Biomedical Engineering Reference
In-Depth Information
to partially solubilize a North Dakota Beulah Zap lignite coal (Polman et al., 1994).
Metal-contaminated soils and sediments have been treated with crude sophorolipids
for the removal of heavy metals (Mulligan et al., 1999a, 2001b).
Oberbremer et al. (1990) added sophorolipids to a 10% soil and 1.35% hydro-
carbon mixture. With the sophorolipids, 90% of the hydrocarbons were degraded
in 79 h compared to 81% in 114 h without the biosurfactant. Schippers et al. (2000)
studied the effect of sophorolipids on phenanthrene biodegradation and determined
that the concentration of phenanthrene within 36 h decreased from 80 to 0.5 mg/L in
the presence of the 500 mg/L of surfactant, compared to 2.3 mg/L without surfactant
in a 10% soil suspension. The maximal degradation by
Sphingomonas yanoikuyae
was 1.3 mg/L-h with the sophorolipid compared to 0.8 mg/L-h without. The sopho-
rolipids seem to enhance the phenanthrene concentration as shown by fluorescence
measurements. In addition, toxicity of the sophorolipid was low for concentrations up
to 1 g/L. The CMC of the sophorolipid increased to 10 mg/L in the presence of 10%
soil suspensions from 4 mg/L in water, thus indicating adsorption of the surfactant
onto the soil. Solubilization tests showed that 232 mg of phenanthrene in water and
80.7 mg in soil were solubilized by 1 g of sophorolipids. This is 10-fold higher than
by other surfactants such as SDS. Therefore, these experiments have indicated that
the sophorolipids enhance biodegradation of the phenanthrene through enhanced
solubilization. More practical experience with more types of contaminants and more
understanding of the mechanisms will be required.
s
urfaCtin
Studies by Surfactin
Surfactin is another biosurfactant evaluated for environmental applications. Although
it is a very effective biosurfactant, fewer studies have been performed with this bio-
surfactant in comparison with rhamnolipids. A strain of
Bacillus subtilis
O9 was
isolated from contaminated sediments (Olivera et al., 2000). Surfactin was produced
from sucrose. A crude form of surfactin was added to ship bilge waste to determine
potential enhancement of biodegradation. Only 6.8% and 7.2% of the aliphatic and
aromatic compounds in a nonsterile environment remained after 10 days as they
were degraded more quickly in the presence of the biosurfactant. However, n-C17
pristane and n-C18 phytane degradation were not enhanced. More effective methods
of production of surfactin are required to improve process feasibility.
A strain of
B. subtilis
was able to produce biosurfactant at 45°C at high NaCl con-
centrations (4%) and a wide pH range (4.5-10.5) (Makkar and Cameotra, 1997a,b).
The biosurfactant was able to remove 62% of the oil in a sand pack saturated with
kerosene. This indicates it could be used for in situ oil removal and cleaning sludge
from sludge tanks.
Because of the presence of two negative charges, one on the aspartate and the other on
the glutamate residues of surfactin, the binding of the metals, magnesium, manganese,
calcium, barium, lithium, and rubidium, has been demonstrated (Thimon et al., 1992).
Batch soil-washing experiments used surfactin from
B. subtilis
for the removal of heavy
metals from a contaminated soil and sediments (Mulligan et al., 1999b). The sedi-
ments contained 110 mg/kg of copper and 3300 mg/kg of zinc. The contaminated soil
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