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Waste Management

Recycling And Composting

Recycling is a simple concept: using disused (or waste) material to make a new product. In practice, however, recycling is far from simple. Recycling consists of three essential elements: collection of the waste materials, also known as secondary materials or recyclables; processing those materials and manufacturing them into new products; and the marketing and sale of those new products. Dozens of different materials can be recycled, including glass bottles, aluminum cans, steel cans, plastic bottles, many types of paper, used motor oil, car batteries, and scrap metal. For each material, the collection, processing, and marketing needs can be quite different.

When the current recycling boom began in the late 1980s, markets for the recyclables were not sufficiently considered. A result was that some recyclable materials were collected in large quantities but could not be sold, and some ended up going to landfills. Today, the development of recycling markets is a high priority. "Close the loop" is a catch-phrase in recycling education; it means that true recycling (i.e., the recycling loop) has not taken place until the new product is purchased and used.

To boost recycling markets, many local and state governments now require that their own agencies purchase and use products made from recycled materials. In a major step forward for recycling, President Bill Clinton issued an executive order in 1993 requiring the federal government to use more recycled products.

Many managers of government recycling programs feel that manufacturers should take more responsibility for the disposal of their products and packaging, rather than letting municipalities bear the brunt of the disposal costs. An innovative and controversial law in Germany requires manufacturers to set up collection and recycling programs for disused packaging of their products.

The high cost of government-created recycling programs is often criticized. Supporters of recycling argue it is still less expensive than landfilling or incineration, when all costs are considered. Another concern about recycling is that the recycling process itself may generate hazardous wastes that must be treated and disposed.

Recycling of construction and demolition (C&D) debris is one of the growth areas for recycling. Although C&D debris is not normally considered a type of municipal solid waste, millions of tons of it have gone to municipal landfills over the years. If this material is separated at the construction or demolition site into separate piles of concrete, wood, and steel, it can usually be recycled.

Composting is considered either a form of recycling, or a close relative. Composting occurs when organic waste, such as yard waste, food waste, and paper, is broken down by microbial processes. The resulting material, known as compost, can be used by landscapers and gardeners to improve the fertility of their soil.

Yard waste, primarily grass clippings and tree leaves, makes up about one-fifth of the weight of municipal solid waste. Some states do not allow this waste to be disposed. These yard-waste bans have resulted in rapid growth for municipal composting programs. In these programs, yard waste is collected by trucks (separately from garbage and recyclables) and taken to a composting plant, where it is chopped up, heaped, and regularly turned until it becomes compost.

Waste from food-processing plants and produce trimmings from grocery stores are composted in some parts of the country. Residential food waste is the next frontier for composting. The city of Halifax, Canada, collects food waste from households and composts it in large, central facilities. For more details on recycling and composting, see the entries on those topics.

Biological treatment, a technique for handling hazardous wastes, could be called a high-tech form of composting. Like composting, biological treatment employs microbes to break down wastes through a series of metabolic reactions. Many substances that are toxic, carcinogenic (cancer-causing), or undesirable in the environment for other reasons can be rendered harmless through this method.

Extensive research on biological treatment is in progress. Genetic engineering, a controversial branch of biology dealing with the modification of genetic codes, is closely linked with biological treatment, and could produce significant advances in this field.

Additional topics

Science EncyclopediaScience & Philosophy: Verbena Family (Verbenaceae) - Tropical Hardwoods In The Verbena Family to WelfarismWaste Management - History Of Waste Management, Municipal Solid Waste, Agricultural, Mining, And Industrial Waste, Hazardous Waste