Novel nano-catalysts for wastewater treatment

Abstract

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.