REFUSE DISPOSAL SYSTEM

technique for the collection and disposal of the solid wastes of a community. The development and operation of these systems is often called solid-waste management. Although all societies have had some systematic form of refuse disposal, it was not until relatively recent times that the modern concept of solid-waste management became recognized as an essential health and welfare service. Carelessly deposited garbage was for centuries a prime source of disease, whether through the infection of water supplies or as a breeding ground and food source for flies, rats, and other carriers of disease. Because pigs were often permitted to feed on raw garbage, they contracted such diseases as trichinosis, which was then passed along to humans. In the early 20th century Britain began heat treatment of garbage to prevent the transmission of such diseases. The industrialization of modern societies resulted in a vast increase in the amount of refuse generated per person. In the late 1970s between 50,000 and 58,000 pounds (22,700 and 26,300 kilograms) of refuse per person per year was produced in the United States alone. Industry has created new types of waste, especially toxic chemicals and radioactive materials, that are highly dangerous to public health and safety if they are disposed of improperly. There have already been several instances of entire communities being contaminated and evacuated because of careless handling or decomposition of toxic chemicals. Individuals share in the carelessness by littering roads and highways with trash and indiscriminately dumping such items as wrecked cars and old refrigerators. Estimates for the United States have put the bulk amount of these materials at 20,000,000 cubic yards (15,300,000 cubic metres) per year. Refuse is generally collected either by manually picking up trash bags from individual households or by mechanically emptying large community trash containers into trucks equipped with compactors to maximize their capacities. The refuse is then taken to a disposal site, of which the favoured design site is a sanitary landfill. Refuse of a landfillas opposed to garbage in an open dump which is left exposedis dumped into trenches, levelled and compacted with a bulldozer, and then covered with a layer of soil. When the landfill has reached its full capacity after a period of years, it may be used as a recreational area. Many cities have begun to run short of landfill space, however, and have begun to transport refuse to areas with sparse populations. Incineration has proved to be a satisfactory means of refuse disposal in areas where there is little or no landfill capacity. Combustible refuse is brought to a plant that is, in effect, an enormous furnace. There it is burned thoroughly by putting it through two combustion stages, and to protect air quality, the exhaust gases are cleansed. The expense of such a system can sometimes be reduced by putting the heat energy to use; plants of this type are in operation in Munich, Frankfurt, Paris, and Montreal. Disposal of refuse in water often creates pollution that can be a hazard for living things; for this reason the long-practiced method of dumping garbage at sea from scows has been greatly restricted. A relatively effective and safe method of disposing of organic refuse in water is the use of a food grinder attached to the sewage system of a household or food-handling establishment. Although these devices add only a small quantity of water to the community sewage system, they do increase the amount of solid material that must be handled at the treatment plant. The practice of recycling such salvageable materials as metal, glass, and newsprint began in earnest during World War II and has been revived to some extent since the early 1970s. Several states have passed laws requiring deposits on beverage containers (refundable with the return of the containers), which has resulted in reduced roadside litter. A variety of salvage companies have been established; products made of recycled paper, for example, have become common.