Characterization of effective nonlinear adsorbing transport in heterogeneou- s porous media
Our investigations focus on the large-scale transport behaviour of nonlinear reactive transport processes in heterogeneous aquifers. The adsorption reaction is described by an equilibrium isotherm of Freundlich type. In a stochastic modelling approach we analyse temporal moments of breakthrough curves and evaluate large-scale parameters, in which the influence of small-scale variations is appropriately considered. We distinguish between two different averaging processes leading to the so-called ensemble averaged and effective parameters. In linear transport theory the large-scale transport is characterized by the same type of homogeneous transport equation as at the smaller scale, replacing the transport parameters by equivalent effective parameters. In the nonlinear transport case we demonstrate that large concentration gradients at the contamination front cause an additional dispersive flux, resulting in a decrease of peak concentrations and less steep profiles of averaged breakthrough curves in the heterogeneous realization. We propose to modify the equivalent large-scale transport equation by a supplementary term.
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