Colloid Transport and Filtration of Cryptosporidium parvum in Sandy Soils and Aquifer Sediments

Abstract

We present theoretical and experimental work on Cryptosporidium parvum oocysts to characterize their transport behavior in saturated, sandy sediments under strictly controlled conditions. Column experiments are implemented with three different sands (effective grain size: 180, 420, and 1400 μm) at two different saturated flow rates (0.7 and 7 m/d). The experiments show that C. parvum oocysts, like other colloids, are subject to velocity enhancement. In medium and coarse sands, the oocysts travel 10−30% faster than a conservative tracer. The classic clean-bed filtration model is found to provide an excellent tool to estimate the degree of C. parvum filtration. Experimentally determined collision efficiencies, α, range from 0.4 to 1.1. The magnitude of α is consistent with the known physical and chemical properties of the oocyst and the transport medium and compares well with, e.g., measured collision efficiencies of similarly sized E. coli bacteria. However, a significant amount of the initial deposition appears to be reversible leading to significant asymmetry and tailing in the oocyst concentration breakthrough curve. We are able to show that the observed late-time oocyst elution can qualitatively be explained by postulating that a significant fraction of the oocyst filtration is reversible and subject to time-dependent detachment.

Processes in microbial transport in the natural subsurface

“…The mechanics and modeling of pore exclusion has been recently debated [44,98]. In coarse-grained media size exclusion is a larger factor than pore exclusion [49], because the excluded particle is far smaller than almost all pores. However, exclusion is not consistently manifest in larger-scale field studies, cf.…”

“…However, exclusion is not consistently manifest in larger-scale field studies, cf. [53] even under consistent conditions, and so the final impact over long-term transport is unknown [49].…”

“…The analysis involves a constitutive ÔspeedupÕ function that tells how travel-times of non-excluded particles map to those of excluded particles. An inverse operator that identifies the speedup function given experimentally observed cumulative arrival distributions (e.g., breakthrough curves) of excluded and unexcluded particles in the same flow field is derived, and used in analysis of data on cryptosporidium breakthroughs in saturated columns, from Harter et al [49]. Scheibe et al [106] modeled exclusion phenomena observed in core experiments using a modified particle tracking approach.…”

E. coliFate and Transport in Macroporous Soils: Short-Circuiting to the Subsurface

“…Numerous researchers have noted that the primary transport of pathogenic microorganisms in soils occurs through macropores that bypass the filtering and adsorptive effects of soil and therefore increases the risk of ground water contamination (Mawdsley et al, 1996a(Mawdsley et al, , 1996bHarter et al, 2000;Logan et al, 2001;McGechan and Vinten, 2003;Darnault et al, 2004). Without macropores, downward percolation of pathogens through the soil matrix is generally insignificant because soils are usually an effective filter (Darnault et al, 2004).…”

Bacteriophage transport through a fining-upwards sedimentary sequence: laboratory experiments and simulation

“…These studies have included investigations into transport and attenuation of the major microbiological groups that pose significant threat to public health, including protozoa, (e.g. Harter et al (2000)), bacteria, (e.g. Bolster et al (1999)) and viruses (e.g.…”