BIOAUGMENTATION WITH DEHALOCOCCOIDES: A DECISION GUIDE - Bioaugmentation for Groundwater Remediation - page 125

(Hirschorn et al., 2007 ). CSIA also can provide a sensitive method to identify the effects of
bioaugmentation, since the isotopic fractionation in the daughter compounds, DCE and VC, is
powerful evidence regarding the nature and rate of biodegradation processes (Morrill et al.,
2005 ). CSIA can provide powerful evidence that bioaugmentation is not needed at a site if the
chloride fractionation in the VC shows evidence of further biodegradation.
CSIA has not been used as a method for testing field samples to determine if bioaugmen-
tation is needed at a specific site. The main reasons are that CSIA is more costly and less
available than MBTs, but also the results may not be as definitive. For example, low levels of
VC-degrading Dehalococcoides may be present and detectable using qPCR, but their
effects may not yet be measurable using CSIA. Because carbon uptake from the chlorinated
solvents does not occur, carbon isotope analyses of the biomass cannot be used to monitor
biodegradation after addition of labeled carbon, as has been done for hydrocarbon degraders
(Geyer et al., 2005 ).
4.7.1.3 Microcosm Testing
Laboratory testing using microcosms is an established method to obtain strong evidence
regarding the need for bioaugmentation. Microcosms using site groundwater (and aquifer
solids from the site, if possible) can be amended with electron donors (and bioaugmentation
cultures, if desired) and incubated under anaerobic conditions following established methods.
Guidance has been developed specifically for testing biostimulation to treat chlorinated ethenes
(the Reductive Anaerobic Biological In Situ Treatment Technology [RABITT] test protocol)
(ESTCP, 2003 ).
The RABITT protocol includes both microcosm and field testing methods, with results
from several sites that showed complete dechlorination with biostimulation only. These meth-
ods may be modified or streamlined to address the need for bioaugmentation. In most cases,
bioaugmentation testing can be done by using replicate anaerobic serum bottles (e.g., Lu et al.,
2009 ). Many replicates can be established and analyzed for relatively little cost, and the
sampling schedule can be modified easily as interim results are obtained. Although serum
bottle tests will be best suited for most purposes, larger and more costly column testing still
may be useful in some cases (Schaefer et al., 2009 ).
Any anaerobic incubation, particularly from a site that has been aerobic and/or donor-
limited, has to continue long enough to allow growth of the native microbial community to
sufficient numbers to biodegrade the chloroethenes to a meaningful extent. It may take several
months to achieve complete dechlorination if populations of the key organisms must increase
by several orders of magnitude, particularly if environmental conditions such as pH or
temperature are suboptimal. Further, genetic transfer within the Dhc population may be partly
responsible for the spread of the genes needed for complete dechlorination (Regeard et al.,
2005 ) and this process may require time.
Results from one site-specific microcosm test are provided in Figure 4.3 to illustrate the
types of information that can be gained. In this case, samples of groundwater and solids from a
TCE-contaminated site (Hunter Army Air Field, Georgia) were incubated in anaerobic micro-
cosms. Test microcosms were bioaugmented with a commercially available culture containing
Dhc strains capable of complete dechlorination (SDC-9 ™ , Shaw Environmental, Inc.) 59 days
after the incubations began. The results show a classic cis -DCE stall without bioaugmentation.
However, after bioaugmentation, complete dechlorination to ethene was observed, if the
pH was adjusted to neutral.
Importantly, microcosms are not necessarily accurate predictors of field performance.
Conditions within a closed incubator differ from the open real-world environment, which is