Microbial Sulfate Reduction Enhances Arsenic Mobility Downstream of Zerovalent-Iron-Based Permeable Reactive Barrier

Abstract

We assessed the potential of zerovalent-iron- (Fe(0)) based permeable reactive barrier (PRB) systems for arsenic (As) remediation in the presence or absence of microbial sulfate reduction. We conducted long-term (200 day) flow-through column experiments to investigate the mechanisms of As transformation and mobility in aquifer sediment (in particular, the PRB downstream linkage). Changes in As speciation in the aqueous phase were monitored continuously. Speciation in the solid phase was determined at the end of the experiment using X-ray absorption near-edge structure (XANES) spectroscopy analysis. We identified thio-As species in solution and AsS in solid phase, which suggests that the As(V) was reduced to As(III) and precipitated as AsS under sulfate-reducing conditions and remained as As(V) under abiotic conditions, even with low redox potential and high Fe(II) content (4.5 mM). Our results suggest that the microbial sulfate reduction plays a key role in the mobilization of As from Fe-rich aquifer sediment under anoxic conditions. Furthermore, they illustrate that the upstream-downstream linkage of PRB affects the speciation and mobility of As in downstream aquifer sediment, where up to 47% of total As initially present in the sediment was leached out in the form of mobile thio-As species.

Enriched Co-Treatment of Pharmaceutical and Acidic Metal-Containing Wastewater with Nano Zero-Valent Iron

“…The EDS qualitative analysis highlighted signals C, O, Al, Fe, Mn, and Si on the solid phase, in addition to small quantities of Zn in a range of 0.1-1%. These results are slightly different from Kumar et al [64], who used zero-valent iron to enhance sulfate reduction, but permeable reactive barriers. Silicon originates from the silica sand used as biomass at the initial stage of the treatment.…”

Thioarsenate Formation Coupled with Anaerobic Arsenite Oxidation by a Sulfate-Reducing Bacterium Isolated from a Hot Spring

“…Previous studies have shown that arsenic in solution could be removed through combination with sulfide minerals derived from microbial SO 4 2- reduction (Moore et al, 1988; Rittle et al, 1995; Kirk et al, 2004), and that the enhanced SO 4 2- reduction may be useful for arsenic remediation (Rittle et al, 1995; Newman et al, 1997; Castro et al, 1999; Macy et al, 2000; Jong and Parry, 2003; Lee et al, 2005; Saunders et al, 2005; Keimowitz et al, 2007; Saunders et al, 2008; Kirk et al, 2010; Luo et al, 2013). However, recently an experiment with permeable reactive barriers (PRB) was performed to test the effect of arsenic remediation in the presence microbial sulfate reduction, and found that up to 47% of total As initially present in the sediment was leached out in the form of mobile thio-As species (Kumar et al, 2016). Thus, more cautions should be taken on the geochemical behaviors of arsenic and sulfate in the environment (where the arsenite and arsenate have the potential to transform to mobile thioarsenates) when sulfate reducing bacteria are employed for arsenic remediation (Burton et al, 2014; Stucker et al, 2014).…”

Anaerobic Corrosion of Zero-Valent Iron at Elevated Temperatures

“…The competition of different hydrogenotrophic bacteria normally leads to the formation of a redox sequence in which hydrogen oxidizing processes with a higher energy gain (e.g., sulfate reduction) preferentially proceed before others (e.g., methanogenesis or acetogenesis) by keeping the hydrogen concentration below a threshold. 18,22,80 However, with (initially) greater hydrogen production at a higher temperature and the subsequent increased hydrogen concentrations, either within or downstream of a PRB, redox processes, like sulfate reduction, methanogenesis, or acetogenesis, 16,18,20,21,80 as well as biodegradation, 22−24 are more likely to occur simultaneously or may even be enhanced. In real groundwater systems, with increasing temperatures, precipitation of iron(II) sulfides 16,18,81 by sulfate reduction could eventually occur due to various species of sulfate-reducing bacteria.…”