Hydrogen peroxide enhanced photocatalytic oxidation of microcystin-LR using titanium dioxide

Cyanobacterial toxins present in drinking water sources pose a considerable threat to human health. Conventional water treatment systems have proven u nreliable for the removal of these toxins and hence new techniques have bee n investigated. Previous work has shown that TiO2 photocatalysis effectivel y destroys microcystin-LR in aqueous solutions, however non-toxic by-produc ts were detected. It has been shown that photocatalytic reactions are enhan ced by utilisation of alternative electron accepters. We report here enhanc ed photocatalytic degradation of microcystin-la following the addition of h ydrogen peroxide to the system. It was also found that hydrogen peroxide wi th UV illumination alone was capable of decomposing microcystin-LR although at a much slower rate than found for TiO2. No HPLC detectable by-products were found when the TiO2/UV/H2O2 system was used indicating that this metho d is more effective than TiO2/UV alone. Results however indicated that only 18% mineralisation occurred with the TiO2/UV/H2O2 system and hence undetec table by-products must still be present. At higher concentrations hydrogen peroxide was found to compete with microcystin-LR for surface sites on the catalyst but at lower peroxide concentrations this competitive adsorption w as not observed. Toxicity studies showed that both in the presence and abse nce of H2O2 the microcystin solutions were detoxified. These findings sugge st that hydrogen peroxide greatly enhances the photocatalytic oxidation of microcystin-LR. (C)2000 Elsevier Science B.V. All rights reserved.