Abstract: Eutrophication leads to the outbreak of algae and the release of algal toxins into water. Microcystins (MCLR), the most common algal toxin, shows high potential toxicity to human health. In this study, the combination of ultraviolet and chlorine was applied to investigate the degradation ability of MCLR. The results show that a synergetic effect between UV and chlorine is produced, and  MCLR can be completely removed in 30 min. The produce of active radicals such as ·Cl and ·OH during the UV/chlorine process is the main reason for the synergetic effect. In the test, the MCLR removal efficiency increased with the increase of chlorine dosage. While pH had negligible effect on MCLR removal during UV/chlorine process under neural and acid conditions.  However, an effect was observed that the remove efficiency decreased significantly with pH increase in alkaline conditions, the remove efficiency was only 41.3% at pH 9. The water matrix can significantly affect  MCLR degradation: the degradation percentage of pure water, filtrated water, and water treatment plant influent was 99.5%, 40.2%, and 63.3%, respectively. The degradation efficiency of MCLR decreased with the increase of humic acid concentration: the removal of MCLR without humic acid was as high as 99.5% within 60 minutes; while the removal of MCLR was only 45.3% with 10 mg/L humic acid. 

Key words: ultraviolet, chlorine, algal toxin, humic acid, degradation