Remoção de sulfato e metais presentes na drenagem ácida de mina utilizando um reator anaeróbio operado em bateladas sequenciais

Abstract

Mining presents as one of the environmental problem a generation of acid solution containing metals and dissolved sulfate, denominated acid mine drainage. This wastewater causes damage to aquatic organisms, flora and humans once present in the food chain. From this, there is a constant need for technologies and treatment processes in order to make the waste able to be released into the water bodies without changing the quality of the water. In this work, the biological treatment was carried out using an anaerobic sequencing batch reactor (ASBR) with a volume of 7 liters, maintained at 30 °C, containing granular biomass, for a 48 hour cycle time with the objective of evaluating the impact of increased concentration of metals (Fe2+, Zn2+ and Cu2+) on reactor performance. The experiment was divided into six phases, gradually increasing the concentration of metals. Samples were collected for analysis of pH, COD, SO42-, sulfide and metals after the total filling time (14 minutes) and at the end of the cycle (48 hours). In treatment, sulfate reducing bacteria (SRB) through dissimilatory metabolism reduced sulfate to sulfide, being precipitated in the form of metallic sulfide and generated alkalinity, which was demonstrated by effluent pH values above 6.5. It was used COD/SO42- ratio equal to 1 in all phases and ethanol as electron donor. The reactor was operated for 392 days and during the six phases of operation the increased concentration of metals generated an increase in SO42- removal and was not harmful to the microbial consortium, verified by the results obtained. COD removals ranged from 68.4 to 94.4% and SO42- from 39.1 to 72.8%, being phase IV with greater removal of SO42-. Fe2+ removals were above 99.2%, Zn2+ - 100% and Cu2+ above 93.3%. At the end of each operation phase, time profiles were performed to quantify the kinetic behavior of sulfate removal. Values of apparent kinetic constant (Kap) obtained showed that there was a decrease in the reaction speed at the same time that the sulfate removal increased. This may have been due to the high concentration of metals throughout the phases, resulting by a longer time required for SO42- removal. However the kinetics were not impaired once the stabilization of the removal within the expected cycle of 48 hours. During operation it can be inferred that the bacterial population showed to be well adapted to the predominant medium in the reactor, indicated by the increase of the effluent pH and removals of COD and SO42- observed in all phases.