Modeling Physicochemical Processes of Microbial Transport in Porous Media

Abstract

The traditional colloid filtration model has been recognized to not fully describe transport of microorganisms in porous media under many conditions. Potential reasons for the discrepancies between colloid filtration theories and observed data are summarized into three aspects in the dissertation, including physicochemical heterogeneity, a blocking effect in the attachment process, and irreversible straining. A new transport model is developed to incorporate these non-ideal phenomena. First, both the collision-efficiency coefficient and the detachment-rate coefficient are formulated as probability density functions with log-normal distributions to represent physicochemical heterogeneity of both microbial and porous-medium grain surfaces. Second, the blocking effect is represented by appending a modified random sequential adsorption (RSA) function to the kinetic rate equation. Third, a semi-empirical equation is developed to describe the straining effect.The new model is then evaluated with a series of sensitivity analyses and illustrative applications to measured data. Sensitivity analysis on the role of probability density function (PDF) in collision efficiency and detachment rate coefficient shows that heterogeneity causes longer tailing in breakthrough curves, This effect is controlled by the implementation of the PDF in the detachment rate coefficient because the lower values among a series of detachment rate coefficients delay detachment. Straining phenonmena have received more and more attentions for protozoa transport. The new semi-empirical straining equation derived in the dissertation provides reasonable matches to the colloid data and cryptosporidium data. The Blocking effect is another process of concern for microbial transport, as shown in the analysis of microsporidium column experiments herein. The new model also proved to be successful for simulating MS-2 virus transport. The work presented will help enhance our understanding of biocolloid transport in porous media.