Influencing Factors of GHG Emissions from Wastewater Treatment Plants in China: A Comprehensive Analysis and Quantitative Evaluation

Greenhouse gases (GHG) such as CO2, CH4, and N2O are released in significant quantities during wastewater treatment. However, few studies have investigated the variables influencing GHG emissions from wastewater treatment plants (WWTPs). In this study, the GHG emissions from 247 typical urban wastewater treatment plants in China were examined using the emission factor approach (IPCC). An analysis was conducted on the effects of various parameters (the WWTP area, treatment process, treatment scale, effluent discharge standard, influent wastewater quality, and facility type) on GHG emissions. The findings showed that the average GHG emissions of WWTPs in all regions of China were 0.45 kgCO2 eq/m3. WWTPs in South China are larger and their energy usage lower than those in North China, and they emit only 61% of North China’s emissions. Compared to other processes, the cyclic activated sludge system (CASS) process provides the lowest intensity of emissions. GHG emissions are substantially correlated with influent wastewater quality, the facility type, and effluent discharge standards (EDS). GHG emissions were twice as high with EDS 20 (discharging limitations of COD were 20 mg/L) than with grade IA (EDS 50), and 3.4 times higher with grade IB (EDS 60). With a treatment scale smaller than 2 × 105 m3/d, the average GHG emissions were positively correlated with the treatment scale, but only moderately negatively correlated when the scale exceeded 2 × 105 m3/d. Underground wastewater treatment plants emit greater intensity of GHGs (0.53 kgCO2-eq/m3) than above-ground treatment plants (0.43 kgCO2-eq/m3). This study examined the major variables influencing GHG emissions from wastewater treatment facilities, and it is anticipated that the results will offer a theoretical direction for reducing such emissions.