摘要：

The impact of microbiological and geochemical processes has been a major concern for the long-term performance of permeable reactive barriers containing zero-valent iron (Fe 0 ). To evaluate potential biogeochemical impacts, laboratory studies were performed over a 5-month period using columns containing a diverse microbial community. The conditions chosen for these experiments were designed to simulate high concentrations of bicarbonate (1733 mM HCO 3 - ) and sulfate (720 mM SO 4 2 - ) containing groundwater regimes. Groundwater chemistry was found to significantly affect corrosion rates of Fe 0 filings and resulted in the formation of a suite of mineral precipitates. HCO 3 - ions in SO 4 2 - -containing water were particularly corrosive to Fe 0 , resulting in the formation of ferrous carbonate and enhanced H 2 gas generation that stimulated the growth of microbial populations and increased SO 4 2 - reduction. Major mineral precipitates identified included lepidocrocite, akaganeite, mackinawite, magnetite/maghemite, goethite, siderite, and amorphous ferrous sulfide. Sulfide was formed as a result of microbial reduction of SO 4 2 - that became significant after about 2 months of column operations. This study demonstrates that biogeochemical influences on the performance and reaction of Fe 0 may be minimal in the short term (e.g., a few weeks or months), necessitating longer-term operations to observe the effects of biogeochemical reactions on the performance of Fe 0 barriers. Although major failures of in-ground treatment barriers have not been problematic to date, the accumulation of iron oxyhydroxides, carbonates, and sulfides from biogeochemical processes could reduce the reactivity and permeability of Fe 0 beds, thereby decreasing treatment efficiency.

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