The performance and microbial community in response to MnO2 nanoparticles in anammox granular sludge

The response of anaerobic ammonium oxidation (anammox) process and granular sludge in the upflow anaerobic sludge blanket reactor was analyzed under long-term exposure to MnO 2 nanoparticles (NPs) (1–200 mg L −1 ). The addition of 200 mg L −1 MnO 2 NPs had a significantly positive effect on nitrogen removal and this system exhibited excellent performance, with a total nitrogen removal efficiency of 93.1%. Moreover, the specific anammox activity enhanced with increasing concentrations of MnO 2 NPs up to the maximum value of 657.3 ± 9.3 mg TN g −1 VSS d −1 under MnO 2 NPs concentration of 200 mg L −1 . This value was approximately 1.6-fold higher than that of the reactor in the absence of MnO 2 NPs. The extracellular polymeric substances and settling velocity were both increased with MnO 2 NPs addition. Meanwhile, the high-throughput sequencing results revealed that MnO 2 NPs increased the relative abundance of dominant bacteria ( Candidatus Kuenenia ) from 17.3% at the absence of MnO 2 NPs to 23.9% at 200 mg L −1 MnO 2 NPs, which resulted in a higher efficiency of biological nitrogen removal on the anammox system. These results indicated that MnO 2 NPs enhanced nitrogen removal performance of anammox process.