Environmental Engineering Reference
In-Depth Information
negative with very low oxygen concentrations (c(O
2
) < 0.5 mg/L), neutral
pH values in the range of pH = 7, conductivities between 1 and 3 mS/cm,
and temperatures of 12-15°C are typical values for the on-site parameters
of the three sites investigated. Nitrate concentrations are typically low and
sulfate concentrations are high in Lünen. High concentrations of chloride
are typically present in Brunn. Cyanide concentrations (analyzed as the
sum of bound cyanide and free cyanide) were analyzed in Lünen and
found without exception to be below detection limits. Concentrations of
cyanide in Lünen with 660 μg/L are approximately a factor of 3 higher
compared to the site in Karlsruhe and a factor of 10 higher compared to
the site in Brunn.
Typical Fe and manganese concentrations were found to be in the range
of 0.5-4 mg/L. However, severe problems with respect to clogging were not
reported for both PRBs in Karlsruhe and Brunn.
The maximum concentrations found at the three sites investigated are pre-
sented in Table 11.7, based on more than 20 samples from different wells.
Compounds summarized in Table 11.7 represent the spectrum of all com-
pounds analyzed. The maximum concentrations were determined from dif-
ferent contaminated wells (wells 12Q, 22Q, and 23Q for site Lünen, well AB12
for site Karlsruhe and the influent at gate 2, and well B7 and B2006/31 for site
Brunn am Gebirge). However, it has to be noted that at least in one sample
from each site, concentrations for all compounds were found below detection
limits. In addition to some potential degradation products such as hydroxyl-
ated hydrocarbons, nitroaromatics were analyzed in field campaigns in 2007.
Concentrations of these compounds (often below detection limits) are also
presented in Table 11.7.
11.3.4.2 Reactive Barrier in Karlsruhe (Germany)
Although the total concentrations in one of the most contaminated zones
in Karlsruhe are in the range of 1800 μg/L, the influent concentrations at
the gates of the barrier are low (maximum values of ~50 μg/L). Moreover,
most of the mass (about 90%) at the gates results from the concentration of
acenaphthene. Heterocycles were present in the main contaminated region
(~16% of the total); however, they play no role at the gates, with concentra-
tions below 1 μg/L. Nevertheless, for all compounds, effluent concentra-
tions were found to be below detection limits and the efficiency of the PRB
was >98% after more than 8 years of operation. Using a mean flow of approx-
imately 1 L/s for one gate and a maximum total concentration of 50 μg/L, the
mass inflow was in the range of 1-2 kg/year. This was found to be valid for
one gate (and therefore one reactor) for approximately 12 tonnes of activated
carbon. Hence, the estimated mean load of activated carbon was ≪1% even
after a PRB operating time of 8 years. In contrast to organic compounds, the
retardation of cyanide was low and concentrations of cyanide in the influent
and effluent were found to be comparable.
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