UC Riverside

An understanding of the processes that influence the transport and fate of microorganisms in porous media is needed to protect water resources from pathogenic microorganisms and contaminants associated with the colloidal phase, and to optimize bioremediation strategies. As the physical and chemical factors influencing the transport of microorganisms have been well understood in homogeneous systems, accurate description of microorganism transport in field scale is hampered by the existence of preferential flow.

The objective of this research was to better understand and quantify physical and chemical factors that influence microorganism transport and fate in soils that exhibit preferential flow. E. coli D21g and coliphage phiX174 were selected in this study as the representative bacterial pathogen and the surrogate for human viruses, respectively. The transport of microorganisms was examined in well defined and controlled soil columns containing artificial macropores (sand lenses) of different length and configuration under different solution ionic strength (IS).

Transport experiments demonstrated that retention of E. coli D21g and φX174 increased with IS in both homogeneous and heterogeneous systems. The importance of preferential flow on microbe transport was found to be enhanced at higher IS, even though the overall transport decreased. Deposition profiles revealed significant cell retention at the interface of the coarse sand lens and fine sand matrix as a result of mass transfer. The length and configuration of the artificial macropore proved to have a great impact on the transport of E.coli D21g, especially under high ionic strength conditions. At low ionic strength, more extensive transport in the preferential path and earlier arrival time were observed for E.coli D21g compared to bromide as a result of size exclusion. Cell release from the preferential flow system with a reduction of solution IS exhibited multi-pulse breakthrough behavior that was strongly dependent on the initial amount of cell retention, especially at the lens-matrix interface, and the lens configuration. Simulations in 2D models were capable to describe the transport and deposition, and the release process during transients in chemistry in preferential flow systems. Dual-permeability models were also successfully applied to simulate microorganism transport in preferential flow systems with different configuration and length of preferential path, and correlations found between the parameters of dual-permeability model and preferential path characters could promote the upcaling from local to field scale for microorganism transport in preferential flow systems.