Large-sized aerobic granular biofilm: stable biotechnology to improve nitrogen removal and reduce sludge yield

Three parallel sequencing batch reactors (control, small-sized polyurethane sponge (PUS) (3.0 mm), and large-sized PUS (10.0 mm)) were used to investigate aerobic granular biofilm (AGB) characteristics. Results show that 10.0 mm PUS facilitated rapid formation of large-sized AGB (AGB_L), which exhibited higher biomass concentration (8.5 g/L) and faster settling velocity (69.2-159.3 m/h) than aerobic granular sludge (AGS) (3.2 g/L and 38.6-80.0 m/h). The AGB_L system also maintained long-term structural stability with a lower instability coefficient (0.004-0.018 min^-1) than AGS (0.053-0.090 min^-1). Additionally, during long-term operation, the AGB_L system achieved excellent removal efficiencies for NH₄⁺-N (99.6 ± 0.4 %) and total nitrogen (92.3 ± 2.6 %), and exhibited a lower sludge yield (0.05 gVSS/gCOD) than AGS (0.14 gVSS/gCOD). The larger size and compact structure of AGB_L increased anoxic/anaerobic zones, enriching denitrifying and hydrolytic/fermentative bacteria. These findings highlight AGB_L with large PUS as a more promising biotechnology for practical applications than conventional AGS.