consists in two-stage bioreactors, a first one containing A. woodii whole cells (that
possesses CODH and FDH), that convert CO into CO 2 via CODH and where the
electrons from the oxidation are transferred to reduce FDH and to produce formate
and a second bioreactor fed with the produced formate, where this is the only
carbon source, containing M. extorquens which converts it to PHB [61].
3 Microbial Electrosynthesis: Bioelectrochemical Systems
for CO 2 Valorisation
Carbon capture and utilization (CCU) has aroused a notable interest within both
academy and industry sectors as it can provide an efficient approach to curb carbon
dioxide (CO 2 ) emissions, complementing the “natural carbon cycle” by converting
“spent carbon” (CO 2 ) into “working carbon” (valuable chemicals and fuels) [85].
However, since CO 2 displays remarkable chemical stability (carbon in CO 2 is fully
oxidized), its industrial conversion (usually through reduction reactions that involve
high pressure and/or temperature) can turn into an energy-intensive process
[86, 87].
Nature, through its evolutionary process, has developed biocatalysts able to
reduce carbon dioxide (CO 2 ) into organic molecules at moderate (ambient) conditions of pressure and temperature [88], which enables significantly reduce the
energy requirements. The importance of these biocatalysts in the biological carbon
fixation can hardly be underestimated as they allow biochemical reactions to proceed at rates that make possible to sustain biological processes. Microbial electrosynthesis (MES) technology has lately been developed as somehow imitate
natural carbon fixation. It evolves from conventional electrochemistry with the
difference that instead of using inorganic (and many times valuable) catalysts such
as novel metals, it relies on a certain type of microorganisms that are able to interact
electrically with a solid surface (cathode). These microorganisms can use the
electrons arriving at the cathode to convert CO 2 into organic compounds [89]. Since
they somehow “catalyse” the CO 2 reduction reaction, they are usually seen as
“biocatalysts” [90].
Enzymatic electrosynthesis (EES) represents an approach similar to MES for
converting CO 2 into valuable products through a (bio)electrochemical process.
However, instead of using living microorganisms as biocatalysts (as in MES), EES
employs free enzymes [91]. ESS has several advantages over MES: it offers higher
reaction selectivity, better tolerance to solvents and less complex metabolic
mechanisms [91, 92]. However, MES avoids the use of costly enzymes and cofactor
production/addition as microorganisms produce their own enzymes. Moreover,
whole cells are more resilient to changes in reaction conditions such as pH, temperature, salinity or pressure [93].
Carbon Dioxide Utilization—Bioelectrochemical Approaches
93
possesses CODH and FDH), that convert CO into CO 2 via CODH and where the
electrons from the oxidation are transferred to reduce FDH and to produce formate
and a second bioreactor fed with the produced formate, where this is the only
carbon source, containing M. extorquens which converts it to PHB [61].
3 Microbial Electrosynthesis: Bioelectrochemical Systems
for CO 2 Valorisation
Carbon capture and utilization (CCU) has aroused a notable interest within both
academy and industry sectors as it can provide an efficient approach to curb carbon
dioxide (CO 2 ) emissions, complementing the “natural carbon cycle” by converting
“spent carbon” (CO 2 ) into “working carbon” (valuable chemicals and fuels) [85].
However, since CO 2 displays remarkable chemical stability (carbon in CO 2 is fully
oxidized), its industrial conversion (usually through reduction reactions that involve
high pressure and/or temperature) can turn into an energy-intensive process
[86, 87].
Nature, through its evolutionary process, has developed biocatalysts able to
reduce carbon dioxide (CO 2 ) into organic molecules at moderate (ambient) conditions of pressure and temperature [88], which enables significantly reduce the
energy requirements. The importance of these biocatalysts in the biological carbon
fixation can hardly be underestimated as they allow biochemical reactions to proceed at rates that make possible to sustain biological processes. Microbial electrosynthesis (MES) technology has lately been developed as somehow imitate
natural carbon fixation. It evolves from conventional electrochemistry with the
difference that instead of using inorganic (and many times valuable) catalysts such
as novel metals, it relies on a certain type of microorganisms that are able to interact
electrically with a solid surface (cathode). These microorganisms can use the
electrons arriving at the cathode to convert CO 2 into organic compounds [89]. Since
they somehow “catalyse” the CO 2 reduction reaction, they are usually seen as
“biocatalysts” [90].
Enzymatic electrosynthesis (EES) represents an approach similar to MES for
converting CO 2 into valuable products through a (bio)electrochemical process.
However, instead of using living microorganisms as biocatalysts (as in MES), EES
employs free enzymes [91]. ESS has several advantages over MES: it offers higher
reaction selectivity, better tolerance to solvents and less complex metabolic
mechanisms [91, 92]. However, MES avoids the use of costly enzymes and cofactor
production/addition as microorganisms produce their own enzymes. Moreover,
whole cells are more resilient to changes in reaction conditions such as pH, temperature, salinity or pressure [93].
Carbon Dioxide Utilization—Bioelectrochemical Approaches
93