Dados da Tese de Doutorado
Author: Ana Cláudia Pimentel de Oliveira.
Title: Effects of physical and chemical factors in the degradation of microcystin..
Year: 2003. Full text (in Portuguese)
Abstract
Toxic cyanobacterial blooms have been frequently occurring in several reservoirs and water supplies in Brazil. The conventional water treatment train generally leads to break of cyanobacteria cells, promoting release of cyanotoxins to the water, which are poorly removed by that treatment. Taking this into account, this work had as proposal to investigate degradation process of dissolved microcystins under different environmental conditions as well as to investigate the removal of Microcystis aeruginosa cells (NPLJ-4 strain) and microcystins by slow sand filtration and granular activated carbon. The results of the microcystins degradation experiments using different conditions of pH (3,0; 5,0 and 7,0) and temperatures (12, 22 and 30oC) showed that the degradation of these molecules was extremely slow. However, in acidic medium and higher temperatures, the degradation was more intense. The application of different concentrations of ferric chloride (3,5; 7,5 and 10.1mg L-1) and aluminum sulfate (5,14 and 28 mg L-1) favored the breakage of NPLJ-4 cells. Nevertheless, microcystins were not detected in the dissolved fraction. It could be also verified that the water quality influenced on the quantitative analyses of dissolved microcystins. High conductivity water, Fe and Al concentrations promoted a great deal of reduction on the detection of these molecules, as well as on its biologic activity. On the other hand, water with high dissolved organic carbon concentrations favored the degradation of dissolved microcystins and bacteria growth, which makes evident the influence of the bacteria community on the biodegradation of microcystins. Concerning the removal experiments, the results indicated the slow sand filtration system was effective to the complete removal of NPLJ-4 cells in concentrations up to 105 cells.m L-1 with ration flow rate of 2 m3/m2.day. Under these conditions, either intracellular and extracellular microcystins was not detected in filtered water. The experiments carried out to verify the microcystins adsorption capacity of different types of granular activated carbon, commolly used in the purification systems of dialysis centers in Brazil, reveled that those activated carbons were ineffective to complete the adsorption of the dissolved microcystins on the concentrations tested (1,10 e 18 μg L-1). Consequently, the filtered water was considered unsuitable to production of injectable solutions and to the dialysis treatment.
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