Acidic mine drainage (AMD) contains large amounts of heavy metal ions and SO42, which can pose serious risks to human and environmental health. Anaerobic bioreactors are considered to be suitable methods for the treatment of acidic effluents due to some advantages such as the need for a small area, easy control, and simultaneous removal of sulfate and metals even in low concentrations. In this study, sulfate-reducing bacteria (SRB) performance was investigated in a semi-pilot scale down-flow fluidized-bed (DFFB) anaerobic reactor for SO42- and metals removal from the Sungun copper tailings AMD. The results indicated that utilizing SRB in the DFFB anaerobic bioreactor was an efficient, cost-effective, and environmentally friendly method for the treatment of effluents containing large amounts of SO42- and metals. All contaminants except Cr showed more than 70% removal after 24 h. The SO42- and Cu which had the highest initial concentrations showed removal efficiencies of 98.64% and 98.75%, respectively. Besides the removal of hazardous contaminants, the alkalinity of effluent increased remarkably. Also, the SRB had acceptable stability even after six consecutive cycles due to using AC granules as a support in the reactor which is an important parameter in industrial applications. Manuscript profile