waste disposal, the collection, processing, and recycling or deposition of the waste materials of human society. Waste is classified by source and composition. Broadly speaking, waste materials are either liquid or solid in form, and their components may be either hazardous or inert in their effects on health and the environment. The term waste is typically applied to solid waste, sewage (wastewater), hazardous waste, and electronic waste.
In industrialized countries, municipal liquid waste is funneled through sewage systems, where it undergoes wastewater treatment, or sewage treatment. This process removes most or all of the impurities from wastewater, or sewage, before they can reach groundwater aquifers or surface waters such as rivers, lakes, estuaries, and oceans. (For more information on sewage systems and treatment, wastewater treatment.
Refuse, or municipal solid waste (MSW), is nonhazardous solid waste from a community that requires collection and transport to a processing or disposal site. Refuse includes garbage and rubbish. Garbage is mostly decomposable food waste, and rubbish is mostly dry material such as glass, paper, cloth, or wood. Garbage is highly putrescible or decomposable, whereas rubbish is not. Trash is rubbish that includes bulky items such as old refrigerators, couches, large tree stumps, or construction and demolition waste (e.g., wood, drywall, bricks, concrete, and rebar [a steel rod with ridges for use in reinforced concrete]), all of which often require special collection and handling. Refuse is often deposited in sanitary landfills—that is, pits or other sites sealed with impermeable synthetic bottom liners where waste is isolated from the rest of the environment. (For more information on the treatment of solid wastes, see solid-waste management.)
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