Biomedical Engineering Reference
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The poor performance of the lactate-fed PR1 culture compared to the phenol-fed PR1
indicated lactate could not replace phenol in the field, which was later confirmed in field
experiments (Approach II). In addition, the microcosm results indicated problems that were
likely associated with oxygen limitations. The results also demonstrated that lag periods could
be reduced through bioaugmentation, and that additions of strains that effectively transform
TCE could improve transformation as compared to indigenous strains. Finally, this testing
showed that it was feasible to bioaugment groundwater with an induced strain selected for its
catalytic biotransformation potential.
Munakata-Marr et al. (
1997
) studied the long-term (300 days) cometabolism potential of
these aquifer microcosms and measured the presence of G4 or PR1
301
in the column effluent
using molecular methods. Indigenous phenol utilizers transformed about 100
m
g/L of the
250
m
g/L of TCE added for about the first 100 days, but the transformation ability gradually
decreased. The authors suggested that this decreasing effectiveness over time may have
occurred because the introduced microorganisms had a competitive disadvantage due to TCE
transformation product toxicity. In the microcosm, continuously bioaugmented strain G4
grown on phenol, but with no substrate added, transformed TCE to a similar extent as the
indigenous fed phenol. However, after 70 days of operation, DO levels decreased to below
detection. Upon stopping bioaugmentation, DO levels increased but TCE concentrations also
increased to levels of the control, indicating TCE removal had stopped. In the microcosm that
was bioaugmented with phenol-grown G4, but fed lactate as a substrate, TCE removal was
enhanced for the first 100 days, but DO became limiting and TCE eventually reached the same
levels as the control. The microcosms that degraded TCE most effectively were ones that were
fed phenol and bioaugmented with phenol or lactate-grown G4 or PR1
301
. However, while G4
and PR1
301
were detected in the column effluents during the bioaugmented periods, they
generally were not detected once bioaugmentation was stopped. Thus, the enhanced TCE
transformation at a later time could not be attributed to the bioaugmented bacteria.
These microcosm tests demonstrated the importance of maintaining the DO concentrations
to achieve effective TCE removal. Continuous addition of microorganisms likely generated a
large DO demand as a result of the slow biomass decay. This conclusion was supported by mass
balance calculations. Lactate fed microcosms were observed to have an even greater DO
demand than phenol-fed microcosms. The authors speculated that bioaugmentation may be
one means of maintaining TCE transformation activity when indigenous activity declines. The
results also demonstrated that G4 and PR1 strains were lost from the microcosms once
bioaugmentation was stopped, even in the substrate amended microcosms, which is unfavor-
able for bioaugmentation. The constitutive strain also transformed less TCE when stimulated
on lactate compared to phenol.
Matheson et al. (
1997
) developed strain-specific DNA probes for determining the persis-
tence of
Burkholderia cepacia
G4 used in bioaugmentation. For one of the probes with a
650-base-pair (bp) fragment, as few as 10 CFU of
B. cepacia
could be detected. The method
was applied to the long-term microcosm studies of Munakata-Marr et al. (
1997
) discussed
above. In non-bioaugmented microcosms, G4 and PR1 were never detected, but in the bioaug-
mented microcosms, they were detected for periods of up about 83 days, and their presence was
lost several column exchanges after bioaugmentation was stopped.
8.4.2.2 Bioaugmentation with
Burkholderia cepacia
PR1: Column Studies
Snyder et al. (
2000
) performed continuous flow studies of the addition of
Burkholderia
cepacia
PR1 to columns packed with sediments from the Borden aquifer. The goal of this study
was to evaluate the impact of bacterivorous protists on the bioaugmented culture and TCE
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