Geoscience Reference
In-Depth Information
V
C
d
FIGURE 4.11
Sorption data and isotherm.
• Freundlich isotherm:
v
=
K
f
c
d
1/
n
(4.47)
•
BET isotherm:
v
=
(
v
m
B
c
d
)/[(
c
s
-
c
d
) (1
+
(
B
- 1) (
c
d
/
c
s
)]
(4.48)
where
v
=
concentration of pollutant on the solids, [mg g
−1
]
c
d
=
dissolved concentration [mg m
−3
]
maximum concentration attained [mg m
−3
]
b
,
B
,
c
s
,
K
f
, and
n
are coefficients used to calibrate the curves to the measured
data; the curve given in Figure 4.11 commonly occurs
v
m
=
The simplest equilibrium expression uses a linear adsorption isotherm
C
s
′
=
K
ps
⋅
C
w
′
(4.49)
where
C
s
′
=
concentration of sorbed chemicals on sediment in segment
C
w
′
=
concentration of dissolved chemical in water in segment
K
ps
=
partition coefficient of chemical on sediment in segment
At equilibrium, the distribution between the phases is controlled by the partition
coefficient
K
ps
, and the amount of solid phase present controls the total mass of
chemical in each phase. An overview of sorption equations used in WASP/TOXI
module follows.
78
Dissolved chemical in the water column and benthic segments interacts with
sediment particles and dissolved organic carbon to form five phases: dissolved,
DOC-sorbed, and sediment-sorbed (three sediment types “s”). The reactions can
be written with respect to a unit volume of water as:
MC Cn
s
′ + ′
/
(4.50)
w
s
BC Cn
w
′ + ′
/
(4.51)
B
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