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Published Online: 28 June 2016

Impact of Light Screening and Photosensitization by Surface Water Organic Matter on Enterococcus Faecalis Inactivation

Publication: Environmental Engineering Science
Volume 33, Issue Number 6


Sunlight irradiation is known to contribute to microbial inactivation in natural treatment systems (NTS) and surface waters via both direct and indirect processes. This study investigated the influence of various types of organic matter (OM) on endogenous and exogenous photoinactivation of Enterococcus faecalis. Solar simulator exposure experiments were conducted in surface waters and wastewater and in the presence of natural OM isolates and a singlet oxygen (1O2) sensitizer, methylene blue. Presence of both natural and anthropogenic OM resulted in increases in inactivation rates of 17–67% compared to sensitizer-free experiments. This suggests that, while direct and endogenous photoinactivation is hindered with increasing depth due to light screening by OM, its role as a photosensitizer in the formation of reactive intermediates (predominantly involving 1O2) is greater than its negative impact due to light screening at levels typically found in NTS. Specifically, increases in light absorbance (particularly at shorter wavelengths) are estimated to reduce direct and endogenous processes by up to 41% under our experimental conditions; however, presence of external photosensitizers enhances exogenous inactivation processes to a greater degree. A novel approach is presented to help estimate endogenous and exogenous inactivation rates of E. faecalis as a function of depth in the presence of OM based on common optical measurements. Implications of this knowledge in informing design parameters (e.g., depth and retention time) of NTS are discussed, thus contributing to both fundamental understanding of photoinactivation processes in surface waters and improvement of treatment unit design.

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Information & Authors


Published In

cover image Environmental Engineering Science
Environmental Engineering Science
Volume 33Issue Number 6June 2016
Pages: 365 - 373


Published online: 28 June 2016
Published in print: June 2016
Published ahead of print: 6 May 2016
Accepted: 7 April 2016
Received: 24 January 2016


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Simón Mostafa
Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder, Colorado.
Matteo Rubinato
Pennine Water Group, Department of Civil and Structural Engineering, University of Sheffield, Sheffield, United Kingdom.
Fernando L. Rosario-Ortiz*, [email protected]
Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder, Colorado.
Karl G. Linden*, [email protected]
Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder, Colorado.


Corresponding author: Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, UCB 428, 1111 Engineering Drive, Boulder, CO 80309. Phone: 303-492-4798; Fax: 303-492-7317; E-mail: [email protected]
Member of AEESP.

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No competing financial interests exist.

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