Effect of pH in syngas conversion to C4 & C6 acids in mixed-culture trickle bed reactors

Cesar Quintela, Antonio Grimalt-Alemany, Oskar Modin, Yvonne Nygård, Lisbeth Olsson, Ioannis V. Skiadas, Hariklia N. Gavala*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Syngas fermentation allows for the conversion of wastes into useful commodity chemicals. To target higher value products, the conditions can be tuned to be favourable for both acetogenic and reverse beta-oxidation pathways and produce, in one stage, butyric and caproic acid. Studies in CSTR have shown the crucial role of pH, which must be low enough to allow for ethanol generation in the acetogenic step while avoiding the inhibition of reverse β-oxidation in acidic conditions. However, no studies have investigated the effect of pH in reactor configurations suitable for syngas fermentation (i.e., allowing for cell retention and exhibiting high mass transfer rates at low operating costs), such as Trickle Bed Reactors, TBR. In this study, two TBR were used to study the pH effect on the fermentation of syngas to produce C4 and C6 acids, using undefined mixed cultures. Five pH values were tested in the range 4.5–7.5, and pH 6 was found to be the most favourable for simultaneous production of C4 & C6 acids from syngas, which agrees with what was found in suspended growth systems. In addition, the highest titers in literature so far were achieved in the TRB. 16S rRNA analysis was performed showing Clostridium and Rummenliibacillus to be the key genus for the efficient process at pH 6. Finally, the experimental methodology followed, and data collected proved the robustness of mixed culture biofilm reactors in respect to pH changes, as the same reactor performance and bacterial community were achieved regardless of the operation history.

Original languageEnglish
Article number107292
JournalBiomass and Bioenergy
Volume187
Number of pages9
ISSN0961-9534
DOIs
Publication statusPublished - 2024

Keywords

  • Butyric acid
  • Caproic acid
  • Chain elongation
  • Reverse beta oxidation
  • Syngas fermentation
  • Trickle bed reactor

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