Combination of Fe(0) with additional reactive materials in fixed bed reactors for TCE removal

Declines of reactivity and permeability due to mineral and gas accumulations are considered as major risks of Fe(0) fixed bed reactors (permeable reactive barriers) for passive treatment of contaminated aquifers. Reducing the Fe(0) content per volume unit is a simple but effective modification that might enhance longevity. Reducing passivating build-ups on the Fe(0) surface by attracting precipitation on non-Fe(0) surfaces might enhance the long-term reactivity. Calcite and granular ferric hydroxide (GFH) as potential crystallization seeds were combined with Fe(0). Wood in combination with Fe(0) was tested for enhanced microbial activity with potentially positive effects on gas clogging and contaminant removal. Calcite revealed decreased effluent concentration of calcium and inorganic carbon, probably due to initiation of CaCO3 crystallization on its surface. Differing effects were observed for the combination of GFH and Fe(0) in the initial period: Anion exchange caused high chloride effluent concentrations, sulfate retention and subsequent sulfate release and acidic conditions with comparably high corrosion rates. No chlorinated compounds were found in the effluent of the GFH containing column. An increase of cDCE was observed in the effluent of calcite and wood containing columns representing a failure of the tested remediation approach. The combination of different reactive materials as a potential further development of permeable reactive barriers is discussed.

► Combinations of Fe0 and granulated ferric hydroxide (GFH), calcite and wood for reductive TCE dechlorination.
► Increased calcium removal with calcite probably due to crystallization nucleation.
► Various effects of GFH: ion exchange, pH decrease, adsorption and complete dechlorination in the long term.
► Increased cis-dichloroethene concentration in effluents of wood and calcite containing columns.