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 largesized 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 (AGBL), 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 AGBL 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 AGBL 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 AGBL increased anoxic/anaerobic zones, enriching denitrifying and hydrolytic/fermentative bacteria. These findings highlight AGBL with large PUS as a more promising biotechnology for practical applications than conventional AGS.