Early breakthrough of colloids and bacteriophage MS2 in a water‐saturated sand column

Abstract

1] We conducted column-scale experiments to observe the effect of transport velocity and colloid size on early breakthrough of free moving colloids, to relate previous observations at the pore scale to a larger scale. The colloids used in these experiments were bacteriophage MS2 (0.025 mm), and 0.05-and 3-mm spherical polystyrene beads, and were compared with a conservative nonsorbing tracer (KCl). The results show that early breakthrough of colloids increases with colloid size and water velocity, compared with the tracer. These results are in line with our previous observations at the pore scale that indicated that larger colloids are restricted by the size exclusion effect from sampling all paths, and therefore they tend to disperse less and move in the faster streamlines, if they are not filtered out. The measured macroscopic dispersion coefficient decreases with colloid size due to the preferential flow paths, as observed at the pore scale. Dispersivity, typically considered only a property of the medium, is in this case also a function of colloid size, in particular at low Peclet numbers due to the size exclusion effect. Other parameters for colloid transport, such as collector efficiency and colloid filtration rates, were also estimated from the experimental breakthrough curve using a numerical fitting routine. In general, we found that the estimated filtration parameters follow the clean bed filtration model, although with a lower filtration efficiency overall.Citation: Keller, A. A., S. Sirivithayapakorn, and C. V. Chrysikopoulos (2004), Early breakthrough of colloids and bacteriophage MS2 in a water-saturated sand column, Water Resour. Res., 40, W08304,

Fracture Characterization in Enhanced Geothermal Systems by Wellbore and Reservoir Analysis

“…The calculation results indicated that the attachment efficiency values, for all experiments with changing particle sizes, concentrations and fluid velocities varied from 0.0077 to 0.08 with the majority of values in the range of 0.011 to 0.024. Other studies conducted in sand columns (Keller and Sirivithayapakorn, 2004;Bradford et al, 2002 and2006) or sediment cores (Dong et al, 2002) reported values comparable to the values found in this study. The attachment efficiency in this study generally increased with increasing concentration of the particle suspension and fluid velocity.…”

Tracer tests in karst hydrogeology and speleology

“…Colloids were often reported to travel at higher mean velocities than solutes through porous media due to exclusion processes, i.e. preferential transport in the centres of the largest pores (Keller et al, 2004). Similar processes may operate in unsaturated carbonate rocks, although a time�dependent loss function may also explain the observed turbidity BTC.…”

Colloid particle size‐dependent dispersivity

“…This result is in agreement with the work published by Jourak et al [2013] who studied theoretically the effects of particle-size distribution on the longitudinal dispersion coefficient in models of packed columns, and the work published by Bennacer et al [2013] who investigated experimentally the transport and deposition of suspended particles with different size distributions in water-saturated porous media. However, Keller et al [2004], Vasiliadou and Chrysikopoulos [2011], and Syngouna and Chrysikopoulos [2011] reported that a L decreases with increasing d p . These contradictory findings are probably due to the very limited number of experimental data used, and the experimental conditions that led to significant mass retention caused by straining and/or attachment.…”

“…This discrepancy can be attributed to variations in the combined effects of: (a) effective porosity reduction and (b) colloid exclusion from lower-velocity regions within the homogeneous porous media employed in this study, where the distribution of actual pore sizes is quite narrow. It should be noted that early breakthrough of the colloids is an expected result [e.g., Grindrod et al, 1996;Keller et al, 2004]. Furthermore, the breakthrough curves obtained for the transport experiments in a 30 cm column using colloids with d p 5 1000 nm (experiment number 37) and colloids with d p 5 5500 nm (experiment number 52) are presented in Figure 2.…”

“…For nonperiodic or heterogeneous porous media, where REV selection Previous studies have suggested that colloid transport in porous media is significantly affected by particle size [Fontes et al, 1991, Gannon et al, 1991. Early breakthrough of colloids and biocolloids as compared to that of conservative tracers has been observed in several studies [Bales et al, 1989;Toran and Palumbo, 1992;Powelson et al, 1993;Grindrod et al, 1996;Dong et al, 2002;Keller et al, 2004;Vasiliadou and Chrysikopoulos, 2011;Sinton et al, 2012;Syngouna and Chrysikopoulos, 2013;Chrysikopoulos and Syngouna, 2014]. Colloid early breakthrough can be attributed to effective porosity reduction (colloids cannot penetrate smaller pores due to their inability to fit into them), preferential flow paths through high-conductivity regions, and exclusion from the lower-velocity regions [Chrysikopoulos and Abdel-Salam, 1997;Dong et al, 2002;Ginn, 2002;Ahfir et al, 2009], which can also be viewed as a reduction of the effective porosity of the porous medium [Morley et al, 1998].…”