RESEARCH NEEDS FOR BIOAUGMENTATION - Bioaugmentation for Groundwater Remediation - page 344

These techniques also have contributed significantly to site characterization and modeling
efforts. With the discovery of new microbes and new genes, these tools will increase in scope
and usefulness.
Certainly the ability to monitor genes and their products will continue to improve. The ever-
growing genomic database allows the design of highly specific primers for functional genes
with unprecedented specificity. It is already possible to rapidly assay the abundance of
hundreds or thousands of genes in a sample, but what is less clear is how to integrate that
information in a highly efficient and useful way into existing site models.
In many instances, the monitoring tools are not the bottleneck for better bioaugmentation
performance, but rather it is the paucity of measurements and the extreme degree of extrapo-
lation that is the problem. A few discrete measurements cannot be extrapolated reliably to a
whole site. Therefore, the driving force for optimizing or designing monitoring tools has to be
cost and ease of use, or there never will be sufficient measurements taken to adequately
represent a site.

12.4.2 Production, Storage and Shipping

Each individual bioaugmentation culture will require optimization of production on a
large scale. For example, the commercial culture KB-1 # is grown in 100-liter (L) anaerobic
tanks under specific headspace-to-liquid volume ratios at pH 7. While KB-1 # is relatively
robust to different conditions, many cultures will require more specific optimization steps in
order to grow adequate volumes of high cell density cultures for bioaugmentation applications.
Likewise, the conditions used for storage and shipping of an inoculum will be culture-
dependent, with nutrient requirements, rate of gas generation (and thus pressure buildup in
transport containers), oxygen tolerance and community stability as factors that need to be
considered.

12.4.3 Delivery and Mixing

Microbial introduction into the subsurface can proceed via direct injection of free-living
bacteria or by introduction of encapsulated bacteria, with or without amendment supplementa-
tion. Direct injection is most commonly used currently, and is generally effective for introdu-
cing an inoculum into the environment. However, dispersal of the inoculum and subsequent
spread of the dechlorination ability within the subsurface can be inefficient depending on the
subsurface composition and groundwater flow.
For encapsulation methods, a variety of different compounds can be used as the carrier
material, including alginate and gellan gum. Encapsulation can serve a protective role as well as
control the availability of the contaminant to bacteria. For microbeads, the size of the capsules
can influence the degree of exposure and can be modified according to pore size considerations
for different environments. In some cases, electron donors may be included as part of the
encapsulation construct. Incorporating the donor can have beneficial influences on the degra-
dative activity, although it may be detrimental in environments with multiple non-target

electron acceptors.

12.4.4 Electron Donor Choice

As mentioned above, the choice of electron donor for a system can have significant impact
on the bacterial community that flourishes and hence the dechlorination processes and sub-
strates that are seen. A more restrictive electron donor (e.g., hydrogen in the case of KB-1 # )