Complete removal of arsenic and zinc from a heavily contaminated acid mine drainage via an indigenous SRB consortium

Abstract

Acid mine drainages (AMD) are major sources of pollution to the environment. Passive bio-remediation technologies involving sulfate-reducing bacteria (SRB) are promising for treating arsenic contaminated waters. However, mechanisms of biogenic As-sulfide formation need to be better understood to decontaminate AMDs in acidic conditions. Here, we show that a high-As AMD effluent can be decontaminated by an indigenous SRB consortium. AMD water from the Carnoulès mine (Gard, France) was incubated with the consortium under anoxic conditions and As, Zn and Fe concentrations, pH and microbial activity were monitored during 94days. Precipitated solids were analyzed using electron microscopy (SEM/TEM-EDXS), and Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy at the As K-edge. Total removal of arsenic and zinc from solution (1.06 and 0.23mmol/L, respectively) was observed in two of the triplicates. While Zn precipitated as ZnS nanoparticles, As precipitated as amorphous orpiment (am-As^III₂S₃) (33-73%), and realgar (As^IIS) (0-34%), the latter phase exhibiting a particular nanowire morphology. A minor fraction of As is also found as thiol-bound As^III (14-23%). We propose that the formation of the As^IIS nanowires results from As^III₂S₃ reduction by biogenic H₂S, enhancing the efficiency of As removal. The present description of As immobilization may help to set the basis for bioremediation strategies using SRB.

Keywords: Acid mine drainage; Arsenic; Biogenic sulfides; Bioremediation; Sulfate-reducing bacteria.