Gyumin Lee

Sustainable urban water system (UWS) management is vital for climate-resilient, resource-efficient cities. This study presents the first comprehensive life cycle assessment (LCA) of Seoul Metropolitan City (SMC)’s UWS, encompassing water abstraction, treatment, distribution, wastewater collection and treatment, and sludge management. Nine midpoint impact categories from ReCiPe 2016 (H) were analyzed to identify environmental hotspots and mitigation pathways. Results show that wastewater treatment dominates impacts, contributing 57.3% of global warming potential (GWP; 0.947 kg CO₂-eq per functional unit of 1 m³ of potable water supplied) and 71.1% of freshwater eutrophication (FE; 0.00066 kg P-eq/m³), driven by electricity use, sludge disposal, and direct CH₄/N₂O emissions. Electricity consumption is the leading driver across GWP, terrestrial acidification (TA), and fossil resource scarcity (FRS). Infrastructure construction notably influenced terrestrial ecotoxicity (TET) and human toxicity. Sensitivity analysis showed that SMC’s projected 2030 electricity mix could reduce GWP and FRS by up to 18%. Scenario evaluations revealed that sludge ash utilization in concrete and expanded wastewater reuse improve resource circularity, whereas biogas upgrading, solar generation, and heat recovery significantly lower GWP and FRS. The findings underscore the importance of energy decarbonization, resource recovery, and infrastructure longevity in achieving low-carbon and resource-efficient UWSs. This study offers a transferable framework for guiding sustainability transitions in rapidly urbanizing, energy-transitioning regions.

This study proposes a hardware-based approach to address agricultural water shortages by directly improving water supply operations, rather than estimating agricultural water demand or supply. Unlike previous studies that focus on evaluating water supply capacity or predicting reservoir inflows through modeling or data-driven methods, this work proposes an operational strategy involving the physical interconnection of reservoirs. Specifically, the study investigates the coordinated use of surplus storage capacity from reservoirs with high watershed ratios to support those with low watershed ratios, thereby enhancing overall water supply reliability. Reservoir inflows were estimated using the Hydrological Operation Model for Water Resources Systems (HOMWRS). The analysis was conducted on reservoirs managed by the Korea Rural Community Corporation (KRC), selected based on data accessibility and availability.

Water supply systems (WSSs) are energy-intensive infrastructure that present significant opportunities for decarbonization through the integration of renewable energy (RE). This study evaluated the RE generation potential within the WSSs of Incheon Metropolitan City (IMC), Republic of Korea, using a site-specific, data-driven approach. Three RE technologies were considered: solar photovoltaic (PV) systems installed in water-treatment plants (WTPs), micro-hydropower (MHP) utilizing the residual head at the inlet chamber of a WTP, and in-pipe MHP recovery using the discharge from water supply tanks in water distribution networks. Actual facility data, hydraulic simulations, and spatial analyses were used to estimate an annual RE generation potential of 32,811 MWh in the WSSs of IMC, including 18,830 MWh from solar PV in WTPs, 4938 MWh from MHP in WTPs, and 9043 MWh from in-pipe MHP. This corresponds to an energy self-sufficiency rate of approximately 22.3%, relative to the IMC WSS total annual electricity consumption of 147,293 MWh in 2022. The results demonstrated that decentralized RE deployment within existing WSSs can significantly reduce grid dependency and carbon emissions. This study provides a rare empirical benchmark for RE integration in large-scale WSSs and offers practical insights for municipalities seeking energy-resilient and climate-aligned infrastructure transitions.

Achieving carbon neutrality is a priority in global environmental policies, and South Korea is committed to its 2050 carbon neutrality goal. This study explores methods to reduce carbon emissions in urban water cycle (UWC) systems, which are essential urban infrastructures that consume considerable energy. Focusing on Incheon Metropolitan City (IMC), the research identifies UWC components, estimates energy consumption, and calculates carbon emissions across eight administrative districts. The analysis comprises four water abstraction plants (WAPs), four water treatment plants (WTPs), and eleven wastewater treatment plants (WWTPs). Strategies for carbon reduction involve decreasing water and energy consumption and minimizing emissions from wastewater treatment. This study categorizes management targets as water, energy, and carbon, developing different carbon emissions reduction scenarios. A carbon emission calculation model for WTPs and WWTPs was developed to evaluate energy consumption and carbon emissions across scenarios. Notably, the scenario focusing on renewable energy development and energy efficiency improvements yielded the highest carbon emissions reductions, confirming that the government’s renewable energy initiatives are vital for achieving net-zero emissions in IMC’s UWC systems. Conversely, the scenario prioritizing water use reduction proved less effective, but excelled regarding investment costs. These findings can serve as a model for other cities managing UWC systems while striving for sustainability.

Substantial greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs) increase the global warming potential, underscoring the importance of addressing their role in GHG mitigation. This study proposes a strategy development approach that analyzes unit-process-based energy consumption, direct and indirect GHG emissions, and scenario impacts to create integrated water–energy–GHG solutions. The analysis of four WWTPs in Seoul Metropolitan City (SMC) identified aeration as the most energy-intensive process, consuming over 40% of the total energy. In addition, substantial GHG emissions were observed, with total indirect emissions surpassing direct emissions. To address these challenges, five future scenarios targeting 2050 were developed and analyzed: (1) replacing aeration diffusers, (2) reducing wastewater production, (3) adjusting treatment levels, (4) increasing renewable energy production, and (5) integrating all measures. Scenario 1 proved most effective in reducing energy and GHG emission intensity, Scenario 4 achieved high energy self-sufficiency, and Scenario 5 enabled some plants to achieve net-zero energy and carbon conditions. The approach proposed in this study provides actionable insights to support carbon neutrality through targeted water–energy–GHG strategies.

Water and energy are essential resources for human life, and carbon emissions (CEs) occur in tandem with their use. Thus, water, energy, and carbon are closely inter-related. Approximately 4% of the global energy is used in urban water sectors (UWSs), which encompass various processes such as water intake, treatment, and distribution and wastewater collection and treatment, all of which consume significant energy and emit CO₂. Several countries are actively working toward achieving carbon neutrality by 2050–2060. Therefore, increasing energy efficiency and reducing CEs through comprehensive evaluations of UWSs is essential. This study aimed to quantify energy consumption and CEs in UWSs and proposed a methodology for analyzing water–energy–carbon (WEC) links at the city level. By applying it to Incheon Metropolitan City (IMC), we first identified the UWSs and established a WEC database. Based on this database, the WEC consumption and emissions were analyzed by process or administrative district, and visualizations using Sankey diagrams and Geographic Information System Mapping were created to enhance their understandability. In 2021, the UWSs in IMC consumed 308,496,107 kWh of energy, representing 32.7% of the public electricity consumption of IMC, with an average energy intensity of 0.46 and 0.38 kWh/m³ for water supply systems (WSSs) and sewerage systems (SSs), respectively. Their carbon emissions totaled 315,765,358 kg CO₂, accounting for 2.7% of IMC’s total carbon emissions, with an average carbon intensity of 0.21 and 0.58 kg CO₂/m³ for WSSs and SSs, respectively. The proposed methodology was used to comprehensively evaluate WEC consumption and emissions in IMC. It is expected to enable relevant stakeholders to develop measures, such as water reuse and increasing renewable energy usage in water treatment and wastewater treatment plants, to build sustainable UWSs.

In this study, the catchment hydrology cycle analysis tool (CAT) model was used to conduct a comprehensive hydrological analysis of the water balance of agricultural reservoirs. Data from 2010 to 2017, including precipitation, water level data in the reservoir, groundwater usage, and wastewater discharge, were collected and compiled for the upper reaches of the Hantan River Dam. The current conditions and content curves of the 11 reservoirs within the watershed were investigated and recorded. The results were analyzed by simulating three scenarios: treating the entire watershed as 1 unit, dividing the watershed into 5 sub-watersheds according to the standard watershed criteria, and further subdividing it into 27 watersheds, taking into account the presence of agricultural reservoirs. In cases where watershed information is lacking, it is deemed that subdividing the watershed can enhance efficiency. The highest model efficiency was observed in the 27 sub-basins, particularly when accounting for agricultural reservoirs. This study proposed an efficient method for hydrological analysis of watersheds including ungauged areas.

A model that computes the per-unit process energy consumption, energy intensity, CO₂ emission, and CO₂ intensity of water treatment plants is developed. This model is used to estimate the total energy consumption of six water treatment plants in Seoul Metropolitan City (SMC), which is comprised 80–85% for finished water pumping, 6–10% for ozone disinfection, 2–4% for rapid mixing, and 1–3% for non-process loads. The model results are validated against actual data for 2020 and 2021. The net energy consumption considering renewable energy production and use is then calculated, and the corresponding level of CO₂ emissions is predicted. Four scenarios based on the projected water requirements for the year 2045 were evaluated as follows: increased energy efficiency in finished water pumping (Scenario 1), increased renewable energy production in water treatment plants (Scenario 2), increased energy efficiency in raw water pumping (Scenario 3), and reduced water supply per capita (Scenario 4). Compared to a baseline do-nothing scenario (Scenario 0), the net energy consumption is reduced by 3.57%, 2.61%, 3.42%, and 4.67% for Scenarios 1–4, respectively. Scenario 4, which is a water-driven approach, is best for reducing CO₂ emissions, while Scenario 1 and 3, which are energy-driven approaches, are more effective at reducing CO₂ intensity.

Robust water management systems are crucial for sustainable water use, particularly considering rapidly changing, ever-improving water supply system technologies. However, the establishment of specific management standards in upland fields is challenging, as several types of crops are cultivated in upland fields. Hence, the timing and required amount of water vary greatly, further rendering drought response challenging. In this study, we evaluated the agricultural drought vulnerability of South Korean upland fields, considering the lack of water resources, to establish preliminary drought damage prevention measures. The Technique for Order of Preference method was used for the drought vulnerability assessment, and the assessment indicators used were annual rainfall, number of dry days, upland field area, available soil water capacity, and groundwater usage. The 20 areas of highest vulnerability comprised large cultivation areas with minimal subsurface-water usage, except for areas where the number of dry days appeared to be the major factor for drought vulnerability. Damage caused by recurring droughts accumulated over time; thus, upland-field-oriented management may be required and can even be used in cases where insufficient drought information is available. Future studies can use the proposed method while considering assessment factors that describe upland field conditions.