Biomedical Engineering Reference
In-Depth Information
has a high
Dhc
concentration relative to non-
Dhc
organisms. Finally, DWT measurements
eliminate variability in qPCR results that can occur when the culture is diluted several orders of
magnitude to have the
Dhc
concentration range suitable for qPCR analysis. Results of typical
PCE and
cis
-DCE bottle assays used for evaluating specific activity are shown in Figure
3.9
.
The timing of specific activity measurements is an important consideration for QA/QC
assessment. These measurements can be made before harvesting culture, before or after
packaging, or after they arrive at a site for injection. Prior experience has shown that removing
a small quantity of the packaged culture prior to shipping provides an adequate assessment of
the specific activity of cultures delivered by overnight courier. However, if the cultures are
shipped by other methods that require several days of transport, or if they are stored at a site
for a few or several days prior to injection, it may be prudent to collect samples for specific
activity measurements just prior to injection.
3.4.4 Other QA/QC Considerations
An often overlooked aspect of QA/QC is the presence of potential groundwater pollutants
in injected cultures. As shown in Figure
3.2a
and
b
, the finished fermentation broth can contain
relatively high concentrations of VFAs that can be injected with the bacterial culture. Although
these components likely will not affect water quality in an aquifer, especially an aquifer
undergoing biological treatment facilitated by electron donor injection, injection of this mate-
rial may violate groundwater injection regulations. As such, QA/QC monitoring of culture
broth composition may be prudent for addressing such concerns or to allow full disclosure of
the solution characteristics for injection permit applications. More importantly, some bacterial
growth broths may contain residual levels of chlorinated solvents or daughter products such as
cis
-DCE and VC, the injection of which would certainly violate groundwater injection regula-
tions. This is of particular concern if PCE or TCE are added to shipping containers to maintain
activity during shipment. Again, careful analysis for these compounds prior to culture injection
may be warranted. Concentrating cultures (Section
3.5.1
) can reduce the amount of fermenta-
tion byproducts remaining in the culture and allow for overnight shipment of large culture
volumes, thereby minimizing some of the above concerns.
3.5 CONCENTRATINGANDSTORINGINOCULA
The use of relatively large volumes of bioaugmentation cultures presents several challenges
for culture producers and users. For example, the timing of bioaugmentation injection events
is usually controlled by other field activities including weather events and the availability of field
staff or drilling equipment. As a result, culture injection schedules can be uncertain and delays
are commonplace, and culture producers often must unexpectedly extend culture preparation
activities or delay culture shipments. Such delays can disrupt scheduling of upcoming deliveries
or force producers to keep a culture in the reactor beyond its optimal growth and activity period.
Likewise, production of large
Dhc
cultures requires considerable time (Figure
3.1
) and shipping
delays can reduce the amount of time available to produce consistent cultures, especially for
short-lead orders. In addition, injection of large culture volumes may take several days in
the field depending on the injection method and site conditions. As a result of these challenges,
the ability to store cultures, or at least understand the stability of stored cultures, becomes an
important consideration.
Another significant cost consideration for use of large culture volumes is transportation to
the treatment location. Ground-based shipping of cultures to distant areas can require several
days and often refrigeration is necessary to maintain the stability of large cultures. Similarly,
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