Transport of Cryptosporidium Oocysts in Porous Media:  Role of Straining and Physicochemical Filtration

Abstract

The transport and filtration behavior of Cryptosporidium parvum oocysts in columns packed with quartz sand was systematically examined under repulsive electrostatic conditions. An increase in solution ionic strength resulted in greater oocyst deposition rates despite theoretical predictions of a significant electrostatic energy barrier to deposition. Relatively high deposition rates obtained with both oocysts and polystyrene latex particles of comparable size at low ionic strength (1 mM) suggest that a physical mechanism may play a key role in oocyst removal. Supporting experiments conducted with latex particles of varying sizes, under very low ionic strength conditions where physicochemical filtration is negligible, clearly indicated that physical straining is an important capture mechanism. The results of this study indicate that irregularity of sand grain shape (verified by SEM imaging) contributes considerably to the straining potential of the porous medium. Hence, both straining and physicochemical filtration are expected to control the removal of C. parvum oocysts in settings typical of riverbank filtration, soil infiltration, and slow sand filtration. Because classic colloid filtration theory does not account for removal by straining, these observations have important implications with respect to predictions of oocyst transport.

Surface Characteristics and Adhesion Behavior of Escherichia coli O157:H7: Role of Extracellular Macromolecules

“…The average sand diameter (d 50 ) was approximately 275 µm and the shape of the sand was irregular. 66 The quartz sand was thoroughly cleaned using 12 N HCl (Fisher Scientific) and baked at 800°C for at least 8 h to remove any organic impurities from the sand. 22 Five different solution IS were considered in this study (0.01, 0.1, 1, 10, and 100 mM).…”

Solid mechanics in colloidal and bacterial filtration

“…The particle/bacterial concentration at outlet are measured as function of time which is named as breakthrough curve (Hendry et al, 1999;Y. Li et al, 2014;Tufenkji & Elimelech, 2004a, 2004bTufenkji, Miller, Ryan, Harvey, & Elimelech, 2004 Compared to field scale test, column test provides a better degree of control and thus, allows a detailed investigation of specific factors affecting microbial/particle filtration, for example, flow rate, grain size and column length. However, it cannot account for coupled effects of different factors, especially more factors were reveal and proven to affect filtration.…”

“…Grain size and shape contribute potentially to physical straining and clogging (Tufenkji, 2007;Tufenkji et al, 2004). Bradford investigated the impact of grain size and particle size on particle transport using column packed with glass spheres (Scott A Bradford, Bettahar, Simunek, & Van Genuchten, 2004;Scott A Bradford, Simunek, Bettahar, van Genuchten, & Yates, 2003;Scott A Bradford, Yates, Bettahar, & Simunek, 2002).…”

“…Physical straining and clogging could play a significant role when the ratio of the particle diameter to the medium grain diameter is greater than 0.05. Some studies showed that this critical ratio could be as low as 0.002 (Scott A Bradford et al, 2004;Scott A Bradford et al, 2002;Tufenkji et al, 2004). Note that Tufenkji (Tufenkji et al, 2004) tested the contribution of physical straining in removal by using DI water.…”

“…Some studies showed that this critical ratio could be as low as 0.002 (Scott A Bradford et al, 2004;Scott A Bradford et al, 2002;Tufenkji et al, 2004). Note that Tufenkji (Tufenkji et al, 2004) tested the contribution of physical straining in removal by using DI water. With grain diameter of 0.21 mm, degree of removal for particle with diameter from 0.32-1.9 m is minor.…”