Effects of different electron shuttles on the degradation of penoxsulam in single-chamber air microbial fuel cells.

The bioremediation of penoxsulam, a commonly encountered aquatic herbicide, was investigated using a single-chamber air microbial fuel cell (MFC) system. This study focused on how the modulation of electron transfer through exogenous electron shuttles (riboflavin (RF), anthraquinone-2-sulfonate (AQS)) and respiratory inhibitors (rotenone, capsaicin) affects electrogenesis and the degradation of penoxsulam. The addition of electron shuttles significantly improved both MFC power generation and pollutant removal efficiency in a dose-dependent manner, with optimal concentrations identified for maximum performance. In contrast, respiratory inhibitors strongly suppressed both processes, leading to an increase in charge transfer resistance. This study links macroscopic changes in performance with intracellular bioenergetic parameters, showing that electron shuttles maintain higher intracellular NAD⁺ levels and current densities, likely by promoting NAD⁺ regeneration, whereas inhibitors deplete NAD⁺ availability and hinder electron flow. Additionally, an analysis of key respiratory enzymes indicated that Cytochrome C oxidase plays an important role in facilitating extracellular electron transfer to the anode. Inhibitor studies provide further support for the importance of Complex I and downstream cytochrome pathways for power generation and degradation. By establishing the relationships between mechanisms and performance and proposing an integrated electron transfer model, this research highlights important enzymatic and metabolic control points for optimizing MFC-based bioremediation. These findings provide important insights into enhancing bioelectrochemical systems for concurrent environmental remediation and sustainable energy recovery.