Biomedical Engineering Reference
In-Depth Information
had levels of copper, zinc, and cadmium of 550, 1200, and 2000 mg/kg, respectively.
Water alone removed minimal amounts of copper and zinc (less than 1%). A series of
five washings of the soil with 0.25% surfactin (1% NaOH) were required to remove
70% of the copper and 22% of the zinc. To determine the mechanism of metal removal
by surfactin, the techniques of ultrafiltration, octanol-water partitioning and the mea-
surement of zeta potential were used. Surfactin could remove the metals by sorption at
the soil interface and metal complexation, followed by desorption of the metal through
lowering of soil-water IFT and fluid forces, and finally complexation of the metal with
the micelles (Figure 10.6).
The ability to produce lipopeptide biosurfactants by a
Bacillus
strain in situ in an
oil reservoir was evaluated by Youssef et al. (2007). The amount of 90 mg/L was pro-
duced and is sufficient to mobilize entrapped oil in sandstone cores. Microorganisms
were injected into the wells and showed enhanced oil recovery through in situ bio-
surfactant production. Limitation of nitrogen was necessary. Costs could be in the
range of $10 per m
3
. The rates of biosurfactant production were more than required.
This is a clear indication of the feasibility of field tests, which can have implications
for remediation of contaminated sites.
Remediation of Heavy-Metal-Contaminated Water by Surfactin
Using MEUF, Mulligan et al. (1999b) studied the removal of various concentrations
of metals from water by various concentrations of surfactin by a 50,000 Da molecu-
lar weight cutoff ultrafiltration membrane. Cadmium and zinc rejection ratios were
close to 100% at pH values of 8.3 and 11, while copper rejection ratios were 85% at
pH 6.7. The addition of 0.4% oil as a cocontaminant decreased slightly the retention
of the metals by the membrane. The ultrafiltration membranes also indicated that
metals were associated with the surfactin micelles as the metals remained in the
retentate as shown in Figure 10.6. The ratio of metals to the surfactin was deter-
mined to be 1.2:1, which was only slightly higher than the theoretical value of 1 mol
metal:1 mol surfactin due to the two charges on the surfactin molecule.
Ultrafiltration
membrane
Benzene
molecule
Rhamnolipid
monomer
Membrane pore
Clean water
(permeate)
Copper ion
Micelle containing
solubilized benzene
molecules and attracted
copper ions
Flow direction
FIGURE 10.6
Simultaneous removal of Cu (II) ions and benzene molecules from aque-
ous solutions utilizing micellar-enhanced ultrafiltration. (Adapted from Ridha, Z.A.M. and
Mulligan, C.N., Simultaneous removal of benzene and copper from contaminated water using
micellar-enhanced ultrafiltration,
CSCE General Conference
, Ottawa, Ontario, Canada, June
14 -17, 2011.)
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