Adsorption is the process by which a substance attaches to a surface. A Water Distribution System (WDS) presents surfaces, such as the pipe wall, to which dissolved contaminants may adsorb. This will affect the fate and transport of contaminants that have been accidentally or intentionally introduced into the system. This thesis investigates models for contaminant transport in a WDS that account for adsorption to the pipe wall. A literature review is conducted to determine the characteristics of the pipe wall and what adsorption modeling approaches may be used. Two of these approaches are applied in the context of WDS modeling.
A kinetic adsorption model based on the Langmuir isotherm is presented and applied to a WDS. A sensitivity analysis is performed on the dimensionless form of the model in a single pipe. An arsenic intrusion event is simulated in a model WDS, and an exposure analysis is used to
study the effect of adsorption on the fate and transport of the contaminant. The single pipe and network scale studies indicate that the adsorption model predicts significantly different results from a nonreactive tracer model. Adsorption model results are found to be sensitive to the local equilibrium assumption.
A kinetic adsorption model known as the Homogeneous Surface Diffusion Model (HSDM) is presented and derived for the geometry of a pipe wall. A numerical solution procedure using the finite difference technique is described. Cases of stagnant and turbulent flow are considered. Illustrative results are presented for a single pipe which show the capabilities of the HSDM. A comparison between the Langmuir kinetic model and the HSDM is made. For a given equilibrium time and corresponding parameter sets, the HSDM predicts more adsorption sooner than the Langmuir kinetic model.