Modeling transport of colloid-facilitated contaminants and Cryptosporidium parvum oocysts in riverbank filtration

In the first study, mathematical models are developed to describe the contaminant transport in the presence of dissolved organic matter (DOM) and bacteria as mobile colloids in riverbank filtration. In the first model, an equilibrium approach is used to describe the bacterial attachment onto solid matrix and the sorption of contaminants onto solid matrix, DOM, and bacteria. In the second model, the mobile-immobile region approach is used to consider the nonideality of the contaminant transport due to the physical heterogeneity in porous media. In addition, the kinetic expressions are used to describe the bacterial deposition to solid matrix and the contaminant sorption to DOM and bacteria. The model result shows that contaminants can move faster than expected in the aquifer where riverbank filtration is practiced due to the presence of DOM. If bacteria are present with contaminants in the influent river water during riverbank filtration, the mobility of contaminants is enhanced further. Furthermore, contaminants can move faster in dual-porous media where ineffective micropores are present than in single-porous media.; In the second study, a mathematical model is presented to describe the transport of Cryptosporidium parvum oocysts in porous media. C. parvum is a protozoan parasite, causing a gastrointestinal disease in humans and is transmitted through environment in the form of oocyst. In drinking water treatment systems, C. parvum oocysts frequently pass through the filtration system. In addition, the oocysts, breaching the filtration systems, are not readily inactivated with acceptable chlorine concentration. Therefore, riverbank filtration is recognized as an alternative method to remove the oocysts from source water. After model development, the model parameters are estimated by fitting the experimental data with the numerical solutions. Sensitivity analysis shows that the concentration profile is very sensitive to the change of the Damköhler numbers. In addition, the governing equations are modified to simulate the vertical transport of oocysts in saturated porous media. The settling velocity of oocysts and the permeability reduction are incorporated into the equations. The model result shows that the settling velocity should be counted to simulate the vertical transport of oocysts in porous media.