PNNL-13501 - Pacific Northwest National Laboratory

encountered in the field. The contaminanted soil was then
packed in columns. Ozone was passed through the
columns at discrete time increments of 1, 2, 4, 8, and 16
hours. Each time increment represents one experiment
after which the column was dismantled and the
concentrations of TNT in the soil were measured. A
control column was also conducted by passing oxygen
through the column for 16 hours. Figure 3 shows the
results of these time series experiments.
Concentration TNT (mg/Kg)
60
50
40
30
20
10
0
0 100 200 300 400 500 600 700 800 900 1000
Elapsed Time (min)
Figure 3. Degradation of TNT in ozone
Results and Accomplishments
Initial proof-of-principle data were obtained for treatment
of TNT-contaminated sediment with ozone. In these
tests, a silty sandy alluvium from White Sands was spiked
to a concentration level of about 50 ppm TNT and then
exposed to concentrated ozone gas (several percent in
oxygen). After 2 hours of exposure, 50% of the TNT was
decomposed, and after 16 hours the concentrations were
reduced by 80%. This was not an exponential decline in
concentrations and therefore not a first-order reaction. In
a shorter, 4-hour test, a Hanford sandy loam sediment
spiked to a concentration level of 10 ppm was tested for
two time increments. After 1 hour of exposure, 30% of
the TNT decomposed, and after 4 hours, 70%
decomposed. In this 4-hour experiment, we determined
that essentially all the TNT that was degraded was
converted completely to nitrate and carbon dioxide,
though trace levels of trinitrobenzene were observed.
Summary and Conclusion
Interaction of ozone with the sediment matrix was
determined to be insignificant based on ozone
breakthrough characteristics for a control column test
conducted with uncontaminated sediment. Based on this
limited testing, ozone appears to be capable of degrading
TNT in unsaturated sediment. Additional testing will be
required to determine the factors controlling the
degradation rates in the soil.
Bibliography
Thornton EC, JT Giblin, TJ Gilmore, KB Olsen,
JM Phelan, and RD Miller. 1999. In situ gaseous
reduction pilot demonstration—Final Report. PNNL-
12121. Pacific Northwest National Laboratory, Richland,
Washington.
Earth System Science 229