Recycling is an ancient practice with many modern applications. It refers to the
recovery and reuse of materials from spent products. In recent years recycling
has become a major part of environmental policy, mainly because of the increased
costs of solid- and hazardous-waste disposal, the scarcity of natural resources,
and the growing concern over polluted land, water, and air. There are two types
of recycling operations: internal and external. Internal recycling is the reuse
in a manufacturing process of materials that are a waste product of that
process. Internal recycling is common in the metals industry. External recycling
is the reclaiming of materials from a product that has been worn out or
considered obsolete. An example of external recycling is the collection of old
newspapers and magazines for the manufacture of newsprint or other paper
products. In some areas, industries are required to pretreat wastewater before
it is funneled into a waterway. In homes, wastewater is sent to a
sewage-treatment plant, where it is purified, recycled, and put back into the
water-supply system. Many gardeners recycle organic, biodegradable kitchen
scraps by mixing them with leaves and grass clippings in a compost mound. There
the organic waste decomposes and is biochemically transformed into usable soil.
Successful recycling programs depend on several factors. There must be a general
awareness of the problems caused by solid-waste disposal and an effective,
inexpensive method for separating and collecting the recyclable materials. It
also must be economically possible for industries to use and market recycled
materials. In 1976 the United States Congress passed the Resource Conservation
and Recovery Act, encouraging states to formulate solid-waste recovery plans.
Many states set up special departments to assist local communities in their
recycling efforts. Some communities adopted legislation that gives consumers the
option of returning containers in exchange for a small deposit paid at the time
of purchase. In the United States, more than 150 million tons of solid waste are
generated every year. This amounts to more than 3 pounds (1.4 kilograms) per
person per day. In metropolitan areas, the daily production of solid waste is
usually higher. Residents of New York City, for example, discard 26,000 tons of
solid waste daily almost 7 pounds (3.2 kilograms) for each resident. Domestic
recycling efforts usually involve the salvage of materials associated with
disposable products packages, bottles, and labels. The cost of disposing of the
solid-waste materials mainly paper, glass, aluminum, and steel has steadily
increased. In many cases the land used for garbage disposal, known as landfill
areas, is too valuable to use as a dumping ground. As existing landfills reach
their capacity, many municipalities turn to recycling programs as a relatively
inexpensive alternative to landfill disposal. Some cities also solve
energy-shortage problems and the need to dispose of growing amounts of organic
wastes and garbage by converting waste into energy. This is done by pyrolysis,
the incineration of refuse with a deficiency of air. While pyrolysis permits
recovery of certain fuel gases, chemicals, and heat energy, it can also
contribute to air pollution.