Biomedical Engineering Reference
In-Depth Information
with 4% MEL (pH 5.6) provided low levels of removal (17% of the zinc and nickel
and 36% of the copper). From the sediment, the highest level of zinc (33%) and lead
removal (24%) were achieved with 30 g/L saponin (pH 5). Highest copper removal
(84%) was achieved with 2% rhamnolipids (pH 6.5). Sequential extraction showed
that the oxide fraction of zinc and organic fraction of copper were substantially
reduced by the biosurfactants.
Slizovskiy et al. (2011) compared several surfactants including rhamnolipid for
the removal of Zn, Cu, Pb, and Cd, and soil ecotoxicological reduction; 39%, 56%,
68%, and 43% of the respective metals were removed by the biosurfactant from an
aged-field-contaminated soil. Bioaccumulation of the metals by two worm species
(
Eisenia fetida
and
Lumbricus terrestris
) was reduced and biomass and survival
increased, indicating reduced soil toxicity.
Dahrazma and Mulligan (2007) subsequently evaluated the performance of
rhamnolipid, in a continuous flow configuration (CFC) for the removal of heavy
metals (copper, zinc, and nickel) from sediments to simulate a flow-through reme-
diation technique. Rhamnolipid solution was pumped at a constant rate through the
sediment within a column. The effect of rhamnolipid concentration, additives, time,
and flow rate was investigated. The heavy-metal removal was up to 37% of Cu, 13%
of Zn, and 27% of Ni when rhamnolipid was applied. The addition of 1% NaOH to
0.5% rhamnolipid enhanced the removal of copper by up to four times compared
with 0.5% rhamnolipid.
The size and morphology of rhamnolipid micelles were evaluated by Dahrazma
et al. (2008). The SANS technique was used to perform the investigation. At high
pH, large aggregates and micelles in the order of 17 Å were found. In acidic condi-
tions, however, larger 500-600 Å diameter vesicles were formed. Therefore, there
should not be any filtering effect in regard to soil flushing through pores that are
typically in the order of 200 nm. Larger molecules such as exopolymers could thus
cause plugging of the pores. Complexation of the micelles with metals did not have
any significant effect on the size of the micelles.
A new approach for metal stabilization by biosurfactants was discovered (Massara
et al., 2007). A study was conducted on the removal of Cr(III) by rhamnolipids from
chromium-contaminated kaolinite. Results showed that the rhamnolipids have the
capability to extract 25% of the more stable form of chromium, Cr(III), from the
kaolinite, under optimal conditions. The removal of hexavalent chromium by rham-
nolipids was also enhanced compared to the control by a factor of 2. The sequential
extraction procedure results showed that rhamnolipids remove Cr(III) mainly from
the carbonate, and oxide/hydroxide portions of the kaolinite. The rhamnolipids have
also the capability of reducing almost completely the extracted Cr(VI) to Cr(III) over
24 days. The rhamnolipids, thus, could be beneficial for the removal of and the long-
term conversion of Cr(VI) to Cr(III).
This work was continued to evaluate the use of rhamnolipid for the removal and
reduction of hexavalent chromium from contaminated soil and water in batch experi-
ments (Ara and Mulligan, 2008). The initial chromium concentration, rhamnolipid
concentration, pH, and temperature affected the reduction efficiency. Complete
reduction by rhamnolipid of initial Cr(VI) in water at optimum conditions (pH 6, 2%
rhamnolipid concentration, 25°C) occurred at low concentration (10 ppm). For higher
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