English

Abstract

Sulfate-reducing biochemical reactors (BCRs) were installed to provide a basis for substrate selection for a final treatment remedy for mining influenced water (MIW) from the National Tunnel adit. Black Hawk, CO. The MIW was characterized by elevated metal and SO4 2- concentrations as well as pH fluctuations from 4.8-6.4. Three pairs of BCRs were installed in 2006, each of which contained a different mixture of solid or liquid-phase substrates. The above-ground BCRs partially froze during the first winter, prompting a redesign of the hydraulic system in May 2007 and the installation of heating and insulation in preparation for the following winter in October 2007. During the hydraulic system re-design, a fourth pair of reactors that contained CHITOREM ® SC-20 chitin complex was added to provide data on an alternative solid-phase substrate. Results from 2007 suggest that nearly all of the reactors removed greater than 95% of the Fe and Zn and 50-95% of the sulfate from the MIW during September through December 2007. Copper removal was typically above 95%. In addition, chitin complex reactors demonstrated high Mn removal (average removal was 80%) and high alkalinity (average of 4200 mg/L as CaCO3) during the same period. The high alkalinity was partially due to high concentrations of ammonium (up to 450 mg/L as nitrogen). Operational challenges due to winter conditions in November and December 2007 caused significant temperature and flow fluctuations; however, effective removal of metals was still observed. The BCRs will be monitored through summer 2008 and the data will be evaluated in late-summer 2008 to determine which substrates (CHITOREM ® SC-20, ethanol or solid phase organic mixture) are best suited for long-term treatment of the National Tunnel MIW by BCRs.