Xiaojun Dai

Bio: Xiaojun Dai is an academic researcher from University of Minnesota. The author has contributed to research in topics: Corrosion & Cryptosporidium parvum. The author has an hindex of 3, co-authored 3 publications receiving 155 citations.

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

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...

Effect of particle size and natural organic matter on the migration of nano- and microscale latex particles in saturated porous media

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.

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.

Transport and Fate of Microbial Pathogens in Agricultural Settings

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...