Abstract
The artificial recycling of CO2 into value-added feedstocks and chemicals provides a sustainable approach to mitigate its greenhouse effect and realize a carbon-neutral economy, for which the direct and efficient utilization of CO2 reduction products without additional separation and purification remains challenging. Here an electrochemical–biological hybrid system has been developed to merge CO2 electrolysis with municipal wastewater treatment. In this set-up, the formate produced electrocatalytically (formate-e) in neutral electrolyte (1.0 M KHCO3) is directly applied as a carbon source and energy carrier for biological denitrification using activated sludge from municipal wastewater treatment plants, exhibiting an excellent nitrate nitrogen (NO3−-N) removal rate of ~3.06 mg l−1 h−1. Moreover, after long-term continuous operation of the tailored denitrification bioreactor, the formate-e displayed high denitrification rate of 1.08 mgNO3−-N per gram suspended solids per litre per hour, surpassing that of acetate, widely used as a commercial carbon source. Further environmental and techno-economic analyses suggest that integrating this electrochemical–biological hybrid system with an electrochemical recovery and separation system can significantly lower the cost of the electrolyte, thereby showing promise for the direct use of formate-e in industrial applications for wastewater treatment.
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Data availability
All of the data that support the findings of this study are included in the Article and its Supplementary Information. Source data are provided with this paper. These data are also available via figshare at https://doi.org/10.6084/m9.figshare.29815832 (ref. 56).
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Acknowledgements
G.C., G.Q. and W.-W.Z. thank the support of the National Natural Science Foundation of China (22471077, 21971070, 52270035 and 22374066), the Guangdong Basic and Applied Basic Research Foundation (2022A1515012047), the Guangdong Innovative and Entrepreneurial Research Team Program (2019ZT08L075), the Guangdong Pearl River Talent Program (2019QN01L159, 2019QN01L125), the Science and Technology Program of Guangzhou (202103040002, 2025A04J7050) and the National Key R&D Program of China (2023YFC3708505). K.-S.P., Y.-Y.C. and S.-F.H. acknowledge the support from the National Science and Technology Council, Taiwan (Contract Number NSTC 114-2628-M-A49-005). We thank the support from the Yushan Young Scholar Program (MOE-114-YSFMS-0010-003-P2) and the Center for Emergent Functional Matter Science, Ministry of Education, Taiwan. X.W. acknowledges support through an ECS grant from the Research Grants Council of the Hong Kong Special Administrative Region (project number 21300323) and the CityU start-up fund (project number 9610600).
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G.C. and G.Q. conceived the idea. Q.W., R.D., H.W. and P.W. prepared the catalysts and conducted the CO2 electroreduction tests. S.J., J.C. and Q.W. conducted a denitrification batch experiment. Y.Q., K.Y., Y.Z. and L.Z. contributed to thorough discussions on this work. K.-S.P., Y.-Y.C. and S.-F.H. carried out the operando XAS measurements. X.-Q.T. and W.-J.O. conducted the LCA analysis. G.Q., W.-W.Z. and G.C. proposed the idea, designed the experiments, analysed the data and wrote the paper with editing from G.Q. and X.W. G.C. supervised and coordinated all investigators in this project.
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Wu, Q., Ji, S., Chen, J. et al. Realizing the practical application of CO2 electroreduction for urban wastewater denitrification. Nat Water (2025). https://doi.org/10.1038/s44221-025-00516-6
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DOI: https://doi.org/10.1038/s44221-025-00516-6
