Organic Waste

What is Organic Waste?

Treatments for Organics

Open Composting
Enclosed Composting
Vermicomposting
Anaerobic Digestion
Pyrolysis / Gasification

The organic waste stream is composed of waste of a biological origin such as paper and cardboard, food, green and garden waste, animal waste and biosolids and sludges. Organic waste is usually generated as a component of most waste streams. There are two common sources of confusion about the term organic waste. Firstly, the term is generally not intended to include plastics or rubber even though to an organic chemist, these polymers are certainly organic. Secondly, putrescible wastes are a subset of organic wastes with the distinction being that putrescible wastes, for instance food scraps, tend to biodegrade very rapidly whereas some other organic wastes, for instance paper, tend to require lengthy times or special conditions to biodegrade. For information on the treatments for managing Organic Wastes click on the links to the right.

Waste Volumes and Contribution

Organic wastes are the single largest component of the waste stream. Approximately 1.2 million tonnes of organic waste was generated in Perth in 1996 (Waste 2020, 2001). 25% of this waste originated from green (or garden) waste with other main contributors to this waste stream being manures and sludges (20%), food wastes (18%) and paper and cardboard waste (15%). Land clearing, timber processing and wood combine to form another 18% of the organic waste. In addition to being a valuable resource for nutrient poor soils, this material generates the most significant levels of pollution when disposed of in landfills. Some forms of organic wastes can cause public health problems, such as disease, odours and pests.

Organic Wastes and the Environment

In landfills, organic wastes decompose anaerobically to produce biogas (predominantly methane, a significant greenhouse gas) and leachate that contains nutrients and soluble organics. The leachate has the potential to pollute groundwater and may release and mobilise heavy metals from landfills (Waste 2020, 2001). Some organic wastes such as sludges and biosolids can contain heavy metals or nutrient pollutants. Uncontrolled disposal of biosolids may lead to site contamination or water pollution. To protect our water resources we need to prvent pollution arising from uncontrolled treatment and disposal of organic waste.

Open burning of organic wastes pollutes the air and contributes to the smoke haze problem in metropolitan Perth.

Recycling and Reuse

Organic wastes are resources and can be processed into various useful products. Given the low organic content of soils in Western Australia, any soil improvement products could be utilised, provided that logistics can be made economical. Agricultural and degraded land in WA would also benefit from the application of recycled organics products. Potential products and markets include mulch, compost, vermicompost, soil conditioners, recycled timber, firewood and energy recovery.

Successful recycling of organic waste depends on adequate separation at the source of generation, ensuring the production of a higher quality end product. Anaerobic digestion is an option for more noxious organic compounds such as biosolids and animal sludges, that would not normally be composted due to their offensive nature.

The production of recycled organics products will also conserve landfill space that is becoming increasingly scarce and expensive.

References

Towards Zero Waste: Actions for the Green and Organic Sector, 2001, Waste 2020 Task Force.
Strategy for the Management of Green & Organic Waste in Western Australia - Draft, 1997, DEP.
Organics Market Development Strategy, 1999, Environment Australia, http://www.deh.gov.au/settlements/publications/waste/organics/strategy/

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