Environmental Engineering Reference
In-Depth Information
pH-dependent loads were calculated from the IAS-model for
c
0
= 10 mg/L
and concentrations were obtained from the dissociation curve, defined by
the pK
a
-value. The IAS-model [38] and algorithms are described in detail
in Reference 31 and a Java program was developed to calculate the mixture
loadings used in batch and column experiments. In addition, a fit routine
with the Marquardt algorithm was incorporated and used to fit isotherms
in mixtures (see below). The theoretical pH-dependent loads, included as a
dotted line in Figure 11.6, were found to be in satisfactory agreement with
the experimental results.
The shift of the pH-dependent load with respect to the corresponding frac-
tion of the neutral molecule in the solution (shown in Figure 11.6) is important
to assess the influence of pH on the adsorption for 2-methylquinoline (in partic-
ular), and of N-HETs (in general) on activated carbon in PRBs. Due to the shift
in both curves, a practically maximum load (of the neutral molecule) is found
at pH = 5. As a consequence, the maximum load of 2-methylquinoline should
be found even for pH-values down to 5. This should be true for all N-HETs
investigated due to the lower or comparable pK
a
-values compared to the pK
a
of
2-methylquinoline. Furthermore, phenols with pK
a
≫ 7 should be adsorbed in
the neutral form without any influence of the much more polar anions.
11.3.2.3 Adsorption Isotherms of Mixtures
The knowledge of adsorption processes of mixtures on the activated car-
bon is important in the remediation of aromatic compounds in a PRB. The
adsorption of a compound and therefore its load, is strongly influenced by
other compounds that may be present in the mixture. Multiadsorption pro-
cesses were investigated in batch experiments and are present in column
experiments performed with artificial mixtures and real groundwater. A
model was developed to fit the isotherms, and Freundlich parameters were
obtained, which were compared with corresponding parameters from both
the single-isotherm experiments and column runs.
11.3.2.3.1 Model to Fit Multiadsorption Processes
A maximum number of six compounds can be used in commercial models
(LDF [41] and AdDesignS [36]) to evaluate breakthrough curves in column
runs. Hence, to compare batch experiments with column runs, a mixture
consisting of phenol, benzene, toluene, 2-methylquinoline, benzofuran,
and benzothiophene was used on six different activated carbons: Epibon
Y12×40 and Hydraffin 30N (Donau Carbon), Norit ROW supra and Norit
1240 (Norit), and F200 and F400 (Chemviron). The composition was cho-
sen in such a way that two aromatic hydrocarbons, phenol as the prototype
of a phenolic compound, and three NSO-heterocycles were present in the
mixture. As a representative example, adsorption isotherms of the mixture
investigated using the activated carbon F200 (Chemviron) are shown in
Figure 11.7. The extreme nonlinear behavior for weak adsorbing compounds
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