| Cyanobacterial blooms are of concern in relation to waterbodies because of their abilityto result in filter-clogging, disagreeable tastes and odors, toxins generation, whichtremendously damage to aquatic environment. To protect effectively the aquaticenvironment from the damage of the cyanobacterial overgrowth, it is necessary to counteractcyanobacterial blooms in waterbodies. However, various methods have been used todiscourage cyanobacterial overgrowth in waterbodies at present, and almost all of those wereproved to be cost-consuming, inefficient or injurant-producing. Thus, new methods areneeded to prevent cyanobacteria from fast and excessive growth in the water sourceseffectively.The ability of ultraviolet light with a wavelength of 253.7 nm (UV-C) can kill variousbacteria and virus. However, the cells of cyanobacteria are more resistant to damage thanthose of bacteria and virus. Thus, it poses a greater challenge to the control of cyanobacterialovergrowth.Advantages of nanocrystalline TiO2 in natural surroundings include its non-toxic nature,chemical stability, low cost, and high photoactivity. What exciting is that the UV-Cphotocatalysis by nanocrystalline TiO2 may be more effective method to damage the cells ofcyanobacteria than that of UV-C irradiation alone.In this study, the capacity of the nanocrystalline TiO2 in combination with UV-C lightto restrain cyanobacterial growth in laboratory scale was investigated with Anabaena sp.PCC 7120 and Microcystis aeruginosa as test species. The results lead to the followingconclusions: firstly, the experimental process of UV-C photocatalysis with nanocrystallineTiO2 was investigated for several possible factors influenced the photocatalytic activities,and the effects of cyanobacterial growth by UV-C photocatalysis with nanocrystalline TiO2were studied. The physiological parameter of Anabaena sp. PCC 7120 has been measured,and the results indicate that UV-C photocatalysis at radiation light intensity about 0.10mW/cm2, nanocrystalline TiO2 concentration 100 mg/l, the temperature 30℃, the dissolvedoxygen concentration 9.0 mgO2.1-1 for 60 min, could effectively inhibit the cells growth ofAnabaena sp. PCC 7120. Secondly, the improvement of photocatalytic activity by dopingthe certain metal ions in nanocrystalline TiO2 under the optimal reaction condition wasinvestigated with Anabaena sp. PCC 7120, and the result indicate that the doped nanocrystalline TiO2 with silver ions (Ag-doped TiO2) could effectively reduce theChlorophyll a concentration of Anabaena sp. PCC 7120. Thirdly, the capacity of theAg-doped TiO2 photocatalyst in combination with UV-C light to restrain cyanobacterialgrowth was investigated with Anabaena sp. PCC 7120 and Microcystis aeruginosa. The cellamount, chlorophyll a concentration, phycocyanin concentration, oxygen evolution rate,cellular morphologic structure, lipid peroxidation, antioxidant enzyme activities and dsDNAbreakage of test cyanobacteria were measured. Compared with the UV-C irradiation aloneand the UV-C photocatalysis by nanocrystalline TiO2, the results showed that the testcyanobacteria with UV-C photocatalysis by Ag-doped TiO2 yielded more effects of reactiveoxygen species, promoted peroxidation of cyanobacterial cell membrane and ultimatelycaused the damage of the cell wall, the losses of the cell organelle and viability. The 5atom% Ag-doped TiO2 photocatalysis could damage more seriously the membranes ofcyanobacterial cells than the 1 atom% Ag-doped TiO2, TiO2 photocatalysis and UV-Cirradiation alone, which could be ascribed to the oxidation of the cell membranes caused byROS. Finally, according to the experimental data with UV-C photocatalysis by Ag-dopedTiO2, the photocatalytic reactor was designed for preventing cyanobacteria from growth inthe water sources, and was discussed for applying in future.In this study, it has been found that nanocrystalline TiO2 doped with Ag ion has thepotential to be used as an effective means for controlling cyanobaeterial overgrowth ineutrophic waterbodies。... |
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