Microbial nitrogen removal processes under PFAS stress: mechanisms, functional evolution, and research outlook

Per- and polyfluoroalkyl substances (PFAS), as emerging contaminants with extreme persistence and bioaccumulation, threaten microbially mediated nitrogen removal in wastewater systems. This study systematically reviewed multiscale response mechanisms under PFAS stress, from molecular interfaces to community function. The distribution of PFAS across water, sludge, and sediments was summarized first, with short-chain PFASs observed to have increased mobility owing to their higher aqueous solubility. Second, the dual effects of PFAS were elucidated: low concentrations (< 100 μg/L) temporarily enhanced nitrogen removal by promoting extracellular polymeric substances (EPS) and transiently activating genes (e.g., nosZ), whereas high concentrations (> 50 mg/L) inhibited key genes (amoA, hzsB), reduced the activity of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and anaerobic ammonium-oxidizing bacteria (AnAOB), and impair nitrogen removal efficiency. PFAS also reshaped microbial communities, enriching tolerant taxa (e.g., Proteobacteria, Firmicutes) and suppressing sensitive groups (e.g., Nitrospira). Mechanistically, PFASs disrupted cell membranes, inhibited metabolic enzymes, and induced reactive oxygen species (ROS) accumulation, which damaged catalytic sites of enzymes (Nar, Nir, Nos) and caused DNA damage. Effects of short-chain and emerging PFASs (F-53B, 6:2 FTS) across concentration ranges were integrated, and a multiscale action model was proposed comprising: (1) molecular-interface disruption, (2) gene regulation, and (3) community functional reshaping. Critical research gaps were identified, including low-dose chronic exposure, co-contaminant synergies, and coupled remediation using functional consortia or engineered materials, addressing these gaps was expected to inform PFAS ecological risk assessment and management optimization.