Carbon footprint analysis and assessment of municipal wastewater treatment based on life cycle assessment

Li Chengjie; Huang Sen; Chen Baoguang; Zhao Aiping; Guo Xiaoming; Jiang Fengcheng; Wang Mingshi

doi:10.16186/j.cnki.1673-9787.2025080038

Abstract：Objectives Gaps in existing wastewater treatment carbon-footprint research are addressed in the present study—namely the omission of CO₂ emissions originating from fossil-derived organic carbon in influ-ent wastewater that are released during biological treatment by activated sludge,and the lack of comprehen-sive life-cycle-level evaluation of carbon-reduction pathways.A life-cycle assessment is conducted to ana-lyze and evaluate the carbon footprint of municipal wastewater treatment.Methods An improved carbon-footprint accounting model is developed to identify the key emission sources across the full process of repre-sentative A/A/O(anaerobic/anoxic/oxic)wastewater treatment plants,and integrated,system-level mitiga-tion strategies are proposed.Taking a typical wastewater treatment plant as a case study,a life cycle assess-ment(LCA)method is applied to establish a system encompassing four unit processes:primary treatment,biological treatment,advanced treatment,and sludge treatment.The eFootprint software,along with the CLCD and Ecoinvent databases is used to quantify the carbon footprint.A novel aspect includes the ac-counting of CO2 emissions derived from fossil-origin organic carbon in wastewater during biological treat-ment via the activated sludge process.Based on one year of actual operational data,a sensitivity analysis is conducted to identify key influencing factors.Results The total carbon footprint of the plant is found to be 5.11×10⁻¹ kg CO₂e/m³.The carbon footprint of the four unit processes is ranked as follows:biological treat-ment>sludge treatment>advanced treatment>preliminary treatment.Biological and sludge treatments together account for 73%of the total,identifying them as the primary carbon emission units.From an inventory per-spective,the contributions are ranked as follows:electricity consumption>material consumption>pollutant emissions>direct emissions.Electricity and material consumption are identified as the core influencing fac-tors,with indirect emissions collectively accounting for 82%.Conclusions Based on the carbon footprint ac-counting model constructed in this study,which incorporates fossil-derived CO2 emissions,biochemical treatment and sludge treatment have been identified as the key units for emission reduction,with electricity consumption and material consumption being the primary focuses for management.Accordingly,short-and long-term coordinated emission reduction strategies are proposed:short-term measures include improving equipment energy efficiency,optimizing operational processes,and adopting low-cost material alternatives;long-term strategies involve process upgrades,implementing intelligent control systems,and optimizing the energy mix.This approach provides actionable pathways for carbon emission reduction in wastewater treat-ment plants.