Biomedical Engineering Reference
In-Depth Information
Chemical and biosurfactants were intercalated with layered double hydroxides
(LDHs) to remove organic pollutants from water (Chuang et al., 2010). A concen-
tration of 1000 mg/L of rhamnolipid intercalated in a 2:1 ratio with uncalcined
LDH (K
d
of 2160 mg/kg) was more effective than the chemical surfactant (K
d
of
1770 mg/kg) for naphthalene sorption and is nontoxic.
Chlorinated Hydrocarbons
A soya lecithin biosurfactant followed by a second step of photocatalytic treatment of
the effluents was evaluated for the remediation of a PCB-contaminated site (Occulti
et al., 2007). Compared to Triton X-100, the lecithin removed less soil organic con-
tent, was of lower ecotoxicity, and was more effective in removing PCBs. Although
both surfactants decreased the efficiency of the photocatalytic treatment for PCBs,
lecithin performed better. In a later study, Occulti et al. (2008) further tested a soya
lecithin biosurfactant-based washing for a PCB-contaminated soil. Photocatalytic
treatment of the leachate followed the washing process. They postulated that the sys-
tem was a sustainable remediation as it was an integrated chemical, microbiological,
and ecotoxicological monitoring procedure. Scale-up and field application, however,
would be required as a future step.
Hexachlorobenzene (HCB)-contaminated soil can be treated by surfactant wash-
ing. However, to recover the surfactant for reuse, methods are needed. Granular acti-
vated carbon was evaluated by Wan et al. (2011) to recover the contaminant from
the rhamnolipid solution after washing spiked kaolin or an actual contaminated soil
to enable reuse of the surfactant. With 10 g/L of powdered activated carbon (PAC),
99% of the HCB could be removed. In addition, it was found that if the surfactant
solution (25 g/L of rhamnolipid) was combined with the PAC (10 g/L) as a washing
solution, two cycles could remove more than 86%-88% of the PAC from the soil.
Therefore, this coupling was very effective.
Clifford et al. (2007) evaluated the removal of perchloroethylene (PCE) by a
rhamnolipid biosurfactant. The PCE-biosurfactant solution IFT was 10 mN/m,
which is quite high, indicating that mobilization is not likely. This is beneficial as
it minimizes vertical mobilization. However, partitioning of PCE did occur with a
WSR of 1.2 g of PCE/g of rhamnolipid (mainly by the monorhamnolipid). Thus, this
biosurfactant is a good candidate for surfactant-enhanced recovery of PCE. Albino
and Nambi (2009) evaluated solubilization of PCE and TCE by surfactin and rham-
nolipid. WSR of 3.83 and 12.5 for these compounds, respectively, were found for
surfactin and 2.06 and 8.36 for rhamnolipid (mainly a dirhamnolipid), respectively.
Both were superior to synthetic surfactants (SDS, Tween 80, and Triton X-100) but
surfactin was superior to rhamnolipid. Solubilities of TCE increased from pH 7 to 5,
but the rhamnolipid and surfactin started to precipitate at the lower pH.
Heavy Metals
The anionic nature and the complexation ability of rhamnolipids enable them to
remove metals from soil and ions such as cadmium, copper, lanthanum, lead, and
zinc (Herman et al., 1995; Ochoa-Loza, 1998; Tan et al., 1994). The nature and
mechanism of the biosurfactant-metal complexes are being studied. Ochoa-Loza
et al. (2001) determined stability constants by an ion-exchange resin technique.
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