Dynamic Evolution of the Microbial Community in BIOX Leaching Tanks

Abstract

Laboratory scale (7 L) reactors, inoculated with the L. ferriphilum dominated BIOX inoculum, were used to test the stability of the community under controlled conditions. Further, the effect of increased temperature, solids loading and pH fluctuations on the bioleaching performance and community structure were studied. Both performance and community structure remained stable under controlled conditions (41.5°C, 20% solids loading, 7 day residence time). Increasing the solids loading to 31% did not significantly affect performance or community structure. An increase in temperature (2°C every 10 days) did not have a significant effect up to 48°C, but the increase from 48°C to 50°C resulted in the loss of L. ferriphilum and a decrease in leaching performance. A more gradual increase (1°C increments) from 48°C to 50°C resulted in a stable community, dominated by Ac. cupricumulans and Acidithiobacillus caldus. A similar shift in community structure was observed when the pH fell below pH 0.8, but this was transient and L. ferriphilum recovered dominance upon adjustment to a pH > 1.0. A further increase in temperature to 52°C resulted in the loss of At. caldus and the emergence of Sulfobacilli. However, leaching performance under these conditions was poor, despite the presence of over 10 g/L ferric iron. In addition, yeast extract was required to maintain high cell numbers at 52°C. This work has identified a selection of conditions under which the community in BIOX reactors could evolve dynamically towards those communities currently observed in commercial operations.