Biomedical Engineering Reference
In-Depth Information
was performed with butane enrichments that were effective in CF cometabolism along with an
isolate
Rhodococcus aetherovorans
BCP1. The lag time for stimulation of butane utilizing
organisms was strongly affected by temperature, with less than 2 weeks required in all cases,
and the shortest lags were observed when CF was absent. CF cometabolism by indigenous
butane utilizers was not observed even after several weeks of incubation at groundwater
temperatures of 15
C. Decreases in the lag period were observed in treatments performed
with the two different butane-utilizing inocula even at the lowest concentration of the aug-
mented culture (3.5
10
3
CFU/mL). Sustained CF cometabolism was maintained in bioaug-
mented microcosms at a butane/CF molar ratio of 2.0-3.1. The results showed the potential of
both decreasing the lag phase and promoting more effective cometabolism of CF through
bioaugmentation.
Microcosm studies also were performed on mixtures of CAHs that included VC,
trans
-
DCE,
cis
-DCE, TCE, 1,1,2-TCA and 1,1,2,2-TeCA using aquifer material and groundwater from
a contaminated site (Frascari et al.,
2006
) and methane or propane as cometabolic substrates.
Lag times for the onset of methane or propane utilization were 36-264 days in the non-
bioaugmented microcosms. In microcosms inoculated with cultures directly sampled from
the non-bioaugmented microcosms, the lag period was significantly shortened to 0-15 days
and transformation abilities were maintained. The biodegradation and cometabolism of the
mixture of six CAHs was maintained for up to 410 days, with the less chlorinated CAHs
transformed at the fastest rates. These tests again showed the potential of decreasing lag
times and transferring effective cometabolic potential. Gualandi et al. (
2007
) showed that a
dual-culture fed both methane and propane was most effective in transforming this mixture
of CAHs.
The ability to enhance CF transformation and decrease lag time also was demonstrated with
a butane-enriched culture that was selected for its CF transformation abilities (Frascari et al.,
2005
). The culture was a
Rhodococcus
strain that was later identified as
Rhodococcus aether-
ovorans
BCP1 (Frascari et al.,
2007
). Introducing this strain into autoclaved soil slurry micro-
cosms eliminated any lag time, and produced effective CF cometabolism (a transformation
capacity of 0.031 mg CF/mg protein).
8.4.3.2 Bioaugmentation with Butane-Utilizers: Continuous Column Studies
Continuous flow column studies evaluated the potential of adding a highly enriched
butane-utilizing culture containing
Rhodococcus sp
. microorganisms to promote effective
transformation of 1,1,1-TCA (Semprini et al.,
2005
) through butane addition (Approach III).
The column was packed with aquifer core material from the Moffett Test Facility. The
bioaugmentation approach was to add the culture and then continuously add dissolved butane
(3 to 5 mg/L) and oxygen (20-30 mg/L). A flow rate of 0.2 mL/min resulted in a fluid residence
time in the column of about 1.5 days. The column (2.5 cm diameter; 30 cm length; volume
ΒΌ
150 mL) was bioaugmented at the column influent with a small mass (0.5 mg) of culture and
pulse fed butane, dissolved oxygen and 1,1,1-TCA. Butane was effectively utilized in the
column and about 80% of the added 1,1,1-TCA (200
m
g/L) was effectively transformed.
When the 1,1,1-TCA concentration was increased to 400
m
g/L, less 1,1,1-TCA was transformed,
and upon lowering the concentration about 60-70%, it was again transformed. 1,1,1-TCA
transformation was maintained in the column for a period of 120 days. When 1,1-DCE
(130
m
g/L) was added along with 1,1,1-TCA, concentrations of 1,1,1-TCA, oxygen and butane
increased, while about 50% of the 1,1-DCE was transformed. The results indicated that 1,1-DCE
transformation product toxicity was occurring, and that effective 1,1,1-TCA transformation
was difficult to maintain in the presence of 1,1-DCE.
Search WWH ::
Custom Search