An innovative strategy for inducing Anammox from partial nitrification process in a membrane bioreactor

Anaerobic ammonium oxidation (Anammox) was an innovative process for nitrogen removal. In this study, CuO nanoparticles (NPs) was step-wise increasingly added to an MBR-based partial nitrification system, to investigate its feasibility for inducing Anammox and establishing autotrophic nitrogen removal system. Results showed that when CuO NPs was elevated to 5 mg L^-1, Anammox was successfully induced. The relative abundance of Nitrosomonas reached 13.73% while Candidatus Kuenenia increased to 4.79% from 0.46%, these two bacteria cooperatively contributed to the autotrophic nitrogen removal and improved the nitrogen removal rate (NRR) to 0.56 kg m^-3 d^-1 in 20 mg L^-1 NPs. However, 50 mg L^-1 NPs deeply suppressed the functional bacteria and decreased NRR to 0.14 kg m^-3 d^-1. Finally, the NPs removal, transformation and adsorption in the system were evaluated. It was concluded that CuO NPs in low concentration (5 mg L^-1) was effective for inducing Anammox and contributed to the survival of Anammox bacteria. The mechanism for inducing Anammox was attributed to the aggregation of CuO NPs which enabled the attached growth of AAOB as well as the suitable survival condition supplied by MBR.