Oxidation of microcystin-LR by the Fenton process: Kinetics, degradation intermediates, water quality and toxicity assessment

The Fenton process was assessed as a cost-effective technology for the removal of Microcystin-LR (MC-LR) among UV, UV/H₂O₂, and Fenton process according to efficiency and electrical energy per order (EE/O). The determined practical concentrations of the Fenton reagents were 5 mg/L Fe(II) and 5 mg/L H₂O₂, respectively. The Fenton process is a fast reaction, completed within 5–30 min (Fe(II), H₂O₂ = 0.2–10 mg/L; MC-LR₀ = 200 μg/L). The degradation intermediates of MC-LR by the Fenton process were firstly reported as m/z 1029.5, 1011.5, 835.5, 795.4, and 783.4, associated with the diene bond in the Adda chain, then alleviate their toxicity. The effects of organic matter were examined in the range of Nak-Dong River water, as a drinking water source, monitored for six months in 2015. Fulvic acid was affected more than humic acid and natural organic matter (NOM). The degradation efficiency in the raw water was lower than that of distilled water because of the competing effect of NOM, geosmin, and 2-methylisoborneol, and the higher pH (7.64), furthermore, dissolved organic matter, geosmin, and 2-methylisoborneol was removed 7.39%, 4.28% and 12.30% after the Fenton process in the river water. The final concentration of MC-LR after treatment was under the drinking water guideline level with initial MC-LR concentration of 2 μg/L. No acute toxicity was observed to Daphnia magna (TU = 0) after the Fenton process.