title: N2O emissions from secondary clarifiers and their contribution to the total emissions of the WWTP.
abstract: Recent studies have indicated that the emissions of nitrous oxide, N2O, constitute a major part of the carbon footprint of wastewater treatment plants (WWTPs). Denitrification occurring in the secondary clarifier basins has been observed by many researchers, but until now N2O emissions from secondary clarifiers have not been widely reported. The objective of this study was to measure the N2O emissions from secondary clarifiers and weigh the portion they could represent of the overall emissions at WWTPs. Online measurements over several days were carried out at four different municipal WWTPs in Finland in cold weather conditions (March) and in warm weather conditions (June-July). An attempt was made to define the conditions in which N2O emissions from secondary clarifiers may occur. It was evidenced that large amounts of N2O can be emitted from the secondary clarifiers, and that the emissions have long-term variation. It was assumed that part of the N2O released in secondary clarification was originally formed in the activated sludge basin. The emissions from secondary clarification thus seem to be dependent on conditions of the nitrification and denitrification accomplished in the denitrification-nitrification process and on the amount of sludge stored in the secondary clarifiers.
authors.affiliation: School of Engineering, Aalto University, P.O. Box 14100, 00076 Aalto, Finland E-mail: anna.mikola@aalto.fi.
authors.forename: Anna
authors.initials: A
authors.lastname: Mikola
authors.affiliation: Helsinki Region Environmental Authority HSY, P.O. Box 100, FI-00066 Helsinki, Finland.
authors.forename: Mari
authors.initials: M
authors.lastname: Heinonen
authors.affiliation: Helsinki Region Environmental Authority HSY, P.O. Box 100, FI-00066 Helsinki, Finland.
authors.forename: Heta
authors.initials: H
authors.lastname: Kosonen
authors.affiliation: School of Engineering, Aalto University, P.O. Box 14100, 00076 Aalto, Finland E-mail: anna.mikola@aalto.fi.
authors.forename: Maarit
authors.initials: M
authors.lastname: Leppänen
authors.affiliation: School of Engineering, Aalto University, P.O. Box 14100, 00076 Aalto, Finland E-mail: anna.mikola@aalto.fi.
authors.forename: Pirjo
authors.initials: P
authors.lastname: Rantanen
authors.affiliation: School of Engineering, Aalto University, P.O. Box 14100, 00076 Aalto, Finland E-mail: anna.mikola@aalto.fi.
authors.forename: Riku
authors.initials: R
authors.lastname: Vahala
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D058440:Denitrification; D004784:Environmental Monitoring; D058465:Nitrification; D009609:Nitrous Oxide / Q000032:analysis*; D012722:Sewage; D014865:Waste Disposal, Fluid
chemical_list: D000393:Air Pollutants; D012722:Sewage; D009609:Nitrous Oxide