Revealing the impacts of intermittent aeration on nitrogen and phosphorus removal in powder carrier system from interfacial thermodynamics and metagenomic analysis

Abstract

Intermittent aeration strategy has attracted significant attention due to its benefits of low oxygen and carbon source consumption. However, the feasibility of intermittent aeration in the powder carrier process and its effect on micro-granule formation remain unclear. This study investigated the impacts of intermittent aeration on the powder carrier system through interfacial thermodynamics and metagenomic analysis. The results demonstrated that total nitrogen removal efficiency increased from 61.1 ± 2.6 % to 89.7 ± 3.7 % under intermittent aeration, while the PO43-–P removal efficiency increased from 47.6 ± 4.7 % to 81.6 ± 3.9 %. The interfacial free energy of micro-granules was reduced from –4.85 mJ/m2 to –16.03 mJ/m2 due to aeration mode, resulting in a larger micro-granule size (185.24 ± 15.25 μm) and enhanced aggregation ability. Significant enhancements in tryptophan-like substances and hydrophobic functional groups (β-sheet, protonated amines, and C-(C/H)) in EPS under intermittent aeration likely contributed to the increased hydrophobicity and reduced interfacial free energy. The abundances of norank_NS9_marine_group (4.17 %), norank_Comamonadaceae (4.57 %), and Terrimonas (3.44 %) were increased, further driving the synergy of nitrogen removal of simultaneous partial nitrification and denitrification and endogenous denitrification. Correlation analysis confirmed that intermittent aeration primarily affected gene expression involved in the partial nitrification process, and that denitrification genes were enriched by increased hydrophobic components and micro-granule size. These results provide deeper insights into the key influencing factors and mechanisms of the powder carrier system, and offer a theoretical basis for process optimization.