Sorption and Biodegradation of Organic Solutes Undergoing Transport in Laboratory-scale and Field-scale Heterogeneous Porous Media.
The first study focused on the magnitude and rate of sorption of hydrophobic organic compounds by two, well-characterized soils. The composition of organic matter had a small effect on the magnitude of the organic carbon normalized equilibrium distribution coefficients. The sorbates sorbed more strongly to the humic-coated soil, most likely due to the organic matter's less polar nature as compared to the fulvic material. The molecular solute descriptor, ¹Xᵛ, performed slightly better than the empirical solute descriptor, K(ov), in evaluating equilibrium sorption coefficients. Thus, sorbate structure may have a secondary influence on the overall magnitude of equilibrium sorption. Sorbate structure exhibited a greater influence on sorption kinetics than on sorption equilibrium. Distinct differences in the magnitudes of mass transfer coefficients for the humic and fulvic soils were observed when relating them to the molecular solute descriptor, ¹Xᵛ. The differences in mass transfer coefficients were attributed to both sorbate structure and the quantity and morphology of soil organic matter. The intrasorbent diffusion coefficients were believed to be the same for both the humic and fulvic material. The second study focused on using a biodegradable solute to measure processes that affect in-situ biodegradation during well-controlled field and laboratory experiments. Specifically, this study investigated how residence time and scale influence the extent and rate of in-situ biodegradation of an organic solute undergoing transport. The transport of the biodegradable solute was compared to that of bromide and/or pentafluorobenzoic acid, which are conservative, non-degradable tracers. Laboratory experiments were conducted to simulate both the flow velocity and residence time conditions existent in the field. Mass recovery the biodegradable solute decreased as the residence time increased, ranging from 14 to 95 percent for the field sites. Mass recoveries in the laboratory experiments were approximately 30% to 40 % less than in the field experiments. The first-order biodegradation rate constants did not vary with residence time for either field site. In addition, the average rate constant value for both field sites was very similar (0.21 d⁻¹).
Hydrology., Environmental sciences., Hydrophobic surfaces.
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