Research On The Photodegradation Of Microcystin-LR In Aqueous Solution By Dissolved Organic Matter

The cyanobacterial bloom in eutrophic water source often occurs,and the release of microcystins has threatened drinking water safety.The microcystin-LR(MC-LR)pollution is common and characterized by the most toxic.Thus,its harmless degradation is of great concern.Dissolved organic matter(DOM)is a natural photosensitizer which is prevalent in water.It has the potential to promote the photocatalytic degradation of pollutants in water.The study of the photodegradation of MC-LR in water by DOM is a leading edge in the field of water environment.In this study the typical cyanobacteria species of Microcystis aeruginosa and Anabaena were cultured,and the MC-LR was extracted,purified and tested.The ratio of fulvic acid(FA)is the highest content component in DOM,which is widely existed in the drinking water source of lake and reservoir,and as a typical representative of the photosensitive organic matter.The effects of FA on photodegradation of MC-LR in water under UV and visible conditions were studied,and the optimum degradation conditions of the initial pH and the initial concentration of FA on the photodegradation of MC-LR were discussed.At the same time,the degradation mechanism of reactive oxygen species in the photocatalytic degradation process was studied.The results show that FA promote the degradation of MC-LR under the UV light,while inhibite degradation under the visible light.No matter unde which kind of light conditions,the photodegradation process of FA to MC-LR is in accordance with the second-order reaction kinetics equation.The initial pH and FA content of the solution will affect the degradation of MC-LR.The degradation rate was the fastest in pH=3,while slowest in pH=9.Under UV irradiation of 120min,visible light reaction 10h and pH was 3,5,7 or 9,the degradation rate was not significantly different,93.3%?95.6%,85.0%-89.9%,respectively.Under the UV light,the promotion on the degradation of MC-LR of FA was weak and the optimum content of FA was 9.86mgC/L.Under the visible light,the inhibition on the degradation of MC-LR increased with the FA content increasing for strong light shielding effect of FA.The active species in UV and visible light reaction system was studied.The results show that the 3FA,1O2 and ·OH play an important role in the photodegradation of MC-LR.On the basis of the experimental results,the design of photocatalytic MC-LR reactor was carried out in order toapply in engineering.