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Abstract
BackgroundThe conversion of CO2 into high value-added products has a very important environmental and economic significance. Microbial electrosynthesis (MES) is a promising technology, which adopts a bioelectrochemical system to transform CO2 into organic chemicals.ResultsIn this study, Clostridium scatologenes ATCC 25775T, an anaerobic acetogenic bacterium, demonstrated its utility as a biocatalyst in a MES system, for the first time. With the cathodic potential of the MES system decreased from − 0.6 to − 1.2 V (vs. Ag/AgCl), the current density of the MES, and the production of organic chemicals, increased. Combining the genetic analysis and the results of the wet lab experiments, we believe C. scatologenes may accept electrons directly from the cathode to reduce CO2 into organic compounds at a potential of − 0.6 V. The acetic and butyric acid reached a maximum value of 0.03 and 0.01 g/L, respectively, and the maximum value of total coulombic efficiency was about 84%, at the potential of − 0.6 V. With the decrease in cathodic potentials, both direct electron transfer and exogenous electron shuttle, H2 might be adopted for the C. scatologenes MES system. At a potential of − 1.2 V, acetic acid, butyric acid and ethanol were detected in the cathodic chamber, with their maximum values increasing to 0.44, 0.085 and 0.015 g/L, respectively. However, due to the low H2 utilization rate by the C. scatologenes planktonic cell, the total coulombic efficiency of the MES system dropped to 37.8%.ConclusionClostridium scatologenes is an acetogenic bacterium which may fix CO2 through the Wood–Ljungdahl pathway. Under H2 fermentation, C. scatologenes may reduce CO2 to acetic acid, butyric acid and ethanol. It can also be used as the biocatalyst in MES systems.
Highlights
The conversion of CO2 into high value-added products has a very important environmental and economic significance
The concentration of acetic acid and butyric acid increased with the growth of C. scatologenes, The highest concentration of acetic acid reached 1.25 g/L, on the 6th day, and the highest concentration of butyric acid reached 0.320 g/L, on the 7th day, respectively
The concentration of ethanol was stable in the fermentation growth, reached a maximum value of 0.192g/L on the 7th day
Summary
The conversion of CO2 into high value-added products has a very important environmental and economic significance. With the cathodic potential of the MES system decreased from − 0.6 to − 1.2 V (vs Ag/AgCl), the current density of the MES, and the production of organic chemicals, increased. Combining the genetic analysis and the results of the wet lab experiments, we believe C. scatologenes may accept electrons directly from the cathode to reduce CO2 into organic compounds at a potential of − 0.6 V. At a potential of − 1.2 V, acetic acid, butyric acid and ethanol were detected in the cathodic chamber, with their maximum values increasing to 0.44, 0.085 and 0.015 g/L, respectively. The development of novel technologies for the conversion of CO2 into high value-added products has a very important environmental and economic significance. The major technologies for CO2 reduction include biotransformation (Nowak and Crane 2002), electrochemical reduction (Olah et al 2013; Nevin et al 2010; Zhang et al 2013; Lovley and Nevin 2013; Lovley 2011a), photocatalytic reduction (Chu et al 2008), catalytic hydrogenation (Karelovic et al 2012) and so on
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