Deciphering the spatial distribution along the upflow anammox reactor: Sludge characteristics and interspecies interactions.

Here, nitrogen conversion, granular characteristics and microbial dynamics were combined to reveal the longitudinal heterogeneity along anammox-UASB with nitrogen removal efficiency of 92.6%. The reactor was divided into Bottom-zone, Middle-zone, Upper-zone, and Top-zone with height increasing. Results indicated that particle size decreased from Bottom-zone to Upper-zone, while granular floatation caused an increase in Top-zone. Protein secondary structure in EPS was loose and hzsA transcription ratio was only 4.45% due to the limited mass-transfer and serious mineralization of ultra-large granules in Bottom-zone. Smaller granules in Middle-zone were more robust and active, with compact tryptophan- and aromatic-like protein in EPS and 23.71% hzsA transcription. Intriguingly, coexisting denitrification survived on EPS and/or microbial metabolites was observed. Transcription of narG was stimulated with height increasing, resulted in performance improvement through combining partial denitrification and anammox in Upper-zone. The findings deciphered stratification characteristics along the height-partitioned anammox-UASB, and reveal cross-feedings between denitrification and anammox bacteria.