Evaluating the effects of aeration intermittency on treatment performance and the granule microbiome in continuous-flow aerobic granular sludge systems

Intermittent aeration (IA) is a promising strategy to improve treatment performance and reduce energy consumption in continuous-flow (CF) aerobic granular sludge (AGS) systems. However, most research has focused on sequencing batch reactors (SBR), with limited data on simplified CF-AGS systems using internal solid-liquid separators. This study evaluated IA in three CF-AGS reactors with different aeration durations: 3 h (R1), 12 h (R2), and 21 h (R3) per day, while a control reactor (R4) received continuous aeration (24 h/day). The removal of chemical oxygen demand (COD) and total inorganic nitrogen (TIN), granule properties, and microbial community composition were assessed. COD and TIN removal in R1 (93 % and 42 %), R2 (95 % and 54 %), and R3 (94 % and 47 %) were comparable to R4 (95 % and 52 %). However, IA improved granule quality and altered the microbiome. Reactor R2 (12 h aeration) exhibited the best performance, producing granules with a final diameter of 0.9 mm, good settleability (sludge volume index of 74.8 mL g⁻¹), and high alginate-like exopolymers (416.2 mgALE gTS⁻¹). R2 also showed the highest enrichment of functional bacterial genera involved in nitrogen removal and exopolymer production - particularly Thauera , Pseudomonas , Acinetobacter , and Zooglea - compared to the inoculum. This study demonstrates that IA can enhance the efficiency of CF-AGS systems and promote the growth of key microbial taxa essential for complete nitrogen removal. • Continuous-flow AGS performance under intermittent aeration (IA) was investigated. • An internal settling device proved satisfactory for maintaining sludge within the reactor. • The 12 h of aeration/d strategy exhibited enhanced treatment performance. • ALE yield increased in the reactor with 12 h aeration/d, promoting cell aggregation. • IA (12 h/d) enriched denitrifiers like Thauera , Pseudomonas , and Acinetobacter .