Anaerobic Disposal of Arsenic-Bearing Wastes Results in Low Microbially Mediated Arsenic Volatilization

Abstract

The removal of arsenic from drinking water sources produces arsenic-bearing wastes, which are disposed of in a variety of ways. Several disposal options involve anaerobic environments, including mixing arsenic waste with cow dung, landfills, anaerobic digesters, and pond sediments. Though poorly understood, the production of gaseous arsenic species in these environments can be a primary goal (cow dung mixing) or an unintended consequence (anaerobic digesters). Once formed, these gaseous arsenic species are readily diluted in the atmosphere. Arsenic volatilization can be mediated by the enzyme arsenite S-adenosylmethionine methyltransferase (ArsM) or through the enzymes involved in methanogenesis. In this study, methanogenic mesocosms with arsenic-bearing ferric iron waste from an electrocoagulation drinking water treatment system were used to evaluate the role of methanogenesis in arsenic volatilization using methanogen inhibitors. Arsenic volatilization was highest in methanogenic mesocosms, but represented <0.02% of the total arsenic added. 16S rRNA cDNA sequencing, qPCR of mcrA transcripts, and functional gene array-based analysis of arsM expression, revealed that arsenic volatilization correlated with methanogenic activity. Aqueous arsenic concentrations increased in all mesocosms, indicating that unintended contamination may result from disposal in anaerobic environments. This highlights that more research is needed before recommending anaerobic disposal intended to promote arsenic volatilization.

LCA of Disposal Practices for Arsenic-Bearing Iron Oxides Reveals the Need for Advanced Arsenic Recovery

“…For the strategy of mixing As WTRs with organic waste, the system boundary does not include the organic residues (e.g., cow dung). The fraction of As converted to volatilized species (90%) and the aqueous phase (10%) during disposal was estimated from the available scientific literature. − Finally, for open disposal, this strategy was assumed to occur via dumping As WTRs directly into surface waters, consistent with the documented literature. , This system boundary includes the As flows arising from As leaching from the WTRs, which is estimated to be 90% to the aqueous phase and 10% to soils (sediment). , …”

The Microbiology of Metal Mine Waste: Bioremediation Applications and Implications for Planetary Health

“…The volatilization of As via methylation will in principle lower the As content of contaminated soils, and this is favored under reducing conditions (Frohne et al, 2011). Methanogenic conditions also slightly favor the methylation of As (Webster et al, 2016). Arsenic methylation is widespread in the environment, including in mining environments (Héry et al, 2014;Ngegla et al, 2020).…”

Arsenic Transformation in Swine Wastewater with Low-Arsenic Content during Anaerobic Digestion

“…MMA was mostly detected in the sample of MP. This may be due to the presence of different As(V)-reducing microorganisms in the biogas slurry that transform As(V) to As(III) under reduction conditions, subsequently converting it to MMA, DMA, and trimethylarsine (TMA), which is released with the methane through As methylation [18]. MMA is the intermediate phase of methylation.…”

“…It has been reported that a range of arsine and methyl-arsine species from arsenate were produced by cultures of methanogens [26]. The impact of methanogenesis on As volatilization has been studied in As-bearing ferric iron waste, in which As volatilization represented <0.02% of the total As added [18]. The quantification of genes involved in As biotransformation processes can be taken as an indicator for As transformation.…”