The present study was performed to investigate the effects of NH3-N and nitrifying microorganisms on the increased BOD of downstream of the Yeongsan river in Gwangju. Water samples were collected periodically from the 13 sampling sites of rivers from April to October 2021 to monitor water qualities. In addition, the trends of nitrogenous biochemical oxygen demand (NBOD) and microbial clusters were analyzed by adding different NH3-N concentrations to the water samples. The monitoring results showed that NH3-N concentration in the Yeongsan river was 22 times increased after the inflow of discharged water from the Gwangju 1st public sewage treatment plant (G-1-PSTP). Increased NH3-N elevated NBOD levels through the nitrification process in the river, consequently, it would attribute to the increase of BOD in the Yeongsan river. Meanwhile, there was no proportional relation between NBOD and NH3-N concentrations. However, there was a significant difference in NBOD occurrence by sampling sites. Specifically, when 5 mg/L NH3-N was added, NBOD of the river sample showed 2-4 times higher values after the inflow of discharged water from G-1-PSTP. Therefore, it could be thought other factors such as microorganisms influence the elevated NBOD levels. Through next-generation sequencing analysis, nitrifying microorganisms such as Nitrosomonas, Nitroga, and Nitrospira (Genus) were detected in rivers samples, especially, the proportion of them was the highest in river samples after the inflow of discharged water from G-1-PSTP. These results indicated the effects of nitrifying microorganisms and NH3-N concentrations as important limiting factors on the increased NBOD levels in the rivers. Taken together, comprehensive strategies are needed not only to reduce the NH3-N concentration of discharged water but also to control discharged nitrifying microorganisms to effectively reduce the NBOD levels in the downstream of the Yeongsan river where discharged water from G-1-PSTP flows.

ABSTRACT
1. 서 론
2. 연구방법
    2.1 연구지점
    2.2 하천 수질특성 및 통계분석
    2.3 NBOD 발생 특성 및 경향 조사
    2.4 질산화 미생물 군집 분석
3. 결과 및 고찰
    3.1 하천 수질특성 및 통계분석
    3.2 NBOD 발생 특성 및 경향 조사
    3.3 하수처리장 방류수 유입 전･후 지점 질산화 미생물군집 분석
    3.4 NBOD 발생 특성과 질산화 미생물 군집 상관관계
4. 결 론
사 사
References

• 장동(광주광역시 보건환경연구원 환경연구부) | Dong Jang (Department of Environmental Research, Health & Environment Research Institute of Gwangju)
• 조광운(광주광역시 보건환경연구원 환경연구부) | Gwangwoon Cho (Department of Environmental Research, Health & Environment Research Institute of Gwangju)
• 손경록(광주광역시 보건환경연구원 환경연구부) | Gyeongrok Son (Department of Environmental Research, Health & Environment Research Institute of Gwangju)
• 김하람(광주광역시 보건환경연구원 환경연구부) | Haram Kim (Department of Environmental Research, Health & Environment Research Institute of Gwangju)
• 강유미(광주광역시 보건환경연구원 환경연구부) | Yumi Kang (Department of Environmental Research, Health & Environment Research Institute of Gwangju)
• 이승기(광주과학기술원 지구･환경공학부) | Seunggi Lee (School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology)
• 황순홍(국립환경과학원 영산강물환경연구소) | Soonhong Hwang (Yeongsangang River Water Environment Research Institute, National Institute of Environmental Research)
• 배석진(광주광역시 보건환경연구원 환경연구부) | Seokjin Bae (Department of Environmental Research, Health & Environment Research Institute of Gwangju)
• 김연희(광주광역시 보건환경연구원 환경연구부) | Yunhee Kim (Department of Environmental Research, Health & Environment Research Institute of Gwangju) Corresponding author