Avaliação da remoção de Microcystis aeruginosa e microcistina-LR de águas eutrofizadas utilizando fotocatálise heterogênea

Abstract

The present work has the following objectives: to evaluate the process of heterogeneous photocatalysis using TiO2 and ultraviolet radiation for the removal of Microcystis aeruginosa and microcystin-LR from eutrophic waters; to study the effect of pH and time of exposure to UV radiation in removing colour, chlorophyll a and cyanobacteria in photocatalytic reactors of the cylindrical, parabolic type-PTR; evaluate the performance of a sand filter for the removal of total dissolved solids, COD, colour, cyanobacteria and cyanotoxins and evaluate the performance of a PTR reactor for the removal microcystin-LR using TiO2 and solar radiation. The research was performed at the Experimental Research Station for the Biological Treatment of Sewage EXTRABES Campina Grande, Paraiba Brazil. The water used was prepared by adding Microcystis aeruginosa cells. The photo-catalytic reactor typePTR was operated in two distinct experimental phases, in the first an artificial source of UV was used with a 24 factorial experimental design incorporating time and pH. Each factor had two levels: times of 2 and 4 hours and pHs of 6.0 and 9.0. Four experiments in triplicate were carried out. In the second phase solar radiation was used with a fixed time (2 hours) and pHs of 6,0 and 9.0. The water sample was initially passed through a sand filter and then to the photocatalytic reactor. The photoreactor functioned in batch mode with 2L of sample and the catalyst was TiO2 (0.5%). Quantative analyses were performed for cyanobacteria and cyanotoxins as well as physico-chemical analyses of the water for turbidity, colour, pH, alkalinity, chlorophyll a and COD. In phase 1 all the treatments were efficient but treatment T3 of 2h duration and pH 9.0 was the most efficient in terms of the removal of COD, chlorophyll a and Microcystis aeruginosa cells. The results from the second phase showed removal efficiencies for cyanobacteria of 89% and chlorophyll a of 73% when solar radiation was used for 2 hours. Heterogeneous photocatalysis shows good potential for the treatment of water containing cyanobacteria and cyanotoxins. However, it is essential to readjust the operational parameters, principally the time of exposure to solar and UV radiation for the removal of microcystin. It is important to carry out additional studies that better define the optimum conditions for heterogeneous photocatalysis for the elimination of cyanotoxins to values below those permitted in existing legislation.