WO1996037664A1

WO1996037664A1 - A device for disposal of waste and recovery of biogas

Info

Publication number: WO1996037664A1
Application number: PCT/IT1995/000091
Authority: WO
Inventors: Antonino Bellinghieri; Bruno Copat
Original assignee: Antonino Bellinghieri; Bruno Copat
Priority date: 1995-05-25
Filing date: 1995-05-25
Publication date: 1996-11-28
Also published as: AU2574495A

Abstract

A device for the disposal of solid city waste, waste of a special kind, or toxic/harmful waste, comprising a polymeric cylindrical geomembrane let down into a bore (1) realized in a kind of soil having a degree of permeableness such that the displacement velocity of any liquid in said soil is less than 10-4 cm/sec. In the gap between the bore wall (1) and the geomembrane, the device comprises a layer of cement mortar, whose casting is performed by means of suitable hoses from the bottom towards the top. The device also comprises means (2, 2', 2'', 3) for centering the geomembrane, and a collar (4) with a related cover, in order to seal also the upper part of the device. The cover comprises a valve in order to collect and adjust the flow rate of the collected biogas.

Description

A device for disposal of waste and recovery of biogas

Technical Field

The present invention relates to the realization of a device for the disposal of solid city waste and waste of a specific kind, inside a sealed space, with the recovery of the resulting biogas.

Background Art

Nowadays, the procedures of disposal of solid city waste and waste of a specific kind, even if they employ various methods and technologies, they always involve an enour ous risk of pollution of the environment. In fact, examining the different methods which are employed nowadays, it is easy to point out these risks. The controlled garbage dumps used nowadays are open-air (i.e. uncovered) and comprise very wide ditches realized for this purpose, made impervious on their bottom and walls, and filled now and then with waste which is subsequently compacted and covered with mould. This method has the following serious disadvantages: - the garbage dump is open-air, so that huge problems arise in relation to the disposal of the rain water which, whenever it rains, fills this artificially obtained storage capacity, and mixes with the waste and with the percolation material resulting from the waste. These great quantities of water, besides being necessarily collected and processed in adequate plants before being disposed of, thereby increasing the costs of the garbage dump, represent a noticeable hindrance for the daily compaction and covering works, since they make impracticable a large part of the storage capacity;

- it results in a remarkable source of atmospheric pollution. The miasma produced by the waste decomposition saturates completely the region of the garbage dump, and according to the main wind direction, is spread in large neighbouring areas, thereby causing noticeable trouble to the resident people. This phenomenon, which is often made worse by the simultaneous presence of smoke produced by combustion phenomena of the waste mass so preserved, does not cease until the final reclamation of the area occupied by the garbage dump;

- it represents a constant danger for the people's health with respect to the untrontrolled proliferation of insects and harmful animals like rats etc., both inside the area of the garbage dump, and in the neighbouring areas, since the presence of the open-air waste represents an illimited food source for said animals; - it represents a remarkable source of noise pollution in relation to the presence, in the garbage dump area, of heavy vehicles which move continuously. The operations of compaction and covering of the waste, also cause, especially during the warm season, high and dense dust columns which increase the atmospheric pollution in an area which is much greater than the garbage dump itself; - it is impossible to collect, before the final covering fo the garbage dump, the whole biogas which is continuously produced by the biochemical transformation of the products. The biogas collection at the end of the life of the garbage dump, is possible only if expensive and particular devices are employed, in order to prevent the biogas from spreading, i.e. dispersing itself. The means used nowadays imply a low efficiency of the collection and conveyance methods, and therefore a low efficiency of the systems which employ this biogas. These must be necessarily set or calibrated for obtaining medium conditions of inflow, thereby loosing great amounts of biogas, which instead of being reused is only burnt in the free atmosphere; - it is impossible to reuse the area of the garbage dump, until completion of the same. Further, the inevitable ground settling of the soil forming the "body" of the garbage dump, produced by the decrease in volume of the compacted waste, leads to the absolute prohibition to build on the entire area, thereby preventing the reuse of the same.

Another method of disposal is that which makes use of incinerators. It is superfluous to outline the numberless disadvantages which result from the use of these systems, both with reference to the problems deriving from the high atmospheric pollution rate and to the installation and operation of the plants themselves. At last, we can group together all the other more or less new methods of waste recycling, for producing the most different products as for instance artificial fertilizers etc., since all these methods require very high initial investments, great problems for the sorting of the collected materials which presently are impracticable on a large scale with economical gains or profits which are greatly delayed, and with the necessity, in most cases, to enlarge the areas of incluence for each plant, to an area including several regions and/or provinces, because of the very high costs.

Disclosure of Invention

In order to overcome these drawbacks, according to the present invention, it has been provided a device which comprises a double shell or layer of impervious materials, wherein the first is directly realized "in situ" by boring a clayey ground or a ground of a different kind having however permeability features such that the displacement velocity of any liquid is less than 10~ cm/s, and the second by introducing coaxially with respect to the first layer, a geomembrane or geodiaphragm of a polymeric and reinforced kind, perfectly sealed both on its lateral walls and its PCMT95/00091

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bottom, and such as to resist, without lateral support, to induced pressures equal to 6 atm, without being deformed.

In the gap between the first and the second shell or layer there will be injected under a controlled pressure, a self-hardening or setting mixture based on cement and additives, so as to fill every space and seal the gap between the two shells, and so as to realize at the same time a support and protection structure of the geomembrane.

The device will be completed by realizing a perfect hermetic seal on the upper part of both shells, by using a metallic collar and cover. On the cover there will be applied a valve with a pressure resistant seal so as to be able to connect, if required, the present device to the network for recovering the biogas.

The device, as described above, represents a very remarkable innovation in the methods for the disposal of solid city wastes and special wastes, as they are classified by the Italian law (D.P.R. n. 915/82), because it is the most simple and economical system, to which there corresponds a maximum degree of safety, as regards the preservation of the superficial and underground characteristics of the environment which exist in the place choosen for the installation of the device.

The device of the present invention exploits mainly the 96/37664 PCMT95/00091

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natural feature of certain soils of being practically impervious to liquids and gaseous substances. The first shell or layer is in fact directly obtained in the soil, "in situ", and therefore under conditions of the same of maximum stability.

By boring with machines of adequate power, cilindrical containers may be realized, having variable length, and self-supporting compart walls, due to the nature of the soil in question. The distance between each bore will be such as to determine a thickness of the lateral wall at least, equal to 100 cm, whereas the thickness at the site of the bottom wall of the cylinder, will vary as a function of the thickness of the chosen impervious bank of ground and in any case will not be less than 10 m.

Inside this natural container, having the above described properties, there will be introduced coaxially, a second shell or layer, formed by a cylinder comprising a geomembrane produced using polymer based products welded at the manufacturing place, so as to form a perfectly sealed container, both at the wall site and the bottom site. The physical and chemical features of the employed geomembrane are such as to ensure not only a perfect imperviousness of the same, but also, in the first place, to ensure resistance properties to induced pressures, both internal and external, up to a value of at most 6 atm, without causing irreversible deformation. The cylinder formed by the geomembrane will have diameter at least 20 cm less than the bore diameter, i.e. the diameter of the first shell. The gap between the two cylinders will be filled completely by injecting under a controlled pressure, by means of hoses let down into the gap, a cement based self-hardening mixture starting from the bottom of the gap towards its top, said mixture comprising fluidifying and shrinkage preventing substances, so as to realize at the same time a rigid support structure which protects the geomembrane.

In this way there will be formed the body of the container - or device -, inside which the waste materials will be subsequently introduced. A single body formed by the impervious soil, the mortar, and the geomembrane.

Brief Description of Drawings The present invention will now be described for illustrative and non limitative purposes with reference to the annexed drawings, in which:

Fig. 1 shows according to a longitudinal sectional view, the shape of the bore realized in the impervious soil, possibly an argillaceous soil;

Fig. 2 shows the top view and respectively the sectional view of a pair of concentric rings let down into the bore of Fig. 1 between the geomembrane and the wall of the bore;

Fig. 3 shows the collar arranged at the top of the bore of Fig. 1, according to a top view and a cross section respectively.

Best Mode of Carrying out the Invention

As concerns the method, after the perforation has been carried out (Fig. 1) in order to realize the bore 1, a plurality of double rings 2 will be let down inside the first cylinder, said rings being coaxial and metallic (Fig. 2) and spaced radially 8 cm from each other through spacers 3. The external ring 2' will have the function of a guide element for the centering of the geomembrane (not shown) with respect to the bore, whereas the internal ring 2" will confine the geomembrane by correctly spacing it out radially. The metallic couble rings 2 will be connected to each other by means of four metallic cables, at a distance of 2 metres from each other, so as to center the second cylinder made up by the geomembrane, along the whole length of the bore. The double ring 2 and the cylinder made up by the geomembrane (not shown) will be let down simultanously inside the first cylinder, i.e. the wall of the bore 1, by means of a weight connected to the bore bottom double ring 2.

Once the above described system has been arranged, at its lower end on the bore bottom, it will be fixed at its upper end to a metallic collar 4 (Fig. 3) which, laying on the ground at the upper end of the bore, on the shoulder 5, through its projection 6, will support the whole system comprising the metallic rings and the geomembrane. In the space between the two centering rings 2', 2" spaced at intervals along the whole length of the cylinder 1 formed by the bore, there will be let down one or more hoses which, starting from the bore bottom, will inject the cement mortar used for sealing and filling the annular region between the first and second cylinder (the latter is formed by the geomembrane and is not shown) .

In order to allow this operation to be performed, inside the second cylinder made up by the geomembrane, there will be blown air, until an inner pressure value of 4-5 atm is reached, so that the geomembrane will itself form a kind of caisson for receiving the casting of cement mortar.

Once the casting has set, the air inside the geomembrane will be discharged. The whole device will therefore form a monolithic element, absolutely impervious, wherein the intermediate layer formed by the injected cement mortar, besides making up a connection element between the different parts, will represent the element preventing the relaxation (yielding) of the walls of the first shell, thereby insuring the preservation of the initial geomechanical properties. At last, the end of the device will be sealed, by embedding the metallic collar in a an amount of cast concrete.

The device so realized can be completed, depending on circumstances, with a system for collecting and removing the percolation material resulting from the waste mass located inside it.

This system will comprise a layer of arid granulated material having a thickness of 70 cm. , placed at the bottom of the bore, inside the second cylinder, having the function of drainage of the percolation material. In said layer, there will be introduced ducts of plastics, wherein the end of the ducts carries micro- slists. The ducts will extend upwardly forming tubes having walls with no slits or holes, until the upper end or head of the device is reached, said tubes passing through a suitable hole provided for this purpose in the metallic cover.

According to the principle of communicating vessels, the ducts will be filled to a certain level with the percolation material produced by the waste, which will be mechanically sucked now and then, and coveyed directly to the collection center. The device, completed in this way, will be immediately O 96/37664 PC17IT95/00091

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ready to receive the waste material which will be introduced and compacted inside it.

Once filled to the desired level, it will be sealed by means of a sealed cover fixed to the above described collar.

The device as described, represents a miniature garbage dump which is complete as regards its functions. The simple methods used to realize it, and its extremely low cost, allow to realize it on a large scale, by installing a large number of them in a concentrated area.

The realization of a large number of devices in each hectare, allows to concentrate the operations of loading, trituration and introduction of the waste, with the following very remarkable advantages: - it is not open-air, so that there are absolutely no problems related to meteoric water;

- it does not produce miasma or free smoke, thereby absolutely preventing atmospheric pollution;

- it does not produce pollution of underground water beds due to the absolute impermeableness resulting from the combination of both shells. The choice of working on soils having a permeability as established in this specification, realizing even deep bores, allows to operate in large territorial areas, without interfering, in no way, with the normal conditions of the underground water beds;

- it is absolutely safe as regards the presence of harmful animals and insects, since the rapidity of the filling operations of the containers, and their final sealing, do not allow their proliferation at all;

- it is possible to work simultaneously in separate areas of the garbage dump as conceived herein, without any kind of interference between the various operations, so as to be able to use immediately the already complete sectors for the most different activities, even productive activities, as for example the use of these sectors for the realization of hothouses heated with the recovered biogas, for growing plants or the like;

- it is possible to recover immediately and with a maximum efficiency, a sector after the other, the resulting biogas, in order to reuse and convert it into heat and electric energy, thereby employing it both for external uses, and for the energetic needs of the auxiliary machines operating in the garbage dump (trituration machines, conveyor belts, etc.). The recovery system of the biogas can be easily adjusted by determining, therefore, the exact and constant inflow to the burners, with a maximum efficiency of the latter and without dispersion and waste of the biogas;

- it is possible to assign certain sectors of the garbage dump, to the disposal of special waste or harmful/toxic waste, without interfering at all with the nature of the other waste. This is made possible by the fact that each single container represents, by itself, a "controlled" and complete garbage dump of the type C or third category, as established by the realization standards of the Italian law (D.P.R. 915/85), such as to be suited for any kind of waste classified both under the denomination of "special" waste or "harmful/toxic" waste. Under this point of view, each device can be filled with any of the products classified in the D.P.R. 915/85, without interfering at all with what has been stored inside the neighbouring device;

- it is possible to effect the final settlement of the garbage dump at the very moment in which it is made operative, in such a way as to respect at most the existing environment, both inside the area of the garbage dump and in the neighbouring territory. The possibility of using non-stationary structures for the machines used for receiving, triturating, and the arrangement of the waste, will allow to clear each sector of the garbage dump so as to reestablish very quickly the initial conditions;

- it can be effectively integrated in the existing environment, also during the activity period, modifying in a minimum way its original characteristics;

- at last, an important feature is that it allows, with respect to city waste, to recover very easily the final transformation product of the deposited waste.

The physical and chemical transformations occurring in the course of time, in the stored mass, produce substances which may be reused in various applications so that there will be a double economical gain, since on the one hand the material extracted from this very small garbage dump making up the device of the invention may be put on the market, and on the other hand it will be possible to introduce other fresh waste. The production cycle of the garbage dump can be adjusted at will in order to attain this object, without interfering on any of the single operations.

Claims

1. A device for the disposal of solid city waste, waste of a special kind or toxic/harmful waste, in a controlled environment, allowing recovery of the resulting biogas, comprising a first shell (1) obtained by perforation "in situ" of soils having a permeability such that the displacement velocity of any liquid will be less than 10^~ cm/s, said first shell being obtained by perforating soils of any kind, also permeable ones, on condition that they are submitted to a pre-treat ent or a post-treatment in order to obtain the necessary characteristics of impermeableness by means of injection under pressure of impervious mixtures of any kind and chemical composition, whereby the perforation diameter of the first shell is within 200 mm and 5000 mm, and the perforation depth starting from the natural country-side surface or from artificial surfaces obtained both by excavation or in relief, may reach 200 meters, and further the form of the first shell (1) being cylindrical, parallelepipedal, prismatic or the like, characterized in that concentric rings (2* 2") which are connected to each other, are used in order to center a geomembrane with respect to the wall (1) of the bore, said concentric rings (2', 2") comprising a bore bottom ring (2', 2") provided with a ballast.

2. A device according to claim 1, characterized in that a polymeric geomembrane is used in order to form the second impervious shell.

3. A device according to any of the preceding claims, characterized in that air is injected under pressure inside the second shell or geomembrane, in order to let said geomembrane form the inner caisson necessary for casting the mortar between the bore wall (1) and the geomembrane, said mortar being usual cement mortar or mortar provided with fluidifying or shrinkage preventing substances.

4. A device according to claim 3, characterized in that any kind of liquid is used in place of air in order to oppose the thrust excerted by the mortar which is injected under pressure outside of the second shell or geomembrane.

5. A device according to claim 3 and 4, characterized in that the intermediate shell is obtained by casting the mortar starting from the bottom towards the top, using a plurality of hoses.

6. A device according to any of the preceding claims, characterized in that a metallic collar (4) provided with a related sealed cover, is used for sealing the upper end of the ensemble formed by the three shells including the bore wall (1), the geomembrane and the mortar layer.

7. A device according to claim 6, characterized in that the collar (4) and the related cover are made of plastics.

8. A device according to claim 6, characterized in that the collar (4) and the related cover are made of wood.

9. A device according to claim 6, characterized in that the cover includes a pressure resistant seal valve, suited to connect the device with the network for the biogas collection.

10. A device according to the preceding claims, characterized in that there is provided a system for collecting the percolation material produced inside the device, said system including a drainage bed, and a plurality of ducts provided at their lower end with micro-slits, and extending towards the upper end, forming tubes which are integral i.e. not provided with slits and which form a column inside the device, reaching the sealed cover of the latter.