Environmental Engineering Reference
In-Depth Information
1.6
1.6
Freundlich model
Langmuir model
β
-param
eter
0.5
0.75
1
1.5
2
3
5
η
-param
eter
0.5
0.75
1
1.5
2
3
5
1.2
1.2
0.8
0.8
0.4
0.4
0
0
0
0.4
0.8
1.2
1.6
0
0.4
0.8
1.2
1.6
Dissolved concentration [M L
-3
]
Dissolved concentration [M L
-3
]
=
Fig. 18.13
Plots of the Freundlich adsorption isotherm given by Eq. (
18.40
), with
K
f
1and
β
defined in the caption (
left
), and the Langmuir adsorption isotherm given by Eq. (
18.41
), with
K
d
=
1and
η
defined in the caption (
right
)
physicochemical properties of the contaminant itself as well as such environmen-
tal variables as temperature and solar energy. Even though only a small fraction of
a pesticide may exist in the gas phase, air-phase diffusion rates can sometimes be
comparable to diffusion in the liquid phase since gaseous diffusion coefficients are
about 4 orders of magnitude greater than liquid phase diffusion coefficients.
The general transport equation given by Eq.
18.34
can be simplified considerably
when assuming linear equilibrium sorption and volatilization such that the adsorbed
(
s
) and gaseous (
g
) concentrations are linearly related to the solution concentration
(
c
) through the distribution coefficients
K
d
(Eq. (
18.38
)) and
K
H
, the latter appearing
in
g
=
K
H
c
(18.42)
where
K
H
is the dimensionless Henry constant [
].
Assuming linear partitioning, Eq. (
18.34
) for one-dimensional transport then has
the form
−
aD
g
K
H
∂
∂
(
ρ
b
K
d
+
θ
+
aK
H
)
c
∂
∂
D
h
∂
c
∂
∂
c
−
∂
(
qc
)
∂
=
θ
+
−
φ
(18.43)
∂
t
z
∂
z
z
∂
z
x
or
∂θ
Rc
∂
∂
∂
D
E
∂
c
−
∂
(
qc
)
∂
=
θ
−
φ
(18.44)
t
z
∂
z
x
where the retardation factor
R
[
−
] and the effective dispersion coefficient
D
E
[L
2
T
−
1
] are defined as follows
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