Biomedical Engineering Reference
In-Depth Information
Desorption of phenanthrene from a marine sediment (Zhu et al., 2011) by a rham-
nolipid was found to be more effective than SDS. Sorption of the rhamnolipid was
also occurring as the CMC increased to 111.6 mg/L in the presence of the sediment.
Four different biosurfactants were compared for washing of a low level and a high
TPH-contaminated soil (Lai et al., 2009). The biosurfactants were more effective
than synthetic ones. Highest TPH removal was by rhamnolipids in the range of 23%
and 63% for the two soils, respectively. Surfactin was almost as effective and was
superior to serrawettin and a novel bioemulsifier.
Pei et al. (2009) studied the effect of biosurfactant on sorption of phenanthrene on
soil. Organic matter content was highly influential. Phenanthrene sorption decreased
in the presence of biosurfactant for the black loamy soil, whereas for the red sandy
soil, the biosurfactant increased sorption. The biosurfactant was shown to be very
biodegradable, indicating that multiple additions would be required.
Nguyen et al. (2008) compared mixtures of biological and synthetic surfactants.
A mixture of rhamnolipids and synthetic surfactants reduced the IFT, thus enabling
mobilization of the hydrocarbons. The hydrophobicity of the mixture was increased
to close to that of the hydrocarbon and reduced oil-solution IFT by a factor or two to
less than 0.1 mN/m compared to the individual surfactants. This means they could
be used for remediation purposes or enhanced oil recovery and could improve the
economic viability of the system.
The feasibility of removing styrene from contaminated soil by rhamnolipid was
evaluated by Guo and Mulligan (2006). More than 70% removal of styrene could
be achieved for an initial content in soil of 32,750 mg/kg after one day and 88.7%
removal after 5 days while a 90% removal was obtained for an initial 16,340 mg/kg
of styrene after 1 day. Longer contact times (5 days) enhanced removal efficiencies
(up to 90%). A weight solubilization ratio of 0.29 g styrene was solubilized per gram
of rhamnolipid added (R
2
= 0.9738). After removal from the soil, the leachate con-
taining styrene and rhamnolipid must be treated. It was determined that more than
70% of the styrene in the leachate could be biodegraded by an anaerobic biomass
(Guo and Mulligan, 2006).
Nguyen et al. (2008) mixed hydrophilic rhamnolipids with synthetic hydrophobic
biosurfactants to reduce IFT for environmental remediation applications. The IFT
values were reduced to less than 0.1 mN/m for all hydrocarbons, including tolu-
ene, hexane, decane, and hexadecane. For example, a ratio of biosurfactant to C12,
13-8PO sulfate of 4 to 1 (wt/wt basis) reduced IFT of toluene to 0.032 mN/m. More
hydrophobic biosurfactants will need to be investigated.
Further studies were performed by Guo et al. (2011) to determine the aggrega-
tion behavior of rhamnolipid mixed with styrene by small angle neutron scattering
(SANS). Styrene was used as a representative of hydrophobic molecules commonly
found in contaminated soils. Deuterated and hydrogenated styrene was used to
resolve the morphologies of aggregates. A structural transformation from cylindri-
cal micelles to a binary mixture of cylindrical micelles and vesicles was induced by
both elevated rhamnolipid and styrene concentrations. The resultant structure of the
aggregates, vesicle, is different from the “oil droplets” commonly reported in the
microemulsions of water-oil-surfactant mixtures. It was also determined that sty-
rene solubility may be constrained by various factors that are not known at this time.
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