Effect of Step-Feeding on Granulation in an Activated Sludge Inoculated System

Abstract Aerobic granular sludge (AGS) is a microbial aggregate utilized in wastewater treatment, often coexisting with flocculent sludge. This study applied a step-feeding strategy in a sequencing batch airlift reactor (SBAR) to treat synthetic sewage. The sludge morphology and nitrogen removal performance were assessed under different feeding steps. The results indicated that both hydraulic shear force and feeding steps significantly contributed to the formation of dense AGS. Under three feeding steps, the average biomass particle size increased from 223 to 245 μm after 25 days, with mixed liquid suspended solids (MLSS) of 5.6 g / L and sludge volume index (SVI) of 50 mL / g . When the influent NH 4 + - N concentration was 43 mg / L , the effluent total nitrogen (TN), NO 3 − - N , and NH 4 + - N decreased to 6.84, 6.80, and 0.0 mg / L , respectively. High-throughput sequencing revealed a substantial enrichment of extracellular polymeric substance (EPS) producing and denitrifying bacteria after 60 days. Variations in nitrogen conversion pathways further demonstrated that three steps of step-feeding effectively enhanced the denitrification capacity of AGS. This study highlights that step-feeding can optimize nitrogen removal while simultaneously enhancing granulation, providing a theoretical basis for advanced nitrogen removal in AGS systems.