Microbial driving mechanism for nitrogen removal performance of anammox with combined fillers addition: Microbial community dynamics, metabolic function and network analysis

Abstract

Microbial community is vital for efficient nitrogen removal in an anaerobic ammonium oxidation (anammox) system. However, the mechanisms of microbially driven anammox denitrification are far from clear. The results showed that the nitrogen removal efficiency (especially the removal rate of NH4+-N, which reached 85.6 ± 3.1 %) significantly increased (p < 0.05) by combined fillers addition. Scanning electron microscope (SEM) images showed the microflora changed gradually from short rod-shaped to spherical aggregates, improving shock loading resistance in the system. The dominant microflora shifted from Proteobacteria and Bacteroidetes to Chloroflexi and Planctomycetes, in which Candidatus Jettenia reached a maximum abundance of 30.7 %. Meanwhile, the abundance of denitrifying bacteria (Denitratisoma and Thiobacillus) was significantly diminished. Significant enhancements in the energy metabolic capacity of microorganisms, especially nitrogen metabolism, were observed in the anammox process. Moreover, the increase in abundance of hzo gene suggested the enhancement of the anammox process. Co-occurrence network analysis demonstrated that the genera Longilinea, Thiobacillus, Candidatus Jettenia, Dokdonella, and Candidatus Brocadia were the keystones, and complex microbial interactions (stronger symbiotic than competitive relationships) enhanced the nitrogen removal capability. Overall, the results of this study provided more comprehensive information regarding community succession, coexistence and collaboration in anammox process for nitrogen removal.