Assessment of greenhouse gas emission from A/O and SBR wastewater treatment plants in Beijing, China

•GHG emission (CO2-eq m−3 wastewater) in SBR WWTP was 53% higher than in A/O WWTP.•Direct GHG emission in A/O WWTP was contributed on 49.2% of total GHG emission.•Direct GHG emission in SBR WWTP was contributed on 61.8% of total GHG emission.•N2O was the major source contributing to GHG emission in two processes.

Wastewater treatment plants (WWTPs) are a significant source of greenhouse gas (GHG) emission in China, which is one of the major causes of global warming. Anoxic/Oxic (A/O) and sequencing batch reactors (SBR) are two commonly used methods for wastewater treatment in China. In this study, GHG emission levels were investigated in both full-scale A/O and SBR wastewater treatment systems in Beijing, China, over a period of 12 months. GHG emission, calculated by carbon emission (CO2-equivalent) from WWTPs, is composed of the direct emission of CO2, CH4, and N2O during the treatment processes and indirect emission due to the consumption of electricity and chemicals. The total GHG emissions were 404.93 gCO2-eq m−3 wastewater and 864.98 gCO2-eq m−3 wastewater during the A/O and SBR processes, respectively, including the direct carbon emissions of 199.12 gCO2-eq m−3 wastewater, and 534.93 gCO2-eq m−3 wastewater from the A/O and SBR WWTP, respectively. N2O was the major contributor towards total GHG emissions during both the A/O and SBR process. In addition, the dominant source of direct GHG emission occurred during the aerobic unit/period, and was caused by aeration stripping as well as the degradation and transformation of nutrition. The indirect emission varied only slightly during both wastewater treatment processes.