Operational insights into carbon dynamics and decarbonization pathways in megacity water supply plants

Urban water supply systems are significant contributors to global greenhouse gas (GHG) emissions. Water supply plants in megacities, as crucial components of water supply systems, face unique challenges in achieving net-zero GHG emissions due to higher water quality and quantity requirements. However, detailed emission data and future pathways under climate change scenarios are currently lacking. In this study, we collected over 140,000 operation data entries from all 37 water supply plants in Shanghai. Based on real operational data, we have established GHG emissions inventory and projected emissions from 2023 to 2035. Future scenarios were developed through coordination with government officials, water plant managers, and academic experts. The results show that the GHG emission intensities from Shanghai's water supply plants were 0.14 kg CO2-eq/m3 in 2021 and 0.12 kg CO2-eq/m3 in 2022. Suburban plants incur higher GHG emission intensity, while urban plants benefit from economies of scale. The dependence of GHG emission intensity on source water characteristics enables targeted mitigation strategy development. Scenario analysis shows implementation of five low-carbon measures under normal water quality conditions would reduce GHG emissions by up to 56.15 % by 2035, where smart platforms contribute the largest share (17.1 %). This study provides insights into low-carbon management policies and technologies for water supply plants in highly urbanized worldwide regions facing evolving environmental challenges.