United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-89/008 Oct. 1989
&EPA Project Summary
Radio Frequency Enhanced
Decontamination of Soils
Contaminated with Halogenated
Hydrocarbons
H. Dev, J. Bridges, G. Sresty, J. Enk, N. Mshaiel, and M. Love
There has been considerable effort
in the development of innovative
treatment technologies for the clean-
up of sites containing hazardous
wastes such as hydrocarbons and
chlorinated hydrocarbons. Typical
examples of such waste material are:
chlorinated solvents, polychlorinated
biphenyls, waste aviation fuels, gaso-
line, etc. The feasibility of treating
waste sites containing such materials
by in-situ radio frequency heating
was established by this study
through bench- and pilot-scale exper-
iments. A design for an in-situ field
test was developed for the treatment
of sites containing solvents and
aviation fuel. Cost studies were
performed to estimate the treatment
cost of a system for the decontam-
ination of sites containing fuel, etc.
This Project Summary was
developed by EPA's Risk Reduction
Engineering Laboratory, (formerly
HWERL) Cincinnati, OH, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Each year, various agencies of the
U.S. Government and institutions in the
private sector discover yet new locations
of previously forgotten waste disposal
sites which pose a continuous threat to
the environment, public safety, and
health. Such sites pose a threat because
they contain hazardous chemical
substances which were disposed of
improperly in uncontrolled burial sites or
due to failure of controlled sites to
prevent migration of mobile chemicals.
Two large families of hazardous chem-
icals of commerce which were disposed
in such sites as waste are hydrocarbons
and chlorinated hydrocarbons.
Over the last 50 to 80 years, millions
of tons of such chemicals have been
disposed of by this and other environ-
mentally unsound methods. For many
chemicals, their hazardous and toxic
properties were not known at the time of
disposal; therefore, burial in uncontrolled
landfills was considered appropriate. For
example, polychlorinated biphenyls, DDT,
hexachlorobenzene, pentachlorophenol,
creosote, etc., were large-volume chem-
icals that were routinely produced, used,
and disposed of until their harmful effects
on the environment were understood.
Although many such chemicals are now
banned from commercial use or have
strict use limitations, they persist in the
environment due to their chemical
stability. They are also widespread,
having escaped from their original sites
of disposal due to fluid mobility, leaching
action of rain, and airborne dispersion as
vapor and aerosol emissions from the
disposal sites.
Summary
The feasibility of the radio frequency
(RF) in-situ heating and soil decontam-
ination process was successfully
established in this project. In a related
but different project funded by U.S. Air
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Force, a successful field test has been
conducted in which 500 ft3 of soil
containing jet fuel and chlorinated
solvents were decontaminated by in-situ
heating, The results of these two studies
warrant further optimization and scale-up
of the process.
In this project the feasibility of the
following was established:
• Sandy soil containing jet fuel and
chlorinated solvents can be
decontaminated by heating to 88° to
160°C for a period of 14 to 40 hr.
• Decontamination of 90% to 99% was
achieved for fuels and solvents.
• PCB 1242 can be removed from
sandy soil by heating to a temperature
range of 150° to 300° C.
• Removal of 72% to 99% was obtained
for PCB 1242 depending on the
treatment conditions.
• In the above experiments, vaporiza-
tion, steam distillation, or stripping is
used as the decontamination mechan-
ism.
• The vaporized contaminants are
recovered as a high concentration gas
mixture from the soil surface. Steam is
also present from soil moisture. This
gas stream will require onsite
treatment.
• Chemical decontamination of PCB
1260 with the in-situ application of
potassium polyethylene glycol fol-
lowed by in-situ heating does not ap-
pear to be feasible.
• Feasibility of the in-situ heating
process should be evaluated for polar
materials and for different types of
soil.
Decontamination of Soil
Containing Fuels and Solvents
Bench- and pilot-scale experiments
were performed on 75 to 4000 g of
spiked soil containing tetrachloroethylene
and chlorobenzene mentioned above. In
these experiments, 90% to 99% removal
of the contaminants was observed. The
initial contaminant concentration level
ranged between 0.5 to 1000 ppm. Mass
balance calculations were done for the
bench-scale experiments. Mass balance
closure of 75% to 104% was demon-
strated in most of the experiments. The
pilot-scale experiments were performed
on 6-ft tall columns of soil. It was shown
that uniform decontamination occurs
along the length of the soil bed.
Jet fuel-contaminated soil was heated
in 6-ft tall columns. It was shown that
90% to 99% removal of total aromatics
and total non-aromatic fraction is feasible
by treatment at 150° to 160°C for a
period of 14 to 40 hr.
In-Situ Field Test
A field test design was prepared for
heating 500 ft3 of soil containing solvents
and jet fuel An in-situ field test has been
conducted under a separate project
funded by U.S. Air Force, Headquarters,
Air Force Engineering and Service
Center, Tyndall Air Force Base, Florida.
Preliminary results of this in-situ test
indicate 90% and 99% removal of total
aliphatics and total aromatics, respec-
tively.
Thermal Decontamination of
PCB 1242
Soil spiked with PCB 1242 was heated
to a temperature range of 150° to 300°C.
Depending on the temperature, 72% to
99% removal of PCB was observed. It
was discovered that mass balance clo-
sure on PCB 1242 is inversely related to
the treatment temperature. For example,
at 300°C, 99% removal of PCB 1242 was
observed, but the mass balance closure
was only 7% to 17%. On the other hand,
at 150°C, 72% to 87% removal and a
mass balance closure of 73% to 82%
was observed. In these experiments,
Soxhlet extraction of soil was utilized to
determine PCB concentration in soil.
Further work is necessary to determine
the fate of PCB in those experiments
where good removal but poor mass
balance was obtained.
Chemical Decontamination of
PCB 1260
The feasibility of in-situ chemical
treatment of PCB 1260 with potassium
polyethylene glycol (KPEG) was
investigated. The RF in-situ heating
technique is used to promote the reaction
by removing the moisture and increasing
the reaction rate at higher temperature.
When the soil is well mixed with KPEG
and heated in a loosely covered container
in an oven at 140°C, up to 99%
destruction of PCB 1260 is obtained in
2.5 to 8 ht. When a soil column con-
taining PCB 1260 and KPEG is heated in
a cylindrical reactor, only 16% to 35%
destruction of PCB 1260 was observed.
Additional experiments are necessary to
determine whether air is necessary to
support the reaction between KPEG and
PCB 1260-containing soil. The prelim-
inary conclusion, however, is that in-situ
treatment of soil containing PCB 1260
with KPEG reagent and RF heating may
not be feasible.
Cost for Treatment of Fuels
and Solvents
Treatment cost for soil containing jet
fuel and chlorinated solvents was
developed for 74,000 ft3 (96 ft x 96 ft x 8
ft) of soil. The capital cost of the RF
treatment system is estimated to be $1.6
million. The total treatment cost per 100
Ib varies between $1.50 to $2.90
depending on the soil moisture content
(5% to 20%) and treatment temperature
(100° to250°C).
Description and Advantages of
the Heating System
In-situ RF heating is performed by
energizing the soil with electromagnetic
energy in the radio frequency band. The
heating mechanism is similar to that of a
microwave oven. The energy is deposited
by means of an electrode array emplaced
in bore holes drilled through the soil. The
array is covered by a vapor barrier for the
containment and collection of gases and
vapors rising up to the surface.
The frequency of the applied power is
selected from the industrial, scientific and
medical (ISM) band set aside by the
Federal Communications Commission.
The specific frequency is selected based
on the dielectric properties of the soil, the
depth of treatment, and the size of the
heated volume.
The main advantages of RF heating
are: true in-situ process is feasible, heat
transfer fluids or fuel combustion
products do not dilute the gases and
vapors, heating is not dependent on
relatively slow processes of conduction
or convection, and the process is cost
effective.
Recommendations
It is recommended that the feasibility
of thermal recovery of fuels, solvents.
and lower chlorinated PCBs be extended
to other types of soils such as clayey and
loamy. All the thermal recovery exper-
iments performed in this project were
done with sandy soil.
Other types of chemical contaminants
should be evaluated for decontamination
by the thermal method. Specifically, polar
materials which are likely to exhibit
stronger adsorption characteristics should
be evaluated for each of the three
different soil types. For example,
materials like phenols, amines, organic
acids, etc., should be studied. Different
types of other chemicals may be
amenable to decontamination by the in-
situ heating methods. For example,
pesticides and other agricultural chem-
icals, and coal-derived liquids present as
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contaminants at the sites of old coal-gas
plants, should be evaluated in laboratory
studies.
Through a simple modification of the
heating system, it should be possible to
treat contaminated soil surrounding
leaking underground storage tanks.
Feasibility studies should be conducted
on this concept.
Significant reduction of PCB 1242 can
be achieved by thermal treatment of
PCB-contaminated soil. However, prob-
lems were encountered in closing a mass
balance on PCB. Additional studies
should be performed to determine the
fate of the PCB molecule when soil is
heated to a temperature range of 150° to
300°C.
In-situ chemical decontamination of
soil by the application of KPEG reagent
should be further studied to evaluate the
effects, if any, of reaction atmosphere.
Experiments on soil decontamination
should be performed under nitrogen as
well as under different compositions of
nitrogen/oxygen blends.
The full report was submitted in
fulfillment of Cooperative Agreement CR
811529 by NT Research Institute under
the sponsorship of the U.S. Environ-
mental Protection Agency.
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H. Dev, J. Bridges, G. Sresty, J. Enk, N. Mshaiel, and M. Love are with IIT
Research Institute, Chicago, IL 60616
Charles J. Rogers is the EPA Protect Officer (see below).
The complete report, entitled "Radio Frequency Enhanced Decontamination of
Soils Contaminated with Halogenated Hydrocarbons," (Order No. PB
89-161 7641 AS; Cost: $21.95, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-89/008
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