Environmental Engineering Reference
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following inoculation with pyrene-degrading Pseudomonas species, but the
use of the surfactant Witconol SN-70 inhibited the introduced organism. The
introduction of Mycobacterium strain PYR-1, a pyrene degrader, enhanced
the removal of pyrene from contaminated soil. Erikson et al. (2000) had some
success in the degradation of PAHs following inoculation with a mixed
culture enriched for PAH degradation capability. They attributed some of
the effect to the possible production of biosurfactants by the inoculum.
Interestingly, they found that certain degradation products, specifically
4-hydroxy-9H-fluorenone, increased substantially during the biological
treatment. This metabolite could be a degradation product of fluorene or
fluoranthene. Kastner et al. (1998) showed that inoculation with a fluoran-
thene-degrading Sphingomonas strain and a pyrene-degrading Gordona strain
resulted in no enhanced degradation of these PAHs, but the strains survived
well in the contaminated soil. Weir et al. (1995) showed similar results
with inoculation of a phenanthrene-degrading Pseudomonas strain that was
encapsulated.
To treat hydrocarbon contamination, it is often fruitless to compete with
the degradative capabilities of the indigenous microbial communities, espe-
cially where mixing, oxygenation, and nitrogen supply have been optimized.
Large biomasses are required, and although initial degradation rates may
be enhanced, the time-saving effect may not balance the cost of adding the
organisms. In addition, a rapid die-off of introduced organisms invariably
occurs in the field; therefore, one should not expect to impact degradation
processes for weeks after treatment initiation. Reinoculation is possible, but
the cost-benefit ratio is likely to be unreasonable. Bioaugmentation works
best if nature is supplemented as an event, rather than trying to replace
nature with a long-term management approach. That is, it is best to use
bioaugmentation as a boost to something that nature is slow to generate or
unable to produce consistently.
Our goals for bioaugmentation in the land-farming treatment of
PAH-contaminated soils were to:
Use an inoculation process that is designed to supplement and ac-
celerate the activities of natural microbial communities rather than
replace or ignore them
Increase the metabolic capability to promote cometabolism of HMW
PAHs
Enhance bioavailability using biosurfactants introduced via bioaug-
mentation
Use vermiculite as an inexpensive carrier for the microorganisms
added to the soil
7.3.5.4 Carrier technology development
Producing large quantities of biosurfactant to apply during a bioremediation
process is currently cost prohibitive (Lang and Wullbrandt, 1999) and logis-
tically complex. Alternatively, it is possible to add a microbe that produces
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