Biomedical Engineering Reference
In-Depth Information
stimulation of indigenous organisms were conducted with methane-utilizing microorganisms at
the Savannah River Department of Energy (DOE) Site, South Carolina (Hazen et al.,
1994
) and
at Edwards Air Force Base (AFB), California with toluene-utilizing microorganisms (McCarty
et al.,
1998a
). The results of microcosm and field studies of biostimulation for aerobic
cometabolism are reviewed briefly in the following section to provide a background for
understanding the potential benefits and challenges for the different bioaugmentation
approaches that have been developed.
8.3 AEROBIC COMETABOLISM BY INDIGENOUS
MICROORGANISMS
8.3.1 Microcosm Studies with Indigenous Microorganisms
Microcosm studies using aquifer solids and groundwater from sites have proven useful for
predicting the performance of
in situ
cometabolic treatment where indigenous microbial
populations were stimulated. Packed column studies with aquifer solids and groundwater
from the Moffett Test Facility, California performed by Lanzarone and McCarty (
1990
)
showed that stimulation of indigenous methane utilizers did not effectively transform TCE,
which was consistent with the results observed in the pilot-scale field demonstration (Semprini
et al.,
1990
). Hopkins et al. (
1993a
,
b
) also found good agreement between microcosm results
and the
in situ
pilot-scale studies where TCE was effectively cometabolized by indigenous
microcosms stimulated through either phenol or toluene addition. The transformation yields
(mg TCE/mg substrate) achieved in the
in situ
field tests agreed with those obtained in
microcosms. Jenal-Wanner and McCarty (
1997
) showed TCE removal (93-94%) in their micro-
cosms, which was close to the field-scale results from the Moffett Test Facility when similar
amounts of phenol and toluene were supplied (Hopkins and McCarty,
1995
). Microcosm
studies with aquifer material and groundwater from Edwards AFB (Jenal-Wanner and
McCarty,
1997
) also agreed with the TCE removals of 87-100% measured after toluene
additions in the large-scale field test performed at the site (McCarty et al.
1998a
).
The results from batch/slurry microcosms that were supplied with propane (Timmins et al.,
2001
) also agreed with observations from a pilot-scale field demonstration of cometabolic
sparging performed at McClellan AFB, California (Tovanabootr et al.,
2001
; Connon et al.,
2005
). Lag times in the microcosms of several weeks were similar to those observed in the field.
In addition,
cis
-DCE was transformed more rapidly than TCE, which was consistent with the
results from the field tests. The agreement between microcosm and field tests when testing
biostimulation for aerobic cometabolism led to the use of similar column and microcosm tests
for evaluating bioaugmentation approaches, as will be discussed Section
8.4
.
8.3.2 Field Studies with Indigenous Microorganisms
The most detailed field studies evaluating
in situ
aerobic cometabolism by indigenous
microorganisms have been performed at the Moffett Test Facility and at Edwards AFB, both
located in California. Studies at the Moffett Test Facility were conducted at the pilot scale in a
shallow alluvial aquifer under induced gradient conditions of injection and extraction. Since
indigenous microorganisms were stimulated on a broad range of substrates under a consistent
set of test conditions, the results illustrate why bioaugmentation has been considered for
specific cases. All of the tests were performed using the same experimental approach, in
which the growth substrates and oxygen were added as dissolved components in the
injected groundwater. The CAHs of interest also were added at known concentrations to
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