Biomedical Engineering Reference
In-Depth Information
within these communities. Understanding the microbial community shifts associated with
fluctuating environmental conditions provides remediation engineers an opportunity to manip-
ulate microbial populations towards more beneficial metabolic activities. Monitoring the health
of these communities through the techniques outlined above provides information useful in
determining if nutrient addition or bioaugmentation is required for the continued degradation
or sequestration of harmful compounds.
6.8 DATA EVALUATION AND INTERPRETATION OF MBTS
The evaluation of data obtained through use of MBTs necessitates a broader examination
of site-wide characteristics for effective site management. Combined with traditional monitor-
ing approaches, a more holistic picture can be obtained rather than relying solely on MBTs for
assessing the performance of bioremediation activities. At a minimum, monitoring of geo-
chemical parameters, such as pH, ORP and dissolved oxygen, should be conducted in parallel
with MBT analysis, verifying appropriate conditions exist for effective bioremediation.
Measuring concentrations and valence state (or inferred valence state through the use of
filtered and unfiltered samples) of iron, nitrate, sulfate and sulfide can provide additional
information on the conditions that may affect bioaugmentation performance. Along with
geochemical parameters, measuring concentrations of both the parent contaminant and appli-
cable daughter products assists in verifying sufficient activity is coupled with the presence of
the appropriate microbes. Other chemical parameters, such as volatile fatty acids and total
organic carbon, are useful indicators of electron donor abundance and distribution, and also
may provide further indirect evidence of microbial biomass and activity.
Sampling using MBTs (and associated chemical parameters) should be conducted at a
sufficient number of locations such that conditions are understood throughout the treatment
zone. Sampling should confirm that favorable conditions exist throughout the targeted treat-
ment zone, and that appropriate distribution and abundance of the necessary microorganisms
and other amendments, as appropriate, has been achieved, and is maintained until treatment
objectives are met. If inappropriate conditions and/or insufficient concentrations of micro-
organisms exist, corrective actions should be taken. These may include injection of additional
microbes, electron donor or acceptor, or redistribution using hydraulic controls (e.g., ground-
water recirculation systems).
As an example of a comprehensive site strategy for assessing and interpreting MBTs,
consider a TCE-contaminated site bioaugmented with a
Dhc-
containing consortium. The site-
wide monitoring approach should confirm the following:
General anaerobic conditions within the targeted bioaugmentation distribution area.
An increase in the concentration of
Dhc
(as determined through qPCR) after injection.
A steady or increasing concentration of
Dhc
genes, along with a concomitant decrease
in TCE concentrations and rise in daughter product and ethene concentrations during
subsequent temporal sampling.
A transient increase (and subsequent decrease) of DCE and VC concentrations likely
will be observed (depending upon sampling frequency and the level of microbial
activity), further confirming the effectiveness of the bioaugmentation remedial
approach.
The
Dhc
cell titers should remain elevated until TCE (and daughter product) concen-
trations fall below cleanup levels. If
Dhc
concentrations begin decreasing, or if
anaerobic conditions begin to deteriorate (i.e., become more aerobic), then additional
amendments (e.g., electron donor) may be required.
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