The movement of bacterial particles through porous media

Abstract

The movement of microorganisms through porous media is particularly significant as pathogens may be present in wastes which may be transported by the water percolating through the soil. These pathogenic microorganisms can enter ground water and become involved in disease outbreaks such as in the United States where almost half of the waterborne outbreaks of disease reported annually are due to contaminated groundwater (Keswick et al., 1982). This is important to understand the processes governing the movement of microorganisms in porous media, as this influences the hazard pathogens pose to groundwater. A column containing a porous medium (aluminium oxide 63-88µm diameter) was used to study the effects of viscosity changes on the movement of Bacillus subtilis var niger endospores using methods outlined by Bailey, (1994). It was concluded that this method was unsuitable for studying the effects of viscosity on the movement of bacteria through porous media. A second column containing a 14mm diameter column made up of glass beads (300 - 500µm diameter)a, centrally located in a column of aluminium oxide (63-88µm diameter)b was setup. This was used to investigate movement of B. subtilis var niger endospores from the microporous media (b) into the macroporous media (a) in a microbially saturated porous media. In order to ascertain how rapidly the macroporous media was drained of Bacillus subtilis var niger endospores a third column of glass beads only of similar proportions to the middle of the second column was designed. Data from the combined macroporous / microporous and macroporous experiment was processed through the UNIFIT programme, fitting it most closely in both cases to an exponential function. The data was natural log transformed and linearly regressed, producing an R squared value of 0.5157. The line of best fit was calculated for the exponential function. Due to experimental faults, the data from the combined macroporous / microporous and the single macroporous column was unable to be directly compared. However the behaviour of the breakthrough curves of the two columns was observed. The regressed data from the combined macropore and micropore column exhibited a gradual decrease to low levels. The single macroporous column exhibited a rapid decrease in endospore concentration, beginning at a high concentration and decreasing to levels lower thanthat found in the macropore / micropore column.