Biomedical Engineering Reference
In-Depth Information
An evaluation was made of the capability of a rhamnolipid biosurfactant (JBR425)
foam for the treatment of PAH-contaminated freshwater sediments with elevated lev-
els of Pb, Zn, and Ni (Alavi and Mulligan, 2011). The biosurfactant foam was injected
in the sediment column. The pressure gradient was monitored during the flushing
tests to determine possible problems due to high pressure. Foam-quality rhamnolipid
was varied between 85% and 99% with stabilities from 15 to 43 min. PAH and metal
removal was then evaluated for sediment samples. Highest PAHs removal after 20
pore volumes obtained by a removal by biosurfactant foam (99% quality by a 0.5%
rhamnolipid solution) was 44.6% of pyrene, 30% of benz(a)anthracene, and 37.8%
of chrysene, while total removal efficiency (mobilization + volatilization) for the
biosurfactant foam was 56.4% of pyrene, 41.2% of benz(a)anthracene, and 45.9% of
chrysene. With biosurfactant liquid solution at the same pH as the aforementioned
foam (pH 6.8), maximum removal (mobilization) was 31.4% of pyrene, 20.5% of
benz(a)anthracene, and 27% of chrysene. No volatilization of PAHs was observed.
The control (deionized water) did not remove any PAHs. The highest removal of
metals was achieved with 0.5% rhamnolipid foam (99% quality, pH 10.0 was 53.3%
of Ni, 56.8% of Pb, and 55.2% of Zn). Removal levels were reduced to 11%-17% for
metals when a liquid 0.5% rhamnolipid solution was used instead of the foam or the
control. The rhamnolipid foam could be a nontoxic and effective method of reme-
diating PAH- and heavy-metal-contaminated soil/sediments. Further efforts will be
required to optimize the performance of the foam.
Remediation of Oil-Contaminated Water by Rhamnolipids
The Amoco Cadiz spill off the Britanny coast in 1978 and the Exxon Valdez spill
near Prince William Sound in 1989 are examples of significant coastline contam-
ination. Biosurfactants can be useful for oil spills since they could be less toxic
and more degradable than synthetic surfactants. Chakrabarty (1985) showed that
an emulsifier produced by
P. aeruginosa
SB30 could disperse oil into fine droplets,
which could enhance biodegradation. Chhatre et al. (1996) showed that four bacteria
isolated from crude oil were able to degrade 70% of the Gulf and Bombay High
Crude Oil. One of the isolates produced a rhamnolipid biosurfactant that enhanced
biodegradation by emulsification of the crude oil.
The feasibility of using biosurfactants for dispersing oil slicks was studied
(Holakoo and Mulligan, 2002). At 25°C and a salinity of 35‰, a solution of 2% rham-
nolipids applied at a dispersant-to-oil ratio (DOR) of 1:2, immediately dispersed 65%
of a crude oil. Applied at a DOR of 1:8, co-addition of 60% ethanol and 32% octanol
with 8% rhamnolipids improved dispersion to 82%. Dispersion efficiency decreased
in freshwater and at lower temperatures, but altering the formulation could improve
efficiencies. A comparison of the dispersion behavior to the control showed that the
rhamnolipids had excellent potential as nontoxic oil dispersing agents. Laboratory
toxicity tests of the biosurfactant showed that IC
50
values are low for marine flag-
ellates, microalgae, and the bioluminescence of
Photobacter phosphoreum
(Lang
and Wagner, 1987). Low concentrations of rhamnolipid (1 g/L) were able to con-
vert a mousse oil into an oil-in-water emulsion. De-emulsification was performed
to remove the oil. Subsequent rhamnolipid-assisted bioremediation of the remaining
aqueous phase decreased the oil to undetectable levels (Nakata and Ishigami, 1999).
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