Advances in Development of Bioreactors Applications for the Treatment of Acid Mine Waters

Abstract

Demonstrations and technology development conducted under the Mine Waste Technology Program (MWTP) have lead to significant improvements of sulfate-reducing bacteria (SRB) bioreactors used to treat acid rock drainage (ARD). Benefits of this technology include the reduction of dissolved metal ions to insoluble metal sulfides and the neutralization of the acid rock drainage resulting from the production of bicarbonate from the oxidation of organic nutrients by the sulfate-reducing bacteria. Over the past 15 years, MSE has conducted many bench-scale and design tests along with several pilot-scale field demonstrations. This paper addresses engineering design criteria including the selection of organic media, maintenance of system permeability, and strategies for mitigation of ARD at remote sites with relatively small discharge. Specific applications and results from field SRB bioreactors and associated research are presented. They include: (1) An in situ bioreactor in flooded subsurface mine workings where the bioreactor was operated from 1993 to 2005. (2) A set of field bioreactors that allowed various operational attributes to be evaluated including pretreatment and operational temperature. This demonstration was conducted over a three-year period. (3) A set of both anaerobic and aerobic field bioreactors that operated in staged fashion to show the comprehensiveness of bioreactor applications for acid rock drainage treatment. (4) A bench-test study that focused on the effectiveness of SRB to reduce dissolved sulfate and heavy metals. (5) A bench test and field verification of the advantages of horizontal flow configuration in SRB bioreactors. (6) A reactive cartridge, a component of a modular SRB bioreactor that can be easily transported to remote sites.