Impact of Particle Aggregated Microbes on UV Disinfection. II: Proper Absorbance Measurement for UV Fluence
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Volume 132, Issue 6
Abstract
Ultraviolet (UV) absorbance measurements are subject to significant error using a standard spectrophotometer when particles or aggregates that scatter light are present. True UV absorbance for highly turbid waters should be measured using integrating sphere (IS) spectrophotometry that allows the collection of reflected and transmitted radiation simultaneously. This is especially important when the effects of scattering impact UV disinfection—such as with the presence of aggregates. The impact of light scattering of particle-aggregated microbes on UV disinfection was evaluated by comparing standard spectrophotometer and integrating sphere absorbance measurements for UV fluence determination. Spore–clay aggregates in simulated drinking waters and spore aggregates with natural particles from raw waters were induced by flocculation with alum. Coagulated systems significantly decreased the UV inactivation effectiveness compared to the noncoagulated system with the effects more pronounced for raw natural water. Absorbance measurement of suspensions and aggregates using standard spectrophotometry in the calculations of fluence resulted in overdosing whereas the use of IS spectroscopy did not. The results demonstrated that aggregation protected spores from UV disinfection, and that use of proper absorbance measurement techniques, accounting for particle scattering, is essential for correct interpretation of the results.
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Acknowledgments
The writers gratefully acknowledge Professor Regina Sommer, Institute of Hygiene, University of Vienna, Vienna, Austria, for providing Bacillus subtilis spores for this research, and Professor Robert Bagnell, the University of North Carolina at Chapel Hill, who provided microscopic facilities and advice for aggregate imaging. They also thank Professor Michael Lavine and Gil Bohrer, Duke University, Durham, N.C. for their assistance in statistical analysis. The Wilson Water Treatment Plant in Durham, N.C. supplied water used in this research. This research was funded by the USEPA Science to Achieve Results (STAR) Program, Grant No. UNSPECIFIEDR82-9012. At the time of this research, Dr. Mamane was a doctoral candidate in the Department of Civil and Environmental Engineering at Duke University.
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Published In
Journal of Environmental Engineering
Volume 132 • Issue 6 • June 2006
Pages: 607 - 615
Copyright
© 2006 ASCE.
History
Received: Aug 13, 2004
Accepted: Oct 12, 2005
Published online: Jun 1, 2006
Published in print: Jun 2006
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