The revolution of performance, sludge characteristics and microbial community of anammox biogranules under long-term NiO NPs exposure

Given the increasing applications of NiO nanoparticles ( NPs) in battery products, the potential effects of NiO NPs on anaerobic ammonium oxidation (anammox) systems were studied for the first time. The results showed that the anammox system performance obviously differed under the stresses of different NiO NPs concentrations. After the withdrawal of NiO NPs, the nitrogen removal performance of the anammox reactor returned to nearly that of the initial phase within 35 days. Compared with 0 mg L-1 NiO NPs, the specific anammox activity first increased and then decreased to the minimum value of 116.8 +/- 13.8 mg TN g(-1) VSS d(-1) at 60 mg L-1 NiO NPs. The variations in the heme c contents and extracellular polymeric substance amounts were similar to the variations in the specific anammox activity throughout the whole experiment. Additionally, the relative abundance of the dominant bacteria (Candidatus kuenenia) increased from 20.44% at 60 mg L-1 NiO NPs to 23.14% at the end of the last phase. Thus, the potential effects of NiO NPs on anammox systems should be a cause for great concern. (C) 2018 Published by Elsevier B.V.