Reductive Methods

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 relatively inexpensive. These reactive barriers are capable of destroying CHCs over long time periods without maintenance. Unfortunately, iron fails completely as a reducing agent for aromatic CHCs, such as chlorinated benzenes or PCBs. The Department of Environmental Technology of the UFZ strongly integrates the catalytic hydrodehalogenation into their studies, because palladium catalysts allow high reaction rates and are able to destroy the aromatic CHCs 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. Objective of the research in the field of water treatment is the supply of efficient and cost-effective catalysts and technologies which are adjusted to the specific features of the environment. The department follows several pathways in order to achieve that goal:

Increase in catalyst life-time by hydrophobic protection against water constituents which also prevents Pd from leaching.

Enrichment of hydrophobic pollutants by adsorption at the catalyst carrier and chemical conversion of the contaminats in the sorbed state.

On the basis of ferromagnetic carrier colloids, extremely active catalysts for cyclic batch application can be produced which are easily filtered by magnetoseparation from the treated water. In further studies of the department the step to nano catalysts for waste water treatment was made.

Another way to improved catalytic conditions is the transfer of the highly diluted volatile contaminants from the "unfavourable" water phase into the "favourable" gas phase. Most organic contaminants are enriched by stripping into the gas phase by several orders of magnitude ( mass-stream basis) which makes the treatment gas streams at higher temperature (>100°C) economically feasible. The combination of stripping and heterogeneous gas phase reaction increases the application area of catalytic process for water treatment. A site-tailored ex-situ multi-step process with a catalytic step as principal item was tested successfully at several field sites. Groundwaters which was contaminted by chloro- and bromohydrocarbons (AOX > 150 mg/L) were treated in the pilot scale to meet the discharger permissible limits of 1... 3 mg/L AOX. The photos above show the praxis test of our pilot plant.

The hydrogen supply for the hydrodechlorination reaction in aqueous solution is limited by the limited water solubility of molecular hydrogen. This limitation could be conquered by means of alternative water soluble H-donators.