Vertical transport of Cryptosporidium parvum oocysts through sediments

A mathematical model is presented to describe the vertical transport of Cryptosporidium parvum oocysts through sediments. C. parvum oocyst has a particle diameter of 4.5-5.5 microm and density of 1.025-1.070 g cm3, and so the gravitational sedimentation may play a role in the vertical transport of the oocysts. The setting velocity of the oocystsis calculated and on saturated porous media, was found to be between 2.2 x 10(-5) a nd 8.9 x 10(-5) cm sec(-1). The permeability of porous media may be altered due to the deposition of the oocysts on the solid matrix. In the simulation, the permeability change is determined with an equation from other researches. The model equations are used to simulate the experimental data of an ealier work by other authors and the numerical results show a good fit with them. Simulation results show that when the oocyst suspension is injected continually, the relative permeability of sediments decreases since the volume of theoocysts deposited on the solid matix increases. Sensitivity analysis demonstrates that the profile of the relative permeability is very sensitive to the change of the irreversible deposition rate coefficient of the oocysts, k(ci). As k(ci) increases, the volume of the oocysts immobilized around the inlet boundary increases, resulting in the decrease of the relative permeability.