Synergistic enhancement of quinoline degradation and nitrogen removal in a coupling FeS-ZVI microelectrolysis and partial denitrification-anammox system: performance and mechanisms.

Quinoline in coal chemical wastewater severely inhibits the performance of partial denitrification-anammox (PD/A) process. This study innovatively developed a FeS-ZVI microelectrolysis coupled PD/A system to simultaneously enhance quinoline degradation and nitrogen removal under quinoline stress. The coupled system achieved quinoline and nitrogen removal efficiencies of 92.0 ± 2.4% and 81.7 ± 1.7%, respectively, outperforming the control (32.8 ± 6.0% and 17.8 ± 9.5%), FeS (73.3 ± 6.8% and 53.8 ± 5.4%), and ZVI (75.3 ± 9.3% and 51.6 ± 5.6%) groups. Mechanistically, the FeS-ZVI microelectrolysis facilitated reactive species generation, thereby enhancing the abiotic removal of quinoline (30.0 ± 0.7%). Meanwhile, FeS-ZVI microelectrolysis maintained higher microbial electron transport and energy metabolism, with electron transport system activity, electron-donating capacity, and ATPase activity being 31.9-133.1%, 30.4-116.5%, and 104.1-771.3% higher, respectively, than those in the other groups. Crucially, quinoline degradation into chain compounds and the release of Fe2 +/S2- via FeS-ZVI microelectrolysis, enhanced heterotrophic and autotrophic partial denitrification, respectively, ultimately supporting anammox. Metagenomics analysis revealed enrichment of the electroactive bacteria (Pseudomonas), quinoline-degrading bacteria (Exiguobacterium), and genes involved in carbon (Ior A/B, PcaD, LigC), nitrogen (hdh, hzs, narB), and sulfur (Sox) metabolism. Therefore, the FeS-ZVI microelectrolysis-PD/A system achieved synergistic carbon and nitrogen removal under quinoline stress.