Recently, there has been increased interest in microcystin-LR and other fresh water cyanotoxins because of their toxicity and occurrence throughout the world. Although previous studies have shown that free chlorine can degrade microcystin-LR, there are insufficient data to develop the contact times and free chlorine doses that achieve targeted levels of microcystin-LR degradation. Furthermore, there are insufficient microcystin-LR degradation data that would allow for the development of feasible microcystin-LR criteria or standards. To systematically develop this critical information, a total of 34 batch chlorination experiments were performed at different pH values, chlorine doses, and toxin concentrations. For all conditions, Ct (C = chlorine concentration, t = contact time) values required for degradation of microcystin-LR were calculated and safety factors were estimated. Twenty seven of the 34 experiments were conducted with reagent-grade water and seven of the 34 experiments were conducted with natural waters. At all pH values tested, the degradation of microcystin-LR increased with increasing Ct. For Ct values usually observed in drinking water treatment, a 1-log degradation of microcystin-LR in reagent-grade water was observed only at pH 6.0. The results also suggest that the Ct values obtained from reagent-grade water experiments are appropriate for application to natural waters that have been subjected to conventional coagulation, flocculation, sedimentation, and filtration prior to chlorine addition.
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Research Article|
June 01 2006
Ct values required for degradation of microcystin-LR by free chlorine
Irene Xagoraraki;
1Department of Civil and Environmental Engineering, Michigan State University, A136 Engineering Research Complex, East Lansing, MI, 48824, USA
E-mail: xagorara@egr.msu.edu
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Kimberly Zulliger;
Kimberly Zulliger
1Department of Civil and Environmental Engineering, Michigan State University, A136 Engineering Research Complex, East Lansing, MI, 48824, USA
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Gregory W. Harrington;
Gregory W. Harrington
2Department of Civil and Environmental Engineering, University of Wisconsin-Madison, 1415 Engineerign Dr, Madison, WI, 53706, USA
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Benjamin Zeier;
Benjamin Zeier
3EarthTech, Inc., 200 Indianan Avenue, Stevens Point, WI, 54481, USA
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William Krick;
William Krick
4Wisconsin State Laboratery of Hygiene, 2601 Agricultrure Dr., Madison, WI, 53718, USA
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Dawn A. Karner
Dawn A. Karner
4Wisconsin State Laboratery of Hygiene, 2601 Agricultrure Dr., Madison, WI, 53718, USA
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Journal of Water Supply: Research and Technology-Aqua (2006) 55 (4): 233–245.
Citation
Irene Xagoraraki, Kimberly Zulliger, Gregory W. Harrington, Benjamin Zeier, William Krick, Dawn A. Karner; Ct values required for degradation of microcystin-LR by free chlorine. Journal of Water Supply: Research and Technology-Aqua 1 June 2006; 55 (4): 233–245. doi: https://doi.org/10.2166/aqua.2006.0008
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