RESEARCH NEEDS FOR BIOAUGMENTATION - Bioaugmentation for Groundwater Remediation - page 334

to the water activity, pH, temperature, cocontaminants and other physicochemical conditions
of the environment to which they will be introduced (Cameron et al., 2010 ; Kristensen et al.,
2010 ;Schaeferetal., 2010 ; Schuetz et al., 2007 ). Microbes also disburse across environments,
and the longer-range transport of microbes and their catabolic activity, including their genes,
has implications for the long-term fate of contaminants and the impact and regulation of
introduced bioaugmentation cultures. The ability of many microbial communities to form
aggregates on particles and in biofilms has implications for their ability to utilize sorbed
contaminants (as compared to the limitations of free-living microbes) and also is a critical
consideration for transport (short- and long-range) and survival of the introduced microbes,
and by extension the fate of the target contaminants.
Microbial interactions with solid surfaces are an influencing factor in interspecies nutrient
transfer and microbial survival. From a contaminant perspective, both abiotic chemical trans-
formations and biotic metabolic and cometabolic transformations need to be included when
developing a mechanistic understanding of the ultimate fate of contaminants. Combined
remedies that take optimal advantage of physical, chemical and biological attenuation mechan-
isms for a given contaminant suite are very much needed.
A major challenge to this work is the inherent heterogeneity in natural environments. This is
a very difficult challenge, as each point in space will offer a different environment with
different concentrations of donors, acceptors, other nutrients and inhibitors. A microbial
consortium must be robust to the full range of conditions present within a site. Therefore,
perhaps the most important determinant of success is the degree to which the site under
remediation is hydrogeologically and chemically characterized.
The single most difficult problem to overcome at full scale is mixing. Thus, a major
research need is developing clever and cost effective ways to bring the microbial community,
contaminant and electron donor together. Part of this effort requires an improved mechanistic
understanding and better models of microbial transport, growth and dechlorination, particu-
larly models that incorporate the complexity of electron donor fermentation and dechlorination
in competition with methanogenesis and other terminal electron accepting processes (TEAPs)
in the context of a flowing multiphase system. In addition, such models should consider
combined and integrated remedies involving chemical or physical treatment, as well as
biological treatment.
To continue improving bioremediation, fully instrumented field sites, such as those at
Bemidji (Minnesota, USA), Moffett Federal Airfield (California, USA), Canadian Forces
Base (CFB) Borden (Canada), and others have been and will continue to be essential to
developing practical tools that capture the important rate-determining processes at real
sites. Only by working at a field scale, while integrating knowledge from all scales (from
molecular to ecosystem), can practical solutions be discovered. How complex subsurface
ecosystems behave was a major focus of a DOE Office of Biological and Environmental
Research (BER) workshop in August, 2009 (DOE/SC-0123, March 2010; www.science.gov/
ober/BER_workshops.html ). The workshop report identified three major research gaps:
(1) research approaches must embrace a hybrid of bottom-up reductionism with top-down
complexity; (2) such hybrid research efforts are needed on relevant field sites with iterative
experimental and modeling activities; and (3) novel complex system science approaches are
needed.