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Sammanfattning

Anaerobic digestion (AD) is a microbial process for converting organic matter into methane-rich biogas, serving as both a renewable energy source and a waste treat-ment strategy. High ammonia concentrations, often stemming from the degradation of protein-rich feedstocks, can destabilise AD systems by inhibiting microbial activ-ity, particularly among acetate-utilising methanogens and certain propionate degrad-ers. Under these conditions, ammonia tolerant syntrophic propionate-oxidising bac-teria (SPOB) and syntrophic acetate-oxidising bacteria (SAOB) become vital for volatile fatty acid (VFA) conversion. These bacteria depend on hydrogenotrophic methanogens to consume metabolic products like hydrogen and formate, rendering the acid oxidation thermodynamically favourable. However, these ammonia-tolerant syntrophic communities are often present at low abundance in AD systems, limiting propionate and acetate degradation rates. Current knowledge about these communi-ties is constrained by challenges in studying them in complex AD systems. This the-sis aimed to deepen the understanding of syntrophic propionate-oxidising bacteria under high-ammonia mesophilic conditions and their interactions with SAOB and hydrogenotrophic methanogenic archaea. The research utilised a highly enriched syntrophic communities from a high-ammonia digester, employing molecular and cultivation-based methods, complemented by thermodynamic calculations and novel visualisation tools. This research identified the metabolic pathway and cooperating strategies used by syntrophic microbial partners crucial for propionate and acetate oxidation under high ammonia. Furthermore, a novel methanogen was identified, demonstrating electron transfer via both hydrogen and formate. Findings revealed that disrupting microbial aggregation significantly impeded propionate degradation. Moreover, it was demonstrated that the community adapted to high salt and ammo-nia stress by inducing aggregation and employed specific tolerance strategies like ion transport and compatible solutes. Overall, this thesis deepened the understanding of the factors that disrupt the intricate interplay between syntrophs and highlighted their unique stress-resilience features. In the long term, these insights may support the development of strategies to mitigate VFA accumulation in high-ammonia bio-gas digesters.

Nyckelord

syntrophic propionate oxidation; syntrophic acetate oxidation; hydrogen-otrophic methanogenesis; anaerobic digestion; ammonia inhibition; syntrophy; bio-gas; flocculation; interspecies electron transfer

Publicerad i

Acta Universitatis Agriculturae Sueciae
2025, nummer: 2025:42
Utgivare: Swedish University of Agricultural Sciences

SLU författare

UKÄ forskningsämne

Molekylärbiologi
Bioenergi

Publikationens identifierare

  • DOI: https://doi.org/10.54612/a.5npuc4rg9r
  • ISBN: 978-91-8046-477-2
  • eISBN: 978-91-8046-527-4

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/132982