China's Urban Methane Emissions From Municipal Wastewater Treatment Plant

Abstract

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.

Greenhouse gas emissions associated with urban water infrastructure: What we have learnt from China's practice

“…Studies at a regional level are usually based on a mass balance approach derived from the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, 2006). Researchers have evaluated CH 4 emissions at the regional level (Du et al, 2018; Ma et al, 2015) and city level (Zhao et al, 2019), and these estimations showed similar results to total national emissions (Table 4). Zhao et al (2019) found that CH 4 emissions from municipal WWTPs for China's 229 prefectural‐level cities were over three times that of the municipal WWTPs in the United States in 2016.…”

“…Researchers have evaluated CH 4 emissions at the regional level (Du et al, 2018; Ma et al, 2015) and city level (Zhao et al, 2019), and these estimations showed similar results to total national emissions (Table 4). Zhao et al (2019) found that CH 4 emissions from municipal WWTPs for China's 229 prefectural‐level cities were over three times that of the municipal WWTPs in the United States in 2016. Although the IPCC approach has considerable uncertainty (Law et al, 2012), it is still a suitable way to quantify CH 4 of WWTPs at a regional level compared with the onsite monitoring approach (Zhao et al, 2019).…”

Sustained methane emissions from China after 2012 despite declining coal production and rice-cultivated area

“…Freshwater aquaculture areas are from Bureau of Fisheries China 33 . Activity data for waste water treatment plants are from Zhao et al 34 . Other activity data are from the National Bureau of Statistics of China 35 .…”

“…small, village or town-owned coal mines 16,34 . Our CMM prior inventory includes 11,000 operating coal mines in 2010/2011, of which about 4000 mines have been abandoned over 2010-2017 16 (Fig.…”

“…3f). In addition, the number of wastewater facilities has increased by 40% from 2010 to 2014 based on the most recent available data 34 (Fig. 3f), which is potentially a significant source contributing to the waste trend.…”