Degradation of microcystin-RR in water by chlorine dioxide

Due to the potent hepatotoxicity and tumor-promoting activity of microcystins, a successful removal of these toxins during drinking water treatment processes is of increasing concern. The oxidation kinetics of MC-RR by chlorine dioxide (ClO2) was studied with HPLC and characterization of the reaction products was performed with UV-spectrometry, TOC and LC-MS. Our experimental results show that the oxidation process is a second order overall and a first order with respect to ClO2 and MC-RR. The activation energy of MC-RR degradation by ClO2 is 53.07 kJ/mol. The rate constant k of the action can be increased by increasing temperature and decreasing pH value and ranged from 6.11×102 L/(mol·min) to 5.29×102 L/(mol·min) at pH from 3.44 to 10.41 at 10 °C. Reaction products were determined to be organic and volatile, because they could be almost removed from aqueous solution by heating for 15 min at 60 °C. In addition, the main oxidation products have m/z values of 1072 and are identified as di-hydroxy isomers of MC-RR.