Interfacial electron transfer facilitated the bioreduction of biochar-sorbed organic pollutants: Division-of-labor roles of electroactive structures

The inherent porosity and aromatic structures of biochar (BC) enable it to adsorb large amounts of organic pollutants. However, the fate and potential reaction pathways of BC-sorbed organic pollutants (BSOPs) remain largely unexplored. We hypothesized that distinct electroactive structures in BC selectively modulated the transcriptional responses of electroactive bacteria (EAB) to drive interfacial electron transfer (IET) and thereby facilitate BSOP degradation. To validate this hypothesis, we investigated the degradation of 2,5-dichloronitrobenzene (DCBN) sorbed onto BCs produced at 500 °C and 900 °C (BC5, BC9), as well as modified biochars (MBC5, MBC9) prepared using the modified Hummer's method, in the presence of Shewanella oneidensis MR-1, a typical EAB in the environment. A strong correlation between the reduction rate constants of sorbed DCBN and the electron transport rate constants confirmed that the bioreduction of sorbed DCBN was primarily governed by IET within the “bacteria–carbon” aggregations (r² = 0.90). Among all BCs, MBC9 exhibited the highest reduction rate constant (k_sd = 0.012 h^-1). Mechanistically, C=O/O–C=O functional groups promoted the up-regulation of the c-type cytochrome genes mtrC and mtrF, whereas graphitic structures facilitated electron transfer toward sorbed DCBN, revealing clear division-of-labor roles in the IET pathway. These findings highlight the crucial roles of BC electroactive structures in shaping EAB–BC interactions and offer fresh insights into the reaction pathways of BSOPs.