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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Reactivity and longevity of zero-valent nano iron for the in-situ remediation of CHC-contaminated groundwater"

In recent years permeable reactive barriers (PRBs) have been used more and more to remediate groundwater polluted with chlorinated hydrocarbons (CHCs). Thereby the usage of zero-valent iron as a reductive component has proved its worth. A new alternative to build a PRB is the injection of zero-valent nano-sized iron particles suspended in water. The reactive iron is distributed in the pore space by injecting the suspension into a well to form a “reactive zone”. Contaminants in the groundwater that pass through this reactive zone are chemically reduced to environmental benign products.

The goal of the presented work was to investigate the reactivity and longevity of zero valent nano iron with the model contaminant Perchloroethylene (PCE) at the laboratory and semi-field scale. In batch experiments under ideal conditions as well as in a simulation of a natural aquifer in column experiments it was shown that it is possible to degrade PCE with the used reactive nano iron particles (RNIP). Anaerobic corrosion reduces in time the amount of zero valent iron and releases hydrogen (H2) gas in a stored suspension. Therefore a simple construction was designed to determine the actual weight percentage of zero valent iron in the suspension. The results of the batch experiments showed that due to anaerobic corrosion a certain stoichiometrical excess of iron compared to the pollutant is needed for full degradation. Furthermore the batch experiments showed that it was possible to eliminate 60% of the model contaminant within 42 days. The hydrogen production caused clogging of the pore space in the column experiments. This proved that the particles are not stable in a pH-neutral environment. In following column experiments calcium hydroxide (slaked lime) was added to the nano iron suspension before the injection into the column. With this modification the hydrogen production was reduced severely and the long-term stability was increased considerably. This approach has been filed for patent in Germany by VEGAS.