Enhancement of Remediation Technologies with Biosurfactants - Biosurfactants: Research Trends and Applications - page 245

Following the USEPA's biological effectiveness test methods, and gas chromato-
graphic (GC) analysis, 21 day experiments were conducted. Biological agents with
the addition of the rhamnolipid enhanced significantly the remediation for PCE
removal. PCE removal occurred in the following order for the various agents: bio-
logical agent + rhamnolipid > biological agent > rhamnolipid > control. Microbial
analysis showed a direct correlation between microbial density and PCE removal,
indicating that PCE removal occurred through biodegradation.
Ex Situ Washing Studies by Rhamnolipids
Hydrocarbons Besides studies on biodegradation, rhamnolipid surfactants have
been tested to enhance the release of low solubility compounds from soil and other
solids. They have been found to release three times as much oil as water alone
from the beaches in Alaska after the Exxon Valdez tanker spill (Harvey et al.,
1990). Removal efficiency varied according to contact time and biosurfactant
concentration.
Scheibenbogen et al. (1994) found that the rhamnolipids from P. aeruginosa UG2
were able to effectively remove a hydrocarbon mixture from a sandy loam soil and
that the degree of removal (from 23% to 59%) was dependent on the type of hydro-
carbon removed and the concentration of the surfactant used. Van Dyke et al. (1993)
had previously found that the same strain could remove at a concentration of 5 g/L,
approximately 10% more hydrocarbons from a sandy loam soil than a silt loam soil
and that SDS was less effective than the biosurfactants in removing hydrocarbons.
Lafrance and Lapointe (1998) also showed that injection of low concentrations of
UG2 rhamnolipid (0.25%) enhanced transport of pyrene more than SDS with less
impact on the soil.
Bai et al. (1998) showed that after only two pore volumes, 60% of the hexadecane
was removed by a 500 mg/L concentration of rhamnolipid at pH 6 with 320 mM
sodium. Various biological surfactants were compared by Urum et al. (2003) for
their ability to wash a crude-oil-contaminated soil, including aescin, lecithin, rham-
nolipid, saponin, tannin, and SDS. The following conditions were evaluated: surfac-
tant concentration (0.004%, 0.02%, 0.1%, and 0.5%), surfactant volume (5, 10, 15, and
20 mL), temperature (5°C, 20°C, 35°C, and 50°C), shaker speed (80, 120, 160, and
200 strokes/min), and wash time (5, 10, 15, and 20 min). A temperature of 50°C
and 10 min were optimal for most of the surfactants. More than 79% of the oil was
removed by SDS, rhamnolipid, and saponin.
Rhamnolipid was also evaluated for the removal of oil for contaminated sandy
soil (Santa Anna et al., 2007). The removal of oil was monitored for 101 days and the
biosurfactant was shown to be effective. The composition of the aromatic and paraf-
finic oil did not change and could be recycled.
A completely different approach for oil cleanup was performed by Shulga et al.
(2000) who examined the use of the biosurfactants for oil removal from coastal
sand, and the feathers and furs of marine birds and animals. Pseudomonas PS-17
produces a biosurfactant and biopolymer that reduced the surface tension of water to
29.0 mN/m and the IFT against heptane to between 0.01 and 0.07 mN/m. The molec-
ular weight of the biopolymer is from 3 to 4 × 10 5 . The biosurfactant/biopolymer was
able to remove oil from marine birds and animals contaminated by oil.