Effect of powdered activated carbon (PAC) addition and nitrogen mixing during anaerobic fill period on aerobic granular sludge (AGS) sequencing batch reactor (SBR) process performances

This study investigated the effects of powdered activated carbon (PAC) addition and feeding strategy on aerobic granular sludge (AGS) formation and organic micropollutant (OMP) removal. Three sequencing batch reactors were operated: PAC-AGS1 (PAC addition and static fill without mixing), PAC-AGS2 (PAC addition and anaerobic mixing during fill period), and a control AGS reactor (anaerobic mixing during fill period). Results demonstrated that PAC significantly accelerated granulation and improved sludge settleability during early operation period. PAC-AGS1 exhibited the fastest decrease in SVI30 (25 mL/g) and achieved a granular fraction of approximately 90% by day 49, indicating rapid formation of compact and stable granules. Meanwhile, anaerobic fill with nitrogen purging slightly delayed early-stage granulation in PAC-AGS2. All systems achieved effective COD removal; however, PAC-AGS1 showed enhanced OMP removal efficiency, probably due to the combined effects of adsorption and biodegradation within stable granular structures. Microbial community analysis revealed distinct shifts at the family level, with PAC-AGS1 enriching structure-supporting bacteria. The results indicated that PAC addition under stable aerobic feeding conditions promotes rapid granule formation, structural stability, and improved micropollutant removal. This study highlights the significance of both PAC as an adsorptive nucleus and static feeding strategy to enhance AGS performance for advanced wastewater treatment applications.