Virus Transport in Saturated and Unsaturated Sand Columns

Abstract

The transport of viruses in unsaturated porous media has been a subject of great interest in recent years because of the enhanced removal of these microorganisms compared with saturated conditions. We studied the transport of bacteriophages MS2 and ϕX174, used as surrogate pathogenic viruses, at various water contents and solution chemistries in terms of pH and ionic strength (IS). The objective was to explore the interaction of viruses with the solid–water interfaces (SWI) and air–water interfaces (AWI) for a range of conditions. The experimental data were fitted with a transport model to determine the adsorption (attachment and detachment rate) parameters. Our results show that the retention of viruses in the soil column increases as water saturation decreases when the chemical conditions are favorable for adsorption (pH 7 and relatively high IS). Our analysis indicates that the enhanced retention of ϕX174 viruses at lower water contents is caused by increased attachment to the SWI and that retention by the AWI is not significant. Results obtained from a first series of experiments (pH 9 and low IS) showed insignificant attachment of MS2 viruses to both the SWI and the AWI. The MS2 breakthrough data for a second series of experiments (pH 7 and high IS) did not allow us to separate out the role of the AWI. Although attachment of MS2 viruses to the AWI cannot be ruled out in our experiments, we suspect that the increased retention of this phage under unsaturated condition was also due to enhanced attachment to the SWI. Increased attachment to the SWI under unsaturated conditions is attributed to increased mass transfer of viruses to the SWI due to a reduced diffusion length at lower water contents. Our results demonstrate that if there is any attachment to the AWI, it is reversible. When unfavorable conditions occur for attachment to the SWI, the attached viruses may be detached by moving solid–water–air contact lines (SWA).

Transport of Pathogen Surrogates in Soil Treatment Units: Numerical Modeling

“…Model fits were good with R 2 values ranging from 0.97 to 0.99. The dispersivity value calculated by CXTFIT 2.1 was approximately 0.289 cm, which is typical for these types of experiments, and is consistent with the range of values (0.06 to 0.816 cm) reported by others [38][39][40][41][42][43]. Next, the hydraulics of the HYDRUS model domain was calibrated using the conservative tracer breakthrough curves (BTC).…”

“…That is, with decreasing water content, higher retention of bacteria and viruses in the soil has been observed [24,38,50,51]. Because the air-water interface increases at decreasing water content, the removal and retention of microbes in fine-grained soil, such as the clay loam, should be, at a given water content, greater than in granular soils [24,38,52]. In our study, the water content of the sand and sandy loam soils at the end of the experiment was lower (0.15 and 0.23 g/g, respectively), compared to the clay loam soil (0.32 g/g; Table 2).…”

Persistence and Leaching Potential of Microorganisms and Mineral N in Animal Manure Applied to Intact Soil Columns

“…The percentages of surviving microorganisms recovered in S2 to S4 followed the order Enterococcus species Ͻ E. coli Ͻ phage. Movement of microorganisms as the slurry infiltrates into the soil after application will be impeded by physical straining and chemical attachment to the soil matrix (10,49), so size and shape are likely important for their transport in soil. Enterococcus species cells are spherical and approximately 0.5 to 1 m in size (50), but the cells are organized in chains; E. coli cells are rod shaped and are 0.7 to 1.5 m long (44,51); and phages are circular, with a diameter of 0.03 to 0.07 m (52).…”

Internalization of Murine Norovirus 1 by Lactuca sativa during Irrigation

“…Low water content could increase virus particle attachment to soil-water interfaces, favor virus adsorption, and result in retention of virus movement in soil with a lesser access to plants (20). To favor the virus uptake, in this study saturated soil conditions were maintained with nutrient buffer during the entirety of the experiments.…”