antraquinone-2,6-disulfonate—AQDS) have also been used in some studies
(Adelaja et al. 2015; Aulenta et al. 2007a, 2008a, 2010a; Leitão et al. 2016; Lin
et al. 2014). Their use is limited to laboratory experiments since these molecules
can be toxic and, if used during bioremediation of contaminated environments,
they can have disadvantages similar to the ones reported for the soluble electron
acceptors, e.g., diffusion away from the reaction area or occurrence of side
reactions (Daghio et al. 2017). However, recent studies suggested that the limits
linked to the diffusion of soluble electron shuttles (e.g., AQDS) could be overcome
by the immobilization of the mediator on the electrode surface (Leitão et al. 2017).
A third mechanism of EET involves long-range electron transport through the
biofilm via electrically conductive pili called nanowires (Lovley 2011). Experimental evidences suggest that in G. sulfurreducens the electrons transported along
the pili are transferred to the electrode by extracellular c-type cytochromes that
accumulate near the anode surface (Inoue et al. 2011; Lovley and Nevin 2011).
EET by outer membrane c-type cytochromes and mediators can also be involved in
the electrons uptake from the cathode (Rosenbaum et al. 2011). Furthermore, the
cathodic electron uptake can involve hydrogenases, which can accept the electrons
from the electrode. The electrons can then be used for the H 2 production or for the
reduction of the final electron acceptor (Rosenbaum et al. 2011).
17.3 Use of Bioelectrochemical Systems for Bioremediation
of Oil-Contaminated Environments
Several authors have reported on the possibility of using electrodes as electron
acceptors for the microbial respiration during the bioremediation of environments
polluted by a wide range of organic contaminants (Daghio et al. 2017). Refinery
wastewater and diesel-contaminated groundwater were used in the first studies,
which showed the possibility of coupling the current production with the hydrocarbons removal (Morris et al. 2009; Morris and Jin 2007). Later, a high number of
studies reported the degradation of total petroleum hydrocarbons (TPH) and diesel
in laboratory-scale BES reactors (Chandrasekhar and Venkata Mohan 2012;
Cheng et al. 2017; Cruz Viggi et al. 2015; Li et al. 2014, 2015; Lu et al. 2014a,
b; Morris and Jin 2012; Venkata Mohan and Chandrasekhar 2011; Wang et al.
2012; Zhang et al. 2015). Other studies showed the degradation of BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene) such as
toluene (Espinoza Tofalos et al. 2018; Daghio et al. 2016; Lin et al. 2014; Zhang
et al. 2010) and benzene (Adelaja et al. 2015; Rakoczy et al. 2013; Wei et al. 2015;
Wu et al. 2013; Zhang et al. 2010), which were removed by both pure cultures and
mixed cultures using the anode of a BES. The bioelectrochemical degradation of
monoaromatic hydrocarbons was also assessed using a mixture containing all the
BTEX compounds. The authors showed that the removal of toluene, m-xylene, and
p-xylene was improved by using a MEC at different applied external voltages
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
377
(Adelaja et al. 2015; Aulenta et al. 2007a, 2008a, 2010a; Leitão et al. 2016; Lin
et al. 2014). Their use is limited to laboratory experiments since these molecules
can be toxic and, if used during bioremediation of contaminated environments,
they can have disadvantages similar to the ones reported for the soluble electron
acceptors, e.g., diffusion away from the reaction area or occurrence of side
reactions (Daghio et al. 2017). However, recent studies suggested that the limits
linked to the diffusion of soluble electron shuttles (e.g., AQDS) could be overcome
by the immobilization of the mediator on the electrode surface (Leitão et al. 2017).
A third mechanism of EET involves long-range electron transport through the
biofilm via electrically conductive pili called nanowires (Lovley 2011). Experimental evidences suggest that in G. sulfurreducens the electrons transported along
the pili are transferred to the electrode by extracellular c-type cytochromes that
accumulate near the anode surface (Inoue et al. 2011; Lovley and Nevin 2011).
EET by outer membrane c-type cytochromes and mediators can also be involved in
the electrons uptake from the cathode (Rosenbaum et al. 2011). Furthermore, the
cathodic electron uptake can involve hydrogenases, which can accept the electrons
from the electrode. The electrons can then be used for the H 2 production or for the
reduction of the final electron acceptor (Rosenbaum et al. 2011).
17.3 Use of Bioelectrochemical Systems for Bioremediation
of Oil-Contaminated Environments
Several authors have reported on the possibility of using electrodes as electron
acceptors for the microbial respiration during the bioremediation of environments
polluted by a wide range of organic contaminants (Daghio et al. 2017). Refinery
wastewater and diesel-contaminated groundwater were used in the first studies,
which showed the possibility of coupling the current production with the hydrocarbons removal (Morris et al. 2009; Morris and Jin 2007). Later, a high number of
studies reported the degradation of total petroleum hydrocarbons (TPH) and diesel
in laboratory-scale BES reactors (Chandrasekhar and Venkata Mohan 2012;
Cheng et al. 2017; Cruz Viggi et al. 2015; Li et al. 2014, 2015; Lu et al. 2014a,
b; Morris and Jin 2012; Venkata Mohan and Chandrasekhar 2011; Wang et al.
2012; Zhang et al. 2015). Other studies showed the degradation of BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene) such as
toluene (Espinoza Tofalos et al. 2018; Daghio et al. 2016; Lin et al. 2014; Zhang
et al. 2010) and benzene (Adelaja et al. 2015; Rakoczy et al. 2013; Wei et al. 2015;
Wu et al. 2013; Zhang et al. 2010), which were removed by both pure cultures and
mixed cultures using the anode of a BES. The bioelectrochemical degradation of
monoaromatic hydrocarbons was also assessed using a mixture containing all the
BTEX compounds. The authors showed that the removal of toluene, m-xylene, and
p-xylene was improved by using a MEC at different applied external voltages
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
377