AU701210B1

AU701210B1 - Mechanical-biological treatment of residual waste

Info

Publication number: AU701210B1
Application number: AU69875/98A
Authority: AU
Inventors: Hans Jurgen Collins; Karl-Wilhelm Faber; Dirk Maak
Original assignee: FABER RECYCLING GmbH
Current assignee: FABER RECYCLING GmbH
Priority date: 1998-02-02
Filing date: 1998-06-03
Publication date: 1999-01-21
Anticipated expiration: 2018-06-03
Also published as: BR9806438A; DE19804018C2; DE19804018A1

Description

Mechanical-Biological Treatment of Residual Waste The present invention refers to a method of carrying out a mechanical-biological treatment of residual waste, wherein the waste is first homogenized, reduced in size and soaked, whereupon its biological treatment takes place in aerobic rick-type rotting arrangements which are aerated by means of the chimney-draught method and the surface of which is formed by a biological filter layer.

The present invention also refers to a rick-type rotting arrangement for the biological residual-waste treatment of waste which has been reduced in size, homogenized and soaked, the waste in said rick-type rotting arrangement being deposited on an air-permeable material through which o aeration elements extend, and ambient air being drawn through said aeration elements up to an into a chimney, which is arranged in said rick-type rotting arrangement, according to the chimney-draught method so as to aerate the waste, the surface of said rick-type rotting arrangement being formed by a biological filter layer, Such a method and such a rick-type rotting arrangement are already used in the modern waste disposal industry. The residual waste, such as domestic waste, bulky refuse, industrial waste that is similar to domestic waste and sewage sludge are first subjected to an initial check in the course of which coarse useful materials and coarse disturbing materials are sorted out. Subsequently, the waste is mechanically pretreated, the waste being reducd in size, homogenized and soaked e.g. in mixers with addition of sewage sludge or seeping water, where appropriate. The biological treatment then takes place in aerobic ricks over a period of at least 9 months, said ricks being aerated by the so-called chimneydraught method. In the case of the known rick-type rotting arrangements, the waste is deposited on air-permeable 2 material, preferably wood pallets, which are placed one top of the other in oblique type of arrangement, as can be seen in Fig. 4, so that aeration elements can pass below said pallets. Subsequently, the waste is screened, whereby a 60 mm fraction of high calorific value is separated and used as waste to be decomposed. The waste to be decomposed is preferably made up of particles larger than 60 mm. The other fraction is then dumped in a thin layer. Part of this fraction 60 mm) is reused as a cover layer for the rick-type rotting arrangements. It may, however, happen that the gas/air-exchanging activity of the rick is impaired by excessively dense storage.

Starting from this prior art, it is the object of the 15 present invention to provide a method for carrying out a mechanical-biological treatment of residual waste which permits a more efficient treatment by avoiding especially an impairment of the gas/air-exchanging activity. In addition, a suitable rick-type rotting arrangement is to be 20 provided.

Making use of a method of the type referred to in the generic clause of claim 1, this object is achieved in accordance with the present invention by the features that, for producing the biological filter layer, the waste has applied thereto a structured layer consisting of particles having a particle size of 25-80 mm and a cover layer is applied on top of said structured layer.

The application of the structured layer below the cover layer, i.e. in other words directly above the waste, causes a structuring which permits fine aeration channels, through which the rick-type rotting arrangement can breathe, to remain even after a prolonged period of time. The cover layer applied on top of this structured layer can then, on the whole, be thinner than the cover layers known in the prior art. It follows that the cover layer and the \\melb01\home$\ARyier\Keep\Speci\69875-98.doc 26/11/98 4 cV/ 3%^ 2a structured layer jointly form a biological filter layer which will not be impervious not even after a prolonged period of time. The gas/air-exchanging activity of the rick-type rot-

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0 000, C C *0.0C \\.elb~l\home$\ARymer\Keep\Speci\6 9875 -98 .doc 26/11/98 3 ting arrangement is therefore permanently guaranteed.

In accordance with a preferred embodiment, a fraction of screening residues produced in compost plants is used for producing the structured layer. Such screening residues are a waste product of compost plants, i.e. they are available practically free of charge. The particles screened out in compost plants and having the above-mentioned particle size are normally particles of solid structure so that they are particularly suitable for producing the structured layer.

According to a preferred embodiment of the present method, the structured layer and the cover layer each have a layer thickness of approx. 15 cm so that, in total, a biological filter layer having a thickness of 30 cm is obtained. This sea biological filter layer then keeps back water-vapour particles as well as unpleasant smells, it improves the outward appearance and prevents cooling down of the waste in an efficient manner, which has the effect that biological decomposition takes place more rapidly.

The rick-type rotting arrangement according to the present invention is characterized in that the biological filter layer consists of a structured layer applied to the waste o m e and comprising particles having a particle size of 25 to mm and of a cover layer applied on top of said structured layer. The cover layer is formed of part of a fraction which is separated from the waste by screening out and whose partidcle is 60 mm.

According to a preferred embodmient of the present invention, wood pallets are used as an air-permeable material.

Such wood pallets are available at a moderate price. In the area in which the aeration element extends through the pallets, said pallets are preferably arranged in such a way that two respective pallets are arranged at a distance from one another which is smaller than the dimension of a pallet, 4 and that a third pallet rests on these two pallets, whereby a cavity is formed through which the aeration element extends, said aeration element being e.g. a perforated tube.

Whereas the pallets according to the prior art can easily slip, as can be seen in Fig. 4, and squash the aeration elements, the arrangement according to the present invention is stable and reliable.

The aeration elements can e.g. consist of slotted tubes, especially PVC tubes. Such slotted tubes permit a uniform aeration of the waste.

3 to 6, preferably 4, pallets are arranged in a direction perpendicular to the direction in which the aeration elements extend. Such a structural length has the advantage that the length of an excavator arm will suffice to cover the rick-type rotting arrangement with waste.

0* .0 S: In the following, the present invention will be described with the aid of the figures following hereinbelow: Fig. 1 shows a schematic cross-section of a rick-type rot- 0We@ ting arrangement according to the present invention, Fig. 2 shows a schematic cross-section through a detail of the wood pallets, 0O @0 o, Fig. 3 shows a top view of wood pallets which are displaced relative to one another, Fig. 4 shows a cross-section through a detail of a pallet arrangement known from the prior art and Fig. 5 shows a pespective view of a detail of the arrangement of wood pallets.

5 As can be seen from the schematic cross-section of the ricktype rotting arrangement according to the present invention in Fig. 1, a solidified dewaterable surface 6 is arranged on the ground 7, said surface 6 being additionally provided with discharge troughs 8 for backwater. This solidified surface 6 has arranged thereon air-permeable material, in the present embodiment wood pallets 5. The pallets are arranged in the manner shown in Fig. 2, two respective pallets 5a being arranged in juxtaposed relationship on said solidified surface 6 at a distance d from one another. A further pallet is placed above said pallets 5a and rests thereon so that a cavity 10 is formed through which one or more aeration elements 4 can extend, said aeration elements 4 being a slotted PVC tube in the present embodiment. As can be seen from Fig. 5, four pallets are arranged in a direction perpendicular to the direction in which the aeration elements 4 extend so that a width b of approx. 4m is obtained. The length of an excavator arm will therefore suffice to shovel the waste from an area K over the pallets up to and into an area L. As can be seen from the top view in Fig. 3, the pallets 5b can also be arranged such that they are displaced relative to one another. The waste 9 is stored on top of the pallets. At the centre of the rotting arrangement, aeration elements 4 extend upwards and define a chimney 3 in this way.

e On top of the waste 9, the biological filter layer 11 is arranged, the height h of said layer 11 being approx. 30 cm.

This biological filter layer is composed of two layers. The lower layer facing the waste 9 is a structured layer which is preferably composed of screening residues of a compost plant and which comprises particles having a particle size of from 25 to 80 mm. These particles should be particles of solid structure which, when piled up, define air-permeable channels so that the rick-type rotting arrangement can breathe through this structured layer 13. The structured layer, which is approx. 15 cm high, is then covered by the 6 cover layer 12 which is placed on top of said layer 13. For producing the cover layer, part of the 60 mm fraction which has been screend out of the waste is used. The structured layer 13 and the cover layer 12 form together the biological filter layer 11 which covers the rick-type rotting arrangement at the top and which takes care that the gas/air-exchanging activity is maintained while preventing the rick-type rotting arrangement from cooling down.

The rick-type rotting arrangement, which is shown in the figures, is produced as follows: When the waste (residual waste of the domestic-waste type) has been subjected to an initial check and when coarse useful materials and coarse disturbing materials have been re- 9. moved, the waste is mechanically pretreated in that it is homogenized and reduced in size and soaked, e.g. in a mixer, under addition of sewage sludge or seeping water, where appropriate, so that it is prepared for the subsequent biological treatment in an optimum manner. The biological treatment takes place in a rick-type rotting arrangement of the type shown in Fig. 1. Wood pallets which can be arranged in the way shown in the additional figures serve as a support for the waste; the waste 9 is deposited on said wood pallets. Aeration elements, preferably slotted PVC tubes, extend through these wood pallets, said aeration elements in- 9. troducing air into the rick-type rotting arrangement from eeoo below along the length thereof; this air then moves upwards in the rick-type rotting arrangement. This aeration permits an aerobic decomposition of the waste 9. Since the rick-type rotting arrangement as a whole warms up in the course of this process, it will draw in additional ambient air via the aeration elements 4. The warming-up air rises and can be discharged via the chimney 3 as exhaust air. By means of this function, a uniform aeration of the waste 9 is guaranteed.

7 The aerobic decomposition of the waste results in the formation of gases, which rise as indicated by arrows D. Water vapour is produced as well.

By means of the biological filter layer which is applied to the waste 9 and which has a two-layered structure, part of the water vapour can be held back. The emission of smells and dust can be reduced as well. The structured layer 13 guarantees that the superimposed cover layer does not excessively consolidate so as to preserve the gas/air-exchanging activity of the rick-type rotting arrangement. After the rotting process which lasts for months, e.g. for 9 months, the fraction having a high calorific value can be separated.

The other fraction can be dumped at a disposal site in a Sthin layer.

e 0* o o 8 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A method of carrying out a mechanical-biological treatment of residual waste, wherein the waste is first homogenised, reduced in size and soaked, whereupon its biological treatment takes place in aerobic rick-type rotting arrangements which are aerated by means of a chimney-draught method and the surface of which is formed by a biological filter layer, characterised in that, for producing said biological filter layer, the waste has applied thereto a structured layer consisting of particles having a particle size of 25 to 80 mm which define air .permeable channels and a cover layer is applied on top of said structured layer.

2. A method according to claim 1, characterised in that, a fraction of screening residues produced in compost plants is used as a structured layer.

3. A method according to claim 1 or 2, characterised in that the structured layer and the cover layer each have a layer thickness of approximately 15 cm.

4. A rick-type rotting arrangement for a biological residual-waste treatment of waste which has been reduced in size, homogenised and soaked and which is deposited on an air-permeable material through which aeration elements extend, ambient air being drawn through said aeration elements and into a chimney, which is arranged in said rick-type rotting arrangement, according to a chimneydraught method so as to aerate the waste and the surface of said rick-type rotting arrangement being formed by a biological filter layer, characterised in that the biological filter layer consists of a structured layer applied to the waste and a cover layer applied on top of said structured layer, wherein the structured layer consists of particles have a particle size of 25 to 80 mm \\melb01\home$\ARymer\Keep\Speci\69875-98.doc 26/11/98 'K 09

Claims

6. A rick-type rotting arrangement according to claim 5, characterised in that, in the area in which the aeration element extends through the pallets, said pallets are arranged in such a way that two respective pallets are arranged in juxtaposed relationship at a distance from one another which is smaller than the dimension of a pallet, and that third pallet rests on these two pallets, whereby a cavity is formed though which the aeration element extends.
7. A rick-type rotting arrangement according to any one of the claims 4 to 6, characterised in that the aeration elements are slotted tubes. 2 20 8. A rick-type rotting arrangement according to claim 7, characterised in that the slotted tubes are made of PVC.
9. A rick-type rotting arrangement according to claim 6, characterised in that 3 to 6 pallets are arranged in juxtaposition in a direction perpendicular to the direction in which the aeration elements extend. A rick-type rotting arrangement according to claim 9, characterised in that 4 pallets are arranged in juxtaposition in a direction perpendicular to the direction in which the aeration elements extend.
11. A method substantially as herein described with reference to the accompanying drawings. \\melb01\home$\ARymer\Keep\Speci\69875-98.doc 26/11/98 10
12. A rick-type rotting arrangement substantially as herein described with reference to the accompanying drawings Dated this 24th day of November 1998 FABER RECYCLING GMBH By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia S S. a. S a .i S S U. a a S S. S \\melbl\home$\ARymler\Keep\Speci\69875-98.doc 26/11/98 'I Abstract Mechanical-Biological Treatment of Residual Waste The present invention refers to a mechanical-biological treatment of residual waste and to a suitable rick-type rot- ting arrangement. In order to permit a more efficient and a more hygienic treatment of residual waste, the rick-type rotting arrangement is covered by a biological filter layer consisting of a structured layer and of a cover layer. to S000 o 9* 9 *5 S. SS **S a ro° oe oo•