Carbon emission efficiency system of wastewater treatment in China’s Yangtze river economic belt: spatial-temporal evolution and influencing factors

Introduction Improving the carbon emission efficiency of wastewater treatment (CEEWT) is essential for achieving the coordinated goals of pollution reduction and carbon mitigation. As a key economic and ecological region in China, the Yangtze River Economic Belt (YEB) provides an important context for examining the low-carbon performance of regional wastewater treatment systems. However, existing studies mainly focus on plant-level efficiency or single environmental indicators, with limited attention to regional-scale efficiency and its spatiotemporal evolution. Methods Based on the IPCC carbon accounting framework and an entropy weight–TOPSIS method, this study evaluates the CEEWT across provinces in the YEB from 2011 to 2020. The spatiotemporal evolution and regional disparities are systematically analyzed, and the underlying mechanisms are discussed from economic, technological, and institutional perspectives. Results The results indicate that CEEWT in the YEB shows an overall upward but fluctuating trend, while significant and persistent regional disparities remain. Downstream provinces such as Jiangsu, Shanghai, and Zhejiang consistently exhibit higher efficiency levels, whereas many midstream and upstream provinces lag behind. No clear convergence pattern is observed, suggesting strong path dependence shaped by long-term structural conditions. Discussion/Conclusion These findings highlight the necessity of differentiated, region-specific policy approaches to promote the low-carbon transition of wastewater treatment systems. This study provides a scientific basis for optimizing regional pollution and carbon reduction strategies in large-scale economic belts.