Biomedical Engineering Reference
In-Depth Information
remediation. A single column was used for a series of experiments including culture addition,
culture addition with TCE, and culture addition with TCE and substrate. The PR1 culture was
added at concentrations ranging from 6.3 to 6.6
10
7
CFU/mL. Bacterivores increased with
repeated additions of PR1 to the column, resulting in a decrease in the half-life of PR1. The
addition of TCE and growth substrate (phthalate, 4 mM) resulted in prolonged survival of PR1
and TCE transformation. The results indicated significant and predictable losses of PR1 in the
column due to native bacterivores.
In aquifer sediment column studies with
B. cepacia
G4 5225-PR1, Winkler at al. (
1995
) used
highly specific monoclonal antibody techniques to track its survival. The microorganisms were
continuously added to sterilized sediments and non-sterile sediments. 5225-PR1 survived well in
the sterilized sediments but rapidly decreased in the non-sterile sediments. The loss in the non-
sterile sediment was presumed to be due to predation by bacteriovorous protists. Their study
showed the utility of monoclonal antibody tracking methods and the importance of biotic
interaction in the persistence of introduced microorganisms.
Komlos et al. (
2004
) performed column studies to investigate the concept of developing
biofilm barriers to control migration of TCE through the creation of a thick biofilm capable of
treating influent TCE. The studies were performed with two cultures to form a dual species
TCE degrading/reduced permeability biofilm barrier using
Burkholderia cepacia
PR1-
pTOM31c and
Klebsiella oxytoca
.
B. cepacia
was used for its ability to transform TCE and
to constitutively express its oxygenase enzyme, and
K. oxytoca
was selected for its ability to
form thick biofilms. Studies were performed in columns packed with 1 mm glass beads. The
columns studies were conducted with the pure culture of
B. cepacia
and a column inoculated
with the combined cultures. The columns were continuously fed TCE, dissolved oxygen and
diluted Luria-Bertani (LBG) medium as a growth substrate.
TCE removal was most effective in the column inoculated with the pure culture of
B.
cepacia
(79% removal), compared to 49% removal in the dual culture column fed the same
concentration of substrate (30 mg/L chemical oxygen demand [COD]). This greater removal
corresponded to a higher population of
B. cepacia
in the single culture column. The presence of
K. oxytoca
had a negative effect on TCE removal performance. As the concentration of COD
was increased, TCE removal in the dual species column decreased with only 27% achieved at
70 mg/L COD, and no removal achieved at 700 mg/L COD. Dissolved oxygen limitations in the
columns fed higher concentrations of COD were likely responsible for the lower TCE removals.
Permeability reductions were correlated with the higher COD concentrations, and corresponded
with the
K. oxytoca
population density. The COD was reduced by as much as a factor of 5 as
compared to the initial conditions
.
The study provides a good example of how the competition
for a benign substrate between TCE transforming and non-TCE transforming microorganisms
can result in decreased remediation performance.
8.4.2.3 Bioaugmentation with
Burkholderia cepacia
G4
with Glucose Addition: Field Study
Bourquin et al. (
1997
) performed a feasibility study evaluating bioaugmentation with
Burkholderia cepacia
G4 PR1
301
in a shallow aquifer in Wichita, Kansas, USA. Strain G4
PR1
301
is highly effective in transforming TCE, but requires neither phenol nor toluene to
induce the oxygenase activity (McCarty et al.,
1998b
). The sandy aquifer was contaminated with
TCE (125
m
g/L),
cis
-DCE (95
m
g/L) and
trans
-DCE (4
m
g/L). The remediation system consisted
of an injection well, extraction well and multi-depth multiport monitoring wells. The PR1
culture was grown in a 16 L stirred-tank bioreactor on site using a drain-and-fill protocol
with glucose (7.2 g/L) as a growth substrate to achieve a cell density of 10
12
cells/mL
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