Roles of MnO₂ on performance, sludge characteristics and microbial community in anammox system

The long-term impacts of MnO₂ on performance, sludge characteristics and microbial community of biogranule-based anaerobic ammonium oxidation (anammox) process were evaluated in an up-flow anaerobic sludge blanket reactor. It was found that the total nitrogen removal efficiency of reactor was fluctuated between 90%-93% at 1-200mgL^-1 MnO₂. Notably, the specific anammox activity was increased to maximum value of 657.3±10.6mgTNg^-1VSSd^-1 at 50mgL^-1 MnO₂ and then slightly decreased, but still higher than that achieved at 0-15mgL^-1 MnO₂, which had similar variation trends to the content of heme c and extracellular polymeric substances in anammox granules. High throughput sequencing indicated that MnO₂ could improve the microbial richness and diversity of anammox granules and Candidatus Kuenenia was always the dominant species, and its abundance continued to increase to 21.3% at the end of operational experiment. Therefore, MnO₂ could be applied to enhance the anammox process and the optimal influent MnO₂ concentration was lower than 50mgL^-1 in view of the reactor performance and cost issues.