The paper focuses on the improvements to engineered features of a passive technology that has been used for remediation of acid rock drainage (ARD). This passive remedial technology, a sulfate-reducing bacteria (SRB) bioreactor, takes advantage of the ability of SRB that, if supplied with a source of organic carbon, can increase pH and alkalinity of the water and immobilize metals by precipitating them as metal sulfides or hydroxides.The remoteness of ARD sites and their abundance require that the design of an SRB bioreactor be simple and inexpensive. Therefore, bioreactors need to be designed to a size that allows for transportation using primitive roads. To satisfy these requirements a design for a modular treatment system was developed using reactive cartridges (RC) that are prefabricated as 2.44-meter diameter vessels. The RC has been designed so it supports the prime functional aspects of a bioreactor such as high permeability, ample supply of organic carbon, ability to maintain anaerobic conditions, and capacity to accumulate precipitated metals and means for their periodical removal, as needed. In addition, the configuration of the RC allows for an easy replacement of the organic carbon. The RCs can be transported to an ARD site and assembled into a treatment system with a number of modules as required by the ARD flow rate and the metals load. A bioreactor system consisting of four RCs will be installed at an abandoned mine site with ARD of pH 5 or lower and a significant load of metals. The process of site selection is in progress.The RC design was developed by the Mine Waste Technology Program (MWTP) at MSE Technology Applications (MSE), Butte, Montana, USA.
Abstract. Over the past 15 years, MSE Technology Applications has conducted several notable technology demonstrations of biologically based technologies to treat acid rock drainage (ARD). These projects have progressively evolved under the U.S. Environmental Protection Agency's Mine Waste Technology Program (MWTP) and have resulted in significant advances in the development of bioreactor application of sulfate-reducing bacteria (SRB) technology. In this paper, summary information from four separate demonstration projects will be presented for the purpose of providing overviews of the bioreactor design parameters and the operation and development of each bioreactor system. Test methods and data analysis information for each project is not fully provided within this paper, as it is available from other sources. Summarized treatment results will be presented in this paper for three field-demonstrations. Additionally, results of one laboratory design project will be presented. A different bioreactor configuration was employed for each of the four projects. The first design to be presented will be an in situ bioreactor. This configuration was installed within the flooded subsurface workings of the Lilly Orphan Boy Mine in Montana and was operated between 1994 and 2005. The second design to be presented will be a set of on-site SRB bioreactors that were configured in parallel at the Calliope Mine in Montana. These test bioreactors allowed various operational attributes to be evaluated including lime pretreatment and temperature. The configuration of the third design to be presented will be a set of both anaerobic and aerobic bioreactors in staged fashion at the Surething Mine in Montana. This bioreactor design has been in operation since 2001 and shows the comprehensive applicability for biological treatment of ARD. The focus of the last project to be presented will be an investigative approach to bioreactor design. This resulted in a proposed bioreactor configuration to effectively treat ARD by reducing dissolved sulfate and heavy metals concentrations. In general, MWTP results from these four bioreactor configurations show that SRB bioreactors are effective for passive ARD treatment.
A two-stage passive treatment approach was assessed at a bench-scale level using two Colorado Mining Influenced Waters (MIWs). The first-stage was a limestone drain with the purpose of removing iron and aluminum and mitigating the potential effects of mineral acidity. The second stage was a sulfate reducing bioreactor composed solely of 50% corn stover and 50% walnut shells by volume. The primary difference in the two MIWs was the concentration of zinc 5-7 mg/L for the National Tunnel Adit drainage (NTA) vs. 65-75 mg/L for the Silver Cycle Adit drainage (SCA). The limestone pretreatment columns reduced the zinc in the NTA MIW to 1-2 mg/L and the SCA MIW to 38 -56 mg/L. The two SCA biocolumns had similar zinc removal but different sulfate removal with time. The sulfate reduction rate (SRR) for the SCA columns peaked at day 50 but at 0.5 mol S/m 3 /d for column 1 and 0.3 mol S/m 3 /d for column 2. Average SRR after day 50 was 0.24 and 0.13 mol S/m 3 /d for columns 1 and 2, respectively. The NTA columns (3 and 4) sustained an averaged SRR of 0.3 mol S/m 3 /d for days 30-130. The effluent zinc after startup from the two systems were < 0.1 mg/L and <2 mg/L for the NTA and SCA treatment systems, respectively. Other significant results included startup of sulfate reduction in both sets of bioreactors without the typical "manure" inoculum. The time to start up was not negatively affected by the lack of a designated inoculum. Another important result was the longer start up time required and the overall lower sulfate reduction observed for the higher zinc MIW. Additional
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.
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