Overcoming barriers to net-zero emissions in wastewater treatment: insights from a comparative analysis

Abstract

The wastewater treatment sector contributes to greenhouse gas emissions, thereby exacerbating global warming. Achieving net-zero emissions in wastewater treatment plants (WWTPs) is pivotal to meeting carbon neutrality targets. This study evaluated the carbon footprint (CF) of six representative WWTPs in southern and northern China to elucidate the current status of carbon neutrality. The analysis covered CF composition, offsets achieved through carbon compensatory measures, and the CF seasonal and spatial variations. The average CF per population equivalent of the selected Chinese WWTPs with offsets was 58 kg CO₂-eq/PE/yr, representing a 22.8% reduction compared with the pre-offset value. Energy recovery from sludge incineration and reclaimed water reuse emerged as the vital carbon offset strategies for the studied facilities in southern and northern China, respectively. Unlike those in typical European WWTPs, indirect emissions driven by substantial electricity and chemical consumption were the primary CF sources in Chinese plants (> 60%). When pollutants removed were used as the functional unit, peak CF values were observed during summer or autumn. Energy input was determined to be the primary factor influencing the CF. Further CF reductions can be realized through process optimization, energy recovery, and chemical reduction, and other measures. This study provides a valuable reference for formulating targeted mitigation strategies in WWTPs and advancing towards carbon neutrality.

Graphical abstract

Keywords

Wastewater treatment plant / Carbon footprint / Seasonal variation / Spatial variation / Low-carbon pathways

Highlight

	● Seasonal and spatial variations of CF in typical WWTPs were explored.
	● Indirect carbon emissions dominated, with energy use being the largest contributor.
	● The examined WWTPs remained far from achieving net-zero emissions.
	● The CF per cubic meter of treated wastewater was highest in winter.
	● Energy recovery and chemical saving are key for WWTPs to realize carbon neutrality.

References

[1] Alnahhal S, Spremberg E. (2016). Contribution to exemplary in-house wastewater heat recovery in Berlin, Germany. Procedia CIRP, 40: 35–40

[2] An Y, Zhang Y B, Li P, Lu M. (2021). Current situation and experience summary of municipal sewage sludge treatment and disposal in China. Water & Wastewater Engineering, 47(S1): 94–98

[3] Asadi M, Mcphedran K. (2021). Estimation of greenhouse gas and odour emissions from a cold region municipal biological nutrient removal wastewater treatment plant. Journal of Environmental Management, 281: 111864

[4] Chen H, Yan S H, Ye Z L, Meng H J, Zhu Y G. (2012). Utilization of urban sewage sludge: Chinese perspectives. Environmental Science and Pollution Research, 19(5): 1454–1463

[5] Chen H X, Zheng Y N, Zhou K, Cheng R, Zheng X, Ma Z, Shi L. (2023a). Carbon emission efficiency evaluation of wastewater treatment plants: evidence from China. Environmental Science and Pollution Research, 30(31): 76606–76616

[6] Chen S, Liu H L. (2024). Achieving low-carbon and sustainable wastewater treatment by controlling the flow of pollutants: a pilot scale investigation on reducing greenhouse gas emissions and enhancing resource recovery. Journal of Water Process Engineering, 64: 105665

[7] Chen S Q, Zhang L M, Liu B B, Yi H, Su H S, Kharrazi A, Jiang F, Lu Z M, Crittenden J C, Chen B. (2023b). Decoupling wastewater-related greenhouse gas emissions and water stress alleviation across 300 cities in China is challenging yet plausible by 2030. Nature Water, 1(6): 534–546

[8] Du W J, Lu J Y, Hu Y R, Xiao J X, Yang C, Wu J, Huang B C, Cui S, Wang Y, Li W W. (2023). Spatiotemporal pattern of greenhouse gas emissions in China’s wastewater sector and pathways towards carbon neutrality. Nature Water, 1(2): 166–175

[9] Du Y J, Zhang J R, Zhong W, Qian H J, Han F L, Wang H, Zhang L B. (2024). The potential of wastewater-source heat pump in decarbonising buildings sector of China. Environmental Technology, 45(22): 4467–4481

[10] Fang Y T, Xie H Y, Chen B, Han Z X, An D, Cai W X, Zhang W, Wang Y T. (2024). Achieving carbon neutrality in Shanghai's municipal wastewater treatment sector requires coordinated water conservation and technical improvement. Journal of Cleaner Production, 443: 141134

[11] Foley J, Lant P A, Donlon P. (2008). Fugitive greenhouse gas emissions from wastewater systems. Water, 38(2): 18–23

[12] Fu X R, Hou R R, Yang P, Qian S T, Feng Z Q, Chen Z B, Wang F, Yuan R F, Chen H L, Zhou B H. (2022). Application of external carbon source in heterotrophic denitrification of domestic sewage: a review. Science of The Total Environment, 817: 153061

[13] Gruber W, Niederdorfer R, Ringwald J, Morgenroth E, Bürgmann H, Joss A. (2021). Linking seasonal N₂O emissions and nitrification failures to microbial dynamics in a SBR wastewater treatment plant. Water Research X, 11: 100098

[14] Gustavsson D J I, Tumlin S. (2013). Carbon footprints of Scandinavian wastewater treatment plants. Water Science and Technology, 68(4): 887–893

[15] Hanson E, Nwakile C, Hammed V O. (2025). Carbon capture, utilization, and storage (CCUS) technologies: evaluating the effectiveness of advanced CCUS solutions for reducing CO₂ emissions. Results in Surfaces and Interfaces, 18: 100381

[16] Hao X D, Li J, van Loosdrecht M C M, Jiang H, Liu R B. (2019a). Energy recovery from wastewater: heat over organics. Water Research, 161: 74–77

[17] Hao X D, Wang X Y, Liu R B, Li S, Van Loosdrecht M C M, Jiang H. (2019b). Environmental impacts of resource recovery from wastewater treatment plants. Water Research, 160: 268–277

[18] He X X, Li Z, Xing C Y, Li Y C, Liu M M, Gao X, Ding Y S, Lu L H, Liu C, Li C. . (2023). Carbon footprint of a conventional wastewater treatment plant: an analysis of water-energy nexus from life cycle perspective for emission reduction. Journal of Cleaner Production, 429: 139562

[19] Huang Z, Jiang D Q, Lu L, Ren Z J. (2016). Ambient CO₂ capture and storage in bioelectrochemically mediated wastewater treatment. Bioresource Technology, 215: 380–385

[20] IPCC(2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Geneva: Intergovernmental Panel on Climate Change

[21] IPCC(2014). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Geneva: Intergovernmental Panel on Climate Change

[22] Kim E, Shin S G, Jannat M a H, Tongco J V, Hwang S. (2017). Use of food waste-recycling wastewater as an alternative carbon source for denitrification process: a full-scale study. Bioresource Technology, 245: 1016–1021

[23] Li L Q, Wang X H, Miao J Y, Abulimiti A, Jing X S, Ren N Q. (2022). Carbon neutrality of wastewater treatment-A systematic concept beyond the plant boundary. Environmental Science and Ecotechnology, 11: 100180

[24] Longo S, d'Antoni B M, Bongards M, Chaparro A, Cronrath A, Fatone F, Lema J M, Mauricio-Iglesias M, Soares A, Hospido A. (2016). Monitoring and diagnosis of energy consumption in wastewater treatment plants. A state of the art and proposals for improvement. Applied Energy, 179: 1251–1268

[25] Lu L, Guest J S, Peters C A, Zhu X P, Rau G H, Ren Z J. (2018). Wastewater treatment for carbon capture and utilization. Nature Sustainability, 1(12): 750–758

[26] Luo Y S, Yao J Q, Wang X Y, Zheng M Y, Guo D Y, Chen Y G. (2020). Efficient municipal wastewater treatment by oxidation ditch process at low temperature: bacterial community structure in activated sludge. Science of The Total Environment, 703: 135031

[27] Maktabifard M, Al-Hazmi H E, Szulc P, Mousavizadegan M, Xu X B, Zaborowska E, Li X, Mąkinia J. (2023). Net-zero carbon condition in wastewater treatment plants: a systematic review of mitigation strategies and challenges. Renewable and Sustainable Energy Reviews, 185: 113638

[28] Maktabifard M, Awaitey A, Merta E, Haimi H, Zaborowska E, Mikola A, Mąkinia J. (2022). Comprehensive evaluation of the carbon footprint components of wastewater treatment plants located in the Baltic Sea region. Science of the Total Environment, 806: 150436

[29] Maktabifard M, Zaborowska E, Makinia J. (2020). Energy neutrality versus carbon footprint minimization in municipal wastewater treatment plants. Bioresource Technology, 300: 122647

[30] Marinelli E, Radini S, Foglia A, Lancioni N, Piasentin A, Eusebi A L, Fatone F. (2021). Validation of an evidence-based methodology to support regional carbon footprint assessment and decarbonisation of wastewater treatment service in Italy. Water Research, 207: 117831

[31] Mccarty P L, Bae J, Kim J (2011). Domestic wastewater treatment as a net energy producer–can this be achieved? Environmental Science & Technology, 45(17): 7100–7106

[32] Mora C, Spirandelli D, Franklin E C, Lynham J, Kantar M B, Miles W, Smith C Z, Freel K, Moy J, Louis L V. . (2018). Broad threat to humanity from cumulative climate hazards intensified by greenhouse gas emissions. Nature Climate Change, 8(12): 1062–1071

[33] Onnis-Hayden A, Srinivasan V, Tooker N B, Li G Y, Wang D Q, Barnard J L, Bott C, Dombrowski P, Schauer P, Menniti A. . (2020). Survey of full-scale sidestream enhanced biological phosphorus removal (S2EBPR) systems and comparison with conventional EBPRs in North America: process stability, kinetics, and microbial populations. Water Environment Research, 92(3): 403–417

[34] Periyasamy S, Temesgen T, Karthik V, Beula Isabel J, Kavitha S, Rajesh Banu J, Sivashanmugam P. (2022). Wastewater to biogas recovery. Clean Energy and Resource Recovery, 2: 301–314

[35] Posadas E, García-Encina P A, Soltau A, Domínguez A, Díaz I, Muñoz R. (2013). Carbon and nutrient removal from centrates and domestic wastewater using algal-bacterial biofilm bioreactors. Bioresource Technology, 139: 50–58

[36] Qu S, Hu Y C, Wei R K, Yu K, Liu Z Y, Zhou Q, Wang C C, Zhang L J. (2025). Carbon footprint drivers in China’s municipal wastewater treatment plants and mitigation opportunities through electricity and chemical efficiency. Engineering, 50: 106–116

[37] Rahimi S, Modin O, Mijakovic I. (2020). Technologies for biological removal and recovery of nitrogen from wastewater. Biotechnology Advances, 43: 107570

[38] Ren Z Q, Wang H, Zhang L G, Du X N, Huang B C, Jin R C. (2022). A review of anammox-based nitrogen removal technology: from microbial diversity to engineering applications. Bioresource Technology, 363: 127896

[39] Shahid M K, Choi Y. (2023). Comprehensive analysis of greenhouse gas emissions and emission factors in a Korean domestic wastewater treatment plant: insights into mechanisms and pathways for climate change mitigation. Journal of Water Process Engineering, 56: 104476

[40] Shen C, Lei Z Y, Wang Y, Zhang C H, Yao Y. (2018). A review on the current research and application of wastewater source heat pumps in China. Thermal Science and Engineering Progress, 6: 140–156

[41] Shi X F, Tal G, Hankins N P, Gitis V. (2014). Fouling and cleaning of ultrafiltration membranes: a review. Journal of Water Process Engineering, 1: 121–138

[42] Song Y P, Du L L, Wang B G, Zhang L M, Lin H Y, Ma F, Bai Y, Wang A J, Wang H C, Ren N Q. (2025). Flexible carbon source regulation for mitigating greenhouse gas emissions in full-scale wastewater treatment. Environmental Science & Technology, 59(19): 9517–9528

[43] Tang K, Xie J W, Pan Y W, Zou X Y, Sun F Q, Yu Y B, Xu R, Jiang W H, Chen C J. (2022). The optimization and regulation of energy consumption for MBR process: a critical review. Journal of Environmental Chemical Engineering, 10(5): 108406

[44] TheInternational Water Association (2024). Global Best in Water Projects Announced at IWA 2024 Project Innovation Awards. London: International Water Association

[45] TheState Council of the People’s Republic of China (2021). China Maps Path to Carbon Peak, Neutrality Under New Development Philosophy. Beijing: The State Council of the People’s Republic of China

[46] Tong Y D, Liao X W, He Y Y, Cui X M, Wishart M, Zhao F, Liao Y L, Zhao Y X, Lv X B, Xie J W. . (2024). Mitigating greenhouse gas emissions from municipal wastewater treatment in China. Environmental Science and Ecotechnology, 20: 100341

[47] UNFCCC(2015). The Paris Agreement. What is the Paris Agreement? Paris: United Nations Framework Convention on Climate Change

[48] Valk L C, Peces M, Singleton C M, Laursen M D, Andersen M H, Mielczarek A T, Nielsen P H. (2022). Exploring the microbial influence on seasonal nitrous oxide concentration in a full-scale wastewater treatment plant using metagenome assembled genomes. Water Research, 219: 118563

[49] VA-teknikSödra (2014). Carbon footprint calculation tool for WWTPs: Now available in english! Stockholm: VA-teknik Södra

[50] Wang J L, Zhang N, Xu S J, Shao Z P, Jiang C C, Yuan H Y, Wang C, Zheng X X, Chi Y Z, Zhang W J. . (2023a). Carbon footprint analysis and comprehensive evaluation of municipal wastewater treatment plants under different typical upgrading and reconstruction modes. Science of The Total Environment, 880: 163335

[51] Wang K, Bastos A, Ciais P, Wang X H, Rödenbeck C, Gentine P, Chevallier F, Humphrey V W, Huntingford C, O'sullivan M. . (2022). Regional and seasonal partitioning of water and temperature controls on global land carbon uptake variability. Nature Communications, 13(1): 3469

[52] Wang Q B, Chen Q W, Chen J. (2017). Optimizing external carbon source addition in domestics wastewater treatment based on online sensoring data and a numerical model. Water Science and Technology, 75(11): 2716–2725

[53] Wang Y Q, Wang H C, Song Y P, Zhou S Q, Li Q N, Liang B, Liu W Z, Zhao Y W, Wang A J. (2023b). Machine learning framework for intelligent aeration control in wastewater treatment plants: automatic feature engineering based on variation sliding layer. Water Research, 246: 120676

[54] Wei L L, Zhu F Y, Li Q Y, Xue C H, Xia X H, Yu H, Zhao Q L, Jiang J Q, Bai S W. (2020). Development, current state and future trends of sludge management in China: based on exploratory data and CO₂-equivaient emissions analysis. Environment International, 144: 106093

[55] Wu H R, Cai C, Yu L, Shang Z X, Zhang Y M, Ni X J, Guo R, Liu J, Peng K M, Huang X F. . (2024a). Technology-driven carbon-neutral pathway analysis for Urban Wastewater Treatment Plants. Journal of Cleaner Production, 475: 143696

[56] Wu Z Q, Zhu Z X, Zhang X N, Zhou L, Zhang K Y, Wu P. (2024b). New insights into carbon capture and re-direction technologies for wastewater resource recovery: a critical review. Journal of Water Process Engineering, 59: 105105

[57] Yan Y J, Xu J C. (2014). Improving winter performance of constructed wetlands for wastewater treatment in northern China: a review. Wetlands, 34(2): 243–253

[58] Yang M D, Pan H Y, Ma X H, Zhang Y Y, Lyu Y F, Zhang X H, Shui W, Yang Z S. (2024). Energy self-sufficiency and carbon neutrality potential of Chinese urban wastewater treatment. Journal of Cleaner Production, 475: 143657

[59] Yuan Q, Li M L, Wang T J, Lou Y Q, Chen S, Jia Z, Wells G, Sun Y X, Wang K J. (2023). Integrated PN/A and EBPR process for real low C/N mainstream municipal wastewater treatment. Chinese Journal of Environmental Engineering, 17(8): 2458–2467

[60] Zhang L J, Hu Y C, Li P, Wei R K, Pang H T, De Kreuk M, Qu S, Lam K L, Van Der Meer W, Liu G. (2024). Maximizing eco-environmental gains: exploring underground wastewater treatment plants in Beijing for sustainable urban water manage-ment. Resources Conservation and Recycling, 207: 107698

[61] ZhangQ HYangW NNgoH HGuoW SJinP KDzakpasuMYangS JWangQWangX CAoD (2016). Current status of urban wastewater treatment plants in China. Environment International, 92–93: 92–93

[62] Zhang X Y, Zhong J T, Zhang X L, Zhang D, Miao C H, Wang D Y, Guo L F. (2025a). China can achieve carbon neutrality in line with the Paris Agreement’s 2 °C target: navigating global emissions scenarios, warming levels, and extreme event projections. Engineering, 44: 207–214

[63] Zhang Y X, Huo J Z, Zheng X J. (2021). Wastewater: China’s next water source. Science, 374(6573): 1332

[64] Zhang Z T, Qi F, Liu Y, Asif M B, Ikhlaq A, Wang Z B, Chen C C, Li C, Chang J, Li Q. . (2025b). Comprehensive assessment, intelligent prediction, and precise mitigation strategies for greenhouse gas emissions in full-scale wastewater treatment plants. Environmental Research, 270: 121052

[65] Zhao Y X, Yang Z F, Niu J J, Du Z H, Federica C, Zhu Z, Yang K C, Li Y, Zhao B F, Pedersen T H. . (2023). Systematical analysis of sludge treatment and disposal technologies for carbon footprint reduction. Journal of Environmental Sciences, 128: 224–249

[66] Zhou X, Yang J X, Zhao X Y, Dong Q Y, Wang X H, Wei L L, Yang S S, Sun H H, Ren N Q, Bai S W. (2023). Towards the carbon neutrality of sludge treatment and disposal in China: a nationwide analysis based on life cycle assessment and scenario discovery. Environment International, 174: 107927

[67] Zou L X, Li H B, Wang S, Zheng K K, Wang Y, Du G C, Li J. (2019). Characteristic and correlation analysis of influent and energy consumption of wastewater treatment plants in Taihu Basin. Frontiers of Environmental Science & Engineering, 13(6): 83

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