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Journal ArticleDOI

Evaluation of microspheres as surrogates for Cryptosporidium parvum oocysts in filtration experiments.

01 Mar 2003-Environmental Science & Technology (American Chemical Society)-Vol. 37, Iss: 5, pp 1037-1042
TL;DR: Comparisons of zeta potential, hydrophobicity, and filterability of a surrogate particle, 5 microm carboxylated latex microspheres, and oocysts in filtration and particle transport experiments suggest that micro Spheres can be used to provide a conservative estimate of oocyst removal in filters containing hydrophilic negatively charged filter media.
Abstract: The size and surface characteristics of a surrogate particle and Cryptosporidium parvum oocysts are important in determining the ability of the particle to mimic the behavior of C. parvum oocysts in filtration and particle transport experiments. The ζ potential, hydrophobicity, and filterability of a surrogate particle, 5 μm carboxylated latex microspheres, and oocysts were compared for a variety of solution conditions. C. parvum oocysts had a slightly negative ζ potential (−1.5 to −12.5 mV) at pH 6.7 over a wide range of calcium concentration (10-6−10-1 M), while the fluorescent microspheres were more negatively charged under the same conditions (−7.4 to −50.2 mV). After exposure to 5 mg of C/L of Suwanee River natural organic matter (NOM), the ζ potentials of both particles became significantly more negative, with the microspheres consistently maintaining a more negative ζ potential than the oocysts. Alum was able to neutralize the negative ζ potentials of both particles when in the presence of NOM, but...
Citations
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Journal ArticleDOI
TL;DR: Technical information on conventional and alternative drinking water treatment technologies for removal and inactivation of the protozoan parasites Cryptosporidium and Giardia is provided.

424 citations


Cites background from "Evaluation of microspheres as surro..."

  • ...…oocysts, like Giardia cysts, are organisms that can be physically removed from water supplies by conventional particle separation processes including chemical coagulation–flocculation, clarification (sedimentation), and granular media filtration (Bellamy et al., 1993; Dai and Hozalski, 2003)....

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Journal ArticleDOI
TL;DR: Traditional modeling approaches used to predict the migration and removal of microorganisms in saturated porous media are systematically evaluated and recently proposed improvements to the most commonly used filtration model are discussed, with particular consideration of straining and microbe motility.

320 citations


Cites background from "Evaluation of microspheres as surro..."

  • ...Specifically, the role of solution ionic strength and composition [33,65,133,134], grain size and shape [21,54,82,134], fluid velocity [54], and collector surface heterogeneity [1] has been examined....

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  • ...The limited body of literature on this subject is focused on the filtration behavior of Cryptosporidium parvum [1,21,33,54,65,82,133,134] and Giardia lamblia [65]— two waterborne pathogens of considerable concern [81,143]....

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Journal ArticleDOI
01 May 2008
TL;DR: Results of particle transport experiments combined with particle characterization measurements suggest that the decrease in colloid attachment in the presence of SRHA is related to the combined influence of the mechanisms of charge stabilization and steric stabilization.
Abstract: In the interest of fully assessing the potential environmental risks linked to "nanolitter," we need to be able to predict the persistence, toxicity, and mobility of engineered nanomaterials in the natural subsurface environment. To examine the effects of particle size and natural organic matter on nanoparticle mobility, laboratory-scale filtration experiments were performed using different sized model nanomaterials (i.e., latex colloids having diameters of 50, 110, and 1500 nm) in the presence and absence of 5.0 mg/L Suwannee River humic acid (SRHA). At low ionic strengths (1-10 mM KCl), an increase in attachment efficiency (alpha) with increasing particle size was observed. This result contrasts with predictions of particle filtration based on attachment in the primary energy minimum of the particle-grain interaction energy profile evaluated using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The presence of SRHA generally resulted in a decrease in alpha over the range of experimental conditions investigated. Results of particle transport experiments combined with particle characterization measurements suggest that the decrease in colloid attachment in the presence of SRHA is related to the combined influence of the mechanisms of charge stabilization and steric stabilization.

268 citations

Journal ArticleDOI
TL;DR: The results of this study indicate that irregularity of sand grain shape contributes considerably to the straining potential of the porous medium, and 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 filtrations.
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.

248 citations

Journal ArticleDOI
TL;DR: In this article, a number of transport pathways, processes, factors, and mathematical models often are needed to describe pathogen fate in agricultural settings, and the level of complexity is dramatically enhanced by soil heterogeneity, as well as by temporal variability in temperature, water inputs, and pathogen sources.
Abstract: An understanding of the transport and survival of microbial pathogens (pathogens hereafter) in agricultural settings is needed to assess the risk of pathogen contamination to water and food resources, and to develop control strategies and treatment options. However, many knowledge gaps still remain in predicting the fate and transport of pathogens in runoff water, and then through the shallow vadose zone and groundwater. A number of transport pathways, processes, factors, and mathematical models often are needed to describe pathogen fate in agricultural settings. The level of complexity is dramatically enhanced by soil heterogeneity, as well as by temporal variability in temperature, water inputs, and pathogen sources. There is substantial variability in pathogen migration pathways, leading to changes in the dominant processes that control pathogen transport over different spatial and temporal scales. For example, intense rainfall events can generate runoff and preferential flow that can rapidly transport...

197 citations


Cites background from "Evaluation of microspheres as surro..."

  • ...DOM has also been reported to sorb onto bacterial cell walls and alter their electrophoretic mobility (Gerritsen and Bradley, 1987) and hydrophobicity (Dai and Hozalski, 2003; Harvey et al., 2011; Mohanram et al., 2012)....

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References
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Journal ArticleDOI
TL;DR: The data indicate that C. parvum oocysts are 30 times moreresistant to ozone and 14 times more resistant to chlorine dioxide than Giardia cysts exposed to these disinfectants under the same conditions.
Abstract: Purified Cryptosporidium parvum oocysts were exposed to ozone, chlorine dioxide, chlorine, and monochloramine. Excystation and mouse infectivity were comparatively evaluated to assess oocyst viability. Ozone and chlorine dioxide more effectively inactivated oocysts than chlorine and monochloramine did. Greater than 90% inactivation as measured by infectivity was achieved by treating oocysts with 1 ppm of ozone (1 mg/liter) for 5 min. Exposure to 1.3 ppm of chlorine dioxide yielded 90% inactivation after 1 h, while 80 ppm of chlorine and 80 ppm of monochloramine required approximately 90 min for 90% inactivation. The data indicate that C. parvum oocysts are 30 times more resistant to ozone and 14 times more resistant to chlorine dioxide than Giardia cysts exposed to these disinfectants under the same conditions. With the possible exception of ozone, the use of disinfectants alone should not be expected to inactivate C. parvum oocysts in drinking water.

773 citations

Journal ArticleDOI
TL;DR: In this paper, a model for the initial particle deposition in a deepbed filter with a sphere-in-cell porous media model was presented, and the results indicated that deposition occurs under favorable surface interactions.
Abstract: This paper presents a model for the initial particle deposition in a deepbed filter with a sphere-in-cell porous media model used. The analysis includes all the relevant mechanisms, and the results indicate that deposition occurs under favorable surface interactions. A semiempirical expression relating collection efficiency and operating parameters is presented.

745 citations

Journal ArticleDOI
TL;DR: Techniques for the large-scale isolation of Cryptosporidium oocysts and sporozoites, obtained from the feces of experimentally infected Holstein calves, were developed employing discontinuous sucrose gradients and isopycnic Percoll gradients.
Abstract: Techniques for the large-scale isolation of Cryptosporidium oocysts and sporozoites, obtained from the feces of experimentally infected Holstein calves, were developed employing discontinuous sucrose gradients and isopycnic Percoll gradients. The oocyst recovery method utilized 2 sequential discontinuous sucrose gradients followed by 1 Percoll gradient. Recovered oocysts were essentially free of debris and bacteria and represented 34% of the original oocyst suspension. Sporozoites were recovered from excystation mixtures on a single Percoll gradient. Sixty-three percent of the original sporozoites were recovered with 2.2% contamination by intact oocysts and virtually no oocyst walls. Experimental investigations dealing with the biology of Cryptosporidium and host immune responses to cryptosporidiosis have been imped- ed by the absence of an efficient technique yield- ing contaminant-free oocysts and sporozoites in large numbers. Recently reported oocyst recov- ery techniques (Current and Haynes, 1984; Heine et al., 1984) have been based on the Sheather's flotation method used to isolate other coccidian oocysts. Other methods designed to concentrate oocysts for diagnostic purposes (Willson and

420 citations

Journal ArticleDOI
TL;DR: The present publication briefly describes the technique and its modifications, summarizes results obtained using this method, and suggests several directions for further investigation.
Abstract: Bacterial adherence to hydrocarbons (BATH) is a simple and rapid technique for determining cell-surface hydrophobicity. During recent years, this method has found application in the study of the surface characteristics of a wide variety of bacteria and bacterial mixtures. Correlations have been found between the adherence of bacteria to hydrocarbons and their attachment to other surfaces, including non-wettable plastics, epithelial cells, and teeth. A slight modification of the assay enables the isolation of nonhydrophobic mutants. The present publication briefly describes the technique and its modifications, summarizes results obtained using this method, and suggests several directions for further investigation.

407 citations

Journal ArticleDOI
TL;DR: It is proposed that under these solution conditions, particle deposition and reentrainment are the result of a dynamic process, in which particles are continuously captured and released from secondary minima.
Abstract: The role of humic acid in the transport of negatively charged colloids through porous media was examined. Adsorption of humic acid on latex colloids and silica collectors reduced the deposition of suspended particles and enhanced the reentrainment of deposited particles in porous media. These effects are considered to arise from additional electrostatic and steric contributions to the repulsive interaction energy due to the adsorption of negatively charged humic acid on both the suspended particles and the media collectors. At low ionic strength reversible deposition in shallow secondary minima is hypothesized to be the principal attachment mechanism, independent of the presence of humic acid. It is proposed that under these solution conditions, particle deposition and reentrainment are the result of a dynamic process, in which particles are continuously captured and released from secondary minima. At higher ionic strengths, deposition may be regarded as a combination of two mechanisms: capture in the primary well and capture in the secondary minimum. Theoretical calculations of the attachment efficiency were conducted using two existing mathematical models. The first model is based on deposition in the primary well (interaction force boundary layer, IFBL), and the second model is based on the Maxwell kinetic theory and deposition in the secondary minimum (Maxwell model). Simulations conducted with the Maxwell model provide significantly better fits of the experimental results than those conducted with the IFBL model.

283 citations