Effect of nitrite on the N2O and NO production on the nitrification of low-strength ammonium wastewater

• Nitrite effect on N2O–NO emission in a low strength nitrifying system was studied.
• Nitrite presence in the reactor increases N2O and NO emissions.
• High nitrite concentrations affect more NO emissions than N2O emissions.
• The intermediate NO cannot be neglected during autotrophic denitrification.
• High nitrite concentrations inhibit the ammonium oxidising activity.

The effect of nitrite on N2O and NO emission was assessed in a nitrifying lab-scale reactor fed with low strength ammonium wastewater. The effect of nitrite pulse additions (5–50 mg NO2−-N L−1) and of step-wisely increasing nitrite concentrations (0–150 mg NO2−-N L−1) was studied. For the pulse addition experiments, N2O and NO emissions increased upon pulse addition of nitrite, decreasing to the original concentration once nitrite was consumed. The highest peak emissions were detected at nitrite concentrations of 50 mg NO2−-N L−1. For the step-wisely increasing nitrite tests, N2O-N emission per NH4+-N converted increased linearly from 0.16% to 1.5%. NO emissions were substantially affected at nitrite concentrations higher than 50 mg NO2−-N L−1, reaching 3.8% NO-N per NH4+-N converted at 150 mg NO2−-N L−1. The results provide one of the first evidences of the combined effect of nitrite on N2O and NO emissions, showing a stronger effect on NO emissions at high nitrite concentrations.

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