Emprego da flotação a ar dissolvido no tratamento de cursos d'água: avaliação de desempenho da estação de tratamento dos córregos Ressaca e Sarandi afluentes à Represa da Pampulha

Abstract

The investigated treatment plant has a capacity of 750 L/s and uses dissolved air flotation (DAF) for the direct treatment of polluted water courses. The plant treats the water from Ressaca and Sarandi streams, which drain an area of 61,5 km2, and receive, besides diffusedsources, also domestic and industrial wastewater, as well as solid wastes. As a result, their water has high organic matter and nutrients contents, which have contributed to the eutrophication of Pampulha Reservoir, in Belo Horizonte, Brazil. In the study, water quality monitoring data from upstream (raw water) and downstream (treated water) of the treatment plant were used, ranging from July/2003 to February/2006.Additionally, operational records were obtained, complemented with the sludge characterization. These results showed that the plant obtained satisfactory average removal efficiencies for turbidity (72%), suspended solids (70%), settleable solids (68%), BOD (71%), COD (65%),soluble phosphorus (70%), total phosphorus (74%) and aluminium (39%). For the other analyzed parameters (nitrogen, coliforms, dissolved solids, sulfates and oils/greases), the average removal efficiencies were below the expected ones. The analysis of the main operational variables was also made to evaluate their influence on the plant performance, since they are directly related with the inflow, that presented frequentand large fluctuations. It was observed that many of the operational variables were outside the recommended ranges, what may have contributed to the non-compliance with some of the project treatment goals. The results of this work show that DAF, when applied directly in the water course, is an attractive alternative for surface water treatment, from the technical and environmental points of view, especially for the protection of lakes