Life cycle assessment comparison of municipal wastewater treatment processes and technology upgrading pathways in China

This study conducts a life cycle assessment (LCA) comparing four municipal wastewater treatment scenarios in Southwest China: conventional A/A/O and CASS processes meeting Class 1A standard, and their upgraded versions (A/A/O + MBR and CASS with advanced treatment) meeting Quasi-Class IV standard. A ‘cradle-to-grave’ model was developed covering chemical production, operation, and sludge disposal. Results show that under Class 1A standard, CASS outperforms A/A/O in most impact categories due to lower chemical dependence. Under the upgraded standard, both processes achieve significant eutrophication reduction but incur substantial increases in global warming potential (188% average), primary energy demand (481% average), and sludge-related impacts, revealing a ‘pollution shifting’ effect. Chemical overdosing and sludge incineration are identified as key environmental hotspots. The findings highlight the need for tiered discharge standards and region-specific upgrading strategies to balance water quality improvement with broader environmental sustainability.