Particle transport through porous media

Abstract

The authors are to be commended for their thorough and timely review [McDowell-Boyer et al., 1986] on the subject of particle transport through porous media. It was felt, however, that they have not followed far enough their own streams of thoughts. Despite the detailed descriptions of current perceptions how particles get separated from the carrying liquid and how they interact with the porous media, little attention was paid to the fact why they can be transported over hundreds of meters. The authors mentioned the studies by Smith et el.[1985], who reported microbial breakthrough at the 0.3-m depth of undisturbed soil columns within 17-50 min. Gerba and Goyal's [1985] study is also cited according to which bacteria had moved over distances of more than 800 m. However, no discussion is offered about the discrepancy between these and many other reported observations on fast and farreaching particle transport in porous media and the lack of models dealing with this kind of transport. Corapcioglu and Haridas [1985], for instance, presented an approach to the transport of microorganisms through porous media. No matter how these authors stressed the flow parameters (they went to the permissible limits), their model strongly indicated that bacteria cannot be transported over distances exceeding 0.2 m under the commonly accepted constrains of the model.The reasons for these deficiencies in the perception of particle transport through porous media, as they are well represented in this review article, can be traced back to the early beginnings of groundwater hydrology. It was Darcy's [1856] cracks. Voids which support particle transport have diameters at least an order of magnitude greater than the particles that move. This movement results in readily recognizable accumulations of silt (siltants) or clay (argilans) coatings on the surfaces of the voids, eventually plugging them. Filter theory conceptualizes the porous media as homogenous, whereas microscopists conceptualize the same media as inhomogeneous [Jeans, 1986; Bullock et al., 1985]. Thus surface accumulation is, indeed, observed but at much smaller scales. Pores only 50/•m wide are often distinctly lined with clay particles. Apparently, water carrying them through those pores lost its dragging power due to loss of momentum. This 10ss can be caused by decreasing flow velocity, by the reduction of mass flow due to water sorption into the finer pores surrounding the flow paths, or by any combination of the two. Gerba and Biton [1984], for instance, reported from groundwater flow studies that the bulk of larger Escherichia coil appeared about 1 hour earlier in an observation well 160 m downstream from an injection well than the bulk of the much smaller coliphage f2. Likewise, Harvey et al. [1986] reported that the peak abundance during fractional breakthrough of carboxylated microspheres at 1.5 m from the point of injection was highest for the 1.2-/•m diameter size class, followed by the 0.7-and 0.2-#m microspheres. This indicates that some of the larger partic...

Processes in microbial transport in the natural subsurface

“…Indeed, the impact of biological processes in a flowing groundwater system can only be evaluated within this physicochemical framework. Readers are referred to reviews by Harvey et al [51] and McDowell-Boyer et al [167] for more thorough discussions of these processes.…”

“…Straining is the trapping of microbes in pore throats that are too small to allow passage and is exclusively a result of pore geometry [25]. Estimates based on purely geometric relations between the effective diameter of biocolloids and the diameter and packing (coordination number) of grains suggest that mass removal by straining is not significant where the colloid diameter is less than 5% of the porous media grain diameter [25,51,155,167,176,177]. It should be noted that in natural heterogeneous porous media, a fraction of the pore diameters may be small enough to cause straining of colloidal particles even though the average grain diameter passes this rule of thumb for non-significance of straining.…”

“…The literature contains a helpful clarification on the use of the analytical expressions for g [70], as well as a summary of CFTÕs major assumptions and the implications for modeling bacterial transport in natural porous media [83]. Sedimentation is filtration due to gravity [25,167] and depends on particle buoyancy [185]. Many natural bacteria and viruses are neutrally buoyant, in which case sedimentation is negligible.…”

Self-assembly of three-dimensional open structures using patchy colloidal particles

“…They possess striking properties such as negative Poisson's ratio [1][2][3][4], negative thermal expansion [5,6], and beyond [7,8], leading to many interesting applications in engineering.…”

Imaging of colloidal deposits in granular porous media by X‐ray difference micro‐tomography

“…Filtration models, summarized by [McDowell-Boyer et al, 1986;Elimelech et al, 1995;Tufenkji and Elimelech, 2004], normally assume fixed pore geometry and parameterize deposition rates in terms of the size ratio between mobile suspended particles and pore spaces. Recent investigations have shown that the internal variability of the porous medium plays an important role in the overall filtration process, and that enhanced deposition can be caused by straining at grain contacts [Johnson et al, 1996;Bradford et al, 2004;Li et al, 2006;Xu et al, 2006].…”