Fast formation of anammox granules using a nitrification-denitrification sludge and transformation of microbial community.

A lengthy start-up period has been one of the key obstacles limiting the application of the anammox process. In this investigation, a nitrification-denitrification sludge was used to start-up the anammox EGSB process. The transformation process from nitrification-denitrification sludge to anammox granule sludge was explored through the aspects of nitrogen removal performance, granule properties, microbial community structure, and evolution route. A successful start-up of the anammox process was achieved after 94 days of reactor operation. The highest nitrogen removal rate (NRR) obtained was 7.25±0.16 gN/L/d at a nitrogen loading rate (NLR) of 8.0 gN/L/d, and the corresponding nitrogen removal efficiency was a high 90.61±1.99%. The results of the microbial analysis revealed significant changes in anammox bacteria, nitrifying bacteria, and denitrifying bacteria in the sludge. Notably, the anammox bacteria abundance increased from 2.5% to 29.0% during the operation, and Candidatus Kuenenia and Candidatus Brocadia were the dominant genera. Distinct-different successions on Candidatus Brocadia and Candidatus Kuenenia were also observed over the long-term period. In addition, the settling performance, anammox activity and biomass retention capacity of the granules were significantly enhanced during this process, and the corresponding granule evolution route was also proposed. The results in this study indicate the feasibility of using available seed sludge source for the fast-transformation of anammox granules, it is beneficial to the large-scale application of anammox process and the utilization of excess sludge.