Dynamics of nitrogen oxides emission from a full-scale sludge liquor treatment plant with nitritation

Biological treatment in wastewater treatment plants (WWTPs) is a source of nitrogen oxides (N₂O, NO and NO₂) emitted to the atmosphere. Aerobic ammonia-oxidising bacteria (AOB) have been suggested to be the main source of these emissions. In a full-scale sludge liquor treatment plant at Sjölunda WWTP, it was shown that significant emissions of N₂O, NO and NO₂ do occur. The plant is operated with nitritation alone, which gives an environment enriched in aerobic AOB. During normal operation, emissions of N₂O, NO and NO₂ were found to be 3.8%, 0.06% and 0.01% of the ammonium nitrogen load. The N₂O emissions were larger than the recommended estimated figure of the Intergovernmental Panel on Climate Change (IPCC) for a complete wastewater treatment plant. The N₂O emissions correlated positively with the length of the previous anoxic period, i.e., settling and decantation, and with the ammonium oxidation rate. The NO and NO₂ emission profiles were similar and dependent on ammonium oxidation and DO level, but the NO₂ concentrations were always lower.