Ansätze zur Erweiterung des Anwendungsspektrums reaktiver Wände : Optimierung von Kombinationsreaktionswänden und Nutzung schadstoffabbauender Prozesse im abstromigen Aquifer
Two approaches for new applications of permeable reactive barriers (PRBs) for ground water remediation were studied by laboratory sequenced column experiments. One part of the study was aimed at demonstrating that a complex contaminant mixture (trichloromethane, chlorobenzene and various other compounds) can be remediated using a sequenced PRB containing zero valent iron (ZVI) and granular activated carbon. Results show that the complex contaminant mixture can be remediated by a such a sequenced PRB. Investigations of geochemical reactions downgradient of PRBs were another focus of this study. One experiment was conducted to assess the impact of elevated pH caused by two possible reactive medium combinations for PRBs on the ground water quality in a lignite sand. Results show that for the investigated sediment, high pH values downgradient of PRBs will be limited to a narrow zone even in the long run. In another experiment, the potential for the degradation of residual tetrachloroethylene concentrations downgradient of a ZVI PRB was evaluated. Due to the significant retardation of the propagation of high pH values in the sediment compared to the ground water flow velocity, a zone with nearly neutral pH and strongly reduced redox potential developed. In this zone, microbial reductive dechlorination of tetrachloroethylene was observed. The results of the present study show that the spectrum of possible applications of PRBs can be extended to the degradation of complex mixed contaminations by using sequenced PRBs and that natural attenuation processes downgradient of PRBs may become increasingly important in the future if the limitation of microbial contaminant degradation by high pH can be minimised.
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