Carbon Emission Accounting and Reduction Pathways for a Municipal Wastewater Treatment Plant in Lanzhou

• • The WWTP emitted 61,399.80 t CO2-eq in 2023, with an intensity of 0.71 kg CO2-eq/t; monthly variation was low (CV=3.46%), indicating stable operation. • • Direct emissions (47.47%) were dominated by N2O (61.89% of direct), while indirect emissions (52.53%) were dominated by electricity (95.15% of indirect), making electricity the single largest source (49.98% of total). • • Pearson correlation (P<0.01) linked direct emissions to influent BOD5 and TN concentrations and their removal rates, highlighting process control targets. • • Sensitivity analysis showed sewer retention time (0.42), fossil carbon fraction (0.35), and solids retention time (0.28) as key operational levers; uncertainty analysis gave a 95% CI of 0.64–0.79 kg CO2-eq/t.