Résumé
Arsenic (As) is a toxic element ubiquitous in acid mine drainage (AMD). It represents a threat for freshwaterressources in the vicinity of closed and active mines. Passive bioremediation techniques based on biological iron (Fe)oxidation represent an opportunity to treat efficiently and economically this kind of pollution.A field bioreactor was implemented at the Carnoulès mine (France) for the treatment of acid Reigous Creek (pH ~3.2) thatcontains ~120 mg/L As (81% As(III)) and ~1 g/L Fe (97% Fe(II)). It consisted in five shallow trays of 1.5 m2 in series,continuously fed with AMD by gravitational flow. For 7 months, we monitored the physico-chemistry of the inlet andoutlet AMD water, as well as the As speciation, the mineralogy and the bacterial community structure in the biogenicprecipitate that formed inside the bioreactor.The bioreactor removed 4 to 97% As, depending on the flow rate, whereas Fe oxidation and precipitation did notexceed 20% and 11%, respectively. The resulting biogenic precipitate was extremely As-rich; the As/Fe molar ratio andthe As(V)% increased with the experiment duration, until 0.86 and 99%, respectively, indicating that As oxidation took placein the bioreactor. Analysis of the bacterial community structure associated with As and Fe removal also showed temporalvariations.This bioreactor provided information about the treatment perfomance and the biogenic precipitate production under fieldconditions, which may serve in designing future bioremediation system.