Operational Strategies for Enhanced Aerobic Granulation and Simultaneous Denitrification in SBR Systems

Aerobic Granular Sludge (AGS) has attracted attention as an alternative to conventional activated sludge due to its excellent settling properties, high biomass retention, and the ability to simultaneously remove various pollutants. However, challenges such as granulation speed, structural stability, and denitrification performance remain for full-scale implementation. In this study, a lab-scale AGS-SBR (Sequencing Batch Reactor) system was operated through four stages to examine the interactions between AGS formation and denitrification performance under varying operational parameters, including Feast/Famine ratios, initial MLSS concentrations (500~2,500 mg/L), mixing conditions, bubble sizes, settling times (5~20 min), influent feeding durations (5~40 min), and coagulant addition. Under an influent COD concentration of 300 mg/L, AGS formation was most stable at an HRT of 4 h and MLSS of 2,500 mg/L, with the average granule size reaching approximately 546 μm. Excessive famine conditions led to sludge loss. Coagulant addition enhanced granulation and settleability even under short settling times but showed limited improvement in denitrification efficiency. Notably, when the initial MLSS was 500mg/L, sufficient organic matter remained after the start of aeration, allowing NO<sub>3</sub>⁻-N concentrations to be maintained below 5mg/L and enabling stable simultaneous denitrification. In contrast, at 2,000mg/L MLSS, rapid organic depletion hindered denitrification. These results suggest that the physical formation of AGS alone is insufficient to ensure denitrification performance, and the availability of organics at the onset of aeration is a key factor. Rather than optimizing individual parameters, integrated management of operational conditions is essential to improve AGS-SBR performance, and long-term studies reflecting actual wastewater characteristics are recommended.