Geoscience Reference
In-Depth Information
Fig. 8.19 Solubility of
polycyclic aromatic
hydrocarbons (PAH)in
sodium dodecyl sulfate (SDS,
10 mg/L) and Suwannee
River natural organic matter
(NOM, 10 mg/L) solution.
C denotes increased solubility
in SDS and NOM solutions,
and C
0
is the solubility in
water (Cho et al.
2002
)
solution. Enhanced PCP dissolution into water from the NAPL was achieved at
aqueous Tergitol concentrations [200 mg/L. Surfactant addition of 1,200 mg/L
increased the aqueous PCP concentration by 14-fold at pH 5 and by twofold to
threefold at pH 7. This result is explained by the ionizable nature of PCP and the
effect of pH and ionic strength on equilibrium partitioning. The significant
response at the lower pH may be explained by the greater hydrophobicity of PCP
molecules at a low pH. To the ionizable nature of PCP and the effect of pH on the
equilibrium partitioning, one must also add the effect of ionic strength. These
results can be used to improve the use of surfactants for remediation of subsurface
sites contaminated by NAPLs.
A combined effect of natural organic matter (NOM) and surfactants on the
apparent solubility of polycyclic aromatic hydrocarbons (PAHs) is reported in the
paper of Cho et al. (
2002
). Kinetic studies were conducted to compare solubili-
zation of hydrophobic contaminants such as naphthalene, phenanthrene, and
pyrene into distilled water and aqueous solutions containing NOM and sodium
dodecyl sulfate (SDS) surfactant. The results obtained after 72-h equilibration are
reproduced in Fig.
8.19
. The apparent solubility of the three contaminants was
higher in SDS and NOM solutions than the solubility of these compounds in
distilled water. When a combined SDS-NOM aqueous solution was used, the
apparent solubility of naphthalene, phenanthrene, and pyrene was lower than in the
NOM aqueous solution.
Properties of surfactant and cosolvent additives affect the rate of apparent
solubilization of organic contaminants in aqueous solutions and may serve as a
tool in remediation of subsurface water polluted by NAPLs. Cosolvents (synthetic
or natural) are organic solutes present in sufficient quantities in the subsurface
water to render the aqueous phase more hydrophobic. Surfactants allow NAPLs to
partition into the micelle core, when present at levels above the critical micelle
concentration, causing an apparent solubility increase. An extensive discussion of
surfactant- and cosolvent-induced dissolution of NAPLs in porous media is given
