The Spatial Difference in Nitrogen Removal Pathways and Microbial Function Diversity Along the Elevation of an Egsb Reactor During Start-Up of Pd/Anammox

Abstract

In this study, the start-up of a relatively high nitrogen load PD/Anammox in an EGSB reactor was achieved through strategies of bioaugmentation, enhanced mass transfer, and COD/NO3--N control, with NRR of 5.2 g N/L/d. Longitudinal heterogeneity in the EGSB reactor induces divergent nitrogen conversion pathways and enriches different functional microorganisms in the stratified sludge. Along the longitudinal distribution of the reactor, the proportion of removed nitrogen through anammox increased continuously, which were 68.5%, 79.8%, and 84.1%, respectively. The bottom zone played a role in mixed nitrogen conversion to provide NO2--N accumulation (26.9 mg/L), while achieved 60.8% of TN removal through completed denitrification and anammox. The middle part was enriched Candidatus_Kuenenia (12.51%), and the up part inhibited completed denitrification, together forming the anammox dominant zone. The proposed functional zones in the EGSB reactor provided approaches for the optimisation of high-load PD/Anammox systems.

Keywords: PD/Anammox, EGSB reactor, Longitudinal heterogeneity, Nitrogen conversion pathways, Function diversity