title: Longevity of granular iron in groundwater treatment processes: solution composition effects on reduction of organohalides and nitroaromatic compounds.
abstract: Although granular iron permeable reactive barriers (PRBs) are increasingly employed to contain subsurface contaminants, information pertaining to system longevity is sparse. The present investigation redresses this situation by examining the long-term effects of carbonate, silica, chloride, and natural organic matter (NOM) on reactivity of Master Builders iron toward organohalides and nitroaromatic contaminants. Six columns were operated for 1100 days (approximately 4500 pore volumes) and five others for 407 days (approximately 1800 pore volumes). Nine were continuously exposed to mixtures of contaminant species, while the other two were only intermittently exposed in order to differentiate deactivation induced by water (and inorganic cosolutes) from that resulting from contaminant reduction. Contaminants investigated were trichloroethylene, 1,2,3-trichloropropane, 1,1-dichloroethane, 2-nitrotoluene, 4-nitroacetophenone, and 4-nitroanisole. Column reactivity declined substantially over the first 300 days and was dependent on the feed solution chemistry. High carbonate concentrations enhanced reactivity slightly within the first 90 days but produced poorer performance over the long term. Both silica and NOM adversely affected reactivity, while chloride evinced a somewhat mixed effect. Observed contrasts in relative reactivities suggest that trichloroethylene, 1,2,3-trichloropropane, and nitroaromatic compounds all react at different types of reactive sites. Our results indicate that differences in groundwater chemistry should be considered in the PRB design process.
authors.affiliation: Department of Geography and Environmental Engineering, The Johns Hopkins University, 313 Ames Hall, Baltimore, Maryland 21218-2686, USA.
authors.forename: Jörg
authors.initials: J
authors.lastname: Klausen
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Vikesland
authors.forename: Tamar
authors.initials: T
authors.lastname: Kohn
authors.forename: David R
authors.initials: DR
authors.lastname: Burris
authors.forename: William P
authors.initials: WP
authors.lastname: Ball
authors.forename: A Lynn
authors.initials: AL
authors.lastname: Roberts
mesh_terms: D002712:Chlorides / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D009930:Organic Chemicals; D010539:Permeability; D012037:Refuse Disposal; D012822:Silicon Dioxide / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D014876:Water Pollution / Q000517:prevention & control*
chemical_list: D002712:Chlorides; D009930:Organic Chemicals; D012989:Soil Pollutants; D012822:Silicon Dioxide; D007501:Iron