Biomedical Engineering Reference
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Another study on diesel was performed by Whang et al. (2008) to evaluate two
biosurfactants, rhamnolipid and surfactin. A quantity of 80 mg/L of rhamnolipid
showed a greater than twofold enhancement. Enhancement of diesel-contaminated
soil remediation was also shown. Surfactin (40 mg/L) was able to enhance biomass
production and diesel biodegradation by more than two times compared to the
control. Due to its antibiotic characteristics, higher surfactin concentrations (up to
400 mg/L) showed substantial growth and biodegradation inhibition.
As oil spills can pose significant threats and damage to the marine and coastal
ecosystems, the objective of the study by Vasefy and Mulligan (2008) was to evalu-
ate the effectiveness of a rhamnolipid biosurfactant (JBR 425™) in combination
with two commercial biological products, ASAP™ and Degreaser™ on the biodeg-
radation of weathered light crude oil, heavy crude oil, and diesel fuel spilled on
saline water. The two products were used as supplementary additives to enhance
the biodegradation rate as they contain bacterial consortia and nutrients. Chemical
and microbiological analyses were performed. At 20°C and 35 g/L salinity, a rham-
nolipid solution: oil ratio (1:1, v/v) showed 65% removal of diesel fuel, 70% of light
crude oil, and 59% of heavy crude oil after 28 days of biodegradation. The biodegra-
dation was in the order of diesel fuel > light crude oil > heavy crude oil in terms of
removal percentage and microbial densities.
Mehdi and Giti (2008) evaluated 25 strains of bacteria isolated from the marine
environment and determined that
Pseudomonas
strain could reduce the quantity of
crude oil by 83%. A correlation was found between the emulsification ability, cell
adherence to hydrocarbon and growth rate in the crude oil.
Although there have been numerous evaluation tests regarding biosurfactants,
there have been few efforts to develop models. An attempt was thus made to simulate
biosurfactant enhanced bioremediation by Yu et al. (2012). A pilot scale model for
BTEX contamination was designed to verify the developed model which indicated a
high accuracy. However the mechanisms of desorption and enhanced biodegradation
are not clear. Further investigation at full scale is necessary.
Rhamnolipid (JBR 425) was evaluated for the ability to enhance bioremediation
of refinery oil sludge (Zhang et al., 2011). Optimal biodegradation occurred at a
100:50:10 of C:N:P ratio nutrient and 400 mg/kg of rhamnolipid addition. Up to
50.8% TPH reduction occurred by the strain
Luteibacter sp
.
Cameotra and Singh (2008) also evaluated the bioremediation of a soil contami-
nated with an oily sludge in field tests in India. They used a consortium of two
isolates of
P. aeruginosa
and a rhodococcal strain. When nutrients and a crude bio-
surfactant were added together with inocula, more than 98% of the hydrocarbons
could be removed compared to a negligible amount for the control without any addi-
tives or inoculum. The biosurfactant mixture consisted of 11 rhamnolipid congeners
and was produced by the consortium. It stimulated biodegradation and was able to
be used in crude form without expensive purification procedures.
Yan et al. (2011) investigated the washing of oil-based drill cuttings by a rham-
nolipid biosurfactant prior to biodegradation by a mixed culture. The cuttings are
wastes generated during petroleum exploration and production. The organic content
decreased by 83% from 85,000 mg/kg. A rhamnolipid concentration above 360 mg/L
was not beneficial. The polar fraction was removed the most (88.4%), followed by the
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