Estudo do efeito da temperatura e da origem do inóculo na partida de reator anaeróbio empregado para remoção biológica de sulfato

Abstract

Acid mine drainage (AMD) currently represents one of the greatest environmental risks and impacts associated with the activity of mineral extractive industries. The treatment is indispensable as the damages may be irreversible. However, due to the diversity of rocks and extraction methods, AMD may present diverse characteristics and specific treatment requeirements. Considering this problem, the present work aimed to evaluate the startup period of sequencing batch l reactors in the removal of sulfate present in synthetic AMD in different regimes. For that, an anaerobic sequencing batch reactor (ASBR) was used, altering the parameters of operation temperature and origin of the inoculum. Sulfate reduction efficiencies, metal removal and microbial diversity were evaluated under the temperatures of 15, 30 and 55ºC with the use of two different inoculums, one with sulfidogenic and another with methanogenic characteristics influent. The ratio COD/SO42- of 1 was maintained, with the initial concentration of sulfate and ethanol as the carbon source being 1500 mg/L, in cycles of 48 hours. For the operations at 30°C, using the adapted to the treated effluent (sulfidogenic) and the unadapted sludge (methanogenic), an average of 80 and 43% sulfate removal was obtained, respectively, during reactor start-up. For the temperature of 15ºC, 27% was obtained for the sulfidogenic sludge and 31% for the methanogen sludge. While at 55°C, an average of 36 and 45% of sulfate reduction efficiency was obtained for the adapted and unadapted inoculum, respectively. With respect to the consumption of organic matter in the form of COD, the startup at 30°C presented an average efficiency of 50%, when using the sulfidogenic sludge, and of 92% for the methanogenic sludge, whilst at 15°C, on average, 26 and 47% of removal and at 55°C, 31 and 19%, for the respective inoculum. As for iron metal removal, the inoculums operated in mesophilic range had an average removal of more than 99%, whereas for 15 and 55°C, respectively, 35 and 85% were found for the inoculum adapted to AMD and 60 and 93% for the unadapted inoculum. These results suggest an influence of operating temperature and origin of the inoculum adopted on the removal efficiency of sulfate, organic matter and iron. The use of sulfidogenic sludge obtained better performance at the end of the phases, however, the adaptive capacity of the methanogenic sludge, in different temperatures, infers a greater microbial diversity present.