Enhancement of anammox performance by Cu(II), Ni(II) and Fe(III) supplementation

•The short-term effects of Fe3+, Cu2+ and Ni2+ on the SAA were investigated.•RSM was applied to determine the optimal metal dosage.•The joint effectiveness of Fe3+, Cu2+ and Ni2+ addition was verified.•The effectiveness of Fe3+ addition alone was confirmed.•An appropriate addition of metals enhanced the psychrophilic anammox performance.

This study explored the influence of metal ion addition on specific anaerobic ammonium oxidation activity (SAA). Batch assays were used to demonstrate the enhancement of the SAA upon the addition of Cu2+, Ni2+ and Fe3+. The SAA was enhanced by 41.0% when the Cu2+ concentration was below 1 mg L−1, while it was improved by 63.5% at Ni2+ concentrations below 1.74 mg L−1. An enhancement of 533.2% was obtained when 3.68 mg L−1 Fe3+ was supplied. The effects of Fe3+, Cu2+ and Ni2+ on the SAA were analyzed and optimized by a response surface methodology, which demonstrated that the interaction between Fe3+ and Cu2+ was significant and that 6.61 mg Fe3+ L−1, 1.18 mg Cu2+ L−1 and 1.11 mg Ni2+ L−1 were the optimal values for metal dosing. Subsequently, an Fe3+-Cu2+-Ni2+ continuous test was carried out under optimal conditions and revealed that the addition of Fe3+, Cu2+ and Ni2+ could stimulate the reactor potential at ambient temperature. The maximum nitrogen removal rate (NRR) of the test reactor was 52.8% higher than that of the control reactor (8.1 versus 5.3 kg N m−3 d−1). Moreover, a continuous test conducted by adding Fe3+ achieved an average nitrogen removal efficiency and maximum NRR of 67.4% and 4.9 kg N m−3 d−1, respectively, while the corresponding values of the control test were 64.7% and 4.1 kg N m−3 d−1, respectively. Altogether, appropriate dosages of Cu2+, Ni2+ and Fe3+ can significantly enhance the SAA and improve the reactor capacity at ambient temperature.