This invention relates to the processing of materials, particularly materials which are processed as a body of ingredients which requires a supply of oxygen as a component of the process. Composting of biodegradable material is an example of such a process. Other examples can be found in horticulture, particularly in hydroponics and in mushroom growing.

Composting in this context refers to the exothermic, aerobic decomposition of said biodegradable material, in the presence of oxygen. This exothermically degradable material, as defined, would normally include garden waste, paper, food materials and wood, with the potential for the addition of manures, agricultural slurries, sewage or similar to accelerate, enhance or otherwise improve biodegradability. The natural processes of decomposition of such materials as have been previously detailed is a well appreciated phenomenon, widely used for centuries by gardeners, horticulturalists and the like to provide a relatively stable, nutrient-rich compost of a kind suitable for use on the land. Changes in legislation and waste management practice, together with the need to reduce the traditional problems associated with organic wastes in landfill disposal, have

combined to make the treatment of the biodegradable fraction of refuse increasingly important. Accordingly, composting or, more accurately, aerobic decomposition, is receiving additional interest as a means of reducing the amount of biological or organic waste destined for landfill dumping. The composting of such large quantities of organic refuse, derived from household, domestic or council waste streams, amongst other sources, involves a much larger scale of operation than the traditional backgarden compost heap. This has certain implications for these operations, particularly in materials handling and oxygenation of the decomposing matrix.

It is well known that to effect proper breakdown, the micro-organisms responsible for compost production must be provided with an adequate supply of oxygen. Without this, the areas affected become anaerobic, the decomposition ceases to be exothermic and slows, and bad odours characteristically arise.

While in a traditional compost heap this tends to be avoided because of the relative ease with which oxygen can diffuse into the degrading waste, the larger amounts of waste involved in a commercial operation present a lower surface area to volume ratio, which limits natural

oxygen ingress to the central core.

Presently, commercial large scale composting relies either on mechanical turning of the decomposing material to introduce the required oxygen, or direct pumping of air through the matrix. In both cases, external energy is required to effect this, which has its own implications for the commercial side of the operation as a viable waste management solution for organic waste.

In the case of horticultural processes, it is important that the roots of growing plants are not starved of oxygen and this is a significant risk where soil is densely compacted or in hydroponic systems where liquid feeds blanket out any naturally diffused air at the roots .

According to the present invention there is provided an apparatus for the processing of materials of the kind in which a body of ingredients is subject to a process which requires a supply of air, said apparatus comprising aeration pipe means having opposed ends each of which is open to air and which pipe means provides a passage for air through said body of ingredients, and the pipe means being so disposed that a naturally occurring pressure difference arises between said ends to provide a flow of

air through said body of ingredients from one end of the pipe means to the other end.

By referring to a naturally occurring pressure difference we mean that the pressure difference arises naturally due to the location or configuration of the pipe means in use. This can be due to naturally occurring effects such as arise in a chimney (which provides draw) , a throated flue, differential effects at different parts of an aerofoil or following from differences in local air velocity, or due to differential heating resulting in changes in density in different parts of said pipe means.

This contrasts with pump drive systems which the present invention eliminates.

Preferably the pipe means is in the form of an unbalanced U-tube having an apertured lower end situated within said body of ingredients and where the pressure difference arises through the location or configuration of the unbalanced U-tube.

The imbalance of the U-tube can be achieved in a number of ways.

A preferred example is where the U-tube has two limbs each with an outlet end opening to atmosphere and

one is at a higher level than the other. Then, if any wind or movement of air occurs past the two outlet ends the velocity is likely to be higher over the higher outlet end so that there will be a pressure differential (due to a difference in V ² /2g) causing flow of air through the U-tube.This differential can be enhanced by locating the outlet ends adjacent different parts of an aerofoil or one of them within a venturi.

Another example is to provide differential heating between the two limbs of the U-tube. If one limb is located within the body of ingredients while the other is not and an exothermic reaction is taking place, e.g. in a mass of composting material, the difference in temperature and hence density of the air in the different sides of the U-tube will result in a flow of the air.

In another arrangement according to the invention said pipe means is in two parts, one constituting an inlet end in a lower region of the apparatus and the other constituting an outlet end in a higher region of the apparatus and each communicating with said body of ingredients.

In the case of a composting process this flow of air enables the breakdown processes to be better managed both

initially and throughout the period of decomposition.

In a specific form of the invention a container consists of a cavity formed by a structure, pit or excavation, covered or open, which contains exothermically biodegradable material and is allowed to undergo decomposition, thus to provide a usable, stable, soil medium, which is characterised in that the said container is equipped with aeration pipes, tubes or ducts so designed and arranged as to promote the free ingress of oxygen containing air without the need for powered means or moving machinery, so as to bring about optimum conditions for the commencement of said decomposition and its continuance thereafter.

In a practical application of the invention to process a relatively large amount of organic waste, either as a total treatment or as one stage in a multi-stage management system, the container described can be a single large unit, or a series of smaller ones, which may be static, fixed, mobile or removable from the site of operation and which may be themselves contained within a building or other structure.

A specific embodiment of the invention will now be described by way of example with reference to the

accompanying drawing in which:

Figure 1 is a cross section through a system in accordance with the invention;

Figures 2 to 5 show variations on this system; and

Figures 6 and 7 show side and front elevations of another system.

As described previously, the invention relates to an apparatus for processing materials where a body of ingredients is equipped with one or more aeration pipes, tubes or ducts so designed and arranged as to promote the free ingress of oxygen containing air due to a naturally occurring pressure difference across the outlet ends of the pipes, and without the need for powered means or moving machinery. This is achieved by placing the aeration pipes in such a position relative to the body of ingredients that they make use of any available wind movement, using a variant on the aerofoil principle, or they make use of differential heating between different parts of the pipe means..

Referring now to the drawings, by excavation, construction or otherwise, a container 1 is created.

This provides a void space 2 , into which a body of ingredients in the form of waste containing organic material is deposited, with the possible addition of sewage, manures or other biodegradable matter. Moisture levels within the waste are maintained at those suitable for the processes of aerobic decomposition taking place.

Perforated, gas permeable aeration pipes 4 are located within the void space 2 , towards the bottom of the container 1. The waste is placed around these. Each of the aeration pipes 4 is in turn connected to an inlet pipe 3 and an outlet pipe 5, so forming a U-tube, in which the outlet end of pipe 5 is situated significantly higher than the outlet end of pipe 3.

Moving air, either by natural wind or breeze activity, or otherwise, is allowed to blow around the area of the container 1. The air travelling over the outlet end of the pipe 5 moves more quickly than over the outlet of the lower inlet pipe 3. The faster moving air stream creates a nett lowering of pressure below it (due to the Bernoulli's Law) within the outlet pipes 5. This then tends to draw air into the partial vacuum created from the aeration pipes 4, which in turn causes air to be drawn into the said aeration pipes through the open top of the inlet pipes 3. In this way, air is drawn into

the container 1 without the need for powered means or moving machinery and since a proportion of the air drawn into the system escapes directly through the perforations in the aeration pipe 4, the decomposing organic matrix is itself aerated.

When the decomposition process is complete, the material is removed for disposal or use, allowing the void space 2 to be reused in the manner described for the treatment of further suitable wastes or other biodegradable materials .

Figures 2 to 5 show various alternative ways of achieving the pressure differential across the pipe ends. Figure 2 shows a system where the limb 3 is wholly outside the body of ingredients and the limb 5 is at least partially immersed within the body of ingredients . In the case of an exothermic reactions taking place, the air in limb 5 becomes warmer than that in limb 3 and so become less dense, or lighter, and so air flows down the limb 3 and up the limb 5.

Figure 3 shows an arrangement where a venturi disc 6 is located at the outlet end of limb 5. This reduces the pressure within limb 5, so promoting air flow through the pipe.

Figure 4 shows an arrangement where an aerofoil 7 in the form of an object which in plan view is circular and in side elevation has an upper domed surface 8 and a lower flat surface 9. Air will flow at a greater rate across the upper surface 8 than the lower surface 9 so causing a pressure differential between the outlet ends of limbs 3 and 5 so that air will then flow naturally through the pipe 4.

Figure 5 shows an arrangement where a pipe 10 in the form of a throated chimney leads out of the body of ingredients while pipes 11 lead into the body of ingredients . Naturally occurring drafts of air across the top of the chimney will draw air through the system.

All the embodiments up to now show the pipe means as essentially in the form of a U-tube. This however is not always essential. If the container 1 is located at ground level the inlet pipes can lead out laterally from the container, or indeed if the container is located above ground level the inlets can lead out underneath. These possibilities are shown dotted in the Figure.

When the body of ingredients is located at ground level a U-tube is much more convenient and has the further advantage that the whole system (as in Figure 3)

can be lifted out for cleaning. Systems where the pipe inlets emerge through the container wall cannot be as easily detached.

Referring to Figures 6 and 7, the apparatus comprises a main chamber 21, having a door 22 which can be opened to load the ingredients for treatment into the container, and, at the end of the process, to remove these ingredients .

The pipe means in accordance with the invention in this case comprises, looking at the Figure 6 side elevation an inlet 24 at the lower left hand edge of the container wall and an outlet chimney 25 at the right hand upper region of the wall. Looking at Figure 7, it will be seen that these occur on both sides of the container.

The interior of the container includes a false perforated base 26 so that the ingredients can remain above this level.

In practice, since the lower inlets of the pipe means will be in a region of still air, while the upper outlet chimneys will be in a region of moving air and will thereby be at a lower pressure, there will be a flow of air from the lower inlets through the ingredients and

out through the upper outlets. Thus, a naturally flowing stream of air will pass through the ingredients to facilitate the process of aerobic decomposition.