Contaminant transport in riverbank filtration in the presence of dissolved organic matter and bacteria: a kinetic approach

In riverbank filtration, the removal of organic contaminants is an important task for the production of good quality drinking water. The transport of an organic contaminant in riverbank filtration can be retarded by sorption on to the solid matrix and facilitated by the presence of mobile colloids. In the presence of dissolved organic matter (DOM) and bacteria, the subsurface environment can be modeled as a four-phase porous medium: two mobile colloidal phases, an aqueous phase, and a solid matrix. In this study, a kinetic model is developed to simulate the contaminant transport in riverbank filtration in the presence of DOM and bacteria. The bacterial deposition and the contaminant sorption on bacteria and DOM are expressed with kinetic expressions. The model equations are solved numerically with a fully implicit finite difference method. Simulation results show that the contaminant mobility increases greatly in riverbank filtration due to the presence of DOM. The mobility can be enhanced further when the bacteria and DOM are present together in the aquifer. In this system, the total aqueous phase contaminant concentration, Cct+, includes the contaminant dissolved in the aqueous phase, Cc+, the contaminant sorbed to DOM, σcd+, and the contaminant sorbed to mobile bacteria, Cb+σcbm+, (i.e. Cct+=Cc++σcd++Cb+σcbm+). Sensitivity analysis illustrates that the distribution of the total aqueous phase contaminants among the dissolved phase, DOM and bacteria is changed significantly with various Damköhler numbers related to the contaminant sorption on mobile colloids.