Arsenic remediation by formation of arsenic sulfide minerals in a continuous anaerobic bioreactor

Arsenic (As) is a highly toxic metalloid that has been identified at high concentrations in groundwater in certain locations around the world. Concurrent microbial reduction of arsenate (As V ) and sulfate (SO 4 2− ) can result in the formation of poorly soluble arsenic sulfide minerals (ASM). The objective of this research was to study As biomineralization in a minimal iron environment for the bioremediation of As‐contaminated groundwater using simultaneous As V and SO 4 2− reduction. A continuous‐flow anaerobic bioreactor was maintained at slightly acidic pH (6.25–6.50) and fed with As V and SO 4 2− , utilizing ethanol as an electron donor for over 250 d. A second bioreactor running under the same conditions but lacking SO 4 2− was operated as a control to study the fate of As (without S). The reactor fed with SO 4 2− removed an average 91.2% of the total soluble As at volumetric rates up to 2.9 mg As/(L · h), while less than 5% removal was observed in the control bioreactor. Soluble S removal occurred with an S to As molar ratio of 1.2, suggesting the formation of a mixture of orpiment‐ (As 2 S 3 ) and realgar‐like (AsS) solid phases. Solid phase characterization using K‐edge X‐ray absorption spectroscopy confirmed the formation of a mixture of As 2 S 3 and AsS. These results indicate that a bioremediation process relying on the addition of a simple, low‐cost electron donor offers potential to promote the removal of As from groundwater with naturally occurring or added SO 4 2− by precipitation of ASM. Biotechnol. Bioeng. 2016;113: 522–530. © 2015 Wiley Periodicals, Inc.