Study On Photocatalytic Degradation Of Microcystins

With the grave concern of pollution and eutrophication degree of fresh water, algal bloom has become more and more serious. The potent toxin microcystin is frequently released during cyanobacterial blooms in eutrophic waters and may impose a risk to human health and environment. The usual microcystins in China are MC-RR and MC-LR. This thesis discusses microcystins'retention characteristic and isolation conditions by using High Performance Liquid Chromatography, and optimizes parts of the analysis steps. Taking water sample during the eutrophication period in Taihu lake, it optimizes the conditions of extracting and isolating microcystins. It also focuses on the photo degradation of microcystins by irradiation with various pigments, such as chlorophyll a,β-carrotene and mixed pigment in cyanobacteria cells. This thesis discusses the influences of pigment concentrations, temperatures, intensities and pH to the photo degradation.The determination conditions of HPLC are as follows: Mobile phase: acetonitrile-water-TFA(35:65:0.05); flow rate:0.8 ml/min; UV detection wavelength:239 nm; injection volume: 10μl. It is found that the concentration of MC-LR and MC-RR are 0.30 mg/L and 1.16 mg/L in the Taihu lake in June,2007, it is far over the limitation regulated by WHO.The efficiency of extraction and purification is much better when eluting with 70% methanol from SPE-C18 and extracting with 50% methanol.After irritation with fluorescent lamp, the results show as follows: Under the temperature of 30℃, 4320μmol/m2·s light intensity and MC-LR concentration of 5 mg/L, with pigments concentration of 0.5 mg/ml, the half-life of MC-LR is 1 hour . Different pigment solutions have different catalytic effects during photo degradation, results show that the mixed pigments in Cyanobacteria cells have a better catalytic effect than the bought pigments. MC-LR degradation is also more favorable in alkaline environment, when temperature increases, the rate of photo degradation will also becomes faster. Under the conditions of pH 9 and temperature of 40℃, the degradation rate of MC-LR reaches 7.735μg/h. In addition, the light intensity also has an effect on photo degradation, the higher the light intensity is, the faster the photo degradation reaction gets.