Synergistic energy recovery and removal of organics and ammonium from moderate-strength wastewater through an MEC–flue gas–anammox system

Abstract

The treatment of wastewater characterized by high levels of NH₄⁺-N and a moderate organic strength with a low ratio of chemical oxygen demand (COD) to total nitrogen, poses significant challenges to conventional biological processes. In this study, an energy-harvesting microbial electrolysis cell (MEC)–flue gas–anaerobic ammonium oxidation (anammox) system was proposed to treat manure-free piggery wastewater (707 ± 8 mg/L COD and 321 ± 3 mg/L NH₄⁺-N). The MEC first effectively removed wastewater organics and recovered chemical energy in the form of H₂ (with trace CH₄ production). Flue gas-derived nitrogen oxides were subsequently absorbed by MEC effluent, providing a sustainable nitrite source for the anammox process. The residual NO₃^–-N generated from anammox metabolism and flue gas absorption could be further removed through hydrogenotrophic denitrification using in situ MEC-derived H₂. The integrated system eliminates the need for energy-intensive aeration (required in aerobic processes) while also addressing the inefficiency of anaerobic treatment in handling moderate-strength wastewater. The system demonstrated an outstanding performance, with effluent concentrations of COD < 40 mg/L, NH₄⁺-N < 0.8 mg/L, NO₂^–-N < 0.5 mg/L, and NO₃^–-N < 0.8 mg/L. Moreover, the MEC enabled the continuous production of H₂ (0.50–0.91 m³/(m³·d)) and CH₄ (0.01–0.14 m³/(m³·d)) with an energy recovery efficiency of ~249% (the ratio of the energy content of the produced H₂ and CH₄ to the input electrical energy). This study provides an energy-effective strategy for the highly efficient treatment of moderate-strength wastewater.

Graphical abstract

Keywords

Microbial electrolysis cell (MEC) / Flue gas / Anammox / Biological nitrogen removal / Energy recovery

Highlight

	● An MEC–flue gas–anammox system was developed for low C/N ratio wastewater treatment.
	● MEC achieved 85% COD removal with simultaneous H2 energy recovery.
	● Flue gas absorption provided a stable nitrite source for anammox to remove ammonium.
	● MEC-derived H2 was used for hydrogenotrophic denitrification for nitrate removal.
	● The integrated system achieved 95% COD removal and > 99% nitrogen removal.

References

[1] APHA (2017). Standard Methods for the Examination of Water and Wastewater. 23rd ed. Washington: American Public Health Association

[2] Bardi M J , Müller F , Polag D , Habtu N G , Koch K . (2025). Threshold and recovery of anaerobic digestion under high ammonia stress: influence of COD/NH₄⁺ ratio and CO₂ enrichment. Bioresource Technology, 434: 132832

[3] Behera S , Das S . (2023). Potential and prospects of Actinobacteria in the bioremediation of environmental pollutants: cellular mecha-nisms and genetic regulations. Microbiological Research, 273: 127399

[4] Bovio-Winkler P , Guerrero L D , Erijman L , Oyarzúa P , Suárez-Ojeda M E , Cabezas A , Etchebehere C . (2023). Genome-centric metagenomic insights into the role of Chloroflexi in anammox, activated sludge and methanogenic reactors. BMC Microbiology, 23(1): 45

[5] Breyer C , Khalili S , Bogdanov D , Ram M , Oyewo A S , Aghahosseini A , Gulagi A , Solomon A , Keiner D , Lopez G . (2022). On the history and future of 100% renewable energy systems research. IEEE Access, 10: 78176–78218

[6] Cao S B , Du R , Zhou Y . (2021). Coupling anammox with heterotrophic denitrification for enhanced nitrogen removal: a review. Critical Reviews in Environmental Science and Technology, 51(19): 2260–2293

[7] Cao S B , Oehmen A , Zhou Y . (2019). Denitrifiers in mainstream anammox processes: competitors or supporters?. Environmental Science & Technology, 53(19): 11063–11065

[8] Chen D , Yang K , Wei L , Wang H Y . (2016). Microbial community and metabolism activity in a bioelectrochemical denitrification system under long-term presence of p-nitrophenol. Bioresource Technology, 218: 189–195

[9] Chen H H , Liu S T , Yang F L , Xue Y , Wang T . (2009). The development of simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process in a single reactor for nitrogen removal. Bioresource Technology, 100(4): 1548–1554

[10] Cheng S A , Logan B E . (2007). Sustainable and efficient biohydrogen production via electrohydrogenesis. Proceedings of the National Academy of Sciences of the United States of America, 104(47): 18871–18873

[11] Cheng S A , Logan B E . (2011). High hydrogen production rate of microbial electrolysis cell (MEC) with reduced electrode spacing. Bioresource Technology, 102(3): 3571–3574

[12] Cheng Y F , Zhang Z Z , Ma W J , Li G F , Huang B C , Fan N S , Jin R C . (2022). Response of the mainstream anammox process to the biodegradable carbon sources in the granule-based systems: the difference in self-stratification of the microbial community. Science of the Total Environment, 851(Pt 1): 158191

[13] Cotterill S E , Dolfing J , Jones C , Curtis T P , Heidrich E S . (2017). Low temperature domestic wastewater treatment in a microbial electrolysis cell with 1 m² anodes: towards system scale-up. Fuel Cells, 17(5): 584–592

[14] De Cocker P , Bessiere Y , Hernandez-Raquet G , Dubos S , Mozo I , Gaval G , Caligaris M , Barillon B , Vlaeminck S E , Sperandio M . (2018). Enrichment and adaptation yield high anammox conversion rates under low temperatures. Bioresource Technology, 250: 505–512

[15] Di Capua F , de Sario S , Ferraro A , Petrella A , Race M , Pirozzi F , Fratino U , Spasiano D . (2022). Phosphorous removal and recovery from urban wastewater: current practices and new directions. Science of the Total Environment, 823: 153750

[16] Di Capua F , Pirozzi F , Lens P N L , Esposito G . (2019). Electron donors for autotrophic denitrification. Chemical Engineering Journal, 362: 922–937

[17] Dou Y Y , Du Y Q , Xu Y F , Li Y , Wu X Q , Wang D Q . (2025). Phosphorus recovery from sewage sludge: progress, challenges, policies, and future directions. Chemical Engineering Journal, 520: 165735

[18] Feng Y , Zhao Y P , Guo Y Z , Liu S T . (2018). Microbial transcript and metabolome analysis uncover discrepant metabolic pathways in autotrophic and mixotrophic anammox consortia. Water Research, 128: 402–411

[19] Ferrera I , Sánchez O . (2016). Insights into microbial diversity in wastewater treatment systems: How far have we come?. Biotechnology Advances, 34(5): 790–802

[20] Fu J W , Hou Z Y , Zhao H X , Li Q , Chen R , Li Y Y . (2024). Enhanced nitrogen removal from low strength anaerobic membrane bioreactor (AnMBR) permeate using complete nitrification and partial denitrification-anammox processes. Frontiers of Environmental Science & Engineering, 18(12): 155

[21] Furukawa K , Lieu P K , Tokitoh H , Fujii T . (2006). Development of single-stage nitrogen removal using anammox and partial nitritation (SNAP) and its treatment performances. Water Science & Technology, 53(6): 83–90

[22] Guerrero-Sodric O , Baeza J A , Guisasola A . (2025). Scaling up microbial electrolysis cells (MECs) for hydrogen production: design, construction and operation of a 1m³ pilot plant in an urban wastewater treatment plant. Chemical Engineering Journal, 523: 168035

[23] Guo Y , Luo Z B , Shen J H , Li Y Y . (2022). The main anammox-based processes, the involved microbes and the novel process concept from the application perspective. Front Environ Sci Eng, 16(7): 84

[24] Hamza R A , Iorhemen O T , Tay J H . (2016). Advances in biological systems for the treatment of high-strength wastewater. Journal of Water Process Engineering, 10: 128–142

[25] He Q L , Song Q , Zhang S L , Zhang W , Wang H Y . (2018). Simultaneous nitrification, denitrification and phosphorus removal in an aerobic granular sequencing batch reactor with mixed carbon sources: reactor performance, extracellular polymeric substances and microbial successions. Chemical Engineering Journal, 331: 841–849

[26] Heidrich E S , Edwards S R , Dolfing J , Cotterill S E , Curtis T P . (2014). Performance of a pilot scale microbial electrolysis cell fed on domestic wastewater at ambient temperatures for a 12 month period. Bioresource Technology, 173: 87–95

[27] Hu Z T , Liu T , Wang Z Y , Meng J , Zheng M . (2023). Toward energy neutrality: novel wastewater treatment incorporating acidophilic ammonia oxidation. Environmental Science & Technology, 57(11): 4522–4532

[28] Huang J M , Wang C R , Zhang S J , Han X Y , Feng R F , Li Y , Huang X Y , Wang J B . (2023). Optimizing nitrogenous organic wastewater treatment through integration of organic capture, anaerobic digestion, and anammox technologies: sustainability and challenges. Environmental Science and Pollution Research, 30(31): 76372–76386

[29] Jenni S , Vlaeminck S E , Morgenroth E , Udert K M . (2014). Successful application of nitritation/anammox to wastewater with elevated organic carbon to ammonia ratios. Water Research, 49: 316–326

[30] Jetten M S M , Strous M , Van De Pas-Schoonen K T , Schalk J , Van Dongen U G J M , Van De Graaf A A , Logemann S , Muyzer G , Van Loosdrecht M C M , Kuenen J G . (1998). The anaerobic oxidation of ammonium. FEMS Microbiology Reviews, 22(5): 421–437

[31] Jin R C , Yang G F , Yu J J , Zheng P . (2012). The inhibition of the anammox process: a review. Chemical Engineering Journal, 197: 67–79

[32] Kadier A , Simayi Y , Abdeshahian P , Azman N F , Chandrasekhar K , Kalil M S . (2016). A comprehensive review of microbial electrolysis cells (MEC) reactor designs and configurations for sustainable hydrogen gas production. Alexandria Engineering Journal, 55(1): 427–443

[33] Kalyuzhnyi S , Gladchenko M , Mulder A , Versprille B . (2006). DEAMOX—new biological nitrogen removal process based on anaerobic ammonia oxidation coupled to sulphide-driven conversion of nitrate into nitrite. Water Research, 40(19): 3637–3645

[34] Kartal B , Kuenen J G , Van Loosdrecht M C M . (2010a). Sewage treatment with anammox. Science, 328(5979): 702–703

[35] Kartal B , Tan N C , Van de Biezen E , Kampschreur M J , Van Loosdrecht M C , Jetten M S . (2010b). Effect of nitric oxide on anammox bacteria. Applied and Environmental Microbiology, 76(18): 6304–6306

[36] Katuri K P , Ali M , Saikaly P E . (2019). The role of microbial electrolysis cell in urban wastewater treatment: integration options, challenges, and prospects. Current Opinion in Biotechnology, 57: 101–110

[37] Kim J R , Zuo Y , Regan J M , Logan B E . (2008). Analysis of ammonia loss mechanisms in microbial fuel cells treating animal wastewater. Biotechnology and Bioengineering, 99(5): 1120–1127

[38] Kim K Y , Yang W L , Logan B E . (2018). Regenerable nickel-functionalized activated carbon cathodes enhanced by metal adsorption to improve hydrogen production in microbial electrolysis cells. Environmental Science & Technology, 52(12): 7131–7137

[39] Kouba V , Bachmannová C , Podzimek T , Lipovová P , Van Loosdrecht M C M . (2022). Physiology of anammox adaptation to low temperatures and promising biomarkers: a review. Bioresource Technology, 349: 126847

[40] Kuenen J G . (2008). Anammox bacteria: from discovery to application. Nature Reviews Microbiology, 6(4): 320–326

[41] Li G F , Huang B C , Cheng Y F , Ma W J , Li S T , Gong B , Guan Y F , Fan N S , Jin R C . (2020). Determination of the response characteristics of anaerobic ammonium oxidation bioreactor disturbed by temperature change with the spectral fingerprint. Science of the Total Environment, 719: 137513

[42] Liu G L , Yates M D , Cheng S A , Call D F , Sun D , Logan B E . (2011). Examination of microbial fuel cell start-up times with domestic wastewater and additional amendments. Bioresource Technology, 102(15): 7301–7306

[43] Liu S L , Daigger G T , Liu B T , Zhao W Y , Liu J . (2020). Enhanced performance of simultaneous carbon, nitrogen and phosphorus removal from municipal wastewater in an anaerobic-aerobic-anoxic sequencing batch reactor (AOA-SBR) system by alternating the cycle times. Bioresource Technology, 301: 122750

[44] Liu Y , An T Y , Xie J W , Tang K , Wu P , Liu W R , Sun F Q , Gayflor S F , Chen C J . (2024). The influencing mechanisms and optimization strategies of organics on anammox process: a critical review. Chemical Engineering Journal, 493: 152743

[45] Logan B E , Call D , Cheng S A , Hamelers H V M , Sleutels T H J A , Jeremiasse A W , Rozendal R A . (2008). Microbial electrolysis cells for high yield hydrogen gas production from organic matter. Environmental Science & Technology, 42(23): 8630–8640

[46] Lotti T , Kleerebezem R , Van Erp Taalman Kip C , Hendrickx T L G , Kruit J , Hoekstra M , Van Loosdrecht M C M . (2014). Anammox growth on pretreated municipal wastewater. Environmental Science & Technology, 48(14): 7874–7880

[47] Lotti T , Kleerebezem R , Van Loosdrecht M C M . (2015). Effect of temperature change on anammox activity. Biotechnology and Bioengineering, 112(1): 98–103

[48] Lovley D R , Ueki T , Zhang T , Malvankar N S , Shrestha P M , Flanagan K A , Aklujkar M , Butler J E , Giloteaux L , Rotaru A E . et al. (2011). Geobacter: the microbe electric’s physiology, ecology, and practical applications. Advances in Microbial Physiology, 59: 1–100

[49] 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

[50] Lu L , Huang Z , Rau G H , Ren Z J . (2015). Microbial electrolytic carbon capture for carbon negative and energy positive wastewater treatment. Environmental Science & Technology, 49(13): 8193–8201

[51] Lu L , Ren Z J . (2016). Microbial electrolysis cells for waste biorefinery: a state of the art review. Bioresource Technology, 215: 254–264

[52] Lu L , Xing D F , Ren N Q , Logan B E . (2012). Syntrophic interactions drive the hydrogen production from glucose at low temperature in microbial electrolysis cells. Bioresource Technology, 124: 68–76

[53] Marchetti A , Cerrillo Moreno M , Lauri R , Zeppilli M . (). Optimizing hydrogen production through efficient organic matter oxidation performed by microbial electrolysis cells.. Processes,, 13(4): 1231

[54] Pynaert K , Smets B F , Beheydt D , Verstraete W . (2004). Start-up of autotrophic nitrogen removal reactors via sequential biocatalyst addition. Environmental Science & Technology, 38(4): 1228–1235

[55] Qiu S J , Liu J J , Zhang L , Zhang Q , Peng Y Z . (2021). Sludge fermentation liquid addition attained advanced nitrogen removal in low C/N ratio municipal wastewater through short-cut nitrification-denitrification and partial anammox. Frontiers of Environmental Science & Engineering, 15(2): 26

[56] Rader G K , Logan B E . (2010). Multi-electrode continuous flow microbial electrolysis cell for biogas production from acetate. International Journal of Hydrogen Energy, 35(17): 8848–8854

[57] Rittmann B E, McCarty P L 2020 Environmental Biotechnology: Principles and Applications. New York: McGraw-Hill

[58] Schmidt I , Hermelink C , Van De Pas-Schoonen K , Strous M , Op Den Camp H J , Kuenen J G , Jetten M S M . (2002). Anaerobic ammonia oxidation in the presence of nitrogen oxides (NO_x) by two different lithotrophs. Applied and Environmental Microbiology, 68(11): 5351–5357

[59] Shao M F , Zhang T , Fang H H P . (2010). Sulfur-driven autotrophic denitrification: diversity, biochemistry, and engineering applications. Applied Microbiology and Biotechnology, 88(5): 1027–1042

[60] Sliekers A O , Derwort N , Gomez J L C , Strous M , Kuenen J G , Jetten M S M . (2002). Completely autotrophic nitrogen removal over nitrite in one single reactor. Water Research, 36(10): 2475–2482

[61] Strous M , Kuenen J G , Jetten M S M . (1999). Key physiology of anaerobic ammonium oxidation. Applied and Environmental Microbiology, 65(7): 3248–3250

[62] Valenzuela-Heredia D , Panatt C , Belmonte M , Franchi O , Crutchik D , Dumais J , Vázquez-Padín J R , Lesty Y , Pedrouso A , Val Del Río Á , Mosquera-Corral A . et al. (2022). Performance of a two-stage partial nitritation-anammox system treating the supernatant of a sludge anaerobic digester pretreated by a thermal hydrolysis process. Chemical Engineering Journal, 429: 131301

[63] Van Dongen L G J M, Jetten M S M, Van Loosdrecht M C M 2001 The Combined SHARON/Anammox Process: A Sustainable Method for N-Removal from Sludge Water. London: IWA Publishing

[64] Victoria M , Haegel N , Peters I M , Sinton R , Jäger-Waldau A , Del Canizo C , Breyer C , Stocks M , Blakers A , Kaizuka I . et al. (2021). Solar photovoltaics is ready to power a sustainable future. Joule, 5(5): 1041–1056

[65] Wang L S , Gu W C , Liu Y C , Liang P , Zhang X Y , Huang X . (2022a). Challenges, solutions and prospects of mainstream anammox-based process for municipal wastewater treatment. Science of the Total Environment, 820: 153351

[66] Wang S K , Wang Y J , Li P , Wang L , Su Q X , Zuo J E . (2022b). Development and characterizations of hydrogenotrophic denitrification granular process: nitrogen removal capacity and adaptability. Bioresource Technology, 363: 127973

[67] Wang X J , Xu X C , Liu S T , Zhang Y , Zhao C Q , Yang F L . (2016). Combination of complex adsorption and anammox for nitric oxide removal. Journal of Hazardous Materials, 312: 175–183

[68] Wang X J , Xu X C , Zou Y , Yang F L , Zhang Y . (2018). Nitric oxide removal from flue gas with ammonium using anammox DeNO_x process and its application in municipal sewage treatment. Bioresource Technology, 265: 170–179

[69] Wang Y N , Ren S , Wang P , Wang B , Hu K Y , Li J , Wang Y , Li Z X , Li S M , Li W . et al. (2023). Autotrophic denitrification using Fe(II) as an electron donor: a novel prospective denitrification process.. Science of the Total Environment, 858(Pt 1): 159721

[70] Wett B . (2007). Development and implementation of a robust deammonification process. Water Science & Technology, 56(7): 81–88

[71] Whitman W B (2015). Bergey’s Manual of Systematics of Archaea and Bacteria. Hoboken: John Wiley Sons, Inc.

[72] Xiao R , Ni B J , Liu S T , Lu H J . (2021). Impacts of organics on the microbial ecology of wastewater anammox processes: recent advances and meta-analysis. Water Research, 191: 116817

[73] Yenigün O , Demirel B . (2013). Ammonia inhibition in anaerobic digestion: a review. Process Biochemistry, 48(5−6): 901–911

[74] Zhang D J , Ren L L , Yao Z B , Wan X Y , Lu P L , Zhang X T . (2017). Removal of nitrogen oxide based on anammox through Fe(II) EDTA absorption. Energy & Fuels, 31(7): 7247–7255

[75] Zhen J Y , Zhao Y Y , Yu X F , Guo W S , Qiao Z M , Ismail S , Ni S Q . (2022). Feasibility of partial nitrification combined with nitrite-denitrification phosphorus removal and simultaneous nitrification–endogenous denitrification for synchronous chemical oxygen demand, nitrogen, and phosphorus removal. ACS ES&T Water, 2(6): 1119–1131

[76] Zhou J J , Deng Z X , Sun C D , Ma G Y , Zhang X Z , Zhang T , Zhou X F , Zhang Y L , Hu Y , Rong C . et al. (2025). Anaerobic digestion enhanced by biochar additives for effective treatment of industrial wastewater containing refractory organic matters: a comprehensive review. Frontiers of Environmental Science & Engineering, 19(8): 106

[77] Zhou J M , Ding L , Shi M , Lindeboom R E F , Cui C Z . (2022). The key factor in high pressure hydrogenotrophic denitrification: hydrogen partial pressure. Journal of Water Process Engineering, 49: 103195

[78] Zhu W L , Xiao R , Xu M , Chai W B , Liu W L , Jin Z Y , Ikumi D , Lu H J . (2024). Unraveling the role of formate in improving nitrogen removal via coupled partial denitrification-anammox. Frontiers of Environmental Science & Engineering, 18(9): 112

RIGHTS & PERMISSIONS

Higher Education Press 2026