At the beginning of the 1990s, a method developed by Gillham & co-workers (1994) at the University of Waterloo in Canada caused worldwide interest. In this passive in situ process, granular metallic iron is introduced into the contaminated groundwater stream, where it acts as a reducing agent. Iron is environmentally acceptable and utilized in various forms, where nanoscale zero-valent iron is the most widely known material for in-situ generation of permeable barriers. The Department of Environmental Technology of the UFZ developed
® which is a composite with nano-iron structures as reducing component but embedded in activated carbon in-situ generation of permeable sorption-reaction barriers became possible.
Unfortunately, all iron-based methods fail for reduction of contaminants with aromatic halogen-carbon bonds, such as chlorinated benzenes. Here we have to switch to the catalytic hydrodehalogenation as treatment method, because catalysts such as
allow high reaction rates and are able to rapidly destroy the aromatic contaminants as well. However, the extremely high reactivity of palladium catalysts is always accompanied by a high sensitivity against catalyst poisons often leading to short catalyst life-times under environmental conditions.