Biological attenuation of arsenic and iron in a continuous flow bioreactor treating acid mine drainage (AMD)

Abstract

Passive water treatments based on biological attenuation can be effective for arsenic-rich acid mine drainage (AMD). However, the key factors driving the biological processes involved in this attenuation are not well-known. Here, the efficiency of arsenic (As) removal was investigated in a bench-scale continuous flow channel bioreactor treating As-rich AMD (∼30-40 mg L). In this bioreactor, As removal proceeds via the formation of biogenic precipitates consisting of iron- and arsenic-rich mineral phases encrusting a microbial biofilm. Ferrous iron (Fe(II)) oxidation and iron (Fe) and arsenic removal rates were monitored at two different water heights (4 and 25 mm) and with/without forced aeration. A maximum of 80% As removal was achieved within 500 min at the lowest water height. This operating condition promoted intense Fe(II) microbial oxidation and subsequent precipitation of As-bearing schwertmannite and amorphous ferric arsenate. Higher water height slowed down Fe(II) oxidation, Fe precipitation and As removal, in relation with limited oxygen transfer through the water column. The lower oxygen transfer at higher water height could be partly counteracted by aeration. The presence of an iridescent floating film that developed at the water surface was found to limit oxygen transfer to the water column and delayed Fe(II) oxidation, but did not affect As removal. The bacterial community structure in the biogenic precipitates in the bottom of the bioreactor differed from that of the inlet water and was influenced to some extent by water height and aeration. Although potential for microbial mediated As oxidation was revealed by the detection of aioA genes, removal of Fe and As was mainly attributable to microbial Fe oxidation activity. Increasing the proportion of dissolved As(V) in the inlet water improved As removal and favoured the formation of amorphous ferric arsenate over As-sorbed schwertmannite. This study proved the ability of this bioreactor-system to treat extreme As concentrations and may serve in the design of future in-situ bioremediation system able to treat As-rich AMD.

Biological Fe(II) and As(III) oxidation immobilizes arsenic in micro-oxic environments

“…This might facilitate arsenic adsorption and/or co-precipitation. During Fe(II) oxidation, arsenic can also be co-precipitated with Fe(III), resulting in the formation of amorphous ferric arsenate (Fernandez-Rojo et al, 2017;Tian et al, 2017). In this study, although a large proportion of arsenic was co-precipitated during Fe(III) precipitation (Fig.…”

“…Previous reports show that arsenic is toxic to many microorganisms, which consequently affects the distribution of FeOB (Fernandez-Rojo et al, 2017). The cluster analysis showed that the structure of microbial community in the iron oxide layer was significantly affected by the presence of arsenic (Fig.…”

“…These microaerophilic FeOB precipitate biogenic Fe(III) oxyhydroxides at circumneutral pH in the form of twisted ribbon-like stalks, hollow tubular sheaths, and granular or amorphous structures that can adsorb and immobilize organics, arsenic, and other metals (Emerson et al, 2010;Muehe and Kappler, 2014). Although previous studies have shown that biogenic Fe(III) oxyhydroxides formed by FeOB play an important role in arsenic cycling (Hohmann et al, 2009;Xiu et al, 2016;Fernandez-Rojo et al, 2017;Sowers et al, 2017), few studies have explored microaerophilic microbial Fe(II) oxidation for the mechanisms by which arsenic is immobilized by biogenic Fe (III) oxyhydroxides formed from paddy soil microbes under micro-oxic conditions.…”

“…As(III) oxidation by microorganisms is usually catalyzed by As(III) oxidases, which are encoded by arsenite oxidase genes (aioA) (Slyemi and Bonnefoy, 2012). Recent studies have revealed the distribution of the diverse aioA in arsenic-contaminated soils and found that some FeOB encoded aioA are essential in As(III) oxidation (Fernandez-Rojo et al, 2017;Nitzsche et al, 2015;Zhang et al, 2015). Although arsenic is highly toxic to many microorganisms in paddy soils, some FeOB are able to metabolize arsenic for growth.…”

Simple or complex organic substrates inhibit arsenite oxidation and aioA gene expression in two β-Proteobacteria strains

“…real-time PCR (qPCR), respectively from DNAs and cDNAs obtained from cultures of "T.arsenivorans" and H. arsenicoxydans. qPCR was carried out using m4-1F forward (GCCGGCGGGGGNTWYGARRAYA) and m2-1R reverse (GGAGTTGTAGGCGGGCCKRTTRTGDAT) primers, as designed in[30] and applied in[31]. The expected product size was 110 bp.…”