Arsenic removal by acidophilic iron-oxidizing microorganisms: Moderate and extreme thermophiles

The treatment of arsenic-rich effluents poses a significant challenge for the mining industry. Conventional chemical methods often create unwanted byproducts and unspecific reactions. Thus, the problem of arsenic treatment in these effluents is not completely resolved. Biological approaches are a promising, eco-friendly, and low-cost alternative for removing arsenic. This study aims to evaluate the effectiveness of moderate thermophilic (50 °C) and thermophilic (70 °C) iron oxidizing microorganisms in removing arsenic from an arsenic-rich solution. Factors including arsenic species, temperature, iron, and initial cell concentration are addressed in this paper. Results indicated that arsenic species significantly influenced arsenic removal efficiency. Higher arsenic removal yield was achieved when As(V) is the initial arsenic species at both temperatures. Iron concentration positively affected the maximum As(III) and As(V) removal rates. While temperature negatively affected the maximum As(III) removal rate and has no effect on maximum As(V) removal rate, which instead depended on the microbial Fe(II) oxidation capacity. Biomineral analysis revealed two arsenic removal mechanisms: adsorption onto iron compounds and the formation of amorphous ferric arsenates. Energy Dispersive Spectroscopy confirmed that precipitates were composed primarily of arsenic and iron, while Scanning Electron Microscopy revealed morphological differences between biological and chemical precipitates were observed. These findings enhance our understanding of the role of iron-oxidizing microorganisms in arsenic removal and facilitate the identification of better conditions for arsenic biomineralization processes.