Optimization of Greenhouse Gas Accounting Methods for Wastewater Treatment Plants in East Chinese Regions: A Comparative Analysis of IPCC and Group Standards Based on 49 Plants in Shandong Province

In order to achieve China’s carbon neutrality target by 2060, accurate carbon accounting for wastewater treatment plants (WWTPs) is imperative. This study takes Shandong Province as the research object, through large-scale empirical analysis, research method differences, and the annual operation data of 49 sewage treatment plants, for the first time to realize the systematic comparison of multiple methods on the provincial scale. The main findings show a 19.7% reduction in calculated emissions from Standard for Carbon Emission Reduction Assessment of Urban WWTPs (T/CUWA 50055-2023, GS 2023) compared to Intergovernmental Panel on Climate Change (IPCC 2019), thanks to its inclusion of CO2 from fossil sources (5.0% of total emissions) and optimized CH4/N2O emission factors. Indirect emissions accounted for 56.8% of total emissions, with electricity consumption (43.3%) and chemical use (13.5%) being the main contributors. Carbon sources (27.6%) and phosphorus removal agents (15.2%) were the most important chemical-related emissions. The scale effect of indirect emissions is significant. It was found that there was a large difference in emission factors (such as a 236.9% difference in carbon source factors), and optimization strategies were proposed: preferentially using low-emission carbon sources (methanol reduced emissions by 77.6% compared with sodium acetate) and developing alternative carbon sources.