Removal of Manganese from An Alkaline Mine Drainage Using a Bioreactor with Different Organic Sources

Drainage from a surface mine in eastern Kentucky is contaminated with high concentrations of manganese and sulfate.  As part of the reclamation process, a sulfate reducing bioreactor will be installed to treat the drainage.  The treatment of Mn and SO₄^2-  contaminated mine drainage via a sulfate reducing bioreactor is expected to result in near-permanent immobilization of significant amounts of Mn and a portion of the sulfates within the matrix.  This study tested several different combinations of organic amendments and inorganic substrates in an attempt to optimize sulfate reducing conditions and Mn removal capacity.  Five different organic carbon sources, including corn mash, mulch, biosolids, soybean oil, and sorghum syrup in combination with five different inorganic substrates, including creek sediment, marble and limestone chips, polished gravel, and sand were tested in batch experiments.  Results indicate a widely variant potential among the treatments to remove Mn from solution, ranging from 35% reduction for soybean oil to 97% for the mulch mixture, with respective Eh ranges of +60 mV and -320 mV.  The most favorable combinations were tested in small scale bioreactors under dynamic conditions.  Greater than 90% of Mn and 70% of sulfate was removed over a 65 day test period in the bioreactors. Results from both phases indicate Mn removal mechanisms include sulfide, oxide, and carbonate formation and simple sorption and SO₄^2- removal mechanisms of sulfide gas evolution, gypsum and MnS precipitation, and anion sorption/cation bridging.