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A stochastic model for colloid transport and deposition
1USDA-ARS, United States Salinity Lab., 450 W. Big Springs Rd., Riverside, CA 92507-4617, USA. sbradford@ussl.ars.usda.gov
Journal of Environmental Quality
|July 20, 2007
Summary
This study introduces a stochastic model to explain non-exponential colloid deposition profiles in porous media. Simulation results show variations in deposition and velocity drive these observed profiles.
Area of Science:
- Environmental science
- Geosciences
- Colloid and surface chemistry
Background:
- Standard filtration theory predicts exponential colloid deposition profiles.
- Observed colloid retention profiles in porous media often deviate, showing hyper-exponential or non-monotonic behavior.
- Unfavorable attachment conditions contribute to these deviations.
Purpose of the Study:
- To develop and test a stochastic model for colloid transport and deposition.
- To investigate the underlying mechanisms causing deviations from predicted exponential profiles.
- To explore the impact of stochastic parameters on colloid deposition patterns.
Main Methods:
- Developed a stochastic model based on the advective dispersion equation with first-order kinetics.
- Incorporated stochastic parameters: deposition coefficient, release coefficient, and pore water velocity.
- Utilized log-normal, bimodal log-normal, and joint log-normal probability density functions (PDFs).
Main Results:
- Variations in deposition coefficient and average pore water velocity were found to produce hyper-exponential profiles.
- Bimodal PDF formulations also generated hyper-exponential profiles with lower deposition coefficient variance.
- Profile shape sensitivity was observed concerning correlations between deposition/release coefficients and pore water velocity/deposition coefficient.
Conclusions:
- Stochastic variations in transport parameters can explain observed hyper-exponential colloid deposition profiles.
- Chemical heterogeneity alone may not fully account for observed behaviors.
- Variability in pore size and water velocity distributions offer alternative explanations for colloid transport deviations.
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