United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-F-96-005
April 1996
&EPA
A Citizen's Guide to
Thermal Desorption
Technology Innovation Office
Technology Fact Sheet
What is thermal desorption?
Thermal desorption is an innovative treatment
technology that treats soils contaminated with
hazardous wastes by heating soils to tempera-
tures of 200-1,000°F so that contaminants with
low boiling points will vaporize (turn into gas)
and, consequently, separate from the soil. (The
other soil contaminants, if any, are treated by
other methods.) The vaporized contaminants
are collected and treated, typically by an air
emissions treatment system.
Thermal desorption is a different treatment
process than incineration. Thermal desorption
uses heat to physically separate the contami-
nants from the soil. The contaminants then
require further treatment. Incineration uses heat
to actually destroy the contaminants.
How does thermal desorption work?
Typical thermal desorption systems (Figure 1
on page 2) consist of three components: the pre-
treatment and material handling system, the
desorption unit, and the post-treatment system
for both the gas (vaporized contaminants) and the
solid (remaining soil).
Pretreatment and Material Handling System
Pretreatment of contaminated material involves
sifting it to remove large clods and foreign de-
bris. If the contaminated material is very wet or
has a high level of contaminant, it may need to
be blended with sand or dried to make it a more
uniform mass for treatment in the desorption unit.
Desorption Unit
The function of the desorption unit is to heat the
contaminated soil to a sufficient temperature for
a sufficient period to dry it and vaporize the
contaminants from the soil. A common design
for the desorber unit is a rotary desorber, which
consists of a rotating cylindrical metal drum. In
a direct-fired rotary desorber, the material en-
ters the rotating cylinder and is heated by direct
contact with a flame or the hot gases coming off
a flame. In an indirect-fired rotary desorber, the
contaminated soil does not come into contact
A Quick Look at Thermal Desorption
Heats soil at relatively low temperatures to vaporize contaminants and remove them.
Is most effective at treating volatile organic compounds, semi-volatile organic compounds and other
organic contaminants, such as polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons
(PAHs) and pesticides.
Is useful for separating organic contaminants from refining wastes, coal tar wastes, wood-treatment
wastes and paint waste.
Printed on Recycled Paper
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Figure 1
The Thermal Desorption Process
Organic Liquid for
Further Treatment
or Disposal
'ater for Reuse
Yes
Further Treatment
or Disposal
Soil Redeposited or Reused
with a flame or combustion gases. Instead, the
outside of the metal cylinder is heated and the
hot metal indirectly heats the soil tumbling in-
side. As the waste is heated, the contaminants
vaporize, and then become part of the gas
stream of air and contaminated vapors flowing
through the desorber towards the post-treatment
system. An inert, or non-reactive gas, such as
nitrogen, may be added to the gas stream to
prevent the vaporized contaminants from catch-
ing fire in the desorption unit and to aid in va-
porizing and removing the contaminants.
Post-treatment System
"Offgas" from the desorber is typically pro-
cessed to remove particulates that remained in
the gas stream after the desorption step. Vapor-
ized contaminants in the offgas may be burned
in an afterburner, collected on activated carbon,
or recovered in condensation equipment. De-
pending on the contaminants and their concen-
trations, any or all of these methods may be
used. All disposals must meet federal, state, and
local standards.
Treated soil from the desorber is tested to mea-
sure how well the process removed the target
contaminants. The performance of thermal des-
orption is typically measured by comparing the
contaminant levels in treated soils with those of
untreated soils. If the treated soil is non-
hazardous, it is redeposited on-site or taken else-
where to be used as backfill. If, however, the
soil requires further treatment (for example, the
soil contained contaminants that did not respond
to this process), it may be treated with another
technology or transported off-site for disposal.
Why consider thermal desorption?
Thermal desorption is effective at separating
organics from refining wastes, coal tar wastes,
waste from wood treatment, and paint wastes. It
can separate solvents, pesticides, PCBs, dioxins
and fuel oils from contaminated soil. The
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T36
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equipment available is capable of treating up to
10 tons of contaminated soil per hour. Finally,
the lower temperatures require less fuel than
other treatment methods.
Will it work at every site?
Thermal desorption is not applicable to most
metals, although mercury can be removed by the
process. Other metals will either remain in the
treated soil, in which case the soil must be
retreated, or vaporize, in which case they may
complicate the offgas treatment. The presence
of metals and their fate must be determined
before the soil is processed.
Thermal desorption is not equally efficient at
treating all types of soil. If the soil is wet, water
will vaporize along with the contaminants.
Because of the additional substance (water)
being vaporized, more fuel is required to
vaporize all of the contaminants in the wet soil.
Soils with high silt and clay content are also
more difficult to treat with thermal desorption.
When heated, silt and clay emit dust, which can
disrupt the air emission equipment used to treat
the vaporized contaminants. In addition, tightly
packed soil often does not permit the heat to
make contact with all of the contaminants.
Therefore, it is difficult for them to vaporize.
Finally, thermal desorption would not be a good
choice for treating contaminants such as heavy
metals, since they do not separate easily from
the soil, and strong acids, since they can corrode
the treatment equipment.
Where is thermal desorption being
used?
Thermal desorption has been selected as a treat-
ment method at numerous Superfund sites. For
example, thermal desorption was used at the TH
Agriculture & Nutrition Company site in Alba-
ny, Georgia. Thermal desorption was used at the
site to treat 4,300 tons of oil contaminated with
pesticides (dieldren, toxaphene, DDT, lindane).
The system ran from July to October 1993.
Thermal desorption met the cleanup goals, re-
moving over 98% of the pesticides in the treated
soil. Table 1 on page 4 lists some additional Su-
perfund sites where thermal desorption has been
used or selected for use.
What Is An Innovative Treatment Technology?
Treatment technologies are processes applied to hazardous waste or contaminated
materials to permanently alter their condition through chemical, biological, or physical
means. Treatment technologies are able to alter, by destroying or changing, contami-
nated materials so they are less hazardous or are no longer hazardous. This may be
done by reducing the amount of contaminated material, by recovering or removing a
component that gives the material its hazardous properties or by immobilizing the
waste. Innovative treatment technologies are those that have been tested, selected or
used for treatment of hazardous waste or contaminated materials but lack well-docu-
mented cost and performance data under a variety of operating conditions.
Although thermal desorption is widely used, innovative variations are continually being
developed. It is still difficult to predict with certainty the time and cost to clean a site
using thermal desorption. For these reasons, it retains its "innovative" label as EPA
continues to track its performance.
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Table 1
. Examples of Superfund Sites Using Thermal Desorption (all projects completed)*
Name of Site
Re-solve, MA
Metattec/Aerosystems, NJ
Reich Farms, NJ
American Thermostat, NJ
U.S.A. Letterkenney SE Area, PA
Wamchem, SC
Type of Facility
Chemical reclamation
Metal manufacturing
Chemical drum storage/disposal
Thermostat manufacturing
Munitions manufacturing/storage
Dye manufacturing
Jacksonville NAS, FL Fire training site
Outboard Marine/Waukegan Harbor, IL Marine products manufacturing
Pristine, OH Industrial waste treatment facility
Sand Creek Industrial, CO Pesticide manufacturing
Contaminants
Volatile organic compounds (VOCs),
polychlorinated biphenyls (PCBs)
VOCs
VOCs, semi-volatile organic compounds
(SVOCs)
VOCs
VOCs
Benzene, toluene, ethylbenzene & xylene
(BTEX), VOCs, SVOCs
Polyaromatic hydrocarbons (PAHs)
PCBs
BTEX, pesticides, herbicides, VOCs
Pesticides, herbicides
For a listing of Superfund sites at which innovative treatment technologies have been used or selected for use,
contact NCEPI at the address in the box below for a copy of the document entitled Innovative Treatment
Technologies: Annual Status Report (7th Ed.), EPA 542-R-95-008. Additional information about the sites listed in
the Annual Status Report is available in database format. The database can be downloaded free of charge from
ERA'S Cleanup Information bulletin board (CLU-IN). Call CLU-IN at 301-589-8366 (modem). CLU-IN's help line is
301-589-8368. The database also is available for purchase on diskettes. Contact NCEPI for details.
Not all waste types ana site conditions are comparable. Each site must be individually investigated and tested.
Engineering and scientific judgment must be used to determine if a technology is appropriate fora site.
For More Information
The publications listed below can be ordered free of charge by calling NCEPI at 513-489-8190 or faxing your
request to 513-489-8695. If NCEPI is out of stock of a document, you may be directed to other sources. You may
write to NCEPI at:
National Center for Environmental Publications and Information (NCEPI)
P.O. Box42419
Cincinnati, OH 45242
• Selected Alternative and Innovative Treatment Technologies for Corrective Action and Site Remediation: A
Bibliography of EPA Resources, EPA 542-B-95-001. A bibliography of EPA publications about innovative
treatment technologies.
• Physical/Chemical Treatment Technology Resource Guide, September 1994, EPA 542-B-94-008. A listing of
publications and other sources of information about thermal desorption and other treatment
technologies.
• Engineering Bulletin, Thermal Desorption, February 1994, EPA540-S-94-501.
• Abstracts of Remediation Case Studies, March 1995, EPA 542-R-95-001.
• WASTECH* Monograph on Thermal Desorption, ISBN #1-883767-06-7. Available for $49.95 from the American
Academy of Environmental Engineers, 130 Holiday Court, Annapolis, MD 21401. Telephone 410-266-3311.
NOTICE: This fact sheet is intended solely as general guidance and information. It is not intended, nor can It be relied upon, to create any rights enforceable by any
party in litigation with the United States. The Agency also reserves the right to change this guidance at any time without public notice.
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