Magnetite-contained biochar derived from fenton sludge modulated electron transfer of microorganisms in anaerobic digestion.

Biochar, with redox moieties or conjugated π-bond, can act as electron shuttle or conductor to facilitate electron transfer of syntrophic metabolism to enhance anaerobic digestion. High pyrolysis temperature (>500 ℃) is usually required to prepare conductive biochar, which however may cause biochar to loss redox moieties such as quinone/hydroquinone that are capable of serving as electron shuttle. Considering that magnetite is an excellent conductor which has been applied in improving syntrophic metabolism of anaerobic digestion, a novel magnetite-contained biochar was prepared using iron-rich Fenton sludge as raw material in this study. Amorphous iron oxides of Fenton sludge were transformed into magnetite at 400 ℃ of pyrolysis, while redox quinone/hydroquinone moieties of biochar were preserved well. Correspondingly, this magnetic biochar owned both high capacitance and excellent conductivity. When supplementing the biochar into an anaerobic digestion system, methane production was significantly enhanced. This study also offered a new approach to recycle Fenton sludge that is regarded as hazardous material.