Potential acid mine drainage treatment utilizing acidophilic sulfate reducing bacteria in an upflow bioreactor

During coal and iron mining, pyrite is often exposed to oxygen, causing acid mine drainage (AMD). Acid mine drainage has characteristic traits of: a rust color, low pH levels (around 3 or 4) and high concentrations of sulfate, metal sulfates and heavy metals. Sulfate reducing bacteria (SRB) are often utilized in acid mine drainage treatment by implementing them into biochemical reactors (BCR). As SRB break down various carbon sources, bicarbonate is produced, raising the pH and generating hydrogen sulfide which reacts with numerous metals. This approach can be troublesome, as SRBs do not thrive at low pH levels often associated with AMD. Previous studies have found acidophilic sulfate reducing bacteria (aSRB) able to reduce sulfate and remove metals at pH values as low as 3.25. However these studies often use easily degradable carbon sources like ethanol, lactic acid and glycerol. In the present study, various solid carbon sources at a pH range of 3.0 to 6.0, high and low sulfate concentration, and media that provided either sulfate or iron as an electron acceptor were tested. Of the five carbon sources, sweet potato and horse manure resulted in black precipitate, indicating possible sulfate reduction. To mimic a BCR, column studies were conducted. After flowing pH 3.5 to 4.0 synthetic AMD through the upflow columns for 117 days, pH was raised to between 6.0 and 7.0. Sulfate reduction was evident in one column containing sweet potato and inoculum, but no others were active in this ongoing study. A leading hypothesis is that complete reduction was inhibited by the presence of fermenting bacteria.