A microbial electrolysis cell (MEC) is a technology related to microbial fuel
cells (MFC). While MFCs produce an electric current from the microbial decomposition of organic compounds, MECs partially reverse the process to generate
hydrogen or methane from organic materials by applying an electric current possibly generated from perennial sources.
In a basic bioelectrochemical system, electrons are generated at the anode from
water or organic waste and sulfides [68], while microorganisms perform CO 2
reduction to organics at the cathode. The advantage of using BES is their productivity which is higher (5–7% efficiency) than photo-biological systems (3–4%
solar conversion efficiency) [69].
By coupling BES with a photovoltaic device, the capacity of converting CO 2
using solar light may be considerably increased.
An interesting application of BES is the production of methane through electrochemical reduction of carbon dioxide at ambient conditions (Eq. 11.1).
CO 2 þ 8H
þ
þ 8e
À
! CH 4 þ 2H 2 O
ð11:1Þ
This latter process can be carried out using chemo-catalysis, using special-design
reactors and catalysts with high activity under pressure (3 MPa) and at high temperature, despite it being a hexoergonic reaction. BESs target high selectivity and
low overpotentials to be made applicable on a large scale. By using BES, the action
of microorganisms is fastened by introducing electrons in the system that are used
for reduction processes [70] of carbon dioxide that is converted into a variety of
products. It can be reduced to methane, acetate, and other low-carbon products such
as isobutanol and 3-methyl-1-butanol, depending on the used microorganism and
the operational conditions [71].
Methane production has been reported by Villano et al. [72] using a hydrogenophilic methanogenic culture (Fig. 11.15) that reduces carbon dioxide to
methane, at high rates (up to 0.055 ± 0.002 mmol d
−1 mg VSS
−1 ) (VSS =
Volatile Suspended Solids) and electron capture efficiencies (over 80%). The oxidation of organic waste is required in order to make both electrons and CO 2
available. Power can be supplied by a PV-Cell.
The reduction of carbon dioxide to methane by BES catches the attention of
several groups and several papers have recently been published [73–77].
Moreover, in a recent study [78] a techno-economic assessment of biomethane
production has been presented using a CO 2 -containing effluent generated applying
the ABAD Bioenergy® [79] technology, which is applied at demonstration scale
(TRL8–9) in a variety of Wastewater Treatment Plants (WWTPs). CO 2 is reduced
at the cathode of a BES, while the anode reaction is valorized by producing
chloro-derivatives (Fig. 11.16) used as disinfectant of the treated wastewater. The
application of such methodology increases the biomethane production by 17.4%
and produces enough chlorine compounds for water sanitization.
11.4 Bioelectrochemical Systems
209
cells (MFC). While MFCs produce an electric current from the microbial decomposition of organic compounds, MECs partially reverse the process to generate
hydrogen or methane from organic materials by applying an electric current possibly generated from perennial sources.
In a basic bioelectrochemical system, electrons are generated at the anode from
water or organic waste and sulfides [68], while microorganisms perform CO 2
reduction to organics at the cathode. The advantage of using BES is their productivity which is higher (5–7% efficiency) than photo-biological systems (3–4%
solar conversion efficiency) [69].
By coupling BES with a photovoltaic device, the capacity of converting CO 2
using solar light may be considerably increased.
An interesting application of BES is the production of methane through electrochemical reduction of carbon dioxide at ambient conditions (Eq. 11.1).
CO 2 þ 8H
þ
þ 8e
À
! CH 4 þ 2H 2 O
ð11:1Þ
This latter process can be carried out using chemo-catalysis, using special-design
reactors and catalysts with high activity under pressure (3 MPa) and at high temperature, despite it being a hexoergonic reaction. BESs target high selectivity and
low overpotentials to be made applicable on a large scale. By using BES, the action
of microorganisms is fastened by introducing electrons in the system that are used
for reduction processes [70] of carbon dioxide that is converted into a variety of
products. It can be reduced to methane, acetate, and other low-carbon products such
as isobutanol and 3-methyl-1-butanol, depending on the used microorganism and
the operational conditions [71].
Methane production has been reported by Villano et al. [72] using a hydrogenophilic methanogenic culture (Fig. 11.15) that reduces carbon dioxide to
methane, at high rates (up to 0.055 ± 0.002 mmol d
−1 mg VSS
−1 ) (VSS =
Volatile Suspended Solids) and electron capture efficiencies (over 80%). The oxidation of organic waste is required in order to make both electrons and CO 2
available. Power can be supplied by a PV-Cell.
The reduction of carbon dioxide to methane by BES catches the attention of
several groups and several papers have recently been published [73–77].
Moreover, in a recent study [78] a techno-economic assessment of biomethane
production has been presented using a CO 2 -containing effluent generated applying
the ABAD Bioenergy® [79] technology, which is applied at demonstration scale
(TRL8–9) in a variety of Wastewater Treatment Plants (WWTPs). CO 2 is reduced
at the cathode of a BES, while the anode reaction is valorized by producing
chloro-derivatives (Fig. 11.16) used as disinfectant of the treated wastewater. The
application of such methodology increases the biomethane production by 17.4%
and produces enough chlorine compounds for water sanitization.
11.4 Bioelectrochemical Systems
209