Measurement-based assessment reveals key drivers and mitigation potential of methane emissions from China's wastewater treatment

Wastewater treatment is an increasingly important yet poorly quantified source of anthropogenic methane (CH₄). Here we report facility-level emissions based on atmospheric measurements from 105 wastewater treatment plants (WWTPs) across five climatic-economic regions in China-the largest dataset to date. We found that emission factors are primarily driven by organic load and concentration. Using updated facility-level emission factors, our analysis shows that emissions from Chinese WWTP, driven by rising organic loads, grew by 12% per year since 2003, reaching 254 ± 26 Gg CH₄ year^-1 in 2023. However, the rapid expansion of WWTPs lowered the average emission factor for the urban domestic wastewater sector, limiting total emissions growth to 32% over the same period. Scenario modeling suggests that, under current technology, emissions will peak around 2040. Deploying low-emission configurations and CH₄ recovery technologies could advance the peak by 15 years and reduce 2040 emissions by 23%. Incorporating such measures into China's decarbonization strategy will be essential for achieving climate mitigation goals.