Effect of Endogenous and Exogenous Butyric Acid on Butanol Production From CO by Enriched Clostridia

Abstract

Butanol is a potential renewable fuel. To increase the selectivity for butanol during CO fermentation, exogenous acetic acid and ethanol, exogenous butyric acid or endogenous butyric acid from glucose fermentation have been investigated using CO as reducing power, with a highly enriched Clostridium sludge. Addition of 3.2 g/L exogenous butyric acid led to the highest 1.9 g/L butanol concentration with a conversion efficiency of 67%. With exogenous acetate and ethanol supply, the butanol concentration reached 1.6 g/L at the end of the incubation. However, the presence of acetic acid and ethanol favoured butanol production to 2.6 g/L from exogenous butyric acid by the enriched sludge. Finally, exogenous 14 g/L butyric acid yielded the highest butanol production of 3.4 g/L, which was also among the highest butanol concentration from CO/syngas fermentation reported so far. CO addition triggered butanol production from endogenous butyric acid (produced from glucose, Glucose + N2) with as high as 58.6% conversion efficiency and 62.1% butanol yield. However, no efficient butanol production was found from glucose and CO co-fermentation (Glucose + CO), although a similar amount of endogenous butyric acid was produced compared to Glucose + N2. The Clostridium genus occupied a relative abundance as high as 82% from the initial inoculum, while the Clostridia and Bacilli classes were both enriched and dominated in Glucose + N2 and Glucose + CO incubations. This study shows that the supply of butyric acid is a possible strategy for enhancing butanol production by CO fed anaerobic sludge, either via exogenous butyric acid, or via endogenous production by sugar fermentation.

A Systematic Review of Syngas Bioconversion to Value-Added Products from 2012 to 2022

“…The production of long-chain value-added products is a means of increasing carbon capture efficiency, especially in cases where it is coupled with other CO 2 capture technologies and a catalytic transformation to syngas [66]. In 2022 there seems to have been a shift of the research focus to the production of butanol [67][68][69], whereas the publications focusing on ethanol production were lowered considerably. This shift could be justified by the fact that butanol is considered to be an advanced biofuel that offers numerous advantages over ethanol.…”

Ethanologenesis from glycerol by the gut acetogen Blautia schinkii

“…Since a third mol of acetate from hexoses has then to be formed by the WLP, this fermentation is also referred to as homoacetogenesis (Müller, 2003). However, certain metabolic scenarios such as lack of Na + or CO 2 , growth on highly reduced nutrients such as CO or acidification of the medium leads to a shift of metabolism towards ethanol formation, but typically ethanol is a minor component (Abrini et al, 1994; Buschhorn et al, 1989; He et al, 2021; Moon & Müller, 2021). Only after long adaptive laboratory evolution ethanol becomes the major component as in Clostridium autoethanogenum that produces ethanol from syngas, a mixture of CO, H 2 and CO 2 , on an industrial level (Bertsch & Müller, 2015; Liew et al, 2016).…”