Transport of Cryptosporidium parvum oocysts in soil columns following applications of raw and separated liquid slurry

The potential for the transport of viable Cryptosporidium parvum oocysts through soil to land drains and groundwater was studied using simulated rainfall and intact soil columns which were applied raw slurry or separated liquid slurry. Following irrigation and weekly samplings over a 4-week period, C. parvum oocysts were detected from all soil columns regardless of slurry type and application method, although recovery rates were low (<1%). Soil columns with injected liquid slurry leached 73 and 90% more oocysts compared to columns with injected and surface-applied raw slurries, respectively. Among leachate samples containing oocysts, 44/72 samples yielded viable oocysts as determined by a dye permeability assay (DAPI [4′,6′-diamidino-2-phenylindole]/propidium iodide) with the majority (41%) of viable oocysts found in leachate from soil columns with added liquid slurry. The number of viable oocysts was positively correlated (r = 0.63) with the total number of oocysts found. Destructively sampling of the soil columns showed that type of slurry and irrigation played a role in the vertical distribution of oocysts, with more oocysts recovered from soil columns added liquid slurry irrespective of the irrigation status. Further studies are needed to determine the effectiveness of different slurry separation technologies to remove oocysts and other pathogens, as well as whether the application of separated liquid slurry to agricultural land may represent higher risks for groundwater contamination compared to application of raw slurry

Effect of the Lower Boundary Condition and Flotation on Colloid Mobilization in Unsaturated Sandy Sediments

In unsaturated soil columns, the boundary condition imposed at the column outlet may cause experimental artifacts. Our objective was to study in situ colloid mobilization during transient, unsaturated flow as affected by the boundary condition at the column outflow. We conducted colloid mobilization experiments by infiltrating unsaturated sandy sediment columns under different bottom boundary conditions: a seepage and a suction control. The mechanisms of colloid mobilization were investigated using force calculations (adhesive and interfacial forces), complemented with flotation experiments, where colloids in the bulk fluid and at the liquid–gas interface were measured separately. More colloids were mobilized under seepage than under suction‐controlled boundary conditions. The shape of the colloid breakthrough curves also differed: for the seepage boundary, the maximum of the colloid concentration occurred at the beginning of the column outflow, but for the suction‐controlled boundary, colloid concentrations in the outflow increased gradually before reaching a maximum. Colloid mobilization increased with flow rate and decreased with ionic strength for both boundary conditions; however, colloids were mobilized even at ionic strength exceeding the critical coagulation concentration (CCC). Flotation experiments showed that colloids were located both in the bulk fluid and at the liquid–gas interface at electrolyte concentrations less than the CCC, but only at the liquid–gas interface when the CCC was exceeded. Theoretical considerations confirm that interfacial forces at the liquid–gas interface exceeded adhesive forces at all ionic strengths. Both experiments and theory show that the liquid–gas interface had a dominant effect on colloid mobilization

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

Pathogens may reach agricultural soils through application of animal manure and thereby pose a risk of contaminating crops as well as surface and groundwater. Treatment and handling of manure for improved nutrient and odor management may also influence the amount and fate of manure-borne pathogens in the soil. A study was conducted to investigate the leaching potentials of a phage (Salmonella enterica serovar Typhimurium bacteriophage 28B) and two bacteria, Escherichia coli and Enterococcus species, in a liquid fraction of raw pig slurry obtained by solid-liquid separation of this slurry and in this liquid fraction after ozonation, when applied to intact soil columns by subsurface injection. We also compared leaching potentials of surface-applied and subsurface-injected raw slurry. The columns were exposed to irrigation events (3.5-h period at 10 mm h(−1)) after 1, 2, 3, and 4 weeks of incubation with collection of leachate. By the end of incubation, the distribution and survival of microorganisms in the soil of each treatment and in nonirrigated columns with injected raw slurry or liquid fraction were determined. E. coli in the leachates was quantified by both plate counts and quantitative PCR (qPCR) to assess the proportions of culturable and nonculturable (viable and nonviable) cells. Solid-liquid separation of slurry increased the redistribution in soil of contaminants in the liquid fraction compared to raw slurry, and the percent recovery of E. coli and Enterococcus species was higher for the liquid fraction than for raw slurry after the four leaching events. The liquid fraction also resulted in more leaching of all contaminants except Enterococcus species than did raw slurry. Ozonation reduced E. coli leaching only. Injection enhanced the leaching potential of the microorganisms investigated compared to surface application, probably because of a better survival with subsurface injection and a shorter leaching path