Continuous removal of sulfate and metals from acidic mining-impacted waters at low temperature using a sulfate-reducing bacterial consortium

The aim of this study was to develop a biological method for the simultaneous removal of sulfate and metals from acidic low-temperature mining effluents. A mixed consortium of cold-tolerant sulfate-reducing bacteria (SRB) and other microorganisms was immobilized on glass beads and exploited in an up-flow biofilm reactor for the continuous treatment of actual and synthetic mining-impacted waters (MIWs) with initial sulfate concentrations between 1580 and 5350 mg L-1. The proton acidity of the mine waters was neutralized by microbial sulfidogenesis. Metals present in the MIWs were precipitated either off-line or in-line, inside the reactor vessel. High sulfate reduction rates (SRRs), from 1000 to 4500 mg L-1 at a temperature of 11.7 +/- 0.2 degrees C, were achieved (sulfate removal 43-87%). The bacterial consortium was found to be robust and resistant to changes in growth conditions during the bioreactor experiment. The relative abundance of SRB and the SRR increased at higher sulfate concentrations. Sulfidogenic bioreactors have the potential for treatment of acid mine drainage even at low temperature. It was demonstrated that neutral reactor conditions and high SRRs were maintained when acidic influent was fed into the reactor.