10    USE OF OZONE FOR THE OXIDATION OF VOCs AND PAHs
IN THE PRESENCE OF NATURALLY OCCURRING
ORGANIC MATTER
Jehng-Jyun Yao, Graduate Research Assistant
Susan J. Masten, Assistant Professor
Department of Environmental Engineering
Michigan State University
East Lansing, MI  48824-1326
INTRODUCTION
In this study we investigated the applicability of ozone for the oxidation of volatile organic chemicals (VOCs) and polycyclic aromatic hydrocarbons (PAHs) in aqueous solutions containing humic
acid and in soils.
Ozone is a very strong oxidant, more powerful than other oxidants commonly used in water and
wastewater treatment. Ozone reacts with olefinic compounds by a 1,3-dipolar cyclic addition across
the double bond to yield an unstable intermediate, known as a molozonide. These intermediates
rapidly decompose to form aldehydes, ketones and/or organic acids.
In the systems described here, the ozone concentration present at any time will affect the decomposition reaction. If the oxidation of the organic chemical occurs by a direct mechanism, then an
increase in the ozone decomposition rate will result in a decrease in the extent to which the target
compounds reacts. However, if the target compound does not or only very slowly reacts with ozone
directly, but reacts with other oxidants such as OH radicals, the decomposition of ozone and the
resulting formation of OH radicals may increase the removal efficiencies of these compounds.
In water, ozone degrades to form OH radicals; the rate of degradation depends on pH, and on the
concentration, and types of chemicals and ions present. Staehelin and Hoigne1 have shown that the
most important reactive species present in "pure" water are ozone, OH radicals and superoxide. Both
superoxide and OH radicals enter into the cyclic reaction which then enhance the decomposition of
ozone. Additionally, hydroxide will react with ozone to form superoxide and, thus, will result in an
enhancement of the rate of ozone decomposition.
Only a few studies have been conducted to study ozone reactions in soil systems and on the other
surfaces.2,3 These systems are extremely complex since the target organic compound may react by one
or more of several possible mechanisms. In an attempt to simplify the systems, most of the work
conducted was performed in homogeneous aqueous systems containing humic acid as a model of
naturally occurring organic matter. Several experiments were conducted in heterogeneous systems
containing either a synthetic soil4 or a sandy soil containing approximately 0.5% organic matter.
MATERIALS AND METHODS
Materials
Unless otherwise noted, the reagents used were prepared accoiding to methods described by Mas-
ten.5 Ozone was produced using a Polymetrics Model T—408 ozone generator. Naphthalene was
prepared by dissolving the solid in methanol, then, diluting the stock solution in distilled water (pH 3)
to 10"4 M.
The soil samples used to study the ozone and VOCs reactions were prepared according to Masten.5
The PAH contaminated soils were prepared in the following manner. The soils were air —dried, then
sieved through a 0.5 mm sieve. 50 mg of the target PAHs were dissolved in <35 mL methanol. A
known volume of PAH solution was added to a known amount of soil. The mixture was shaken by
hand. The solution was added until the total soil weight was 500.0 g and all of PAH solution was
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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