Removal Efficiency Of Microcystis And Microcystin-Lr In Raw Water By Chlorine Dioxide

Blooms in eutrophic water body had become an serious problem threatening the safe drinking water. Besides aesthetic aspects such as unattractiveness to bathers,odor, and bad taste of treated drinking water, many species or strains of cyanobacteria also produce potent cytotoxins, hepatotoxins, and/or neurotoxins. Microcystis is the mainly species in eutrophic water and easily lead to Blooms. Microcystins (MC) produced by Microcystis are hepatotoains containing cyclic heptapeptides. Microcystin-LR(MC-LR) is the most strong liver tumour promotor at present. MC are chemically stable in water and can't be effectively removed by conventional water treatment processes. It becomes a great threaten of drinking water when Microcystis growth excessly and produce MC. As a sort of excellent disinfectant and oxidant, chlorine dioxide (ClO2) has promising future for its excellent ability in removing both organic and inorganic contaminants without forming halo-substituted organics such as trihalogenmethane (THMs).The effects of ClO2 on the degradation of two typical Microcystis including M. aeruginosa and M. wesenbergi in aqueous solution were investigated systematically and the results showed that ClO2 could effectively remove M. aeruginosa and M. wesenbergi. The removal efficiency of chlorophyll was in positive correlation to ClO2 dosage and the reaction time and in negative correlation to initial concentration chlorophyll, whereas it was affected by temperature and pH value slightly. The removal ratios of M. wesenbergi and M. aeruginosa(905#和915#)could reach to their maximum as approximately 97.23%,96.2%和92.33% respectively under the conditions as follows: the ClO2 dosage 2.5mg/L, reaction time15 min, and pH 7.17.The removal effectiveness of MC-LR oxidation by ClO2 was studied and Orthogonal experiment was used to discuss detailedly the influence factors as ClO2 dosage, reaction time, temperature and pH in removing MC-LR by ClO2 in this chapter.The results were shown as follow, ClO2 could remove MC-LR effectively, the efficiency of removal was in positive correlation to the ClO2 dosage and the reaction time and in negative correlation to the initial concentration of MC-LR, but it was affected by temperature slightly and was effictive in wide range of pH value. The significance rank of the four factors affecting degradation efficiency was the concentration of ClO2, pH, temperature, time by the orthogonal test results. The residual concentration of microcystins-LR removed by ClO2 could meet the national guideline (1.0μg/L).The research on the kinetics of MC-LR oxidation by ClO2 was systematically performed in this chapter. The results showed that the kinetics of MC-LR degradation by ClO2 followed second order reaction equation, reaction orders of the ClO2 and MC-LR were first order respectively, the reaction rate constant was 7.86 L/(mol?s) and activation energy was 78.81 kJ/mol. In conclution, ClO2 could be taken as an effective technology for removal microcystin-LR from drinking water resources in traditional drinking water supplies.Research on the differences between preoxidation treatment and conventional water treatment processes to removal of Microcystis and MC-LR .Also analyze the charateristics of the breakage of Microcystis after being oxidated by ClO2. The results were shown as follow, as the dosage of ClO2 was 3.0mg/L, removal efficiency of chlorophyll and Microcystis were 98.5% and 95% respectively and turbidity decreased to 89.08%. Compared with conventional water treatment methods,preoxidation treatment of ClO2 could effectively remove Microcystis aeruginosa, decreased turbidity and guarantee the drinking water quality. The study of the mechanism of intracellular microcystins release showed that ClO2 dosage 3.0mg/L, intracellular and extracellular microcystins had fallen to a very little level.Therefor, ClO2 is a suitable oxidant for the degradation of microcystins in drinking water treatment processes.Work of this dissertation has great theoretical and practical value as it provided enough scientific basis for the application of ClO2 in removing Microcystis and MC from aqueous solution.