Short- and long-term effects of manganese, zinc and copper ions on nitrogen removal in nitritation-anammox process.

This study provided a deep insight into the impacts of trace elements (Mn, Zn and Cu) on nitritation-anammox process. For short-term exposure, all the three elements could improve the nitrogen removal rate (NRR) and the optimal concentrations were 2.0 mg/L, 2.0 mg/L and 0.5 mg/L for Mn, Zn and Cu, respectively. Accordingly, the NRRs were enhanced 54.62%, 45.93% and 44.09%. The long-term experiments were carried out in lab-scale sequencing batch reactors. The surprising results showed that only Mn addition could enhance the long-term nitritation-anammox process, and the NRR increased from 0.35 ± 0.01 kg N/m/d (control, no extra trace element addition) to 0.49 ± 0.03 kg N/m/d. Vice versa, the amendment of Zn reduced the NRR to 0.28 ± 0.02 kg N/m/d, and Cu had no significant effect on the NRR (0.36 ± 0.01 kg N/m/d). From the analysis of microbial community structure, it was explained by the increasing abundance of anaerobic ammonium oxidizing bacteria (AnAOB) only in Mn treatment, whereas Zn predominantly promoted ammonium oxidizing bacteria (AOB). Additionally, the majority of Mn was identified inside AnAOB cells, and Zn and Cu were mainly located in AOB. Our results indicated the synergistic effects of trace elements on nitritation-anammox, both short-term encouraging activities of AnAOB and long-term altering microbial community structure. This work implies the importance of trace elements addition in nitritation-anammox process.