Aplicação do processo de eletrodiálise na remoção de cromo em efluente sintético advindo de biorreator anaeróbio

Abstract

Pollution and contamination of water resources by productive processes is a global problem that has emerged since the Industrial Revolution, but only in recent decades has the concern about the disposal of contaminated effluents started to be a concern due to the scarcity of natural resources such as, for example, water. Some processes can be used in the treatment of effluents, such as electrodialysis, which is a separation technique by ionic membranes, that is, that have loads in its matrix, and has been considered by many as one of the most promising clean technologies. In this technique, ions that can not be retained by the cationic or anionic membranes are transported from the feed (diluted solution) to the concentrated solution by the influence of the electric current generated by a source with a potential difference. The big advantage of this method is to treat large volumes of effluents generating as final residue a small volume of solution contaminated with large concentrations of toxic ions. Thus,this work aimed to evaluate the electrodialysis in treating of synthetic effluents from tanneries, which are contaminated with chromium (VI) in the form of ion Cr2O7-2. To this end, the initial concentrations of hexavalent chromium were determined from a previous study in anaerobic bioreactor, using values of 10, 65 and 100 mg/L and the electrolyte used was a solution of 0.25 M Na2SO4. It evaluated the current density limit of electrodialysis, the optimal flow system operation, the efficiency of the electrodialysis with and without the application of electric current, as well as the impact of the saturation of the concentrated solution in the process. In addition, estimates for stacking resistance and columbiometric yield were also studied. The best results provided as a current density limit 0.0005 A.cm-2, great flow operating 20-60-60 L / h for electrolyte, feed and concentrated solution, respectively. It was possible to verify that the electrodialysis with current application is more efficient than in the absence of electric current, having more than 90% hexavalent chromium percentage extraction of the diluted solution, since the electric current acted as a cleaning agent, removing ions of the membranes when tthese were already saturated, which allows more volume of wastewater that can enter the unit to receive treatment. Regarding the concentrated solution, which early in the process was distilled water, it was noticed that the maximum concentration that could have to Cr (VI) was approximately 570 mg/L of chromium (VI), because after this value was no longer possible to have ions removed from the feed even with the membranes clean. The highest estimate of the electrical resistance to the stacking was 2.1 Ohm.cm² and the columbiometric yield 0.36. Finally, it is suggested that electrodialysis can be a promising technique for the treatment of effluents contaminated with chromium, because when electric current was applied it was possible to treat 78 liters of effluents, generating as a residue only 4 liters a contaminated solution, that is, 5 % of total volume treated. There is also the possibility of recovering the metal present in these 4 L of final residue, which could return to the production process.