Lab- and Pilot-Scale Sulfate-Reducing Bioreactors Treating Acid Mine Drainage from an Abandoned Nevada Gold Mine
Loading...
Authors
Kaps, Thomas Berg
Issue Date
2024
Type
Thesis
Language
en_US
Keywords
Acid Mine Drainage , Bioreactors , Metal Removal , Sulfate Reducing Bacteria , Water Treatment
Alternative Title
Abstract
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 (SRB) use sulfate as a terminal electron acceptor for their metabolism 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 had slightly greater sulfate reduction than those inoculated with AMD-impacted soil. The colder temperature averages (0 to 10 °C) in these months were hypothesized to be responsible for the lower performance and preventing the microbial community from becoming established in the bioreactors, which led to minimal or no AMD treatment even after the temperatures increased during the summer months. The lab-scale SRBR operated in parallel were found to have high sulfate removal over the first 5 months, but then started to decrease as the acidity of the effluent also decreased. This change can be linked to the consumption of limestone sand leading to a decrease in pH and a corresponding inhibiting the SRB that gradually decreases sulfate reduction and bacterial pH neutralization. The concurrent operation of field- and lab-scale SRBR in this work 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 the potential to be a cost-effective option for AMD remediation at locations around the world.