Response of anammox to long-term stress of Ni(II): Nitrogen removal, microbial products and microbial community

Anaerobic ammonium oxidation (anammox) has been successfully applied to the practical wastewater treatment due to a high nitrogen removal performance, low sludge yield and low operating cost. Heavy metals in wastewater have received extensive attention because of their non-degradability and biotoxicity. In order to apply anammox system to treat wastewater containing heavy metals and explore the anammox system recovery to complex engineering environments, Ni(II) was used as representative substance to investigate its long-term effects on the anammox process in continuous flow reactors. The self-recovery ability of the anammox system after long-term exposure to Ni(II) was also investigated. The results showed that low concentrations of Ni(II) (≤ 5mg/L) had a slight inhibitory effect on the anammox system, while high concentrations of Ni(II) (≥ 10mg/L) could lead to the deterioration of the anammox system. Extracellular polymeric substance (EPS) content increased with increasing Ni(II) concentration. High-throughput sequencing results showed that Ni(II) severely impacted the microbial community of the anammox system, especially Candidatus Kuenenia. The abundance of Candidatus Kuenenia decreased from 32.11% to 13.99% with increasing Ni(II) concentration from 0mg/L to 15mg/L. After stopping Ni(II) addition, EPS and functional bacterial abundance recovered to some extent, and nitrogen removal efficiency (NRE) only returned to 44.53% of normal levels. The self-recovery of the anammox system was a longer process. [Display omitted] •Low concentration Ni(II) (≤ 5mg/L) has a slight inhibitory effect on anammox system.•Long-term Ni(II) stress had a significant response to EPS secretion, especially for PN.•Ni(II) stress significantly changed AnAOB abundance.•Candidatus Brocadia had a more resistant to long-term Ni(II) stress than Candidatus Kuenenia.•AnAOB recovery needs a longer process after stopping Ni(II) addition.