Integrating multiphysics simulation and biological insights to optimize fungal-bioaugmented soil microbial fuel cells.

Soil contamination by persistent herbicides like haloxyfop-P-methyl (B) poses substantial environmental risks. Microbial fuel cells (MFCs) offer a solution but require in-depth optimization. We designed a single-chamber soil MFC with a graphite felt anode and air cathode. A 2D equivalent model coupling secondary current distribution and diluted species transport was built in COMSOL Multiphysics. A specific factor (ffungi) for fungal bioaugmentation was introduced, alongside a substrate promotion-toxicity inhibition function (fB(x)) for the herbicide. The model validated the experimental performance ranking (2B + Myrothecium verrucaria (Mv) > B + Mv + Carbon fiber > B + Talaromyces > B + Mv/Talaromyces) and achieved high calibration accuracy, with relative errors below0.6% for current density(CD) and5.7% for power density (PD) across multiple groups. Parameter scans revealed that increasing ffungi linearly boosts performance, with CD and PD enhancements of approximately 2.5 times at ffungi=5. The initial pollutant concentration exhibited a non-monotonic "substrate promotion-toxicity inhibition" window based on model-predicted extrapolations beyond the experimentally tested x  = 1 and x  = 2 cases, suggesting an optimal concentration range (x = 2-4) that requires future experimental validation.Carbon fibers predominantly lower interfacial contact impedance and enhance the effective reaction area. Mechanistically, the simulated electrochemical behavior is consistent with the reported biological data (e.g. metagenomics and EIS), suggesting that the "xeno-fungusphere" formed by M. verrucaria promotes biofilm formation and electron transfer. The model serves as a robust tool for designing efficient fungal-augmented MFC for herbicide remediation and energy recovery.