Adequação das condições operacionais e estruturais de uma estação de tratamento de água por filtração direta

Abstract

Changes in the quality of surface water sources have been recurrent in developing countries due to their accelerated urbanization processes. In this sense, it is essential that water treatment plants (WTPs) in these regions are capable of producing safe water even in the face of variations in water quality. In some cases, this can be achieved through adjustments in the WTP operation, and eventually it is necessary to reformulate the treatment system. Downflow direct filtration is an effective, low-cost and easy-to-operate treatment technology, requiring, however, that the color and turbidity values of the influent water are low, among other requirements. One way to circumvent this limitation in water sources with seasonal variations in water quality is to use a pre-treatment unit. Among the alternatives, the upflow sand filter (constituting, together with the downflow direct filtration, the double filtration system - DF) - shows great potential, also due to its low cost, high robustness and operational simplicity. This configuration allows the treatment of raw water of worse quality (compared to downflow direct filtration), with less susceptibility to sudden changes in quality, and the application of higher filtration rates. Thus, the objective of this work is to investigate alternatives to adjust the operational and structural conditions of a water treatment plant by downflow direct filtration that treats the water of a tropical coastal lagoon. For this, tests were carried out in a jar test device + Laboratory Sand Filter (LSF) and in a pilot installation of direct filtration that could be operated as downflow direct filtration or as double filtration, with different treatment configurations being tested in dry periods and after the occurrence of heavy rains. Tests in a pilot installation showed that the direct filtration and double filtration systems presented stable final effluent with turbidity lower than 0.5 NTU and apparent color lower than 15 uC. However, the filtration run of the direct filtration system was very short, due to the rapid evolution of head loss in the tested filter media. The double filtration system presented long filtration runs, slow evolution of head loss and adequate removal of color and turbidity, even for tests with raw water of worse quality, bringing great robustness to the treatment system.