Stack Emissions

views updated

Stack emissions

Stack emissions are those gases and solids that come out of the smoke stack after the incineration process. Incinerators can be designed to accept wastes of any physical form, including gases, liquids, solids, sludges, and slurries. Incineration is primarily for the treatment of wastes that contain organic compounds. Wastes with a wide range of chemical and physical characteristics are considered suitable for burning. Most of these wastes are by-products of industrial manufacturing and chemical production processes, or result from the clean-up of contaminated sites.

There is a great deal of controversy about the content of incinerator stack emissions. The Environmental Protection Agency (EPA) supports incineration as a waste management tool and claims that these emissions are not dangerous. In an official publication, the EPA has stated: "Incinerator emission gases are composed primarily of two harmless inorganic compounds, carbon dioxide and water. The type and quantity of other compounds depends on the composition of the wastes, the completeness of the combustion process, and the air pollution control equipment with which the incinerator is equipped. These compounds include organic and inorganic compounds contained in the original waste and organic and inorganic compounds created during combustion."

Contrary to the EPA, many environmentalists believe that burning hazardous waste , even in "state-of-the-art" incinerators, releases far more heavy metals , unburned wastes, dioxins, and new chemicals formed during the incineration process (PICs) than is healthy for the environment or humans. In a report published in 1990, Playing with Fire, Greenpeace disagrees strongly about the toxic materials emitted from incinerator stacks.

The report argues that metals are not destroyed during incineration; in fact, they are often released in forms that are far more dangerous than the original wastes. At least 19 metals have been identified in the air emissions of hazardous waste incinerators. An average-sized commercial incinerator burning hazardous waste with an average metals content emits these metals into the air at the rate of 204 lb (92.6 kg) per year and deposits another 670,000 lb (304,180 kg) of metals per year in its residual ashes and liquids, which must be properly disposed of in landfills designed for that purpose.

The consequences to human health are significant. Cancer , birth defects , reproductive dysfunction, neurological damage, and other health effects are known to occur at very low exposures to many of the metals, organochlorines, and other pollutants released by waste-burning facilities. Increased cancer rates, respiratory ailments, reproductive abnormalities, and other health effects have been noted among people living near some waste-burning facilities, according to scientific studies in other countries and surveys conducted by community groups and local physicians in the United States.

Hazardous waste incinerators in the United States are producing at least 324 million lb (147 million kg) per year of ash residues. These ashes, which are buried in landfills, are contaminated by PICs, many of which are more toxic than the original waste. The ashes also contain increased concentrations of heavy metals, often in more leachable forms than in the original wastes.

Trial burns are used to determine an incinerator's destruction and removal efficiency (DRE). Under current federal regulations, an incinerator of general hazardous waste must, during the trial burn, demonstrate a DRE of 99.99% with just a few chemicals to be tested—perhaps one or two. Many environmentalists consider these standards unsatisfactory. In the unlikely event that this standard could be met at all times with all wastes burned throughout the lifetime of an incinerator, a hazardous waste incinerator of average size (70 million lb [32 million kg] per year) would still be emitting 7,000 lb (3,178 kg) per year of unburned wastes. With corrections and accidents, emissions may be as high as 700,000 lb (317,800 kg) per year. Environmentalists also argue that DRE addresses only the stack emissions of the few chemicals selected for the trial burn, and that it does not reflect other substances that are released. These include unburned chemicals other than those selected for the trial burn, heavy metals, or newly formed PICs. In addition, the present method for determining DREs does not account for the retention within the combustion system of the chemicals selected for the trial burn and their continued release for hours, or even days, after stack gas sampling has ceased.

[Liane Clorfene Casten ]