Environmental Engineering Reference
In-Depth Information
Hydrocarbon biodegradation by naturally occurring microbial popula-
tions is the primary mechanism for hydrocarbon contaminant removal from
the environment. The addition of biosurfactant stimulated indigenous bac-
teria to degrade hydrocarbons at higher rates than those achieved by nutrient
addition alone (Atlas, 1993). Contradictory results are found in the literature
concerning the effects of biosurfactants on PAH biodegradation (Banat, 1995;
Churchill et al., 1995; Deschenes et al., 1996; Finnerty, 1994; Guha et al., 1998;
Miller, 1995; Providenti et al., 1995; Rocha and Infante, 1997; Volkering et al.,
1998; Zhang and Miller, 1995). Many reports indicate that surfactants can
enhance hydrocarbon biodegradation by increasing microbial accessibility
to insoluble substrates (Zhang and Miller, 1994; Zhang et al., 1997). The
bioavailability of organic contaminants in soil decreases significantly during
aging (Hatzinger and Alexander, 1995); therefore, the effect of biosurfactants
on aged pollutants may be particularly significant and make them potentially
useful for bioremediation.
7.1.3.5.5.3 Solubilization of PAHs.
Rhamnolipid (monorhamno-
lipid and dirhamnolipid), lichenysin B, and Triton X-100 have CMCs of 40,
10, and 106 mg/l, respectively (Edwards et al., 1991; Lin et al., 1994; Zhang
and Miller, 1992). Mass solubility ratios (MSRs) for several PAHS are shown
in Table 7.6 for
P. aeruginosa
strain 64 biosurfactant (rhamnolipid) and Triton
X-100 (nonionic synthetic surfactant). The MSR of phenanthrene for
B. licheni-
formis
ATCC 39307 biosurfactant (lichenysen, a cyclic lipopeptide) is also
shown in Table 7.6. In general, the MSR declines with increasing molecular
weight of the PAH. Both rhamnolipid and lichenysin solubilized more
phenanthrene than Triton X-100. Rhamnolipid solubilized more pyrene and
fluoanthene than Triton X-100. The MSRs for benzo(a)pyrene and chrysene
could not be calculated for Triton X-100 because the solubilization of these
compounds was too low for detection even at the highest surfactant concen-
tration tested (30× CMC).
Table 7.6
Comparison of the Mass Solubility Ratios of Several PAHs in
Commercial Surfactants and Biosurfactants
Chemical Surfactant
Biosurfactant
Compound
Triton X-100
P. aeruginosa
strain 64 rhamnolipid
a
Phenanthrene
7.0 ×
10
-2
1.3 × 10
-1
Pyrene
7.5 × 10
-3
2.9 × 10
-2
Fluoranthene
6.5 × 10
-4
3.8 × 10
-3
Benzo(a)pyrene
N.D.
b
3.8 × 10
-3
Chrysene
N.D.
b
1.1 × 10
-3
a
Lichenysin, lipopeptide biosurfactant from
B. licheniformis
ATCC 39307, was tested only
with phenanthrene and the MSR was 1.1 × 10
-1
.
b
Too low for detection.
