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Comparing Chitin And Organic Substrates On The National Tunnel Waters In BlackHawk, Colorado For Manganese Removal - (Presentation)
Citation:
Venot, C., L. Figueroa, R. A. Brennan, T. R. Wildeman, D. J. REISMAN, AND M. R. Sieczkowski. Comparing Chitin And Organic Substrates On The National Tunnel Waters In BlackHawk, Colorado For Manganese Removal - (Presentation). Presented at 25th Annual Meeting American Society of Mining and Reclamation (ASMR): New Opportunities to Apply our Science, Richmond, VA, June 14 - 19, 2008.
Impact/Purpose:
To describe the differences between the chitin reactors and the sulfate-reducing bioreactors, and to provide some preliminary opinions on why these differences occurred.
Description:
The National Tunnel is a part of the Central City/Idaho Springs Superfund site. Because passive treatment is an important possibility for removal of contaminants from the water, the USEPA and the Colorado Division of Public Health and Environment (CDPHE) have been sponsoring a bench-scale study of different organic substrates for sulfate-reducing bioreactors (SRBRs). The substrates being tested include ethanol, woodchips and hay, woodchips and corn stover, and crab-shell chitin. After 6-18 months of operation, all of the reactors are showing significant amounts of sulfate reduction. In all of the reactors, copper and zinc are removed to below their respective ambient water quality criteria of 0.010 and 0.100 mg/L. As is commonly observed in SRBRs, manganese removal is significantly less, with the exception of the chitin reactors. The reason for chitin's superior manganese removal may be the dissolution of calcite from the crab shell. In the chitin reactors, calcium has increased from 210 to 870 mg/L and alkalinity has increased from zero to up to 5,000 mg CaCO3/L. Futhermore, the pH of the effluent leaving the chitin systems averages 6.9. In most SRBRs, manganese is precipitated as MnCO3 and significant removal does not occur until the pH is raised to between 7 and 8. This is the case in the other types of SRBRs being tested at the National Tunnel, as their manganese removal efficiencies have only approached 50% at pH values ranging from 6.5 to 7.5. However, in the chitin reactors, 86% of the influent manganese is being removed from 21.5 mg/L to an average of 3 mg/L. The high removal is very similar to the removal of manganese in pulsed limestone beds that are maximized for the dissolution of calcite. These chitin reactors have been operating for six months while the other substrate reactors have been operating for over one year.