The possibility of using the electrical signal produced in a BES for monitoring the
bioremediation process has also been explored in the field. An MFC-based biosensor
was successfully applied in a field study to assess the rate of U(VI) bioreduction
providing acetate as the electron donor (Williams et al. 2010). Similar devices could
be easily installed in existing monitoring well networks with the main benefit of
decreasing both the number of analyses and the time required to assess the microbial
activity (Tront et al. 2008a).
For the development of BES-based biosensors, it is, however, important to
consider that the oxidation/reduction of chemical compounds other than the contaminant could lead to the presence of a background signal (Daghio et al. 2017). The
placement of control sensors outside the contaminated areas or the development of
selective enzymatic biosensors could be possible strategies to overcome issues due
to the generation of background currents (Daghio et al. 2017).
One of the main drawbacks linked to the use of BES-based technologies to
stimulate the bioremediation in anaerobic environments is the lower efficiency of
the degradation, which leads to a slower biodegradation compared to the aerobic
metabolisms (Weelink et al. 2010). The degradation rate at the anode can also be
limited by the kinetic of the cathodic reaction when an MFC configuration is used
(Logan 2009; Wei et al. 2011).
The scale-up of the technology is challenging and the data from field-scale
plants are not currently available (Daghio et al. 2017). One of the most important
aspects that has to be considered when applying a BES to the bioremediation in
real plants is the radius of influence, which can greatly affect the process. Attempts
to evaluate the radius of influence have been made during TPH degradation with
anodes serving as electron acceptors (Lu et al. 2014a, b; Wang et al. 2012). In a
biodegradation study performed over 120 days with cylindrical anodes (radius
7.5 cm), the authors predicted the maximum radius of influence of 90 cm, assuming
a linear correlation between the distance of the electrode and the stimulation of
TPH removal (Lu et al. 2014b). Water content, mass transport, and the type of soil
as well as the design of the treatment plant (e.g., the type of electrode) can
potentially affect the radius of influence; thus, the site-specific conditions have to
be considered (Daghio et al. 2017).
Future scale-up of this innovative technology will lead to a more detailed
comprehension of the advantages and the limitations linked to the use of BESs for
bioremediation, which is now mainly limited to small-scale reactors.
17.6 Possible Opportunities for Future Development
Several studies proved that a broad range of halogenated and non-halogenated
hydrocarbons can be successfully reduced/oxidized in BESs and that this technology
could be effective in the stimulation of the microbial metabolism in contaminated
environments. From the analysis of the literature reported in this chapter it is clear
that the main challenge that has to be faced in the near future is the progressive scale386
M. Daghio and A. Franzetti
bioremediation process has also been explored in the field. An MFC-based biosensor
was successfully applied in a field study to assess the rate of U(VI) bioreduction
providing acetate as the electron donor (Williams et al. 2010). Similar devices could
be easily installed in existing monitoring well networks with the main benefit of
decreasing both the number of analyses and the time required to assess the microbial
activity (Tront et al. 2008a).
For the development of BES-based biosensors, it is, however, important to
consider that the oxidation/reduction of chemical compounds other than the contaminant could lead to the presence of a background signal (Daghio et al. 2017). The
placement of control sensors outside the contaminated areas or the development of
selective enzymatic biosensors could be possible strategies to overcome issues due
to the generation of background currents (Daghio et al. 2017).
One of the main drawbacks linked to the use of BES-based technologies to
stimulate the bioremediation in anaerobic environments is the lower efficiency of
the degradation, which leads to a slower biodegradation compared to the aerobic
metabolisms (Weelink et al. 2010). The degradation rate at the anode can also be
limited by the kinetic of the cathodic reaction when an MFC configuration is used
(Logan 2009; Wei et al. 2011).
The scale-up of the technology is challenging and the data from field-scale
plants are not currently available (Daghio et al. 2017). One of the most important
aspects that has to be considered when applying a BES to the bioremediation in
real plants is the radius of influence, which can greatly affect the process. Attempts
to evaluate the radius of influence have been made during TPH degradation with
anodes serving as electron acceptors (Lu et al. 2014a, b; Wang et al. 2012). In a
biodegradation study performed over 120 days with cylindrical anodes (radius
7.5 cm), the authors predicted the maximum radius of influence of 90 cm, assuming
a linear correlation between the distance of the electrode and the stimulation of
TPH removal (Lu et al. 2014b). Water content, mass transport, and the type of soil
as well as the design of the treatment plant (e.g., the type of electrode) can
potentially affect the radius of influence; thus, the site-specific conditions have to
be considered (Daghio et al. 2017).
Future scale-up of this innovative technology will lead to a more detailed
comprehension of the advantages and the limitations linked to the use of BESs for
bioremediation, which is now mainly limited to small-scale reactors.
17.6 Possible Opportunities for Future Development
Several studies proved that a broad range of halogenated and non-halogenated
hydrocarbons can be successfully reduced/oxidized in BESs and that this technology
could be effective in the stimulation of the microbial metabolism in contaminated
environments. From the analysis of the literature reported in this chapter it is clear
that the main challenge that has to be faced in the near future is the progressive scale386
M. Daghio and A. Franzetti