the liquid manure
M and which is entrapped beneath the gas-impermeable membrane 26,
away from the chamber 18. When it is not desired to recover the
generated methane, the flexible hose 52 can simply open to the
ambient air, and the pressure within the closed volume 28 will
cause the methane to flow through the coupling sleeve 50 and the
flexible hose 52 to the ambient air. However, it is understood that
the flexible hose 52 can be connected to a pump (not shown) or the
like to draw the methane from the sealed chamber 18 and collect the
same in a tank (not shown)for subsequent use as a combustible
agent.
[0034] As best seen in FIG. 4, the coupling sleeve 50 is maintained
in a vertical orientation by a support structure 54 floating on top
of the inner gas-impermeable membrane 26 within the closed volume
28. The support structure 54 includes a number of floats 56
circumferentially distributed about the coupling sleeve 50. The
coupling sleeve 50 is structurally connected to the floats 56 by
means of flexible legs 58 extending from an upper end portion of
the coupling sleeve 50 to rigid discs 60 provided on respective top
surfaces of the floats 56. The legs 58 can be loosely connected to
the coupling sleeve 50 and pivotally mounted to respective discs 60
to allow the support structure 54 and the coupling sleeve 50 to
move relative to one another. The circumferential spaces between
the floats 56 allow the gas generated (the methane) by the
anaerobic transformation of the liquid manure M to flow to the
mouth of the coupling sleeve 50.
[0035] Referring to FIGS. 1, 2, 8a, 8b and 9, it can be seen that
the system 10 further includes an insulating foam generator 62
(FIGS. 1 and 2) adapted to be continuously or intermittently
operated to produce a replaceable insulating layer of foam liquid
64 (FIG. 1) on top of the central portion of the gas-impermeable
membrane so as to maintain the liquid manure M within the chamber
18 at a predetermined temperature. The thickness of the replaceable
foam layer 64 can be controlled according to the requirements of
each application.
[0036] The foam generator 62 includes an air pump 66 (FIGS. 1 and
2) mounted within the closed volume 28 and connected to a network
of tubes 65 (FIGS. 2, 8a and 8b) comprising a main circumferential
branch 68 from which depends a number of circumferentially
distributed branch segments 70. The lower end of each branch
segment 70 extends into the fold 36 below the level of liquid 42
contained in the pocket 40 thereof and defines an air outlet in
which an air stone 72 (FIG. 8b), such as those used in aquariums,
is provided to diffuse the air and, thus, promote the generation of
bubbles as air is supplied into the liquid 42 through the air
outlet. The liquid contained in the fold 36 can be provided in the
form of a foam producing liquid, such as liquid soap. By blowing
air from the pump 66 through the network of tubes 65 and into the
liquid 42, bubbles will emerged from the fold 36 and eventually
fill all the space between the central portion 34 of the
gas-impermeable membrane 26 and a retention membrane 74 (FIGS. 1,
2, 8a and 9) extending thereabove. If there is a gradual
degeneration of the so-formed foam layer 64, the liquid produced
from the collapsed foam will drain back into the fold 36 for
regeneration. The central portion 34 of the inner gas-impermeable
membrane 26 is preferably stretched so as to define a slope from
the center thereof to the fold 36 in order to ensure proper outward
drainage of the liquid into the fold 36.
[0037] The retention membrane 74 has a surrounding side wall 76
(FIGS. 8a and 9) which extends into the fold 36. As shown in FIG.
9, the lower edge portion of the surrounding side wall 76 can be
folded over to form a pocket 78 into which some of the liquid 42
will be entrapped, thereby offering a resistance to the withdrawal
of the surrounding side wall 76 from the fold 36. The pocket 78
also acts as a barrier for breaking the foam coming into contact
therewith. As shown FIG. 2, a plurality of vents 80 are defined in
the retention membrane 74 for releasing the air generated from the
degradation of the insulating foam while preventing escape of the
liquid content thereof. Each vent 80 can consists of a patch of
material which is liquidtight but permeable to gases.
[0038] As shown in FIGS. 1 and 2, the submersible pump 22 is placed
in a well 82 formed by a rampart 84 and the adjacent inner surface
30 of the surrounding containing wall 16 of the reservoir 14. The
wall overlying portion 32 of the inner gas-impermeable membrane 26
is deviated at this location so as to overly the rampart 84 rather
than the inner surface 30. A pneumatic plug 86 is provided within
the well 82 at the level of the liquid manure M to prevent gas
leakage. A sealing membrane 88 extends from an upper end of the
rampart 84 to the outer membrane 24 to preserve the integrity of
the closed volume 28.
[0039] As shown in FIGS. 5 and 6, the feed line 20 includes a
vertical pipe segment 90 extending downwardly into the reservoir 14
between the inner surface 30 of the surrounding containing wall 16
and the wall overlying portion 32 of the inner gas-impermeable
membrane 26. A seal 92 is provided about the vertical pipe segment
90 to limit gas leakage therealong, while allowing a slight leak in
order to evacuate any gas present where the wall overlying portion
32 of the inner gas-impermeable membrane 24 is deviated by the
vertical pipe segment 90.
[0040] As shown in FIG. 7, the inner gas-impermeable membrane 26
can be attached to the upper end portion of the inner surface 30 of
the surrounding containing wall 16 of the reservoir 14 by means of
brackets, one of which being shown at 94 in FIG. 7, secured at
circumferential spaced-apart locations on a top surface 98 of the
surrounding containing wall 16 of the reservoir 14 via appropriate
threaded fasteners 96. Each bracket 94 includes a flat arm portion
100 extending on top of the reservoir 14 and a C-shaped channel
member 102 welded to an undersurface of the flat arm portion 100 at
an inner distal end thereof. The C-shaped channel member 102 is
oriented so that its open side faces the inner surface 30 of the
surrounding containing wall 16 of the reservoir 14 once the flat
arm portion 100 has been secured on the top surface 98. The
peripheral portion of the inner gas-impermeable membrane 26 is
folded over so as to form a peripheral loop 104 into which a rope
106 is passed. A pipe 108 is provided within the C-shaped channel
member 102 to wedge the rope 106 against the inner surface 30 of
the surrounding containing wall 16 of the reservoir 14. A resilient
pad 110 or the like can be inserted between the inner surface 30 of
the surrounding containing wall 16 and the inner gas-impermeable
membrane 26 to improve the airtightness of the arrangement.
[0041] The outer membrane 24 is preferably secured on the outer
surface of the surrounding containing wall 16 by means of pipe (not
shown) wedging a rope (not shown), which is passed in a loop (not
shown)formed at the periphery of the outer membrane 24, against the
outer surface of the surrounding containing wall 16, as described
hereinbefore with respect to the inner gas-impermeable membrane
26.
[0042] Although the roof structure 12 has been described as being
inflatable, it is also contemplated to replace the outer membrane
24 by a rigid cover (not shown) . It is also understood that the
present invention is not limited to be used in conjunction with a
liquid manure reservoir but could be used with a large variety of
organic waste reservoirs as well.
* * * * *