Biogeochemical Dynamics in Zero-Valent Iron Columns:  Implications for Permeable Reactive Barriers

• Published in: Environmental science & technology Vol. 33; no. 13; pp. 2170 - 2177
• Main Authors: Gu, B, Phelps, T. J, Liang, L, Dickey, M. J, Roh, Y, Kinsall, B. L, Palumbo, A. V, Jacobs, G. K
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.07.1999
• Subjects: Applied sciences; Biochemistry; Biogeochemistry; Bioremediation; Chemistry; Contamination; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Engineering geology; Exact sciences and technology; Geology; Groundwater; Groundwater geochemistry; Groundwaters; Iron; Mechanical permeability; Microbiology; Natural water pollution; Pollution; Water treatment and pollution; Microbial activity; Chemical precipitation; Zerovalent metal; Iron; Material weathering; Long term; Biogeochemistry; Adsorption; Decontamination; Barrier material; Water pollution; Performance; Chemical reactivity; Permeability barrier; Ground water; Physicochemical method
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es981077e

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 (Fe0). 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 (17−33 mM HCO3 -) and sulfate (7−20 mM SO4 2-) containing groundwater regimes. Groundwater chemistry was found to significantly affect corrosion rates of Fe0 filings and resulted in the formation of a suite of mineral precipitates. HCO3 - ions in SO4 2--containing water were particularly corrosive to Fe0, resulting in the formation of ferrous carbonate and enhanced H2 gas generation that stimulated the growth of microbial populations and increased SO4 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 SO4 2- that became significant after about 2 months of column operations. This study demonstrates that biogeochemical influences on the performance and reaction of Fe0 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 Fe0 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 Fe0 beds, thereby decreasing treatment efficiency.