Almost anything can be recycled, but certain things are more common.
The use of paper in industrialized nations continues to increase, in some cases accounting for almost 20 percent of all household garbage [source: Essential Guide]. Although the trees used to make new paper are a renewable resource, old-growth forests are often chopped down to make room for the pulpwood trees, which are quickly planted and harvested to make paper. Recycled paper results in a significant net savings in terms of water and energy used, as well as pollutants emitted into the environment.
From curbside and workplace collections, paper is sorted based on the type of paper, how heavy it is, what it's used for, its color and whether it was previously recycled. Then a hot chemical and water bath reduces the paper to a soupy, fibrous substance. Magnets, gravity and filters then remove things like staples, glues and other unwanted chemicals from the pulp. The ink is removed by either a chemical wash, or by blowing the ink to the surface where it's skimmed off. The pulp -- which may be bleached -- is then sprayed and rolled into flat sheets, which are pressed and dried. Sometimes new pulp is added to the recycled pulp to make the paper stronger. The giant sheets of paper, when dry, are then cut into the proper size for resale back to consumers [source: Essential Guide].
Recycling glass represents significant energy and cost savings over making virgin glass, because there's virtually no down-cycling when glass is recycled. There are two ways to recycle glass. Some companies collect bottles from their customers and thoroughly wash and disinfect them before reuse. Other glass recyclers sort the glass by color (clear, green and brown glass shouldn't mix because it'll give it a mottled effect). The glass is ground up into fine bits known as cullet, thoroughly sifted and filtered using lasers, magnets and sifters, then melted down and reformed into new glass.
Only glass used in containers like jars and bottles is commonly recycled. Window glass and glass used in light bulbs is too expensive and difficult to recycle.
The recycling of scrap steel from cars and old buildings has a long history in the United States. Steel is relatively easy to recycle -- giant machines shred junk cars and construction waste. In addition, U.S. law requires a certain proportion of all steel to be made with recycled steel -- all U.S. steel contains at least 25 percent recycled steel.
Once sorted, scrap steel is melted down and re-refined into huge sheets or coils. These can be shipped to manufacturers to make car bodies or construction materials.