Quantitational life cycle assessment of Effluent-Energy-Carbon synergies and trade-offs in drinking water treatment plant upgrades

Abstract

Upgrading drinking water treatment plants (WTPs) plays a critical role in ensuring reliable urban water supply. However, an exclusive focus on water quality improvements may overlook its critical trade-offs in energy consumption and carbon emissions. This study developed a specific Effluent-Energy-Carbon Evaluation Model (EECEM) to assess the lifecycle impact of WTP upgrading and was verified in a full-scale water treatment plant in Fuzhou City, China. The result revealed that ozone-bioactivated carbon retrofitting improved the normalized Effluent Quality Index (EQI’) by 58.9 % but decreased the normalized Energy Index (EI’) and the normalized Carbon emission Index (CI’) by 70.7 % and 55.9 %, respectively. Economic analysis further revealed that upgrading raised construction costs by 18.9 % but reduced operational costs by 15.4 %. Notably, the coupling coordination degree (D) dropped by 17.3 %, indicating a decoupling between water quality gains and energy‑carbon trade-offs. 3D ternary mapping further identified regional divergences. Upgrading with advanced processes achieved 56 % higher D values in water-quality-sensitive zones, while conventional processes attained 104 % superiority in energy‑carbon-constrained areas. These findings highlight the complex trade-offs between treatment effectiveness and system sustainability. The study establishes a decision-support framework for WTP upgrades, emphasizing the necessity of adaptive optimization strategies to reconcile water-energy‑carbon (WEC) nexus conflicts.