Mechanism of gel immobilization driving efficient anammox in mainstream partial nitritation/anammox process: Structural characterization and multi-perspective microbial analysis

Abstract

Here, the mechanism of encapsulated anammox bacteria (AnAOB) driving efficient nitrogen removal in the mainstream partial nitritation/anammox process is revealed. The results show that a high nitrogen removal rate (1.21±0.02 kgN·(m³·d)^-1) was achieved due to the abundant micropore structure inside the anammox immobilized filler, ensuring good connectivity, and a stable aggregation capacity, reducing dependence on extracellular polymeric substances. AnAOB were uniformly distributed throughout all regions of the immobilized filler, and their abundance was higher than that of the control anammox granular sludge (AnGS). Conversely, cracks appeared on the surface of the AnGS, and hollows formed inside. The metagenome analysis revealed that the immobilized filler supported the coexistence of multiple AnAOB, and the appropriate niche enhanced coordination between the AnAOB and dominant companion microorganisms. In contrast, AnGS exhibited stronger NH₄⁺-N and NO₂^--N loops, potentially reducing the total nitrogen removal efficiency. This study promotes the mainstream application of anammox.

Keywords: Mainstream PN/A; Metagenome; Microbial immobilization; Pore structure; Spatial distribution.