Bio-precipitation of antimony in a sulfate-reducing bioreactor treating a real As-rich acid mine drainage water

Arsenic (As) and antimony (Sb) can be disseminated from mining sites to aquatic ecosystems by acid mine drainage (AMD). The precipitation of metal sulfides, based on sulfide production by sulfate-reducing bacteria (SRB) is a promising treatment option. Although As and Sb present structural analogies, the bio-precipitation of these two elements as sulfides, when they are both present in a single AMD, has not been studied yet. Here, the possibility to remove concomitantly As and Sb from acidic waters by the activity of SRB was investigated in a fixed-bed column bioreactor. The real AMD water used to feed the bioreactor contained nearly 1 mM As and increasing Sb concentrations (0.008 ± 0.006 to 1.01 ± 0.07 mM) in order to reach a molar ratio Sb/As = 1. Results showed that the addition of Sb did not negatively influence the efficiency of As bio-precipitation. Sb was removed efficiently (up to 97.9% removal) between the inlet and outlet of the bioreactor, together with As (up to 99.3% removal) at all tested Sb conditions. The concentrations of dissolved Sb and As varied along the reactor height. Similarly, the diversity of the bacterial communities developing inside the reactor changed in time and space. Polymers degraders, fermenters, and acetate degraders dominated the bacterial community. Appreciable sulfate reduction occurred in the bioreactor and could be linked to the stable presence of an SRB OTU affiliated to the Desulfosporinus genus. The efficiency of the bioreactor towards the elimination of As and Sb and the presence of functional groups with biotechnological relevance suggested that this treatment system could be a suitable bioremediation process for the simultaneous removal of Sb and As from AMD.