Modeling the Impact of Microbial Intrusion on Secondary Disinfection in a Drinking Water Distribution System
Publication: Journal of Environmental Engineering
Volume 134, Issue 4
Abstract
The purpose of this study was to quantify the potential level of protection that secondary disinfection may provide in response to an intrusion event. Although several uncertainties exist regarding intrusion events, this study presents an analysis of the inactivation provided by disinfectant residuals by using a distribution system model, inactivation and disinfectant decay models, and conservative assumptions based on available data. A variety of conditions were modeled, including a range of water quality parameters (pH, temperature); inactivation of two microorganisms, Giardia and E. coli O157:H7; and intrusion water dilution ratios. Despite the assumptions inherent in the model, several generalizations were derived from the study. A free chlorine residual of may be insufficient to provide adequate control of disinfectant-resistant Giardia even at low pH (6.5) and high temperature conditions that enhance chlorine effectiveness. For E. coli, an organism of “average” disinfectant resistance relative to others, a residual of may provide ample protection against intrusion even assuming that the chlorine residual is reduced within several minutes, such as would be predicted to occur with sewage intrusion at levels below 1% of the total flow. Importantly, chloramines may have a negligible benefit in terms of protecting against intrusion for even relatively susceptible organisms such as E. coli. Consequently, systems should consider protection against intrusion when choosing their secondary disinfectant.
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Acknowledgments
This study was funded as part of American Water Works Association Research Foundation Project No. UNSPECIFIED2771. The writers gratefully acknowledge that the AWWA Research Foundation (AWWARF) is the joint owner of the technical information upon which this manuscript is based. The writers also thank the Foundation and the U.S. Government, through the Environmental Protection Agency for its financial, technical, and administrative assistance in funding and managing the project through which this information was discovered. The comments and views detailed herein may not necessarily reflect the views of the AWWA Research Foundation, its officers, directors, affiliates or agents, or the views of the U.S. Federal Government. The views expressed in this article are those of the individual writers and do not necessarily reflect the views and policies of the U.S. Environmental Protection Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 134 • Issue 4 • April 2008
Pages: 231 - 237
Copyright
© 2008 ASCE.
History
Received: Apr 24, 2006
Accepted: Jul 13, 2007
Published online: Apr 1, 2008
Published in print: Apr 2008
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