Environmental Engineering Reference
In-Depth Information
In the sequel, we deal with a column experiment that was set up in order to
identify the DTPA degradation processes in porous media. The reported
column experiment was performed in a series of columns with an entire
flowpath length of 30 m. The set-up and the evaluation of the experiment
was already reported by (Holzbecher et al.
2005
). Inflow velocity and disper-
sion coefficient were obtained from the evaluation of a tracer experiment.
Mean interstitial velocity and longitudinal velocity for the entire duration of
the experiment are
v ¼
a
L
¼
0.86 m/d and
0.06 m. Advection dominates
within the system.
Concentrations were measured at several locations along the flowpath.
Figure
7.2
depicts the measured
breakthrough curves
for Gd concentration at
four selected positions, 0.22 m, 10 m, 20 m and 30 m from the inlet to the first
column. After an initial time period with initial zero concentrations,
c
increases fast when the front approaches. Clearly, the length of the initial
time depends on the position of the observation point. Following the sharp
increase, finally a level is reached which is constant over time. The concen-
tration level of that steady period depends on the position along the flowpath.
Minor fluctuations are due to difficulties maintaining a constant concentration
at the inlet. In Fig.
7.2
on the first breakthrough curve a rectangle indicates the
time period with steady concentration.
The constant concentration levels in dependence of travel distance are
depicted as dots in Fig.
7.3
. The figure also shows two curves obtained by two
different modeling approaches. If the approach (
7.12
) is assumed to be valid,
according to the presented derivation, one has to solve (
7.21
).
For
n ¼
2, one has the alternative to solve the implicit formula (
7.23
),
which is implemented by using the MATLAB
fzero
command. The com-
®
plete M-file sequence is:
(continued)
