Assessing degradation rates of chlorinated ethylenes in column experiments with commercial iron materials used in permeable reactive barriers.
Multiple column experiments were performed using two commercial iron materials to evaluate the necessity and usefulness of preliminary investigations in permeable reactive barrier (PRB) design for chlorinated organics. Experiments were performed with contaminated groundwater and involved fresh iron granules or altered iron material excavated from PRBs. The determination of first-order rate coefficients by global nonlinear least-squares fittings indicated a variability in rate coefficients on 1 or 2 orders of magnitude. Geometric mean values of surface area normalized rate coefficients (in 10(-5) L m(-2) h(-1)) for fresh gray cast iron and iron sponge, respectively, are: tetrachloroethene (4.5, 2.6), trichloroethene (8.1, 3.3), cis-1,2-dichloroethene (3.1, 2.9), trans-1,2-dichloroethene (9.5, 5.3), 1,1-dichloroethene (4.0, 4.4), and vinyl chloride (1.6, 6.1). The increasing rate coefficients with decreasing grade of chlorination, which characterize degradation at iron sponge are linearly related to diffusion coefficients in water, suggesting diffusion limitation in the degradation process for this particular material, possibly due to a high inner surface. The variability in rate coefficients seems to be too high to use mean rate coefficients from published studies in the design procedure of PRBs, and variabilities cannot be related to groundwater characteristics, waterflow through the reactive cells, or secondary corrosion reactions.
Institute of Geosciences, Christian-Albrechts-Universität zu Kiel, Ludewig-Meyn Strasse 10, 24118 Kiel, Germany. me@gpi.uni-kiel.de
Markus
M
Ebert
Ralf
R
Köber
Anika
A
Parbs
Volkmar
V
Plagentz
Dirk
D
Schäfer
Andreas
A
Dahmke
D004000:Dichloroethylenes / Q000032:analysis / Q000737:chemistry; D004058:Diffusion; D004784:Environmental Monitoring; D006843:Hydrocarbons, Chlorinated / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D010539:Permeability; D012989:Soil Pollutants / Q000032:analysis*; D013750:Tetrachloroethylene / Q000032:analysis / Q000737:chemistry; D014241:Trichloroethylene / Q000032:analysis / Q000737:chemistry; D014752:Vinyl Chloride / Q000032:analysis / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply
D004000:Dichloroethylenes; D006843:Hydrocarbons, Chlorinated; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D007501:Iron; D013750:Tetrachloroethylene; D014752:Vinyl Chloride