Biochar-Facilitated Microbial Reduction of Hematite

Abstract

As an important component of soil organic matter (SOM), the transformation of pyrogenic carbon plays a critical role in the biogeochemical cycles of carbon and other redox-active elements such as iron (Fe). Herein, we studied the influences of wheat straw-derived biochars on the microbial reduction of 100 mM of hematite by the dissimilatory metal reducing bacteria Shewanella oneidensis MR-1 under anoxic conditions. The long-term microbial reduction extent and initial reduction rate of hematite were accelerated by more than 2-fold in the presence of 10 mg L(-1) biochar. Soluble leachate from 10 mg L(-1) biochar enhanced Fe(III) reduction to a similar degree. Microbially prereduced biochar leachate abiotically reduced hematite, consistent with the apparent electron shuttling capacity of biochar leachate. Electron paramagnetic resonance (EPR) analysis suggested that biochar leachate-associated semiquinone functional groups were likely involved in the redox reactions. In addition to electron shuttling effects, biochar particles sorbed 0.5-1.5 mM biogenic Fe(II) and thereby increased the long-term extent of hematite reduction by 1.4-1.7 fold. 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.

Rapid electron transfer by the carbon matrix in natural pyrogenic carbon

“…5a clearly confirmed the feasibility of cyclic voltammetry for studying the charging and discharging behaviours of surface quinone groups in pyrogenic carbon immobilized on a graphite working electrode. We used wood biomass as feed stock for preparation of pyrogenic carbon due to its low ash, mineral and leachable organic compound content after pyrolysis50, which minimized the contribution of unstructured redox-active species to the charging and discharging cycles of surface quinone groups1314. Increasing the amount of immobilized pyrogenic carbon resulted in an increased peak current and total charging and discharging capacity, but the sensitivity (expressed by capacity per gram of pyrogenic carbon) decreased possibly due to the screening of effective contact between surface quinone groups and the working electrode (inset in Supplementary Fig.…”

“…Such redox processes have been demonstrated to play important roles in suppression of greenhouse gas emissions48, iron mineral reduction9 and decontamination10. Recently, pyrogenic carbon has been found to reversibly accept and donate large amount of electrons11, and functions very similarly to natural organic matter in many biogeochemically and environmentally relevant redox reactions, such as reductions in nitrous oxide emission and total denitrification12, iron mineral reduction1314 and organic contaminant transformation15. Since pyrogenic carbon is now recognized as a ubiquitous and major component of natural organic matter worldwide1617, the contribution of pyrogenic carbon to electron fluxes could be considerable.…”

Surface Interactions between Gold Nanoparticles and Biochar

“…Biochar releases DOC of varying molecular weight (MW), aromaticity, and carboxyl content, including low MW organic acids structurally similar to citrate 14–16 . Biochar could stabilize nAu by (i) replacing citrate capping agent by its DOC having higher MW and aromaticity, (ii) increasing the solution pH, (iii) providing negatively charged surfaces at pH above its point of zero charge (PZC, typically below 3) 17 , and (iv) serving as a reductant 18, 19 . Conversely, biochar could destabilize nAu by (i) providing attractive surface interactions, (ii) decreasing the solution pH, and (iii) increasing the ionic strength by releasing salts 15 .…”

Sulfate Removal in Biochemical Reactors and Scrubbers Treating Neutral Low-Metal Concentration Miw

“…Biochar behaves as an "electron shuttle" (Xu et al, 2016) and this property prompted its inclusion as a possible catalyst to improve BCR performance. Therefore, it was inferred that the biochar included in the BCR 3 substrate was responsible for the increased sulfate removal efficiency by increasing carbon availability.…”