Assessment of colloid filtration in natural porous media by filtration theory

Mobile colloids in groundwater aquifers can act as carriers for sorbing contaminants and thereby facilitate contaminant transport. Therefore, the removal efficiency of two natural porous media for colloids with regard to the ionic strength of the solution and the counterion valence has been investigated. Short-pulse experiments were conducted using fluorescence labeled latex colloids in order to investigate their transport behavior. The predictions of the filtration theory concerning the filtration of colloids were confirmed qualitatively. The removal efficiency of a filter bed is influenced by both the type of electrolyte and its concentration as well as the type of the porous medium. An attachment parameter α, which was introduced into Happel's Sphere-in-Cell-Model, describes the dependence of the removal efficiency on the electrolyte concentration qualitatively. The normalization of α by the valence of the dominant counterion describes the removal efficiency independent of the kind of electrolyte.