Abstract
For reactive transport process in porous media, limited mixing and non-Fickian behavior are difficult to understand and predict. To explore the effects of anomalous diffusion and limited mixing, the column-based experiments of bimolecular reactive migration were performed and simulated by the CTRW-FEM model (continuous time random walk-finite element method). Simulated parameters were calibrated and the correlation coefficients between modeled and observed BTCs (breakthrough curves) were greater than 0.9, indicating that CTRW-FEM can solve over-prediction and tailing problems effectively. Porous media with coarser particle size show enhanced mixing and the non-Fickian behavior is not affected by particle size. β (a parameter of CTRW-FEM) and Da (Damköhler number) of CTRW-FEM under different Pe (Péclet number) values showed logarithmic linear relationship. Model sensitivity analysis of the CTRW-FEM model show that the peak concentration is most sensitive to the average pore velocity and the arriving peak time of peak concentration is most sensitive to β. These findings provide a theoretical basis for handling mixing and non-Fickian behavior patterns under actual environmental conditions.
Highlights
In porous media, reactive pollutants like heavy metals, organic compounds and nitrogen may undergo anomalous diffusion [1,2,3,4] and limited mixing [5], because transport patterns are affected by boundary conditions, media characteristics and reactive processes collectively
Based on the advection-dispersion-reaction equation (ADRE) equation, Eulerian continuum models are developed to upscale the transport equation from pore scale to larger scales and they can be implemented by various approaches such as volume-averaging [10,11], effective upscale parameter [12,13] techniques and the spatial Markov model (SMM) [14]
That demonstrates outlet concentration change with time of product NQAB (40.063, 60.094, and 80.126 mL/min) are concentration fluctuations in theofreactive migration process related to the particle size
Summary
Reactive pollutants like heavy metals, organic compounds and nitrogen may undergo anomalous diffusion [1,2,3,4] and limited mixing [5], because transport patterns are affected by boundary conditions, media characteristics and reactive processes collectively. Such behaviors can lead to the complicated concentration fluctuation in space and time, which make prediction difficult. It is still a challenge to across the scales of larger transport and smaller reaction in heterogeneous media [15]
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