Estudo da performance de processos de separação por membranas para remoção de manganês e ferro de águas

Abstract

Water Treatment Plants face several problems during droughts, as a result of the intensification of water withdrawal from the lower levels of dams, where there is a higher percentage of organic matter and availability of metal ions, among them manganese and iron present in high concentrations in the water source. These metals are dissolved in water, oxygen in the water is oxidizing and precipitating the iron and manganese, because of that the appearance and taste of water change, when in excess in the body they can affect the human neurological and muscular system. These metals when dissolved in water can come into contact with oxygen from the atmosphere and oxidize, giving color and taste to the water, and when in excess in the body can affect the human neurological and muscular system. In view of this, this research aims to suggest an option for improving the treatment processes used by Brazilian public supply systems, with the addition of membrane separation processes of reverse osmosis and electrodialysis, in order to adjust the concentration of these ions in treated water to the legislation applied by the Ministry of Health in Directive 5/2017, which highlights limits of 0.1 mg.L-1 and 0.3 mg.L-1 for manganese and iron, respectively. To reach this objective, three synthetic solutions were used in the process feed, distinguished by the ions present in solution, to study the removal of metals in individual and in combination. The solutions were synthesized from two hydrated salts and named as follows: Solution A (MnSO4), B (FeSO4) and C (MnSO4 and FeSO4). In the test with the reverse osmosis membrane, the initial hydraulic permeability and compaction tests were carried out and after the retention tests with each study solution, the pressure applied in the system were 6 bar. The test with the electrodialysis technique occurred in a three-compartment system, with the cationic and anionic membrane (used alternately), with the objective of demineralizing the central compartment, and to verify the quality of the tests, prior to the retention tests, the limiting current for the system with each feed solution was determined. The two processes studied achieved promising results regarding the percentage of retention, a reverse osmosis obtained 99% retention for solution A (manganese present), 93% for B (iron present) and 98% for C (mixed solution) and electrodialysis system reached 99.76% for solution A, 98.45% for B and 99.32% for C. The electrodialysis technique was able to meet the Brazilian legislation required for the concentration of manganese and iron ions in treated water, for all the retention tests performed in the system. The Separation Process by Membranes studied were promising for the proposal to improve conventional water treatment, further deepening in this context is necessary for the actual implementation of the techniques in water treatment plants. [resumo fornecido pelo autor]