China's Urban Methane Emissions From Municipal Wastewater Treatment Plant

The increased number and capacity of municipal wastewater treatment plants (WWTPs) in China has driven the emission of methane (CH₄). Few studies have focused on quantification of CH₄ emissions from municipal WWTPs of different cities and analysis of socioeconomic factors influencing the quantity of emissions. Here we estimated CH₄ emissions from WWTPs in China for 229 prefectural-level cities, based on data from 2,019 working municipal WWTPs. The results show the total CH₄ emissions to be 1,169.8 thousand tons (29.2 MtCO₂e) in 2014, which is over three times that of the municipal WWTPs in the United States in 2016. Large cities along the east coast regions had larger CH₄ emissions in absolute and per capita terms. Correlation analysis shows that cities with higher gross domestic product, household food consumption expenditure, or household consumption expenditure produced more degradable organics in wastewater, thus more CH₄ emissions. Measures to control the sources of degradable organics and regulate WWTP processes with less emission factor are key to mitigate CH₄ emissions. In addition to aerobic or anaerobic wastewater treatment systems, factors such as wastewater temperature, length of sewer, and the addition of nitrate that influencing emission factor are suggested to be involved in CH₄ emission modeling.