Stabilization and Management of Sulfate-Reducing Bioreactor Residues After Acid Mine Drainage Treatment

Passive and semi-passive sulfate-reducing bioreactors (SRBRs) are attracting increasing attention worldwide for the treatment of contaminated mine effluents. This study focuses on the management of post-treatment residues from these bioreactors. The residues of two bioreactors with different medium compositions were studied after they were mixed with different alkaline amendments (25% biomass ash, 30% aluminum red mud, 10% lime kiln dust, or 15% hydroxyapatite). Weathering cell tests showed that aluminum red mud and Bedford lime kiln dust efficiently maintain the leachate at neutral pH (≥ 7.0) and immobilize some metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in the post-treatment residues with average dissolved concentrations < 0.5 mg/L for all toxic metals, except for Mn, which are less than 3.2 mg/L. Column tests were also performed on the unamended post-treatment residues under unsaturated, saturated, and immersed conditions. The storage of the post-treatment SRBR residues under saturated and immersed conditions preserved the reducing conditions of the media and the neutrality of the leachate pH and also limited the leaching of metals retained by the bioreactor media.