Removal of microcystin-LR using UV-assisted advanced oxidation processes and optimization of photo-Fenton-like process for treating Nak-Dong River water, South Korea

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>UV-assisted advanced oxidation processes (AOPs) are promising for the removal of microcystin-LR (MC-LR), one of cyanotoxins released during harmful algal blooms. Nevertheless, the efficiency and potential of the photo-Fenton-like process (UV-C/Fe(III)/H<SUB>2</SUB>O<SUB>2</SUB>) in treating MC-LR have not been explored in much detail. In this study, MC-LR degradation efficiencies of various UV-assisted AOPs were compared that they were higher in the order: UV-C/Fe(III)/H<SUB>2</SUB>O<SUB>2</SUB> > UV-C/Fe(II)/H<SUB>2</SUB>O<SUB>2</SUB> > UV-A/TiO<SUB>2</SUB> > UV-C/H<SUB>2</SUB>O<SUB>2</SUB> > UV-C > UV-A/Fe(II)/H<SUB>2</SUB>O<SUB>2</SUB> > UV-A/H<SUB>2</SUB>O<SUB>2</SUB> > UV-A. The concentrations of Fe(III) and H<SUB>2</SUB>O<SUB>2</SUB> used in the photo-Fenton-like process were varied to evaluate their influences on MC-LR degradation in both deionized water and a water sample from Nak-Dong River, Daegu (South Korea). The highest removal efficiency (>80%) for MC-LR was achieved after 15 min by the photo-Fenton process at a low optimum Fenton reagent concentration (Fe = 0.5 mg L<SUP>−1</SUP> and H<SUB>2</SUB>O<SUB>2</SUB> = 1 mg L<SUP>−1</SUP>) in the river water. Twelve transformation products of MC-LR were identified with 1029.5, 1012.5, 1015.5, 1011.5, 965.6, 835.5, 815.4 and 783.4 <I>m</I>/<I>z</I> (two products) with the presence of four reaction sites: the conjugated diene bond of Adda, the methoxy group of Adda, the CC bond of Mdha, and the acid group of MeAsP. Theses alleviated the hepatotoxicity of MC-LR, as indicated by a protein phosphatase (PP) 2A assay. Considering the impacts of the chemistry for the treatment of river water, natural organic matter has a slightly higher impact on MC-LR degradation than the initial pH and alkalinity. The k<SUB>MC-LR</SUB> were maintained at 0.167–0.187 min<SUP>−1</SUP> and t<SUP>1/2</SUP> (min), obtained from the different river water samples, were all within 5 min in spite of the relatively high dissolved organic carbon concentrations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photo(UV-C)-Fenton-like is effective to remove MC-LR among UV-assisted AOPs. </LI> <LI> A low optimum Fenton reagent concentration enhanced the MC-LR removal. </LI> <LI> MC-LR transformation products and their toxicity were determined by PP2A activity. </LI> <LI> NOM has a slightly greater impact on MC-LR degradation than pH and alkalinity. </LI> <LI> k<SUB>MC-LR</SUB> ranged from 0.167 to 0.187 min<SUP>−1</SUP> in the water of the Nak-Dong River. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>