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The increased number and capacity of municipal wastewater treatment plants (WWTPs) in China has driven the emission of methane (CH 4). Few studies have focused on quantification of CH 4 emissions from municipal WWTPs of different cities and analysis of socioeconomic factors influencing the quantity of emissions. Here we estimated CH 4 emissions from WWTPs in China for 229 prefectural-level cities, based on data from 2,019 working municipal WWTPs. The results show the total CH 4 emissions to be 1,169.8 thousand tons (29.2 MtCO 2 e) 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 CH 4 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 CH 4 emissions. Measures to control the sources of degradable organics and regulate WWTP processes with less emission factor are key to mitigate CH 4 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 CH 4 emission modeling. Plain Language Summary The increased number and capacity of municipal wastewater treatment plants (WWTPs) in Chinese cities has driven the emission of methane, a potent greenhouse gas. Understanding and balancing the trade-offs between increased municipal wastewater treatment capacity and the demands for greenhouse gas emissions reduction is a big challenge for cities in developing countries like China. We estimated methane emissions from 2,019 working municipal WWTPs in China for 229 cities. The results show the total methane emissions to be 1,169.8 thousand tons in 2014, which is over three times that of the municipal WWTPs in the United States in 2016. Large and wealth cities along the east coast regions had larger methane emissions in absolute and per capita terms. Cities with higher gross domestic product, household food consumption expenditure, or household consumption expenditure produced more degradable organics in wastewater, thus more methane emissions. Measures to control the sources of degradable organics and regulate WWTP processes are key to mitigate methane emissions.

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The change in diet structure is one of the critical features of social transformation, and diet structure is directly related to human health. In China, with rapid economic development, changes in the diet structure of the population have begun and are proceeding at a fairly rapid rate. In order to reveal how the Chinese diet is approaching or deviating from the nutritional goal, a novel index, NDBI (National Dietary Balance Index), is developed in this study to investigate the Chinese diet from 1961 to 2017 at a national level. The results show that the Chinese diet has transitioned from the under-intake stage to the over-intake stage. Before the 1980s, Chinese people ate all foods inadequately except staple foods; after the 1980s, the issue of under-intake began to fade, and the intake of meats even became excessive. The intake of staple foods is always excessive during this period. Currently, the Chinese diet is still unhealthy because of the inadequate intake of dairy products and the excessive intake of staple foods and meats. By evaluating diet structure on a national level, this study can help people to better understand how the Chinese diet deviated from the nutritional goal and provides information for policymakers intervening in China’s food consumption.