BIOAUGMENTATION FOR THE IN SITU AEROBIC COMETABOLISM OF CHLORINATED SOLVENTS - Bioaugmentation for Groundwater Remediation - page 218

the injected groundwater, along with conservative tracers, so that accurate estimates of the
degree of removal could be performed.
Table 8.1 provides a summary of the tests performed at the Moffett Test Facility, the
substrates used, the CAH tested, the extent of treatment achieved and some key observations.
A broad range of growth substrates were tested including methane, phenol, toluene and butane.
Oxygen was added as pure oxygen dissolved in water or as hydrogen peroxide (H 2 O 2 ). A range
of chlorinated ethenes (TCE, trans -DCE, cis -DCE, 1,1-DCE and VC) and chlorinated ethanes
(1,1,1-TCA and 1,1-dichloroethane [1,1-DCA]) were evaluated.
Studies were first performed using methane as a growth substrate and the transformation
of mixtures of chlorinated ethenes (TCE, trans -DCE, cis -DCE and VC) was evaluated along
with 1,1,1-TCA as a background contaminant. Methane utilization was observed after about
10 days of addition. In successive seasons of testing, methane utilization was much more rapid,
indicating the indigenous microorganisms stimulated in the previous season were still present in
the test zone. The degrees of treatment achieved were compound specific with very effective
removal of VC and trans -DCE, followed by cis -DCE, with limited removal of TCE. 1,1,1-TCA
was not transformed. The tests demonstrated that treatment to drinking water standards of VC
(less that 2 m g/L) could be achieved. Inhibition of the rates of cometabolic treatment with
methane as the primary substrate was observed and the addition of energy yielding substrates,
such as formate and methanol that were non-inhibitory, resulted in temporary enhanced
transformation. Cometabolism was strongly linked to methane utilization, demonstrating that
the continuous addition of substrate was needed to promote cometabolism. Microbial growth
and cometabolic treatment were achieved close to the injection well. The results obtained with
methane also were consistent with observations from laboratory microcosms and columns. The
pattern of contaminant transformation, of limited TCE and no 1,1,1-TCA removal, and trans -
DCE transformed to a greater extent than cis -DCE, also suggested that microorganisms that
express pMMO likely were stimulated since conditions of copper limitation required for the
expression of sMMO likely did not exist (Semprini, 1997 ).
Studies conducted at the Moffett Test Facility with indigenous microorganisms grown on
phenol showed greater potential for the treatment of TCE and cis -DCE with up to 90% removal
achieved. VC also was very effectively removed. Concentrations up to 1,000 m g/L of TCE could
be effectively transformed and greater extents of transformation could be achieved through the
addition of more phenol. The maximum transformation yield reached 0.06 g TCE/g phenol,
indicating that effective cometabolic treatment could be achieved. This value compared with a
value of 0.11 g TCE/g phenol observed with a mixed phenol utilizing culture derived from the
field site (Hopkins et al., 1993b ). Like the methane tests, about 10 days were required for
effective phenol utilization and cometabolism to be achieved. The results demonstrated effec-
tive utilization of TCE, cis -DCE and VC. In addition, cis -DCE and VC, which are often present
as anaerobic transformation products, also could be effectively transformed. The results of
laboratory studies in microcosms using mixed cultures enriched from the site groundwater
were consistent with those obtained in the field with respect to the transformation potential of
the compounds tested.
A later study at the Moffett Test Facility (Hopkins and McCarty, 1995 ) demonstrated that
indigenous microorganisms stimulated on toluene were as effective as those stimulated on
phenol in promoting TCE, cis -DCE and VC transformation. When toluene was transformed,
transient evidence of the formation of o -cresol, and not m -or p -cresol, indicated that o -toluene
monooxygenase ( o TOM) was expressed. o TOM is the same oxygenase used by Pseudomonas
cepacia G4 for phenol and toluene oxidation, and this microorganism is one of the most
effective in transforming TCE with respect to transformation yield and rates (Alvarez-Cohen
and Speitel, 2001 ). 1,1-DCE also was transformed, but its transformation resulted in transfor-
mation product toxicity, thereby decreasing the removal of TCE from over 90% to around 50%.