Biomedical Engineering Reference
In-Depth Information
two strains, which will need further investigation. Also, although addition of the
rhamnolipid enhanced release of the phenanthrene, it did not necessarily enhance
biodegradation.
Rahman et al. (2002) showed that addition of rhamnolipid produced by
Pseudomonas sp
. DS10-129 along with poultry litter and coir pith enhanced ex situ
bioremediation of a gasoline-contaminated soil. Another strain,
P. marginalis
, pro-
duced biosurfactants that solubilized PAHs such as phenanthrene and enhanced
biodegradation (Burd and Ward, 1996). The addition of rhamnolipids led to attach-
ment to the phenanthrene that enhanced bioavailability and hence degradation by
P. aeruginosa
(Garcia-Junco et al., 2001).
Straube et al. (2003) evaluated the addition of
P. aeruginosa
strain 64, a biosur-
factant-producer with slow-release nitrogen and a bulking agent (ground rice hulls)
to enhance bioremediation of PAH (13,000 mg/kg) and pentachlorophenol (PCP)
(1,500 mg/kg) contaminated soil during landfarming. However, the added strain
does not degrade PAHs. This biostimulation/bioaugmentation approach led to an
87% decrease in total PAHs and a 67% decrease in total benzo(a)pyrene (BaP) toxic
equivalents compared to the control, 23% and 48% respectively, in microcosm stud-
ies. Larger-scale pan experiments showed decreases of 86% in the PAHs and 87% in
total BaP toxicity by biostimulation/bioaugmentation after 16 months compared to
a 12% decrease in PAHs for the control. Overall, the biosurfactants produced in the
soil by the bacterial strain 64 enabled PAH biodegradation.
Yin et al. (2008) evaluated the characteristics of a rhamnolipid biosurfactant pro-
duced by an isolate of
P. aeruginosa
from oil-contaminated wastewater. The surface
tension was 33.9 mN/m of the biosurfactant and the CMC was 50 mg/L. The solu-
bility of phenanthrene increased by 23 times in the presence of the biosurfactant.
The stability under a range of pH and salinities was good. Thus, it has potential
for bioremediation of crude oil. The weight solubilization ratio (WSR) and micelle-
phase/aqueous-phase partition coefficient (k
m
) were determined to be 0.2022 and
4.82 (log). These are much higher than the synthetic surfactants, Tween and Triton.
Electrokinetic treatment of contaminated soil is not very efficient for low
solubility organic contaminants. Chang et al. (2009) compared Triton X-100 with
rhamnolipid addition during electrokinetic treatment of phenanthrene-contaminated
soil. Rhamnolipid enhanced electroosmotic flow more than the synthetic flow.
Microbial growth may also be improved. Gonzini et al. (2010) evaluated the addition
of rhamnolipid to enhance the treatment process. Gazoil removal of 86% could be
achieved from a 20,000 ppm contaminated soil with addition of 2 g/kg of rhamno-
lipid. In addition, the condition of the soil after treatment was evaluated. The con-
tents of nitrogen, carbonates, organic matter, and salts did not decrease, and thus the
microbial activity of the soil should be maintained for future use.
Chlorinated Hydrocarbons
Halogenated aromatic compounds include pesticides, DDT, 2,4-D and 2,4,5-T,
plasticizers, pentachlorophenol, PCBs, among others. Their high stability and toxicity
are causes of great concern for the environment and public health. The position and
number of halogens are important in determining the rate and mechanism of biodeg-
radation. The mineralization of PCBs was followed after the addition of rhamnolipid
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