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J Water SRT - Aqua 55 (2006) 233-245
Ct values required for degradation of microcystin-LR by free chlorine
Irene Xagoraraki, Kimberly Zulliger, Gregory W. Harrington, Benjamin Zeier, William Krick and Dawn A. Karner
Department of Civil and Environmental Engineering, Michigan State University, A136 Engineering Research Complex, East Lansing, MI, 48824, USA, xagorara@egr.msu.edu
Department of Civil and Environmental Engineering, Michigan State University, A136 Engineering Research Complex, East Lansing, MI, 48824, USA, xagorara@egr.msu.edu
Department of Civil and Environmental Engineering, University of Wisconsin-Madison, 1415 Engineerign Dr, Madison, WI, 53706, USA
EarthTech, Inc., 200 Indianan Avenue, Stevens Point, WI, 54481, USA
Wisconsin State Laboratery of Hygiene, 2601 Agricultrure Dr., Madison, WI, 53718, USA
Department of Civil and Environmental Engineering, Michigan State University, A136 Engineering Research Complex, East Lansing, MI, 48824, USA, xagorara@egr.msu.edu
ABSTRACT
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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