Abstract
Syngas, the product of biomass gasification, can play an important role in moving towards the production of renewable chemical commodities, by using acetogenic bacteria to ferment those gaseous mixtures. Due to the complex and changing nature of biomass, the composition and the impurities present in the final biomass-derived syngas will vary. Because of this, it is important to assess the impact of these factors on the fermentation outcome, in terms of yields, productivity, and product formation and ratio. In this study, Clostridium ljungdahlii was used in a fed-batch fermentation system to analyze the effect of three different biomass-derived syngases, and to compare them to equivalent, clean syngas mixtures. Additionally, four other clean syngas mixtures were used, and the effects on product ratio, productivity, yield, and growth were documented. All biomass-derived syngases were suitable to be used as substrates, without experiencing any complete inhibitory effects. From the obtained results, it is clear that the type of syngas, biomass-derived or clean, had the greatest impact on product formation ratios, with all biomass-derived syngases producing more ethanol, albeit with lesser total productivity.
Highlights
Nowadays, there is a growing interest and increased research efforts towards finding more environmentally friendly and renewable energy sources
Biomass is seen as an important source for renewable commodity chemicals and some liquid hydrocarbon fuels: it can be gasified, including lignocellulosic biomass, waste and non-food crops, to produce syngas, which is composed mainly by CO, CO2, and H2 [4]
Theoretical yields and ideal gas ratios only apply for resting cells, and it can be of interest to know how the gas composition affects the growing phase of the cells, to try and optimize this stage : in one report it was stated that cells took up to 8 days for the optical density (OD) to stabilize [25], and, in another study, it was reported that even with bottled, clean syngas, a lag phase of 4 days was observed [18]
Summary
There is a growing interest and increased research efforts towards finding more environmentally friendly and renewable energy sources. Biomass is seen as an important source for renewable commodity chemicals and some liquid hydrocarbon fuels: it can be gasified, including lignocellulosic biomass, waste and non-food crops, to produce syngas, which is composed mainly by CO, CO2 , and H2 [4]. This gasification technology is well-established and has been broadly studied [5]. The fermentation products are mainly acetate, but ethanol and other longer-chain products, such as butyrate, butanol, Fermentation 2020, 6, 84; doi:10.3390/fermentation6030084 www.mdpi.com/journal/fermentation
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