Date of Award

Winter 2004

Project Type

Thesis

Program or Major

Natural Resources: Water Resource Management

Degree Name

Master of Science

First Advisor

Carl H. Bolster

Second Advisor

Serita D. Frey

Third Advisor

Stephen H. Jones

Abstract

Recent studies suggest that bacterial contamination of groundwater is a national health concern in the United States. The movement of bacteria-laden water through soil and aquifer sediments often results in significant removal of bacteria from the aqueous phase, however, elevated concentrations of indicator organisms in drinking water aquifers are often detected and may be due, in part, to the slow release of sediment-associated bacteria. This condition, referred to as tailing, is caused by the detachment of previously attached cells over time, with aqueous concentrations often orders of magnitude below the peak concentration. Extended tailing has often been observed in laboratory and field transport experiments. The factors controlling bacterial attachment to aquifer sediments have been well investigated, however the processes controlling bacterial detachment from sediment surfaces at steady state are not well understood.

To address this research gap in understanding bacterial detachment in the subsurface, laboratory column experiments were performed to investigate the attachment and detachment of a nonmotile strain of Escherichia coli cells at resting state through uncoated or Fe-coated quartz sand (350-500 µm diameter) in KCl solution at low or high ionic strength (0.001 M or 0.01 M). For each experimental run, a pulse of 3 [H]-labeled E. coli cells was injected into flow-through columns, and column effluent was sampled for ~17-23 pore volumes (8.5-11.5 h). To account for biological effects on detachment, experiments were also run using E. coli cells treated with 0.5% formaldehyde rendering them “dead”. To calculate bacterial attachment and detachment rates, the one dimensional advection-dispersion equation modified to account for deposition and detachment was fit to the bacterial breakthrough curves (BTCs) for each treatment combination. To compare protein composition within cells, protein analysis was performed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDSPAGE).

Tailing of “live” E. coli cells was higher than the cells that were rendered “dead” and therefore biologically inactive, which was opposite than expected. This difference was attributed to cell surface characteristics and to the low carbon content within the columns. In addition, protein analysis indicated that there was a difference between the protein profiles of “live” and “dead” cells. As expected, bacterial BTC peaks for coated sand experiments were significantly lower than peaks for experiments using uncoated sands, indicating that attachment was more prevalent in coated sands. Tailing was observed for experiments using Fe-coated sands, however, which is contradictory to the reporting of others. Bacteria have been found to irreversibly attach to Fe-coated sands due to the positive charge of the coating and negative charge of bacteria. This irreversible attraction is thought to permanently remove bacteria from the aqueous phase, yet this research indicates that E. coli cells can reversibly attach to coated sand. In addition, detachment rates did not significantly change for the different treatments under the steady state conditions, indicating detachment may be more of a concern in perturbed systems. More research is necessary to elucidate the factors controlling detachment for the future protection of groundwater supplies from contamination by pathogenic microorganisms.

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