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Abstract
Nitrous oxide (N(2)O), a potent greenhouse gas, can be emitted during wastewater treatment,
significantly contributing to the greenhouse gas footprint. Measurements at lab-scale
and full-scale wastewater treatment plants (WWTPs) have demonstrated that N(2)O can
be emitted in substantial amounts during nitrogen removal in WWTPs, however, a large
variation in reported emission values exists. Analysis of literature data enabled
the identification of the most important operational parameters leading to N(2)O emission
in WWTPs: (i) low dissolved oxygen concentration in the nitrification and denitrification
stages, (ii) increased nitrite concentrations in both nitrification and denitrification
stages, and (iii) low COD/N ratio in the denitrification stage. From the literature
it remains unclear whether nitrifying or denitrifying microorganisms are the main
source of N(2)O emissions. Operational strategies to prevent N(2)O emission from WWTPs
are discussed and areas in which further research is urgently required are identified.