Fluidized-Bed Adsorption Bioreactor for the
Treatment of Groundwater Contaminated with Solvents
at Low Concentration
Paul H. Miyares, Cynthia V. Teeter, and C. James Martel
INTRODUCTION
waxes, resins, oils, rubber, paints, and varnishes. It
Background
has been also used as a dry-cleaning solvent and
Volatile organic compounds (VOCs) are a major
for food extraction, such as in the decaffeination of
source of water contamination in the U.S. They
coffee.
pose a threat to the environment and are a poten-
TCE, though, has been shown to induce hepato-
tial hazard to human health, having been shown to
cellular carcinomas in mice and thus is a suspected
induce cancer and mutations in animals exposed
human carcinogen (Lam 1994). In response to the
to parts per billion (ppb) concentrations. The U.S.
potential for human health effects, the U.S. EPA has
Environmental Protection Agency (EPA) stated
set limits for a maximum TCE contaminant level in
that chlorinated organics are the most frequently
drinking water supplies at 5 ppb.
reported VOCs and have ranked them number
Commercially available technologies for treat-
one on the priority pollutants list (Gantzer and
ment of environmental contamination by VOCs
Wackett 1991). Large scale production of chlorin-
include recyclereclamation, thermal incineration,
ated solvents, coupled with years of uncontrolled
vapor extraction, and bioremediation. Recycle
disposal, has lead to the widespread contamina-
reclamation involves treatment of spent solvents
tion problem that exists today (Lam 1994).
either on or off site. This minimizes waste handling
as well as production through the reuse of re-
Cl
CI
Table. 1. Physical properties of TCE (after Fares
C= C
=
1994).
Property
Value
Units
Cl
H
C2HCl3
Formula
Figure 1. Chemical
Molecular weight
131.39
g/mol
structure of TCE.
Density (at 20C)
g/cm3
1.46
Vapor pressure (at 20C)
58
torr
Trichloroethylene (TCE) (Fig. 1) is the most
C
Freezing point
86.8
common of these priority pollutants, having been
C
Melting point
70
reported at 246 of 1035 Superfund sites (Shannon
C
Boiling point
86.7
1995). Many of the Department of Defense (DOD)
C
Flash point
89.6
C
and Department of Energy (DOE) sites have re-
Auto ignition temperature
420
Physical state (at 15C and 1 atm)
Liquid
ported TCE contamination in the groundwater.
Liquid surface tension (at 20C)
0.0293
N/m
TCE is a clear, colorless, nonflammable liquid,
g/cm3
Vapor specific gravity
4.5
whose properties (Table 1) make it an ideal solvent
Ratio of specific heats of vapor
1.116
for many industrial processes. TCE has been used
2.4 105
Latent heat of vaporization
J/kg
an effective degreaser and as a solvent for fats,
Viscosity
0.57
cP
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