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Research article - Peer-reviewed, 2021

Post-treatment of dewatered digested sewage sludge by thermophilic high-solid digestion for pasteurization with positive energy output

Nordell, E.; Moestedt, J.; Osterman, J.; Yekta, S. Shakeri; Bjorn, A.; Sun, L.; Schnurer, A.


This study investigated the possibility to use thermophilic anaerobic high solid digestion of dewatered digested sewage sludge (DDS) at a wastewater treatment plant (WWTP) as a measure to increase total methane yield, achieve pasteurization and reduce risk for methane emissions during storage of the digestate. A pilot-scale plug-flow reactor was used to mimic thermophilic post-treatment of DDS from a WWTP in Linkoping, Sweden. Process operation was evaluated with respect to biogas process performance, using both chemical and microbiological parameters. Initially, the process showed disturbance, with low methane yields and high volatile fatty acid (VFA) accumulation. However, after initiation of digestate recirculation performance improved and the specific methane production reached 46 mL CH4/g VS. Plug flow conditions were assessed with lithium chloride and the hydraulic retention time (HRT) was determined to be 19-29 days, sufficient to reach successful pasteurization. Degradation rate of raw protein was high and resulted in ammonia-nitrogen levels of up to 2.0 g/L and a 30% lower protein content in the digestate as compared to DDS. Microbial analysis suggested a shift in the methane producing pathway, with dominance of syntrophic acetate oxidation and the candidate methanogen family WSA2 by the end of the experiment. Energy balance calculations based on annual DDS production of 10 000 ton/year showed that introduction of high-solid digestion as a post-treatment and pasteurization method would result in a positive energy output of 340 MWh/year. Post-digestion of DDS also decreased residual methane potential (RMP) by >96% compared with fresh DDS. (C) 2020 The Authors. Published by Elsevier Ltd.


Digestate post treatment; Dry digestion; Ammonia; Microbial community structure; Residual methane potential

Published in

Waste Management
2021, volume: 119, pages: 11-21

Authors' information

Nordell, E.
Linkoping University
Moestedt, J.
Linkoping University
Österman, J.
Tekniska verken i Linköping AB
Yekta, S. Shakeri
Linkoping University
Bjorn, A.
Linkoping University
Swedish University of Agricultural Sciences, Department of Molecular Sciences
Swedish University of Agricultural Sciences, Department of Molecular Sciences

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