Biomedical Engineering Reference
In-Depth Information
8.4.3.3 Bioaugmentation with Butane Utilizers: Field Studies
A pilot-scale study was performed at the Moffett Test Facility to evaluate the potential to
bioaugment a butane-utilizing culture that had better transformation abilities than the indige-
nous microorganisms. Environmental isolates of
Rhodococcus
sp. strains that were capable of
cometabolizing a broad range of chlorinated ethenes and ethanes were evaluated (Semprini
et al.,
2007a
,
b
,
2009
). A mixture of CAHs including 1,1,1-TCA, 1,1-DCA and 1,1-DCE was
tested, since the abiotic and biotic transformations of 1,1,1-TCA produce 1,1-DCE and 1,1-DCA,
respectively (Vogel and McCarty,
1987
). The cometabolism resulted from the transformation by
a butane monooxygenase enzyme (BMO) which has been shown to be able to transform a broad
range of CAHs (Kim et al.,
2000
) including this CAH mixture (Kim et al.,
2002
).
Field studies were conducted in the saturated zone at the Moffett Test Facility following
the protocols of previous tests (Roberts et al.,
1990
; Semprini et al.,
1990
)
.
The tests were
conducted in two experimental legs, a bioaugmented test leg and a control leg operated under
the same conditions as the test leg, but not bioaugmented. Dissolved butane and oxygen were
both added to the treatment legs, with butane continuously added as a high concentration pulse
of about 15 min followed by 45 min of dissolved oxygen, resulting in time averaged injection
concentrations for butane ranging from 3.5 to 8.8 mg/L and oxygen of 20 mg/L. In order to
obtain pseudo-steady-state concentrations in the test legs, 1,1-DCE, 1,1-DCA, and 1,1,1-TCA
were added to the injected groundwater for 9 days prior to bioaugmentation and the addition of
butane and oxygen.
The concentration history of the CAHs at the S1 monitoring well in the bioaugmented leg is
shown in Figure
8.7
(top). The increase in CAH concentrations over the first 10 days of tests as a
result of their injection is evident. The CAH concentrations reached their injection concentra-
tion, indicating little transformation during this stage of the test. Approximately 5 g of culture
was bioaugmented into the test leg after day 8.5, and butane and oxygen addition was initiated.
1,1-DCE concentration began to decrease soon after the bioaugmentation and butane addition.
Butane and oxygen concentrations are shown in Figure
8.7
(bottom). Butane concentrations
reached levels of about 3 mg/L. Around day 15, the butane concentration decreased dramati-
cally, coinciding with decreases in the 1,1-DCE, 1,1-DCA and 1,1,1-TCA concentrations.
Butane concentrations increased over the period of 16-17 days, which coincided with
increases in 1,1-DCE, 1,1-DCA and 1,1,1-TCA concentrations. When butane concentrations
were reduced to low levels as a result of biostimulation, from 19 to 20 days, 1,1-DCE was
effectively removed to very low concentrations, and 1,1-DCA also was reduced significantly in
concentration. 1,1,1-TCA was the least effectively transformed. The increases in butane con-
centrations at 17 days and 21 days both caused increases in the concentrations of all three
CAHs, possibly from strong inhibition by butane of 1,1-DCA and 1,1,1-TCA transformation, as
was observed and simulated in microcosm tests (Figure
8.6
). During the period from days 18 to
20, the CAHs were removed to the following extent: 1,1-DCE (97%); 1,1-DCA (77%); and
1,1,1-TCA (36%).
In the control, non-bioaugmented west leg, there was little evidence of CAH transformation
over the same time period (data not shown). 1,1-DCE concentrations increased to essentially
constant levels that approached injection concentrations at the monitoring wells, indicating
essentially no transformation. Butane concentrations reached higher levels in the indigenous
leg compared to the bioaugmented leg and then decreased more slowly. By day 25 the butane
concentrations were significantly reduced, indicating that biostimulation of indigenous butane
utilizers had likely occurred. Despite indications of butane utilization, 1,1-DCE concentrations
did not decrease, suggesting that 1,1-DCE was not being transformed.
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