Enhancement of nutrient removal in an activated sludge process using aerobic granular sludge augmentation strategy...

To enhance nutrient removal from low-strength municipal wastewater in a continuous-flow activated sludge (CFAS) process using aerobic granular sludge (AGS) augmentation strategy, a pilot-scale demonstration was configured with a mainstream reactor (anaerobic/aerobic process) and a sidestream sequencing batch reactor for AGS production. The aeration of the mainstream reactor was controlled based on dissolved oxygen (DO) and ammonium concentrations during Phases I and II-III, respectively. During Phase III, an anoxic zone was created in the mainstream aerobic tank. Throughout the demonstration period, excellent sludge settleability in the mainstream reactor (SVI30 ≤ 80 mL g^-1) under long sludge retention time conditions (≥12 d) allowed the maintenance of a high mixed liquor suspended solids concentration (≥3000 mg L^-1). The total nitrogen (TN) removal ratio improved significantly during Phases II and III (49.3 ± 4.1% and 50.1 ± 10.2%, respectively) compared to Phase I (43.2 ± 5.5%). Low DO concentration (< 0.5 mg L^-1) by the ammonium-based aeration tended to increase the simultaneous nitrification and denitrification efficiency (> 40%), enhancing TN removal (> 50%). The reduction of DO and nitrate concentrations in the returning sludge liquor can stabilize phosphorus removal (approximately 80% of the 25th percentile). In addition, the aeration efficiency during Phase III decreased by 26-29% compared to Phase I. These results suggest that the introduction of ammonium-based aeration control to the CFAS using the AGS augmentation strategy could contribute to superior sewerage treatment, including nutrient removal and a low carbon footprint.