21    THE USE OF OZONE FOR THE REMOVAL OF RESIDUAL
TRICHLOROETHYLENE FROM UNSATURATED SOILS
Michael I-yuang Hsu, Graduate Research Assistant
Simon H. R. Davies, Assistant Professor
Susan J. Masten, Assistant Professor
Department of Civil and Environmental Engineering
Michigan State University
East Lansing, Michigan 48824
INTRODUCTION
Soil venting is a conventional method for vadose zone soil remediation. It has been widely applied
to remediate sites contaminated with volatile organic chemicals (VOCs), such as benzene, toluene,
ethylene benzene and xylene (BTEX), and for TCE. Its principle is that the liquid organic contaminates vaporize into gas phase, then the clean air carries the vapor of contaminants out of soil. Several
investigations1"5 study the transport and phase transformation of contaminants on a laboratory scale.
It was found that the local equilibrium assumption is valid during most of the venting period.
However, when air stripping is applied in the field, "rest and start" cycles are usually used during at
the last stages of venting before site closure.'
Ozone, a very strong oxidant, can react with many organic chemicals, such as olefins, monocyclic
aromatics, and PAHs (polycyclic aromatic hydrocarbons). Ozone reacts directly with olefinic compounds via a 1, 3 - dipolar cyclic addition across the double bond.7 The ozonated products of olefinic
compounds are aldehydes, ketones or organic acids.7 Ozone can also autocatalytically decompose to
form free radicals,8,9 which can also oxidize many organic chemicals.
Very few studies have been conducted to investigate ozone reactions in soil systems. Yao and
Masten io applied gaseous ozone to phenanthrene contaminated dry soil and obtained removal efficiencies over 95%. Masten" also obtained effective treatment efficiencies for VOCs in soil slurries
treated with ozone. These studies suggest that it may be feasible to use to remediate soils contaminated
with organic chemicals despite the presence of organic matter, which, itself, would be expected to
exert an ozone demand.
In this study, we attempt to use gaseous ozone as a final polishing step after conventional air
stripping to treat volatile organic chemicals in sand. The removal of semi-volatile chemicals from sand
by conventional air stripping and "ozone venting" was compared.
EXPERIMENTAL WORK
Column Preparation
All columns used in this study are the same as those of Annable et al.12 which are 10 cm long and
5.3 cm inside diameter, Pyrex made glass columns. The end caps are made of stainless steel or Teflon
to avoid losses of the chemicals due to sorption. These columns were packed with Ottawa sand ( ELE
International Co., Soiltest Division). A 1 bar ceramic pressure plate was placed at the bottom of
column to control the liquid saturation in column while it was drained. The packed columns were
vacuumed to-0.8 bar to avoid air trapped in pores. For the columns containing dry sand, pure 1,1,1-
trichloroethylene (TCE, Aldrich Chemical Co., 99% + ) was introduced to the bottom of column
through the ceramic plate. When the column was fully saturated with liquid, it was pressurized by
introducing cylinder air from the top of column to drain the liquid from the soil. The draining
pressure was maintained at 6 psi for 2 days to reach residual saturation.
Columns with toluene and naphthalene were prepared using the same procedures as described
above. One gram of naphthalene (Aldrich, 99% + ) was dissolved in 100 mL toluene (Aldrich,
99% + ).
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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