Poorly conductive biochar boosting extracellular electron transfer for efficient volatile fatty acids oxidation via redox-mediated mechanism

This study explored the performances, and associated mechanisms of biochar promoting volatile fatty acids (VFA) oxidation via extracellular electron transfer (EET) pathway. It was found that in a bioelectrochemical system, adding biochar suspension remarkably enhanced electricity generationwhatever acetate or propionate used as an electron donor. The maximum current density in biochar-assisted groups reached 1.6-2.2 A/m(2), which were 69.2-220.0% higher than that of control groups. The lower electrical resistance of anode in biocharassisted groups was potentially attributed to the formed biofilm dominated by electro-active Geobacteraceae, and the electron donor type depending on dominant genus. In specific, with biochar assistance, Desulfuromonas enriched from 1.1% to 25.0% when acetate as an electron donor, and the relative abundance of Geobacter increased from 4.6% to 31.7% as dominant genus in propionate-added group. Electrochemical analysis uncovered that biochar hardly elevated sludge electrical conductivity, while the excellent redox-based electron exchange transfer capacity likely made biochar as a transient electron acceptor, which was more accessible than anode to support the metabolism of electroactive bacteria in the initial stage. Meanwhile, the porous surface area of biochar particle likely provided a bridge between suspended sludge and anode, to support a more directional evolution of electroactive bacteria on anode. This dual-function of biochar achieved a sustainable VFA oxidation via EET-based pathway. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study explored the performances and mechanisms of biochar in promoting volatile fatty acids oxidation via extracellular electron transfer pathway. The results showed that adding biochar suspension significantly enhanced electricity generation in a bioelectrochemical system. The lower electrical resistance of the anode in the biochar-assisted groups was potentially attributed to the formation of a biofilm dominated by electro-active Geobacteraceae. Furthermore, the excellent redox-based electron exchange transfer capacity of biochar made it a transient electron acceptor, which supported the metabolism of electroactive bacteria in the initial stage and provided a bridge between suspended sludge and anode to facilitate the evolution of electroactive bacteria on the anode.