Biomedical Engineering Reference
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positive if 1 mg/L added
cis-
DCE was degraded in them within 3 weeks). At the beginning,
of course, results were negative for both JS666 presence and microcosm activity in down-
gradient samples, since the added JS666 had not yet been transported far from IW-02. On the
other hand, by the end of the study, results were negative for both JS666 and microcosm
activity near the injection well, as JS666 had been transported away from the site of injection
over the 7 months since pulse-bioaugmentation.
Representative results (from sampling about 5 months after bioaugmentation) are sum-
marized in Figure
7.6
. Samples that were positive only for
cis-
DCE degradation in microcosms
are coded in yellow; samples positive for presence of JS666, but negative for microcosm
activity are coded in blue (but there were none); and samples positive for both JS666 presence
and microcosm activity are coded in green. It is apparent from all of the green-coded wells
downgradient of bioaugmentation well IW-02 that JS666 was successfully transported through
the bioaugmentation plot and was capable of effecting
cis-
DCE biodegradation. In the first
2 months of operation,
cis-
DCE also degraded in microcosms prepared from upgradient well
MW-11, though qPCR analysis of water samples and post-run microcosms showed no detect-
able JS666 associated with this activity. It appears that extraction/injection and buffering
activities might have stimulated some short-lived, aerobic, perhaps cometabolic, degradation.
The microcosm activity from downgradient samples is undoubtedly from JS666 because
increases in isocitrate lyase genes of JS666 were confirmed at the end of the 3-week microcosm
tests compared to levels in the water samples from which the microcosms were constructed.
Microcosm results demonstrated
in situ
survival and activity of JS666 over the course of
the study in the bioaugmentation plots. Though the levels of JS666 were low (i.e., 3
10
3
to 10
4
colony forming units [CFUs]/mL), they were adequate to effect
cis-
DCE degradation if suitable
environmental conditions (adequate oxygen, pH and absence of inhibitory levels of TCE) were
present as was the case in microcosms constructed from samples of site material, but not
in the test plot itself. Positive microcosm activity was generally correlated with detectable
(by qPCR) JS666.
7.5 SUMMARY AND FUTURE PROSPECTS
The isolation of JS666 allowed the growth-coupled aerobic oxidation of
cis-
DCE to be
explored as a remediation strategy at
cis-
DCE contaminated sites. Progress has been made in
laboratory studies to characterize the metabolic capabilities of the organism including its ability
to (1) completely mineralize high concentrations of
cis-
DCE to levels well below drinking water
standards, and (2) transform mixtures of chlorinated solvents including TCE, VC, DCA,
trans-
DCE and
cis-
DCE. Knowledge from fundamental microbiological and biochemical studies was
used to develop an effective protocol for growth of JS666 to high densities appropriate for
bioaugmentation.
Microcosm studies demonstrated that the bioaugmentation of JS666 stimulated complete
cis-
DCE degradation in a variety of soil types. Molecular tools were developed to track JS666 in the
subsurface to monitor the progress of bioaugmentation in the field. A pilot-scale field test was
successful in demonstrating the spread and stability of the JS666 organisms in the bioaugmented
plot, though interpretation of the field results was compromised by fluctuations in incoming
cis-
DCE concentrations and low DO. Results demonstrated that the JS666 cells maintained their
potential for
cis-
DCE degradation, even when field conditions precluded activity.
Future work is needed on several fronts if the technology is to become widely applicable:
Elucidate the
cis-
DCE degradation pathways in JS666 to enable the optimization of
bioaugmentation and the ability to search for other
cis-
DCE degraders that use similar
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