Waste, Industrial. All industries have waste products. Among the great variety of industrial wastes that are generated are acids, metallic compounds, oils, and complex synthetic chemicals. The wastes from metallurgical industries include slag and scrap metal. Mining operations leave tailings (rock of little or no value) as a waste. Manufacturing processes yield many kinds of chemical waste products, and nuclear reactors produce radioactive wastes.

The disposal of wastes is a major task. Many types of wastes are disposed of in landfills. Incineration (burning) is another method of disposing of wastes. High-temperature incineration destroys even durable synthetic compounds. Some wastes are disposed of in the oceans; some in caverns deep underground. In deep-well injection, wastes are pumped into porous rock at the bottom of deep wells.

Wastes that contain toxic, radioactive, corrosive, or explosive substances pose a serious threat to the environment and to human health; such wastes, called hazardous wastes, must be treated before disposal to make them harmless. Among the methods used to treat hazardous wastes are chemical treatment and biological treatment, or bioremediation. In chemical treatment, waste is made harmless by altering its chemical structure through such processes as catalysis. (See Catalysis.) In biological treatment, waste is decomposed into harmless substances by microorganisms. Biological treatment is often used to decompose toxic substances that pollute the environment. Some of the microorganisms used in biological treatment occur naturally; others are genetically engineered.

Some wastes can be recycled—that is, they can be used again as material for new products. Among the materials that are recycled are metals and glass. One commonly recycled inetal is aluminum. It is generally less costly to produce aluminum from scrap metal and discarded aluminum products than to produce it from natural ores. In addition to reducing costs of production, the recycling of wastes can help preserve natural resources.

For some manufacturing processes, commercially valuable uses have been found for products that would otherwise be treated as wastes. These products are often referred to as by-products. For example, before the invention of the automobile, gasoline was dumped as a waste product produced during the refining of petroleum. Glycerin, once a waste product of the soap industry, is now one of the industry's chief products.

Some wastes can be used as fuel. The wastes may be used directly, or they may be used to produce another substance, such as methane gas, that can be used as a fuel.

The disposal of hazardous wastes is a serious and expensive problem. If not properly treated, wastes remain hazardous to human health for a very long time. Careless disposal of hazardous wastes has resulted in severe contamination of the water and land in several areas of the United States. In response to this problem, Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act (commonly called the Superfund Act) in 1980. This act, administered by the Environmental Protection Agency, authorizes the use of federal funds to clean up abandoned hazardous waste sites. In addition, the act requires that any company found to be responsible for a waste site must contribute funds to its cleanup.