BIOAUGMENTATION FOR THE IN SITU AEROBIC COMETABOLISM OF CHLORINATED SOLVENTS - Bioaugmentation for Groundwater Remediation - page 246

at Edwards AFB (Figure 8.2 ). Transformation product toxicity appeared to play an
important role in this process, since results were less impressive in the field and in column
tests when 1,1-DCE was present. Here microbes that do not transform the contaminant, but
consume the growth substrate, will likely outcompete the introduced microbes that effectively
transform the contaminant. Additional research is needed to document strains that have
effective transformation abilities for contaminants, such as 1,1-DCE and 1,1,1-TCA. In addition
the application of molecular and chemical detection methods that are monooxygenase specific
would be useful in determining the effectiveness of added strains.
Microcosm and column studies have been successful at predicting the performance of
bioaugmentation in the field. Studies of Munakata-Marr et al. ( 1996 , 1997 ) showed that
Approach II with PR1 301 was likely to fail in the field test, and this outcome was later observed
(McCarty et al., 1998b ). Column studies and microcosm studies of Approach III (Semprini
et al., 2005 , 2007b ) showed the potential for enhanced 1,1,1-TCA degradation that was later
achieved in the field when an effective strain was added. The column test also revealed the
problem associated with transformation product toxicity when 1,1-DCE was present. Since
microcosm and column studies are much cheaper than field tests, future research should take
advantage of these methods in evaluating bioaugmentation approaches.
Approach IV, priming the target aquifer by adding microbes with desirable cometabolic
activities from another aquifer, is one of the simplest approaches to implement. Although
limited in applicability, this approach may be beneficial in aquifers undergoing intrinsic
remediation where the aerobic processes might be occurring. For example, methanotrophs
might be stimulated in an aerobic zone downgradient from an anaerobic zone where methane
is being produced. Groundwater from this aerobic zone could be injected into areas where
enhanced methanotrophic treatment is desired. A similar approach may be used to add ethene-
utilizing microorganisms that have been naturally stimulated by ethene produced from the
anaerobic transformation of PCE and TCE. Research in this area could provide a better
understanding of whether microorganisms obtained from spatially different areas actually
become established and improve treatment as compared to biostimulation of the indigenous
bacteria. In addition, the potential value of continuous priming of a treatment zone deserves
research. For example, recirculating groundwater from a treatment zone that contains indige-
nous microorganisms might be used as a means of overcoming the effects of transformation
toxicity.
REFERENCES
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Bourquin AW, Mosstellar DC, Olsen RL, Smith MJ, Reardon KF . 1997. Aerobic bioremediation
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