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Photocatalytic Fe3O4@CDs Drives Nitrite-Independent extracellular respiration of anammox via efficient bidirectional electron transfer.

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Title: Photocatalytic Fe3O4@CDs Drives Nitrite-Independent extracellular respiration of anammox via efficient bidirectional electron transfer.
Authors: Song Z; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China., Yang J; China Coal Technology & Engineering Group Co., Ltd., Tokyo 100-0011, Japan., Zhang L; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China. Electronic address: zhangli19821115a@163.com., Peng Y; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China.
Source: Bioresource technology [Bioresour Technol] 2026 Jul; Vol. 451, pp. 134489. Date of Electronic Publication: 2026 Mar 23.
Publication Type: Journal Article
Language: English
Journal Info: Publisher: Elsevier Applied Science Country of Publication: England NLM ID: 9889523 Publication Model: Print-Electronic Cited Medium: Internet ISSN: 1873-2976 (Electronic) Linking ISSN: 09608524 NLM ISO Abbreviation: Bioresour Technol Subsets: MEDLINE
Imprint Name(s): Original Publication: Barking, Essex, England : New York, N.Y. : Elsevier Applied Science ; Elsevier Science Pub. Co., 1991-
MeSH Terms: Nitrites*/metabolism , Sulfides*/chemistry , Cadmium Compounds*/chemistry , Ammonium Compounds*/metabolism , Extracellular Space*/metabolism , Extracellular Space*/drug effects , Anaerobic Ammonia Oxidation*, Bacteria/metabolism ; Nitrogen/isolation & purification ; Nitrogen/metabolism ; Electron Transport ; Catalysis ; Oxidation-Reduction ; Photochemical Processes
Abstract: Anaerobic ammonium oxidation (Anammox) process relying on extracellular electron transfer (EET) overcomes nitrite scarcity in practical wastewater, but inefficient EET rate constrains nitrogen removal. Herein, Fe3O4 with carbon dot shell (Fe3O4@CDs) was self-assembled with anammox bacterial as a photocatalytic hybrid. Building on bacteria inward uptake of photogenerated electrons from CDs and outward transfer of respiratory electrons to Fe3O4, a bidirectional electron pathway was established firstly. This novel route achieved efficient nitrite-independent Anammox, enabling direct and rapid removal of 80 mg/L NH4+-N. To elucidate efficient nitrogen removal essence, metagenomics was employed to reveal photogenerated electrons fate and their mediated nitrogen metabolism mechanism. Results showed that, following assembly via -PO bonds, bacteria internalized CDs photogenerated electrons (0.82 µA/cm) into menaquinone (MQ) pool. This influx activated energy-generation route constructed by bc1 and Rnf enzymes, increasing intracellular ATP level by 3.36---6.51-fold. Consequently, energy drove electrons pumping from MQ pool to cytochrome c, followed by transport outward via CDs, pili and flavin, amplifying electrons eflux by 1.77-fold. Such efflux generated MQ pool electron vacancies, which were efficiently replenished by electrons from hydrazine synthase- and hydrazine dehydrogenase-catalyzed NH4+-N oxidation to N2 without nitrite. Underpinned by the photogenerated electron-driven EET process, Anammox bacteria was enriched from 25.26% to 48.02%, thus sustaining a total nitrogen removal efficiency of > 97% for over 80 days-far exceeding the performance of existing system. This technology provides an efficient and sustainable theoretical framework for the application of anammox in practical wastewater treatment.
(Copyright © 2026. Published by Elsevier Ltd.)
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Contributed Indexing: Keywords: Anaerobic ammonium oxidation; Biohybrid; Extracellular electron transfer; Nitrite-free; Nitrogen removal
Substance Nomenclature: 0 (Nitrites)
0 (Sulfides)
0 (Cadmium Compounds)
057EZR4Z7Q (cadmium sulfide)
N762921K75 (Nitrogen)
0 (Ammonium Compounds)
Entry Date(s): Date Created: 20260325 Date Completed: 20260713 Latest Revision: 20260713
Update Code: 20260714
DOI: 10.1016/j.biortech.2026.134489
PMID: 41881128
Database: MEDLINE
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  Data: Photocatalytic Fe<subscript>3</subscript>O<subscript>4</subscript>@CDs Drives Nitrite-Independent extracellular respiration of anammox via efficient bidirectional electron transfer.
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  Data: <searchLink fieldCode="AU" term="%22Song+Z%22">Song Z</searchLink>; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China.<br /><searchLink fieldCode="AU" term="%22Yang+J%22">Yang J</searchLink>; China Coal Technology & Engineering Group Co., Ltd., Tokyo 100-0011, Japan.<br /><searchLink fieldCode="AU" term="%22Zhang+L%22">Zhang L</searchLink>; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China. Electronic address: zhangli19821115a@163.com.<br /><searchLink fieldCode="AU" term="%22Peng+Y%22">Peng Y</searchLink>; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China.
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  Data: <searchLink fieldCode="JN" term="%229889523%22">Bioresource technology</searchLink> [Bioresour Technol] 2026 Jul; Vol. 451, pp. 134489. <i>Date of Electronic Publication: </i>2026 Mar 23.
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  Data: <i>Publisher: </i><searchLink fieldCode="PB" term="%22Elsevier+Applied+Science%22">Elsevier Applied Science </searchLink><i>Country of Publication: </i>England <i>NLM ID: </i>9889523 <i>Publication Model: </i>Print-Electronic <i>Cited Medium: </i>Internet <i>ISSN: </i>1873-2976 (Electronic) <i>Linking ISSN: </i><searchLink fieldCode="IS" term="%2209608524%22">09608524 </searchLink><i>NLM ISO Abbreviation: </i>Bioresour Technol <i>Subsets: </i>MEDLINE
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  Data: <i>Original Publication</i>: Barking, Essex, England : New York, N.Y. : Elsevier Applied Science ; Elsevier Science Pub. Co., 1991-
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  Group: Su
  Data: <searchLink fieldCode="MM" term="%22Nitrites%22">Nitrites*</searchLink>/<searchLink fieldCode="MM" term="%22Nitrites+metabolism%22">metabolism</searchLink> <br /><searchLink fieldCode="MM" term="%22Sulfides%22">Sulfides*</searchLink>/<searchLink fieldCode="MM" term="%22Sulfides+chemistry%22">chemistry</searchLink> <br /><searchLink fieldCode="MM" term="%22Cadmium+Compounds%22">Cadmium Compounds*</searchLink>/<searchLink fieldCode="MM" term="%22Cadmium+Compounds+chemistry%22">chemistry</searchLink> <br /><searchLink fieldCode="MM" term="%22Ammonium+Compounds%22">Ammonium Compounds*</searchLink>/<searchLink fieldCode="MM" term="%22Ammonium+Compounds+metabolism%22">metabolism</searchLink> <br /><searchLink fieldCode="MM" term="%22Extracellular+Space%22">Extracellular Space*</searchLink>/<searchLink fieldCode="MM" term="%22Extracellular+Space+metabolism%22">metabolism</searchLink> <br /><searchLink fieldCode="MM" term="%22Extracellular+Space%22">Extracellular Space*</searchLink>/<searchLink fieldCode="MM" term="%22Extracellular+Space+drug+effects%22">drug effects</searchLink> <br /><searchLink fieldCode="MM" term="%22Anaerobic+Ammonia+Oxidation%22">Anaerobic Ammonia Oxidation*</searchLink><br /><searchLink fieldCode="MH" term="%22Bacteria%22">Bacteria</searchLink>/<searchLink fieldCode="MH" term="%22Bacteria+metabolism%22">metabolism</searchLink> ; <searchLink fieldCode="MH" term="%22Nitrogen%22">Nitrogen</searchLink>/<searchLink fieldCode="MH" term="%22Nitrogen+isolation+%26+purification%22">isolation & purification</searchLink> ; <searchLink fieldCode="MH" term="%22Nitrogen%22">Nitrogen</searchLink>/<searchLink fieldCode="MH" term="%22Nitrogen+metabolism%22">metabolism</searchLink> ; <searchLink fieldCode="MH" term="%22Electron+Transport%22">Electron Transport</searchLink> ; <searchLink fieldCode="MH" term="%22Catalysis%22">Catalysis</searchLink> ; <searchLink fieldCode="MH" term="%22Oxidation-Reduction%22">Oxidation-Reduction</searchLink> ; <searchLink fieldCode="MH" term="%22Photochemical+Processes%22">Photochemical Processes</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Anaerobic ammonium oxidation (Anammox) process relying on extracellular electron transfer (EET) overcomes nitrite scarcity in practical wastewater, but inefficient EET rate constrains nitrogen removal. Herein, Fe<subscript>3</subscript>O<subscript>4</subscript> with carbon dot shell (Fe<subscript>3</subscript>O<subscript>4</subscript>@CDs) was self-assembled with anammox bacterial as a photocatalytic hybrid. Building on bacteria inward uptake of photogenerated electrons from CDs and outward transfer of respiratory electrons to Fe<subscript>3</subscript>O<subscript>4</subscript>, a bidirectional electron pathway was established firstly. This novel route achieved efficient nitrite-independent Anammox, enabling direct and rapid removal of 80 mg/L NH<subscript>4</subscript><superscript>+</superscript>-N. To elucidate efficient nitrogen removal essence, metagenomics was employed to reveal photogenerated electrons fate and their mediated nitrogen metabolism mechanism. Results showed that, following assembly via -PO bonds, bacteria internalized CDs photogenerated electrons (0.82 µA/cm) into menaquinone (MQ) pool. This influx activated energy-generation route constructed by bc1 and Rnf enzymes, increasing intracellular ATP level by 3.36---6.51-fold. Consequently, energy drove electrons pumping from MQ pool to cytochrome c, followed by transport outward via CDs, pili and flavin, amplifying electrons eflux by 1.77-fold. Such efflux generated MQ pool electron vacancies, which were efficiently replenished by electrons from hydrazine synthase- and hydrazine dehydrogenase-catalyzed NH<subscript>4</subscript><superscript>+</superscript>-N oxidation to N<subscript>2</subscript> without nitrite. Underpinned by the photogenerated electron-driven EET process, Anammox bacteria was enriched from 25.26% to 48.02%, thus sustaining a total nitrogen removal efficiency of > 97% for over 80 days-far exceeding the performance of existing system. This technology provides an efficient and sustainable theoretical framework for the application of anammox in practical wastewater treatment.<br /> (Copyright © 2026. Published by Elsevier Ltd.)
– Name: Abstract
  Label: Competing Interests
  Group: Ab
  Data: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
– Name: SubjectMinor
  Label: Contributed Indexing
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  Data: <i>Keywords: </i>Anaerobic ammonium oxidation; Biohybrid; Extracellular electron transfer; Nitrite-free; Nitrogen removal
– Name: NumberCAS
  Label: Substance Nomenclature
  Group: ID
  Data: 0 (Nitrites)<br />0 (Sulfides)<br />0 (Cadmium Compounds)<br />057EZR4Z7Q (cadmium sulfide)<br />N762921K75 (Nitrogen)<br />0 (Ammonium Compounds)
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  Data: <i>Date Created: </i>20260325 <i>Date Completed: </i>20260713 <i>Latest Revision: </i>20260713
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  Data: 10.1016/j.biortech.2026.134489
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  Data: 41881128
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        Value: 10.1016/j.biortech.2026.134489
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      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        StartPage: 134489
    Subjects:
      – SubjectFull: Bacteria metabolism
        Type: general
      – SubjectFull: Nitrogen isolation & purification
        Type: general
      – SubjectFull: Nitrogen metabolism
        Type: general
      – SubjectFull: Electron Transport
        Type: general
      – SubjectFull: Catalysis
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      – SubjectFull: Photochemical Processes
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      – SubjectFull: Nitrites metabolism
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      – SubjectFull: Sulfides chemistry
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      – SubjectFull: Cadmium Compounds chemistry
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      – SubjectFull: Ammonium Compounds metabolism
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      – SubjectFull: Extracellular Space metabolism
        Type: general
      – SubjectFull: Extracellular Space drug effects
        Type: general
      – SubjectFull: Anaerobic Ammonia Oxidation
        Type: general
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      – TitleFull: Photocatalytic Fe3O4@CDs Drives Nitrite-Independent extracellular respiration of anammox via efficient bidirectional electron transfer.
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              Text: 2026 Jul
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