EPA/540/2-89/024
PROTECTION
BALLAS, TE
A,
SUPERFUNDTREATABILITY
CLEARINGHOUSE
Document Reference:
International Technology Corp., AFESC, EG&G Idaho, Inc. 'Technology Demonstration
of a Thermal Desorption/UV Photolysis Process for Decontaminating Soils Containing
Herbicide Orange." Prepared for EG&G Idaho. 14 pp. Technical report.
EPA LIBRARY NUMBER:
Superfund Treatability Clearinghouse -EWGE
HOE DO HT IMO'/E Ffi
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SUPERFUND TREATABILITT CLEARINGHOUSE ABSTRACT
Treatment Process: Physical/Chemical - UV Photolysis
Media: Soil/Generic
Document Reference: International Technology Corp., AFESC, EG&G Idaho,
Inc. "Technology Demonstration of a Thermal
Desorption/UV Photolysis Process for Decontamin-
ating Soils Containing Herbicide Orange."
Prepared for EG&G Idaho. 14 pp. Technical report.
Document Type: Contractor/Vendor Treatability Study
Contact: Major Terry Stoddart
U.S. DOD/AFESC
BLDG 1117
Tyndall Air Force Base, FL 32403
904-283-2949
Site Name: NCBC Gulfport, MS; Johnston Island; and Guam
(Non-NPL)
Location of Test: Gulfport, MS and Guam
BACKGROUND; This treatability study report presents the results of
laboratory and field tests on the effectiveness of a new decontamination
process for soils containing 2,4-D/2,4,5-T and traces of dioxin. The
process employs three operations, thermal desorption, condensation and
absorption of contaminants into a solvent and photo decomposition.
Bench-scale tests were conducted to establish the relationships between
time and temperature and treatment efficiency. A pilot-scale (100 Ibs/hr)
system evaluation was conducted at two sites to evaluate system performance
and develop scale-up information.
OPERATIONAL INFORMATION; The intent of the laboratory and pilot-scale
tests was to reduce the combined dibenzo dioxin and furan constituents,
which originate from Herbicide Orange (HO), to less than 1 ng/g. This
level represents the anticipated soil cleanup criteria. The soils used had
similar concentrations of HO contaminants, but were different types of
soil. In the laboratory the contaminated soil is passed through thermal
desorber and the off gases from the soils, including the contaminants, are
passed through a scrubber that uses a hydrocarbon solvent. Contaminants
dissolve in the solvent and the solvents are passed through a flow reactor
which subjects the contaminant to UV radiation to decompose the contaminant
molecules. Testing was conducted on soil samples from three HO contami-
nated sites; Johnson Island, Eglin AFB and NCBC in Biloxi, MS. The soils
tested had 2,3,7,8-TCDD concentrations greater than 100 ng/g of soil and
2,4,-D/2,4,5-T levels greater than 1000 ng/g soil. Tests were run at three
different temperatures and two different power levels using high intensity
UV quartz mercury vapor lamps.
Pilot tests were conducted at the NCBC site using a rotary indirect
calciner as the desorber, an off gas transfer and scrubber system and a
3/89-43 Document Number: EWGE
NOTE: Quality assurance of data «ay not be appropriate for all uses.
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photo chemical reactor to irradiate the contaminants contained in the
scrubber solution. A 1200-watt high intensity mercury vapor lamp was used
to irradiate the contaminated scrubber solution. No QA/QC plan was con-
tained in the document. No discussion of analytical techniques utilized to
detect HO and associated compounds is contained in the paper. A detailed
list of soil properties (particle size distribution, surface area, organic
matter, etc.) from the three different sites is contained in the document.
PERFORMANCE; Laboratory studies revealed that thermal desorption/UV
photolysis destroyed all compounds to below their analytical detection
limit (which was generally less than 0.1 ng/g). The concentration of
2,3,7,8-TCDD was reduced from 200 ng/g to less than 1 ng/g. Insoluble
brown tars (presumably phenolic tars) were deposited on the surfaces of the
reactor vessel and lamp well. Reaction kinetics quantum yields' and rate
constants were determined. Pilot tests also produced soil containing less
than 1 ng/g of 2,3,7,8-TCDD. Table 1 shows the results of the tests.
CONTAMINANTS!
Analytical data is provided in the treatability study report. The
breakdown of the contaminants by treatability group is:
Treatability Group CAS Number Contaminants
W02-Dioxins/Furans/PCBs 1746-01-6 2,3,7,8-Tetrachlorodibenzo-
p-dioxin (TCDD)
TABLE 1
EFFECT OF TREATMENT CONDITIONS ON RESIDUAL 2,3,7,8-TCDD
DURING NCBC PILOT THERMAL DESORPTION TESTS
Soil Feed Residence Soil 2,3,7,8-TCDDb
Rate Time3 Temperature (ng/g)
Test No. (kg/hr) (min) (°C) Initial Residual
1 13.6 40 560 260 ND
2 13.6 40 560 272 ND
3 25 19 560 236 ND
4 44 10.5 560 266 ND
5 20 24 460 233 0.5
Notes: a) Soil residence time in heated zone.
b) Detection level for 2,3,7,8-TCDD was generally less than 0.1
ng/g with a range of 0.018 to 0.51 ng/g.
c) This is a partial listing of data. Refer to the document for
more information.
3/89-43 Document Number: EWGE
NOTE: Quality assurance of data Bay not be appropriate for all uses.
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Technology Demonstration of a Thermal Desorption/UV Photolysis
Process for Decontaminating Soils Containing Herbicide Orange
R. Helsel, E. Alperin, T. Geisler, A. Groen, R. Fox
International Technology Corporation, 312 Directors Drive,
Knoxville, Tennessee 37923
Major T. Stoddart
U.S. Air Force, Engineering and Services Center,
Tyndall Air Force Base, Florida 32403
H. Williams
EG&G Idaho, Inc., Waste Technology Programs,
Idaho Falls, Idaho 83415
Laboratory and field testing determined the effec-
tiveness of a new decontamination process for soils
containing 2,4-0/2,4,5-T and traces of dioxin. The
process employs three primary operations - thermal
desorption to volatilize the contaminants, conden-
sation and absorption of the contaminants in a
solvent, and photochemical decomposition of the
contaminants. Bench-scale experiments established
the relationship between desorption conditions (time
and temperature) and treatment efficiency. Labora-
tory tests using a batch photochemical reactor
defined the kinetics of 2,3,7,8-TCDD disappear-
ance. A pilot-scale system was assembled to process
up to 100 pounds per hour of soil. Tests were
conducted at two sites to evaluate treatment per-
formance and develop scale-up information. Soil was
successfully decontaminated to less than 1 ng/g
2,3,7,8-TCDD at temperatures above 460°C.
As part of a major program being conducted by the U.S. Air Force to
restore to normal use several Department of Defense sites where
soils have been contaminated with low levels of Herbicide Orange
(HO), International Technology Corporation (IT), .under subcontract
to EG&G Idaho, has been conducting a project involving laboratory
bench-scale and field pilot-scale tests to demonstrate a new soil
treatment process - thermal desorption/UV photolysis (TD/UV). The
intent of the demonstration was to reduce the combined tetra-,
penta-, and hexa-chlorinated dibenzodioxin (CDD) and furan (CDF)
congeners, which originated from the HO, to less than 1 ng/g, which
represented the anticipated soil clean-up criteria. Treatment
should also effectively remove the primary HO constituents, 2,4-D
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and 2,^,5-T. Two sites were included in the field demonstration
project for the TD/UV process, each having substantially different
types of soil but reasonably similar, concentrations of the HO
constituents. Testing at the Naval Construction Battallion Center
(NCBC) at Gulfport, Mississiopi was conducted by IT during May
'985; testing at Johnston Island (JI) in'cne Pacific Ocean occurred
in July 1986. Based on the results of these field pilot demonstra-
tions, an engineering and cost evaluation is being performed for
applying TD/UV technology using large, mobile systems for these two
sites or other sites having similar contaminated soil problems.
This paper describes the technology, highlights the results of the
initial laboratory test phase, and summarizes the field demonstra-
tion results.
Process Description
The thermal desorption/UV photolysis process developed by IT
accomplishes substantial volume reduction and toxicity reduction by
concentrating the hazardous constituents contained in the soil into
a small volume which is easier to treat than large quantities of
soil. The process incorporates three steps:
Desorption - heating the soil to volatilize the organic
contaminants
Scrubbing - collecting the volatilized organics in a
suitable solvent
Photolysis - converting the contaminants to relatively
non-hazardous residues through photochemical
reactions.
A schematic block-flow diagram is presented as Figure 1.
Contaminated soil is passed continuously through an indirectly
heated desorber which can be one of many types of conventional
equipment applicable for thermal processing of solids. The treat-
ment performance of the desorber is controlled by the residence
time and temperature of the soil. Treatment requirements (i.e.,
operating conditions) are determined by the volatility of the soil
contaminants and the required contaminant removal efficiency (final
versus initial concentration).
The off-gas leaving the desorber contains organic vapors,
water vapor originating as initial soil moisture, and small
quantities of air which enter with the soil. Scrubbing using a
high boiling hydrocarbon solvent is used to treat the off-gas to
remove the organic contaminants and water vapor by cooling, conden-
sation, and absorption. Particulates (e.g., fine soil) which may
be entrained by the off-gas are also collected by the scrubbing
solvent. Scrubbed off-gas is passed through a conventional emis-
sion control system, such as carbon adsorption, to ensure that no
organic contaminants or solvent vapors are released. Scrubber
solvent is recirculated to the scrubber after being processed
through a system of phase separation, filtration, and cooling.
Condensed water, which is immiscible with the solvent, is separated
and either directly treated using conventional techniques, such as
filtration and carbon adsorption, or discharged to an existing
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wastewater treatment facility. Filtered solids are recycled to the
desorber or packaged as process waste for off-site disposal,
depending on the relative quantity and composition.
A small portion of the recirculated solvent stream is
diverted to a UV photolysis system to treat (detoxify) and remove
the organic contaminants, with the treated solvent purge recycled
to the scrubbing system. The equilibrium concentration of the
contaminants in the scrubber solvent is maintained as high as
practical to minimize the purge stream and afford higher photolysis
reaction rates, thereby decreasing the size of the photolysis
treatment system. The concentration limitation is dependent on the
solubility properties and partial pressure of the contaminants in
the solvent, and the resultant effect on scrubber efficiency and
emission potential. The photolysis system contains a specially
designed flow reactor which subjects the contaminant-laden solvent
to UV radiation to induce molecular decomposition. High intensity
mercury vapor lamps produce' a band of wavelengths, some of which
match the absorption energy of the specific organic molecules being
treated. Cooling is provided to the reactor to remove the thermal
output of the lamp. The photolyzed solvent is treated by using
selected conventional physical or thermal, separation processes,
such as distillation, to remove the reaction product residue.
Alternatively, a purge of the photolyzed solvent can be discarded
as waste to control the levels of reaction products in the
recirculated solvent system.
Other configurations of treatment processes using thermal
desorption as the primary separation technique can be applied to
organically contaminated soils. Alternative physical/chemical
processes can be used to treat the desorber off-gas and the
contaminants. To achieve complete contaminant destruction, the
off-gas can be treated by using conventional fume incineration or
other thermal treatment technology. The choice of the type of
desorber and off-gas treatment system depends on the concentration
and properties of the chemical contaminants, soil characteristics,
quantity of contaminated material, site characteristics, availabil-
ity of off-site disposal, and regulatory and related requirements.
Laboratory Testing and Results - Thermal Desorption
Thermal desorption is a physical separation process, although
chemical transformation of the organic contaminants may occur
depending on the thermal stability and the operating temperatures
required to achieve adequate decontamination efficiency. Thermal
desorption has been used only in a limited number of cases (1-4)
for treating contaminated soil, and these applications have
involved relatively volatile organic compounds, such as solvents.
Because of the extremely low volatility of CCD and CDFs, the
development' of basic treatability data was essential to confirm
that 1 ng/g levels in soil could be achieved and that the required
desorption conditions were practical, considering the design
features and operating rates of equipment available for performing
such treatment.
Desorption treatability testing- was conducted on samples of
contaminated soil from three HO contaminated sites - NCBC, JI, and
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Eglin Air Force Base. The goals of the test effort were to
evaluate the effect of time and temperature on 2.3,7,8-TCDD removal
efficiency and to establish the importance of soil type. The
samples were selected by the Air Force based on results of site
surveys to yield high contamination levels in order to investigate
a broad range of treatability. This testing was an extension of
earlier testing performed for the EPA on two dioxin-contaminated
soil samples from Missouri to support EPA's mobile incinerator
trial burn in 1985 (5).
After each soil sample was blended, air dried, and screened
(2 mm sieve opening) triplicate aliquots were taken and analyzed
for 2,3,7,8-TCDD, CDD and CDF congeners, and 2,4-D and 2,4,5-T.
The three prepared soils had 2,3,7,8-TCDD levels greater than
100 ng/g and 2,4-D/2,4,5-T levels of about 1000 ug/g. The JI soil
had significant concentrations of hepta and octa CDD compared with
the other two samples. In addition, selected physical and chemical
properties presented in Table I, were measured (6). The EPA test
program (5) had indicated that soil properties had only a minor
influence on removal efficiencies for 2,3,7,8-TCDD.
Table I. Physical-Chemical Analysis of Prepared Soil Samples
Used for Laboratory Thermal Desorption Tests
Parameter
pH
Conductivity (millimhos/cm)
Organic matter (percent)
Cation exchange capacity
milliequivalents/100g)
Oil and grease content
( grams/ 100g)
Surface area (nr/g)
Particle size distribution
(percent)
Medium sand
Fine sand
Silt
Clay (<5 microns)
Moisture
JI
8.4
5.0
4.2
0.73
0.19
6.7
41
37
19
3
2.3
Eglin
3.8
0.15
1.2
0.77
0.41
2.5
41
52
5
2
0.79
NCBC
8.6
0.21
2.3
2.4
0.34
12.3
26
59
12
3
1.1
A series of 10 individual tests was performed using
temperatures between 430 and 560°C and treatment times of 8 to 30
minutes. Table II presents the test results, which are comparable
to the earlier results for Missouri soils. The objective of 1 ng/g
2,3,7,8-TCDD residual in soil was achieved for all three soils
subjected to the highest temperature. There was some difference in
treatability observed between the three soils at the lower tempera-
tures. Also, longer treatment times were required for the NCBC
soil because of the higher initial 2,3,7,8-TCDD level (500 ng'g vs.
100 ng.'g). One set of treated tesr samples which contained less
than 1 ng'g 2,3,7,8-TCDD was also analyzed for the other CDD and
CDF congeners and 2,4-0/2,4,5-T. These results, shown in Table
III, indicate greater than 99.999 percent removal of the initial
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2.4-D/2,4,5-T and the effective removal of higher chlorinated CDDs
and CDFs.
Table II. Effect of Treatment Conditions on Residual 2,3,7,8-TCDD
in Soil During Laboratory Thermal Desorption Tests
Nominal Test
Temperature
Soil
Time at Test
Temperature
2,3,7,8-TCDD
Concentration
(ng/g)
(8C)
430
U81
558
Identification
JI
Eglin
NCBC
JI
JI
Eglin
Eglin
NCBC
NCBC
JI
Eglin
NCBC
(min)
20
20
30
15
30
15
30
15
30
8
8
15
Initial
106
101
494
106
106
101
101
494
494
106
101
494
Final
38.5
4.4
26. 6a
4.5
1.6
1.1a
0.45
10.1
4.6
0.56a
0.71
0.76a
Average of duplicate tests or duplicate analyses.
Table III. Residual 2,4-D, 2,4,5-T, and CDD/CDF in Soil Samples
Treated at 558°C in Laboratory Thermal Desorption Tests
Concentration (ng/g)
Compound
2,4-0
2,4,5-T
TCDF
OCDFb
JI
ND*
16
0.6
0.3 .
Eglin
ND
0.8
0.4
ND
NCBC
ND
3
ND
ND
^ND = Not detected.
bNo other COD and CDF congeners were detected.
Laboratory Testing and Results - Photolysis
Photolysis has had limited application for treatment of hazardous
waste or detoxification of chemically contaminated materials. The
susceptibility of chlorinated aromatics, including herbicides such
as 2,4-D and 2,4,5-T, to UV-induced decomposition is well estab-
lished (7.8). Photodecomposition of such compounds leads to
successive dechlorination followed by condensation reactions to
form phenolic polymers (7,8). Other research-has demonstrated that
CDD and CDF decompose in the presence of UV light (6\ 9 JO).
Development of a photochemical process for Destroying 2,3,7,8-TCDD
in a waste tar indicated similar dechlorination anc condensation
reactions and products (8). The nigh-molecular weight end products.
which are similar in structure to humic acids, would be expected to
have low toxicity and mobility. Therefore, essentially complete
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conversion of toxic constituents could produce a potentially non-
hazardous (according to RCRA), easily disposable residue.
Laboratory photolysis experiments were designed to confirm
that 2,3,7,8-TCDD contained in the selected scrubber solvent could
be reduced to 1 ng/g and to determine the reaction rates of the
primary HO constituents and 2,3,7,8-TCDD in that solvent matrix. A
previous photolysis process for 2,3,7,8-TCDD used hexane as a
solvent (8). The solvent selected for use in the TD/UV process was
different"- a high boiling (kerosene-like) mixture of isoparaf-
fins. This hydrocarbon solvent was selected because of its very
low vapor pressure and water solubility, nontoxic and nonflammable
characteristics, relatively low cost, chemical stability, and good
solvent properties for HO constituents. A second major difference
from earlier IT photolysis studies was the presence in the scrubber
solution of significant concentrations of other chlorinated organic
reactants (2,4-D and 2,4,5-T) which were also subject to photoly-
sis. In fact, the typical concentration ratio between 2,4-D or
2,4,5-T and 2,3,7,8-TCDD in the soil samples used in the desorption
treatability testing was 2000:1.
The three steps of the laboratory program included generation
of scrubber solution, bench-scale batch photolysis reactions, and a
pilot system trial. In order to generate a representative sample
of scrubber solution for photolysis tests, a small desorption and
scrubbing system was assembled. . A portion of the prepared samples
of both NCBC and JI soil used for the thermal desorption tests was
used to generate scrubber solution. Contaminated soil (-100 g) was
placed in a standard tube furnace apparatus which was heated to
about 500°C for 15 to 30 minutes. A nitrogen purge swept the
vapors into the scrubbing system, which consisted of several
solvent-filled impingers. Analysis of the prepared scrubber
solutions indicated thermochemical conversion of the 2,4-D and
2,4,5-T in the contaminated soil to the corresponding chlorophenols
at molar equivalents. In addition to using prepared scrubber
solutions, solvent spiked with 2,4-D and 2,4,5-T, the corresponding
chlorophenols, or 2,3,7,8-TCDD was used for baseline photolysis
tests.
Most photolysis experiments were conducted in a 0.5 liter
capacity standard quartz photochemical reactor using either
recirculation or bottom agitation for heat and mass transfer. Both
100- and 450-watt high pressure quartz mercury vapor lamps (Canrad-
Hanovia, Inc., Catalog Nos. 608A and 679A) were used, depending on
the initial reactant concentration in the particular solvent
solution being tested. The wavelengths of interest based on
spectrophotometric absorbance measurements of 2,3t7,8-TCDD, 2,4-D
and 2,4,5-T were in the 280 to 320 nm region. Isopropyl alcohol
(-0.05 g/g solvent solution) was used as a proton donor to minimize
formation of polymeric reaction by-products which tend to foul the
light transmission surfaces (8). The bench-scale photolysis tests
gave the following results:
'. All compounds disappeared to below .the analytical detection
limits.
2. The concentration of 2,3,7,8-TCDD was reduced to less than
1 ng/g from initial concentrations as high as 200 ng/g.
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3. For a given reactor configuration and lamp wattage, the
reaction rates of 2,3,7,8-TCDD and 2.4,5-tricnloropnenol were
proportional to the concentration, indicating pseudo-first
order kinetics in agreement with previous work (8).
4. Absorbence of UV energy by the solvent, which increased during
irradiation, resulted in low quantum yields and low rate
constants.
5. Insoluble brown reaction products (presumably phenolic tars)
were deposited on the surfaces of the reactor vessel and lamp
well. This expected phenomenon plus the high solvent absorb-
ence demanded a careful reactor selection and photolysis system
design.
Trials using a pilot reactor system described in the following
section were performed in the laboratory to establish reactor
efficiencies and operating characteristics prior to transport to
the field. A synthetic scrubber solution was prepared containing
2,4,5-trichlorophenol at a concentration (-2,000 ug/g) projected to
be representative of the planned field tests. Kinetics were
determined to be first-order with a rate constant of 0.07 sec"1.
On-site Pilot Testing and Results
Based on the information developed from the laboratory test
program, a pilot-scale TD/UV system was designed and assembled.
Three skids were used to mount the desorber, scrubber, and
photolysis systems; the largest skid was 1.5 meters by 4.3
meters. A conventional pilot-scale, rotary, indirect-fired
calciner was used as the desorber. The calciner consisted of a
3.3 meter long by 16 cm internal diameter rotating tube through
which the soil was transferred, and a gas-fired furnace which
surrounded the middle 2.0 meters of the tube length. The initial
and final tube sections were used for soil feeding and cooling.
The flow rate and residence time of soils traveling through the
desorber were controlled by varying the tube inclination "and
rotational speed. Temperature of the soil was measured at
different locations by a thermowell probe extending inside the
tube. Soil was fed to the desorber from a small hopper using a
variable speed screw conveyor. Soil leaving the tube was collected
in a sealed metal can.
The off-gas transfer and scrubbing system was designed to
enable recirculation of scrubbed off-gas through the desorber. The
entire off-gas treatment and recirculation system, including the
desorber and scrubber, was operated at a slightly negative pressure
to prevent potential fugitive emissions. A small amount of air
entered the system with the soil feed or through seal leakage.
Nitrogen was added to the recirculated gas stream to maintain the
oxygen concentration below the level necessary to support combus-
tion. This was an extra safety feature since the vapor pressure of
tne solvent at normal scrubber operating conditions is very low. A
portion of the scrubbed off-gas was vented from the recircuianion
system to maintain proper pressure ;n tne system. This purge
stream was passed through a small HEPA filter and caroon adsoroer
before being discharged to the atmosphere. The soivent system
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consisted of a scrubber, receiving and separation tank, storage
tank, recirculation pump, filters for removing suspended solids,
and solvent cooler.
The photolysis system was independent of the desorber and
scrubber systems; its design capacity was lower than necessary to
match the desorber's soil-processing rate. A portion (about UO kg)
of contaminant-laden solvent was taken from the scrubber system
after completion of one or more desorption tests and transferred to
the photolysis system. This system consisted of an agitated
storage tank, solvent recirculation pump, and photochemical reactor
with associated cooling, DC power supply, and controls. The
selected type reactor was a standard quartz falling-film unit,
approximately 10 cm in diameter and 50 cm long (Ace Glass, Inc.,
Part No. 7898). A 1200 watt high intensity mercury vapor lamp was
inserted through a central quartz tube within the reactor to
irradiate the solvent as it flowed by gravity down the circum-
ference of the reactor body. The solvent was recirculated through
the reactor for many cycles to achieve sufficient irradiation
(e.g., reaction) time.
Five desorption tests were carried out at NCBC at various
treatment conditions. A total of 800 kg of soil was processed;
soil was prepared by drying and crushing to less than 1/2 inch to
allow proper flow in the desorber feed mechanism, and blending for
uniformity. Each test lasted 5 to 10 hours, including the heat-up
and cool-down cycle. Samples of feed soil and treated soil were
taken during steady-state operation, and samples of the scrubber
solvent and vent carbon were taken at the conclusion of each run.
Samples were analyzed for 2,4-D, 2,U,5-T, other HO indigenous
compounds, priority pollutant organics and metals, and tetra-hexa
congeners of CDD and CDF. In addition, 2,3.7,8-TCDD concentrations
of treated soil and photolyzed solvent samples were determined on a
quick-response basis to enable adjustment of the operating condi-
tions in subsequent tests. Fresh solvent and carbon were used for
each test, and the entire desorber and scrubber network was cleaned
out between tests. This cleaning enabled thorough inspection of
the condition of the equipment and provided several different
compositions of contaminated solvent to use in the photolysis
tests.
Table IV shows the effect of different soil temperatures and
residence times on residual 2,3,7,8-TCDD for NCBC pilot tests.
Table V presents the analytical results for 2,4-D, 2,4,5-T, and
total CDD and CDF. Analytical detection levels for 2,3,7,8-TCDD
and the various congeners were generally less than 0.1 ng/g but
varied from sample to sample, ranging from 0.018 ng/g to 0.51 ng/g.
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Table IV. Effect of Treatment Conditions on Residual 2,3,7,8-TCDD
During NCBC Pilot Thermal Desorption Tests
Test No.
1
2
3
4
5
Soil Feed
Rate
(kg/hr)
13.6
13.6
25
44
20
Residence
Timea
(min)
40
40
19
10.5
24
Soil
Temperature
CO
560
560
560
560
460
2,3
,7,8-TCDD
(ng/g)
Initial Residual
260
272
236
266
233
ND
ND
ND
ND
0.5
3Soil residence time in heated zone.
Table V. Residual 2,4-D, 2,4,5-T, and CDD/CDF in
NCBC Pilot Thermal Desorption Test
Concentration (ng/g)
Compound
2,4-D
2,4,5-T
TCDD
PCDD
HCDD
TCDF
PCDF
HCDF
CDD and
Test 1
180
500
NDa
ND
ND
ND
ND
ND
ND
Test 2
150
270
0.23
ND
ND
ND
0.14
ND
0.37
Test 3
20
60
0.11
ND
ND
ND
ND
ND
0.11
Test 4
.
_
0.61
ND
ND
0.13
0.54
ND
1.28
Test 5
170
1240
0.75
ND
ND
0.95
1.0
ND
2.70
CDFC
aNDa not detected.
bTotal of quantified values for detected cogeners.
All test conditions produced soil containing less than 1 ng/g
2,3,7,8-TCDD. The total quantified tetra-hexa congeners were less
than the treatment goal of 1 ng/g for the first three tests, which
were performed at the lower feed rates. Test 4, made at the
highest feed rate, nearly met this value, whereas the much lower
soil temperature used for the final test resulted in almost 3 ng/g
combined residual CDD and CDF. A longer residence time could have
improved this performance. Residual 2,4-D and 2,4,5-T concentra-
tions were less than 1 ug/g for all but the final test. This
reduction represents greater than 99.97 percent removal efficiency
for these primary HO constituents.
Because of the very low moisture content of the prepared soil
feed, an insufficient volume of aqueous condensate was collected
from the tests to perform analysis or treatability tests. A vent
gas sample was taken, but no valid analytical results were gener-
ated because of delays in sample processing. However, analysis of
the carbon used in the emission control adsorbers enabled some
evaluation of scrubber performance and process emission poten-
tial. Or.iy tne front (upstream) portion of carbon from one of the
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tests showed detectable levels of any CDD or CDF. Mo HO consti-
tuents were detected in the downstream portion of carbon. Calcu-
lated scrubber removal efficiencies exceeded 99-9 percent for CDD,
CDF, 2,4-D, and 2,4,5-T. Vent gas volume was about 0.05 nr/minute
for all tests.
Results of the photolysis tests are presented in Table VI.
The total solvent volume (-10.5 1) was recirculated through the
reactor at 0.75 1/min for 6.5 hr, resulting in 28 cycles with an
irradiation time of about 1.5 sec/cycle. The photolysis system
operating time was selected based on the laboratory trials to
achieve less than 1 ng/g 2,3,7,8-TCDD; the actual residual level of
0.36 ng/g represented greater than 99 percent conversion. The
reaction conversion of the other CDD and CDF congeners varied from
85 to 99 percent. Photolysis reduced the concentrations of 2,4-
dichlorophenol (2,4-DP) and 2,4,5-trichlorophenol (2,4,5-DP),
(corresponding to the 2,4-D and 2,4,5-T present in the initial
soil) by 85 and 97 percent respectively. Figure 2 shows the rate
of disappearance of 2,3,7,8-TCDD, 2,4-DP, and 2,4,5-TP. As
demonstrated during the laboratory tests, the reaction kinetics
were pseudo-first order over the given range of concentrations.
The reaction rate constants were similar for the three species
(0.11 sec"1, 0.04 sec , and 0.08 sec" , respectively); the rate
constant for 2,4,5-TP was comparable to that determined in the
laboratory trials of the pilot system.
Table VI. Initial vs Final Concentration of Selected Compounds
in Scrubber Solution from NCBC Pilot Photolysis Tests
Compound
2 , 4-Dichlorophenol
2 ,4 ,5-Trichlorolorophenol
2,3,7,8-TCDD
Total TCDD
Total PCDD
Total HCDD
Total TCDF
Total PCDF
Total HCDF
Concentration
Initial
490,000
977,000
43.3
46.3
15.7
0.84
31.0
3-7
1.7
(ng/g)
Final
82,000
31,000
0.36
0.92
2.3
0.037
3.8
1.1
0.0031
Three desorption tests and one photolysis test were conducted
at JI to compare the effects of different soil characteristics and
investigate higher processing rates. The coral-like soil used for
the tests contained lower levels of HO contamination than NCBC
(about 50 ng/g versus 250 ng/g). As much as 95 kg/hr of soil was
successfully decontaminated to less than 1 ng/g 2.3.7,8-TCDD using
desorption temperatures of 550°C. Treated soil from all three
desorption tests had nondetectable residual tetra-hexa CDD and 'JDF
cogeners, 2,4-D and 2,4,5-T, and corresponding chiorophenols.
Analysis of carbon removed from the desorber-scrubber system vent
showed no detectable concentration of CDD or CDF. Gas samples
taken downstream of the carbon adsorber showed nondetectable
concentrations of CDD and CDF, 2,4-D and 2,4,5-T, and chloro-
-------
phenols. Photolysis test results were comparable with NCBC
tests. Initial concentrations of HO contaminants were much higher
in the scrubber solvent due to processing of considerably more soil
and use of less solvent. The concentration of 2,3,7,8-TCDD was
reduced from 780 ng/g to less than 0.7 ng/g during 12 hours of
system operation (representing about 80 sec reaction or irradiation
time). Total chlorophenols were reduced from 430 ug/g to less than
6 ug/g, and tetra-hexa CDD and CDF cogeners were effectively
treated. Reaction rate constants for specific compounds were
essentially the same between the NCBC and JI photolysis tests. At
JI as at NCBC, brown residues were deposited on the reactor
surfaces, and solvent discoloration was obvious, but there was no
evidence of rate retardation.
Conclusions
The effectiveness of thermal desorption to decontaminate soil
containing HO and of UV photolysis to destroy HO toxic constituents
has been demonstrated in bench- and pilot-scale tests. Some
additional technical information is needed for a complete evalua-
tion of the process and to provide the basis for design of a full-
scale system for on-site remedial action. This project illustrates
the requirements for developing and implementing new process
technology for solving contaminated-soil environmental problems.
Only through such demonstration efforts can more cost-effective and
environmentally sound remedial action alternatives be made
available.
Literature Cited
1. Noland, J. W.; NcDevitt, N. P.; Koltuniak, D. L. Proc. of the
National Conference on Hazardous Wastes and Hazardous
Materials. Atlanta. GA. March 4-6. 1986. pp. 229-232.
2. Hazaga, D; Fields, S; Clemmons, G. P. The 5th National
Conference on Management of Uncontrolled Hazardous Waste
Sites. Washington. DC. November 7-9. 1984. pp 404-406.
3. Webster, David M. J. Air Pollution Control Association.
1986, 36, PP 1156-1164.
4. Hoogendoorn, D. Proc. of the 5th National Conference on
Management of Uncontrolled Hazardous Waste Sites. Washington,
DC, November 7-9, 1984, pp 569-575.
5. Helsel, R.; Alperin, E.; Groen, A.; and Catalaho, D. "Laboratory
Investigation of Thermal Treatment of Soil Contaminated With
2,3,7,8-TCDD," draft report to U.S. EPA, Cincinnati, OH on
Work Order BAD001, D.U.D-109, IT Corporation, Knoxville, TN,
Dec. 1984.
6. ..Arthur, M. F.; Zwick, T. C. "Physical-Chemical Characteriza-
tion of Soils," Battelle Columbus Laboratories, Columbus, OH,
1984.
7. "Report on 2,4,5-T, A Report on the Panel on Herbicides of
the President's Science Advisory Committee," Executive Office
of the President, Office of Sciences and Technology, March
1971.
-------
8. Exner, J. H.; Johnson, J. D.; Ivins, 0. D.; Wass, M.N.; and
Miller, R. A. "Detoxication of Hazardous Waste," Ann Arbor
Science Publishers, Ann Arbor, MI, 1982, p 269.
9. Exner, J. H.; Alperin, E. S.; Groen, A.; Morren, C. E.;
Kalcevic, V.; Cudahy, J. J.; and Pitts, D. M. "Chlorinated
Dioxins and Dibenzofurans in the Total Environment," Keith,
L. H.; Rappe, C.; Choudhary, G.; Eds., Butterworth
Publishers, Stoneham, MA, 1985, p 47.
10. Exner, J. H., Alperin, E. S.; Groen, A; Morren, C. E.
Hazardous Waste. J., 1984, pp 217-223.
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