Biomedical Engineering Reference
In-Depth Information
(Takeuchi et al.,
2005
). The
cis
-DCE was present as a result of the anaerobic transformation of
TCE. Groundwater from a third aquifer containing 0.16 to 32 mg/L methane, 3.9 to 30 10
3
cells/mL of methanotrophs and low DO was added to aquifer 2 that contained less methane
(0.032 mg/L), fewer methanotrophs (0.088 to 1
10
3
cells/mL) and higher DO. Water from a
first aquifer that contained low methane (0.008 mg/L) and 0.044 to 33
10
3
methanotrophs was
added as a control to the second aquifer. The
cis
-DCE concentrations decreased by about 50%
with injection of the methane-rich water, while no significant decrease was observed with the
same rate of injection of the control water. Dissolved methane concentrations also decreased
when groundwater from the third aquifer was injected. The concentration of methanotrophs
was lower at the observation well (2.9
10
4
cells/mL) compared to the injection well (1.1
10
5
10
4
cells/mL. It was not
determined whether methanotrophs carried in the injected groundwater improved the perfor-
mance of treatment. However, the methodology used here is consistent with the previous study
demonstrating bacteria in the injected groundwater can help prime the aquifer with a trans-
forming culture. Injecting groundwater from the uncontaminated aquifer also provides a cheap
continuous seed of culture and may help overcome effects of transformation product toxicity.
cells/mL), and those expressing sMMO numbered around 1.4
8.5 SUMMARY
The results of the field demonstrations performed to date indicate bioaugmentation to
promote effective cometabolic transformation still should be considered experimental in
nature. Although some benefits have been demonstrated, many of the studies have shown
that performance enhancements cannot be maintained over long periods. In addition, perfor-
mance demonstrated under laboratory conditions of microcosms and columns often cannot be
achieved under field conditions.
Shown in Figure
8.9
is a general overview of the observations from the field tests and
supporting laboratory and microcosm studies, ranging from successful to unsuccessful.
Approaches III and IV
Approaches I and III
Approach II
Decrease lag period for
biostimulation
Biocatalytic transformation
abilities
Enhanced transformation
compared to indigenous
strains
Constitutive strains fed
non-competing substrate,
like lactate
Limited
Success
Successful
Unsuccessful
Easy to implement
Strains can be developed with
enhanced abilities and properties
Competition for easily
utilized substrates
Microorganisms are
adapted to the
subsurface
environment
Tranformation product toxicity
Predation
Transformation product
toxicity
Figure 8.9. Likelihood of success of processes based on the bioaugmentation studies for aerobic
cometabolism performed to date. Italicized text represents processes that are problematic for the
approach taken.
Less effective performance in the
field than in laboratory studies
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