Environmental Engineering Reference
In-Depth Information
surfactant monomers plus the amount associated with surfactant micelles,
which can be expressed as (Pennell et al., 2001; Sun et al., 1995)
*
C
C
o
=+
1
CK CK
+
(6.3)
s mn
,
mn
s mc
,
mw
o
where
C
o
*
is the apparent solubility of organic species in the aqueous sur-
factant solution,
C
o
is the solubility of organic species in water (micelle-free),
C
s,mn
is the concentration of surfactant monomers,
C
s,mc
is the concentration
of surfactant micelles,
K
mn
is the organic species distribution coefficient
between surfactant monomers and water, and
K
mw
is the organic species
distribution coefficient between the micelles and water. This approach can
be extended to include the effect of the sorbed-phase surfactant on the
distribution of solute between the solid and aqueous phases:
(
)
KCK
CK CK
1
+
D
s
/
om
s
/
om
*
K
=
(6.4)
(
)
D
1
+
+
o mn
,
mn
o mc
,
mw
where
K
D
*
is the apparent soil-water distribution coefficient for the organic
species,
K
D
is the soil-water distribution coefficient in the absence of surfac-
tant,
C
s/om
is the concentration of sorbed surfactant per unit mass of native
soil organic matter,
K
s/om
is the solute distribution coefficient between
sorbed-phase surfactant and the native organic matter (
K
s
/K
om
), and
K
s
is the
solute distribution coefficient between the sorbed-phase surfactant and
water.
Equation 6.4 was incorporated into a macro-based spreadsheet to predict
the apparent distribution coefficient (
K
D
*
) as a function of surfactant concen-
tration. Based on data obtained in laboratory experiments, the sensitivity of
K
D
*
to different values of
K
s/om
was investigated over a surfactant concentra-
tion range of 0 to 800 mg/l. An example of the effect of differences in the
K
s/om
value on the overall partitioning of PCB between the solid and liquid
phases is given in Figure 6.23. Note that once the CMC of the surfactant was
exceeded, the effect of surfactant sorption became minimal; that is,
K
D
*
decreases dramatically and approaches zero as the surfactant concentration
is further increased. However, at low concentrations, partitioning of PCB
congeners into the sorbed-phase surfactant may have a substantial impact
on the distribution of PCBs within the system. The mathematical model was
further adapted to account for rate-limited sorption and desorption of both
the surfactant and the PCB congener(s) of interest.
6.4.6 PCB transformation experiments
Microbial growth experiments confirmed the ability of biphenyl-degrading
microorganisms to achieve substantial growth in solutions of Tween 80 and
