Enhanced antimony removal in microbial electrolysis cells via modified bio-electrodes: performance and underlying microbial mechanisms.

Microbial electrolysis cells (MECs) utilizing sulfate-reducing bacteria (SRB) present a promising strategy for remediating antimony (Sb) pollution. Modified metal-organic frameworks (MOFs) may further improve Sb sequestration. However, the combined removal performance and the underlying metabolic mechanisms remain unclear. Herein, three bio-electrodes-SRB (unmodified control), ZIF-67, and ZIF-67/graphene oxide (ZIF-67/GO)-were constructed and systematically evaluated in MECs for Sb removal, with electrochemical, morphological, and metatranscriptomic analyses of the electrode microbiomes. The ZIF-67/GO bio-electrode delivered the best performance, achieving 98% Sb removal (32% higher than the control) and 38% greater sulfate removal than the unmodified control. Notably, the ZIF-67/GO modified bioelectrode exhibited the most substantial electrochemical performance, including the highest current density and redox peak intensity, as well as the lowest charge transfer resistance. These characteristics enabled it to serve as an efficient electron transfer medium, enhancing direct electron transfer between the electrode and the biofilm. Both nanomaterials promoted biomass accumulation and biofilm development. Consistently, transcriptomic profiling showed that ZIF-67/GO markedly upregulated key genes involved in direct (octaheme cytochrome c) and indirect (flavodoxin, riboflavin biosynthesis) extracellular electron transfer, as well as genes associated with dissimilatory sulfate reduction. Moreover, ZIF-67/GO selectively enriched hydrogen sulfide-fermenting and hydrogen-producing bacteria, thereby improving the functional stability of the microbial community. Overall, these results demonstrate that MOF/graphene oxide composites can significantly enhance Sb bioremediation in MECs by stimulating microbial electron transfer and metabolic activity, providing a material-enabled strategy for treating wastewater containing sulfur compounds and heavy metals.