Poster Presentation 2-14

 

Conversion of Synthesis Gas to Organic Compounds by Bacteria

 

 

H. Heiskanen, L. Viikari* and I. Virkajärvi

 

 

VTT Biotechnology

P.O. Box 1500

Espoo. FIN-02044 VTT
Phone:  +358 9 4561

Fax:  +358 9 455 2103

E-mail:  Liisa.Viikari@vtt.fi

 

 

 

During the past several years, ethanol production from biomass has received considerable attention.  An alternative to the enzymatic hydrolysis of biomass and fermentation of sugars into ethanol is the gasification of biomass into CO, H2 and CO2 with subsequent chemical (Fischer-Tropsch) or biotechnical conversion of these gases to ethanol or other organic compounds.  The theoretical yield of ethanol from heterogeneous wastes or lignin-rich biomasses can with this route be almost twice as high as with hydrolysis and fermentation of carbohydrate derived sugars.  Using carbohydrate fermenting organisms, only hexose and pentose sugars can be converted to ethanol. The theoretical yield by gas fermentation is thus significantly higher due to conversion of also other components, such as lignin to ethanol. The gasification process is also less dependent on the variation or type of raw material. As compared with the catalytic conversion routes of synthesis gas into ethanol, the biological conversion may offer some key advantages; such as milder processing conditions, reducing both operating and capital costs, as well as the higher specificity of biocatalysts, as compared with inorganic alternatives.  Acetogens are able to metabolize single-carbon compounds, CO2 and H2 and CO, to multi-carbon products, such as ethanol, acetic acid, butanol and butyric acid and have been used to develop biological CO conversion processes.  CO is inhibitory for bacteria and the conversion of CO usually needs adaptation. In this study, a CO-adapted strain of Butyribacterium methylotrophicum was grown on different gas mixtures of CO, H2 and CO2. Carbon monoxide was completely utilized by the B. methylotrophicum strain, forming acetic and butyric acid as main products.  H2 increased the formation of butyric acid and also made it possible to convert  carbon dioxide to products.

 

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