Bromide and bacterial transport through different porous media: Controlling sediment characteristics and mathematical modeling.

摘要

Bacterial transport through laboratory columns of natural, intact aquifer sediment is investigated with the overall objective of better understanding bacterial transport and developing a predictive capability based on the sediment characteristics. Most previous bacterial-transport studies used artificial or repacked materials as the transport medium. A second objective is, therefore, to compare bacterial transport in natural-intact, natural-repacked and artificial sediments to evaluate the usefulness of experiments on surrogate materials.; As an outgrowth of this work, bromide served as a comparative conservative tracer. A two-region, non-equilibrium model accurately simulated bromide breakthrough, and yet, for the media used in this study, the physical meanings of the model parameters are unclear. This study, therefore, also investigates their meanings by relating the parameter values to sediment properties. The model parameters were found to be highly correlated with sediment heterogeneity and could be estimated based on the sediment's sorting coefficient.; Bacterial breakthrough in all three transport media was rapid with a sharp peak and a long tail of relatively constant concentration. Great variability was observed through natural sediments, but not silica sand. Breakthrough data indicate that bacteria move preferentially through the larger pores resulting in a smaller effective porosity and greater average velocity than for bromide. Bacterial breakthrough data can be simulated with a simple model incorporating kinetic sorption. Relationships between bacterial transport and sediment properties were explored with multiple regression analyses. The resulting regression models indicate that when groundwater chemistry and temperature are held constant, most of the variability in bacterial transport can be explained by grain size, degree of sorting and hydraulic conductivity.; Statistical techniques were used to detect any difference between the transport of bacteria through the three different types of transport media. Bacterial transport through the intact-natural sediment columns is significantly different from transport through silica-sand columns; most of these differences can be explained by the physical difference of the media. Repacking has some effect on the relationships between bacterial transport parameters and sediment properties. There is a tendency to underestimate bacteria transport if artificial sand or repacked sediments rather than intact-natural sediments are used as the transport medium.