Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/3/2007
Publication Date: 1/24/2007
Citation: Gargiulo, G., Bradford, S.A., Simunek, J., Ustohal, P., Vereecken, H., Klumpp, E. 2007. Bacteria transport and deposition under unsaturated conditions: the role of the matrix grain size and the bacteria surface protein. Journal of Contaminant Hydrology. Vol 92:255-273 Interpretive Summary: Bacteria transport experiments were conducted in three sands of differing size but at the same water saturation (80%). Additional transport experiments were conducted to quantify the role of large molecules on the bacteria surface. The amount of retained bacteria increased with decreasing sand size due to the presence of larger numbers of small pores in these sands. Removal of large molecules on the bacteria surface decreased the chemical interactions between the bacteria and the sands. The experimental data were analyzed using a mathematical model that accounts for retention of bacteria in sand by chemical interactions and in small soil pores. The pore structure was found to play an important role in bacteria removal, especially for smaller sand sizes.
Technical Abstract: Unsaturated (80% water saturated) packed column experiments were conducted to investigate the influence of grain size distribution and bacteria surface macromolecules on bacteria (Rhodococcus rhodochrous) transport and deposition mechanisms. Three sizes of silica sands were used in these transport experiments, and their median grain sizes were 607, 567, and 330 'm. The amount of retained bacteria increased with decreasing sand size, and most of the deposited bacteria were found adjacent to the column inlet. The deposition profiles were not consistent with predictions based on classical filtration theory. The experimental data could be accurately characterized using a mathematical modelling that accounted for first-order attachment, detachment, and time and depth dependent straining processes. Visual observations of the bacteria deposition as well as mathematical modelling indicated that straining was the dominant mechanism of deposition in these sands (78-99.6% of the deposited bacteria), which may have been enhanced due to the tendency of this bacterium to form aggregates. An additional unsaturated experiment was conducted to better deduce the role of bacteria surface macromolecules on attachment and straining processes. In this case, the bacteria surface was treated using a proteolitic enzyme. This technique was assessed by examining the Fourier-transform infrared spectrum and hydrophobicity of untreated and enzyme treated cells. Both of these analytical procedures demonstrated that this enzymatic treatment removed the surface proteins and macromolecules protein associated. Transport and modelling studies conducted with the enzyme treated bacteria, revealed a decrease in attachment but that straining was not significantly affected by this treatment.