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Greenhouse gas emissions when freezing and thawing sewage sludge and compost

Bos, Marlies (2013). Greenhouse gas emissions when freezing and thawing sewage sludge and compost. Uppsala: (NL, NJ) > Dept. of Energy and Technology, Sveriges lantbruksuniversitet. Rapport (Sveriges lantbruksuniversitet, Institutionen för energi och teknik) ; 2013:062

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Freezing/thawing cycles can significantly increase greenhouse gas emissions due to physical
and biological mechanisms. Therefore this research was done to see if this is also the case for
compost and sewage sludge. The main focus was on nitrous oxide. The set-up of the
experiments was based on the outcomes of several trial experiments. 4 substrates were tested:
non-nitrified mesophilic sewage sludge, nitrified mesophilic sewage sludge, 2 weeks old
compost and 1 month old compost. The two composts had a clear difference in ammonium
content. The substrates were first frozen at a temperature of -27 °C, and then thawed at a
temperature of 5 °C. Controls were kept at a temperature of 5 °C during the whole
experiment. All substrates were tested in triplicates. Emissions of carbon dioxide, methane
and nitrous oxide were measured. No clear effect of freezing/thawing was observed on the
greenhouse gas emissions from non-nitrified sewage sludge. From the nitrified sewage sludge
the emissions of both carbon dioxide and nitrous oxide increased during thawing. The
cumulative emission of carbon dioxide was 17500 µg g-1 initial C from the frozen and thawed
sewage sludge, and 11170 µg g-1 initial C from the controls. The cumulative emission of
nitrous oxide in the sewage sludge that had been frozen and thawed was about 3500 µg g-1
initial N, for the controls this was 3000 µg g-1 initial N. Both the increase carbon dioxide and
nitrous oxide emissions were probably due to increased substrate availability, caused by the
die-off of micro-organisms during freezing. The nitrous oxide probably came from
denitrification. In both of the composts no effect of the freezing and thawing was observed on
the emissions of carbon dioxide and methane, but it had a clear effect on the emission of
nitrous oxide: in the 1 month old compost a clear emission peak was observed during the first
days of thawing. For the one month compost this was probably due to a physical mechanism
of trapped nitrous oxide inside the compost which could escape during the thawing period. An
unexpected result was the large difference between the two composts considering the amounts
of nitrous oxide emissions, which were expected to be approximately the same due to equal
nitrate amounts. However, the cumulative nitrous oxide emission from the frozen and thawed
2 weeks compost was 3,00 µg g-1 initial N at the end, while from the 1 month compost this
was 1220 µg g-1 initial N. Since the ammonium in the 1 month compost had decreased with
32,5%, and only 17,5% for 2 weeks compost, the large amount of nitrous oxide probably
came from the conversion of ammonium. However, it is still not clear whether this comes
from nitrification of the ammonium, or from denitrification of the nitrate formed during the
experiment. The conclusion was that freezing/thawing increases emissions of carbon dioxide
and nitrous oxide from nitrified sewage sludge during thawing, and the emissions of nitrous
oxide from compost during thawing. Recommendations for further research are to find out
which processes, nitrification or denitrification, are responsible for the nitrous oxide
production. Also research to compost with different nitrate amounts is recommended.

Authors/Creators:Bos, Marlies
Title:Greenhouse gas emissions when freezing and thawing sewage sludge and compost
Year of publishing :2013
Number of Pages:45
Place of Publication:Uppsala
Publisher:Department of Energy and Technology, Swedish University of Agricultural Sciences
Publication Type:Report
Article category:Other scientific
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 2 Engineering and Technology > 207 Environmental Engineering > Environmental Management
(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Climate Research
Keywords:ammonium, compost, denitrification, freezing/thawing, greenhouse gas emissions, nitrate, nitrification, sewage sludge
Permanent URL:
ID Code:16530
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Dept. of Energy and Technology
Deposited By: SLUpub Connector
Deposited On:20 Dec 2019 12:28
Metadata Last Modified:13 Jul 2020 06:56

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