Pyrogenic carbon is an important component of soil organic matter, the transformation of which plays a critical role in the biogeochemical cycles of carbon and other redox-active elements such as iron (Fe). Furthermore, anthropogenic pyrogenic carbon such as biochar and activated carbon has attracted much attention for their potential applications in agricultural soils and water treatment processes. However, to date, scant information is available for the role of pyrogenic carbon in the redox cycles of Fe. Herein, we studied the influences of wheat straw-derived biochars on the microbial reduction of hematite by <i>Shewanella oneidensis</i> MR-1. Microbial reduction of hematite was accelerated by more than 2-fold in the presence of 10 mg/L of biochar. Soluble leachate from 10 mg/L biochar enhanced Fe(III) reduction to a similar degree. The importance of the biochar leachate was supported by the response of Fe(III) reduction to the dose of biochar particles, which was correlated with the change in biochar leachate concentration rather than the amount of biochar particles. Microbiologically pre-reduced biochar leachate abiotically reduced hematite, consistent with the apparent electron shuttling capacity of biochar leachate. Electron paramagnetic resonance analysis demonstrated that biochar-mediated electron transport was mainly governed by its associated semi-quinone moieties. In addition to electron shuttling effects, biochar particles sorbed biogenic Fe(II) and thereby increased the long-term extent of hematite reduction 1.4-1.7 fold by decreasing the fraction of Fe(II) in solution phase. Our results suggest that Fe redox cycling may be strongly impacted by pyrogenic carbon in soils with relatively high content of indigenous pyrogenic carbon or substantial application of biochar.

Biochar-facilitated microbial reduction of hematite

255th National Meeting (2018)

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