Analysis of greenhouse gas emissions from urban wastewater treatment during recent years in China

At present, urban greenhouse gas (GHG) emissions from different wastewater treatment stages are attracting increasing attention. Based on the Guidelines of the China Greenhouse Gas List Compilation (Trial) and the IPCC National Greenhouse Gas List Guidelines in 2006, this paper evaluated urban GHG emissions from wastewater treatment in China from 2011 to 2020. The contribution rates of GHG emissions to the total GHG emissions were calculated for the different wastewater treatment stages. The variations in annual GHG emissions and differences in GHG emissions among different regions and provinces were also analyzed. The total amount of equivalent CO₂ emissions reaches 1478.51 million tons, and the annual average amount of equivalent CO₂ emissions from 2011 to 2020 is 147.9 million tons, which shows a trend of decreasing first and then increasing. The distribution of GHG emissions from wastewater treatment is uneven among provinces and regions; Guangdong Province has the highest emission, while the Xizang autonomous Region has the lowest. The correlation and contribution rate analysis revealed that paper production and chemical and side food production could discharge a large amount of wastewater with a high COD content, which may have an important impact on GHG emissions during the wastewater treatment stages. According to the study results, CH₄ accounts for the largest proportion (63.08%) of the total GHG emissions. The most important source of CH₄ comes from the industrial wastewater treatment stage. The annual average CO₂ emissions account for 22.24% of the total GHG emissions, which are mainly from the power and chemical consumption stage. The annual average N₂O emissions account for 14.68% of the total GHG emissions and are mainly from the wastewater collection and discharge stage. Therefore, in the future, GHG emission reduction strategies should focus on CH₄ emissions in the industrial wastewater treatment stage and develop CH₄ recycling and utilization technologies.