Abstract
Microcystin-LR (MC-LR), the most widely known toxin produced in cyanobacteria, is problematic because of its toxicity. This study was carried out to evaluate the capability of ultraviolet photolysis of chlorine(UV/Cl<sub>2</sub>) and ultraviolet photolysis of hydrogen peroxide(UV/H<sub>2</sub>O<sub>2</sub>). Results showed that direct photolysis with 254 nm UV irradiation achieved substantial toxin removal. In particular, in UV/Cl<sub>2</sub> oxidation treatment, the removal rate of MC-LR was improved through various radical reactions that were similar to UV/H<sub>2</sub>O<sub>2</sub>. In the UV/chlorine process at the pH of 7.0, UV irradiation amount of100 mJ/cm<sup>2</sup> and chlorine concentration of 0.3 mg/L, the MC-LR removal rate was 52.0%, indicating that the removal rate was increased by 24% compared to the UV only treatment. In the UV/chlorine and UV/H<sub>2</sub>O<sub>2</sub> process at pH 7.0, the first-order degradation rate constants of MC-LR were 3.1×10<sup>-3</sup>~3.6×10<sup>-3</sup> s<sup>-1</sup> and 2.9×10<sup>-3</sup>~3.7×10<sup>-3</sup> s<sup>-1</sup>, respectively. It was shown that the degradation rate constant of MC-LR was lowered by 19.4% at pH 9.0 compared to that of pH 7.0, where the analysis found that the change in pH affected oxidation ability. UV/H<sub>2</sub>O<sub>2</sub> was not affected by pH. This result affects the energy consumption needed to meet the required 90% elimination of MC-LR.
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