Evaluating the effects of grain size and divalent cation concentration on the attenuation of viruses and microspheres through crushed silica sand

This study examines the effects of ionic strength, grain size and influent virus concentrations on pathogen transport in porous media. Fourteen column tests were conducted using the bacteriophage MS2 and 1.5 mum microspheres; two commonly used non-pathogenic surrogates representative of human viruses and bacteria, respectively. Two size distributions of crushed silica sand, with median grain diameters of 0.7 and 0.34 mm, and two ionic strengths of 8 and 95 mmol/L were used. A 22 partial factorial design was used with a minimum of two replicates of each combination of the parameters.;The results show that complete breakthrough of both viruses and microspheres occurred in medium sand at low ionic strength. It was found that increasing ionic strength by Ca2+ addition precluded breakthrough of MS2 in both the medium and fine sands. This represents a greater than 8 log reduction in peak effluent concentration and essentially complete attenuation.;Based on the results from this Thesis, in a riverbank filtration environment, there is reason to expect that, at comparable water qualities and in similar porous media, multiple logarithmic reductions of viruses and bacteria would occur over the much longer (than column length) flowpaths associated with RBF. There is also reason to expect this attenuation capability to vary based on riverbank grain size and water chemistry. (Abstract shortened by UMI.).