| Abstract
| - The present study focuses on the impact of microbialactivities on the performance of various long-term operatedlaboratory-scale permeable reactive barriers. The barrierscontained both aquifer and Fe0 compartments and hadreceived either sulfate or iron(III)−EDTA to promote sulfate-reducing and iron(III)-reducing bacteria, respectively.After dismantlement of the compartments after almost 3years of operation, DNA-based PCR−DGGE analysis revealedthe presence of methanogenic, sulfate-reducing, metal-reducing, and denitrifying bacteria within as well as up- anddowngradient of the Fe0 matrix. Under all imposedconditions, the main secondary phases were vivianite,siderite, ferrous hydroxy carbonate, and carbonate greenrust as found by scanning electron microscopy (SEM)combined with energy dispersive X-ray analysis (EDX), andX-ray diffraction (XRD). Under sulfate-reduction promotingconditions, iron sulfides were formed in addition, resultingin 7 and 10 times higher degradation rates for PCE and TCE,respectively, compared to unreacted iron. These resultsindicate that the presence of sulfate-reducing bacteria inor around iron barriers and the subsequent formation ofiron sulfides might increase the barrier reactivity.
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