Pollutant-specific carbon footprint analysis and decarbonization potential for municipal wastewater: A case study in...

Although municipal wastewater treatment serves as a process for water environmental security, the carbon footprint has correspondingly increased with the continuous economic development and increasing pollutant loads. However, studies on the climate change burden from the removal of different pollutants are scarce. To guide the regional-level decarbonization of municipal Wastewater Treatment Plants (WWTPs) while ensuring efficient pollutant removal, this study presents a novel assessment framework for evaluating and reducing the carbon footprint of different pollutant-specific removal processes. Using the 2022 operational data of 35 municipal WWTPs in Xi'an, China, as a case study, this study established a full-process material and energy input-output inventory and developed an innovative pollutant equivalent-based allocation method to assign the plant-scale carbon footprint to COD, TN, and TP removal processes, with full methodological justification and robustness analysis. The results show that sludge disposal contributed the largest share (32.33%) to the total carbon footprint of the studied WWTPs. The carbon footprint per equivalent of COD (1.40 t CO₂e) removal was the lowest, whereas those for TN (6.12 t CO₂e) and TP (6.94 t CO₂e) were comparable. Under the Power Grid Decarbonization Scenario (PDS)1 scenario with grid decarbonization from 2020 to 2050, the combined total carbon footprint from electricity and chemicals consumption was reduced by 76.54%. This study provides a scientific basis for the low-carbon optimisation of municipal wastewater treatment against the background of energy supply decarbonization and offers a replicable decision-making tool for WWTPs worldwide to achieve precise carbon reduction in targeted pollutant removal processes, supporting the synergy between carbon reduction and pollution control.