## 4 Conclusions  
This study systematically reveals the carbon emission characteristics of STPs in eastern China for the first time by integrating actual production data, providing a scientific foundation for regional policymaking on pollution and carbon reduction and promoting low-carbon operation modes. Additionally, the carbon emission accounting system and low-carbon operation evaluation system established herein offer technical support for STP carbon footprint certification and carbon trading mechanisms. The main conclusions are as follows:  
1. In 2024, the total carbon emissions from 98 STPs in eastern China reached 5.17 \(\times\) 10\({}^{8}\) tCO\({}_{2}\)-eq, with an average carbon emission intensity of 0.399 kgCO\({}_{2}\)-eq/m\({}^{3}\)--lower than the average of several developing countries. The carbon emission intensity follows a normal distribution, with 83.1% of STPs having an intensity between 0.2 and 0.6 kgCO\({}_{2}\)-eq/m\({}^{3}\). 2. Indirect carbon emissions are the primary source (62.1%) of STP carbon emissions, with power consumption (47.9%) and chemical use (14.2%) as key contributors. It is recommended to include fossil-derived CO\({}_{2}\) (4.6%) in the accounting system. 3. Treatment scale, operating load rate, treatment process, influent water quality, and pollutant reduction significantly impact STP carbon emissions. Small-scale STPs inherently exhibit higher carbon emission intensities compared to large-scale facilities due to their elevated energy consumption per ton of wastewater. To address this structural disadvantage, we recommend that governmental authorities implement differentiated carbon quota allocation policies tailored to the operational realities of small-scale STPs. 4. To advance low-carbon wastewater treatment, we propose the following strategies: 1. Prioritize the promotion of the anaerobic-anoxic-oxic (AAO) process. Regulatory agencies should encourage municipal design institutes to adopt AAO technology as the preferred option for new construction or retrofitting projects. 2. Deploy intelligent chemical dosing systems to optimize reagent utilization and minimize process-related carbon emissions. 3. Enhance influent load rates through collaborative mechanisms with upstream authorities, such as expanding service coverage, implementing integrated governance of sewer networks, or constructing new infrastructure to improve hydraulic utilization. 4. Strengthen the professional capabilities of STP personnel, as management and operational expertise directly influence plant efficiency, production costs, and carbon performance. Targeted training programs should be established to continuously upgrade the technical proficiency of plant operators and managers,enabling cost-effective achievement of low-carbon operational targets without substantial capital investments. 5. Carbon sources and phosphorus removal chemicals are the main contributors to chemical carbon emissions, accounting for 27.8% and 18.9% of such emissions, respectively. Reasonably controlling the nutrient proportion in influent can effectively reduce chemical carbon emissions. 6. The low-carbon operation evaluation of STPs in eastern China shows that only 19.4% meet the Class 1 standard, while 25% score below 60 points, categorized as high-carbon-emitting STPs, indicating significant carbon reduction potential. Based on the study's findings, the following recommendations are proposed to inform carbon regulation and climate policy development in East China:  
1. Differentiated Regulatory Frameworks:  
Regulatory frameworks should explicitly account for variations in carbon emission intensity across STPs of differing operational scales and treatment processes. Small-scale facilities, which inherently exhibit higher emission intensities due to elevated energy consumption per unit volume, warrant particular policy attention. 2. Technology Adoption Incentives:  
Promote the adoption of intelligent chemical dosing systems and energy-efficient equipment to minimize process-related carbon footprints.