MICROBIAL MONITORING DURING BIOAUGMENTATION WITH DEHALOCOCCOIDES - Bioaugmentation for Groundwater Remediation - page 168

CHAPTER 6
MICROBIAL MONITORING DURING
BIOAUGMENTATION WITH DEHALOCOCCOIDES
Erik A. Petrovskis, 1 Wayne R. Amber 1 and Christopher B. Walker 2
1 Geosyntec Consultants Inc., Ann Arbor, MI 48103; 2 Geosyntec Consultants Inc.,
Seattle, WA 98101
6.1 INTRODUCTION
The use of bioremediation has increased steadily as scientists and engineers have recog-
nized the importance of microbes in the transformation and degradation of toxic compounds
(Lebr ´ n et al., 2011a ). Over the past few decades, the use of bioremediation in aerobic and
anaerobic subsurface environments has permitted closure of hundreds of impacted sites
(USEPA, 2009 ; ESTCP, 2002 ; Regenesis, 2011 ). Guidance documents published by organiza-
tions such as the U.S. Environmental Protection Agency (USEPA), the Interstate Technology &
Regulatory Council (ITRC), the Environmental Security Technology Certification Program
(ESTCP) and the Strategic Environmental Research and Development Program (SERDP),
involving some aspect of microbial degradation of recalcitrant compounds now number in
the dozens. The widespread use of bioremediation has resulted in a broader and more diverse
practitioner group, and so a more thorough understanding of the complexities, strengths,
limitations and difficulties of this remedial option is required. In particular, accurately asses-
sing the potential metabolic ability of microbial communities (and specific organisms) at
contaminated sites provides an opportunity for significant cost- and efficiency-savings
(on the order of tens to hundreds of thousands of dollars per site).
Traditional culture-based methods, useful in assessing microbial activities, are commonly
used in environmental systems such as wastewater treatment plants or for determining the
contribution of stormwater run-off into aquatic systems (e.g., total maximum daily loads).
These techniques, while highly developed, are less useful when dealing with the subsurface
environments encountered during environmental remediation. Methods such as direct plate
counts and most-probable number (MPN) dilution series provide cell concentration estimates
for somewhat generic growth conditions, such as the number of cells present that are capable
of aerobic heterotrophic growth (e.g., growth using oxygen and organic compounds like
glucose).
These methods, while useful in some instances, suffer from biases, low resolution and, in
the case of Dehalococccoides ( Dhc ) and many other microbes relevant for bioremediation, an
inability to selectively screen for these organisms based solely on culture conditions. Additional
issues, such as the differential ability of individual Dhc strains for complete reductive dechlo-
rination to ethene, further complicate the interpretation of these culture-based enumeration
techniques. These methods are analogous to the use of historical photographs for delineating
the entire extent of contamination at a site; while useful, on their own the photographs provide
limited information on the specific contaminant type, its concentration and its distribution.