Disinfection By-Product Formation during Long-Term Water Storage in Alaska
Publication: Journal of Cold Regions Engineering
Volume 20, Issue 4
Abstract
In many areas of Northern and Western Alaska, small streams and shallow lakes serve as community raw water supplies. These water supplies freeze completely during winter. In order to supply drinking water during the 6–9 month winter, communities store water that was treated during summer. A chlorine residual is maintained in the stored water. Raw water sources derived from surface water may be heavily laden with dissolved organic matter. At utilities where organic matter escapes treatment, the potential for accumulation of disinfection by-products (DBPs) during storage is a significant health concern. The following study was performed to evaluate this potential threat. Water was collected from five operating utilities, four that normally store water for 6–9 months and one that produces drinking water year-round. Raw, filtered (i.e., unchlorinated) and “finished” (i.e., filtered and chlorinated) water samples were collected during the summer pumping season and stored in the laboratory for 8 months. In order to mimic practice in the field, the chlorine residual was maintained in the finished water for the full storage period. While the concentration of DBPs in the finished water varied over the study period, there was not a statistically significant trend from the third to the eighth month of storage. The observed DBP values were strongly a function of the type of treatment system used. Those systems passing more organic matter had higher DBP values throughout the storage period. The ultraviolet absorbance at 254 nanometers decreased continuously in the finished water coincident with chlorine consumption. , often used as a surrogate for DBPs, remained constant during the entire storage periodin raw and filtered water samples. Filtered water that was stored prior to chlorination accumulated fewer DBPs than finished water that was continuously chlorinated during the storage period. This result suggests that storing filtered water instead of finished water for long periods would limit DBP exposure to consumers. This conclusion was based on a comparison of DBP formation potentials (i.e., raw and filtered water) to DBPs (i.e., finished water). It is important to note that DBP formation potentials are based on a chlorine contact time. If long term storage were provided for filtered water, a smaller volume of secondary storage would still be needed to provide contact time for disinfection.
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Acknowledgments
This work was supported in part by the USEPA-funded Alaska Training and Technical Assistance Center and National Science Foundation–EPSCoR Grant No. NSFEPS-0092040. The writers gratefully acknowledge the assistance of water plant operators for their cooperation and participation in the study. The writers also thank Dr. John Kennish at the University of Alaska Anchorage ASET Laboratory for the performing the DBP analyses.
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© 2006 ASCE.
History
Received: Mar 15, 2005
Accepted: Feb 7, 2006
Published online: Dec 1, 2006
Published in print: Dec 2006
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