(392a) Lab- and Pilot-Scale Sulfate-Reducing Bioreactors Treating Acid Mine Drainage from an Abandoned Nevada Gold Mine

Acid mine drainage (AMD) is a global environmental hazard that is produced when water flows over exposed rocks containing sulfur-bearing minerals. AMD has many sources and is produced by active and abandoned mines, leading to a need for effective, low-maintenance and low-cost remediation solutions to prevent the contamination of groundwater, the corrosion of infrastructure, and the disruption of reproduction and growth cycles in plants and animals. Sulfate-reducing bioreactors (SRBR) are currently one of the most cost-effective and low-maintenance solutions for treating AMD. Anaerobic sulfate reducing bacteria take in sulfate as a terminal electron acceptor for their metabolisms to create H₂S, provide energy for the bacteria, and lower the pH of the water resulting in the precipitation of metal sulfides.

In this work, four pilot-scale SRBR were installed as in-field bioreactors in Perry Canyon, NV near the abandoned Jones-Kincaid adit. In parallel, eight lab-scale SRBRs were operated at the University of Nevada, Reno. Each SRBR contained organic substrate (corn stover, pine shavings, and dairy manure), pea gravel to maintain porosity, and a microbial inoculum. The inoculum was obtained from either the anoxic soil of a nearby lake environment (the Sparks Marina) or from the AMD-impacted ephemeral stream of Perry Canyon, with both demonstrating high sulfate-reducing performance in past work. The pilot-scale SRBR were fabricated as 115-L upflow drums and were installed below ground to modulate environmental conditions and were fed AMD directly from the adit. The lab-scale SRBR were 2-L upflow columns fed synthetic AMD mimicking the Perry Canyon AMD composition.

Sulfate and metals concentrations of feed and effluent from each SRBR were monitored temporally. Although results to date indicate limited sulfate reduction occurring in the field-scale SRBR during the first six months of the in-field operation, corresponding to October through April,

the reactors inoculated with the marina soil have slightly greater sulfate reduction than those inoculated with AMD-impacted soil. We believe the colder temperature averages (0 to 10 ^oC) in these months are responsible for the lower performance thus far, and we expect performance to increase with increasing spring and summer temperatures to levels comparable to those observed in the lab.

The concurrent operation of field and lab SRBR in this work will provide valuable knowledge of the scale-up process of the treatment technology, as well as insight into how environmental operating conditions may impact the SRBR performance. If designed and operated properly, SRBR have to the potential to be a cost-effective option for AMD remediation at locations around the world.