Dynamics of bacterial communities mediating the treatment of an as-rich acid mine drainage in a field-scale pilot

Passive treatment based on iron biological oxidation is a promising strategy for As-rich acid mine drainage (AMD) remediation. The present study aimed at the characterization of the bacterial diversity in a field-pilot bioreactor treating extremely As-rich AMD in situ. Inside the bioreactor, the bacterial communities responsible for iron and arsenic removal formed a biogenic precipitate. These communities evolved from a structure at first similar to the one of the feed water used as an inoculum to a structure similar to the natural ecosystem developing in situ in the AMD. Diverse FeOB populations largely dominated the bioreactor including: Gallionella, Ferrovum, Leptospirillum, Acidithiobacillus, Ferritrophicum,… Notable shifts were observed in the distribution of these populations inside the bioreactor. Appreciable arsenite oxidation occurring in the bioreactor could be linked to the presence of Thiomonas related bacteria. The spatio-temporal dynamics of the whole communities were tightly linked to variations in the physico-chemistry of the AMD water transiting inside the bioreactor. The main parameters that proved to exert a control on the bacterial communities potentially involved in the water treatment process were: DO, temperature, pH, dissolved sulfates, arsenic and Fe(II) concentrations and redox potential. The ubiquity and the physiological diversity of the bacteria identified (including the genus of biotechnological relevance Ferrovum) suggested that this treatment system could be easily adapted to the treatment of AMD with a large range of physico-chemical characteristics.