Environmental Engineering Reference
In-Depth Information
performed in column and batch experiments using mixtures. The choice of
Epibon Y12×40 resulted from preliminary column tests conducted in an on-
site 6.1-m research container using groundwater at a contaminated site in
Germany (Zeche Viktoria, Lünen, well 12Q) early in the project and repeated
for comparison purposes throughout the project. However, from subsequent
comparisons in the laboratory, AC F400 (Chemviron) and not AC Epibon
Y12×40 was found to be the most efficient activated carbon with respect to the
adsorption parameters from isotherm experiments using artificial mixtures.
For the activated carbons investigated, the adsorption characteristics were
found to be comparable (at least within a factor of 2), and therefore Epibon
Y12×40 was considered to be representative of the activated carbons used in
the remediation of polycyclic aromatics and related compounds.
A detailed protocol was developed to investigate the adsorption isotherms
of single compounds and mixtures in an aqueous solution (deionized water,
buffered solutions, and real groundwater). A very brief overview is given
here. Activated carbons were washed, dried, sieved (63-125 μm), and stored
at 50% relative humidity. Batch experiments were performed in airtight
crimped headspace vials (22.4 or 116 mL, tempered before use at 400°C). A
mass of 50 μg-100 mg of AC was placed into a vial and filled up with the
corresponding solution (head space <1%). Freshly prepared solutions with
single compounds or mixtures of at least a factor of 2 below the solubility in
water were prepared in either deionized water or in buffer solution. Solutions
were checked before use with the suitable analytical method. In addition to
2-4 blank samples, 10-12 samples prepared for one-batch experiment were
shaken in a head-over-head shaker (Heidolph Reax 2) for 72 h at room tem-
perature (
T
= 20 ± 3°C). After being centrifuged 2 times (Heraeus Megafuge
1, 3300×g), the samples were analyzed without further enrichment by either
HPLC or headspace GC. Care had to be taken with respect to the storage of the
activated carbon. Water is adsorbed on activated carbon, quantified by water
isotherms using a differential scanning calorimetry with thermogravimetric
analysis (DSC/TGA) with an instrument from Mettler/Toledo. In addition,
volatile compounds such as benzene or toluene can be lost during sample
preparation. Furthermore, the efficient removal of activated carbon from the
aqueous solution is essential, especially for low-equilibrium concentrations.
Equilibrium concentrations
c
(in mg/L) were always obtained by HPLC or
headspace GC without any corrections. The loading
q
(in mg/g) was calcu-
lated from Equation 11.2:
V
m
(11.2)
q
=
(
cc
−
)
0
where
V
= volume in L
m
= mass-activated carbon in g
c
0
= start concentration in mg/L
Search WWH ::
Custom Search