Sorting refuse into its constituent materials, also known as separation or segregation，is essential in recovery operations but also is useful in other processing steps，where it permits optional adjustment of operating conditions to each category of refuse.
Waste materials can be classified in different categories based on their re-usable functionality, that includes, recyclable waste like paper, metal, plastic, glass, cardboard are used to recycle and reuse; organic waste are used to make compost for agriculture; and non-disposable waste are not reusable and need to be buried as these are harmful for the environment. To ensure the better use of these resources, to promote the cost-effective production and cultivation, and finally to make the environment green, it is utmost important to categories and manage the wastes in to different category. Waste sorting contributes to recycling and saving energy.
Sorting relies on differences in the physical characteristics of refuse mate-rials, including size, shape, specific gravity，brittleness，elasticity, color, reflectance, magnetic susceptibility , electric conductivity，absorption of electro-magnetic radiation, and radioactivity.
Sorting is aided considerably by fragmenting refuse to enhance the cleanliness of individual particles，and by screening to promote dimensional uniformity. In addition，recovering valuable components can be facilitated by tagging these materials, for example, imparting a recognizable coding characteristic (magnetic or radioactive) that does not affect the material's performance.
