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Unformatted text preview: Visualization of biocolloid transport processes at the pore scale under saturated and unsaturated conditions Arturo A. Keller and Maria Auset Bren School of Environmental Science & Mgmt., Univ. of California, Santa Barbara, CA, USA Abstract Field and columns studies of biocolloid transport in porous media have yielded a large body of information, used to design treatment systems, protect water supplies and assess the risk of pathogen contamination. However, the inherent black-box approach of these larger scales has resulted in generalizations that sometimes prove inaccurate. Over the past 10 to 15 years, pore scale visualization techniques have improved substantially, allowing the study of biocolloid transport in saturated and unsaturated porous media at a level that provides a very clear understanding of the processes that govern biocolloid movement. For example, it is now understood that the reduction in pathways for biocolloids as a function of their size leads to earlier breakthrough. Interception of biocolloids by the porous media used to be considered independent of fluid flow velocity, but recent work indicates that there is a relationship between them. The existence of almost stagnant pore water regions within a porous medium can lead to storage of biocolloids, but this process is strongly colloid-size dependent, since larger biocolloids are focused along the central streamlines in the flowing fluid. Interfaces, such as the Air-Water Interface, the Soil-Water Interface and the Soil-Water-Air interface, play a major role in attachment and detachment, with significant implications for risk assessment and system design. Important research questions related to the pore-scale factors that control attachment and detachment are key to furthering our understanding of the transport of biocolloids in porous media 1 Introduction The transport of biocolloids (e.g. viruses, bacteria, spores and other microorganisms) through saturated and unsaturated porous media is of significant interest, from the perspective of protection of groundwater supplies from contamination (e.g. Moe et al., 1985; Harvey et al., 1995; Surampalli et al., 1997; Matthess et al., 1988; Redman et al., 2001; Pitt et al., 1999), assessment of risk from pathogens in groundwater (e.g. Bitton and Gerba, 1984; Frankenberger, 1985; Goyal et al., 1989; Hagerdon et al., 1981; Herbold-Paschke et al., 1991; Scandura and Sobsey, 1997; Yates and Yates, 1988; Adelman et al., 1998; Detay et al., 1989; Snowdon and Coliver, 1989; Bruins et al., 2000; Morris and Foster, 2000; Rose et al., 2000; Nola et al., 2001; Taylor et al., 2004), natural and enhanced bioremediation (e.g. Rittman et al., 1992; Norris et al., 1993; Wilson and Jones, 1993; Allard and Neilson, 1997; Foght et al., 2001; Ebihara and Bishop, 2002; Fiorenza and Rifai, 2003; Adriano et al., 2004; Kalogerakis et al., 2005) and for the design of better water treatment systems to remove biocolloids from drinking water supplies (e.g. Gerba of better water treatment systems to remove biocolloids from drinking water supplies (e....
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