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Identifying targets for increased biogas production through chemical and organic matter characterization of digestate from full-scale biogas plants: what remains and why?

Ekstrand, Eva-Maria and Bjorn, Annika and Karlsson, Anna and Schnürer, Anna and Kanders, Linda and Yekta, Sepehr Shakeri and Karlsson, Martin and Moestedt, Jan (2022). Identifying targets for increased biogas production through chemical and organic matter characterization of digestate from full-scale biogas plants: what remains and why? Biotechnology for Biofuels and Bioproducts. 15 :1 , 16
[Research article]

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Abstract

Background This study examines the destiny of macromolecules in different full-scale biogas processes. From previous studies it is clear that the residual organic matter in outgoing digestates can have significant biogas potential, but the factors dictating the size and composition of this residual fraction and how they correlate with the residual methane potential (RMP) are not fully understood. The aim of this study was to generate additional knowledge of the composition of residual digestate fractions and to understand how they correlate with various operational and chemical parameters. The organic composition of both the substrates and digestates from nine biogas plants operating on food waste, sewage sludge, or agricultural waste was characterized and the residual organic fractions were linked to substrate type, trace metal content, ammonia concentration, operational parameters, RMP, and enzyme activity. Results Carbohydrates represented the largest fraction of the total VS (32-68%) in most substrates. However, in the digestates protein was instead the most abundant residual macromolecule in almost all plants (3-21 g/kg). The degradation efficiency of proteins generally lower (28-79%) compared to carbohydrates (67-94%) and fats (86-91%). High residual protein content was coupled to recalcitrant protein fractions and microbial biomass, either from the substrate or formed in the degradation process. Co-digesting sewage sludge with fat increased the protein degradation efficiency with 18%, possibly through a priming mechanism where addition of easily degradable substrates also triggers the degradation of more complex fractions. In this study, high residual methane production (> 140 L CH4/kg VS) was firstly coupled to operation at unstable process conditions caused mainly by ammonia inhibition (0.74 mg NH3-N/kg) and/or trace element deficiency and, secondly, to short hydraulic retention time (HRT) (55 days) relative to the slow digestion of agricultural waste and manure. Conclusions Operation at unstable conditions was one reason for the high residual macromolecule content and high RMP. The outgoing protein content was relatively high in all digesters and improving the degradation of proteins represents one important way to increase the VS reduction and methane production in biogas plants. Post-treatment or post-digestion of digestates, targeting microbial biomass or recalcitrant protein fractions, is a potential way to achieve increased protein degradation.

Authors/Creators:Ekstrand, Eva-Maria and Bjorn, Annika and Karlsson, Anna and Schnürer, Anna and Kanders, Linda and Yekta, Sepehr Shakeri and Karlsson, Martin and Moestedt, Jan
Title:Identifying targets for increased biogas production through chemical and organic matter characterization of digestate from full-scale biogas plants: what remains and why?
Series Name/Journal:Biotechnology for Biofuels and Bioproducts
Year of publishing :2022
Volume:15
Number:1
Article number:16
Number of Pages:22
Publisher:BMC
Language:English
Publication Type:Research article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Biochemistry and Molecular Biology
(A) Swedish standard research categories 2011 > 2 Engineering and Technology > 209 Industrial Biotechnology > Bioenergy
Keywords:Anaerobic digestion, Degradation efficiency, Residual methane potential, Macromolecules, Full-scale biogas plants, Trace metals, Ammonia, Enzyme activity, Biogas, Digestate
URN:NBN:urn:nbn:se:slu:epsilon-p-116389
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-116389
Additional ID:
Type of IDID
DOI10.1186/s13068-022-02103-3
Web of Science (WoS)000759430500002
ID Code:27488
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Department of Molecular Sciences
Deposited By: SLUpub Connector
Deposited On:31 Mar 2022 13:25
Metadata Last Modified:31 Mar 2022 13:31

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