Environmental Engineering Reference
In-Depth Information
transported and stored in intermediate-bulk containers (IBC), made of
high-density polyethylene (HDPE) with a volume of 1000 L. Carbon dioxide
gas was initially used to maintain an anoxic atmosphere during the trans-
port, and was later replaced with nitrogen gas (the pH did not change using
carbon dioxide). Columns, the sampling equipment, gases, and 2000 L of
groundwater from the contaminated site in the Ruhr area were placed in
a climatized research container on the campus and held at 12°C. An oxy-
gen-free atmosphere (at excess pressure in the tank) was maintained using
nitrogen gas. Hence, the headspace in the tank was always flushed with
nitrogen gas to achieve an anaerobic atmosphere. With the aid of a peristal-
tic pump, a flow rate of 200 μL/min was maintained for both columns for a
period of 98 days.
In addition to the contaminated groundwater, a nutrient mixture (ammo-
nium and phosphate as N and P sources) was used in the first column (biotic
column), and a sodium azide solution was used in the second column (abi-
otic column) to prevent microbial activity. The efficiency of this method was
checked for incubated samples using effluent water from both columns and
in contrast to the “biotic-column,” no colonies were found in the effluent
water from the “abiotic-column.” Weekly samples were taken at seven dif-
ferent ports (port 7 represented 80% of the activated-carbon mass in the col-
umn) and from the influent flow. The influent concentrations were found to
be stable, for instance a loss <10% within 100 days was found for carbazole,
whereas for the highly adsorbing compound fluoranthene, a loss of about
40% was found over the same time period.
11.2.5 Contaminated Sites and Investigated Reactive Barriers
Two PRBs in Germany (Karlsruhe) and in Austria (Brunn am Gebirge, near
Vienna) were investigated using detailed sampling campaigns. In addition
to wells located in the inflow areas of both PRBs, influent and effluent areas
of the reactors located in the gates of both PRBs were sampled. Samples ana-
lyzed for anions were transported without a stabilizer; samples analyzed for
cations were stabilized with nitric acid; and samples analyzed for cyanide
were stabilized with sodium hydroxide. In some cases, total organic carbon
(TOC) was determined and such samples were stabilized with phosphoric
acid. Field campaigns commenced in summer 2006 and individual samples
analyzed for organic compounds were transported in 2.5 L amber-glass bot-
tles. For GC analysis, samples were stabilized by sodium azide. All bottles
containing the samples were transported in ice-cooled transport boxes.
Operating parameters of both PRBs are summarized in Table 11.1. More
information on the PRB in Karlsruhe (Germany) can be found in References
27 and 28, and additional information on the PRB in Brunn am Gebirge
(Austria) can be found in Reference 29. Four sampling campaigns were
organized (the dates are presented in Table 11.2), and samples were taken as
described above.
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