The effects and mechanisms of Fe2+ and FeO on anammox and Fe-N metabolism in anammox system
Iron can not only affect the activity of anaerobic ammonium oxidation (anammox bacteria (AnAOB)), but also participates in complex Fe-N cycles in anammox system. Therefore, it was important to investigate the variations of Fe-N metabolism in anammox system under long-term Fe stress . In this study, 10 mg/L Fe2+-EDTA and equivalent FeO powder were added into anammox reactors, respectively, to investigate the responses of anammox as well as the differences of Fe-N metabolism rates. The results showed that both of Fe2+ and FeO could increase the activity of AnAOB. However, higher activity of Fe-N metabolism and more metabolic diversity were discovered in system added with FeO according to the results of 15N isotope tracing and high-throughput sequencing. It might because the fact that FeO could release Fe2+ gradually and thus provide sufficient available ferrous ions for microorganism. Finally, genera Subgroup_10 and Paludibaculum might be functional bacteria for feammox process and genera Denitratisoma, I-8 and Arenimonas for NDFO process. In this study, the understanding of Fe-N metabolism in anammox system supplied with Fe was deepened, providing the theoretical basis for the development of anammox-dominant Fe-N coupling systems.