광주광역시 합류식 및 분류식 하수관거 수질 및 침입수/유입수(I/I) 분석

다국어 초록 (Multilingual Abstract)

Analysis of Water Quality and Infiltration/Inflow (I/I) of Combined and Separate Sewer System in GwangJu Metropolitan City Jeon, Pilsung Advisor : Prof. Choe, Jaewan, Ph.D. Department of Civil Engineering, Graduate School of Gwangju University Recent unpredictable climate change has increased the frequency of localized heavy rainfall, posing a serious threat to the stable operation of urban sewer system. In Gwangju Metropolitan City, where combined sewer system (CSS) and separate sewer system (SSS) coexist, chronic issues related to infiltration and inflow (I/I) have led to system overloads, the pollution of public water bodies such as the Yeongsan River, and increased operational costs. This study aims to provide foundational data for Gwangju’s Sewerage Maintenance Plan by analyzing flow and water quality characteristics in both sewer system types. The ultimate goal is to quantitatively evaluate the scale of I/I, assess its impact on wastewater treatment efficiency, and propose effective control strategies. To this end, nine monitoring sites (five CSS, four SSS) were selected across the city. Four monitoring campaigns—three during dry weather and one during wet weather—were conducted. Flow rates and key water quality parameters (BOD, CODMn, SS, T-N, T-P) were measured every two hours over 24-hour periods. Infiltration was estimated using the Minimum Nighttime Sewage Analysis method, while inflow was determined via the Hydrograph Separation method. The results confirmed that Gwangju’s sewer network suffers from significant I/I issues across both system types. In combined sewer system, inflow during wet weather was particularly severe, with peak flows at sites Gwangju-1 and Gwangju-2 increasing by up to 480% compared to dry weather. Among separate system, sites Gwangju-4 and Gwangju-8 effectively managed inflow but still showed continuous infiltration. Critically, sites Gwangju-5 and Gwangju-9 exhibited substantial inflow volumes—up to 17,351 m³/day— suggesting serious cross-connections or structural defects. This excessive I/I diluted influent sewage, impaired treatment performance, and increased the risk of untreated discharges during rainfall events. In conclusion, this study underscores the urgent need for a dual management strategy. For CSS, addressing persistent infiltration is as essential as managing rainfall-induced inflow. For SSS, it is crucial to reduce infiltration through pipe rehabilitation and to eliminate inflow by identifying and correcting cross-connections. These findings provide empirical evidence to help prioritize and implement effective sewer maintenance and improvement projects, ultimately enhancing the operational stability of Gwangju’s wastewater infrastructure and improving the water quality of local rivers. Keywords: Combined Sewer System (CSS), Separate Sewer System (SSS), Water Quality, Infiltration/Inflow (I/I)

목차 (Table of Contents)

• 제1장 서 론 1
• 1.1 연구의 배경 및 목적 1
• 1.2 연구의 필요성 및 활용 범위 2
• 1.3 연구 동향· 3
• 제2장 이론적 배경 5
• 2.1 하수관거 시스템 개요 5
• 2.1.1 합류식 및 분류식 하수관거의 특징· 5
• 2.1.2 국내 하수관거 시스템 현황 6
• 2.2 침입수(Infiltration)/유입수(Inflow) (I/I) 8
• 2.2.1 침입수 및 유입수의 정의 및 문제점 8
• 2.2.2 기존 I/I 산정기법 및 적용 한계 10
• 2.2.3 침입수(Infiltration) 산정방법 11
• 2.2.4 유입수(Inflow) 산정 방법 14
• 제3장 연구 대상 및 방법 17
• 3.1 조사 대상 지역 개요 17
• 3.1.1 광주광역시 하수도 현황· 17
• 3.1.2 조사 대상 지점 선정 및 현황 20
• 3.2 조사 기간 및 내용 21
• 3.2.1 건기 및 우기 조사 기간 21
• 3.2.2 조사 항목 22
• 3.3 현장 측정 및 분석 방법 23
• 3.3.1 유량 측정 방법 23
• 3.3.2 수질 시료 채취 및 분석 방법 25
• 제4장 연구 결과 및 고찰 28
• 4.1 지점별 유량 특성 분석. 28
• 4.1.1 건기 및 우기 유량 변동 분석 28
• 4.1.2 합류식 및 분류식 관거의 유량 특성 비교 47
• 4.2 지점별 수질 특성 분석 50
• 4.2.1 건기 및 우기 수질 농도 분석 50
• 4.3 침입수/유입수(I/I) 산정 결과 및 고찰 95
• 4.3.1 침입수(Infiltration) 산정 결과 95
• 4.3.2 유입수(Inflow) 산정 결과 97
• 4.3.3 침입수/유입수(I/I) 저감 효과 분석 99
• 4.3.4 종합 고찰· 103
• 제5장 결론 105