Biomedical Engineering Reference
In-Depth Information
transformation. Such polymers can provide a long-term supply of reducing energy (i.e.,
NADH) to drive the cometabolic process, without added growth substrates (Henrysson and
McCarty,
1993
).
For the field trials, the bioaugmented culture was grown in a 750-L fermentor in 550 L of
basal salt media that contained (1.6% w/w) sucrose as a substrate, and fed alternating batches of
sucrose and phenol as carbon sources. Bacterial storage polymers were produced naturally, as
the ammonium in the reactor became depleted.
The field test was conducted at an industrial facility in Pennsauken, New Jersey, in a
heterogeneous aquifer consisting of silty fine to medium sand interspersed with thin lenses of
clay. The site was contaminated with a mixture of chlorinated ethenes including PCE, TCE,
DCE and VC, and chlorinated ethanes including DCA and TCA. The test plot consisted of a
treatment plot that was bioaugmented with ENV435 and a control plot that did not received
ENV435. The plots measured 4.6 m wide and 12 m long, and were separated by 9.2 m and
contained six injection wells, a recovery well located 12 m downgradient from the injection well,
and nine monitoring wells located in between the injection and monitoring wells.
Oxygen was delivered either by adding pure oxygen to extracted groundwater prior to
reinjection, or by directly adding gaseous oxygen to the injection wells. In the first trial, ENV435
was added to upgradient injection wells at concentrations of 1.2
10
11
CFUs/mL. The second
trial involved injecting ENV435 under pressure into selected monitoring wells to distribute cells
throughout the test zone. Prior to and after the inoculum injection, compressed oxygen was
used to force the culture into the formation. Oxygen was added periodically in this manner to
maintain DO concentrations above 8 mg/L.
Upon bioaugmentation, ENV435 followed the path of the bromide tracer in the test zone.
The highest concentration measured was 1.9 10
8
CFU/mL at a well located 2 m downgradient
of the injection well. The several log reductions in concentration indicated significant numbers
of cells were being filtered out in the aquifer. First-order decay estimates indicated the half-life
for the ENV435 cells in the aquifer was only 1 to 2 days.
DO concentrations decreased significantly, with measureable DO levels occurring only 2 m
from the injection well. DO levels in the control plot usually exceeded 20 mg/L, indicating
significant DO consumption in the bioaugmented plot. The direct injection of oxygen in the
second test trial resulted in higher DO concentrations, often above 20 mg/L after injection and
up to 2 mg/L 3-5 days after the injection.
The total concentration of TCE, DCE and VC decreased from 2,200
m
g/L initially to below
500
m
g/L at most locations in the bioaugmented test plot. Concentrations tended to rebound
several days after the tests. Greater removal spatially was observed in the second test where
ENV435 was added throughout the test zone and pure oxygen was injected into the well. Mass
balance estimates indicated about 141 g of VOC were removed in the treatment process as a result
of the addition of 38.5 kg of culture, corresponding to a transformation capacity of 0.004 g VOC/
g biomass. This value represents about 10% of the transformation capacity measured by Chang
and Alvarez-Cohen (
1995
) for TCE by phenol degraders (0.03 TCE/g biomass).
The adhesion-resistant strain of ENV435 also was evaluated in a bedrock aquifer at a
former chemical manufacturing facility (Walsh et al.,
2000
). To facilitate transport of the
strain, pneumatic fracturing was used to expand the fracture network in the bedrock aquifer.
Bottle tests performed prior to bioaugmentation showed that, to achieve the objective of a 90%
reduction in TCE from the initial concentration of 5-10 mg/L, it would require a concentration
of ENV435 of 5
10
8
CFU/mL. During the fracturing processes, approximately 676 L of
solution was injected into the aquifer that contained strain ENV435 at a cell optical density of
50, and groundwater containing a liquid form of organic carbon. The inoculation occurred in
batches of 114-160 L with pressurized air. To supply needed oxygen, the inoculation was
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