Remediation of Chlorinated hydrocarbons from groundwater pollution [Katalytische Dechlorierung von Chlorkohlenwasserstoffen aus kontaminierten Grundwässern]

In the framework of the joint research project SAFIRA, two novel catalysts were developed and examined in groundwater flow-through reactors at the Bitterfeld testsite. The catalytic active component Pd ought to be protected from deactivating ionic compounds by embedding Pd into hydrophobic polymer membranes on the one hand, and on the other hand by generating Pd clusters in the pores of hydrophobic zeolites. Both catalysts reached only short life times, caused by the formation of H2S and possibly other sulfur compounds by microbiological sulfate reduction. Though the catalysts could be regenerated by treatment with hypochlorite, poisoning occurred after short periods of operation. In conclusion, we assess the utilization of noble-metal catalysts directly in the water phase of the Bitterfeld groundwater as problematic. However, the transfer of the catalytic reaction to the gas phase yielded encouraging results. A multi-stage process, including different pretreatment techniques in the water phase, vacuum stripping of contaminants, and their catalytic hydrodechlorination over Pd catalysts in the gas phase allow the complete conversion of contaminants. The utilization of modern membrane technology and the possibility to heat the strip gas stream in a wide temperature range, provides the process a high potential concerning contaminant spectrum and concentration.