Waste sorting plants themselves can be more or less technically complex, but generally comprise a series of sorting processes supported by a variety of ancillary facilities designed to manage the process and maintain output quality. At the plant, waste undergoes a series of procedures that refine the material stream, extracting specific materials that can be recycled, or removing material suitable only for disposal. Termed positive and negative sorting respectively, most sorting plants rely on both types of sorting to produce clean fractions of sufficiently high quality.
A variety of techniques are used to separate materials in a waste stream. Moving beds, drums and trommel screens, and air separators are used to differentiate materials by size, weight and density, while other sorting technologies utilize magnets and eddy currents to recover ferrous and non-ferrous metals. Some plastic is separated by exploiting its physical properties, but the bulk of plastic recovery relies on identification of the plastic with sensor technology and subsequent mechanical removal from the waste stream.
Sorting plants designed to accept mixed municipal solid waste, where all household waste is collected in a single waste stream, are capable of extracting metals and glass, and typically contaminated plastics. The waste entering such a plant is already too intermingled at the point of collection, prohibiting high-quality recycling.
If planned and operated properly waste sorting plants can help increase recycling, reduce waste disposal and replace virgin raw materials in the manufacture of new products. They are a vital component in advanced waste management.