High temperatures, 870 to 1,200 ¡C (1,400 to 2,200 ¡F), are used to volatilize and combust halogenated and other organics in hazardous wastes. Auxiliary fuels are used to initiate and sustain combustion. Incinerator designs are geared towards different waste streams and different end products, and operating temperatures vary with the different designs. The destruction and removal efficiency for properly operated incinerators is 99.99% for most waste. Off-gases (emissions) and combustion residuals generally require treatment. Air pollution-control systems are employed to remove particulates, as well as to neutralize and remove acids.
Incineration is different from other thermal technologies in that it oxidizes bulk quantities of waste that may be in liquid and solid phase. Pyrolysis, which is described separately, uses heat in the absence of oxygen to destroy contaminants. Thermal and Catalytic Oxidation treats only the vapor phase of contaminants.
Limitations and Concerns
Incinerators may release carcinogenic and toxic chemicals from their stacks, including heavy metals, partially-burned organic material such as polyvinyl chloride (PVC), herbicide residues, and other organic chemicals, including polycyclic aromatic hydrocarbons (PAHs), dioxins and furans.
When chlorinated hydrocarbons are incinerated, products of incomplete combustion are formed. These may include dioxins and furans. Several PAHs, dioxins and furans are known or suspected human carcinogens. Dioxins are toxic in the parts per trillion range. Even with the best practices, formation of these products may take place as gases leave the stack.
Only one off-site incinerator is permitted in the United States to burn wastes that contain polychlorinated biphenyl (PCB) and dioxin. It reportedly achieves 99.9999% destruction efficiency.
Wastes with heavy metals can produce a bottom ash with high concentrations of hazardous substances. The ashes may require disposal and/or stabilization. Some heavy metals, including lead, cadmium, mercury, and arsenic may partially vaporize and leave the combustion unit with the flue gases. This may require gas-cleaning systems for removal.
Metals can react with other elements in the feed stream, such as chlorine or sulfur, forming compounds that are more volatile and toxic than the original species. Most of these compounds are short-lived reaction intermediates that can be destroyed.
If an off-site incinerator is used, the potential risk of transporting the hazardous waste through the community must be considered.
A British study conducted recently found statistically significant increases for all cancers combined among people living within 7.5 kilometers of an incinerator.
Three French solid waste incinerators were closed in January, 1998 because milk from cows on nearby dairy farms was contaminated with excessive levels of dioxins. A municipal incinerator near Maubeuge in northern France has contaminated cows' milk at levels of 22 parts per trillion (ppt) in milk fat.
Incineration is used to remediate soils contaminated with explosives and hazardous wastes, particularly chlorinated hydrocarbons. One incinerator in the U.S. treats soils contaminated with PCBs and dioxins.
Technology Development Status
Incineration is a commercial technology. It has been selected or used as the remedial action at more than 150 Superfund sites.
Other Resources and Demonstrations
See Julia G. Brody and Terry Greene, "Incineration: Decisions for the 1990s" (Boston, Mass.: Tellus Institute and JSI Center for Environmental Health Studies, 1994). Available from JSI Center for Environmental health Studies, 210 Lincoln St., Boston, MA 02111; telephone (617) 482-9485.
See International Agency for Research on Cancer (IARC), "Monographs on the Evaluation of Carcinogenic Risk to Humans: Volume 69, Polychlorinated Dibenzo-Para-Dioxins and Polychlorinated Dibenzo-furans," Lyon, France, February, 1997.
See http://www.clu-in.org/download/contaminantfocus/dioxins/Dioxin-Treatment-Technologies-OTA-9116.pdf for dioxin treatment, including incineration.