(325e) Modeling Mechanisms of Contaminant Transport and Accumulation in Water Systems

Stephen Treado, Nick Martys , Mark Kedzierski, Stephanie Watson, Kenneth Cole National Institute of Standards and Technology Gaithersburg, MD 20899

Prepared for 2007 AIChE Annual Conference

Abstract

This paper describes the results of a measurement and modeling research project investigating the transport, accumulation and removal of contaminants from within water supply systems, including piping, fittings and fixtures. The traditional approach for decontaminating plumbing systems is to flush with water at high volumes, primarily because this methodology is most easily implemented, and there are few simple alternatives. However, the effectiveness of this approach has not been demonstrated, and in fact, for several reasons, this may not be the best way to remove contaminants. High velocity water flows in piping systems are in the turbulent regime, and the eddies that are generated tend to inhibit the transport and removal of entrained contaminants. This effects both the initial distribution of contaminants and the removal.

In the modeling component of this project, we investigate the movement of contaminants in various flow geometries (i.e. pipe flow, around obstructions, inlets and outlets). This entails solution of the Navier-Stokes equations for fluid flow, solution of an advection-diffusion equation for the motion of contaminant, and accurate information of the adsorption or desorption of the contaminant on the surface to include as a boundary condition in the advection-diffusion equation. The modeling results are compared to measurements conducted in idealized and real-world flow systems. The effect of turbulent flows on contaminant distribution and removal is evaluated and described.