Environmental Engineering Reference
In-Depth Information
necessary to develop a better understanding of methods of delivery of the
microorganisms in the desired locations. Our understanding of the move-
ment and survival of augmented microorganisms in the subsurface needs
improvement as well.
Pilot-scale and full-scale demonstrations at different sites are needed
to refine the techniques developed and presented in the design guidance
manual. The design guidance document that describes the SERB technology
should be promoted among technology vendors and the user community. It
is suggested that this be done using the Air Force model for the promotion
and improvement of
in situ
bioventing technology. Additional considerations
needing attention are:
•
Further characterization of shifts in microbial ecology in response to
SERB
•
Evaluation of mixtures of optimal cosolvent/electron donor solutions
•
Modeling of impact of source removal on long-term economics for
site remediation costs
8.4 Polychlorinated biphenyls
Metabolic engineering of pathways involved in aerobic biodegradation of
mono- and dichlorinated polychlorinated biphenyls (PCBs) has shown that
genetically stable genetically engineered microorganisms (GEMs) capable of
growing on PCBs can be generated. Such organisms have been found to be
able to survive in contaminated soils for a considerable time, especially when
delivered in a suitable carrier. Biomarkers for these GEMs have also been
developed for tracking them in engineered systems. The metabolic engineer-
ing approach that produces microbial strains that thrive on complex recal-
citrant contaminants, rather than strains that transform contaminants using
cometabolism, is very interesting. The ability of GEMs to extract energy from
recalcitrant compounds simplifies management of treatment strategies for
such contamination. This approach should be pursued for other, more com-
plex PCBs.
The process of anaerobic dechlorination of highly chlorinated PCBs is very
slow, requiring several years, and it is a major bottleneck in any demonstration
project. The microbial strains capable of doing anaerobic dechlorination have
not been isolated and characterized. Their isolation from the contaminated
sites and maintenance in laboratories/culture collections are highly desirable
in order to promote this technology. Similarly, the GEMs generated in the
present work should also be registered with suitable culture collections in
order to make them more widely available to potential users. Due to the slow
nature of the degradation process, pilot demonstration of the technology has
been lagging. This should be more extensively demonstrated.