Anaerobic digestion is the conversion of complex organic materials by bacteria in the absence of oxygen. This differs from composting which requires oxygen for successful processing.

Anaerobic digestion systems do not produce as much heat as aerobic systems and therefore may require heating to facilitate digestion of the organic material undergoing processing.

Anaerobic digestion systems have traditionally been used in the waste water industry, however, this technology is also used to treat garden organics and food organics.

Commonly, the solid residues from the anaerobic digestor are subsequently composted aerobically to produce compost products. Alternative configurations are also possible to produce other recycled organics products such as dry pelletised products and/or liquid fertilisers. Anaerobic digestors produce methane as a fuel gas.

An EarthPower Pty. Ltd. anaerobic digestion facility is currently operating in Western Sydney.

More information on anaerobic digestion can be found in the report 'Food Organics Processing Options for New South Wales' available free to download. This report also includes a case study of the Atlas Group anaerobic digestion facility located at Perth.