14    VOLATILIZATION OF PERCHLOROETHYLENE
FROM STAGNANT WATER AND SOIL
Richard G. Zytner, Graduate Student
Nihar Biswas, Associate Professor
Jatinder K. Bewtra, Professor
Department of Civil Engineering
University of Windsor
Windsor, Ontario
Canada N9B 3P4
INTRODUCTION
Perchloroethylene, PCE, is a low molecular mass chlorinated hydrocarbon, that is classified as a
priority pollutant by the EPA.1 Furthermore, PCE is extremely volatile as it has a relatively high
Henry's law constant. PCE is used extensively as a solvent, with major applications being as a dry
cleaning agent and metal and computer component degreasing chemical. Frequent spills have
occurred during manufacture and transportation and storage of PCE. These spills can occur on a
water surface, on soil or on any other impervious surface, creating a pool of PCE which may mix with
the existing water or any subsequent precipitation. In any case, conditions may exist under which the
PCE can volatilize into the atmosphere.
Since limited information is available on volatilization of PCE from soil and water surfaces, batch
equilibrium studies were conducted under controlled laboratory conditions to study this behavior. The
experiments were designed to determine if Fick's two-film theory properly expressed volatilization.
Also, a mass flux experiment was conducted to determine the mass transfer of PCE submerged in
stagnant water. From the flux experiment a first order rate equation was derived to express the mass
transport of PCE. Furthermore, the development of a rate equation allowed the determination of
overall liquid film coefficients, for both the chemical-water and water-air interfaces.
THEORY
Figure 1 depicts the mass transport concept during volatilization. The two-film model for volatilization assumes that the bulk air and water phases are uniformly mixed and both phases are separated by
two thin films. The main resistance to mass transport is encountered in these interfacial layers. The
rate of mass transport, 6m/6t, kg/h, can be expressed according to Fick's first law of diffusion.23
5m/at = DLA(6c/6y), (1)
CHEMICAL-WATER
INTERFACE
~T
PURE CHEMICAL Figure 1.    Schematic of mass transport.
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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