(Aulenta et al. 2007b), and controlling H 2 delivery is crucial to prevent electrons
diverting to side processes (e.g., methanogenesis, homoacetogenesis, and sulfate
reduction) (Daghio et al. 2017).
The use of bioelectrochemical technologies, in which electrodes are used as solid
electron acceptors/donors by several groups of microorganisms, has been extensively reviewed and suggested to overcome some of the limitations of the classical
bioremediation approaches (Daghio et al. 2017; Li and Yu 2015; Wang et al. 2015);
therefore, they will be deeply discussed in this chapter.
17.2 Introduction to Bioelectrochemical Systems
Bioelectrochemical systems (BESs) are devices in which the ability of specific
microorganisms to catalyze redox reactions on or near electrodes is exploited
(Logan et al. 2006; Rosenbaum et al. 2011). This technology was initially developed
to convert chemical energy into electrical energy during wastewater treatment
(Logan et al. 2006). The main advantage was the opportunity to recover energy
from the waste, instead of consuming it to supply the oxygen needed for the aerobic
oxidation of the organic substances. In natural environments, several microorganisms are able to oxidize organic substrates in anaerobic conditions using solid
electron acceptors (e.g., iron oxides) (Shi et al. 2016; Weber et al. 2006). In BESs
the electrons obtained from the oxidation of the organic substrate are transferred to
an electrode (anode), which is a solid electron acceptor, and flow through a circuit.
The electrons reach another electrode (cathode) where the reduction of a final
electron acceptor takes place (Logan et al. 2006) (Fig. 17.1). By convention, an
electric current flows into the circuit in a direction that is the opposite to the direction
of the electrons.
Several reactors’ configurations can be used. The traditional H-shaped
two-chamber reactor was widely used for the early studies in which BESs were
investigated. In this configuration, two bottles (one for the anodic chamber and one
for the cathodic chamber) are connected with a tube and separated with a cation
exchange membrane (CEM). The membrane is used to allow the exchange of
protons between the two chambers and to avoid the diffusion of the organic substrate
and of the final electron acceptor (Logan et al. 2006).
BESs can be divided in two main groups: microbial fuel cells (MFCs) and
microbial electrolysis cells (MECs). In a MFC, a net energy gain is achieved because
the redox potential of the oxidation reaction at the anode is lower than the redox
potential of the reduction reaction at the cathode. In a MEC, an energy input is used
to drive the reaction (Daghio et al. 2017).
MECs can be operated at a fixed potential (Rozendal et al. 2006) with the
advantage that the favorable conditions to drive the desired reaction, or for a certain
biocatalyst, can be created. Alternatively, a MEC can be operated by setting a fixed
current (Andersen et al. 2013) to control the reaction rates.
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
375
diverting to side processes (e.g., methanogenesis, homoacetogenesis, and sulfate
reduction) (Daghio et al. 2017).
The use of bioelectrochemical technologies, in which electrodes are used as solid
electron acceptors/donors by several groups of microorganisms, has been extensively reviewed and suggested to overcome some of the limitations of the classical
bioremediation approaches (Daghio et al. 2017; Li and Yu 2015; Wang et al. 2015);
therefore, they will be deeply discussed in this chapter.
17.2 Introduction to Bioelectrochemical Systems
Bioelectrochemical systems (BESs) are devices in which the ability of specific
microorganisms to catalyze redox reactions on or near electrodes is exploited
(Logan et al. 2006; Rosenbaum et al. 2011). This technology was initially developed
to convert chemical energy into electrical energy during wastewater treatment
(Logan et al. 2006). The main advantage was the opportunity to recover energy
from the waste, instead of consuming it to supply the oxygen needed for the aerobic
oxidation of the organic substances. In natural environments, several microorganisms are able to oxidize organic substrates in anaerobic conditions using solid
electron acceptors (e.g., iron oxides) (Shi et al. 2016; Weber et al. 2006). In BESs
the electrons obtained from the oxidation of the organic substrate are transferred to
an electrode (anode), which is a solid electron acceptor, and flow through a circuit.
The electrons reach another electrode (cathode) where the reduction of a final
electron acceptor takes place (Logan et al. 2006) (Fig. 17.1). By convention, an
electric current flows into the circuit in a direction that is the opposite to the direction
of the electrons.
Several reactors’ configurations can be used. The traditional H-shaped
two-chamber reactor was widely used for the early studies in which BESs were
investigated. In this configuration, two bottles (one for the anodic chamber and one
for the cathodic chamber) are connected with a tube and separated with a cation
exchange membrane (CEM). The membrane is used to allow the exchange of
protons between the two chambers and to avoid the diffusion of the organic substrate
and of the final electron acceptor (Logan et al. 2006).
BESs can be divided in two main groups: microbial fuel cells (MFCs) and
microbial electrolysis cells (MECs). In a MFC, a net energy gain is achieved because
the redox potential of the oxidation reaction at the anode is lower than the redox
potential of the reduction reaction at the cathode. In a MEC, an energy input is used
to drive the reaction (Daghio et al. 2017).
MECs can be operated at a fixed potential (Rozendal et al. 2006) with the
advantage that the favorable conditions to drive the desired reaction, or for a certain
biocatalyst, can be created. Alternatively, a MEC can be operated by setting a fixed
current (Andersen et al. 2013) to control the reaction rates.
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
375