Insight into the Regulation Mechanism of Iron Oxide Nanoparticles in Anammox Consortia: Autophagy-Dependent Ferroptosis

Iron oxide nanoparticles (IONPs) have been widely used and pose a high risk to human and animal health. In this study, the fate and regulation mechanism of γ-Fe2O3 NPs in an anaerobic ammonium oxidation (anammox) system were studied from the perspective of morphology, biotransformation, and microbial interaction. The lowest nitrogen removal efficiency (NRE) of the anammox process was 63.8% under γ-Fe2O3 NP stress. The Fe(II) and Fe(III) concentrations increased with the bioaccumulation of γ-Fe2O3 NPs, which caused high-level reactive oxygen species (ROS) and ferroptosis in the anammox consortia. They inhibited the synthesis pathways of ATP and heme c, which further reduced the detoxification ability of microbiota. Moreover, Fe(II) could be oxidized to Fe(III) in the form of Fe(III)-O, which formed biocrusts on the cell surface and limited the microbial substrate utilization. Microbial community analysis showed that the low-concentration γ-Fe2O3 NPs increased the abundance of functional bacteria related to nitrogen transformation, while 50 mg L–1 of γ-Fe2O3 NPs significantly inhibited their activity and metabolism. These findings deepen our understanding of the Fe–N network and provide a guidance for the practical application and operation of anammox process, especially in treating wastewater containing iron oxide nanomaterials.