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  Mine Waste Technology Program Activity III, Project 16, Integrated Passive Biological Treatment System (82 pp, 1.07 MB) (EPA/600/R-09/158) September 2008

This report summarizes the results of the Mine Waste Technology Program Activity III, Project 16, Integrated, Passive Biological Treatment System, funded by the U.S. Environmental Protection Agency and jointly administered by EPA and the U.S. Department of Energy. This project addressed EPA’s technical issue of Mobile Toxic Constituents – Water by performing a field demonstration of a water treatment technology based on the use of passive biological treatment at a remote inactive hardrock mine.

Field demonstration work was conducted at the Surething Mine, located in the Elliston mining district of Montana. This mine was never actively mined and has relatively small workings. However, disturbance of rock at the mine workings resulted in acid rock drainage discharging from the mine portal. This project was undertaken to demonstrate an integrated passive biological system to treat metal-laden water flowing from an abandoned mine. The focus was to assess the effectiveness and reliability of the system to produce a high-quality effluent by reducing the level of dissolved sulfate and heavy metals from the acid rock drainage over five years, between 2001 and 2006. Results and lessons learned for this technology demonstration project are presented in this report.

The integrated passive biological treatment process installed at the Surething Mine was a multistage reactor system that involved sequential treatment of acid rock drainage. Metal-laden acidic water emanating from the mine adit was treated, using a series of three anaerobic reactors followed by aerobic treatment that included a final aerobic bioreactor. The anaerobic treatment relied on sulfate-reducing bacteria (SRB) that converted dissolved sulfate to hydrogen sulfide, which reacted with dissolved metals to form insoluble metal sulfides. This bacterial metabolism also produced bicarbonates that increased water pH and limited further dissolution of metals.

The SRB bioreactors substantially decreased the concentrations of six of the seven target metals, including aluminum, copper, iron, arsenic, cadmium, and zinc. After limited success, the seventh target metal, manganese, was eventually removed from the water using an aerobic bioreactor where manganese removal was consistent with manganese oxidizing bacteria activity.

The bioreactors were commissioned in August 2001 and analytical sampling and field measurements occurred periodically through October 2005. In general, there was a significant reduction in dissolved metals concentrations and the discharge pH was increased from near 3 to a more neutral level around 7. This project showed that this type of integrated passive biological treatment process could offer comprehensive treatment for many abandoned mine sites.

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