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Triggers for N2O Production

Full-scale plants have utilized real-time measurements of N2O concentration and emission as an indication of biological nitrification failure owing to toxic shock loads or insufficient aeration.

What Causes N2O Production?

We are still learning about the exact triggers for N2O production from activated sludge. However, the predominant emission of N2O comes from the aerated nitrification, mainly from the metabolism of NH4 by ammonium oxidizing bacteria.

Especially, the lack of sufficient oxygen during the nitrification process has resulted in high levels of N2O production. Due to the simultaneous aeration, the N2O is stripped into the atmosphere. Generally, sudden perturbations of the bioprocesses, such as changes in dissolved oxygen, NH4+ shock loads, or NO2- spikes, also lead to immediate increases in N2O emissions.

Process Parameters that Promote the Formation and Emission of N2O:

  • Low oxygen set point or operation conditions, typically below 0.5 mg/L, during nitrification
  • Low COD/N ratio for denitrification, typically below 3.5-4
  • Shock loading of NH4+, e.g. reject water pulse
  • NO2- accumulation during the nitrification, e.g. due to high NH4+ conversion rate
  • Oxygen availability during denitrification
  • Short sludge age
  • Low temperatures