The Transport of C. Parvum through saturated sand columns
Some outbreaks of waterborne cryptosporidiosis have raised concern about the presence of the protozoan parasite Cryptosporidium parvum (5 µm) in drinking water. Even very low concentrations of the pathogen can lead to infection. The pathogen is shed in the feces of infected mammals and has mostly been associated with surface water supplies. Recent groundwater surveys in Great Britain and the United States have found that C. parvum is present in a significant amount of groundwater samples taken across these countries. Profound understanding of its transport mechanisms in porous media is still widely lacking. There is a need for analyzing the movement of C. parvum through soils and in groundwater. This study investigates the transport and filtration of C. parvum in saturated sand columns with varying grain size and flow velocity.
Experiments were implemented in dual replicates with 10 cm long, 5 cm diameter sand filled columns. After flushing the columns w/ boiled tap water approximately 2.5 pore volumes of water with a known concentration of C. parvum oocysts were injected, followed by another rinse with boiled tap water, all at constant flow rates. The C. parvum oocysts were collected before each experiment at dairies in Tulare county and double sucrose cleaned twice. Fecal samples from one or two high shedding calves provided enough C. parvum oocysts for one experiment (approx. 80 million). To characterize flow velocity and dispersion, chloride was used as inert tracer. Outflow from the columns was collected in increments of 10 ml (approximately 0.1 pore volumes). Both, the column outflow and the sand profile were analyzed for their oocyst content. The grain size (coarse to fine sand) and the velocity (1.7m/day and 17m/day) varied between the experiments.
The filtration rate increased w/ decreasing grain size and flow velocity and the sticking coefficient of C. parvum varied with mean grain size and mean flow velocity. A velocity enhancement of C. parvum in coarse grained porous media was found. Slow detachment/desorption processes can be a significant source of C. parvum, which could help explaining its spread in the environment.