The international recycling symbol. Environmental technology Air pollution control Air pollution dispersion modeling Alternative energy Biofuel Composting Conservation biology Conservation ethic Ecoforestry Electric vehicle Energy conservation Energy development Energy efficiency Environmental design Environmental impact assessment Environmental preservation Green building Green computing Hydrogen technologies Industrial wastewater treatment Natural building Plug-in hybrid Recycling Renewable energy Renewable energy development Remediation Solid waste treatment Sustainable architecture Sustainable energy Sustainable development Waste water treatment Water purification Waste management Environmental science Recycling is the reprocessing of materials into new products. Recycling generally prevents the waste of potentially useful materials, reduces the consumption of raw materials and reduces energy usage, and hence greenhouse gas emissions, compared to virgin production.[1] Recycling is a key concept of modern waste management and is the third component of the waste hierarchy. Recyclable materials, also called "recyclables", may originate from a wide range of sources including the home and industry. They include glass, paper, aluminium, asphalt, iron, textiles and plastics. Biodegradable waste, such as food waste or garden waste, is also recyclable with the assistance of micro-organisms through composting or anaerobic digestion. Recyclates are sorted and separated into material types. Contamination of the recylates with other materials must be prevented to increase the recyclates' value and facilitate easier reprocessing for the ultimate recycling facility. This sorting can be performed either by the producer of the waste or within semi- or fully-automated materials recovery facilities. There are two common household methods of recycling. In curbside collection (UK: kerbside collection), consumers leave presorted recyclable materials in front of their property to be collected by a recycling vehicle. With a "bring" or carry-in system, the householder takes the materials to collection points, such as transfer stations or civic amenity sites. The term recycling does not generally include reuse, in which existing items are used for a new purpose.