United States Office of Solid Waste and EPA 542-F-01-010

Environmental Protection Emergency Response October 2001

Agency (5102G) www.epa.gov/superfund/sites

www.cluin.org

A Citizen’s Guide to

Chemical Dehalogenation

  EPA uses many methods to clean up pollution at Superfund and other sites. Some, like chemical dehalogenation, are

considered new or innovative. Such methods can be quicker and cheaper than more common methods. If you live,

work, or go to school near a Superfund site, you may want to learn more about cleanup methods. Perhaps they are

being used or proposed for use at your site. How do they work? Are they safe? This Citizen’s Guide is one in a

series to help answer your questions.

	
	
	


Chemical dehalogenation removes halogens from harmful chemicals, making them less toxic.

Halogens are a class of chemical elements that includes chlorine, bromine, iodine, and fluorine. Many harmful chemicals contain halogens. The presence of halogens can be one of the

main reasons such chemicals are toxic. Chemical dehalogenation is most often used to remove

chlorine from PCBs and dioxins contained in polluted soil, sludge, or sediment.



	


Before using chemical dehalogenation the soil must be dug from the polluted area to be

treated. The soil is sifted and crushed to remove large objects, like rocks and debris. The sifted

soil is then mixed with chemicals and heated in a large container called a reactor. During

mixing and heating, a chemical reaction occurs which changes the harmful chemical. The

reaction involves removing the halogens and replacing them with less toxic chemicals. Chemical dehalogenation can also work by evaporating the harmful chemicals, which changes them

to gases. The gases are then destroyed.

There are two common types of chemical dehalogenation: glycolate dehalogenation and basecatalyzed decomposition.

Glycolate dehalogenation adds a combination of two chemicals called “APEG” to soil in the

reactor. During mixing and heating, one chemical combines with the halogens to form a nontoxic salt. The other replaces the halogens to form other non-toxic chemicals. The heat in the

reactor can cause some of the chemicals in the soil to evaporate. The gases are treated by air

pollution control equipment at the site.

The soil is then placed in a separator/washer where the excess APEG is removed from the

soil. Any remaining APEG is removed from the soil with water. The APEG can be reused in

the cleanup of more soil. The wash water is removed from the soil and treated. When the soil

is clean, it can be placed back on the site. If the soil still contains chemicals in harmful

amounts, it is placed back in the reactor to repeat the process.

Base-catalyzed decomposition adds a chemical called “sodium bicarbonate” to soil in the

reactor. The sodium bicarbonate allows the harmful chemicals in the soil to evaporate at a low
2



	


write the Technology

Innovation Office at:

U.S. EPA (5102G)

1200 Pennsylvania Ave.,

NW

Washington, DC 20460

or call them at

(703) 603-9910.

Further information also

can be obtained at

www.cluin.org or

www.epa.gov/

superfund/sites.

temperature. Once the chemicals evaporate, the cleaned soil can be returned to the site. The gases

produced during evaporation are changed into liquids. These liquids are then mixed with other

chemicals, such as sodium hydroxide and heated again. A chemical reaction occurs that removes

the halogens from some of the chemical and replaces them with hydrogen. This produces a nontoxic salt and a non-toxic chemical. The resulting mixture is then treated using other cleanup

methods and recycled.

	
	
	
	

Chemical dehalogenation can be quite safe to use, but there are potential hazards. Chemical

reactions can result in flammable and even explosive conditions in the reactor. Proper design and

operation must be followed to avoid these conditions. Some of the chemicals used are corrosive,

which means they can wear away certain materials and burn the skin. Therefore, workers must

wear protective clothing. During digging and cleanup, air pollution equipment must be used to

control dust and gases. Chemicals are rarely released from the reactor, but EPA tests the air to

make sure that chemicals are not released in harmful amounts. EPA also tests the soil to be sure it

is clean before it is placed back on the site.

		
	
	


Chemical dehalogenation has been used at several sites to remove halogens from PCBs, dioxins,

and certain pesticides. It works best for small amounts of polluted soil or polluted soil that has

small amounts of harmful chemicals. Chemical dehalogenation can be conducted at the site,

which avoids the costly transport of soil to a cleanup facility. It also can be cheaper to operate and

maintain compared to other methods that cleanup similar harmful chemicals. And the cleanup

time is relatively short.

NOTE: This fact sheet is intended solely as general guidance and information to the public. It is not intended, nor can it be relied upon, to

create any rights enforceable by any party in litigation with the United States, or to endorse the use of products or services provided by

specific vendors. The Agency also reserves the right to change this fact sheet at any time without public notice.

Glycolate Dehalogenation

The time it takes to clean up a site using chemical dehalogenation

depends on:

• the amount of polluted soil

• the condition of the soil (Is it wet or dry? Does it contain a lot of debris?)

• type and amounts of harmful chemicals present.

Cleanup can take just a few weeks at sites with small amounts of polluted soil.

air pollution

control

equipment

reactor separator/

washer

gases

APEG

polluted

soil (sifted)

treatment

plant

dewatering

system

wash

 water

clean soil

(returned to site)

clean 

water