| 1. |
- Moestedt, Jan, et al.
(author)
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Acetate and Lactate Production During Two-Stage Anaerobic Digestion of Food Waste Driven by Lactobacillus and Aeriscardovia
- 2020
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In: Frontiers in Energy Research. - : FRONTIERS MEDIA SA. - 2296-598X. ; 8
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Journal article (peer-reviewed)abstract
- Background: In a previous study, single-stage processes were compared with two-stage processes, using either food waste alone or mixed with thin stillage as substrate. Overall methane yield increased (by 12%) in two-stage compared with single-stage digestion when using food waste, but decreased when food waste was co-digested with thin stillage (50:50 on VS basis). The obtained difference in methane yield was likely caused by a higher acetate level in the first stage reactor operating with food waste alone (around 20 g/L) compared to the reactor also treating thin stillage (around 8 g /L). The present study sought to shed additional light on possible causes of the large difference in methane yield by scrutinizing the microbial community in the first- and second-stage reactors, using a combined Illumina sequencing and qPCR approach. Results: In the first-stage process, acid-tolerant Aeriscardovia and Lactobacillus formed a highly efficient consortium. For food waste with high levels of acetate (20 g/L, equal to 0.14 g acetate/g VS) was produced but when thin stillage was added the pH was lower (<4), resulting in lactate production exceeding acetate production. This difference in hydrolysate composition between the reactors resulted in development of slightly different communities in the second-stage, for both hydrolysis, fermentation, and acetogenesis. High acetate concentration appeared to promote proliferation of different syntrophic consortia, such as various syntrophic acetate oxidizers, members of the genus Syntrophomonas and candidate phylum Cloacimonetes, likely explaining the higher methane yields with two-step compared with single-stage digestion of food waste. Conclusion: Using food waste as sole substrate resulted in enrichment of Lactobacillus and Aeriscardovia and high acetate yields in the first-stage reactor. This was beneficial for biogas yield in two-stage digestion, where efficient acid-degrading syntrophic consortia developed. Addition of thin stillage contributed to low pH and higher lactate production, which resulted in decreased methane yield in the two-stage process compared with using food waste as sole substrate.
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| 2. |
- Odnell, Anna
(author)
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Influencing anaerobic digestion early stage processes for increased biomethane production from different substrate components
- 2018
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Licentiate thesis (other academic/artistic)abstract
- Finding alternatives to petroleum-based energy sources is of interest since it could reduce the emissions of net carbon dioxide to the atmosphere by increasing the usage of renewable energy sources. To do so improvements are needed in the renewable energy production sector. Biogas production is of interest since the anaerobic digestion process can degrade many different biomolecules and is, contrary to e.g. bioethanol and biodiesel, not dependent on specific molecules. Thus, many wastes such as slaughterhouse waste, sludge from waste water treatment and lignocellulose residual material etc. can be used as substrates for biogas production. However, there are limitations in the degradation process depending on the composition of the selected substrate. To overcome these limitations such as inhibition of different microorganisms, or recalcitrant substrate, different methods can be used to increase the biogas production. In this study different substrates were selected and analyzed/treated for remedies of early stage rate limiting problems of the anaerobic digestion process. Different analyzes and techniques were selected depending on the limitations correlated to the main problematic component of the specific substrate. Improvements could be reached for the degradation of slaughterhouse waste by augmentation with the clay mineral zeolite. Addition of different enzymes to the substrate environment of different waste water treatment plant sludges resulted in limited life time of the selected enzymes. However, certain enzymes proved to be promising candidates with an effect of increased biogas production rate and yield for the time that the enzyme remained active. In an additional experiment, cellulolytic enzymes, naturally produced by a biogas producing microbial community, were induced, collected and added to a biogas experiment of ensiled forage ley, by which it was shown that these cellulases led to an increase in biogas production rate and yield. Thus, the studies demonstrate different techniques for improving the anaerobic digestion process of different types of substrates.
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