Abstract:The Peerless Jenny King treatment system is a series of four sulfate reducing bioreactor cells installed to treat acid mine drainage in the Upper Tenmile Creek Superfund Site located in the Rimini Mining District, near Helena MT. The system consists of a wetland pretreatment followed by the four cells connected in a serpentine manner. The mining impacted water flows from the wetland through each cell before discharge. Sulfate reducing bioreactors mitigate acidity and metal contamination through the microbial production of sulfide. The produced biogenic sulfide precipitates metals, and the microbial process of reducing sulfate to sulfide produces alkalinity.The health of the entire microbial community present in such systems is important for remediation to be effective. Classes of microbes generally present in such systems include fermenters, methanogens and sulfate reducers. The health can be measured in terms of active microbial populations and positive interactions between populations for the support of sulfate reduction. The goal of this research is to measure the activity of each class utilizing analyses that quantify the groups by their function, as opposed to the traditional molecular techniques of identifying bacteria. Gas chromatography, HPLC-DAD, and ICP-AES are used to identify and quantify the end products of metabolism. The microbial activity can then be characterized and changes can be monitored over time. Results from 2005 sampling of Cell 3 within the system indicate that the activity of sulfate reducing bacteria is much higher than the numbers present would indicate. These results combined with those from 2006 sampling indicate that methanogenesis is a minor process within this cell. The calculation of the stoichiometry of carbon utilization by SRB is much higher than what would be predicted from known stoichiometric ratios of carbon used per sulfate reduced.

The effective use of anaerobic passive treatment systems (APTS), such as sulfate-reducing bioreactors, to treat acid mine drainage will help to mitigate water contamination from mines located in remote areas as well as cut current treatment costs. One draw back to these systems has been the inhibition of sulfate reduction with high concentrations of metals. APTS contain a complex microbial ecosystem, and metal toxicity could be indirectly affecting sulfate-reduction by inhibiting other important microbes. If microbes such as the cellulolyticfermenting bacteria are inhibited from producing viable substrate for the sulfatereducing bacteria, then the rate of sulfate reduction over time in APTS will ultimately decline.

The effective use of anaerobic passive treatment systems (APTS), such as sulfate-reducing bioreactors, to treat acid mine drainage will help to mitigate water contamination from mines located in remote areas as well as cut current treatment costs. One drawback to APTS has been an observed decline in long-term performance. Several environmental factors, such as initial metals concentration and temperature, may contribute to observed declines in sulfate reduction carried out by the microorganisms. APTS contain a complex microbial ecosystem, and metal toxicity could be indirectly affecting sulfate-reduction by inhibiting other important microbes. Previous research has found that organisms capable of degrading cellulose (cellulolytic-fermenters) are dominant within a sulfate reducing bioreactor (Pruden et al., 2005), and their ability to produce viable substrates for the sulfate-reducing bacteria is the rate-limiting step in sulfate reduction (Logan, 2003). This investigation examines the individual effect of zinc and copper, and then the combination of both metals, on a pure culture of cellulolytic fermenters, specifically Cellulomonas flavigena (ATCC 482). C. flavigena exhibited 50% growth inhibition between a copper concentration of 0.00188 mM and 0.0038 mM. Further investigation of growth inhibition within this range of copper concentrations is currently underway. Glucose consumption was also much less in the copper containing bottles, as expected due to the low biomass observed in these bottles. The pH remained relatively constant throughout the experiments, staying within an optimal microbial growth range between pH 6 and 7. Possible changes in solution phase metals concentration and organic acid production throughout the experiments were monitored, and these results will be available during the ICARD conference. Concentrations of Zn(II) at 0, 0.125, 0.25 and 0.5 mM were also examined to determine the effects on cell growth for C. flavigena. The results for zinc toxicity and a binary metal mixture will be presented at the 2006 ICARD conference.

The U.S. Environmental Protection Agency (EPA) is planning to construct an Anaerobic Passive Treatment System (APTS) to treat acid mine drainage from the National Tunnel in North Clear Creek near the City of Blackhawk, Colorado. North Clear Creek is part of the Clear Creek/Central City Superfund Site, and the National Tunnel is a major contributor of contaminants to this tributary. The EPA would like to determine the feasibility of constructing an APTS at this location.Two modes of sulfate reducing bioreactor (SRBR) configurations are under consideration. One mode is an ethanol fed SRBR and the other mode is a solid substrate fed SRBR (two different mixtures). Laboratory proof-of-concept studies to test the performance of locally available microbial inoculum and the effects of start-up conditions were conducted.The rationale for the laboratory experiments was to establish the best start-up inoculum for two different types of bioreactors: solid phase substrate basedwood, corn stover/hay, limestone/quartz and ethanol basedethanol as the food source, limestone/quartz, reducing additive. Bag tests were conducted with 3 different substrates (two solids phase mixtures and ethanol), and 7 different inoculum. Sulfate and copper removal from the proof-of-concept experiments suggest that domestic sewage sludge provided the best bacterial inoculum for the ethanol-fed SRBR with horse and goat manure tied for second best.