Environmental Engineering Reference
In-Depth Information
aquifer gives
rate in
=
rate out (water
+
micelles)
+
accumulation (water
+
solids
+
micelles).
= Q ( [ A ]−[ A ] mic ) + ε V T d [ A ]
d t + ε V T d [ A ] mic
− ε ) V T ρ s d W A
0
+ ( 1
d t .
(6.221)
d t
Since [A] mic =[
Surf
]
K mic [A] and W A =
K sw [A] i ,wefind
Q
V T
,
d
[
]
d t =−
A
( 1
+[
Surf
]
K mic )
(6.222)
ε + ε[
Surf
]
K mic +
( 1
− ε
)
ρ s K sw
] tot -[CMC],
where [Surf] tot is the total added surfactant concentration and [CMC] is the critical
micellar concentration. Integrating, we obtain
[
]=[
where K mic is the micelle-water partition constant for i .
Surf
Surf
exp
Q
V T
t .
[
A
]
( 1
+[
Surf
]
K mic )
] 0 =
(6.223)
[
ε + ε[
]
K mic +
− ε
ρ b K sw
A
Surf
( 1
)
E XAMPLE 6.31 E XTRACTION OF NAPL R ESIDUAL USING A S URFACTANT
S OLUTION
For Example 6.30, determine the number of pore volumes required for 99% removal
of benzene if a 100 mM solution of sodium dodecyl sulfate (SDS) is used for flushing.
CMC of SDS is 8 mM.
From Chapter 4, log K mic = 1.02 log K ow 0.21 = ( 1.02 )( 2.13 ) 0.21 = 1.92.
[ Surf ]= 100 8 = 92 mM = 36 g/L. R F = 0.3 + ( 1.4 )( 1.6 ) + ( 0.3 )( 10 1.92 )( 0.036 )
= 3.4. Note that N PV = (Qt)/ ε V T . Hence, [ A ]
[ A ] 0 = exp
.
( 1 + [Surf] K mic ) ε N PV
R F
For [A]/[A] 0 = 0.01,
N PV = ( 4.605 )
R F
= 13.
ε ( 1
+ [Surf] K mic )
Hence N PV is reduced to 13 from 38 with pure water.
6.4.2.2
In Situ Soil Vapor Stripping in the Vadose Zone
In the vadose zone, applying vacuum using a pump can remove contaminant (Wilson
and Clarke, 1994). Figure 6.63 is a schematic of a soil vapor stripping well. Volatile
contaminants desorb into the pore air that is pulled out of the subsurface. The mecha-
nism of removal is similar to that for in situ water flushing in the saturated zone. Just
as in the case of the saturated zone, the vadose zone can be considered to be a CSTR
and the change in concentration in pore air is obtained from a mass balance between
 
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