Bioremediation of highly toxic arsenic via carbon-fiber-assisted indirect As(III) oxidation by moderately-thermophilic, acidophilic Fe-oxidizing bacteria

Objective: To enable removal of highly toxic As(III) from acidic waters by inducing indirect microbial As(III) oxidation by Fe-oxidizing bacteria via carbon-assisted redox-coupling between As(III) oxidation and Fe³⁺ reduction.

Results: Carbon-fiber (CF) was shown to function as an electron-mediator to catalyze chemical (abiotic) redox-coupling between As(III) oxidation and Fe³⁺ reduction. Accordingly, by taking advantage of Fe³⁺ regeneration by Fe-oxidizing bacteria, it was possible to promote oxidative removal of As(III) as ferric arsenate at moderate temperature. This reaction can be of use under the situation where a high-temperature treatment is not immediately available. Arsenic once concentrated as ferric arsenate on carbon-fibers can be collected to undergo phase-transformation to crystalline scorodite as the next re-solubilization/re-crystallization step at a higher temperature (70 °C).

Conclusions: While extremely acidophilic Fe-oxidizing bacteria are widely found in nature, the As-oxidizing counterparts, especially those grown on moderately-thermophilic and mesophilic temperatures, are hardly known. In this regard, the finding of this study could make a possible introduction of the semi-passive, low-temperature As-treatment using readily available Fe-oxidizing bacteria.