Computational Models to Determine Transport and Hydrolysis Rate Parameters of Contaminants in a Water Distribution System

摘要

The anthrax attacks of September 18, 2001 refocused attention on methods of asymmetric warfare including introduction of contaminants into water distribution systems. To predict the outcome of such an event, previous chemical models of transport in water distribution systems assumed that any contaminant would move through the system via pure hydraulic transport, meaning that the contaminant would not interact with the pipe wall. Such models predict that flushing a system with uncontaminated water would clear away contaminants fairly rapidly. Previous field experience with actual contamination events (O'Brien, 2003) showed that flushing contaminants was quite slow and difficult in practice. For example, in 1980, a chlordane contamination event in Pittsburgh, PA required a flushing program of 8 months duration for 2000 affected customers. For military installations, such a long delay represents an intolerable risk to mission capability (Hock et al., 2005; Ginsberg and Hock, 2004). The research described uses computational chemistry to calculate, ab- initio, time constants associated with sorption, desorption, and hydrolysis using only selective verification by empirical methods. The computational methods used include: molecular dynamics using NAnoscale Molecular Dynamics (NAMD) to describe sorption and desorption, Turbomol and Cosmotherm to obtain correlations to molecular morphology that are less computationally expensive than NAMD, and density functional theory (DFT) combined with the polarizable continuum model (PCM) in Gaussian03 to predict reaction rates of hydrolysis.