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Author:Leppänen, Maarit
Title:Prosessiolosuhteiden vaikutus jätevedenpuhdistamoiden N2O -päästöihin
The impact of the process conditions on nitrous oxide emission from wastewater treatment plants
Publication type:Master's thesis
Publication year:2012
Pages:97 + [17]      Language:   fin
Department/School:Yhdyskunta- ja ympäristötekniikan laitos
Main subject:Vesihuoltotekniikka   (Yhd-73)
Supervisor:Vahala, Riku
Instructor:Heinonen, Mari ; Mikola, Anna
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto     | Archive
Keywords:biological nitrogen removal
denitrification
nitrification
nitrous oxide
wastewater treatment
jäteveden käsittely
biologinen typen poisto
nitrifikaatio
denitrifikaatio
Abstract (eng): Nitrous oxide (N2O) is a greenhouse gas with tremendous global warming potential.
It can be emitted during wastewater treatment.
N2O is mainly emitted during nitrogen removal when conditions are not optima for nitrification and denitrifikation.
Previously most studies on N2O emission focused on the emissions from the aeration basin and often only anoxic zones, because N2O was considered to be mainly produced there.

In this study nitrous oxide emissions were measured from the water surface in the aeration basin and in secondary clarification basins in six wastewater treatment plants (WWTRs) in Uusimaa in Finland.
Measurements were made in two periods during spring and summer.
Emissions were measured with off-gas method directly from the water surface continuously.
During the measurements conditions in WWTPs were different because of different process condition in the plants and cycle of the seasons.

In special attention was put to the secondary settling tank because it has not been studied widely before.
The results show that there are N2O emissions from the WWTPs.
Emission from the secondary settling tank were as significant as emission from the activated sludge unit.
The results show also that there was lots of diurnal variation in N2O emission from the secondary settling tank.
Flux can be a consequence of the changing nitrogen load to the WWTP or of the changing level of sludge blanket in the secondary clarifier.
N2O emissions occurred more in winter time than in summer time.
Very large variation in emission values show that it is important that studies are full-scale and measurements are continuously and the measurement period is long enough.
Abstract (fin): Osasta jätevedenpuhdistuslaitokselle päätyvästä typestä muodostuu typpioksiduulia (N2O) biologisen typenpoiston yhteydessä.
Typpioksiduuli on voimakas kasvihuonekaasu, jota pääsee muodostumaan jätevedenpuhdistamolla, jos olosuhteet eivät ole otolliset nitrifikaatiolle ja denitrifikaatiolle.
Kirjallisuudessa ei esiinny tutkimuksissa, joissa olisi selvitetty jälkiselkeytysaltaiden N2O-päästöjä.
On vain vähän tutkimuksia joissa on käytetty jatkuvatoimisia mittalaitteita, ja joissa on tehty pitkäkestoisia mittauksia.

Kuudella eri jätevedenpuhdistamolla Uudellamaalla selvitettiin laitosten N2O päästöjä.
Typpioksiduulipäästöjä mitattiin ilmastusaltailla eri lohkoissa, ilmastetuissa ja ilmastamattomissa ja jälkiselkeytysaltailla.
Mittaukset tehtiin jatkuvatoimisella kaasuanalysaattorilla suoraan veden pinnalta mittakuvun avulla, joten mittaustuloksia oli mahdollista saada usean päivän ajalta.
Kevään mittaukset pyrittiin suorittamaan lumien sulamisajankohtana, jolloin laitoksien prosessien toiminta oli vaikeutunut kylmien sulamisvesien takia.
Kesän mittauksiin mennessä laitosten prosessit olivat toipuneet kevään hankalista oloista.

Merkittävänä tuloksena mittausten perusteella voidaan pitää sitä, että jälkiselkeytysaltailta vapautui lähes yhtä paljon N2O:ta kuin ilmastusaltailta.
Jälkiselkeytysaltaita voidaan pitää paikkana, jossa N2O:ta pääsee vapautumaan.
Jälkiselkeytysaltaiden N2O-pitoisuus vaihteli suuresti eri vuorokauden ja vuodenaikojen aikaan.
N2O:n määrän synnylle ei voi perustaa muutamille satunnaisesti otetuille näytteille.
N2O-päästöjä täytyy tarkkailla pitkäaikaisesti ja jatkuvasti.
ED:2013-02-27
INSSI record number: 45882
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