Biomedical Engineering Reference
In-Depth Information
By adding low concentrations of rhamnolipid (90 mg/L), the diameter of the particles
was reduced to less than 10 nm due to the coating and stabilization of nanoparticles by the
rhamnolipid. This was confirmed by zeta-potential measurements on the modified iron
nanoparticles. Furthermore, the effect of the presence of rhamnolipid on reductive reme-
diation of hexavalent chromium, Cr (VI), to trivalent, Cr (III), was investigated and evalu-
ated. By combining 0.034 g/L chromium (VI) with iron nanoparticles and rhamnolipi,
the only positive effect was observed with concentrations of 0.08 g/L iron and 2% (w/w)
of rhamnolipid. At this concentration, the remediation of chromium increased by 123%
in 15 h compared with solutions containing only iron nanoparticles or only rhamnolipid.
However, at lower rhamnolipid concentrations, the extent of remediation decreased.
Biosurfactants may also be beneficial for enhancing other remediation technol-
ogies. Zhu and Zhang (2008) investigated the enhanced uptake of pyrene in rye-
grass by rhamnolipids. Low rhamnolipid concentrations (25.8 mg/L or 0.5 × CMC)
seemed to enhance the uptake, possibly by enhancing permeability of the root cells.
The effect of tea saponin on
Zea mays
L. and
Saccharum officinarum
L. phytore-
mediation was studied (Xia et al., 2009). A tea saponin concentration of 0.2 × CMC
(0.01%) enhanced PCB and cadmium uptake from water and soil.
CONCLUSION AND FUTURE DIRECTIONS
Jeneil Biotech Corp (http://www.jeneilbiotech.com) has produced commercially bio-
surfactants such as rhamnolipids. Another company, AGAE Technologies, (http://
www.agaetech.com/) also produces rhamnolipids from a unique strain of the bac-
terium
P. aeruginosa
. Various applications including remediation are emphasized
such as in situ or ex situ soil remediation projects concerning hydrocarbons includ-
ing PAHs. Elimination of heavy metals and pesticides from soil are also available
applications. Remediation of industrial waste water from food processing, oil/gas
operations, and other industries are also possible with our rhamnolipid biosurfactant.
The economics of producing the biosurfactants has limited commercial applica-
tions. Costs can be reduced by improving yields, rates, and recovery, using crude prep-
arations and using cheap or waste substrates (Mulligan and Gibbs, 1993). Although
more information is available concerning biosynthesis of rhamnolipids and surfactin,
there is still a lack of information regarding the secretion of the biosurfactants, met-
abolic route, and primary cell metabolism (Peypoux et al., 1999). Research is thus
required to accelerate the knowledge in this area as it could possibly enhance the appli-
cations of the surfactant. New forms of the biosurfactants could also become available.
According to Technical Insights, a division of Frost & Sullivan, Nonionic
Surfactants, microbial surfactants have begun to enjoy a market (O'Connor, 2002).
The most promising applications are oil spill (Figure 10.7) and oil-contaminated
tanker cleanup, removal of crude oil from sludge, enhanced oil recovery (Figure 10.8),
bioremediation of sites contaminated with hydrocarbons, other organic pollutants,
and heavy metals. Contaminants such as PCB could also be bioremediated by
biosurfactant addition, since natural surfactants such as humic acids were able to
enhance the microbial degradation of PCBs (Fava, 2002). A summary of some of the
studies involving the use of biosurfactants for biodegradation is shown in Table 10.2
and for washing or flushing is shown in Table 10.3. It can be seen that most of the
Search WWH ::
Custom Search