学位论文详细信息
Impact of cyanobacterial toxins on water quality and supply
["Dissertation (M.Sc. (Plant Sciences))--University of the Free State, 2011","Water-purification -- South Africa -- Bloemfontein","Water quality management -- South Africa -- Bloemfontein","Water quality -- Bloemfontein -- South Africa","Eutrophication","Cynobacterial blooms","Mockes Dam","Maselspoort Dam","Rustfontein Dam","Treatment processes","Safe drinking water","Microcystin-LR"]
Mohale, Lineo Rose ; ["Grobbelaar, J. U."]
University of the Free State
Others  :  http://scholar.ufs.ac.za/xmlui/bitstream/11660/2208/1/MohaleLR.pdf
Subject:["Dissertation (M.Sc. (Plant Sciences))--University of the Free State, 2011","Water-purification -- South Africa -- Bloemfontein","Water quality management -- South Africa -- Bloemfontein","Water quality -- Bloemfontein -- South Africa","Eutrophication","Cynobacterial blooms","Mockes Dam","Maselspoort Dam","Rustfontein Dam","Treatment processes","Safe drinking water","Microcystin-LR"]
瑞士|英语
 issued in 2011-01-01, available in 2016-01-14, published in 2011-01
来源: University of Iowa
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【 摘 要 】
English: The occurrence of cyanobacterial blooms that may be toxic is one of the major consequences of eutrophication. The prevalence of cyanobacteria and their toxins in reservoirs create a significant water quality problem and complicates the water purification process for producing safe drinking water. Microcystin is the dominant group of cyanotoxins and the most commonly occurring variant is microcystin-LR. The purpose of this study was to determine the presence of cyanotoxins in the reservoirs and drinking water supplied to the city and towns of Bloemfontein, Thaba Nchu and Botshabelo, in the central region of South Africa. To achieve this, the microcystin-LR concentrations were determined in Rustfontein, Mockes and Maselspoort Dams and the efficiency of treatment processes at Rustfontein and Maselspoort treatment plants in removing this cyanotoxin were investigated. In situ measurements of electrical conductivity (EC), dissolved oxygen (DO), pH and surface water temperature were done at two-weekly intervals over the study period. Water samples were collected and analysed upon return to the laboratory for NO3-N, PO4-P, chlorophyll-a, dominant algal species and microcystin-LR. Final treated water from Rustfontein and Maselspoort water treatment facilities was also analysed for microcystin-LR. Physico-chemical variables displayed no clear-cut seasonal trends except for surface water temperature which followed a distinctive seasonal pattern with lower values in winter and higher values in summer. The concentration of DO seemed to be influenced by water temperature, photosynthetic activity of phytoplankton, wind induced mixing and decomposition of organic matter. Based on the nutrient content, these impoundments were found to be eutrophic. However, in terms of chlorophyll-a concentrations, Maselspoort Dam was mesotrophic, Rustfontein Dam eutrophic and Mockes Dam hypertrophic. Cyanobacteria genera that were commonly found in the three impoundments were Microcystis, Anabaena and Oscillatoria. Oscillatoria was occasionally dominant in Mockes Dam with Ceratium as co-dominant. Microcystis was occasionally dominant in Rustfontein Dam. Euglenoids such as Euglena, Trachelomonas and Phacus, that are indicative of presence of organic matter, were occasionally present, especially in Mockes and Maselspoort Dams. There were no severe cyanobacterial blooms during the study period except for a single bloom of Microcystis in Rustfontein in April 2010. This explains why the concentrations of microcystin-LR or microcystin-LR equivalents in the three impoundments were generally low or undetectable. The highest concentration measured was 1.19 μg/L and this was in Rustfontein Dam during the bloom. Microcystin-LR was never detected in the final treated water from Rustfontein but was detected once in treated water from Maselspoort (0.043 μg/L). This is lower than the 1 μg/L proposed by WHO as an acceptable level of microcystin-LR or microcystin-LR equivalents in drinking water. Based on these results it was concluded that the treatment processes at both facilities were relatively efficient in removing microcystin-LR and that the water supplied to Bloemfontein, Botshabelo and Thaba Nchu is indeed safe. However, it is believed that the efficiency of these treatment processes might be compromised when high concentrations of microcystin-LR or microcystin-LR equivalents occur in source waters. Rustfontein Dam seemed to have the potential to develop massive cyanobacterial blooms and this could result in occurrence of high concentrations of microcystin-LR or microcystin-LR equivalents in the water. It is, therefore, recommended that the water treatment facilities at Rustfontein and Maselspoort should consider introducing more advanced treatments such as an activated carbon polishing step. It is also recommended that cyanotoxin analysis should be part of routine water quality monitoring.
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