Novel nano-catalysts for wastewater treatment

The present paper aims at a treatment technique designed for special industrial wastewaters contaminated with only traces of halogenated organic compounds (HOCs) - concentrations which are nevertheless large enough to make a discharge into municipal sewage works impossible. Our research follows the idea to detoxify the water by a selective destruction of the HOCs by hydrodehalogenation (HDH) reactions on palladium-containing nano-catalysts. Detoxification means that persistent HOCs are converted into organic compounds which can easily be removed by biodegradation in a wastewater treatment plant. A novel promising trend in environmental research is the application of nano-reagents (such as zero-valent iron) and nano-catalysts. As known from nano-sized metal particles, nanocatalysts have the advantage of very high reaction rates due to high specific surface areas and low mass-transfer restrictions. For special applications in wastewater treatment we were able to generate extremely active palladium catalysts on the basis of ferromagnetic carrier colloids. The magnetic nano-sized carriers (such as zero-valent iron or magnetite) were spiked with traces of Pd (0.1 wt.-%). These nano-catalysts have been successfully tested in different reactor systems at the laboratory scale. Using Pd on nano-scale supports leads to enormous activity of the catalyst which is several orders of magnitude higher than reached in conventional fixed-bed reactors. The ferromagnetism of the carriers enables a separation of the catalysts from the treated water by means of magneto-separation. This gives the chance to reuse the catalyst several times. The preferred reductant for the HDH reaction is molecular hydrogen. For highly contaminated waters, alternative hydrogen donors such as formic acid have been successfully tested.