Environmental Engineering Reference
In-Depth Information
(that penetrates the cutoff wall) to a ZVI reactor located downstream (Parbs
and Birke, 2005).
In PRBs, ZVI is used to degrade chlorinated volatile organic carbons (cVOCs)
such as chlorinated ethenes (perchloroethene, PCE, trichloroethene, TCE, cis-
dichloroethene, cis-DCE, and vinylchloride, VC) to chlorine-free degradation
products (i.e., in the case of PCE or TCE via DCE and VC to halogen-free
ethane, ethene, and/or ethine as the major degradation products). Besides
chlorinated hydrocarbons (CHCs), certain heavy metals, such as chromium
as chromate (Cr
VI
), or arsenic (arsenite or arsenate) and certain radioactive ele-
ments such as uranium can also be treated successfully with ZVI that reduces
these elements to a lower oxidation number/degree forming barely soluble
compounds, thus precipitating inside the ZVI bed. Full-scale PRBs are now
being used at former manufactured gas and coking plants in Europe (chiefly
in the United Kingdom and Germany) to effectively treat polycyclic aromatic
hydrocarbons (PAHs), hetero-(NSO)-PAHs, benzene, toluene, ethyl benzene
and xylenes (BTEXs), phenols, and related compounds: either GAC or microbi-
ological treatment or both of these approaches in a combined-treatment train
have successfully been applied to adsorb and/or degrade these pollutants so
far. Activated carbon is a very promising reagent for the adsorptive removal
of PAHs, NSO-PAHs, and other contaminants such as highly persistent CHC,
because PAHs as well as chlorinated aromatics (such as chlorobenzenes, chlo-
rophenols, and polychlorinated biphenyls, PCBs) cannot be degraded by ZVI
due to their relatively low reduction potentials.
13.2 Overview and Performance of Selected PRB Sites
in Europe
13.2.1 PRB Projects in Germany
In 2012, the German long-term R&D program (cluster) for PRBs named
“RUBIN” (German: “
R
eingungswände
u
nd -
b
arrieren
i
m
N
etzwerkverbund”)
was concluded after 12 years of comprehensive work (Birke and Burmeier,
2012a,b, RUBIN, 2014). RUBIN has been funded by the Federal Government
(the Federal Ministry of Education and Research, BMBF) with around 8.5
million € during that period. The authors coordinated, managed, and evalu-
ated all work that had been implemented by 19 RUBIN member projects
between 2000 and 2012. In addition, they had conducted an R&D project
on the origin of differing reactivities of technical ZVI brands and produc-
tion batches regarding the degradation of cVOCs, mainly chlorinated eth-
enes, in groundwater. The member projects overall delivered a significant
and highly valuable new insight into the PRB technology. R&D work cov-
ered field scale, semitechnical, and laboratory investigations. Taking into
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