Biomedical Engineering Reference
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maximum concentrations of about 4 mg/L in the west leg, and about 3 mg/L in the bioaugmented
east leg. The butane concentration decreased to below detection by day 25 in the bioaug-
mented east leg, and decreases in DO were observed in response to butane utilization. Upon
bioaugmentation and biostimulation, with continuous addition of butane and dissolved
oxygen and/or hydrogen peroxide as sources of dissolved oxygen, there was about 70%
removal of 1,,1,1-TCA (Figure
8.8
, top). In contrast, there was no removal of 1,1,1-TCA in the
non-augmented test leg (Figure
8.8
, bottom), although butane and oxygen consumption by
the indigenous population was similar to that in the bioaugmented test leg. Some 1,1-DCE
removal, about 40%, was observed in the control leg, while 80% removal was observed in the
bioaugmented leg (data not shown). With prolonged treatment, removal of 1,1,1-TCA in the
bioaugmented leg decreased to 50-60%. Hydrogen peroxide (H
2
O
2
) injection increased
dissolved oxygen concentration, thus permitting more butane addition into the test zone,
but more effective 1,1,1-TCA treatment did not result.
The results showed that bioaugmentation with the enrichment cultures was effective in
enhancing cometabolic treatment of both the 1,1,1-TCA and the low concentrations of 1,1-DCE
over the entire period of the 50-day test. Compared to the first season of testing, cometabolic
treatment of 1,1,1-TCA was not lost. The better performance achieved in the second season of
testing may be attributed to less 1,1-DCE transformation product toxicity, more effective
addition of butane, and bioaugmentation with the highly enriched dual culture. The results
showed that the addition of an enrichment culture improved the performance of cometabolic
treatment of 1,1,1-TCA, while no treatment was achieved in the control leg, even though the
indigenous butane utilizers were successfully stimulated.
8.4.4 Bioaugmentation Approach IV
An interesting bioaugmentation approach is to add indigenous CAH-cometabolizing micro-
organisms by injecting groundwater that contains the organisms of interest into target areas
where the desired organisms are absent or present in low numbers. For example, microbes
present in one aquifer might be added to another aquifer for their bioremediation potential.
This approach has been called the “primed” method of bioaugmentation (Singer et al.,
2005
).
An example of this approach is the field study conducted by Takeuchi et al. (
2004
) for a TCE
contaminated aquifer in Mobara, Japan. Groundwater along with methanotrophic bacteria
from an aquifer rich in naturally occurring methane, which seeped into the aquifer from a
methane gas formation, was injected into a nearby TCE-contaminated site. Groundwater
containing methane at 0.016 mg/L, along with methanotrophic bacteria at 1.1
10
4
cells/mL,
was injected into a shallower aquifer through an injection pit.
Field observations showed that the initial concentration of about 128
m
g/L of TCE was
reduced to below the detection limit. The authors concluded that removal was due to methano-
trophs present in the amended groundwater, and not in the indigenous groundwater. They
reached this conclusion based on microcosm tests that supported the field experiments. Most of
the methanotrophs that were added became attached because the numbers of methanotrophs in
the remediated groundwater were lower than numbers in the injected groundwater and the
highest activity occurred close to the injection pit. The added methanotrophs expressed sMMO,
which is effective in transforming TCE. The authors concluded that the methane-enriched
groundwater from the natural gas area was valuable both for its supply of methane and also for
its microbial content.
At another site in Chikura, Chiba, Japan, bioremediation of
cis
-DCE was accomplished by
injecting uncontaminated water containing dissolved oxygen and methanotrophic bacteria into
another aquifer that contained
cis
-DCE and higher concentrations of dissolved oxygen
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