Elucidating the pathways of nitrogen removal and perfluorooctanoic acid biotransformation in Anammox system: From chemical calculations to microbial analysis

The stoichiometric ratios can indicate the nitrogen removal pathway in Anammox system. • Most of the PFOA was adsorbed by the Anammox biofilm, reaching a maximum uptake at 1 μg/L. • PFOA was bio-transformed into less toxic short-chain PFASs as predicted by ECOSAR. • Under PFOA stress, Candidatus Kuenenia excessively proliferated while hzsB gene was down-regulated. • Denitrification that reduces nitrite was enhanced with the up-regulation of nirS and nirK genes. Perfluorooctanoic acid (PFOA) is an emerging pollutant frequently detected in nitrogenous wastewater. In this study, the transformation of PFOA in an Anammox system was investigated using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and density functional theory (DFT) calculations. Additionally, the synergistic removal of nitrogen, as well as the evolution of the microbial community and functional genes in response to PFOA (at concentrations of 0.001–100 μg/L) were examined. Results showed that PFOA was primarily adsorbed into the biofilm while biotransformation also occurred, which was achieved via defluorination pathways and initiated by carboxylate-mediated decarboxylation. Several transformation products were detected, most of which exhibited lower toxicity than PFOA. 0.001 μg/L of PFOA had slight influence on nitrogen removal, whereas 1–100 μg/L continuously suppressed it. As a protective strategy, Anammox system up-regulated the growth of anaerobic ammonia-oxidizing bacteria (AnAOB). However, the gene abundance associated nitrate reduction ( nar G) and nitrite reduction ( nir S and nir K) both increased, which may hinder nitrite consumption by AnAOB. In conclusion, when treating PFOA-containing wastewater using the Anammox process, the activity of denitrifying and nitrifying bacteria should be maximally inhibited, while the biotransformation of PFOA should be enhanced. These findings provided a new perspective for the synergistic removal of PFOA and nitrogen. Download: Download high-res image (249KB) Download: Download full-size image