The remediation of contaminated groundwater by passive systems is expected to be a economically favorable technology compared to classical pump and treat technologies. Passive remediation systems like porous and permeable reactive walls or “Funnel and Gate” systems intersect the path of the contaminant plume. The pollutants are transported into the reactive zones by the natural groundwater flow. The objective of this joint research project is to develop a long lasting granular activated carbon barrier for the adsorption and simultaneous biological degradation of the contaminants.

Trichloroethene (TCE), chlorobenzene (CB), and benzene are used as model pollutants. In the first barrier, that is operated under anaerobic conditions with sucrose and ethanol as auxiliary substrates, TCE was completely converted to lower chlorinated metabolites, predominantly cis-dichloroethene (cis-DCE). The reductive dechlorination process was stable for about 300 d, although the concomitant sulphate-reducing and methanogenic processes varied considerably. In the second barrier, that was operated with addition of hydrogen peroxide and nitrate, dechlorination was limited by a lack of oxygen and restricted mainly to CB biodegradation.

Additional aerobic batch tests revealed that the metabolites of anaerobic TCE dechlorination, i.e. cis-DCE and vinyl chloride, were oxidatively dechlorinated in the presence of suitable auxiliary substrates such as ethene, CB, benzene, or sucrose and ethanol. During periods of low biological activity, elimination of TCE and CB occurred by adsorption in the GAC barriers. The pre-sorbed pollutants were available for subsequent biodegradation resulting in a bioregeneration of the activated carbon barriers.

The results demonstrate the feasibility of the sequential anaerobic/aerobic activated carbon barrier concept. At present, examinations in pilot scale are made at a former chemical production area, located in Bitterfeld, Germany.