GB2423766A

GB2423766A - Waste treatment

Info

Publication number: GB2423766A
Application number: GB0504402A
Authority: GB
Inventors: Martin Roche
Original assignee: LANDAIR; Rockbourne Environmental Ltd
Current assignee: Landair (europe) Ltd
Priority date: 2005-03-03
Filing date: 2005-03-03
Publication date: 2006-09-06
Anticipated expiration: 2025-03-03
Also published as: GB0504402D0; GB2423766B

Abstract

A method of treating waste comprises forcing oxygen through the waste in a site at a first location at a first depth below the surface of the waste and extracting gas from a second location as a second depth. Oxygen is also forced through the waste at the first location at a third depth and is extracted from the second location at a fourth depth. An apparatus 50 for treating waste within a well is also disclosed, which comprises a hollow body 51 having a perforated or fluid permeable wall 54 and a conduit system 55 to supply or withdraw fluid to or from the interior of the body. A sealed region (550, Fig. 7B) is also included into which or from which fluid can be supplied or withdrawn. The sealed region is preferably defined by inflatable seals 57 which provide a tight seal between the body and the well wall.

Description

TREATMENT OF BIODEGRADABLE WASTE MATERIALS

The present invention relates to the treatment of biodegradable waste material and, in particular to the treatment of such waste utilising aerobic degradation.

Landfill sites are known in which municipal or other waste is buried in a bespoke site.

The site may be lined to prevent leachate from contaminating the surrounding water table or soil or, as is the case in older landfill sites, not lined, in which case there may be significant pollution of the surrounding area.

An aerobic degradation system is illustrated in US 5,888,022 in which waste material is deposited in a landfill site. The site is lined and/or has a leachate collection apparatus for recirculation of the leachate. The site is provided with a plurality of oxygen injection wells through which oxygen is injected into the deposited waste material to encourage aerobic respiration of the bio-degradeable waste materials. The oxygen concentration within the waste is maintained at above 0%. The injection of oxygen is controlled so as to maintain an optimum temperature within the waste material for aerobic respiration.

The temperature may be monitored and is controlled by changing the rate of addition of oxygen. If the temperature is increasing too rapidly (outside of the optimum range 57 - 66 C) then increased oxygen supply will cool the waste material by conducting the excess heat from the site and by destroying anaerobic microbes which generate heat.

using a method and apparatus disclosed in us 5,888,022 it is possible to stabilise a landfill site in a matter of months and the site has reduced emissions of methane (and any other gases caused by excessive anaerobic respiration).

It is known that for large landfill sites it is necessary to install a large number of air injection wells to ensure that all of the material is subject to aerobic respiration. This is expensive and may result in the installation of more or less wells than are strictly necessary thereby resulting in wasted capital or reduced efficiency and consequently longer periods for reclamation.

DE 10005243 discloses a four stage treatment process for landfill sites comprising low pressure aeration and exhaustion of gas from four vertical wells to accelerate aerobic respiration of waste.

Accordingly, it is an object of the current invention to provide a method and apparatus which improves the performance of prior art methods. It is a further non-exclusive aspect of the invention to provide a method and apparatus which can ensure that the number or amount of dead spots within a stabilised landfill site is reduced, preferably significantly reduced over prior art methods and, in some cases, to ensure that the stabilised landfill site has no such dead spots. It is a yet further object to ensure that heat dissipation within the waste being stabilised is controlled.

In this application the term dead spots' (or the term untreated spots' or similar) refers to parts of the mass of landfill which have not been stabilised by aerobic respiration due to little, insufficient or no oxygen flow therethrough.

A first aspect of the invention provides a method of treating waste material, the method comprising locating waste material to be treated in a site forcing oxygen through the waste material at a first location at a first depth below the surface of the waste material, extracting gas from a second location at a second depth to stabilise waste in a first layer, and forcing oxygen through the waste material at said first location at a third depth and extracting gas form the second location at a fourth depth to stabilise waste in a second layer.

Preferably, the second depth is at or about the depth of the first depth. Preferably, the fourth depth is at or about the depth of the third depth.

The method may further comprise subsequently forcing oxygen through the waste at the first location at a fifth depth and extracting gas from the second location at a sixth depth to stab ilise waste in a third layer, and so on.

The oxygen may be forced into the waste material at the first and third and, if present, subsequent depths sequentially, i.e. in a step-wise' fashion, or simultaneously i.e. at or about the same time. Typically, gas will be extracted in accordance with the method used to force oxygen through the waste.

Oxygen may be forced through the waste as a continuous stream or in a pulsed fashion.

Leachate may be extracted from the waste material or from the proximity of the waste material and reintroduced into the waste material. Leachate may be reintroduced by one or more of surface irrigation, direct injection at a required depth of the waste material or saturation of the oxygen to be forced into the waste material.

A yet further aspect of the invention provides apparatus for the treatment of waste for use within a well having a well wall, the apparatus comprising a hollow body comprising a perforated or fluid permeable wall, fluid conduit means to supply or withdraw fluid to or from the internal volume of the hollow body, supplied fluid being forceable through the perforations in the perforated wall and withdrawn fluid being withdrawable through the perforations in the intermediate wall and further comprising seal means able to provide a sealed region into which or from which the fluid is supplyable or withdrawable.

In one embodiment, the hollow body comprises a closed top wall and a closed bottom wall between which the perforated or fluid permeable wall is disposed. Preferably, said fluid conduit means is in communication with the hollow body to supply or withdraw fluid to or from the internal volume of the and fluid may be supplied to or withdrawn from the sealed region through perforations in the perforated wall of the hollow body.

Preferably, said seal means comprises an inflatable seal, which is inflatable to provide a substantially fluid-tight seal between the body and the well wall. In a preferred embodiment, the body will carry upper and lower seal means to provide a sealed region between the body and the well wall into which fluid may be forced, or from which fluid may be withdrawn.

Fluid supply means may be provided to cause inflation of the inflatable seal. Said means may comprise a seal fluid supply conduit, which may or may not be a dedicated conduit or may be provided by, if present, the fluid supply conduit.

The apparatus may further comprise means to raise or lower the body within, into and out of the well.

The well may comprise a perforated tube, preferably a perforated metal (e. g. steel) tube.

In a second embodiment, the hollow body is a perforated tube, preferably having a solid conduit located therein, said seal means providing the seal region between the conduit and the perforated tube.

A plurality of seal means may be provided at various depths, to provide a plurality of seal regions.

A plurality of fluid conduit means may be provided, one or more in communication with each of said plurality of seal regions.

The apparatus may further comprise leachate extraction means. Preferably, said leachate extraction means is arranged to extract leachate from the bottom of the well and may comprise a leachate conduit and pump to effect leachate extraction. The leachate extraction means may extend through the hollow body. The leachate extraction means may extend through the solid conduit of the second embodiment.

In order that the invention may be more fully understood, it will now be described, by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a prior art treatment site comprising oxygen injection well apparatus; Figure 2 is a schematic elevation of oxygen injection and gas extraction apparatus useful in the method with the apparatus of the invention; Figure 3 is a schematic plan of a line pattern of injection and extraction sites useful in the invention; Figure 4 is a schematic plan of a linear pattern of injection and extraction sites useful in the invention; Figure 5 is a schematic plan of a five-point injection/extraction site pattern useful in the invention; Figure 6 is a schematic plan of a seven-point injection/extraction site pattern useful in the invention; Figure 7A is a schematic sectional view of apparatus according to an embodiment of the invention; Figure 7B is a schematic sectional view of the apparatus of Figure 7A installed in a notional well; Figures 8A, B and C show the apparatus of Figure 7B in use; Figure 9A is a schematic sectional view of apparatus according to a further embodiment of the invention; Figure 9B is a schematic plan view of the apparatus of Figure 9A; and Figure 10 shows the apparatus of Figure 9A in use.

Referring to Figure 1, a site 100 comprises a liner (not shown) which is filled with municipal waste 101. A plurality of injection wells 102 are installed in the site 100 and are arranged to inject compressed air into the waste 101 below the surface thereof. As is indicated by the arrows, the air percolates or otherwise flows through the waste 101 to encourage aerobic respiration within the waste and consequently to speed the stabilisation of the landfill site.

Figure 2 shows a site 10 utilising apparatus 11 of the invention. Waste 12 is located within a lined site 10 and is covered, either with soil or a bespoke cover (not shown). A gas injection well 2 is installed in the waste 12 as are two gas extraction wells 3.

The gas injection well 2 is arranged to inject compressed air into the waste 12 at various depths through gas injection ports, as indicated by arrows A. Gas is extracted from the waste 12 via the gas extraction wells 3 via gas extraction ports.

Figure 3 shows a relatively narrow landfill site 20 in which is installed a plurality of gas injection wells 22 and a plurality of gas extraction wells 23. As before, gas is arranged to be injected through the injection wells 22 at a plurality of vertical positions along their height within the waste 12 and gas extracted from the waste 12 at a plurality of vertical positions along the height of the extraction wells 23.

Figure 4 shows an alternative arrangement to Figure 3, wherein the injection wells 22 and extraction wells 23 are each aligned in rows.

Figure 5 shows a typical "five-point" pattern of injection 22' and extraction 23' wells.

The injection well 22' is located within the centre of a cell 40 of waste 12 and is arranged to supply oxygen to the waste 12 at a plurality of vertical positions and, at each vertical position, in a plurality of radial directions, as indicated by the arrows, to ensure that the gas is properly and effectively distributed throughout the waste 12. Four extraction wells 23' are located about the injection well 22' in a square' array and each is arranged to extract gas at a plurality of vertical positions along their height and, at each position, from a plurality of radial directions. The cell 40 may lie adjacent other cells to provide an array of cells or a close packed' arrangement wherein each injection well 22' is located within a square array of extraction wells 23' (i.e. the extraction wells may be shared by adjoining cells 40).

Figure 6 shows a typical "seven-point" pattern of injection 22" and extraction 23" wells The injection well 22" is located within the centre of a cell 50 of waste 12 and is arranged to supply oxygen to the waste 12 at a plurality of vertical positions and, at each vertical position, in a plurality of radial directions, as indicated by the arrows, to ensure that the gas is properly and effectively distributed throughout the waste 12. Six extraction wells 23" are located about the injection well 22" in a hexagonal' array and each is arranged to extract gas at a plurality of vertical positions along their height and, at each position, from a plurality of radial directions. The cell 50 may lie adjacent other cells to provide an array of cells or a close packed' arrangement wherein each injection well 22" is located within a square array of extraction wells 23" (i.e. the extraction wells may be shared by adjoining cells 50).

The "seven-point" pattern will lend itself to more stringent control of the air within the cell 50.

The gas which is extracted through the extraction wells may be monitored for its oxygen and/or methane and/or sulphur-containing gas concentrations and the amount of compressed air which is injected into the waste may be controlled to ensure that the methane (or other deleterious gas) concentration is not too high. The temperature of the so- extracted gas may also be monitored and the temperature used to control the amount of oxygen injected into the waste.

In cases where the leachate is collected, it may be processed at a processing plant and/or some or all of the collected (and/or processed) leachate may be redirected into the cells to aid in the decomposition of the biodegradeable material. To augment or replace some or all of the redirected leachate, water may be added. Damp or wet conditions may favour aerobic respiration in certain conditions.

When it is necessary to stabilise landfill sites which have not previously had any oxygen injection, bores are drilled into the site and gas injection wells and gas extraction wells are located in the bores. Also, where gas injection wells have been installed in a landfill site, further bores may be drilled for the installation of gas extraction wells. In such cases, one or more gas injection wells may be replaced with, or modified to, gas extraction wells.

It will be appreciated that the provision of gas extraction and gas injection wells improves the flow dynamics of gas injected into the wells and makes the flow around the sites more reproducible. This leads to faster stabilisation of a site or reduced capital outlay by increasing the distance between injection wells (and thereby reducing the complexity of the associated supply conduits).

It will further be appreciated that using extraction and injection wells it is possible to control the oxygen concentration, moisture content and temperature of the waste throughout the site. If required, certain gas injection wells could inject more compressed air or other oxygen containing substance than others. Also, certain gas extraction wells could extract more gas than others.

Monitors could be provided along the length of the extraction and injection wells to monitor the condition of the waste.

Apparatus useful in the injection/extraction well patterns discussed above will now be described with reference to Figures 7 to 10.

Turning to Figures 7A and 7B, there is shown apparatus for forcing a gas (e.g. air or oxygen) through waste material 50, comprising an elongate cylindrical metal body 51 having a top 52 and bottom 53 wall and a perforated cylindrical wall 54 therebetween.

The body 51 has a gas flow conduit 55 connected thereto for the supply of gas to, or the withdrawal of gas from, the interior volume of the body 51.

Running through the body 51 is an exudate conduit 56 for the withdrawal of exudate, which conduit is operably connected to a pump or eductor 560.

The body carries upper and lower seal members 57 which comprise inflatable seals which may be inflated by the supply of a fluid (e.g. a gas) from a seal fluid supply conduit 58.

The apparatus 50 is located in a well which is provided with a perforated metal liner 60.

In use, the apparatus 50 is located at a desired depth within the well and fluid is supplied (as indicated by the arrow X) to the seal members 57 via the supply conduit 58 to provide a sealed region 580 between the seal members. The seal members bear on the metal liner 60. Gas is supplied to the interior of the body 51 (as indicated by the arrow Y) via the supply conduit 55 and, form there, exits the body 51 through the perforated waIl 54, into the sealed region 580 and through the perforated metal liner 60 and into the waste adjacent the sealed region 580, as indicated by the arrows A. Exudate is withdrawn from the well via the exudate conduit 56 using the pump or eductor 560, as indicated by the arrow Z. Once sufficient gas has been supplied to a particular region of waste, fluid supply via conduit 55 is arrested, the seal members 57 are deflated (as indicated by arrow X') and the apparatus 50 is moved to a next depth within the waste for the supply of gas to that layer.

It will be appreciated, that the same apparatus 50 can be used to withdraw gas from the waste, as indicated by the arrow Y'.

Figures 8A to 8C show a typical operative program for the treatment of waste 70. The waste (in Figure 8A) has four distinct areas, a clay cap 71 to seal the waste 70, a layer being treated 72, a layer for subsequent treatment 73 (which may comprise a plurality of sub-layers, each to be treated in sequence) and a layer for further subsequent treatment 74 in which exudate is present (which may be below the water table).

The apparatus 50 is first located at a first depth 72 in each of two wells W1 and W2, one set of apparatus for the supply of gas (in well W1) and one for the withdrawal of gas (in well W2). The seal members 57 of each apparatus 50 are operated and gas is supplied to the first apparatus 50 and withdrawn from the second set of apparatus 502.

Exudate is removed from both the first and second well W1, W2 and is recirculated for subsequent reintroduction into the waste 70. The exudates may be treated (i.e. chemically and/or physically) prior to reintroduction. Reintroduction of exudates may be by surface irrigation, direct pumping or by saturation of the gas supplied via the fluid supply conduit 55.

Once a layer 72 has been treated (as determined by the temperature and/or the gas generated thereby and/or after a known and determined time period) , gas supply via the conduit 55 is arrested, the seal members 57 are deflated and the apparatus moved to a second depth 73, as indicated in Figure 8B, where the process is continued.

The process is continued through layer 73 and into layer 74 (see Figure 80). The process may be known as phased-layer stabilisation.

The apparatus may be used in any of the well patterns previously described, although it may be preferentially used in the five-well pattern of Figure 5.

As will be appreciated, the amount of exudates added to the waste will depend on the waste to be treated and may be controlled to ensure that the optimum stabilisation characteristics are provided within the waste 70, as determined by the temperature profile and/or gas evolution. In some cases, it may be necessary to augment or replace the exudates with other liquids.

In some cases, extraction (via well W2 or via both well W1 and well W1) may be commenced to reduce the levels of methane within the waste 70. Once the methane concentration is suitably low (e.g. below 12%) gas supply and extraction may be commenced, as indicated above.

Referring now to Figures 9A and 9B there is shown further apparatus 80 for the treatment of waste comprising a perforated metal well liner 81 in which is housed an insert 82 having a perforated or open lower region. At various depths within the liner 81 are seals 83 to define a plurality of seated regions 830, which may be filled with gravel or other granular material.

A fluid supply or withdrawal conduit 84 is present to communicate with each sealed region 830 for the supply and/or withdrawal of gas to that sealed region 830.

An exudate withdrawal conduit 56' is located within the insert 82 through which exudates are withdrawable from the well using a pump or eductor 560'.

As indicated in Figure 10, stabilisation may occur in one layer Li or in a plurality of different layers Li to L5 at the same time by supply of gas to one or more fluid supply conduits 84. As before, gas withdrawal may be commenced before gas supply to reduce the concentration of methane within the waste.

The apparatus 80 may be used in any of the well patterns previously described, although the five and/or seven point patterns (Figures 5 and/or 6) may be particularly useful.

In either apparatus 50; 80 the gas supply may be constant or may be pulsed. The use of vertical phase layer stabilisation ensures that the number, amount and/size of dead spots is minimised whilst ensuring that the waste is stabitised faster and/or more efficiently than in prior art methods. Using the apparatus 50; 80 the temperature profile within the waste can be more accurately controlled by either or both of controlling the gas supply and exudate or other liquid supply.

It will be appreciated that the temperature of the waste will be monitored and the composition of the withdrawn gas will be monitored to determine one or more of the concentration of oxygen, methane, carbon dioxide, carbon monoxide and hydrogen.

Claims

Claims 1. A method of treating waste material, the method comprising

locating waste material to be treated in a site, forcing oxygen through the waste material at a first location at a first depth below the surface of the waste material, extracting gas from a second location at a second depth to stabilise waste in a first layer, and forcing oxygen through the waste material at said first location at a third depth and extracting gas form the second location at a fourth depth to stabilise waste in a second layer.
2. A method according to Claim 1, wherein the second depth is at or about the depth of the first depth.
3. A method according to Claim 1 or 2, wherein the fourth depth is at or about the depth of the third depth.
4. A method according to any of Claims 1 to 3, further comprising subsequently forcing oxygen through the waste at the first location at a fifth depth and extracting gas from the second location at a sixth depth to stabilise waste in a third layer, and so on.
5. A method according to any preceding Claim, wherein the oxygen is forced into the waste material at the first and third and, if present, subsequent depths sequentially, i.e. in a step-wise' fashion, or simultaneously i.e at or about the same time.
6. A method according to any preceding Claim, comprising forcing oxygen through the waste as a continuous stream or in a pulsed fashion.
7. A method according to any preceding Claim, comprising extracting leachate from the waste material or from the proximity of the waste material and reintroducing it into the waste material.
8. A method according to Claim 7, comprising reintroducing leachate by one or more of surface irrigation, direct injection at a required depth of the waste material or saturation of the oxygen to be forced into the waste material.
9. Apparatus for the treatment of waste for use within a well having a well wall, the apparatus comprising a hollow body comprising a perforated or fluid permeable wall, fluid conduit means to supply or withdraw fluid to or from the internal volume of the hollow body, supplied fluid being forceable through the perforations in the perforated wall and withdrawn fluid being withdrawable through the perforations in the intermediate wall and further comprising seal means able to provide a sealed region into which or from which the fluid is supplyable or withdrawable.
Apparatus according to Claim 9, wherein the hollow body comprises a closed top wall and a closed bottom wall between which the perforated or fluid permeable wall is disposed.
11. Apparatus according to Claim 9 or 10, wherein said fluid conduit means is in communication with the hollow body to supply or withdraw fluid to or from the internal volume of the body
12. Apparatus according to any of Claims 9, 10 or 11, wherein fluid is supplyable to or withdrawable from the sealed region through perforations in the perforated wall of the hollow body.
13. Apparatus according to any of Claims 9 to 12, wherein said seal means comprises an inflatable seal, which is inflatable to provide a substantially fluid- tight seal between the body and the well wall.
14. Apparatus according to Claim 9 to 13, wherein the body carries upper and lower seal means to provide a sealed region between the body and the well wall into which fluid may be forced, or from which fluid may be withdrawn.
15. Apparatus according to Claim 14, wherein fluid supply means are provided to cause inflation of the inflatable seal.
16. Apparatus according to any of Claims 9 to 15, further comprising means to raise or lower the body within, into and out of the well.
17. Apparatus according to any of Claims 9 to 16, wherein the well comprises a perforated tube, preferably a perforated metal (e.g. steel) tube.
18 Apparatus according to Claim 9, wherein the hollow body is a perforated tube having a solid conduit located therein, said seal means providing the seal region between the conduit and the perforated tube.
19. Apparatus according to Claim 18, comprising a plurality of seal means provided at various depths, to provide a plurality of sealed regions.
20. Apparatus according to Claim 19, comprising a plurality of fluid conduit means, one or more in communication with each of said plurality of sealed regions.
21. Apparatus according to any of Claims 9 to 20, further comprising leachate extraction means.
22. A method of treating waste material using the apparatus of any of Claims 9 to 21, the method comprising locating waste material to be treated in a site, covering the waste material in the site, injecting oxygen-containing gas from the apparatus of any of Claims 9 to 21 into the waste material at a first location below the surface of the waste material and extracting gas from a second location below the surface of the waste material.
23. A method according to Claim 22 or 23, comprising forcing or injecting oxygen- containing gas into the waste material at a plurality of vertical locations below the surface of the waste.
24. A method according to Claim 22 to 23, comprising extracting gas from a plurality of vertical locations below the surface of the waste.
25. A method according to any of Claims 22 to 24, comprising monitoring the composition and/or physical characteristics of extracted gas.
26. A method according to Claim 25, comprising altering the amount of gas introduced to the waste to maintain optimum conditions for aerobic respiration.
27. A method of treating waste comprising a combination of the method of any of Claims 1 to 8 with the method of any of Claims 22 to 27.
28. Apparatus as hereinbefore described with reference to Figures 7 to 8 or 9 to 10 of the accompanying Figures.
29. A method as hereinbefore described.