The effect of SRT on nitrate formation during autotrophic nitrogen removal of anaerobically treated wastewater

Po Heng Lee, Wonji Kwak, Jeaho Bae, Perry L. McCarty

Research output: Journal article publicationJournal articleAcademic researchpeer-review

14 Citations (Scopus)


Autotrophic nitrogen removal, coupling nitritation (ammonium to nitrite) with anaerobic ammonium oxidation (anammox), offers a promising nitrogen-removal alternative, especially for post-treatment of anaerobically-treated wastewater. However, previous reports suggest that less than 90% total nitrogen removal should be expected with this process alone because over 10% of the ammonium removed will be converted to nitrate. This is caused because nitrite conversion to nitrate is required for reduction of carbon dioxide to cell carbon. However, recent research results suggest that more limited nitrate formation of only a few per cent sometimes occurs. It was hypothesized such lower nitrate yields may result from use of long solids retention times (SRT) where net biological yields are low, and providing that the ratio of oxygen added to influent ammonium concentrations is maintained at or below 0.75 mol/mol. Overall reaction equations were developed for each process and combined to evaluate the potential effect of SRT on process stoichiometry. The results support the use of a long SRT to reduce net cell yield, which in turn results in a small percentage conversion to nitrate during ammonium removal and high total nitrogen removals in the range of 90 to 94%.
Original languageEnglish
Pages (from-to)1751-1756
Number of pages6
JournalWater Science and Technology
Issue number8
Publication statusPublished - 29 Nov 2013


  • Anaerobic ammonium oxidation (anammox)
  • Autotrophic nitrogen removal
  • Nitrate formation
  • Solids retention time
  • Stoichiometry

ASJC Scopus subject areas

  • Environmental Engineering
  • Water Science and Technology


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