BIOGEOCHEMICAL EVALUATION OF THE TAB SIMCO MINE DRAINAGE TREATMENT SYSTEM

Tab Simco is an abandoned coal mine located southeast of Carbondale in Jackson County, Illinois. Acid mine drainage (AMD) discharges from the abandoned mine workings have low pH (~2.5) and high average concentration of dissolve ions: Fe = 597 mg/L, Al = 140 mg/L, Mn = 39.7 mg/L, and SO₄^2- = 3,540 mg/L. To abate this problem a passive-type treatment system was constructed in 2007 by the Illinois Department of Natural Resources, Office of Mines and Minerals.  The principle technology employed has been a 0.75-acre sulfate-reducing bioreactor, which is one of the first full scale system employed for the treatment of acidic, coal mine drainage in the US.  The bioreactor was constructed in three layers: a shallow acid impoundment, an underlying thick layer of compost, and finally limestone with embedded drain pipes.  A series of oxidation cells follow the bioreactor unit before discharge into Sycamore creek. 

To analyze the bacterial community associated with the site, molecular analysis of DNA extracted from the acid mine pond, the bioreactor outlet, and the post-treatment pond was performed by amplification and cloning of the 16S rRNA gene (present in all bacteria) and the dissimilatory sulfite reductase genes (only found in sulfate-reducing bacteria).  Preliminary results show that DNA sequences corresponding to bacteria capable of sulfate reduction were present.  However, the sequences were most similar to bacterial species that preferentially reduce nitrate over sulfate.  This molecular data was supported by the subsequent isolation of Desulfovbirio strains capable of anaerobic sulfate reduction under controlled laboratory conditions.  Sequences related to bacterial species that are not capable of sulfate reduction, but are able to use complex carbon sources such as cellulose were also detected.  While this finding is expected due to the presence of compost in the bioreactor, it suggests that simple dissolved organic carbon sources often utilized by sulfate reducers, such as lactate, may not be available to promote efficient bacterial sulfate reduction.  Thus, the relatively high level of sulfate detected in the post-treatment pond is likely due to both the available organic substrate and the presence of nitrate. These results will be used to improve bioreactor design and ultimately the water quality at the AMD treatment site.