Greenhouse Gas Emissions of an Urban Water System in Korea: A case study of Paju city

Objectives : This study assessed the greenhouse gas emissions (GHG) in the urban water system from a life cycle perspective in the city of Paju. It serves as a case study to provide a quantitative basis for the net-zero water management.Methods : The scope of the study included the centralized local water supply and inter-basin water import system (water abstraction facilities, water treatment plants, pump stations, and water pipelines), wastewater system (wastewater pipelines, pump stations, and wastewater treatment plants, public industrial wastewater treatment plants, on-site wastewater treatment facilities), and circular water use (rainwater harvesting, greywater reuse, and wastewater recycling). This study considered scope 1 emissions, specifically CH4 and N2O emissions generated from wastewater treatment plants, scope 2 emissions from the electricity use during the operation of water infrastructure, and scope 3 emissions associated with the production of water and wastewater pipelines and chemicals. Scope 1 emissions were quantified using both the national guidelines and the 2019 IPCC guideline, and the estimates based on the two methods were compared. Scope 2 and scope 3 emissions were evaluated using life cycle assessment. To quantify GHG emissions for the year 2018, data were collected or estimated from various sources, including public statistics, field interviews, and the literature.Results and Discussion : In 2018, the total GHG emissions from Paju’s water system were 197.4 thousand tons of CO2 eq. Among these emissions, the scope 2 emissions accounted for the largest share, comprising 66.3% of the total. Notably, circular water use, which included wastewater recycling for high-quality industrial uses, accounted for 41.0% of the scope 2 emissions. Scope 1 emissions accounted for 25.5% and scope 3 emissions accounted for 8.2% of the total emissions. However, in the case of scope 1 emissions, the estimates varied significantly by 2.9 to 6.5 times, depending on the calculation methods and emission factors provided by two different guidelines.Conclusion : To achieve carbon neutrality in the water sector of the city of Paju, two approaches are required: enhancing energy efficiency to reduce scope 2 emissions and implementing measures to reduce scope 1 emissions. However, to obtain accurate and reliable estimates of the GHG emissions, it is crucial to develop applicable scope 1 emission factors based on field data. Furthermore, to gain a comprehensive understanding of GHG emissions in the water sector, further studies are necessary to analyze embodied GHG emissions in water infrastructure and GHG emissions associated with the end use of water.