Comprehensive Sustainability Evaluation of Low-Carbon Technology in Wastewater Treatment System Based on Carbon Reduction–Economy–Technology Coupling Index

Amid the escalating challenges of global climate change, promoting the sustainable and low-carbon transformation of wastewater treatment systems has become a critical pathway toward achieving carbon neutrality and sustainable urban infrastructure development. However, existing low-carbon technologies for wastewater treatment still lack systematic and sustainability-oriented evaluation approaches, which constrains the scientific selection of technologies and the optimization of low-carbon transition pathways. In this study, a comprehensive inventory of 30 low-carbon technologies was established across five categories, including equipment energy saving, process improvement, intelligent control, energy recovery, and resource recycling. Based on three dimensions, namely carbon reduction potential, economic performance, and technology readiness level, a Carbon Reduction–Economy–Technology Coupling Index (CRETCI) was developed to enable systematic quantitative evaluation and sustainability-oriented assessment of low-carbon technologies in wastewater treatment systems. The analysis of carbon reduction potential indicated that process improvement technologies exhibited the highest average carbon reduction potential, reaching approximately 0.136 kg CO2e/m3, demonstrating significant advantages in deep emission reduction. Economic analysis revealed that energy recovery technologies showed the best economic performance, with all marginal abatement costs being negative, indicating strong synergistic benefits between economic returns and carbon mitigation. The technological maturity assessment demonstrated that both intelligent control and energy recovery technologies achieved a Technology Readiness Level (TRL) of 9, indicating a well-established foundation for engineering application. The TCECI evaluation results showed that energy recovery technologies achieved the highest comprehensive score (0.71), significantly outperforming process improvement technologies (0.57). This finding suggests that the current low-carbon technology system for wastewater treatment is characterized by a structural trade-off between high carbon reduction potential and high technological maturity. Overall, this study establishes a multidimensional sustainability evaluation framework integrating environmental benefits, economic feasibility, and technological applicability, thereby providing important theoretical support and practical decision-making guidance for sustainable wastewater management, low-carbon technology selection, and carbon-neutral transition pathway optimization in the wastewater treatment sector.