[Analysis of Carbon Emission Characteristics and Influencing Factors in Urban Wastewater Collection Systems under the Background of Quality Improvement and Efficiency Enhancement].

Abstract

Against the background of today's increasingly serious global climate change problem, this study focuses on the carbon emission problem of urban drainage systems and proposes a carbon accounting method for the operation stage of urban drainage systems based on the emission factor method and mass balance idea. The method considered CH₄ from biochemical reactions of pollutants in the drain, CH₄ and N₂O from biochemical reactions of uncollected pollutants, and carbon emission from the electrical consumption of equipment such as lifting pumping stations, and the application was carried out based on the operational data of the case city from 2019 to 2022. The results of the study showed that the total carbon emission from the drainage system in the five areas （Ⅰ, Ⅱ, Ⅲ,Ⅳ, and V） of the case city decreased from 50,186 t in 2019 to 35,134 t in 2022. The sum of regions Ⅰ and Ⅴ contributed nearly 70% to the total carbon emissions, which were the two regions with the largest emissions. The largest contribution in terms of emission activities was CH₄ emission from biochemical reactions of uncollected pollutants （40.3%-51.6%）. Regarding emission intensity, the carbon emission intensities of different regions were, in descending order, Ⅴ（0.22 kg·m^-3） > Ⅲ（0.19 kg·m^-3） > Ⅳ（0.17 kg·m^-3） = Ⅱ（0.17 kg·m^-3） > Ⅰ（0.10 kg·m^-3）. The carbon emission intensities of different emission activities in descending order were： CH₄ emission intensity from the biochemical reaction of uncollected pollutants （0.075 kg·m^-3） > CH₄ emission intensity from the biochemical reaction of pollutants in drains （0.027 kg·m^-3） > N₂O emission intensity from the biochemical reaction of uncollected pollutants （0.026 kg·m^-3） > carbon emission intensity from electricity consumption （0.025 kg·m^-3）. The results of the analyses showed that ① The differences in the amount of sewage generated, the amount of water intake to the sewage treatment plant, the concentration of pollutants in the sewage treatment plant intake, and the consumption of electricity were the reasons for the total carbon emissions from the drainage system showing regional variability. ② CH₄ emission intensity from biochemical reactions of uncollected pollutants in discharge activities was high and needs further attention. ③ Actions to improve the quality and efficiency of the drainage network contribute to the reduction in carbon emissions from the drainage system.