Carbon Footprint Drivers in China’s Municipal Wastewater Treatment Plants and Mitigation Opportunities through Electricity and Chemical Efficiency

Reducing greenhouse gas (GHG) emissions to address climate change is a global consensus, and municipal wastewater treatment plants (MWWTPs) should lead the way in low-carbon sustainable development. However, achieving effluent discharge standards often requires considerable energy and chemical consumption during operation, resulting in significant carbon footprints. In this study, GHG emissions are systematically accounted for, and the driving factors of carbon footprint growth in China’s MWWTPs are explored. In 2020, a total of 41.9 million tons (Mt) of carbon dioxide equivalent (CO2-eq) were released by the sector, with nearly two-thirds being indirect emissions resulting from energy and material usage. The intensity of electricity, carbon source, and phosphorus removing agent consumption increasingly influence carbon footprint growth over time. Through statistical inference, benchmarks for electricity and chemical consumption intensity are established across all MWWTPs under various operational conditions, and the potential for mitigation through more efficient energy and material utilization is calculated. The results suggest that many MWWTPs offer significant opportunities for emission reduction. Consequently, empirical decarbonization measures, including intelligent device control, optimization of aeration equipment, energy recovery initiatives, and other enhancements to improve operational and carbon efficiency, are recommended.