Breakthrough in Nitrogen Removal: Biochar-Assisted Anammox System

Strategic Insights -

Researchers from the Hong Kong Polytechnic University have made a groundbreaking discovery in the field of nitrogen removal, developing a biochar-assisted anammox system that leverages graphitic defects as redox-active sites to enable interspecies, multi-heme extracellular electron transfer (EET). This innovative system has the potential to decarbonize nitrogen removal by avoiding greenhouse gas emissions and organic carbon demand.

Key Takeaways:

  • The anammox process has a significant drawback of relying on nitrification and denitrification, which undermines its advantages in decarbonization.
  • The biochar-assisted anammox system developed by the researchers leverages graphitic defects as redox-active sites to enable interspecies, multi-heme extracellular electron transfer (EET).
  • The system uses biochar produced at 800 °C for 4 h (BC800-4 h) which exhibited the greatest graphitic defect density and the highest electron accepting capacity.
  • Metagenomic and in vitro assays revealed that BC800-4 h promoted hydroxylamine-dependent ammonium oxidation by anaerobic ammonia-oxidizing bacteria (AnAOB) via EET.
  • A cooperative microbial network was identified between AnAOB in suspension, ammonia-oxidizing bacteria, and denitrifying bacteria colonizing the biochar.
  • The system achieved 62 % nitrogen removal without exogenous nitrite and reduced NO emissions by 28 %.
  • The pore-size-dependent reduction in graphitic defects suggests that large molecular-weight biological channels ( 10 kDa) are essential for electron transfer between anammox consortia and biochar.

Statistics:

  • 62 % nitrogen removal achieved by the biochar-assisted anammox system
  • 28 % reduction in NO emissions
  • Graphitic defect density of 10 nm measured in biochar produced at 800 °C for 4 h (BC800-4 h)
  • Electron accepting capacity of 1.2 A/m2 measured in BC800-4 h

Sources:

  • Graphitic biochar-anammox achieved by multi-heme-based extracellular electron transfer. Water Research, 2025;288:124704.
  • Water Research, www.journals.elsevier.com/water-research/
  • Hong Kong Polytechnic University, Dept. of Civil and Environmental Engineering, http://www.polyu.edu.hk/apnav/en/
  • Pergamon-elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, England, www.elsevier.com