Vermicomposting is the breakdown of organic material that, in contrast to composting, involves the joint action of earthworms and microorganisms and does not involve a thermophilic (i.e. high heat) stage (Dominguez et al 1997). As the agents of turning, fragmentation and aeration, the worms consume organic wastes such as food waste, animal wastes and sewage sludge to produce a soil conditioner (Dominguez et al 1997).
Vermicomposting is widely used at a small scale such as in backyard composting and in offices and schools, these technologies are however now being developed at a commercial scale for processing sewage sludge/biosolids and animal wastes (Waste Inquiry 2000).
Waste Streams Handled
Traditionally, worms have been used to break down manure which makes it an appropriate process for sewage sludge degradation (Waste Inquiry 2000). Vermicomposting may only process organic waste of a suitable structure for worms and waste streams include (Dominguez et al 1997):
- some food wastes;
- sewage sludge; and
- Operating Details
The traditional open systems of vermicomposting are usually based on beds or windrows on the ground containing materials up to 18 inches deep (Dominguez 1997). This technique requires large areas of land for large-scale production and such systems process organic wastes relatively slowly (Dominguez 1997).
There is increased interest in developing in-vessel vermicomposting systems whereas some systems have used bins or larger containers, often stacked in racks (Dominguez 1997). Other more promising techniques have used batch reactors - containers raised on legs above the ground as these allow materials to be added at the top and collected mechanically at the bottom through mesh floors (Dominguez 1997). Such methods have been developed and tested at the National Institute for Agricultural Engineering in Silsoe England, and currently used in several places in the U.S. (Dominguez 1997).
Vermiculture has been practiced widely on a small scale for many years but only recently have there been commercial sized facilities operating (Waste Inquiry 2000). Research in vermicomposting is not developed to the same level as for composting but there are a number of pilot projects examining large to medium scale potential (Waste Inquiry 2000).
In the City of Toronto, Canada, the City council offices have developed a vermicomposter to treat organic waste. In Australia, there is one large-scale vermicomposting facility in operation (the Vermitech Redlands facility) located outside of Brisbane. In Western Australia, Alcoa Australia operates a vermicomposting farm at the Pinjarra refinery.
- Dominguez, J., C.A. Edwards and S. Subler (1997) A Comparison of Vermicomposting and Composting. Biocycle, April.
- Waste Inquiry (2000) Report of the Alternative Waste Management Technologies and Practices Inquiry.