Dehalococcoides, however, can be influenced by the cathode potential. Catalyzed
reporter deposition-FISH (CARD-FISH) analysis was performed on the cathode
effluent of a bioelectrochemical reactor run at different potentials (from À750 mV
to À250 mV). Members of the Chloroflexi represented from 65% to 100% of the
total bacteria at all the tested potentials. However, at potentials from À750 mV to
À550 mV, when the dehalogenation was probably sustained by H 2 evolution, the
genus Dehalococcoides accounted for almost all the Chloroflexi, but it strongly
decreased at higher potentials (from À450 mV to À250 mV), when the process was
probably driven by a direct electron uptake from the cathode, and was partially
outcompeted by an unidentified member of the Chloroflexi (Di Battista et al. 2012).
17.5 Advantages and Disadvantages of Bioelectrochemical
Processes
Several potential advantages could be linked to the use of novel BES-based
approaches for the bioremediation of contaminated environments. The main benefit
that can be achieved when using a BES to remove contaminants is the decrease in
operational costs. Since no information about field-scale plants is currently available,
a complete estimation of the costs associated with the application of
bioelectrochemical technologies for the bioremediation is not possible yet. Electrodes can serve as virtually inexhaustible electron donors/acceptors because a stable
electron flow can be maintained for long operational periods without the need of
continuous supply of water-soluble electron donors/acceptors (Morris and Jin 2007).
In a recent review, a 2.4 kWh energy input was calculated for the complete PCE
dehalogenation to ethane with a dehalogenation rate of ~10 (mol PCE)/day (i.e.,
1.66 kg/day) (Daghio et al. 2017). This estimation, however, does not consider any
possible unwanted side reactions that may occur leading to a lower efficiency of the
process, and, thus, a higher energy input might be required in field operations. In
terms of installation costs it is reasonable to presume that the main cost will be
associated to the electrode material, which could be variable from € 30–50 for 1 m
2
up to € 500 for 1 m
2 for DSA (Daghio et al. 2017). However, it is important to point
out that this evaluation has to be based on considering the lifetime of the components
that has never been tested in real applications.
The choice of the electrode material is crucial. Appropriate electrode materials
have to be biocompatible and stable, ensuring high electrical conductivity and a low
cost/life ratio (Daghio et al. 2017). For the stimulation of the oxidation with anodes,
some authors used stainless steel electrodes or even DSA when high potential anodes
were used for oxygen evolution. However, carbon materials (e.g., graphite or
activated carbon) are used in the majority of studies (Daghio et al. 2017). Carbon
materials can adsorb the contaminants and colocalize the electron donor, the electron
acceptor, and the catalyst (i.e., microorganisms) in the same highly metabolically
active area (Zhang et al. 2010). Adsorption usually decreases the bioavailability of
384
M. Daghio and A. Franzetti
reporter deposition-FISH (CARD-FISH) analysis was performed on the cathode
effluent of a bioelectrochemical reactor run at different potentials (from À750 mV
to À250 mV). Members of the Chloroflexi represented from 65% to 100% of the
total bacteria at all the tested potentials. However, at potentials from À750 mV to
À550 mV, when the dehalogenation was probably sustained by H 2 evolution, the
genus Dehalococcoides accounted for almost all the Chloroflexi, but it strongly
decreased at higher potentials (from À450 mV to À250 mV), when the process was
probably driven by a direct electron uptake from the cathode, and was partially
outcompeted by an unidentified member of the Chloroflexi (Di Battista et al. 2012).
17.5 Advantages and Disadvantages of Bioelectrochemical
Processes
Several potential advantages could be linked to the use of novel BES-based
approaches for the bioremediation of contaminated environments. The main benefit
that can be achieved when using a BES to remove contaminants is the decrease in
operational costs. Since no information about field-scale plants is currently available,
a complete estimation of the costs associated with the application of
bioelectrochemical technologies for the bioremediation is not possible yet. Electrodes can serve as virtually inexhaustible electron donors/acceptors because a stable
electron flow can be maintained for long operational periods without the need of
continuous supply of water-soluble electron donors/acceptors (Morris and Jin 2007).
In a recent review, a 2.4 kWh energy input was calculated for the complete PCE
dehalogenation to ethane with a dehalogenation rate of ~10 (mol PCE)/day (i.e.,
1.66 kg/day) (Daghio et al. 2017). This estimation, however, does not consider any
possible unwanted side reactions that may occur leading to a lower efficiency of the
process, and, thus, a higher energy input might be required in field operations. In
terms of installation costs it is reasonable to presume that the main cost will be
associated to the electrode material, which could be variable from € 30–50 for 1 m
2
up to € 500 for 1 m
2 for DSA (Daghio et al. 2017). However, it is important to point
out that this evaluation has to be based on considering the lifetime of the components
that has never been tested in real applications.
The choice of the electrode material is crucial. Appropriate electrode materials
have to be biocompatible and stable, ensuring high electrical conductivity and a low
cost/life ratio (Daghio et al. 2017). For the stimulation of the oxidation with anodes,
some authors used stainless steel electrodes or even DSA when high potential anodes
were used for oxygen evolution. However, carbon materials (e.g., graphite or
activated carbon) are used in the majority of studies (Daghio et al. 2017). Carbon
materials can adsorb the contaminants and colocalize the electron donor, the electron
acceptor, and the catalyst (i.e., microorganisms) in the same highly metabolically
active area (Zhang et al. 2010). Adsorption usually decreases the bioavailability of
384
M. Daghio and A. Franzetti