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

Abstract

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 (AsV) and sulfate (SO42-) 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 AsV and SO42- reduction. A continuous-flow anaerobic bioreactor was maintained at slightly acidic pH (6.25-6.50) and fed with AsV and SO42-, utilizing ethanol as an electron donor for over 250 d. A second bioreactor running under the same conditions but lacking SO42- was operated as a control to study the fate of As (without S). The reactor fed with SO42- 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- (As2S3) and realgar-like (AsS) solid phases. Solid phase characterization using K-edge X-Ray absorption spectroscopy confirmed the formation of a mixture of As2S3 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 sulfate by precipitation of ASM.

Adaptation of a Methanogenic Consortium to Arsenite Inhibition

“…The natural widespread occurrence of As and As-utilizers have facilitated that a large diversity of organisms have the ability to detoxify and respire As (Yang et al 2012), including methanogenic archaea as proven by the presence of the Ars operon genes in the genomes of Methanosarcina mazei , and Methanothermobacter thermautothrophicus , among others (Bini 2010) and the ability of methanogenic consortia to reduce As V (Field et al 2004, Rodriguez-Freire et al 2015). Recently, Wang et al (2014) isolated the gene MaarsM in the archaeon Methanosarcina acetivorans .…”

“…A further description of the reactor is described in the previous study by Rodriguez-Freire et al (2015). The arsenic exposed microorganisms were obtained from a continuous-flow laboratory scale UASB bioreactor inoculated with the granular sludge (13.3 g volatile suspended solids (VSS)/l) and fed with 1.02 mM arsenate (As V ) and 4.40 mM ethanol as electron donor for 160 d. The endogenous activity of the inocula was measured to be 8 e − meq/g VSS.…”

“…At the beginning of the operation, acetate accumulated at 3.31 mM and CH 4 production was negligible. After an initial period of adaptation that lasted 22 d, acetate utilization and CH 4 production increased progressively with the operational time (Rodriguez-Freire et al 2015). …”

“…enrichment of a new dominant species or death of more sensitive species) (Giller et al 1998). The main objective of this study was to evaluate the adaptation capacity of a methanogenic granular sludge consortium to As III toxicity, after being exposed to 1 mM As III during 160 d in a bioreactor (Rodriguez-Freire et al 2015). …”

Resource Recovery from Wastewater by Biological Technologies: Opportunities, Challenges, and Prospects

“…Even during long-term metals leaching caused by corrosion and/or dissolution processes, the biogenic ferrous sulfide creates a protective barrier avoiding the metals to be in contact with highly sensitive methanogens (Gonzalez-Estrella et al, 2015, 2016). An interesting example of usage of the iron-sulfur cycle is the renmediation and recovery of arsenate by iron-sulfides and sulfates (Rodriguez-Freire et al, 2014, 2016). Other precipitative processes are indirectly related with microbial redox metabolism and are derived from biogenic alkalinity, as in the case of microalgae, fungi, and phototrophic bacteria technologies (Das et al, 2009; Ye et al, 2015).…”