The waste can be classified into many types or fractions, each of them carrying its own different environmental problem: organic waste, recyclable waste, non-recyclable waste, toxic waste, nuclear toxic waste, and space waste.

The organic waste is easier resorbed by nature, but the speed and the geographical concentration of its production due to urbanization generate pollution of rivers, lakes, proliferation of disease vectors and environmental degradation of towns. The recyclable waste is composed of residuals that can be reprocessed, used again by humans, like plastics and metals. The problem regarding recyclable waste is that the separation of such material is not culturally diffused and there is not enough social organization to use them; so the recyclable waste is mixed to other wastes increasing even more the volume of waste depositories. The non-recyclable waste is formed of residuals that the technology cannot yet recycle, like ceramics, photographic paper, mirrors, cigarrettes, plasticized papers, etc; this kind of waste in the future may become recyclable waste and should be separated.