Mitigation of BPA toxicity in anaerobic granular sludge by Fe3O4 NPs: Synergistic adsorption and electron transfer enhancement

Bisphenol A (BPA) severely inhibits anaerobic digestion (AD), reducing treatment efficiency and methanogenesis. Critically, this work establishes the first evidence of Fe₃O₄ NPs conferring BPA resilience via synergistic adsorption-bioaugmentation—an unreported mechanism in AD systems. This study demonstrates that Fe₃O₄ nanoparticles (NPs) mitigate BPA inhibition in anaerobic granular sludge (AnGS) systems. Electrochemical characterization confirmed enhanced capacitance and redox reversibility in Fe₃O₄-doped AnGS. The modified system achieved significant performance improvements: 24.4 % higher chemical oxygen demand removal, 31.8 % increased methane production, and enhanced extracellular polymeric substance stability versus control. Microbial analysis revealed enriched hydrolytic bacteria and methanogens, alongside elevated metabolite production. Mechanistically, Fe₃O₄ NPs function through: (1) adsorbing BPA, reducing its bioavailability, and (2) enhancing direct interspecies electron transfer (DIET) by serving as electron conduits, accelerating BPA degradation. This dual-action model—combining adsorption and DIET enhancement—effectively strengthens system resilience against BPA shock loads, providing a validated strategy for maintaining AD performance under toxicant stress.