Environmental Engineering Reference
In-Depth Information
Figure 7.17 Emulsification of PAH-contaminated soil from microcosms. Left, untreat-
ed soil. Center, soil amended with bulking agent and dried-blood fertilizer. Right,
soil amended with bulking agent, dried-blood fertilizer, and P. aeruginosa strain 64
on the vermiculite carrier.
microcosms that received P. aeruginosa strain 64, which could be the result
of pyocyanin pigment production. Production of pyocyanin is coordinately
regulated with rhamnolipid (biosurfactant) production in P. aeruginosa .
When soil from the amendments inoculated with P. aeruginosa strain 64 was
suspended in saline, fines remained suspended in the tubes for hours to days
compared to controls (no amendments), where the soil settled immediately
(Figure 7.17). Suspensions of soil amended with bulking agent and fertilizer
settled in less than an hour. The data suggests that although P. aeruginosa
strain 64 did produce biosurfactant in situ , the concentration of the rhamno-
lipid did not reach or exceed the CMC of this biosurfactant. Therefore, the
increased PAH biodegradation may not be due solely to the presence of
biosurfactant micelles in the soil aqueous phase. It is possible that in micron-
iches, the concentration of rhamnolipid did achieve sufficient concentration
to mobilize sorbed PAHs into the aqueous phase via micelle formation.
There are other postulated mechanisms not dependent on micelle for-
mation by which in situ biosurfactant production by P. aeruginosa strain 64
might increase the bioavailability of PAHs sorbed to soil particles. For exam-
ple, rhamnolipid may form or integrate into an organic matrix sorbed onto
soil particles. This matrix could either assist in the association of bacteria
with soil-sorbed PAHs or partially desorb the PAHs from the particles,
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