title: Efficient butanol-ethanol (B-E) production from carbon monoxide fermentation by Clostridium carboxidivorans.
abstract: The fermentation of waste gases rich in carbon monoxide using acetogens is an efficient way to obtain valuable biofuels like ethanol and butanol. Different experiments were carried out with the bacterial species Clostridium carboxidivorans as biocatalyst. In batch assays with no pH regulation, after complete substrate exhaustion, acetic acid, butyric acid, and ethanol were detected while only negligible butanol production was observed. On the other side, in bioreactors, with continuous carbon monoxide supply and pH regulation, both C2 and C4 fatty acids were initially formed as well as ethanol and butanol at concentrations never reported before for this type of anaerobic bioconversion of gaseous C1 compounds, showing that the operating conditions significantly affect the metabolic fermentation profile and butanol accumulation. Maximum ethanol and butanol concentrations in the bioreactors were obtained at pH 5.75, reaching values of 5.55 and 2.66 g/L, respectively. The alcohols were produced both from CO fermentation as well as from the bioconversion of previously accumulated acetic and butyric acids, resulting in low residual concentrations of such acids at the end of the bioreactor experiments. CO consumption was often around 50% and reached up to more than 80%. Maximum specific rates of ethanol and butanol production were reached at pH 4.75, with values of 0.16 g/h*g of biomass and 0.07 g/h*g of biomass, respectively, demonstrating that a low pH was more favorable to solventogenesis in this process, although it negatively affects biomass growth which does also play a role in the final alcohol titer.
authors.affiliation: Chemical Engineering Laboratory, Faculty of Sciences, University of La Coruña, Rúa da Fraga 10, E-15008, La Coruña, Spain.
authors.forename: Ánxela
authors.initials: Á
authors.lastname: Fernández-Naveira
authors.affiliation: Chemical Engineering Laboratory, Faculty of Sciences, University of La Coruña, Rúa da Fraga 10, E-15008, La Coruña, Spain.
authors.forename: Haris Nalakath
authors.initials: HN
authors.lastname: Abubackar
authors.affiliation: Chemical Engineering Laboratory, Faculty of Sciences, University of La Coruña, Rúa da Fraga 10, E-15008, La Coruña, Spain.
authors.forename: María C
authors.initials: MC
authors.lastname: Veiga
authors.affiliation: Chemical Engineering Laboratory, Faculty of Sciences, University of La Coruña, Rúa da Fraga 10, E-15008, La Coruña, Spain. kennes@udc.es.
authors.forename: Christian
authors.initials: C
authors.lastname: Kennes
mesh_terms: D020001:1-Butanol / Q000378:metabolism*; D019342:Acetic Acid / Q000378:metabolism; D000693:Anaerobiosis; D061249:Batch Cell Culture Techniques; D056804:Biofuels; D019149:Bioreactors; D002087:Butyrates / Q000378:metabolism; D002248:Carbon Monoxide / Q000378:metabolism*; D003013:Clostridium / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics
chemical_list: D056804:Biofuels; D002087:Butyrates; D005227:Fatty Acids; D000431:Ethanol; D002248:Carbon Monoxide; D020001:1-Butanol; D019342:Acetic Acid
keywords: Butanol; Clostridium carboxidivorans; Ethanol; Syngas; Waste Gas