BACKGROUND OF THE INVENTION Earthworms comprise a group of invertebrates, (Phylum Annelida, Class Oligochaeta) which generally live in the ground and consume decomposing organic material. On consumption of organic and inorganic material, earthworms digest and absorb largely organic matter and excrete the waste, known as castings, back into the soil. Castings are known to contain various nutrients, such as nitrogen, phosphate, potash (such as potassium carbonate or hydroxide) and trace minerals such as copper, zinc and iron.

Thus, as a result of their feeding behaviour, earthworms aid in the decomposition of organic material and return a nutrient rich substance to the soil, whilst also ventilating the soil and promoting microbial decomposition of organic material within the soil.

The process of using worms to break down organic waste material is known as vermicomposting. Vermicomposting and worm culture or vermiculture can provide a means for disposing of organic wastes as well as providing worms for a variety of purposes such as raw material for animal feed or live worms for fishing.

There presently exists a need for the efficient conversion of organic waste into an innocuous or useful product that is environmentally friendly. Conventional methods of waste disposal such as tipping or burning, although effectively disposing of such waste, may generally have a negative impact on the environment. Such negative

impacts may include the leaching of toxic material or excessive nutrients into the soil and hence groundwater or the release of emissions into the atmosphere. Methods of waste disposal that are known to be environmentally friendly are increasingly being required to deal with greater quantities of waste whilst also remaining economically viable or profitable. There therefore exists a need to increase the efficiency of existing environmentally friendly waste disposal methods. In particular, there exists a need to increase the commercial viability of environmentally friendly waste disposal methods.

There also exists a need for an environmentally friendly method of disposal of the residue from the extraction of aluminium oxide (A1203) from laterite or bauxite, known as red mud. Red mud is a highly caustic substance with a pH that is generally greater than 13.0. Neutralisation of red mud to render it substantially non-toxic to humans and other animal life is generally a costly and onerous procedure.

The present invention attempts to overcome at least in part some of the aforementioned problems.

SUMMARY OF THE INVENTION In accordance with a first aspect of the present invention, there is provided a process for the conversion of organic waste, characterised by the steps of shredding organic waste, amending the shredded organic waste with red mud to produce amended organic waste, moistening the amended organic waste and introducing earthworms to the moistened amended organic waste, wherein the earthworms consume the amended organic waste and aid in converting the amended organic waste into an innocuous or useful product by the production of castings.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION A process for the conversion of organic waste into an innocuous or useful product is characterised by the first step of shredding an organic waste and then amending the organic waste with red mud.

Organic waste may be defined as including any waste product, containing organic material, which must be disposed of, such as municipal solid waste, sewerage sludge, biosolids, food processing wastes and agricultural wastes such as straws, almond waste, green waste, cotton lint waste, cotton gin trash and manure. Preferably, the organic waste is a combination of green waste with sewerage sludge. Sewerage sludge is generally dewatered to about 60% moisture to render it substantially solid prior to being used in the present invention.

The organic waste may be shredded by any suitable shredding means, such as processing through a tub grinder or chopper. To ensure maximum compactness and minimise space requirements, the organic material is shredded into relatively small pieces. Preferably, the organic waste is shredded to produce fragments that have a mean length of 50 millimetres or less. The organic waste may be shredded to produce fragments that have a length of 1.0 millimetres or less, although such sized organic waste fragments may require more continuous agitation when composting than relatively larger sized fragments.

Following shredding, the organic waste is intimately mixed with red mud to produce an amended organic waste. Preferably, the organic waste is mixed with 5% to 30% of red mud by volume. Red mud is a fine inorganic material which adsorbs organic nutrients and which is well known in the aluminium processing industry as the residue from the extraction of aluminium oxide (A1203) from laterite or bauxite ores. Red

mud is generally obtained by caustic leaching of bauxite or laterite, in a process known as the Bayer process. Red mud is known for its capacity to adsorb organic nutrients. Preferably, the red mud is mixed with the shredded organic waste in a tumbler, such as a trommel screen. Ideally, the amended organic waste is able to pass through a 25-millimetre screen. The physical consistency of the amended organic waste has been found to be particularly suitable for consumption by worms. This is believed to be because the amended organic waste contains fine particles of highly nutrient laden material. The particles of red mud within the amended organic waste are also of a size that is accommodating to the feeding behaviour of worms as well as being highly laden with nutrients. Red mud may be added to the organic waste in a solid or particulate form or may be added to the organic waste as a liquid mixture Optionally, the amended organic waste may be initially composted. This composting may be conducted anaerobically or aerobically. The composting is preferably conducted under aerobic conditions if odour is anticipated as a problem. The composting step initiates the decomposition required by worms for conversion of the amended organic material to castings. Composting also aids in avoiding the problem of overheating the worms in the amended organic waste if composting occurs during the worm feeding process. Composting may also have the added advantage of destroying pathogens and seeds present in the amended organic waste that may prove problematic when the final product is used.

Following shredding, amending the organic waste with red mud and optionally composting, the amended organic waste is moistened, preferably with water. The amended organic waste is moistened with water to a level of at least 60% by weight of the total composition. The moistened amended organic waste may be directly

distributed in windrows or other suitable worm systems such as worm culture vessels.

However, if adequate acreage is not available at the time of preparation to allow for the formation of windrows, the amended organic waste may be placed in suitable storage.

The worm culture vessels or windrows are provided with a collection of worms suitable for the decomposition of organic material. Preferably, the type of worm used in the present invention is a red worm (Lumbricus rubellus), blue worm (Perionyx excavatus) or Tiger worm (Eisenia fetida). Distribution of the amended organic waste to the worm systems may be accomplished by any suitable means, such as common farm equipment, including conveyors, spreaders or feed wagons.

Further moisture is added to the or each worm system as required, so as to maintain the moisture level of the amended organic material to at least 60% by weight of the total composition. This further moistening may be accomplished by the use of sprinklers and the like or any other suitable moistening means. The worm systems are to be well drained so as to avoid waterlogging of the worm systems.

The progressive addition of moisture to the amended organic waste in the worm systems results in a vertical compaction of the worm system, as castings generally settle, with moisture, as a fine deposit at the bottom of the worm system. Additional amended organic waste may be progressively added to the worm system as the amended organic waste in the worm system is converted to castings. To reduce excess heat in the worm system from the addition of further amended organic waste that has undergone composting, the amended organic waste is first moistened to at least 60% moisture by weight. The addition of further layers of moistened amended organic waste may result in a plurality of feed layers within the worm system.

Preferably, the compacted feed layers are of a thickness in the order of between five and ten centimetres.

The castings produced by the worms in the or each worm system may be removed by a screening means. Commercially available screening equipment is available for the separation of castings from worms and pieces of unconverted organic waste that are large relative to the castings produced by the worms in the worm system.

Alternatively, the step of adding amended organic waste may be repeated for each worm system to provide a substantially continuous worm system. Continuous worm systems are commercially available that enable the input of organic waste in a top portion of the worm system, with an output of castings from a lower portion of the worm system and these may be used for this purpose.

EXAMPLES The invention will now be further described with reference to the following example.

Two worm systems, each of equal volumes were prepared, side by side at ambient temperatures, in a vessel that was 3 metres long by 900mm wide (1.5 metres by 900 mm per system). The first system comprised a shredded and composted mixture of 63% green waste and 37% sewerage sludge and the second system comprised a shredded and composted mixture of 20% red mud, 30% sewerage sludge and 50% green waste. Green waste substantially comprised tree prunings from Gosnells City Council, Perth, Western Australia and delivered to the test site by Cleanaway.

Sewerage sludge was dewatered to approximately 60% to render it substantially solid prior to mixing with green waste and red mud. Red mud was supplied by Alcoa, delivered to Cleanaway whereupon the mixing of the red mud was performed by Cleanaway Technical Services in Brookdale, Perth, Western Australia. Each system

was moistened with water to 60% moisture by weight of the total composition. Each system was then inoculated with approximately, 50kg of a mixture of red worms (Lumbricus rubellus), blue worms (Perionyx excavatus) and tiger worms (Eisenia fetida). Worm activity was monitored by observation for a period of 24 hours. It was observed at the conclusion of the 24 hour period that 50% of the worms within the first system migrated to the second system, indicating a preference for the worms for feeding on the composition which included red mud.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.