Validation of a hybrid two-site gamma model for naphthalene desorption kinetics
- Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Civil and Environmental Engineering
- Cornell Univ., Ithaca, NY (United States)
Three models for sorption/desorption of polycyclic aromatic hydrocarbon (PAH) contaminants from soil were compared for their ability to predict the transport of PAH in soil: a gamma model, a two-site/two-region nonequilibrium model, and a hybrid model. In the hybrid model, soil organic matter was conceptually divided into two compartments; a fraction with rapid sorption/desorption kinetics and a compartment with mass-transfer-limited kinetics. Contaminant sorbed in the rapid compartment was assumed to be in instantaneous equilibrium with the aqueous phase, while the release of contaminant from the slow fraction was assumed to be governed by a gamma distribution of rate coefficients. The hybrid model successfully described the initial rapid release of a model PAH contaminant, naphthalene, from a sieved soil sample of moderate organic content ({approx_equal} 2.3%) as well as the following slow release observed over 25 days in batch desorption experiments. Other necessary model parameters, such as the hydrodynamic dispersion coefficient of naphthalene and the macropore porosity, were evaluated in separate experiments. A transport model incorporating the hybrid model for naphthalene sorption/desorption successfully predicted the elution profile of naphthalene in independent soil-column experiments with no adjustable parameters. The success of the hybrid model suggests that a wide array of rate controls govern PAH desorption. This conclusion is consistent with the view of soils as consisting of a mix of different sorptive constituents and heterogeneous physical constraints on PAH release.
- OSTI ID:
- 687360
- Journal Information:
- Environmental Science and Technology, Vol. 33, Issue 18; Other Information: PBD: 15 Sep 1999
- Country of Publication:
- United States
- Language:
- English
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