Operational Lessons Learned During Bioreactor Demonstrations for Acid Rock Drainage Treatment

Abstract

The US Environmental Protection Agency’s Mine Waste Technology Program (MWTP) has emphasized the development of biogeochemically-based treatment technologies for mitigation of acid rock drainage (ARD). Progressive technology demonstrations by the MWTP over the past 15 years have resulted in improved operation of sulfate-reducing bacteria (SRB) bioreactors. Although using SRB to treat ARD is now fairly widespread, it was uncommon in the early 1990s when the MWTP used this innovative biotechnology. The first and longest running demonstration was an in situ bioreactor installed within the flooded subsurface workings of the Lilly/Orphan Boy Mine in 1994. The second project, at the Calliope Mine, compared the performance of several SRB bioreactor configurations and operational attributes, including lime pretreatment and reactor temperature. The third demonstration, at the Golden Sunlight Mine, consisted of two treatment steps with a recycle stream. The fourth project was an investigation of existing bioreactor designs and resulted in an improved bioreactor configuration. Significant findings included: (1) a mineshaft could be used as a long-term, in situ bioreactor, (2) SRB thrive in temperature extremes, (3) sulfide recycle effectively avoids contact of ARD with bacterial populations, and (4) ideal bioreactor substrate provides short-term and long-term nutrients, good support matrix, and enhanced permeability.