CA2051756A1 - Garbage dump - Google Patents

Abstract

Abstract of the Disclosure Title: GARBAGE DUMP

A waterproof cover is placed over the garbage heap, and the heap rests in a sealed basin. A collection system collects liquids and sludges at the base of the heap and sprinkles the liquid on top of the heap. The liquid collection system includes a tower, whereby liquid may be drawn off above a layer of accumulated sludge. A gas collection system collects methane etc rising in the heap. An air distribution system supplies air underneath the heap, through independent outlets. A heating system, powered by the collected methane, corrects any cool spots in the heap.
Bio-chemical parameters are computer controlled. The heap of garbage accordingly undergoes rapid decomposition, and the dump can then be re-used. The garbage is pre-sorted, whereby the decomposed material is suitable as fertiliser.

Description

- 1 - 2051~6 ~A~BA~E ~UMP

This invention relates to the treatment o~ dumped garbage.

The invention is particularly applicable to the treatment of household ~arbage, being garbage which includes only very small quantities of poisonous chemicals or toxic materials, if any.

The invention is particularly applicable to the treatment of garbage which has been pre-separated for the purpose of eliminating non-degradable items.

The invention is particularly applicable to the treatment of garbage which has been passed through a shredder, whereby ths garbage is shredded into small pieces. Shreddin~ greatly assists the degradation process.

BACKGROUND TO THE INVENTION

It has come to be recognized that garbage should not simply be dumped in an abandoned quarry. Abandoned guarries have tended in the past to be the most preferred sites, but concern is growing over the seepags o~ liguid contaminants from such a dump into the surroundin~ groundwater.
Abandoned quarries are o~ten below the water table, and contain standing water uhich is in communication with

- 2 - ~051756 groundwater.

When an old quarry is not available, it has been the general rule that garbage has simply been du~ped on the ground, usually in whatever depressions, basins, or other hollows are available: such hollows o~ten contain run-off strea~s, and again concern is growing that the downstream groundwater ~ay become conta~inated, not only by whatever poisonous liquids may have been present in the dumped garba~e, but also by the liquids e~anating from the garbage as it decomposes.

The emphasis, in past and present garbage dump systems, has been to ensure that the top of a dump is covered over (when the dump is Pull) so that the du~p is rendered unobtrusive.
Little attention has been paid, in the past, to preventing household garbage du~ps from contaminating the surrounding groundwater. The hollows, etc, in which household garbage has been placed have not generally been sealed in any way ~rom the surrounding soil.

On the other hand, containers which are sealed against leakage into the surrounding soil do of course exist. Aside from ~arbage dumps, many industries have the problem o~
handling contaminated effluent watsr. Often, in those industries, the uater is stored in a container formed in the ground, where the container is sealed against leakage into the surrounding soil.

20517~6 It is the practice for these containers to co~prise lagoons or settling ponds~ the botto~ of which is sealed against leakage. Conventionally, the ssaled floor of the lagoon is created by adding one or ~ore layers of co~pacted shredded clay into the bottom of a hollow form in the ground.

A seal created by a layer o~ clay is not proof against a pressure build-up of water from outside and below the lagoon; such a pressure build-up, if it were to develop, would rupture the clay layer. Generally, however, there is always a level of water contained within the lagoon, which means that the clay is always subiect to a greater pressure inside the lagoon than out. Therefore, it is not necessary to build a lagoon in an area that is above the natural water table.

DESCRIPTIO~ OF THE GENERAL FEATURES OF THE INVENTION

In the invention, the garbage is placed in a basin, and the basin is sealed by ~eans of an impermeable sealing means.
The sealing means is effective to prevent any liquids in the garbage ~rom entering, and mixing with, the groundwater in the surrounding ground.

In the invention, a conventional layer o~ compacted shredded clay, or prefarably two such layers, may be used as the 205~756 sealing means.

A sealin~ cover or roof is put in place over the ~arbage.
Many co~munities have by-laws, or are ~ormulating them, under which dumped raw garbage cannot remain exposed to the atmosphere ~or ~ore than a pre-set period -- a few months, for exa~ple. The roof must in those cases be put in place within that period.

Thus the du~p should be small enough in size that, once a start has been ~ade on du~ping garbage into the s~aled basin, the du~p can be filled up, and finished, and the roof put in place, within that said period. Once filled, and roofed over~ the dump will be left for a period, for the garbage to deco~pose.

The residue that remains after the garbage has decomposed can itself be a valuable resource, insofar as the residue contains organic matter which can be re-cycled as fertilizer. Of course, the value of the residue as fertilizer is reduced if it contains more than a few percent of ~etal, plastics, or other non-degradable materials; this percentage is a function of the thoroughness with ~hich the ~arbage was pre-separated prior to being dumped.

The cover or roof is an impermeable seal. The seal is impermeable over the whole area of the dump, to the extent that rainwater and other precipitation cannot come into 2C~5~756 contact with the decompo~ing garbage in the dump.

It follows that the dump must be served ~ith a drainage means, by ~eans of which such precipitation is conve~ed away.

Since this precipitation water has not contacted the garbage, the precipitation water can generally be allowed to pass straight into the surrounding ~roundwater. This ~ay be contrasted with many conv~ntional dumps, in which precipitation falls straight onto, and through, the garbage;
or, if the duDp is covered, the cover is not completely waterproof and allows the precipitation to pass through and int~ the garbage.

Often, once a dump is in use, it is too lats to provide a ~aterproof cover. This is because, if a com~unity wishes its dump to be provided with a waterproof cover, it must also provide a means for collecting the precipitation that falls onto the cover, and a means for conveying that collected body of precipitation water away fro~ the site.
It can be very difficult, and expensive, to provide a precipitation collcction and drainage system as an add-on item after the dump is in place.

The floor of the basin in which the garbage is to rest is sealed in an impermeable manner, for the purpose of ensuring that any liquids present in the garbage cannot escape into the surrounding groundwater. Sinilarly, the garbage dump is roofed over and sealed in such a ~anner that rainwater and other precipitation is conveyed away without coming into contact with the garbage.

Thus J the garbage is contained between an impermeable floor and an impermeable roo~.

The dump includes a gas-collection sYstem, which will now be described.

Garbage, when it~deco~poses, of course produces gases.
Concerns are increasingly being raised concerning possible global greenhouse effects caused by effluent gases. The gas of main concern so far as garbage dumps are concerned i5 methane. Thus it is preferred, from an environmental point of view, that ths ~ethane not be allowed si~ply to escape into the atmosphere, but that a garbage dump should be provided with a ~eans for collecting the msthane it produces.

When mcthanc is burnt, carbon dioxids is created, which is another greenhouse gas. Howevsr, the quantity of carbon dioxide produced by burning a given guantity of msthane is seen as much less of a greenhouse threat than the methane.
Therefore it is better, fro~ the environ~ental point of view, to burn the methane than to allow the methane si.~ply to escape into the atmosphere. Also, when the ~athane is 2 [)S~756 burnt, it can be burnt as a fuel, and thus do useful work.

Before it can be burnt, however, the methane ~ust first be collected, and a ~eans is provided in the du~p for collectin the ~asss. The garbage is sealed between an i~perneable roof and an imper~eable ~loor: it is a si~ple ~atter therefore to contain and collect the gases. It is preferred that the floor and roof are brought together in a manner which provides a ga~-tight seal at the interface.

In any event, the gases cannot be allowed to build up a pressure within the bulk o~ the heap of garbage, because such a pressure ~ight disrupt the i~permeable roof. The decomposing garbage is sealed off from the at~osPhere, and from the surrounding ground, and it is recognized that a ~eans ~ust therefore be provided for venting the gases from the du~p.

The gas-collection syste~ therefore serves two purposes: (a) of preventing the gases generated by decomposition ~rom building up a disruptive pressure, and (b) of collecting the gases, thus pernitting the ~ethane content to be burnt. The methane need not be burnt at the site, but maY be piped away or other~ise disposed of.

In the dump of the invention, a liquid collaction and recirculating ~eans is also included, uhich will now be described.

20S~75t~

Garbage deco~poses at a much faster rate when it is wet.
The slowness of decomposition oP dry garbage may be shown by the fact that fifty-year--old ne~spapers extracted ~rom a dry region of a du~p have still b~en readable.

No water is allowed to seep into the garbage through the floor of the basin. Si~ilarly, no precipitation water is allowed to come into contact the garbage. The required moisture content there~ore comes from whatever li~uids are present in, and created by, the decomposing garbage.
Usually it will be necessary to supplement this with a supply of water from outside the dump This extra water, though, should not be regarded in any sense as a through-flo~ of water which must be disposed of.

Thus it is preferred that provision be made ~or the occasional quantity of make-up water to be added to the garbage.

In contrast, the dump should preferably be so designed that there is never a need to siphon off an excess of water from within the dunp. Even so, the prudent designer does acknowledge that sometimes calculations and predictions can be awry, and a du~p might someday contain an excess of liquid, which has to be removed fro~ the dump. The prudent desi~ner therefore provides a sealed holding tank for containing such an excess. In fact, in practice, the dump 205~5~
g site usually contains several dumps, all in various stages of construction and use~ and an excess of liquid, if such should arise in one of the basins, can be draine~ of~ into an adiacent basin, the floor of which has been sealed, but which has not as yet received garbage.

It may be noted that th~ basins o~ course will receive precipitation water both before and during the period o~
filling with garbageJ before the roof is applied, and such prscipitation cannot naturally escape. However, the dimensions o~, and the manner of use of, the basin will generally be such that the basin will be open to the sky only for a period of a few months, so that there is usually no possibility, in fact, of the basin overflowing due to an accrual of precipitation.

Therefore, the precautions that must be taken to prevent liquid overflowing ~ro~ the basins are not at all demanding.
Again, it should be pointed out that the dump should be sited at a place where the natural water- table is below the floor of the basin.

It is preferred that a level of liquid be present in the basin, ie that the lowest portions of the garbage are constantly under the liquid. The surroundin~ water table can theoretically be allowed to be as high as tha level of liquid in the basin, bearing in ~ind that the clay layer would immediately be at risk if the level of the water table - 10 - ~OSlt756 outside the layer were allowed to be above the level of liquid inside.

The liguid collection and recirculation syste~ as described includes a means (such as a network of collection pipes), prsferably situated at or near the lowest level of the garbage, for collectin~ liquid from the garbage, and for conveying the collected liquid to one or more collection points. The system also provides a means (eg a pump) for transferring the liquid thus collected to, or near, the highest levels of the garbage, and for distributing or sprinkling the liquid therefrom onto the garbage below.

The collection and recirculation system may be put in place in two separate phases. First, the network of collection pipes, or the like, is put in place in the basin, preferably resting on the floor of the basin, before any garbage is du~ped in the basin.

Second, while it is contemplated that the ~eans for sprinkling the collected liquid onto the top of the garbage might be put in place at the same time as the collection pipes are installed on the floor of the basin, it will, however, generally be more convenient to put the sprinkler system and the liguid-trans~er pipes into placc a~t~r the dump has been filled with garbage, and preferably at the same time as the roof is being placed on the dump. The sprinkler system and the transfer pipes can then be - 1 1 - Z05~56 incorporated into the roof structure.

The liquid collection and recirclllation system should be such that substantially all the garbags in the dump is kept wet, substantially all the time. Thus, the invention is aimed at providing a means for keeping the garbage wet, and yet no precipitation water enters the garba~e, and no liquid that has been in contact with the garba~e enters the surrounding groundwater.

It should be noted that as the years go by and the garbage decomposes the volums of the garbage will reduce. Therefore the impermeable roof should be so constructed as to accommodate this progressive falling in. Si~ilarly, the transfer pipes and the sprinkler system, if they are incorporated into the roof, or if they rest on the garbage, shoul~ be able to accommodate the fallin~ in. It is not essential that they do so automatically: ~arbage dump sites are generally managed by technical staff so that in practice the requirement is not for automation but that the drop in the level of the roof and associated components can be accommodated without resorting to expensive reconstruction work.

Another network of pipes, or the like, may be inoluded on or near the ~loor o~ the basin, in addition to the liquid-collection network. This other network allows air to be fed into the lowest levsls of the garbage. There are two - 12 - 2~5175~
r~asons for feeding air into the garbage: (a) that the che~ical and microbiological reactions which constitute the decomposition process are mostly accelerated if fresh air is percolated through the garbage, and (b) that the decomposition process is accelerated if the garbage is gently mechanically agitated ~ro~ time to time, and the fed-in air pro~otes such stirrings.

It is recognized that it is cost-ef~ective if the shape of the garbage du~p is small in plan-area and piled high, rather than being low and widely spread out. The reasons for this are: ~a) the mors the dump is high, rather than wide, the smaller will be the areas of the floor and roof that have to be sealed, and (b) the quantities of the pipes needed for the collection and distribution syste~s are reducad if the shape of the garbage dump is high, rather than wide. The garbage dump is ~ell constrained by the basin and the roof; the invention is thus aimed at providing a design o~ dump which lends itself to the efficient high-rather-than-wide shape.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

By way of further explanation of the invention, an exemplary embodi~ent of the invention will now be described with reference to the accompanying drawings, in ~hich:

205~75~i Fig 1 is a cross-section of a garbage du~p uhich incorporates the invention;

Fig 2 is a diagrammatic or pictorial view of the dump shoan in Fig l;

Fig 3 is a sectionsd view showing details, in close-up, of sealing ~langes o~ the dump o~ Fig l;

Fig 4 is a plan showing details of roof coverings of the dump of Fi~ l;

Fig 5 is a view corresponding to Fig Z showing a number of basins for dumps;

Fig 6 is a section of a modified dump;

Fig 7 is a cross-section o~ another dump;

Fig 8 is a cross-section o~ component o~ the dump o~ Fig 7;

Fig 9 is a view o~ a ~urther dump;

Fig 10 is a cross-section through a garbage dump having a modi~ied gas-collection system;

Fig 11 is a diagram of a heating-pipe layout which is incorporated into the dump of Fig lO;

2~5~;i6 Fig 12 i5 a detail o~ the floor of the dump of Fig 10;

Fig 13 is a cross-section of a component of the dump o~ Fig l;

Fig 14 i a diagram of an air-supply layout, using the compon~nts o~ Fig 13.

The apparatuses shown in the accompanying drawings and described below are exa~ples which embody the invention. It should be noted that the scope o~ the invention is de~ined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.

The manner in which a site is prepared for the dump ~ay be understocd from Fig 1. The site is excavated so as to create a basin 2, and the excavated material is piled around the basin to Por~ side-walls 3. The basin 2 should be totally surrounded, ie. there should be no gaps in the side-walls 3.

The surfaces o~ the side-walls 3 and of the floor 4 of the basin must be sealed and watertight with respect to the surrounding land and groundsoil. One manner in which this sealing can be effected will now be described.

205~t7S~;

A layer of clay 5 is applied directly over the excavated surface. One of the considerations ahen selecting the site for the dump would be the availability of suitable clay. In kesping with conventional procedures ~or for~ing watertight basins, the clay is shredded prior to application, and then co~pressed and s~oothed once in place. Pre~erably, two layers of the clay, each about 50 c~ thick, are put in place.

The clay layers 5 are continued in an unbroken manner to the tops o~ the side-walls 3.

A sheet of waterproof material 6, such as a thick film of plastic or rubber, is applied on top of the clay layer 5.
The ~aterproof sheet 6 is continuous, without gaps, over the whole area o~ the basin 2, and up to the tops of the sids-walls. In order to follow the size and contours of the basin, the sheet 6 may be made o~ glued-together sections.

The edges of the waterproof sheet 6 are secured at the tops of the side-ualls 3 in the manner indicated in Fi~ 3. A
trough 7 is for~ed in the concrete surround 8, and the edge of the sheet ~ is looped underneath a perforated drain collection pipe 9 (of conventional type). A concrete cover 10 rests on the pipe 9, thereby weighting down the edge of the sheet 6.

The above-described manner of sealing the basin ~ is very 2~s~s~

reliable and ef~ective, providing the clay layers 5 are well-supported. The site should be selected on the basis that the ground is stable, ie not liable to subsidence or crackin~, and on th~ basis that the watsr table is lower than the excavated depth of the basin. The clay layers S
cannot be expected to remain secure if a pressure of water were able to develop underneath the layers tending to push the layers upwards.

A typical dump would require that the ground be excavated to a depth in the region o~ 10 metres. Thus the site should be chosen on the basis that the local water table cannot rise to a level higher than 10 metrss below the nominal ground surface.

If such a site on high ground is not available, the invention may still be utilized, but in that case a means has to provided for pumping groundwater from below the clay layers. This is necessary in order to prevent any possibility of pressure build-up below the layers. In that cas~, th~ du~p ~ust be constantly monitored, throughout its life, to ~uard against possible pressure build-up underneath the clay.

The water that is pumped away from under the dump of course is natural groundwater, which can be du~ped in a river etc away fro~ the site. But if it should happen that liquids from ~ithin the dump have been allowed to leak throu~h the 2(~5~L756 bottom of the dump and into the surrounding groundwater, that groundwater is thereby conta~inated. In designing the du~p, great attention should be paid to eliminatin~
conditions that might damage the integrity of the seals.

Placed on the floor of the basin 2, over the waterproof material 6, is a layer 16 of old tires. The old tires of course ~re not de~ra~able; the tires serYe as a ~eans far protecting ths watsrtight laysrs 5,6 from possible damags caused by items placed in the basin 2. Ths tires may be stitched together for the purpose o~ maintainin~ a flat layer, if desired. The tires should be punctured, so that a bubble o~ air cannot accumulate in the tire, which might cause the tire to tend to rise and floa~.

It is contemplated that a network 18 of liquid collection pipes 20 is placed on the layer 16 of tires. The collsction pipes 20 are of ths conventional perforated type of plastic drain pip~s, being typically of 50 cm diameter. Each pipe 20 is surrounded by baskets 23 of crushed stone: these serve to protect the pipes 20 from possible da~age, and the crushed stone serves to filter any liquids flo~ing into the collection pipe 20.

The pipes 20 feed into a holding tank at collection station 25, fro~ which the collected liquids may be trans~erred by ~eans of a pump. The station 25 includes a means for monitoring and controlling the level of the liguid in the 2(~51756 basin 2.

Also placed on the ~loor of the basin is another network 30 of pipes. These pipes are connected to the outside air, and a means is provided for pumping the air into the basin. The pipes are o~ the perforated type, which allows the air to emerge at many outlet points all over the network 30. This system is described in more detail with re~erence to Figs 13 and 14.

The side-walls 3, typically, are built up to a height o~ 30 metres or so above the floor 4 of the basin 2. A roadway 32 is constructed on top of the side-wall 3.

The garba~e to be placed in the dump is household garbage which preferably has been pre-separated. Ite~s such as glass and plastic bottlss, for sxample, ~ay be separated out by each individual householder; ferrous metals may be separated in the same way, or by passing the garbage under a large magnet at the dump. The intention of the community should be that only degradable garbage is actually placed in the dump.

Incoming garbage Pro~ trucks using the roadway 32 is tipped into a garbage shredding ~achine, and conveyors convey the shredded garbage into the basin 2.

Gradually, a heap 36 o~ garbage accumulates in the basin 2.

21~5~56 The designer should set the size of the dump such that the heap fill5 the basin, and is piled high above the walls of the basin, in a period of a few months.

In conventional garba~e dumps, bulldozers or the like are used to spread the garbage out and to cover the garbage over ~ith soil, typically within a few hours of the ~arbage being dumped. In the dump as described, it is not the intention that the garbage be mixed with soil, but rather that the garbage will si~ply stay where it comes to rest from the conveyor (although bulldozers may be used to spread the shredded garbage around, if desired)~ The garbage is thus left exposed until covered over, not by bulldozed earth, but by ~ore incoming garbage. Under these circumstances/ many com~uniti~s have regulations stating that such a du~p must be covered within a period o~, say, a few months.

Once tha dump is ~ull, a cover or roo~ 38 is placed over the hsap of garbage. The roof 38 comprises a sheet 40 of rubber or other waterproof material. The sheet 40 should be completely watertight and without gaps over the whole area of the roof~ although the sheet may be made in several pieces and glued together.

The edges o~ the sheet 40 are brought out at the sides of the du~p, and are sealed into the troughs 7 in the sa~e manner as the edges of the sheet 6, as ~ay be seen in Fig 3.

2~35~756 After the dump is finishsd, and just before ths roof is put in place, a syste~ of gas collection pipes 43 (shown in dashed lines in ~ig 2) is placed on top of the garbage.
Thess collection pipes again are of the conventional perforated type, which allow gases to flow into the pipe all along the length o~ the pipe. The pipes 43 should be spaced at not too great a distance apart: ons of the purposes of collecting the gases within the dump is to prevent a gas pressure from building up, even locally, which could tend to lift the roof 38.

The pipes 43 connect to a vent 45. The gases may be burnt directly at the vent, or ~ay be led away and disposed of in some suitable manner.

Also before the sheet 4U is applied, the network of pipes 49 which co~prise a li~uid irrigation system is put in place over the garbage. These pipes 49 again are of the perforated plastic type, and allow liquids present in the pipes 49 to e~erge on top of the garbage, and to percolate down therethrough. A transfer pipe 50 is provided for transferring the liquids fro~ the collection station 25 to the irrigation pipes 49.

The transfer pipe 50 may be laid either above or below the sheet 40. Preferably, the pipe 50 is laid above the roof, for the following reason. The top of the dumpJ where the liquids emerge Prom the irrigation pipes 49, is typically 80 20S~7StS

~etres or ~ore above the floor of the basin, where the liquids are collected, and therefore the pressure head through which the liquid is to be pumped is 7 bars, or more.
Such high pressure requires that the piping be sturdy. It follows that the pipin~ used for the pipe 50 must be of the ri8id, ie non-~lexible, kind. As explained previously, the dump will collapse gradually as the garbage decomposes, and consequently the need will arise from time to time for the height or reach of the transfer pipe 50 to change. The ~ost convenient manner of shortening the length of a rigid pipe is by removing sections of the pipe. If the pipe 50 could be flexible, it might conceivably be placed under the roof, and the required changes in length be accom~odated within the flsxibility of the pipe. But when the pipe 50 is rigid>
access to the pipe 50 is required for romoving sections of the pipe, and therefore the pipe 50 should be outside the roof.

As the heap of garbage collapses, it will of course collapse unevenly to so~e extent. The irrigation pip~s 49 (and the gas collection pipes 43) will therefore be called upon to t~ist and bend. Because there is very little pressure capability re~uired of the pipes at the top of the dump, these piPes are made from flexible plastic, and can accommodate such movements without being damaged.

Both the vent pipe 45 and the liquid trans~er pipe 50 therefore pass through the covsr 40. Suitabls arrangements 5:~5~

are ~ade to seal the sh0et ~aterial at the holes through which the pipes pass.

Since access to the trans~er pipe 50 is reguired, it is preferred to build an access way alon~side the pipe. This way should be provided with a means for protec$ing the sheet 40 from being da~aged. Again, old tires ~ay be used ~or this purpose, the tires being stitched together to hold the~
in place (Fig 4). Again, the tires should be punctured, to prevent water accumulating, which could increase the weight oP the tires and cause dragging. The protected way as so constructed is robust, yet flexible, which is as reguired.

In fact, the whole sheet 40 may be covered over with stitched-together tires for protection, i~ desired. In addition, or alternatively, a layer of stitched-together tires may be placed under the sheet 40, on top of the garbage.

Usually, it will be preferred that the appearance of the rooP be rendered ~ore acceptable by the application of soil, grass, etc over the roof. For this purpose, a proprietary erosion-control ~at may be placed over the sheet.

The roof sheet 40 may be held in place by cables 69 passing over the cover (Fig 4)J the cables being connected to the surrounds 8. The cables 69 are spaced apart and depress the roof locally, whereby sheds are formed between the cables.

205175Ç`~

The gas pick-up pipes 43 ~ay prefsrably be placed in these sheds, where gas may be expected to accumulate.

Steps must be taken for handling the considerable run-off of precipitation ~ro~ the roof. The run-o~ must be collected and conveyed away ~rom the dump site. The manner in which this is done must be such that the run-off water does not come into contact with the garbage, nor with any liquids enanating from the garbage.

The roadway 3Z is built on top of the side-walls 3, together with the surrounds 8 and the troughs 7. The tops o~ the side-walls preferably should be sealed over to prevent run-off water passing into the side-wall (which might raise the wat~r table) and accordingly a plastic layer 52 is placed on top of the side-wall. The roadway 32 is built on top of the layer 52.

Swales 54 are provided at the sides of the roadway. These swales will contain and convey all the run-off water ~rom the dump, and should be dimensioned and constructed accordingly. The pipes 9 also serve to receive run-of~.
The run-off water, as described, is uncontaminated, never bein~ able to come in contact with the ~arbaga, nor with any liguids contained in the garbags, and can be allowed to pass straight into local rivers, streams, or sewers.

As shown in Fig 5, it will ~enerally be convenient to 2~5~ 5~, - 2~ -provide a num~er of dumps at a single site. Adjacent dumps are separated by common side-walls. Roadways can be placed on top of some of, or all of, the side-walls. If it should happen that the need arises for liquid from one of the dumps to be pumped out, for some unforeseen reason, the pumped-out liquid (which cannot be discharged to the environ~ent) can be transferred to an adiacent basin. In fact, an operational rule should be made that garbage cannot start to be entered into a particular basin until the adjacent basin has been prepared and its floor and ~alls have been sealed~

In the dump as described, the garbage liquid is sealed in, and the precipitation water is sealed out. It may be noted that the described means by which this is achieved are such that a community may, if it so decides, and even after a particular dump site is finished, return to the site and use the site in a much more intensive manner, as will now be described.

Fig 6 sho~s a multi-basin dump site, in which a new dump 56 has been added into the space between adjacent pre-existing finished du~ps 58. It will be noted that the liquid transfer pipes etc from the finished dumps ara all readily accessible, and therefore can easily be modified and re-routed. The ~as collection pipes and the irrigation pipes of the finished dumps 58 may, if desired, be left in place, and may or may not be coupled into the systems ~or the added dump 56; also, the roofs may be left in place, and the extra 2~5~75~

garbage simply piled on top.

Ths construction o~ the dumps, as described, makes it easy to arrange s~aling means, whersby any liquid present in the ne~ garbage cannot escape therefrom, and, when the new du~p is ~inished, makes it easy to arrange that run-off water therefrom is prevented from contacting either the old or the new garbage.

The described dump construction creates, as mentioned, the bene~its o~ a fast dscomposition rate, of oollecting gases from the dump, and of keeping the groundwater, the precipitation water, and the garbage liquid, all ~irmly separated; it will be understood that, even with those benefits, nevertheless the described manner o~ construction is vsrsatile enough to per~it a community to increase the capacity o~ its dump site far bey~nd that for ~hich the site was first designed, without compromising the anti-pollution gualities of the site. This versatility can be important in ti~es of rapid change in a community, when the temptation might be high to compromise pollution standards to permit growth.

In the dump described previously, the liquids e~anating from the garbage have been collected in the liquid collection pipes 20, arranged as a network upon the floor of the basin 2. As shown in Figs 7 and 8, other ~ays are contemplated of collecting the liquids emanating from the garbage.

~:~5~5fi The liquid material that sinks to the botto~ of the garbage can take the form of a thick sludge. It is therefore preferable that the liquid to be ~od through the ra-circulation and irrigation syste~ is drawn, not quite from the bottom of the garbage heap, but from a little higher up.
In the dump shown in Fig 7 the liquid is drawn off at a tower 70.

This sludge ~aterial, though not exactly impermeable, nevertheless imposes a considerable restriction to the flow of li~uid therethrough. Thus, when the liquid collection system consists of pipes laid upon the basin floor, there is likely to be a marked decline, as time passes, in the rate at which liquid can be drawn into the collsction system.

Furthermore, the fact that liquid is moving towards the liquid collection points means that the fine sludge ~aterial will be drawn there also. Another factor is th~t, if one of the collection points should become blocked by sludge (or by anything~ there is little that can be done to clear that collection point: a temporary clearance might be effected by blowing a blast of air through the collection pipe, but doing so would achieve little lasting effect. Besides, it would be difficult to concentrate a blast of air to the blocked point, as the air would tend to dissipate through the unblocked liquid collection points.

- 27 - 2~5~75~
The provision of the tower 70 avoids these difficulties.
Much of the construction of the dump of Fig 7 is as previously described, except that the tower 70 takes the place of the network 18 of liquid collection pipes. The tower co~prises innsr 72 and outer 73 concentric tubes.
5andwiched between these is a body 74 o~ suitable filter ~aterial. The inner and outer tubes 72,73 are perforated, to allow liquid to pa~s through from the garbage and into ths hollow chamber 76 within the inner tube. An immersion pump 78 is provided also in the cha~ber 76, from which liquid may be pumped upwards through a line 80.

The top of the tower 70 is covered with a roof 81. The tower 70, with the roof 81, is erected prior to garbage being admitted into the du~p.

On top of the tower 70 is a tube 83. The tube 83 is in sections, which are added progressively as the height of the heap of garba~e increases. The tube 83 is of solid (ie not perforated) plastic.

~hen the dump is finishedJ the topmost section of the tube ô3 protrudes above the garbage. As the sections were being added, the line 80 was also being extended, and the line 80 is now coupled to a spreader ring 85. The spreader is annular in shape, and rests on top of the garbage; and the spreader may, as shown in Fig 7, be incorporated into the roof 87. Distribution pipes 89 lead away from the spreader;

2~5~56 the pipes 89 are o~ the ~lexible perforated plastic kind, as previously described. Thus, by this arrange~ent, liquids collected in the tower ~ay be raised and distributed over the top of the garbage.

A level-control syste~ may be included, by means of which the pu~p 78 is operated automatically. Alternatively, the pump may be activated in response to ~easurements taken periodically o~ the ~oisture content of the garbage.

As the garbage decomposes, and the heap collapses, the spreader 85 ~ill start to descend. The line 80 should be so arranged as to be able to follow this movement. The distribution pipes 89, being flexible, ~ill easily cope with any distortions due to the ~act that the heap does not collapse quite evenly. The higher sections of the tube 83 may be removed from time to time as the level continues to fall.

As mentioned, the tower 70 is placed in the basin prior to garbage being ad~itted into the basin. A suitable support or foundation is required for the tower, and care should be taken that the integrity of the ~eans for sealing the ~loor of the basin is not compro~issd by the presence of the tower or its supports.

The height o~ the tower is determined by the height at which liquid is to be drawn fro~ the garbage.

2~5175~i - 2~ -Th~ Fig 7 tower and tube arrange~ent is not always preferred ~or large, high dumps. This is because the tube 83 is supported only from the top of the tower 70, and the tube 83 is there~ore quite vulnerable to such deflections as may occur due to the shifting and collapsin~ of the heap of garbage.

The tower arrange~ent may however be used in conjunction with the Fig 1 arrange~ent, as shown in Fig 9. Here, the towers 90 (of which only one is shown) act as the liquid collection points, and pipes 92 convey the collected liquid to a holding tank and pumping station 94. The pipes 92 may the~selves count as additional collection pipes, if per~orated, and surrounded by baskets of crushed stone 96, as praYiously described.

Also shown (diagram~atically) in Fig 9 is a shredder and conveyor apparatus 98.

Gas for~ed in, or emanating from, the garbage in the heap 100 is collected in a network of collection pipes 10~ laid on top of the heap. These pipes lead to a co~mon collection point situated at the top of the heap.

At the collection point, the pipes 102 open into a bag lOB, ~ade of flexible ~aterial. The bag acts as a reservoir for the gases, which are conveyed awaY via an outlet pipe 107.

205~51~

The outlet pipe com~unicates with a gas holding tank 108, where the gases are stored. The gases may be stored under pressurs if necessary, and a pump 109 is provided for drawing the gas from the outlet pipe 107 and compressing it into the tank 108.

The bag 106 is inflatable, and is capable of storing such a volume o~ gas as to prevent the build up of a gas pressure underneath the water~tight (and ~as-tight) cover 110 of the heap. The bag is of loose material, rather than resilient or stretchy material, although the bag may be such that the volume of the bag increases as the pressure inside the bag increases.

The edges of the ba~ 106 are held in place on the waterproof cover by means of suitable weights 112, stitched around the base of the bag~

The mouth of the outlet pipe 107 inside the bag should be kept clear by ~eans of a suitable screen placed thereover.

Depending on the particular heap, more than one bag may be provided.

The nature and composition of the mixture of gases from the dump is to so~e extent unpredictable. There~ore, the contents of the bag should preferably be ~onitored, and, if an explosive concentration o~ gases starts to develop, 2(~ 56 ~ 31 -precautions c n be taken eithsr to allow gases to escape ~ro~ the bag or to dilute the bag by supplying an excess of air, or in some other suitable manner.

The du~p is provided with a heating syste~. The ~uel for the heating system pri~arily is the gas taken fro~ the dump itself, which is predo~inantly ~ethane. However, fuel ~ro~
so~e other source may be provided if re~uired; and excess gases ~rom the dump ~ay be disposed of in some other way if ~ore ~ethane is produced than can be used as fuel.

Decomposing garbage creates its own heat, and the heat serves to accelerate the microbial and che~ical reactions of decomposition. However, particularly in a cold climate, deco~position might be slow to start, and the provision of a heating system can then be highly advantageous. Also, if te~perature monitorin~ sensors are incorporated into the heap, it ~ay be discovered that so~e portions of the heap are colder than other portions, with a consequent local sluggishness in the deco~position rate; the deco~position process can then be accelerated locally by supplying heat locally.

The methane collected in the storage tank 108 is burnt in a water heater 114~ The hot water is piped to hot-water distribution pipes 116. The pipes 116 run either under or over the clay layer 118 that lies underneath the heap.
Suitable water flow monitoring gauges and control valves 119 ~:05~7~6 are provided, at such locations as will enable control to be kept of the temperature over the whole extent of the heap 100 .

As mentioned, the pipes 116 ~ay run either above or below the clay layer 118, and are shown in Figs 12A and 12B. The pipes should not run through the clay layer, however~ as that would make the layer especially vulnerable to leaks.

The pipes 11~ preferably are of metal, and are over-engineered to some extent, as they would be awk~ard to get at in the event of a problem requiring service.

In both cases, the pipes should be surrounded by some such material as crushed stone or crushed glass 120, which has a high inherent heat storage capacity. Also, these materials do not tend to consolidate over a long period of time, which if it haPpened, might lead to a poor heat-spreading characteristic in the material. Generally, the region of the heap i~sdiately above the heater will be constantly i~ersed in liquid, and convection currents will bc created in the liquid, at least to some extent even if the liquid is a thick slud~e. These currents are advantageous in that ~gentle) movement of fluids through the ~arbage is help~ul in maintaining the decomposition reactions. The crushed glass, as a body, is porous, which permits this fluid circulation, and the material retains its porosity substantially inde~initely. Old tires 121 may be spread ~5~7S~

over the ~hole of the floor o~ the basin, including over the heating system co~ponents, f or physical protection~

Generally, the bio-chemical reactions that take place in garbage decomposition occur most speedily Rhen there is no lack of oxygen cr oxidising a~encies. In the botto~ o~ the heap, which is expected to be constantly below the level o~
the liguid in ths heap, however, there is a natural tendency to oxy~en-free (anaerobic) conditions, but this can be alleviated somewhat by bubbling air through the liguid.
So~etimes however, it is preferred to break down the garbage under anaerobic conditions: this can be achieved readily by so arranging the dump that all the garba~e remains under the liquid all the time, or substantially so. In anaerobic decomposition, the supply of heat from a heating system can be even more useful.

The heating system as described is of course installed in ths beginning as the dump is being prepared, especially if ths heating syste~ is to go underneath the clay layers 118.
Like the liguid collection system and the air supply syste~, the heating system as described cannot be installed once the dump is in place.

The various systems in the dumpJ includin~ the heating system, may be monitored and controlled a~tomatically, and under computer control if appropriate. Although the systems themselves have to be prepared and installed beforehand, it 205~75fi is g~nerally possiblc to install sensors o~ various kinds into the ~inished heap o~ g~rbage. Thus a leng~h of tube, for examPle of the kind used to draw off a sampls of gas for analysis, ~ay be inserted several metres into the heap si~ply by driving it in. It is also simple enou~h to inject appropriatc decomposition-promoting organisms, if desired.

A microprocessor may be integrated to sensor monitoring all bioreactor parameters such as te~perature, methanogeneous ~as, pH, toxicity. Suitable software can be used to optimize air flow, heating (and cooling), ~oisturizing, pH, and enzymatic agencies to accelerate decomposition and treatment.

The dump as described can be used in a batch processing mode. The dump is not intended as a final repository of garbage but as a ~acility for the rapid decomposition of large quantities o~ decomposable organic ~aste material.
The du~p basin is intended to be used repeatedly. When one heap o~ ~arba~e is deco~posed, which takes a few ~onths, the residue from that heap can be cleared out and then a new heap can be started in the same basin. This can be repeated more or less indefinitely, the systems built into the basin being repaired as needed during the times the basin is e~pty. It is of course the intention that the residue from the dump itself has value as a fertiliser.

As mentioned, it is preferred to blow ~as periodically Z~51~75~

through the garbage from below. Normally, this gas will be air, but other gases may be used. Air serves to aerate the garbage, which promotes most kinds of decomposition, and also the mechanical hsaving movement in the garbRge created by even a small input o~ air serves to agitate or stir the ~arbage, which again promotes deco~position.

Fig 13 is a cross-section of a gas outlet unit 130, which rests on the floor of the dump. Air is supplied to the unit via an air pipe 131, which ter~inates in a vertical seotion 132. On top of the section 132, and blocking the mouth thereof J iS a flap valve 133.

The unit 130 is ~ounted on a spider 134, which ~ayJ for convenience, be secured inside one of the tires 135 of the layer 16. The spider 134 carries a cap 136. The cap 136 is imperforateJ and the only access for liQuids to enter the valve 133 area is though apertures in the spider 134. A
substantial filter structure 138 is included, which prevents any solid particles from reaching the valve 133.

A spring 139 keeps the flap valve 133 closedJ the valve being openable only by a pressure of air in the air pipe 131. Nhen air is e~itted ~rom the unit, such air passes into the heap of garbage through the spider.

The air pipe 131 leads out of the basin~ From time to time, as determined by parameters set by technical staff, air is 20~75 -- 3~ --passed into the air pipe, and passes out through the outlet unit 130. This process is effected by means oP an air pump 140 which is coupled te~porarily to the air pipe 131.

Many other air outlet units are provided in the system 30, as shown in Fig 14, each with its own individual air pipe.
When air is being pumped through the air pipe 131, the other outlets are not connected thereto. Therefore, if a blockage should appear at the unit 130, or a build-up of sludge around the tire 135, a pressurized blast of air can be fed into the air pipe 131 to clear the blockage.

After the unit 130 has been supplied with air, the pu~p 1~0 may be applied to the next air pipe and supply unit. Each air pipe is independent of the others. Each may be pressurized independently of the others, and each may be given air at a separate volumetric flow rate. Air ~ed into ons air pipe can emerge only fro~ the outlet unit associated with that air pipe, and not through any of the other outlet units.

It may be noted, in a system as described, that if a blocka~e should occur at one of the units, that fact is detectable from outside the dump, in that air will not flow through the air pipe 131, and a detectable back pressure will develop. Furthermore, effective steps can be taken, again fro~ outside the dump, to clear the blockage, ie by sending sufficient pressure down the air line to blast the 37 2 ~ 5 ~ ~ 6 obstruction (within li~its, of course~.

The air outlet units are positioned at strategic points around the du~p. So~e of the outlet units ~ay be placed n~ar the ~oot o~ the tower or towers, to ensure that the area around the tower, through which the liguid has to ~low in order to be collected, can be ~echanically a~itated, i~
that need should arise.

Claims (18)

1. CLAIM 1. Garbage dump, wherein:
   
   the dump includes a basin in the ground;
   
   the basin includes a basin sealing means, in the floor of the basin, which is effective to keep such liquids as are present in the basin substantially totally isolated from the ground around and below the basin;
   
   the dump includes a liquid collection system, which is effective to collect and receive such liquids as are present in the basin;
   
   the dump includes a heap of garbage in the basin;
   
   the dump includes a roof, placed over the heap of garbage in the basin;
   
   the roof includes a roof sealing means, which is effective to keep precipitation substantially totally separate from the garbage beneath the cover;
   
   the dump includes a means for transferring liquid collected in the liquid collection system to, or near to, the top of the heap of garbage;
   
   the dump includes a means for distributing the said liquid over the garbage;
   
   the dump includes a gas collection means, which is effective to collect such gases as accumulate beneath the roof;
   
   the dump includes a means for transferring outside the roof the said gases from the gas collection means;
   
   the dump includes a gas supply system for supplying air or other gas into the interior of the heap of garbage;
   
   the gas supply system includes a plurality of gas outlets;
   
   each one of the gas outlets is located at the bottom of the heap, whereby gas emanating from that outlet can filter upwards through the garbage;
   
   the gas supply system includes, in respect of each one of the outlets, a respective gas pressurization means, one gas pressurization means to each gas outlet;
   
   each one of the respective gas pressurization means is separate from and independent of the other gas pressurization means, in that the pressure of, and the volumetric flow of, the gas supplied respectively to each one of the many gas outlets may be varied independently of, and be different from, the pressure and flow of the gas to any other of the outlets;
   
   and the dump includes means for supplying a pressure and flow of gas independently to each outlet.
2. CLAIM 2. Dump of claim 1, wherein the gas supply system includes respective separate and independent means for determining the pressure of the gas at each one of the many out lets.
3. CLAIM 3. Dump of claim 1, wherein the gas outlet includes a check valve, which permits gas to flow from the outlet into the heap of garbage, but which resists the flow of fluid from the garbage into the gas outlet.
4. CLAIM 4. Dump of claim 3, wherein the check valve comprises, at the gas outlet, a movable flap closure which engages a valve seat, and wherein the dump includes a cap means which is effective to envelop the valve from above, thereby to shield the valve, substantially completely, from contact with silt and other non-fluid materials in the dump.
5. CLAIM 5. Grabage dump, wherein the dump includes a basin in the ground;
   
   the basin includes a basin sealing means, in the floor of the basin, which is effective to keep such liquids as are present in the basin substantially totally isolated from the ground around and below the basin;
   
   the dump includes a liquid collection system, which is effective to collect and receive such liquids as are present in the basin;
   
   the dump includes a heap of garbage in the basin;
   
   the dump includes a roof, placed over the heap of garbage in the basin;
   
   the roof includes a roof sealing means, which is effective to keep precipitation substantially totally separate from the garbage beneath the cover;
   
   the dump includes a means for transferring liquid collected in the liquid collection system to, or near to, the top of the heap of garbage;
   
   the dump includes a means for distributing the said liquid over the garbage;
   
   the liquid collection system includes a tower;
   
   the tower extends vertically upwards from the floor of the basin, and includes an interior hollow chamber;
   
   and the tower is provided with perforations, through which liquid present in the basin may enter the chamber.
6. CLAIM 6. Dump of claim 5, wherein the perforations in the tower, through which liquid present in the basin may enter the chamber, extend to a height that is roughly level with the top of the side-walls of the basin.
7. CLAIM 7. Dump of claim 5, wherein:
   
   the tower extends upwards from the floor of the basin;
   
   the tower is of a heavy construction, having substantial structural strength and robustness;
   
   the dump includes a substantial foundation structure, upon which the tower rests;
   
   the foundation structure is effective to support the weight of the tower;
   
   the foundation structure is effective to transmit the weight of the tower through the basin sealing means to the ground beneath the basin, in such manner as not to compromise the integrity of the sealing means.
8. CLAIM 8. Dump of claim 5, wherein:
   
   the liquid collection system includes an extension tube means, which is located on top of the tower, and extends upwards therefrom;
   
   the extension tubs means includes a hollow interior through which liquid collected in the hollow interior of the tower is conveyable to the said means for distributing the liquid over the garbage;
   
   and the means for transferring the collected liquid comprises a pump means and a conduit line, and the conduit line passes up the hollow interior of the extension tube.
9. CLAIM 9. Dump of claim 8, wherein the pump means is located inside the hollow interior of the tower.
10. CLAIM 10. Dump of claim 8, wherein the extension tube means is of substantially lighter and less robust construction than the tower.
11. CLAIM 11. Dump of claim 8, wherein the extension tube is of extendable sectioned construction, and wherein the height of the tube may be progressively increased as the dump is filled with garbage.
12. CLAIM 12. Dump of claim 5, wherein:
    
    the basin has a floor and side-walls;
    
    the basin sealing means comprises at least one layer of compacted shredded clay, and a basin-sheet of impermeable material;
    
    the sealing means extends, substantially without interruption, over the whole area of the floor and side-walls of the basin.
13. CLAIM 13. Dump of claim 12, wherein the basin-sheet of impermeable material extends over the floor and up the full height of the side-walls and extends over the tops of the side-walls, and the basin-sheet is secured in place by weights.
14. CLAIM 14. Dump of claim 5, wherein the roof comprises a roof-sheet of impermeable material which extends substantially without interruption over the full extent of the heap of garbage.
15. CLAIM 15. Dump of claim 14, wherein:
    
    the basin-sheet of impermeable material extends over the floor and up the full height of the side-walls and extends over the tops of the side-walls;
    
    both the roof-sheet and the basin-sheet are secured in place by weights;
    
    the said weights include lengths of drain pipe, which rest upon the roof-sheet, and which are so arranged and positioned as to receive precipitation water passing from the roof-sheet.
16. CLAIM 16. Dump of claim 5, wherein the dump includes an operable heating means, which includes conduits installed underneath the heap of garbage, for conveying heat into the heap from a source outside the heap, and the conduits comprise hot-water pipes packed in non-consolidating heat-retaining material and installed underneath the heap.
17. CLAIM 17. Dump of claim 14, wherein:
    
    the roof-sheet is held in place by means of cables passing over the roof-sheet, the cables being spaced apart;
    
    whereby the roof-sheet has the form, between the cables, of sheds;
    
    the gas collection means comprises a series of gas-permeable collection pipes, the pipes being disposed in the sheds.
18. CLAIM 18. Dump of claim 1, wherein:
    
    the liquid collection system includes a tower;
    
    the tower extends vertically upwards from the floor of the basin, and includes an interior hollow chamber;
    
    and the tower is provided with perforations, through which liquid present in the basin may enter the chamber.