A mechanistic analysis of the influence of iron-oxidizing bacteria on antimony (V) removal from water by microscale zero-valent iron

BACKGROUND
Microscale zero-valent iron (mZVI) is an efficient material for removing heavy metals from water, and iron-oxidizing bacteria are the primary microorganisms responsible for iron corrosion. We investigated the effects of Sphaerotilus natans on antimony [Sb(V)] removal by mZVI using batch experiments.

RESULTS
At an initial Fe0 dose of 0.1g·L^-1, 40 mg·L^-1 Sb(V) was almost completely removed in an abiotic system. Although S. natans exhibited significant tolerance to Sb(V), its ability to adsorb Sb(V) was poor. Most importantly, the presence of S. natans reduced the removal rate of aqueous Sb(V) by mZVI by up to 39%. The value of the redox potential in the biologically mediated system was lower than that in the abiotic control, indicating oxygen consumption by S. natans. In the presence of S. natans, the main reaction products were FeOOH and FeSb₂O₆, compared to Fe₂O₃ in the abiotic system. Biomineralization of Fe³⁺ ions by S. natans may have occurred during the experiment, but it did not play a significant role in Sb(V) removal.

CONCLUSION
mZVI can be efficiently used to remove Sb(V) from water. However, the presence of S. natans may inhibit its removal ability, likely due to the decreased mass transfer and lower corrosion of iron.