the cathode is a better strategy to avoid the side reactions (e.g., methanogenesis) that
divert the electrons, thus decreasing the efficiency of the process. In compliance with
this line, other works showed the possibility of performing the TCE dehalogenation
with the redox mediators (e.g., MV or the humic acid analogue AQDS) (Aulenta
et al. 2007a, 2008a, 2010a) and without the redox mediators suggesting that TCE
removal is also possible by a direct electron uptake from the electrode (Aulenta et al.
2009, 2010b, 2011; Verdini et al. 2015). Bioelectrochemical dehalogenation with a
cathode as a sole electron donor has been reported also for PCE, which was reduced
to cis-DCE by a pure culture of Geobacter lovleyi (Strycharz et al. 2008).
A key parameter that has to be controlled for the stimulation of the reductive
dechlorination in order to minimize the occurrence of the side reactions is the
cathode potential. TCE dehalogenation via H 2 evolution was studied at cathodic
potentials between À800 mV and À500 mV. The highest dechlorination rate was
obtained at the more negative potentials with a fast increase in the range from
À650 mV to À625 mV. In the same potential range, however, the efficiency of the
process was decreased by diverting the electrons toward methane production
(Aulenta et al. 2008b). Later, the electron uptake from an electrode poised at
À450 mV was observed during the TCE dechlorination. A redox active moiety
potentially involved in the EET (midpoint potential around À400 mV) was detected
in the supernatant (Aulenta et al. 2009). A subsequent study, performed with a
continuous flow reactor, showed an improvement of the dehalogenation rate (from
15.5 Æ 1.2 μmol e
À
/L to 58 Æ 1 μmol e
À /L) linked to the enhancement of the H 2
production by decreasing the cathode potential from À250 mV to À450 mV
(Aulenta et al. 2011). However, at lower potential a drastic drop in the coulombic
efficiency (from nearly 100% at À250 mV to less than 1% at À750 mV) was
observed because of methanogenesis (Aulenta et al. 2011), confirming the conclusions of the previous studies (Aulenta et al. 2008b). A further demonstration of this
trend has been reported with 1,2-DCA. The dehalogenation rate increased from
À300 mV to À900 mV, but the higher coulombic efficiency (about 70%) was
obtained at the higher cathodic potential (À300 mV) (Leitão et al. 2015). Methane
production is not the only side reaction that can decrease the efficiency of the process
during the bioelectrochemical dehalogenation. At potentials below À550 mV also
nitrate reduction and sulfate reduction can have negative effects on the coulombic
efficiency (Lai et al. 2015). Reductive dechlorination can also be affected by mass
transport (e.g., groundwater flow) at different cathodic potentials (Verdini et al.
2015). TCE dehalogenation was studied at different flow velocities (from 0.3 m/
day to 1.7 m/day) by varying the cathode potential (from À450 mV to À250 mV). At
more reducing potentials the dechlorination rate increased with the flow velocity
because the process was influenced by mass transport of H 2 generated at the cathode.
At higher potentials the dehalogenation was sustained by direct EET that was not
affected by the flow rate (Verdini et al. 2015).
A simple configuration suggested for the application of BES-based technologies
during the bioremediation of aquatic environments involves the placement of an
anode in anaerobic benthic sediments (Bond et al. 2002) (Fig. 17.2a). The electrode
can thus be used as electron acceptor for the anodic oxidation of the contaminant.
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
379
divert the electrons, thus decreasing the efficiency of the process. In compliance with
this line, other works showed the possibility of performing the TCE dehalogenation
with the redox mediators (e.g., MV or the humic acid analogue AQDS) (Aulenta
et al. 2007a, 2008a, 2010a) and without the redox mediators suggesting that TCE
removal is also possible by a direct electron uptake from the electrode (Aulenta et al.
2009, 2010b, 2011; Verdini et al. 2015). Bioelectrochemical dehalogenation with a
cathode as a sole electron donor has been reported also for PCE, which was reduced
to cis-DCE by a pure culture of Geobacter lovleyi (Strycharz et al. 2008).
A key parameter that has to be controlled for the stimulation of the reductive
dechlorination in order to minimize the occurrence of the side reactions is the
cathode potential. TCE dehalogenation via H 2 evolution was studied at cathodic
potentials between À800 mV and À500 mV. The highest dechlorination rate was
obtained at the more negative potentials with a fast increase in the range from
À650 mV to À625 mV. In the same potential range, however, the efficiency of the
process was decreased by diverting the electrons toward methane production
(Aulenta et al. 2008b). Later, the electron uptake from an electrode poised at
À450 mV was observed during the TCE dechlorination. A redox active moiety
potentially involved in the EET (midpoint potential around À400 mV) was detected
in the supernatant (Aulenta et al. 2009). A subsequent study, performed with a
continuous flow reactor, showed an improvement of the dehalogenation rate (from
15.5 Æ 1.2 μmol e
À
/L to 58 Æ 1 μmol e
À /L) linked to the enhancement of the H 2
production by decreasing the cathode potential from À250 mV to À450 mV
(Aulenta et al. 2011). However, at lower potential a drastic drop in the coulombic
efficiency (from nearly 100% at À250 mV to less than 1% at À750 mV) was
observed because of methanogenesis (Aulenta et al. 2011), confirming the conclusions of the previous studies (Aulenta et al. 2008b). A further demonstration of this
trend has been reported with 1,2-DCA. The dehalogenation rate increased from
À300 mV to À900 mV, but the higher coulombic efficiency (about 70%) was
obtained at the higher cathodic potential (À300 mV) (Leitão et al. 2015). Methane
production is not the only side reaction that can decrease the efficiency of the process
during the bioelectrochemical dehalogenation. At potentials below À550 mV also
nitrate reduction and sulfate reduction can have negative effects on the coulombic
efficiency (Lai et al. 2015). Reductive dechlorination can also be affected by mass
transport (e.g., groundwater flow) at different cathodic potentials (Verdini et al.
2015). TCE dehalogenation was studied at different flow velocities (from 0.3 m/
day to 1.7 m/day) by varying the cathode potential (from À450 mV to À250 mV). At
more reducing potentials the dechlorination rate increased with the flow velocity
because the process was influenced by mass transport of H 2 generated at the cathode.
At higher potentials the dehalogenation was sustained by direct EET that was not
affected by the flow rate (Verdini et al. 2015).
A simple configuration suggested for the application of BES-based technologies
during the bioremediation of aquatic environments involves the placement of an
anode in anaerobic benthic sediments (Bond et al. 2002) (Fig. 17.2a). The electrode
can thus be used as electron acceptor for the anodic oxidation of the contaminant.
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
379