Study On The Release And Degradation Of Cylindrospermopsin In Killing Cylindrospermopsis Raciborskii By ClO₂

The enhancement of eutrophication in freshwater bodies have increased of blooms of toxic cyanobacteria(blue-green algae)which have drawn attention to environmengtalists worldwide.In recent years,cylindrospermopsis raciborskii becomes one of the main species of cyanobacteria bloom,and produces cylindrospermopsin(CYN)which is hepatotoxic. Chlorine dioxide has good effect in killing cylindrospermopsis raciborskii,but it may influence the safety of drinking water when intracellular CYN releases in the algicidal process.Therefore,in the thesis,the release and degradation characteristics of CYN in killing cylindrospermopsis raciborskii by ClO2were researched,and the release mechanism of CYN were studied.The thesis studied the effects of the initial concentration of cylindrospermopsis raciborskii,the dasages of ClO2,temperature and pH value on the release and degradation of CYN by C102.The results showed that,the release and degradation percentage of CYN in0.5mg/L C1O2and1.0mg/L ClO2were much higher than that of0.7mg/L ClO2in60min.At120min, the release and degradation rate of three ClO2dosage respectively tended to be close.The degradation rate of1.0mg/L ClO2was much faster than that of0.5mg/L ClO2and0.7mg/L ClO2.Cylindrospermopsis raciborskii initial concentration had little influence on the release rate and degradation rate.The release rate and degradation rate in acidity were faster than that of neutral and alkaline conditions,and could be accelerated by increasing temperature.The release and degradation speed of1.0mg/L ClO2were much faster than that of0.5mg/L ClO2and0.7mg/L ClO2in5minutes.The time that the release and degradation speed of CYN were equal and tended to be stable moved forward with the ClO2dosage increasing.The release and degradation speed of CYN could increase with the increase of cylindrospermopsis raciborskii intial concentration and the reaction temperature.Through studying the rule of the release and degradation of CYN in the process of killing cylindrospermopsis raciborskii by ClO2, the thesis got the CYN release equation c=A2+(A1-A2)/[1+(t/a)^p],which could reflect the relationship between CYN release amount and reaction time in different conditions.The release and degradation of CYN coexist in the process of killing cylindrospermopsis raciborskii by C102,and after60minutes,the extracellular CYN concentrations were lower than1.0μg/L in different ClO2dosages,which were in accordance with the WHO standard that the content of algae toxins should not exceed1.0μg/L in drinking water.In order to explore the degradation regularity of CYN by ClO2,this paper also examined the characteristics that the single component CYN were degraded by ClO2. The results showed that the degradation of CYN increased with the increase of ClO2dosage. CYN initial concentration had little influence on the degradation rate.The CYN degradation rate at25℃and30℃were the same,which were higher than the CYN degradation rate at15℃. The CYN degradation rate in acidity were faster than that of neutral and alkaline conditions.Research on reaction kinetics of the degradation of CYN by ClO2showed that the order of reaceion was3, when the CYN initial concentrations were2.82μg/L,15.11μg/L and28.04μg/L,the corresponding rate constants were0.179μg-1·L·s-1,0.057μg-1·L·s-1and0.069μg-1·L·s-1,respectively. Reaction rate constant decreased with the increase of pH.The reaction activation energy E was12.29KJ/mol.The observation of algal cell morphology and structure using Transmission Electron Microscope showed that the algal cell structure had a certain damage in the process of killing cylindrospermopsis raciborskii by ClO2.As the time extended and the ClO2dosage increased,the damage degree of algal cell structure intensified.At60min,the cell wall broke.The release of intracellular CYN was caused by the diffusion effect instead of breaking cell wall.The changes of algal cell structure promoted the diffusion and release of CYN.The CYN release speed was affected by the difference of intracellular CYN concentration and extracellular CYN concentration.