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 (N(2)O, NO and NO(2)) 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 Sjolunda WWTP, it was shown that significant emissions of N(2)O, NO and NO(2) do occur. The plant is operated with nitritation alone, which gives an environment enriched in aerobic AOB. During normal operation, emissions of N(2)O, NO and NO(2) were found to be 3.8%, 0.06% and 0.01% of the ammonium nitrogen load. The N(2)O emissions were larger than the recommended estimated figure of the Intergovernmental Panel on Climate Change (IPCC) for a complete wastewater treatment plant. The N(2)O 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 NO(2) emission profiles were similar and dependent on ammonium oxidation and DO level, but the NO(2) concentrations were always lower.