Greenhouse gas emissions from wastewater treatment plants in China: Historical emissions and future mitigation potentials

Accurate estimation of greenhouse gas (GHG) emissions characteristics and future mitigation potentials of China's wastewater treatment plants (WWTPs) is essential to propose suitable mitigation strategies. Here we employ the population-equivalent method recommended by the IPCC to analyze GHG emission characteristics and hotspots of China's WWTPs from 2005 to 2020 and assess the mitigation potentials by 2035. Results show that GHG emissions from China's WWTPs more than tripled from 13.34 Mt CO₂-eq in 2005 to 30.95 Mt CO₂-eq in 2020. Due to the differences in electricity consumption intensity, emission factors, and economic development level, there is significant spatial heterogeneity in the amount, structure, and intensity of emissions by province. Scenario analysis reveals that energy-saving improvement generates the largest mitigation potential (15%), followed by operational optimization (10%) and thermal energy recovery (10%), while chemical energy recovery (4%) and solar energy utilization (3%) contribute the least. Taking all mitigation measures, emissions can reduce by about 41% to 21.14 Mt CO₂-eq in 2035. What's more, the mitigation effect of different decarbonization measures varies among provinces. Our results highlight the need for targeted policy in priority areas and region-specific strategies.