T11 PM Developments in Bioremediation of Acid Mine Drainage Wastes
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 343-344

(MAR-1117-844333) The Role of Enhanced Heterotrophic Growth on Microbial Pyrite Oxidation.

Marchand, E.¹, Plumb, P.¹, ¹ University of Nevada, Reno, Reno, NV, USA

ABSTRACT- Acid mine drainage (AMD) is formed by the oxidation of reduced sulfur- and iron-containing minerals (pyrite, arsenopyrite, etc.), resulting in the generation of sulfuric acid. This process is catalyzed by certain bacteria (e.g. Acidithiobacillus ferrooxidans) which utilize ferrous iron and reduced sulfur as energy sources and require oxygen to grow. The focus of this research is to assess a method for minimizing acid formation in situ by supplementing contaminated sites with a suitable organic carbon source. It is believed that this will allow naturally occurring heterotrophic bacteria to flourish and out-compete sulfur- and iron-oxidizing bacteria for dissolved oxygen, thereby resulting in a shift in the dominant microbial community. Laboratory experiments have been performed with mixed and enrichment cultures to identify the influence of active heterotrophic growth on pyrite oxidation. In studies with pure and mixed cultures of acidophilic microbes augmented with organic carbon substrate, a number of different phenomena have been observed by our research group. Some of the most important findings are as follow: (1) In studies with pure and mixed cultures of acidophilic microbes in shake flasks containing pyrite at an initial pH of 2.5, the presence and growth of aerobic, heterotrophic bacteria resulted in significantly lower rates of pyrite oxidation even though oxygen was not found to be limiting (DO > 6.0 mg/L). (2) Soluble metabolic products of enhanced heterotrophic growth were found to have a marked effect on both the iron-oxidizing microbial community and the rate of abiotic pyrite oxidation. (3) In systems where the amount of oxygen was limited, it was found that in the presence of heterotrophic bacteria, even lower oxidation rates were observed and iron reduction occurred once oxygen was consumed. With limited oxygen available, ferric iron was used for respiration and the pH increased from 2.5 to 4.0. This is significant because a shift in solution pH is one of the most important steps in remediation of AMD sites. While sulfate reduction has not been specifically addressed during this research, it is likely that in situ sulfate reduction would be possible as a subsequent biogeochemical reaction once the mineral-oxidizing reactions were interrupted.

Key words: Acid Mine Drainage, Inhibition, Heterotroph, Bioremediation