BIOAUGMENTATION FOR THE IN SITU AEROBIC COMETABOLISM OF CHLORINATED SOLVENTS - Bioaugmentation for Groundwater Remediation - page 223

8.4 BIOAUGMENTATION APPROACHES
In order to overcome some of the problems associated with the stimulation of indigenous
microorganisms for aerobic cometabolism, four bioaugmentation approaches have been tested:
Approach I. Bioaugmentation with strains selected for their biocatalytic transformation
ability and grown in aboveground bioreactors prior to injection
Approach II. Bioaugmentation with strains that express the desired oxygenase enzyme
constitutively while maintained on a benign and non-inhibiting growth substrate
Approach III. Bioaugmenation with strains that are more capable of cometabolizing the
contaminants when grown on an inducing growth substrate than the indigenous strains
Approach IV. Bioaugmentation with indigenous strains through injections of groundwater
from active areas into other areas of a site
These approaches range from the fairly complicated method in Approach I, where strains
are grown under very controlled conditions in aboveground reactors and are injected for their
biocatalytic potential, to the very simple method in Approach IV of adding microbes from one
aquifer or section of an aquifer to another to seed an indigenous strain. Approaches II and III
involve addition of selected strains that have specific advantages over the indigenous strains.
Approach II would permit adding non-inhibiting substrates, or would eliminate the need to add
toxic substrates such as phenol or toluene. Approach III involves adding strains that would be
effective for resistant CAHs such as 1,1,1-TCA and 1,1-DCE that cannot be treated effectively
by stimulating the indigenous microorganisms. Laboratory and field scale examples of each of
these approaches are presented in the following sections.
8.4.1 Bioaugmentation Approach I
Approach I tries to overcome the complexities of competitive inhibition and subsurface
environmental conditions by growing the microorganisms in surface bioreactors for their
biocatalytic potential. Cultures are selected for their high transformation capacity, ability to
remain active for long periods after injection, ease of growth to high cell densities on inexpen-
sive substrates, and for their specific transport properties. Transport properties may include
both good adhesion (to form a biobarrier) or poor adhesion (to permit cells to be transported
further after injection). In the following sections, the results of microcosm, column and field
studies of this approach are presented.
8.4.1.1 Bioaugmention with Methylosinus trichosporium OB3b
Duba et al. ( 1996 ) evaluated bioaugmentation with Methylosinus trichosporium OB3b, a
methanotrophic bacterium that expresses sMMO, in both column and field tests. For the field
test, a large number of bacteria were grown aboveground and then injected along a transect to
create an in situ biofilter at a TCE-contaminated site. They concluded that the performance of
the biofilter of resting cells depended on several factors, including the transformation capacity
of the cells (g CAH/g cell), longevity of the enzyme system to maintain the transformation
ability, and the attachment and detachment of bacteria to the biofilter matrix.
The bacterial strain was selected because it is naturally occurring and nonpathogenic, it had
high initial transformation rates of TCE and high resting cell transformation capacities of
~0.25 mg of TCE per mg dry weight of cells. The strain had adequate attachment/detachment
properties to create an in situ biofilter and could be grown effectively ex situ in bioreactors
to high cell densities. Laboratory studies also indicated that the cells maintained TCE