Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Destruction of hazardous or toxic waste
Reexamination Certificate
1998-05-29
2002-06-04
Langel, Wayne (Department: 1754)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Destruction of hazardous or toxic waste
C071S009000, C435S290100, C435S209000
Reexamination Certificate
active
06399359
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to composting systems for treatment of organic waste in a manner accepted to be environmentally sustainable.
BACKGROUND OF THE INVENTION
Each day a large amount of solid municipal domestic waste is produced. Of all solid municipal domestic waste produced in Australia approximately 50-55% consists of food and garden waste. Other components of the waste include paper (20%), plastics (6%), glass (10%), metals (5-7%) and other inorganics (10-15%). The organic fraction has a strong detrimental impact on the environment and may be hazardous.
Detriment results from the large volume of organic waste which may occupy 50-70% of landfill space. The waste is of a putrescible nature, thus making it a potential source of pathogenic organisms. A large volume of greenhouse gases, e.g. carbon dioxide and methane are released during uncontrolled decomposition. Finally, and significantly, decomposing organic matter causes odour, attracts pests and is a major contributor to groundwater pollution through dissolution and its role as a carrier or inorganic pollutants such as heavy metals. In certain cases such pollution may make groundwater unsuitable for safe use.
Therefore, one of the main challenges in any integrated waste management strategy is the appropriate and effective treatment of organic waste. The current practice of landfilling organic waste is rapidly becoming an inappropriate waste treatment practice and will be unsustainable in the long term.
Landfilling consumes large areas of land, results in low land value and is strongly objected to by residents. Consequently, landfilling is fast disappearing in major cities as a sole waste disposal strategy. In cities with low housing densities, transport costs may become prohibitive as suitable landfill space becomes available only well away from waste generation centres.
Organic waste nevertheless has considerable potential as a resource when stabilised through composting. It is high in organic matter and contains nutrients such as nitrogen (2%), phosphorus (0.5-0.7%), potassium (0.7-1.7%) and trace elements.
Composting is the process whereby organic matter is decomposed by a range of microorganisms using oxygen. The process is appropriate for treatment of. a combination of fibrous waste (e.g. green organics) and putrescible waste such as food waste, sewage sludge and industrial and commercial organic residues. Composting has the advantage of reducing the waste volume by 30-40%. In addition, product compost has significant benefits as a soil conditioner.
A typical composting process may comprise four stages. Each stage is characterised by the activity of different generations of bacteria, fungi, protozoa and actinomycetes. During each stage the microbes use original organic compounds present in the waste as well as by-products of the metabolism of the previous generation as a nutrient and energy source. Thus the organic matter decomposes until a stable humus is formed.
The incubation or mesophilic phase lasts for approximately 24 hours during which the organic matter is rapidly invaded by mesophilic composting organisms including bacteria, actinomycetes and fungi. These organisms thrive at a temperature of 25°-45° C. The mesophilic organisms grow in this phase on the more easily assimilated substances present in the organic waste, for example: sugars, soluble protein, starch and organic acids.
The high metabolic activity of the organisms and the exothermic decomposition processes that result, in combination with the insulating properties of the composting material, causes the temperature to rise. The temperature rise strongly favours thermophilic sporogenous bacteria. The activity of these bacteria takes the process into the thermophilic phase.
During the thermophilic phase, organic matter is decomposed rapidly. Temperatures may reach 70° C. in the core of the composting material. This is undesirable, since at this temperature most process participating microbes, including some thermophilics, are killed. This may considerably reduce the decomposition rate of organic material. About 45°-50° C. is optimum and above 55° C. is typically required for pathogen destruction, thus 55° C. is accepted as an optimum temperature compromising between these factors, at which the decomposition rate is highest. These temperatures assist in accelerating the process and sanitising the material from pathogens, weed seeds and plant disease causing agents. This temperature, and below, allows the development of eumycetes and actinomycetes which are the main decomposers of long chain polymers, cellulose and lignin. The oxygen demand is very high in this phase and aeration is required. This phase may last for 2-3 weeks depending on aeration and substrate.
The cooling phase commences when there is insufficient exothermic organic substrate left to maintain the high temperature. Accordingly, water evaporation and heat convection cause temperature to drop. If the temperature drops below 45° C. mesophilic bacteria and other organisms may reinvade the fresh compost. This phase may last a few days.
A maturation or stabilisation phase is required to allow the toxicity of fresh compost to fall to enable effective utilisation by plants. The activity of fungi, protozoa and actinomycetes may be highest during this phase, while bacterial activity slowly falls. At this stage, large polymers such as lignin and cellulose are decomposed and a humidification process sets in. The activity of actinomycetes produces the compound “geosmine” which gives matured compost a fresh earthy smell. Three to four weeks may be sufficient to enable completion of this phase.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a composting system that may enable the respective phases of the composting process to be completed in an efficient manner, under conditions that enable the most advantageous conditions for aerobic microbial decomposition of an organic substrate to occur.
With this objective in view, the present invention provides a composting system comprising an area for holding compostable material; a mass of compostable material located in the area; the area and a weatherproof cover or structure for the area defining an environment in which composting occurs, and an environmental condition which is controlled to optimise the composting process.
In particular, the weatherproof cover is preferably to be secured or appropriately sealed to prevent ingress of water or other environmental, especially climatic, impacts detrimental to efficient composting such as excessive drying out. Entry of pests and vermin is also prevented. A flexible or modular construction for the cover is preferred, particularly a cover which is readily conformable to the volume of material to be composted. The volume of the environment is dictated primarily by the volume of compostable material to be treated.
In this respect, the invention is predicated on the discovery that the composting process is dependent upon a number of variables, the control of which ensures a more efficient composting process. Further, the cover prevents escape of odour, water ingress and generation of leachate. Leachate generation is a particular problem in open air composting systems such as windrow composting and static pile forced aeration composting which are strongly dependent on weather conditions. Where rainfall is high, water may drain through compost windrows, leaching nutrients and soluble organic matter from the compost. The generated leachate may usually require treatment before discharge to surface or ground water and compost quality is reduced.
For a first example, the control of aeration may be important to conducting the composting process. Aeration provides the oxygen necessary to sustain the aerobic organisms that promote composting. In a static pile, oxygen levels can drop to below 1% by volume and carbon dioxide levels can reach 20% by volume. Such levels may be inhibitive to composting.
Therefore, aeration means to aerate the mass of compostable material
Birch Stewart Kolasch & Birch
Langel Wayne
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