Third-Year Performance of 55-Gallon Bioreactors Treating Mining Influenced Water From the National Tunnel in Black Hawk, Colorado

Abstract

Mining influenced water (MIW) from the National Tunnel drains into the North Fork of Clear Creek in Black Hawk, Colorado. Fifty-five gallon bioreactors were set up in June 2006 to investigate the performance of two different solid phase substrate mixtures and an ethanol fed system with limestone support. The MIW from the National Tunnel in 2009 was near neutral and contained major average dissolved metals of Fe = 40 mg/L, Zn = 6, and Mn = 19. The overall goal was to develop design guidance for a full-scale bioreactor system. All bioreactors were effective in removing at least 95% of influent zinc. Average 2009 iron and manganese removals for the solid phase bioreactors were 80% and 45%, respectively. In contrast, the ethanol fed reactors released iron and manganese at 50 to 300% above influent values. The solid phase bioreactors have consistently been effective at removing zinc and a large fraction of iron since startup. The manganese removal capability began to develop after one year of operation and became relatively consistent after two years of operation. The bioreactors constructed with solid phase substrate have effectively removed a significant fraction of the influent metals in the National Tunnel over the three-year operating period.