CA2642174C

CA2642174C - High volume anaerobic digesting of organic material

Info

Publication number: CA2642174C
Application number: CA2642174A
Authority: CA
Inventors: Leslie G. Hill; Paul Jefferson; Philip Leduc; Bryan Lung; Patricia Lung
Original assignee: PRAIRIE AGRICULTURAL MACHINERY INSTITUTE
Current assignee: PRAIRIE AGRICULTURAL MACHINERY INSTITUTE
Priority date: 2008-10-28
Filing date: 2008-10-28
Publication date: 2017-04-25
Anticipated expiration: 2028-10-28
Also published as: CA2642174A1

Abstract

A system and method for anaerobic digestion of an organic material includes a bag in a collapsed position on a bag filling mechanism which receives organic material and inserts same into the bag. The bag filling mechanism moves forward such that a filled portion of the bag rests on the ground behind the bag filling mechanism. When the bag is filled it is released and sealed to prevent gas from leaving or entering the bag. Liquid mixed with anaerobically active bacteria is discharged into an upper portion of the bag such that the liquid flows downward through the organic material to the bottom of the bag where it is withdrawn and circulated back into the upper portion of the bag. A gas recovery conduit is connected to a top portion of an interior of the bag and gas generated in the bag is drawn off to a gas collection site.

Description

HIGH VOLLTME ANAEROBIC DIGESTING OF ORGANIC MATERIAL

This invention is in the field of anaerobic digestion and ~as recovery from various organic matter feed stocks, in particular a system for economically digestin~
hi~h volumes of or~anic matter. Improved aerobic compostin~ of the digested or~anic matter can be provided as well, BACKGROUND

In the process of anaerobic digestion, naturally occurring anaerobically active bacteria degrade organic material in the absence of air and release a gas comprising a mixture of carbon dioxide and methane. A wide variety of systems have been developed to promote and control this process and capture the gas for domestic and commercial use.

Basically the process requires that the material be sealed to exclude air, and then the organic material is inoculated by introducing bacteria. The bacteria multiply and dicrest the organic material, releasing the cras. As the bacteria multiply, the process accelerates and the rate of digestion, and resulting gas production, increases. Digestion and gas production peak at some point and then taper off as the organic material is digested.

In a simple batch diggester system, the subject organic material and a bacteria inoculum are placed in an airtight reactor container. Additional materials may be added to keep pH

2 in the preferred methane producing range of 6 to 7.5. The reactor is then sealed, and digestion is allowed to proceed for a period of time, which in a typical system might be 30 - 180 days, depending on ambient teniperature, organic material properties, and like conditions. During this period, the gas production builds up to a maximum, and then declines. When finished, the container is opened and the remaining digested solid material removed. This digested material, when exposed to the air, will further aerobically decompose or compost in the atmosphere due to the activity of aerobically active bacteria.

This digestion can be conducted on a liquid basis where solids content is typically 6 -10% or as "dry" digestion where solids content is greater than 20% up to about 32%.
Liquid organic material is more easily handled and managed, essentially as a slurry of solids carried in the liquid, and can also be readily used in continuous systems where fresh organic material is fed into the reactor container at one location and decomposed digested organic material is removed at a separated location.

Continuous systems increase efficiency, since once the anaerobic digesting process is proceeding, it can be maintained, in contrast to the batch systems where digestion builds up to a peak, and drops off. The liquid slurry products can also be handled relatively easily with pumps, piping, and tanks.

3 The reactor containers are provided by a variety of vessels including sealed tanks for liquid systems, or sealed buildings for dry systems. Impermeable plastic bags also provide economical vessels that are readily sealed to exclude air.

SLJMMARY OF THE INVENTION

It is an object of the present invention to provide a system for anaerobic di~estion and ~as recovery from various organic matter feed stocks that overcomes problems in the prior art. Further aerobic compostin- of the di-ested organic matter may be provided as well.

In a first embodiment the present invention provides a system for anaerobic digestion and gas recovery from an organic material. The system comprises a bag filling mechanism mounted for travel in an operating travel direction, an impenneable bag mounted in a collapsed position on the bag filling mechanism, and at least one conduit. The bag filling mechanism is operative to receive the organic material and insert the organic material into the bag such that as the bag filling mechanism moves in the operating travel direction, a filled portion of the bag rests on the ground behind the bag filling mechanism and an unfilled portion of the bag remains in the collapsed position mounted on the bag filling mechanism. The bag filling mechanism and the at least one conduit are configured such that, as the bag filling mechanism moves in the operating travel direction, the at least one conduit is inserted into the bag such that the filled portion of the bag contains a length of conduit extending therealong. The at least one conduit is operative to conduct fluid between an exterior location outside the bag and an interior location inside the bag.

4 A gas recovery conduit is connected to a top portion of an interior of a filled bag such that gas generated in the bag can pass into the gas recovery conduit.

In a second embodiment the present invention provides a method for anaerobic digestion and gas recovery from an organic material. The method comprises providing an impermeable bag mounted in a collapsed position on a bag filling inechanism;
operating the bag filling mechanism to receive the organic material and insert the organic material into the bag; moving the bag filling mechanism in an operating travel direction such that a filled portion of the bag rests on the jround behind the bag filling mechanism and an unfilled portion of the bag remains in the collapsed position mounted on the bag filling mechanism; filling the bag to a desired level, releasing the bag from the bag filling mechanism, and sealing the bag to substantially prevent gas from leaving or entering the bag; discharging liquid mixed with anaerobically active bacteria into an upper portion of the bag such that the liquid flows downward through the organic material in the bag;

drawing liquid from a bottom of the bag and circulating the liquid into the upper portion of the bag; and connecting a gas recovery conduit to a top portion of an interior of the bag and drawing gas generated in the bag through the gas recovery conduit to a gas collection site.

Large quantities of organic material can be efficiently placed into the bag, processed by introduction of appropriate ingredients into the sealed bag, and removed by simply slicing open the bag to provide access for excavators and like equipment.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof, preferred embodinients are provided in the accompanying detailed description which may be best understood in

5 conjunction with the accoinpanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where:

Fig. I is a schematic side view of an embodiment of a system of the present invention for anaerobic digestion and gas recovery froin an organic material;

Fig. 2 is a schematic side view of a filled bag of the system of Fig. 1 with conduits connected to a tank and a gas collection site;

Fig. 3 is a schematic sectional end view of the filled bag of Fig. 2;

Fig. 4 is a schematic sectional end view of a filled bag of a system where the second conduit is illustrated as being external to the bag, and also showing how a conduit can be incorporated into a wall of the bag..;

Fig. 5 is a schematic side view of a conduit showin- a variety of means for allowinj fluid to flow from an outside of the conduit to an inside of the conduit, and vice versa;

6 Fig. 6 is a schematic end view of an alternate bag where the bag is on an incline laterally and longitudinally such that liquid in the bag drains to low spot;

Fig. 7 is a schematic side view of the ba- of Fig. 6;

Fig. 8 is a top view of a plurality of systems set up adjacent to a tank;

Fig. 9 is a schematic top view of an alternate embodiment of the system of the invention where the first conduit is external to the bag;

Fig. 10 is a schematic side view of the embodiment of Fig. 9;
Fig. 11 is a schematic end view of the embodiment of Fig. 9.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Fig.1 illustrates a side view of an embodiment of a system 1 of the present invention for anaerobic digestion and gas recovery from an organic material, such as manure, straw, wood chips, or the like and mixtures thereof, and may include other organic waste materials or biomass from crops produced for energy production.

The system I comprises a bag filling mechanism 3 mounted for travel in an operating travel direction T. Such bag filling mechanisms are known in agricultural industries and

7 are used for receiving agricultural products such as grains, silage, and the like and pushing the received material into a plastic bag for storage, sealed away from the elements. In the illustrated embodiment the bag filling mechanism 3 is mounted on wheels, and is towed and powered by a tractor or like vehicle.

An impermeable ba- 5 is mounted in a collapsed position 5A on the ba- filling mechanism 3. The bag filling mechanism 3 is operative to receive the organic material 7 and insert the organic material into the bag 5. As the bag filling mechanisin 3 moves in the operating travel direction T, a filled portion 5B of the bag 5 rests on the ground behind the bag filling mechanism 3 and an unfilled portion of the bag 5 remains in the collapsed position 5A mounted on the bag filling mechanism 3.

The bag filling mechanism 3 is configured such that, as the bag filling mechanism 3 moves in the operating travel direction T, a conduit 9 is placed into the bag 5 such that the filled portion 5B of the bag 5 contains a length of conduit 9 extending therealong.

A filled bag 5 with the bag filling mechanism detached is shown in Fig. 2. The end of the bag 5 is sealed to prevent air or like gases from entering or leaving the bag S.

In the illustrated embodiment a first conduit 9A is placed into the filled portion 5B of the bag 5 at a bottom location therein. The first conduit 9A is placed such that same generally lies along the bottom of the bag 5, and has an outer end 11 located outside the bag 5 so that the conduit 9 is operative to conduct fluid back and forth as required

8 between an exterior location outside the bag 5 and an interior location inside the bag 5.
As seen in Fig. 3, the illustrated bag 5 is placed on a slightly inclined ground surface 6 so that liquid will run alon- the bottom of the bag 5 to the first conduit 9A
located along the low side of the bag 5.

A second conduit 9B is connected to discharge liquid into an upper portion of the bag 5.
In the illustrated system 1, the second conduit 9B is placed into the filled portion of the bag 5 at a top location therein, essentially runnin~ alon~ the bag just under the bag 5 and on top of the organic material 7 filling the bag 5, as illustrated in Fig. 3.

Fig. 4 schematically illustrates an altemate arrangement where the second conduit 9B is located outside the bag 5 and is connected to outlets 19 located at intervals along and inside the bag 5.

The conduits 9 can be configured to conduct fluid between the inside and outside of the bag 5 in numerous ways. As schematically illustrated in Fig. 5 the conduits 9 can include a plurality of screened sections 13 configured such that fluid can pass through the screen.
Sections of conduit 9 could also include a plurality of holes 15 pierced through the wall of the conduit 9 such as in a weeping tile. Porous sections 17 could also be provided in the conduit 9. It may be desirable to use a weepina tile for a conduit, with holes 15 pierced along the entire length thereof, or a soaker hose type conduit which is porous along its entire length.

9 The system 1 thus is arranged such that liquid can be put into the top of the bag 5 such that the liquid filters down through the organic material 7 inside the bag 5 and into the first conduit 9A at the bottom of the bag 5 where it can be drawn out of the bag 5. The liquid used will typically be water mixed with anaerobically active bacteria and other ingredients such as enzymes, chemicals to adjust pH, and like ingredients selected to promote anaerobic digestion of the orjanic material 7 in the bag S.

As anaerobic digestion proceeds, gases such as methane are generated in the sealed bag 5, and a gas recovery conduit 21 is connected to the top portion of the interior of the filled bag 5 as illustrated in Fig. 2, such that gas generated in the bag 5 can pass into the gas recovery conduit 21 and from there to a gas collection site 22.

The conduit 9A in Fig. 1 comprises a plurality of substantially straight pipe sections 23 that are connected together as the bag filling mechanism 3 moves in the operating travel direction T such that the outer end 1 I of the conduit 9A remains forward of the bag. The conduit 9B in Fig. I is mounted in a roll 27 on the bag filling mechanism 3 and unrolls as the bag filling mechanism 3 moves in the operating travel direction T such that an outer end 29 of the conduit 9B remains outside the bag. A further alternate conduit 9C is schematically illustrated in Fig. 4 where the conduit 9C is integrated into an interior side of a wall of the bag 5 such that as the bag moves from the collapsed position to a filled position, the conduit 5 is placed inside the bag 5 and an open end thereof is accessible for connection as required. The conduit 9C is conveniently provided by fixing the edges of a strip of material on the inner surface of the wall of the bag with adhesive, plastic welding, or the like.

When the bag 5 is filled and sealed, as illustrated in Fig. 2, the outer ends 11, 29 are thus 5 available for connection to a tank 31 such that liquid can be circulated from the tank 31 through the first and second conduits 9A, 9B and back to the tank 31. The tank 31 will contain liquid that is typically water mixed with anaerobically active bacteria and other selected ingredients. A heater 33 can be provided to heat the liquid contained in the tank 31 if desired to promote the growth of anaerobic bacteria, and to promote anaerobic

10 digestion of the organic material that the liquid passes through.

Figs. 6 and 7 schematically illustrate a bag 105 wherein the system is configured to be positioned on an ground surface 106 inclined both longitudinally and laterally such that liquid will flow along a bottom inside surface of the bag 105 to a low point of the bag wherein a port 141 is provided such that the liquid can be removed from the bag at the low point and be circulated back into the top of the bag at intervals as described above.

A method of the present invention for anaerobic digestion of an organic comprises providing an impermeable bag 5 mounted in a collapsed position 5A on a bag filling mechanism 3, operating the bag filling mechanism 3 to receive the organic material 7 and insert the organic material 7 into the bag 5, and moving the bag filling mechanism 3 in an operating travel direction T such that a filled portion 5B of the bag 5 rests on the ground behind the bag filling mechanism 5 and an unfilled portion of the bag remains in the

11 collapsed position 5A mounted on the bag filling mechanisin 3, all as shown generally in Fig. 1. One the bag 5 is filled to a desired level, the bag 5 is released from the bag filling mechanism 3 and sealed to substantially prevent gas from leaving or entering the bag 5.

Liquid mixed with anaerobically active bacteria is dischar~ed into the upper portion of the bag 5 such that the liquid flows downward through the organic material 7 in the bag 5 to the bottom of the bag 5 where it is withdrawn and circulated back into the upper portion of the bag 5. Anaerobic digestion of the organic material 7 proceeds, generating ;as in the bag 5 under some degree of pressure. The gas recovery conduit 21 is connected to a top portion of an interior of the bag 5, typically as illustrated through po s rt 24 at intervals along the bag 5, and gas generated in the bag is drawn through the gas recovery conduit 21 to the gas collection site 22. It is contemplated that where digestion activity is high, the pressure of the gas in the bag 5 may be sufficient to raise the top of the bag 5 above the top of the organic material 7 in the bag 5 and facilitate movement of the gas along the gap between the bag 5 and the organic material 7 to the gas conduit ports 24.

In the system 1 of Fig. 1, suitably prepared liquid is placed in the tank 31 and is circulated into the upper portion of the bag 5, filters down through the organic material and is drawn from the bottom of the bag back into the tank 31. It may be desirable in many climates to heat the liquid in the tank 31 to promote activity. Heat can conveniently be generated using a portion of the gas collected from the bag.

12 The system I is thus operated for a period of time, days or weeks as the conditions vary, by drawing liquid from the bottom of the bag 5 and circulating the liquid into the upper portion of the bag 5, either continuously or periodically, and drawin; gas generated in the bag 5 through the jas recovery conduit 21 to the gas collection site 22 until the generation of gas drops to a selected level.

When gas generation falls to a reduced or negligible level in conventional anaerobic digesting containers, the process is usually considered finished, and the decomposed or-anic material is removed from the container.

In the present invention, however, the flow of liquid into the upper portion of the bag 5 is stopped and liquid remaining in the bottom of the bag 5 is drawn into the tank 31. A
compressor 37 or like air pump is then operated to pump air into the bag 5 through the first conduit 9A, or through the second conduit 9B, or through the gas recovery conduit 21, or through all the conduits to create an aerobic atmosphere inside the bag 5 such that aerobic bacteria are provided with oxygen and become active to aerobically compost the organic material 7 in the bag.

During acoinposting period, the org-ariic inalerial 7 uiidergoes fu.rther i;hemical changes which rencter the organic inaterial, susceptible io turther anaerobic dig:stion and jas generation. The composting can be completed at this stage to produce a usable compost product or optionally further cycles of digestion and composting can be conducted after the initial composting period by drawing air out of the bag 5 and then injecting carbon

13 dioxide into the bag 5 through one or more of the conduits to enhance anaerobic conditions in the bag 5.

Liquid from the tank 31 is again circulated into the upper portion of the bag 5, and flows through the bag to be drawn from the bottom of the bag into the tank 31, and gas jenerated in the bag is drawn through the gas recovery conduit 21 to the gas collection site 22 until the generation of gas again drops to a selected level. These anaerobic digesting and aerobic composting cycles can be repeated until the organic material 7 has achieved a desired level of decomposition, and the process is thus considered to be finished, and the organic material is spent.

The external components of the system 1 are then removed, and then the bag 5 is sliced open, in a manner similar to that used for conventionally bagged agricultural products such as silage and grain, to provide access to remove accessible interior components and to provide access for an excavating machine to remove the decomposed or spent organic material 7 from the bag.

A centrally located tank 31 can be used to supply liquid to a plurality of bags 5. It is contemplated that the bags 5 will be placed relatively close together on the ground, or even inside in a building where the weather aets very cold, as schematically illustrated in Fig. 8. The tank 5 can be connected to circulate to each bag 5, and as bags 5 are emptied and removed, new bags can be placed in the removed bags' locations. Thus the liquid, which contains high levels of anaerobic bacteria and other desirable ingredients can be

14 saved for continuous use. There are thus also no issues with respect to the safe disposal of the liquid.

Figs. 9 and 10 schematically illustrate an alternate embodiment of the invention comprising. Ports 241 are provided through the wall of the bag 205 at intervals along a bottom portion of the bag 205. Pipe sections 243 are pushed through the ports 241 under or into the organic material 7 and sealed to the wall of the bag 5. The pipe sections 243 are screened or pierced or open such that liquid can flow through the pipe sections 243 and into a connected first conduit 209A lying on the jround adjacent to the bag 205.

Liquid is drawn from inside the bag 205 out through the ports 241 and into the first conduit 209A for carriage to the tank. An external second conduit 209B, and an external gas recovery conduit 221 run along the top of the bag and are connected at intervals to the interior of the bag 205 to circulate liquid into the upper portion of the bag 205, and take gas to the gas collection site as described above.

The present invention provides a convenient and economic apparatus and method for digesting, and if desired further composting, organic material. The organic material can be from a variety of sources, and may require some processing or mixing in order to be handled by the bag filling mechanism, and the bag filling mechanism will typically be configured for the particular material being used. Such bag filling mechanism as are known in the art process a variety of material of various textures and compositions such as wet silage and dry grain, and it is contemplated that modifications to the bag filling mechanism and/or processing or mixing the organic material will allow the use of a wide variety of or~anic material.

In conventional solid or dry organic material digesting systems, movinj the dry material 5 into and out of a sealed chamber is problematic, and in large scale operations it is common to use a sealed buildina, with large doors to accommodate the large excavators needed to efficiently move organic material into and out of the building.
Sealing such buildin~s is problematic, and the gas ?enerated in such buildings is hazardous.

10 The present invention uses existing technology where, for example, large plastic bags are readily available at an economic cost level. Very large scale digestion can be carried out, and a single tank, a few pumps, and the like can be used to service a large number of bags which can be rotated as they are filled, processed, and then emptied.

15 The foregoing is considered as illustrative only of the principles of the invention.
Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention.

Claims

What is claimed is:

1. A
system for anaerobic digestion and gas recovery from an organic material, the system comprising:
a bag filling mechanism mounted for travel in an operating travel direction;
an impermeable bag mounted in a collapsed position on the bag filling mechanism;
first and second conduits;
a gas recovery conduit;
wherein the bag filling mechanism is operative to receive the organic material and insert the organic material into the bag such that as the bag filling mechanism moves in the operating travel direction, a filled portion of the bag rests on the ground behind the bag filling mechanism and an unfilled portion of the bag remains in the collapsed position mounted on the bag filling mechanism;
wherein the bag filling mechanism and the first conduit are configured such that, as the bag filling mechanism moves in the operating travel direction, the first conduit is placed into a bottom portion of the bag such that the filled portion of the bag contains a length of the first conduit extending therealong; and wherein the gas recovery conduit is connected to a top portion of an interior of a filled bag such that gas generated in the bag can pass into the gas recovery conduit;
wherein the first conduit has an outer end located outside the bag, and the second conduit is connected to a liquid tank and is configured to discharge liquid into an upper portion of the bag

2. The system of claim 1 wherein the second conduit is placed into the filled portion of the bag at a top location therein.

3. The system of claim 2 wherein the second conduit comprises a porous length such that liquid is discharged through the porous length into the bag.

4. The system of claim 1 wherein the second conduit is located outside the bag and is connected to at least one outlet located inside the bag.

5. The system of any one of claims 1 - 4 wherein the first conduit comprises a plurality of screened sections configured such that fluid can pass through the screens.

6. The system of any one of claims 1 - 5 wherein at least one of the first and second conduits comprises a plurality of substantially straight pipe sections that are connected together as the bag filling mechanism moves in the operating travel direction such that an outer end of the at least one conduit remains forward of the bag.

7. The system of any one of claims 1 - 5 wherein at least one of the first and second conduits is mounted in a roll on the bag filling mechanism and unrolls as the bag filling mechanism moves in the operating travel direction such that an outer end of the at least one conduit remains outside the bag.

8. The system of any one of claims 1 - 3 and 5 - 7 wherein at least one of the first and second conduits is integrated into an interior side of a wall of the bag such that as the bag moves from the collapsed position to a filled position, the at least one conduit is placed inside the bag.

9. The system of any one of claims 1 - 8 further comprising a tank and wherein the first and second conduits are connected to the tank such that liquid can be circulated from the tank through the first and second conduits and back to the tank.

10. The system of claim 9 further comprising a heater operative to heat the liquid contained in the tank.

11. A
method for anaerobic digestion and gas recovery from an organic material, the method comprising:
providing an impermeable bag mounted in a collapsed position on a bag filling mechanism;
operating the bag filling mechanism to receive the organic material and insert the organic material into the bag;
moving the bag filling mechanism in an operating travel direction such that a filled portion of the bag rests on the ground behind the bag filling mechanism and an unfilled portion of the bag remains in the collapsed position mounted on the bag filling mechanism;
as the bag filling mechanism moves in the operating travel direction, placing a first conduit into the bag at a bottom location therein such that the filled portion of the bag contains a length of the first conduit extending along a bottom location in the bag, and such that an outer end of the first conduit is located outside the bag, wherein the first conduit is configured such that liquid can pass through a wall of the first conduit from the organic material in the bag into the first conduit;
filling the bag to a desired level, releasing the bag from the bag filling mechanism, and sealing the bag to substantially prevent gas from leaving or entering the bag;

discharging liquid mixed with anaerobically active bacteria into an upper portion of the bag such that the liquid flows downward through the organic material in the bag;
drawing liquid from a bottom of the bag through the first conduit and circulating the liquid into the upper portion of the bag; and connecting a gas recovery conduit to a top portion of an interior of the bag and drawing gas generated in the bag through the gas recovery conduit to a gas collection site.

12. The method of claim 11 wherein the liquid mixed with anaerobically active bacteria is discharged into the upper portion of the bag from a second conduit connected to discharge liquid into an upper portion of the bag.

13. The method of claim 12 wherein the second conduit is placed into the filled portion of the bag at a top location therein.

14. The method of claim 12 wherein the second conduit is located outside the bag and is connected to at least one outlet located inside the bag.

15. The method of any one of claims 11 - 14 comprising providing a tank containing a quantity of liquid mixed with anaerobically active bacteria, drawing the liquid from the bottom of the bag through the first conduit into the tank, and circulating the liquid from the tank into the upper portion of the bag.

16. The method of claim 15 comprising filling a second bag with organic material and circulating liquid from the tank to the second bag.

17. The method of any one of claims 15 and 16 comprising heating liquid in the tank to a desired level prior to circulating the liquid into the upper portion of the bag.

18. The method of any one of claims 15 - 17 comprising;
drawing liquid from the bottom of the bag and circulating the liquid into the upper portion of the bag, and drawing gas generated in the bag through the gas recovery conduit to the gas collection site until a rate of gas generation drops to a selected rate;
stopping flow of liquid into the upper portion of the bag and drawing liquid remaining in the bottom of the bag into the tank;
pumping air into the bag to create an aerobic atmosphere inside the bag such that aerobic bacteria are active to aerobically compost the organic material;
after a composting period, drawing air out of the bag and then injecting carbon dioxide into the bag to enhance anaerobic conditions in the bag; and circulating liquid from the tank into the upper portion of the bag, and drawing liquid from the bottom of the bag into the tank, and drawing gas generated in the bag through the gas recovery conduit to the gas collection site until the generation of gas again drops to a selected rate;
repeating anaerobic digesting and aerobic composting cycles until the organic material has achieved a desired level of decomposition.

19. The method of claim 18 wherein the air is pumped into the bag through the first conduit.

20. The method of any one of claims 11 - 19 comprising, when the organic material has achieved the desired level of decomposition, slicing the bag open to provide access for an excavating machine, and operating the excavating machine to remove decomposed organic material from the bag.

21. The method of any one of claims 11 - 20 wherein the ground behind the bag filling mechanism on which the filled portion of the bag rests is an inclined ground surface such that liquid will flow along a bottom inside surface of the bag to a low point of the bag, and wherein a port is provided at the low point of the bag such that the liquid can be removed from the bag through the port.