The purpose of this study was to evaluate the effects of different Hydraulic Retention Times (HRTs) on the contaminant removal efficiency using Aerobic Granular Sludge (AGS). A laboratory-scale experiment was performed using a sequencing batch reactor, and the Chemical Oxygen Demand (COD), nitrogen, orthophosphate removal efficiency, AGS/MLSS ratio, and precipitability in accordance with the HRT were evaluated. As a result, the COD removal efficiency was not significantly different with the reduction in HRT, and at a HRT of 6 h, the removal rate was slightly increased owing to the increase in organic loading rate. The nitrogen removal efficiency was improved by injection of influent division at a HRT of 6 h. As the HRT decreased, the MLSS and AGS tended to increase, and the sludge volume index finally decreased to 50 mL/g. In addition, the size of the AGS gradually increased to about 1.0 mm. Therefore, the control of HRT provides favorable conditions for the stable formation of AGS, and is expected to improve the contaminant removal efficiency with the selection of a proper operation strategy.

Abstract
1. 서 론
2. 재료 및 방법
    2.1. 하수 성상 및 실험재료
    2.2. 실험장치 및 운전조건
    2.3. 수질분석 및 현미경 관찰
3. 결과 및 고찰
    3.1. 유기물 제거효율
    3.2. 질소 및 오르토인산염 제거효율
    3.3. MLSS 및 물리적 특성
    3.4. 광학현미경 관찰
4. 결 론
REFERENCES

• 김현구(주식회사 블루뱅크) | Hyun-Gu Kim (BlueBank Co., Ltd.)
• 안대희(주식회사 블루뱅크/명지대학교 환경에너지공학과) | Dae-Hee Ahn (BlueBank Co., Ltd./Department of Environmental Engineering and Energy, Myongji University) Corresponding author