Abstract
Sulfide wastes from the extraction of metal ores generate acidic mine drainage (AMD), containing toxic elements such as arsenic (As), antimony (Sb) and thallium (Tl). Remediation processes using microbial communities have been developed to remove these pollutants from AMD, but the biological processes involved in these treatments still need to be controlled to ensure their effectiveness. The scientific obstacles, which are the subject of the thesis, lie in (1) a lack of knowledge on direct and indirect microbial transformations of Sb and Tl, and (2) for As, a weak understanding of relationships that exist between dynamics of microbial communities, their functional potential, water physico-chemistry and efficiency of treatments applied to AMD. A multidisciplinary approach, mainly based on microbial ecology and physico-chemistry tools, allowed to characterize the diversity of microbial communities capable of directly or indirectly transforming As and Sb at increasing experimental scales: batch reactor, laboratory continuously fed systems, and pilot on site. A microbial consortium able of tolerating up to 100 mM of antimonite and oxidizing it under acidic conditions (pH <4), equivalent to those of AMD, was obtained in a batch system in the laboratory from contaminated soil at Sb. A laboratory column bioreactor, fed continuously with a real AMD and inoculated with a bacterial sulfate-reducing consortium enriched from this AMD, allowed the elimination of almost all the As, Sb and Tl present in the water. Finally, the dynamics of the bacterial communities was described under real conditions in an aerobic pilot for the treatment of an AMD rich in As and installed on site. These communities were dominated by Fe-oxidizing bacteria, and their spatial and temporal structure modifications appeared to be associated to variations of water physico-chemistry (dissolved oxygen, temperature, pH, redox potential, sulfate, arsenic and iron(II) concentrations). The knowledge acquired during this thesis may serve as a basis for the design of passive and inexpensive eco-technologies applicable to the management and remediation of former mining sites.