Downend Composter Process
Green waste is received, shredded and mixed to provide an optimum blend of carbon rich (woody) and nitrogenous (leafy/grass clippings) material. This is then formed into blocks/windrows.
The process of composting is the controlled decomposition of carbon based material to base minerals and humus through the action of micro-organisms.
In addition to the green waste food source, the micro-organisms require both oxygen and water to function efficiently. Heat energy is created as a by-product of microbial activity, which in the presence of sufficient levels of oxygen and water, takes place almost immediately. Temperatures range between 55 to 80 degrees centigrade, after only 2 days, which kills all weed seeds and pathogens.
The process continues aerobically (in the presence of oxygen) until any of the food sources (material, water or oxygen) are exhausted. The material will remain on site for a period of 16 to 26 weeks to complete the process.
Temperatures will fall as the available oxygen level in the process reduces. The temperature within the process is therefore monitored to determine the activity within the process and to maintain the microbial activity, material is turned to re-introduce oxygen. Water is also added if moisture content falls below optimum levels.
Where the material is unable to be turned then, in the absence of oxygen, the material turns anaerobic degradation continues under the action of microbes which operate in the absence of oxygen. This then leads to the production of undesirable by-products (ammonia, hydrogen sulphide), most noted by the smell of gaseous compounds produced. Subsequent turning of anaerobic material releases these gases to atmosphere.
Under normal circumstances it is therefore generally essential to maintain aerobic conditions to
- Minimise odour nuisance and
- Maintain optimum degradation to produce the best quality final product.
Once the process is complete material is screened for size and supplied as a soil conditioner.
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